What are the factors that affect the curing effect of tunnel lining concrete?

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The tunnel lining concrete maintenance can be divided into two types in terms of technology: water spray maintenance, spray maintenance and curing agent maintenance. Sprinkler maintenance refers to the use of water pipes or sprinklers to directly spray the maintenance water onto the concrete surface for maintenance, which can be operated manually or by spraying the lining trolley. Spray curing refers to the method of using atomizing equipment to atomize the curing water and then curing the concrete.

Manual sprinkling maintenance has low requirements for equipment, but the frequency, amount and duration of sprinkling water are subjective. Since the spraying trolley is carried out in a non-enclosed space in the tunnel, a large amount of maintenance water is retained and lost in the air when it is sprayed.

Although the curing agent can form a relatively complete film with isolation on the surface of the concrete, it is difficult to achieve a uniform ideal state in the spraying effect; at the same time, as the organic matter continues to volatilize, due to the inevitable uneven spraying, Weak areas will be formed in the areas where the spraying is thinner, and the concrete in these weak areas will undergo internal and external moisture migration and evaporation loss.

The tunnel concrete maintenance formwork

Factors affecting concrete curing effect

Cement concrete refers to the artificial stone formed by mixing water, aggregate and cement and then hardening after hydration reaction. Cement is a hydraulic cementing material. With the participation of water, new cementing compounds are formed, and then slowly harden into cement stone. This process is called hydration. However, after the concrete is poured, due to the humidity difference between the concrete and the air, the moisture inside the concrete has to evaporate and migrate to the external environment through the surface, thereby affecting the moisture required for the hydration of the concrete itself.

In order for the concrete hydration reaction to proceed normally, after the concrete is poured, it is necessary to maintain a temperature and humidity environment conducive to the cement hydration reaction for a considerable period of time. The curing of concrete is to create a curing measure that is conducive to the hydration reaction of cement. In addition, higher-quality concrete also requires good curing conditions in the early stage of hardening.

Curing temperature

Curing temperature is one of the most important factors affecting the performance of concrete. Because high temperature can accelerate the violent degree of cement hydration reaction, the higher the curing temperature, the faster the strength of the concrete will increase. Studies have shown that there is a certain temperature critical value. When the temperature is lower than this value, the hydration reaction of cement basically stops. Therefore, when the ambient temperature is lower than this value, the strength of the coagulant will no longer increase. When the temperature is lower than 0°C, the concrete will undergo frost damage due to the freezing of internal moisture. In addition, it is not that the higher the curing temperature, the more beneficial it is to the strength growth of the concrete. This is because the excessively high environmental temperature in the early stage will cause the strength of the later concrete to grow slowly or even not.

Tunnel waterproof board laying formwork

Curing humidity

The degree of hydration of cement has an important influence on a series of mechanical properties and durability of concrete. The existence of free water in the capillary tube is an important prerequisite for cement hydration. As the cement hydration reaction continues, the hydration products gradually fill the capillary voids. In this process, the water pressure in the capillary voids continues to increase, and the increasing water pressure promotes the migration of water to the surface of the concrete. When the environment is very dry At that time, there was an early large evaporation of water. The rapid evaporation of water will reduce the solubility of the reactants in the capillary voids to below the saturation level, thereby hindering the normal hydration reaction of cement. When the evaporation rate of moisture on the surface of concrete is greater than the rate of moisture migration through the capillary pores, the concrete will undergo plastic shrinkage and cracking, causing a series of concrete quality problems.

Curing time

Cement clinker is composed of different mineral components, and the hydration rate of different mineral components is significantly different. For ordinary Portland cement, according to the speed of hydration rate, it has the following rules: tricalcium aluminate> tetracalcium aluminate ferrite> tricalcium silicate> dicalcium silicate. Law: dicalcium silicate> tricalcium silicate> tetracalcium aluminate> tricalcium aluminate. It can be seen from the above that the different mineral components of cement and their proportions are important for the setting time, early strength and late strength of cement. Influence. Since the hydration reaction of cement will last for a long time, during the whole process of cement hardening, both the early and late curing are very important and indispensable.

In addition, curing time is another important factor that affects the performance of concrete. The increase in the strength of the concrete is achieved in a curing environment where the temperature is constantly changing. Under general conditions, the strength of concrete generally increases with the increase of the curing age. But in different stages, the growth rate is different, and the early strength increases faster with age. The 3 d strength of the concrete can reach about 50% of the 28 d strength, the 7 d strength can reach about 67% of the 28 d strength, and the strength increase after 28 d is gradually slow.

Analysis on the quality control in the secondary lining construction of the tunnel

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During the construction of the secondary lining of the tunnel, lining materials, concrete mix ratios and construction methods should be selected reasonably, and construction experience should be constantly summed up, and the quality awareness of relevant personnel should be improved, and the surface defects of concrete should be controlled to ensure the quality of the project so as to achieve good social benefits and Economic benefits.

The tunnel lining structure can be roughly divided into five processes: tunnel bottom (foundation) treatment, base surface treatment, waterproof material laying, concrete lining, and polyurethane mortar jointing. During the construction process, quality control is mainly done in the following aspects:

1. The bottom of the tunnel is the foundation of the lining structure. If it is loose and not strong enough, the lining structure is prone to settlement and deformation, and the foundation surface is flat. It is the key to ensure the accuracy of the elevation and the elevation error to meet the specification requirements and ensure the realization of the design longitudinal slope. Therefore, the construction process In accordance with the design requirements, do the initial support. When there is no initial support, the flatness and compaction quality of the foundation surface should be removed to remove the scum to ensure that the foundation surface is solid and flat.

2. Base surface treatment is a key process for waterproofing. Monitoring and measurement analysis believes that after the surrounding rock and initial support deformation become stable, cut sharp objects on the surface, remove hard objects, fill up unevenness, and ensure that the base surface is flat The degree meets the specification requirements.

3. The protection and laying of waterproof materials is the quality focus in the construction process. Impervious materials are transported by special vehicles to avoid damage during transportation. After entering the field, check the geometric size, thickness, and strength for holes, pinholes, and flaws. The construction site is welded by professional and technical personnel of the factory using special tools. After the welding is completed, the quality of the weld is checked, whether there is any de-welding or missing welding, and each weld is checked for air inflation. The welding is required to be dense, wheel marks obvious, straight, and free. Wrinkles and waterproof materials are forbidden to step on, slip, slide, and walk, so as to avoid puncture damage to the plastic film. The waterproof board should be protected during the construction of the steel bar project, and the small damage detected before laying and concrete lining should be welded in time with a hand welding gun or repaired as required.

4. Measure before moving the lining trolley to ensure that the center line of the steel mold lining trolley is consistent with the center line of the tunnel, and the arch wall template is fixed after positioning, and the measurement is reviewed. Clean up debris, stagnant water and floating ballast at the foot of the wall, install a steel stopper template at the front end of the lining trolley, and install and fix the waterstop according to the design requirements; remove the waterstop protection mold at the construction joints of the upper group of lining concrete and conduct self-inspection Waterproof system settings.

5. The smoothness and cleanliness of the console car surface during the lining construction ensures the overall appearance quality of the tunnel surface.

Main factors affecting the quality of secondary lining construction

Tunnel waterproof board laying formwork

1. Irregular construction process or on-site operation

(1) The tunnel excavation is poorly formed and the lining concrete thickness is seriously uneven; under-excavation or initial support invades the lining boundary, resulting in insufficient lining concrete thickness; there is void behind the concrete lining of individual tunnels.

(2) The monitoring and measurement work was not carried out, and the construction time of the secondary lining was determined based on experience only. The safety and reliability were poor, which caused the secondary lining to bear the surrounding rock pressure beyond the design load.

(3) The measurement error of raw materials during the production of concrete is large, especially the random addition of admixtures, and the construction water consumption is not adjusted in time according to the actual moisture content of sand and stone, resulting in an increase in the water-to-binder ratio of concrete. The phenomenon of adding water during the transportation and pumping of concrete also exists from time to time.

(4) When the integral steel formwork trolley is used for construction, the concrete is not vibrated during pouring or the homogeneity of the leaking concrete is poor.

(5) Pursuing the construction schedule blindly. The demoulding time is arbitrarily advanced, so that the low-strength concrete bears excessive load and destroys the concrete structure. After demoulding, no moisture curing of the concrete was carried out.

(6) During summer construction, sand and stone materials are stacked in the open air without effective cooling measures, and the concrete entering mold temperature is high. The cold-proof and heat-preservation measures taken during construction in winter are not effective.

2. Poor quality of raw materials and unreasonable mix ratio design

Improper selection of cement varieties, poor stability, and mixing of different batches of cement. The gradation of crushed stone and sand is poor, the mud content exceeds the standard, and the content of stone powder in the crushed stone is too large, needles and flakes, which affects the cement and aggregate coagulation. When designing the mix ratio, neglect the negative impact of the increase in cement content on the performance of concrete. The selection of admixtures and admixtures lacks the guidance of professional and technical personnel, and often fails to achieve the expected results.

Quality control in the construction of secondary lining concrete

Pipeline municipal lining trolley

1. Positioning of the lining trolley

In the concrete construction of the secondary lining of the tunnel, if the lining trolley is not firmly in place, the phenomenon of dislocation and form running is extremely suitable. In order to prevent the occurrence of such problems, the construction technicians should focus on checking:

A. Before lining construction, the assembling design of the overall lining trolley should try to ensure the smooth connection between the plates. After the lining trolley is assembled, the structure size must be checked and adjusted to ensure that the structure size meets the design requirements.

B. The flatness of the steel formwork has an important influence on the appearance of the lining concrete. If the steel mold is uneven or too rough, holes and air bubbles will be left on the surface of the concrete after removing the mold.

C. Check whether the lining trolley is deformed during use. If it is deformed, it should be adjusted in time.

D. Check whether the support rigidity of the lining trolley is enough. If the support rigidity is not enough, the template of the trolley will converge and deform inward under the action of the mixed pressure, resulting in the staggered joints of the lining board. To deal with such problems, the support of the trolley should be strengthened, the number of support screws should be increased, and all supports should be fastened in place to ensure the overall force of the trolley is balanced.

E. Before the formwork trolley is in place, the construction technicians should carefully check whether the formwork is polished cleanly. The improper brushing of the formwork is an important reason for the local pitted surface of the mixed soil.

F. Excessive or uneven coating of mold release agent (use of waste engine oil is strictly prohibited) on the template will cause oil stains and inconsistent color after the lining concrete is demolded, which will affect the appearance quality. After applying the oil, it is advisable to keep the oil on your hands.

2. Concrete construction technology

The improper construction process of the concrete is the main reason for the honeycomb pockmarked surface of the secondary lining concrete surface.

A. Improper mixing ratio of concrete or inaccurate water consumption of sand, gravel, and cement materials, resulting in less mortar, more stones, coarse aggregate sinking, and slurry floating, resulting in honeycomb pitting on the concrete surface near the arching line. Construction The mix ratio should be adjusted at any time with changes in raw materials, climate, machinery and other conditions.

B. When pumping concrete, use the upper, middle and lower three-layer windows of the trolley to pour the concrete in layers. The drop should be less than 1m, and the two sides shall be poured alternately or symmetrically continuous full-section pumping. Strict attention should be paid to this point to prevent the bias voltage from deforming the template.

C. Master the correct vibrating method. If the vibrating time is too short, it is easy to form shrinkage cracks in the upper layer, and the strength is uneven. Prolong the vibrating time appropriately to make the vibrating compact; at the same time, the concrete vibrating can also have the effect of smoothly dissipating air bubbles. The distance between the vibrator and the template is controlled at about 10cm. If the distance is too small, the vibration will easily strike the template and cause vibration, and the vibration of the template will easily cause a large number of bubbles to concentrate on the template. If the bubbles cannot escape effectively, the appearance quality of the concrete will be affected.

D. Demoulding and curing time. When demoulding the secondary lining concrete, ensure that the concrete compressive strength is greater than 25MPa and the tensile strength is greater than 0.5MPa. After removing the mold, the concrete should be sprinkled with water for curing, and the curing should be longer than 14 days.

3. Waterproof and drainage construction

A. Before the waterproof and drainage construction, the base surface should be treated first, all kinds of foreign objects should be thoroughly removed, and all kinds of sharp protruding objects should be removed.

B. For the construction of vertical and circular permeable blind pipes, the key point is to control the installation position. The longitudinal drainage pipe of the tunnel is placed on the low side wall at the corner of the wall. The upper side of the drainage pipe is made of sand-free concrete as the drainage body, and the lower side is wrapped by a waterproof board. The width of the low side wall should be as narrow as possible, based on the principle of not occupying or less occupying the thickness of the second lining, generally about 15cm wide. The height of the low side wall is consistent with the design elevation of the bottom of the longitudinal drainage pipe, the cement content of the drainage body does not exceed 80kg/m’, and the particle size
16mm-32mm, the surface slope is controlled at 1:1 during construction. The vertical and circular permeable blind pipes are equipped with PVC pipes at the second lining to ensure that the outlet is easy to drain.

Water conservancy and hydropower lining trolley

C. The key point of the waterproof board construction is to control the waterproof board and the geotextile closely to the base surface to prevent leaving a cavity behind. After the waterproof board and the hot-melt gasket are heat-sealed, the bonding and peeling strength of the two shall not be less than the tensile strength of the waterproof board. The welding seam of the waterproof board should be welded firmly, and air tightness inspection should be carried out to prevent missing welding in individual places, and hot air guns should be used to repair the missing welds.

D. The positioning and installation of the buried waterstop should be accurate. The hollow ring in the middle shall coincide with the construction joint. The waterstop is fixed on the stopper template. One end is installed first. When the concrete is poured, the other end should be fixed with additional steel bars to prevent the waterstop from shifting and affect the waterstop effect. When the waterstop is positioned, it should be kept flat on the interface. If there is any kinking phenomenon, it should be adjusted in time.

4. Rebar construction structure

Rebar blanking should be accurate to minimize the number of rebar joints. Rebar joints should be set at places with less stress, and they should be distributed. When binding steel bars, control the spacing between the steel bars and control the thickness of the concrete protective layer of the steel bars to prevent the exposed bars or the thickness of the concrete protective layer from being too large. Be careful not to puncture the waterproof board during the process of tying the steel bars.

5. Installation of pre-lined channel

Accurately bury all kinds of curved and straight precision channels according to the design drawings. Use the method of opening bolt positioning holes on the trolley template to locate the installation channels, and each channel must have 2 to 3 fixed points. The construction error of the channel embedded in the concrete surface, the inclined construction error of the channel and the parallel construction error between the two channels (each group) require high precision, and special attention should be paid to strengthen the control during the construction. The already constructed channel shall be protected and shall not be blocked by cement slurry and other debris. If any, it shall be cleaned up in time.

With the rapid development of engineering construction, more and more tunnels are being built. How to control the quality of the secondary lining of the tunnel not only achieves the design function, but also meets the requirements of internal reality and external beauty is the goal of engineering construction.

The cracks in the lining of expressway tunnels and the treatment measures

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Because natural conditions, geological environment, climate conditions, etc. are relatively complex and changeable, the construction difficulty of highway engineering is increased to a large extent. Tunnel engineering is a particularly important project in expressway construction. In recent years, as expressway construction extends to mountainous areas, the number of tunnel projects has also increased greatly. Tunnel construction has a certain degree of danger, concealment, and technology, so it is easy to encounter various technical problems in the process of construction. In addition to being restricted by the technical level of tunnel design, management level, materials and other factors, highway tunnels are prone to various diseases, among which lining cracks are more common. Lining cracks and diseases will affect the quality of highway tunnels to a large extent. Therefore, it is necessary to pay more attention to the diseases. Only by analyzing and finding out the cause of the disease can we formulate more targeted remediation measures and realize effective treatment.

Double-track railway lining trolley

Overview of Lining Cracks

Lining cracks are a very common type of disease in highway operations. When a highway tunnel lining cracks, it is easy to cause water leakage in existing tunnels. If the cracks are serious, it may even cause a sharp drop in the bearing capacity of the highway tunnel structure. Caused the road tunnel instability, collapse and other safety accidents. It can be seen that lining cracks are prone to have many adverse effects on highway tunnels. The distribution of lining cracks is more diversified, such as vertical cracks, longitudinal cracks, diagonal cracks, combined cracks and so on. Different lining cracks in different distribution patterns require different treatment methods. In order to achieve a better control effect, it is necessary to have a full understanding of the different distribution patterns of cracks.

Vertical cracks mainly refer to vertical axis cracks that occur in highway tunnels. The distribution of cracks occurs more in construction joints, settlement joints and the junctions of different addresses. For example, vertical cracks are prone to occur in the middle part of each slab molded concrete. Vertical cracks generally start from the bottom of the side wall, and continue to the end of the arch waist. The cracks are basically symmetrical at the left and right side walls, and some of the cracks will extend upward until they meet the vault. Longitudinal cracks mostly occur in the part of the tunnel vault and arch waist. Relatively speaking, the number of longitudinal cracks is less than the number of vertical cracks, but the harmfulness of longitudinal cracks is greater than that of vertical cracks. With the further development of longitudinal cracks, it is very likely that the tunnel lining will break or even collapse.

Oblique cracks mostly occur in the location of the tunnel arch and side walls, and oblique cracks are also harmful. Combination cracks refer to the cracks formed by any combination of the above three types of cracks. Combination cracks generally show Y-shaped and X-shaped cracks. When the number of cracks is too large, it is easy to form network cracks when the crack distribution is added. .

Analysis of Causes of Lining Cracks in Expressway Tunnels

Pipeline municipal lining trolley

There are many reasons for the cracking of highway tunnel lining, such as natural environment, materials, construction, etc., which are prone to cause lining cracks. In order to better prevent and treat lining cracks, it is necessary to understand the causes of lining cracks. The following section analyzes the causes of lining cracks from the aspects of design, construction, and materials.

1. Design reasons

Compared with other pavement engineering, highway tunnel engineering is more complicated, and it has higher requirements in terms of construction, design, technology and so on. As far as tunnel design is concerned, it includes overall line layout, entrance and exit settings, construction and excavation plan, etc. Any omission in any of the design links will affect the quality of tunnel construction and cause lining cracks. In the design of highway tunnels, the problem of unreasonable structural design is more prominent. Designers often pay attention to the design of structural forces and surrounding rock stability, and ignore structural design and detailed design. For example, the design of the longitudinal drainage pipe of the tunnel did not consider a separate location, which could easily lead to water intrusion and cracks in the lining.

2. Reasons for construction

Highway tunnel construction has higher requirements on technology and technology. Scientific and advanced construction technology can ensure the quality of tunnel construction and improve the reliability of the overall tunnel. As far as the current highway tunnel construction is concerned, due to the limitation of construction technology level, construction environment and construction technology, some shortcomings and problems are prone to occur during the construction process, and improper construction technology will cause tunnel lining cracks. The construction quality directly affects the overall quality and operation efficiency of the tunnel. If there are quality problems in the construction, it will easily cause the tunnel to appear disease in the subsequent operation process.

3. Material reasons

In the construction of highway tunnel engineering, materials are a particularly important subject. Whether the quality of materials passes the customs directly affects the construction quality of the tunnel engineering and the subsequent operation efficiency. For example, during the construction process, the large error in the measurement of raw materials during concrete production will affect the stability and reliability of the tunnel lining, and it will be prone to cracks in the lining.

Treatment measures for cracks in highway tunnel lining

The tunnel concrete maintenance formwork

1. Preventive measures for lining cracks

The treatment of lining cracks is more to take measures to repair and strengthen afterwards. Although repairing and strengthening can also achieve effective treatment effects, it will affect the appearance of the tunnel and the overall operating efficiency to a certain extent. Therefore, for highway tunnel lining cracks, the key to its treatment lies in the prevention and control of cracks. The most important thing for prevention and control is to take effective measures during the design and construction process. For example, in terms of lining structure design and tunnel excavation methods, it is necessary to strengthen construction management and improve the technical level in order to reduce the occurrence of tunnel lining cracks in the later period. During the construction of highway tunnels, by improving the quality of construction and strengthening construction management, the quality and efficiency of the later operation of the tunnel can be ensured to a large extent. This is also the fundamental method of treating tunnel lining cracks, that is, controlling and preventing cracks from the source. happened.

2. Lining crack repair technology

For lining cracks that have occurred, effective repair techniques must be adopted for treatment. According to different types of lining cracks, different crack repair techniques need to be selected. For example, for some small, non-hazardous cracks, spray concrete reinforcement can be used to repair. For some complex, wide, and hazardous cracks, it is necessary to choose the most reasonable repair technology according to the actual situation. In the case of serious diseases, it is even necessary to consider the method of partial dismantling or lining dismantling for disease treatment. Lining crack repair techniques are more diversified, such as steel belt reinforcement, arch reinforcement, anchor rod reinforcement, basin concrete reinforcement and other methods for repair and management. For the phenomenon of severe damage to the tunnel lining structure, peeling off and falling blocks, the method of sleeve arch reinforcement can be used for disease treatment. The arch reinforcement has good durability and bearing capacity, and is a very effective method of structural reinforcement. When the local cracks in the tunnel are large in scale and the cracks are more harmful, it is necessary to consider the way of lining removal and replacement for disease treatment.

3. Strengthen the maintenance and repair of highway tunnels

In the process of putting the highway tunnel into operation, many serious lining cracks were further developed due to the lack of early control. Therefore, during the operation of expressway tunnels, it is necessary to strengthen the regular inspection, maintenance, and maintenance of the tunnel, which can not only improve the operating quality of the tunnel, extend the service life of the tunnel, but also find the diseases and problems in the tunnel in time. , And then take timely and effective measures for governance. By strengthening the maintenance and repair work of highway tunnels, the lining cracks can be effectively prevented from developing further, and the diseases can be strangled in the budding period.

In summary, the lining cracks of expressway tunnels have a direct impact on the normal operation and overall quality of expressway tunnels. Therefore, in order to better ensure the safe and reliable operation of highway tunnels, it is necessary to pay more attention to lining cracks. It is difficult to treat tunnel cracks, and the treatment cost is relatively high. If the construction team does not have professional treatment technology and the treatment equipment is simple, it will be difficult to achieve the ideal treatment effect. Therefore, the key to the treatment of tunnel lining cracks should be to strengthen the construction and management during the construction period, while paying attention to the structural design of the tunnel. For lining cracks that have occurred, methods such as shotcrete reinforcement, steel belt reinforcement, and arch reinforcement can be used to treat them. Only by thoroughly solving the lining cracks can the normal and safe operation of highway tunnels be guaranteed.

Maintenance skills of tunnel lining walking system

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The tunnel lining walking system is an important part of the lining trolley. It must be inspected, maintained, operated correctly, and adjusted carefully in use to keep it in a good technical state.

1. Clean and clean in time

After the lining trolley operation is completed, the sludge contaminated on the wheels and crawlers should be removed (washed) in time to keep the walking system clean, especially the end surface oil seal device of the supporting roller should be cleaned, inspected and maintained in time. In addition, be careful not to stain rubber tires with corrosive substances such as oil, acid, and alkali.

2. Maintain normal tire pressure and track tension

Before using the lining trolley, carefully check whether the tire pressure is normal (it can be slightly higher during transportation operations, lower during pothole operations; slightly higher in winter and lower in summer) to avoid flat tires or A puncture. If the track is too loose or too tight, it is easy to cause accelerated wear of track shoes, track shafts and wheels, so the appropriate tension must be maintained.

Travel system

3. Check and adjust the front wheel alignment

If the front wheel is too large and the toe is too small, it is easy to cause eccentric wear during walking. The main reason is that the front axle bearing and sleeve are deformed by impact, or the fastening device of the front axle telescopic sleeve is loosened, which will change the positioning angle of the front wheel and cause abnormal wear. Therefore, you must always check whether the positioning angle of the front wheel is moderate during use, and adjust the toe.

4. Operate correctly and drive carefully

When the lining trolley is walking, you should be careful not to cross obstacles at high speed, and not to make sharp turns under heavy load; drive at low speed on uneven roads, and try to avoid emergency braking; climb slopes with heavy loads or on muddy roads When driving, the walking system should not be severely slipped.

Travel system

5. Pay attention to operating conditions

When the lining trolley is operating in a low-lying environment, it is necessary to avoid trapping as much as possible. After the trapped vehicle, it must be removed by traction and promotion. The method of increasing the throttle (black smoke) must not be used to adjust the running system to idling. When working in dry land with sharp stubble and high stubble, it is necessary to prevent the tires from being punctured and the shaft from being entangled by the crop stalks.

The walking system affects the safety of the lining trolley. The walking system will inevitably fail after being used for a long time. Although we often maintain the lining too heavy, we ignore the maintenance of the walking system. If the deposits inside the walking system cannot be removed regularly, it is very easy to cause damage to the system, leading to high maintenance costs.

Design and use of tunnel lining trolley

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In the process of tunnel construction, the use of concrete for secondary lining is a very important work, and with the development of the times, there are new requirements for concrete secondary lining work, requiring higher quality and shorter construction period. Under the current trend, a good design of lining trolley has become an inevitable requirement.

Tunnel lining trolley and its requirements

The lining trolley is a special equipment that must be used in the secondary lining of the tunnel construction process, and is used for the concrete lining construction of the inner wall of the tunnel. Concrete lining trolley is an indispensable non-standard product for secondary lining during tunnel construction. There are mainly simple lining trolleys, fully hydraulic automatic walking lining trolleys and net-frame lining trolleys. Full hydraulic lining trolley can be divided into side-top arch type, full circle needle beam type, bottom mold needle beam type, full circle travel type and so on.

General requirements for tunnel lining trolleys

(1) The external dimensions of the formwork must be able to meet the requirements of the tunnel section. The shape error requirements are as follows: when ≤3m, not more than 10mm, when R>3m, not more than 20mm (R refers to the maximum section radius at the tunnel section).

(2) It must be ensured that the center of the formwork coincides with the center line of the tunnel. Therefore, the template can move left and right (that is, horizontally) when the main frame of the trolley does not shift laterally. Generally, the horizontal movement distance does not exceed 150mm from the centerline.

(3) The action of the template must be able to effectively complete the mold supporting, mold dismantling, and locking and positioning work. In the template trolley designed in recent years, the support and demolding of the template are hydraulically driven, and the locking is completed by mechanical devices. The overall formwork should be left with operating windows and grouting holes to meet construction requirements. The length of the overall formwork and the wheelbase of the gantry traveling wheels are related to the turning radius of the tunnel and the construction organization of other supporting machinery. The general formwork length is 6m ~ 12m, and the gantry axis distance is less than about 1m of the entire formwork length.

(4) The design of each component of the trolley should be able to meet the transportation conditions. The clearance in the main frame of the trolley should be able to meet the passing of other construction machinery.

(5) According to user requirements, the trolley has self-propelled and non-self-propelled. Regardless of the type, it should be considered that it can meet the conditions of other mechanical drag driving, and at the same time, the passing capacity of the trolley when it passes through the fork should be considered.

Design of Tunnel Lining Trolley

Pipeline municipal lining trolley

(1) Template

The design of the commonly used tunnel lining trolley formwork system needs to understand the formwork contour line, formwork lining length, work window and grouting port layout and positioning, overlap length, etc., to consider the division of the formwork, the parting situation and the release of the formwork according to the construction requirements. Die gap.

(1) Determination of the position and type of the operation window and grouting port: Arrange the grouting port of the operation window according to the requirements (the height of the bottom row of operation windows is not more than 1500mm from the side base), and the grouting port is generally closed and the outer arc surface is Flat type.

(2) Determination of the length of the panel: According to the overall design, divide the mold and determine the position of the hinge structure, but the length of the panel should not be between 5950 and 6500mm.

(3) Design of formwork panels, webs, angles and other materials: The thickness of the panel is generally between 8mm~12mm, the key points on the webs need to be arranged with corresponding bolt holes, and the appropriate reinforcement materials should be selected between the webs.

(4) The design of the mold release gap of the template: the minimum release gap is not less than 60mm (that is, the hinge between the top mold and the side mold). Generally, the design is 110mm, and the ground gap is greater than 150mm; the space for applying the release agent needs to be considered ( Not less than 350mm). There are four design schemes for the top formwork of the variable section tunnel lining trolley formwork system.

First, use a widening block at the variable cross-section of the top mold. That is to say, according to the section size of the tunnel, the smallest section size is selected as the reference section of the design. The top form is divided into two parts, left and right, which can be used directly at the minimum section of the construction, and in the construction of other widened sections. At the same time, the top mold is separated from the middle, and the top and side molds on both sides are moved to the corresponding positions at the same time. The template rose to the required height of the design.

Second, rotate the top mold and install a widening block. The design and use process of the trolley at the smallest cross-section are the same as in Scheme 1, and during the use of widening the cross-section, the top mold should be separated from the middle connection, and the top mold and the side mold should be moved outward to the corresponding position. , And rotate the top mold of the two halves around the hinge pin shaft until the end of the top mold is tangent to the designed contour line, and then install the required widening block, heightening pad, etc.

Third, rotate a part of the top mold and install a widening block. That is, according to the size of the tunnel section, the smallest section size is used as the design reference section, and the top form is divided into four pieces for design. The formwork is connected by bolts, which can be used directly in the construction process of the smallest section. In the construction of other sections, the top mold is separated from the middle, and the top and side molds on both sides are moved to the corresponding positions at the same time, and then the template on one side is rotated outwards until the end of the top mold and the design The contour lines of the tangent, and then the installation of the required widening block is carried out, and the template is raised to the required height of the design by means of heightening pads, oil cylinders or a combination of the two.

Fourth, replace all the top mold templates on one side at different sections. That is, the tangent point of the top mold at the variable section is connected by bolts, so that during the use of different sections, the top mold template on one side is gradually replaced, and the position of the side mold moves inward or outward. . When adopting this scheme, it should be noted that the connection position of the top mold and the upper mold beam in the support system must meet the size requirements of the top mold on the other side, so as to ensure the operability when changing the section.

(2) Door frame

The role of the gantry system is to support the entire formwork system and prevent the formwork from deforming and shrinking inwardly under pressure when lining the lining. The mast mainly consists of upper and lower longitudinal beams, columns, mast beams, longitudinal joints, reinforced diagonal braces, formwork beams, formwork columns, screw rods, cylinders, transversal mechanisms, walking mechanisms and other components. Among them, the gantry beam is an important load-bearing component of the formwork trolley, which requires high material strength and rigidity. Generally, the section is made of tailor-welded H-shaped steel, industrial steel, etc. For variable-section tunnels, the formwork must be moved to the outside, and the portal beam must be lengthened. When designing, you can add a widening block on one side, and move the lateral movement mechanism to the side of the widening block; or design it into two left and right blocks, add a widening block in the middle part, and the lateral movement mechanism will move with the two blocks. mobile.

(3) Hydraulic system

Trolley design lifting cylinder, template cylinder and traverse cylinder, cylinder stroke, zero stroke length, cylinder diameter and rod diameter size, pipe joint form, connecting pin hole diameter, connecting structure size, oil hole direction and external dimensions are based on the plan Determine; the working pressure of the hydraulic system is generally considered as 12MPa, and the rated pressure is considered as 16MPa. Variable cross-sections need to increase the number of joints and tubing to match this. The hydraulic system can improve the efficiency of the tunnel lining trolley and reduce the workload of workers.

(4) Other auxiliary systems

The formwork trolley should consider the traversing form of the ventilation pipe; sufficient load-bearing screws and screw rods should be provided; the vault of the formwork trolley should be equipped with concrete plugging devices and inspection holes at appropriate positions; the attachment type installed on the formwork trolley The vibrator should be able to start separately; the curve section should consider the change of the left and right side lap length caused by the difference between the inner and outer arc lengths, so as to make the arc smooth, reduce the staggered joints, and ensure the same curvature of the front and rear templates of the trolley; ensure the perfusion hole In the middle of the vault of the formwork trolley, to ensure that the concrete on both sides is poured symmetrically at the same time.

The use of tunnel lining trolley

Pipeline municipal lining trolley

(1) Installation of lining trolley

Due to the different tunnel construction methods, the trolley installation method is divided into two types: self-entry into the tunnel after installation outside the tunnel and hoisting in the tunnel. If installing in a hole, the excavation outline of the installation zone should be appropriately enlarged in advance, generally 50 ~ 80cm. According to the size of the tunnel section and the length of the trolley, 3~6 grouting anchor rods are set along the axis of the arch, with an interval of about 1/4 of the template length, and the ends of the anchor rods are bent into hooks to facilitate the fixed hand gourd. Due to the limited space in the cave, the transportation trolley components should be arranged in a reasonable order.

First assemble the main frame and connect the walking motor to install the template. After the top mold is assembled, lift it with a chain hoist, move the main frame of the trolley under the top mold, and install the top mold. The side form is standing on the side wall of the tunnel. After the top form is installed, it is hoisted and installed on the arch formwork with a chain hoist and connected with a pin. If hoisting outside the tunnel is adopted, the installation site should be selected to facilitate entry into the tunnel before hoisting, and the angle between the axis of the backstage car and the axis of the tunnel should not exceed 5 degrees after installation. For laying the track, the sleepers and rails must meet the requirements, and the gauge error after laying is controlled within 10mm; the track and the sleepers must be fixed with spikes to prevent danger when the trolley is walking; the distance between the sleepers must not be greater than 70cm to prevent the rails from being crushed .

(2) Demolition

When the strength of the concrete meets the requirements, remove the bottom screw support, remove the plug plate from the bottom up, loosen the lateral lead screws of each layer, and recover the part of the trolley below the hinge to separate it from the concrete; operate the lifting cylinder, Make it reach zero stroke to lower the trolley as a whole, and separate the trolley from the concrete above the hinge; at this time, the surveyor should check the clearance of the trolley. If the side form invades the traveling clearance of the passing vehicle, it needs to be re-adjusted. The stroke of the template oil cylinder meets the driving safety requirements, and the mold removal is completed. Check the status of each demoulding step. After confirming that it is in place, move the platform to the lower group of lining position; check the appearance quality of the lining concrete, analyze the cause of the problem, and perform partial repair; check whether the steel template has deformed parts for replacement; Completely remove the concrete on the surface of the formwork, and evenly apply the release agent.

Disassembly, assembly and use characteristics of tunnel invert trestle

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Tunnel invert construction has always been an important factor affecting construction progress and quality control. In order to reduce the interference of invert construction on slag loading and slagging machine and tunnel lining trolley, and to achieve the goal of accelerating the construction progress of mechanized parallel operation, high The fully-automatically controlled and fully hydraulic inverted arch trestle produced by GaoFei company has the following characteristics.

1) Modular assembly structure: The hydraulic inverted arch trestle adopts a plate-beam structure, which can be assembled quickly and modularly, and realizes the characteristics of variable span and convenient transportation.

2) Cantilever mobile structure: The trestle has a front cantilever, and the whole machine can be cantilevered. It has the function of retreating across the pit, effectively avoiding the impact of the face of the tunnel and the inverted blasting flying rocks. The trestle bridge can be crossed or withdrawn from the invert construction area at any time according to the technological requirements of the tunnel construction operation.

3) Full hydraulic drive mode: The whole machine of the trestle bridge adopts hydraulic drive or crawler walking. It has the characteristics of flexible control, simple structure, low noise, stable and reliable performance, and convenient maintenance and repair.

4) Sliding shoe walking method: The trestle adopts a sliding shoe walking method, which has the advantages of compact structure, small footprint, no noise, and stable and reliable walking. Among them, the selected high-performance wear-resistant materials have long service life. , Maintenance and repair are simple and other features. Of course, the crawler chassis is even more advanced.

5) Fully automatic control system: The trestle introduces a fully automatic PLC control system, which uses microcomputer operation to realize fully automated walking, which greatly facilitates driving operations.

6) High construction safety: The overall structure of the hydraulic inverted arch trestle is novel and reasonable in design, with large bearing capacity, stable structure and safety and reliability, which provides safety guarantee for construction vehicles and operators.

Crawler Hydraulic inverting bridge formwork

 

Hoisting sequence and preparation of tunnel invert trestle

1. Preparations for the trestle:

1) Clean the concrete on the foundation to meet the construction conditions;

2) Use theodolite to find the positioning axis, and use the ink fountain to flick the line;

3) Measure the elevation of the steel column foundation with a spirit level, and organize the data for installation;

4) Transport the manufactured steel column to the designated location and place it;

5) Before hoisting, prepare various construction tools and equipment, and the construction machinery is in place, and can be put into use after passing the inspection;

2. Transportation and hoisting of tunnel hydraulic invert trestle:

According to the tunnel invert hydraulic trestle and steel column transportation route and transportation conditions, flatbed trucks are used for transportation. In order to ensure the safe transportation of the trestle bridge and steel columns to the construction site, the following points must be done:

1. The loading of the trestle on the vehicle should be balanced to avoid unbalanced load.

2. Before transportation, the total weight and axle load of the vehicle should be checked, and the error between the two should be within 5%.

3. Trestle transport vehicles and anchor-spraying trolleys should run at a low speed with a speed limit of 5km/h. At the same time, shifting, braking and shaking from side to side are strictly prohibited.

4. It is strictly forbidden to brake suddenly during transportation of the drilling trolley, crawler slag raking machine, and spray anchor trolley to prevent relative sliding. A red light should be set up at night to warn, and a dedicated guard should be set up.

3. Hoisting sequence of tunnel invert trestle:

Hoisting of hydraulic trestle bridge for tunnel inverted arch: mark the axis and elevation in advance, indicate the axis recheck size, measure the top surface with a spirit level and level with the pad, do a good job of leveling and layout of the construction site, and maintain the power and road of the construction site Unblocked and shelf erection work. Use two cranes to lift the hydraulic trestle bridge of the tunnel invert that has been assembled on site to the concrete that has been constructed, use the inverted chain and the pry bar to assist in positioning, and then carry out the calibration according to the axis and elevation. After the review is correct, the formal fixation is carried out.

According to the site conditions and construction plan, the two-piece column is now hoisted. Before hoisting, clean the concrete on the concrete foundation until the construction conditions are met, find out the axis and elevation, and use two cranes to hoist the two columns. After hoisting, use the backing plate, jack, level, and theodolite to check the axis, horizontal elevation, and verticality of the steel column. After the organized tunnel invert hydraulic trestle bridge does not need to be hoisted, it will just move forward with the excavation.

4. Construction of the tunnel invert hydraulic trestle:

Invert construction process: tunnel invert hydraulic trestle in place → invert arch excavation → initial support construction of invert arch → invert arch reinforcement binding → invert lining concrete pouring → invert arch filling concrete pouring → concrete maintenance → enter the next cycle .

The specific arrangements are as follows: The first cycle invert construction: excavation and pouring of the 1# invert trough on the 1st to 3rd days, and the excavation and pouring of the 2# invert trough on the 3rd to 6th days. During this period, the inverted arch trestle bridges above the two inverted arch trough sections are kept in traffic, that is, all trestle bridges above the inverted arch trough will not be removed during the first cycle (1 to 6 days).

On the 7th day of the second cycle invert construction, you can move the trestle bridge originally erected above the l# invert trough to the 3# invert trough, and start the construction of the 3# invert trough. At that time, l# invert concrete has reached strength requirements, vehicles can pass, and so on to complete the construction of other inverts.

There are mainly six construction methods: inverted arch splitting construction method, invert arch trestle construction method, parallel pilot pit transportation inverted arch construction method, buttress construction method, invert precast construction method, and invert sequential construction method.

Crawler Hydraulic inverting bridge formwork

Transverse movement of hydraulic tunnel invert trestle:

1. Operate the approach bridge lifting cylinder to retract the front and rear approach bridges;

2. Operate the horizontal movement cylinder to drive the main bridge and track to move horizontally;

3. Operate the lifting cylinder, the lifting cylinder is supported on the concrete surface through the walking frame and track, and the trestle bridge is raised, and the trestle bridge lifts the underframe through the slide rail and the chute;

4. Operate the lateral movement cylinder to move the underframe laterally;

5. Operate the lifting cylinder, lower the trestle and underframe, and lift the walking frame and track;

6. Operate the traverse cylinder to move the trestle bridge laterally. This reciprocating movement causes the trestle bridge to move laterally to the opposite side.

Front (rear) movement of hydraulic trestle bridge for tunnel inverted arch:

1. Operate the drive motor, the drive motor passes through the sprocket, and the chain pulls the trestle to move 3.5 meters on the track;

2. Operate the lifting cylinder, lower the trestle bridge and lift the walking frame and track;

3. Operate the drive motor, the drive motor moves forward 3.5 meters through the sprocket and the chain traction track;
4. Operate the lifting cylinder, raise the trestle bridge and lower the walking frame and track;

5. Operate the drive motor, the drive motor passes through the sprocket, and the chain pulls the trestle to move 3.5 meters on the track. This repetition drives the trestle bridge to move longitudinally to the next station.

Preliminary preparations for slipform construction:

1. First advance one station to excavate the bottom of the half-side tunnel, remove ballast, tie up steel bars and other lining preparations;

2. Set up the trestle bridge (traverse and move forward through the trestle bridge), and lower the trestle bridge before and after the approach bridge;

3. Carry out the lining preparation work such as excavation at the bottom of the tunnel on the other side, ballast removal and reinforcement.

Slipform construction of tunnel invert hydraulic trestle bridge:

1. Move the trestle bridge to the middle of the tunnel where concrete needs to be poured, and adjust the long approach bridge to level;

2. Operate the sliding mold traction hoist to adjust the sliding mold to the desired position in the longitudinal direction;

3. Operate the sliding mold to raise the hoist level and adjust the sliding mold to the required height;

4. Pour concrete along the slipform and vibrate;

5. According to the concrete solidification status, use the sliding sliding form of the traction hoist, and the speed of 1-1.5 meters/hour is appropriate, until the concrete construction of the warehouse is completed;

6. Pouring invert backfill concrete;

7. Separate the traction and lifting hoist from the sliding form, and move the trestle forward after the invert backfill concrete reaches the strength of 5mpa.

Detailed knowledge of tunnel lining trolley

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The tunnel lining trolley refers to the special equipment that must be used in the secondary lining of the tunnel construction process. The equipment is mainly used for the concrete lining construction of the inner wall of the tunnel. Today we will learn more about the detailed knowledge of the tunnel lining trolley!

Detailed knowledge of tunnel lining trolley

The quality of the tunnel lining trolley is transmitted to the supporting organization through the steel mold of the trolley, and then to the portal frame. The lining concrete is in a solid-liquid state. Large vertical pressure and lateral pressure are generated on the top and side, and a large buoyancy occurs together. When the buoyancy force exceeds the straight pressure and the weight of the trolley, the trolley will float up. It will not work normally.

In order to deal with this technical problem, after careful calculation, optimized planning, and reasonable selection of each supporting position. That is, the lower longitudinal beams inside the mast are supported on the ground to prevent the side pressure from causing the mast columns to retract, and there are several horizontal supports on the outer side of the mast and the longitudinal beams of the side form, at the upper beam and the upper longitudinal beam of the mast. Several straight supports are selected (the top hydraulic cylinders are arranged on the horizontal part of the gantry at both ends, and the middle is a straight supporting screw), and they are uniformly distributed in the longitudinal direction of the trolley.

The hydraulic cylinder is determined by the hydraulic lock, and the supporting screw is used for mechanical determination, which ensures that the hydraulic cylinder does not retract and the template does not deform during the lining construction. Lining formwork trolley (referred to as trolley) is the construction equipment for pouring the secondary lining concrete of the tunnel. Cooperating with other auxiliary machinery, it can greatly reduce the labor force, improve the mechanization efficiency of the second lining construction of the tunnel, and improve the construction progress. It has low investment cost and reliable structure. , Convenient operation, good tunnel forming surface, etc., therefore, it is widely used in highway, railway, hydropower, municipal, national defense, and other engineering constructions.

The tunnel lining trolley is a special equipment that must be used in the secondary lining of the tunnel construction process, and is used for the concrete lining construction of the inner wall of the tunnel. In the construction of hydraulic tunnels and bridges, lifting slipforms, jacking slipforms, and overturning forms are also commonly used. The tunnel lining trolley is a special equipment that must be used in the secondary lining of the tunnel construction process, and is used for the concrete lining construction of the inner wall of the tunnel.

The tunnel lining trolley adopts hydraulic transmission, which simplifies the structure of the trolley frame, reduces the weight, and also improves the flexibility and diversity of the structure. After analysis and comparison of various trolley frame structure schemes, strength calculations, and optimization, 9m four doors are selected With a 12m main portal structure, its structural weight is reduced by more than 40% compared with the mechanical type, and the production cost is reduced by more than 25%.

The steel mold is the working device of the tunnel lining trolley. Its appearance quality and dimensional accuracy directly determine the quality of the concrete lining. At the same time, it is also a difficult part to process. A reasonable processing and welding process has been formulated, and special assembled welded tires have been designed and processed. Die to ensure the accuracy of the overall dimensions, minimize welding distortion, and ensure that the outer surface is smooth and free of defects such as unevenness. In order to control the misalignment of adjacent templates, the stabilizing pins of interference fit are used to fix the connecting plates of adjacent templates as a whole, which effectively controls the problem of misalignment of adjacent templates caused by the gap between the bolt holes.

Causes of tunnel lining erosion and preventive measures

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The generation of tunnel lining erosion affects the overall safety performance of the tunnel lining. Therefore, prevention of tunnel lining erosion should be done well. In fact, the main reasons for the erosion of the tunnel lining are the existence of corrosive media; the existence of easily corrosive substances; the existence and mobility of groundwater. Let’s analyze the specific causes of erosion and the corresponding preventive measures.

  1. Causes of tunnel lining erosion

The corrosive environmental water behind the lining easily seeps along the lining pores, working joints, deformation joints and other holes to the inside of the lining, which becomes tunnel leakage water, which can cause physical or chemical effects on the lining concrete, stone masonry, and mortar joints. Corrosion, causing corrosion of the lining. Where there are geographic conditions such as coal series strata, sulfide mineral strata, gypsum-bearing strata, salt strata, silt peat strata, saline soil, salt fields, sea water and infiltration ranges, etc., areas that may cause environmental erosion and damage to concrete should be treated. note.

Tunnel lining corrosion is divided into physical corrosion and chemical corrosion. There are two main types of physical erosion: frost heave cracks at the alternate freeze-thaw area and salt crystal cracks at the alternate dry-wet area. Chemical attack is a very complex physical and chemical process. Based on the research results at home and abroad, according to the main material factors and corrosion damage mechanism, it can be divided into five types: sulfate attack, magnesium salt attack, dissolution attack, carbonate attack and general attack.

Three elements that produce corrosion:

The presence of corrosive media; the presence of easily corrosive substances; the presence and mobility of groundwater.

Corrosion of the tunnel lining makes the concrete loose and its strength decreases, which reduces the load-bearing capacity of the tunnel lining. It also causes corrosion of steel rails and fasteners, shortens the service life, and endangers driving safety. In order to ensure the safe use of tunnel buildings, lining corrosion diseases should be actively prevented.

  1. Preventive measures for tunnel lining erosion

It is necessary to start with a good survey and design, master the engineering geology and hydrogeology data of the tunnel, find out the source and composition of the corrosive medium in the environmental water, and take preventive measures according to local conditions based on the correct determination of the degree of erosion of the lining concrete . Aiming at the causes and conditions of tunnel corrosion. At present, the main prevention and control measures taken for tunnel erosion are as follows.

(1) Improve the density and integrity of the lining.

(2) The method of admixing materials.

(3) Use corrosion-resistant cement.

(4) Strengthen the external drainage measures of the lining.

(5) Use dense materials that do not chemically interact with concrete, and make an isolation and waterproof layer on the outer surface of the lining.

(6) Use natural stone that does not chemically react with corrosive environment water to build the lining.

(7) Inject anti-corrosion grout to the back of the lining.

(8) Anti-corrosion concrete.

The anti-corrosion layer is a method of treating the surface of concrete. Various corrosion-resistant materials are laid on the surface of the lining concrete to make it a layer of anti-corrosion layer. The tunnel lining generally adopts a combination of anti-corrosion layer and waterproof layer, and is laid on the outside of the lining.

Selection of anti-erosion cement materials: sulfate-resistant cement and pozzolanic cement have good resistance to sulfate and seawater corrosion; bauxite cement has strong resistance to various chemical corrosion; pozzolanic cement is resistant to various chemical corrosive media It also has good resistance, and the price is cheap. It is suitable for use in medium and low corrosive media, but its frost resistance is poor, so you need to pay attention to it when using it. For tunnels resistant to sulfate erosion, it is better to use low-alkali and high-sulfate-resistant cement when grouting and pouring concrete; for operation and maintenance, maintenance, plugging, plastering, spraying concrete or mortar, it is better to use double fast cement .

 

Structure composition and use of tunnel lining trolley

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At present, in the tunnel machinery industry, the design scheme and internal structure of the lining trolley are different, but from the perspective of its use, the nature of the general road and railway trolleys is similar. The structure of the tunnel lining trolley consists of a portal frame assembly, a bracket assembly, a template assembly, an adjustment system, a hydraulic system, a running system, and an operating platform. Let’s take a closer look at it!

    1.Door frame assembly

The gantry assembly is mainly composed of gantry beams, gantry columns, lower longitudinal beams, upper longitudinal beams, lower longitudinal beams, and gantry diagonal braces. Each part is connected by bolts to form the overall gantry, and each beam and column pass through The connecting beam is connected with the diagonal rod. The mast is supported on the traveling wheel frame, and the mast is bolted to the lower longitudinal beam. The bottom surface of the lower longitudinal beam is equipped with foundation jacks. When lining, the concrete load is transferred to the mast through the formwork and is respectively transmitted through the traveling wheels and the foundation jack. To the rails-the ground. Since the mast is the main load-bearing support structure of the trolley, general section steel cannot meet its strength and rigidity requirements, so it is necessary to use steel plate assembly welding to form box beam steel. At the same time, in order to ensure the strength, rigidity and stability of the entire mast, a mast diagonal brace is added between the upright column and the crossbeam. This not only ensures the stability of the column’s compression bar, but also enables the mast to have Sufficient stiffness. The mast diagonal bracing is roughly divided into four types: single diagonal brace, double diagonal brace, triangle diagonal brace and double beam diagonal brace. When making the trolley, choose the appropriate diagonal brace according to the mechanical requirements of the trolley and customer requirements.

    2. Bracket assembly

The bracket is also called the upper frame, which mainly bears the weight of the concrete and formwork poured during the second lining. The lower part of the bracket transmits force through hydraulic cylinders and supporting jacks (for upper jacking design) or translation wheel mechanism (for lower jacking design) In the door frame part. The entire bracket and the template are connected to become a rigid force-bearing entity, which has different structural designs according to different projects and customer needs.

 

    3. template assembly

The template assembly is mainly composed of left and right molds and left and right top molds. The bolts connect several top molds to the side molds. The connection between the top mold and the side molds is generally hinged, so that the side molds can be wound relative to the top mold. The rotation of the pin shaft achieves the adjustment of the trolley components and the demolding effect. When the mold is erected, the jacking hydraulic cylinder extends the top mold to the required height, and then operates the lateral hydraulic cylinder to adjust the side mold in place, and then adjusts the lateral screw jack and the ground jack to complete the mold erecting process. When demoulding, press the reverse operation on the side. The formwork is the working part that directly lining the tunnel concrete, and its appearance quality and external dimension accuracy directly determine the quality of the concrete lining. Therefore, our company pays special attention to the processing and production of the template part, and uses the assembled welding tire mold to ensure the accuracy of the overall shape and size, minimize the welding deformation, and ensure that the outer surface is smooth and free of defects such as unevenness. At the same time, in order to control the misalignment of adjacent templates, the stabilizing pin of interference fit is used to fix the arc plate as a body for processing, which has the problem of controlling misalignment.

 

    4. the adjustment system

The adjustment system is mainly composed of a translation roller mechanism, a translation oil cylinder and a related hydraulic control system. The translation roller mechanism is supported on the cross beam of the mast, and the upper part is connected with the upper longitudinal beam. The upper longitudinal beam can be pushed by the extension and contraction of the translation hydraulic cylinder for translation adjustment to achieve the purpose of adjusting the vertical positioning and demolding of the template. The large adjustment amount of the translation cylinder is 100MM, and the working oil pressure is about 16MPA.

 

    5.  hydraulic system

The hydraulic system of the trolley consists of a hydraulic station, a hydraulic cylinder and a control oil circuit. The four jacking hydraulic cylinders are located at the four corners of the trolley. They can be lifted synchronously or adjusted by a single cylinder to complete the erection, demolding and demolding of the top mold. The top and bottom alignment of the template. The lateral oil cylinders are separately arranged on the left and right sides of the trolley, and the vertical mold of the side mold, demoulding and the left and right alignment of the template are completed by the expansion and contraction of the piston rod. There are two translational oil cylinders (four large trolleys), which are used to push the overall left and right movement of the formwork, so that the formwork can move left and right relative to the mast, so as to realize the alignment between the formwork center and the tunnel center. The trolley and hydraulic system use three-position four-way manual reversing valve to achieve expansion and contraction. The left and right hydraulic cylinders are each controlled by a reversing valve to synchronize the expansion and contraction on the same side; each of the 4 jacking hydraulic cylinders uses a reversing valve to control their actions, and the cylinders are locked by two-way hydraulic control check valves. To avoid the lowering of the trolley due to pressure relief, a one-way throttle valve is used to adjust the speed of the cylinder; the translational hydraulic cylinder can be operated with a reversing valve.

    6. walking system

The walking system consists of two parts, active and passive, with a total of four sets of devices installed under the four-door frame. When the trolley travels, the power is provided by the front two sets of active walking mechanisms. The walking motor drives the reducer, and then the active walking mechanism is driven by the chain drive to drive the trolley to travel, and the rear two passive walking mechanisms follow. The walking system is generally equipped with a track clamp to ensure that the trolley will not automatically slide, especially in places with large slopes.

 

    7. operating platform

The operating platform is the place where the staff operate and use the trolley and the equipment. It is divided into two working platforms at the front and rear, and the aisle between the two longitudinal sides of the trolley and the operating platform. The working platform is generally located on the mast, divided into upper and lower layers, and separated on the front and rear sides of the trolley in a wing shape. The hydraulic system control platform and the electrical control platform are installed on the working platform on the front side of the trolley. When operating the trolley, the commissioning personnel complete the trolley walking, debugging, mold erection, demoulding, etc. on the operating platform with a good plank or grid. When pouring concrete, the staff can observe the concrete pouring situation and the working condition of the trolley on the operating platform. Guardrails are arranged around the working platform to ensure the safety of the staff.

Daily inspection work standard of tunnel lining

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Tunnel lining is very important to the long-term stability and safety of the tunnel. Therefore, in the daily inspection of the tunnel, the inspection of the tunnel lining cracks is a normal work content. The cracks of the tunnel lining mainly include diagonal cracks, circular cracks, longitudinal cracks and network cracks, which are mainly distributed in the Various parts of the tunnel lining.

As the tunnel structure is closely related to the geological conditions and construction methods of the surrounding rock, conventional construction methods include: integral concrete lining, fabricated lining, anchor and shotcrete lining, composite lining, and double-arch lining. The inspection of the lining is divided into internal and external parts. The change of the internal structure requires professional equipment such as ground penetrating radar to check. In our daily work, we mainly check the lining part and surface materials that are visible to the naked eye.

In daily inspections, the length, width, and depth of the cracks are usually used as the main inspection basis. In actual operation, some convenient and easy-to-operate tools are used to measure the data of the cracked parts, including scale magnifiers and plugs. Ruler, ultrasonic concrete test, etc. The use of scale magnifying glass: aim the lens against the crack at the observation point, and determine the width of the crack by adjusting the lens through the scale in the lens. The use of feeler gauge: The feeler gauge is composed of several thin steel sheets. The width and depth of the crack can be obtained by observing the thickness and depth scale of the steel sheet inserted into the crack. Portable ultrasonic concrete detector: According to the speed of ultrasonic propagation in the lining concrete, the travel time curve is obtained, and then the fixed transmitter is the receiver moving in a certain direction of the lining, and the crack is calculated according to the change in the ultrasonic propagation time of the crack position. So as to achieve the non-destructive testing of the lining. The standard for crack inspection of lining structure is (mm/a per year):

  1. The crack width development rate is less than 1mm/a: the crack width is less than 3mm, and the length is less than 5m.
  2. The development rate of the crack width is less than 1~3mm/a: the crack width is less than 3mm and the length is greater than 5m, or the crack width is 3~5mm and the length is less than 5m: the cracks are more than three, and there are crossings.
  3. The development rate of crack width is 3~10mm/a: the crack width is 3~5mm and the length is greater than 5m, or the crack width is greater than 5mm and the length is less than 10m; there are dislocation or dislocation cracks, and the length is less than 5m: the arch part is reticular, There is a risk of falling off the lining.
  4. The crack development rate is greater than 10mm/a: the width of the crack is greater than 5mm, and the length is greater than 10m: there are dislocations or dislocation cracks, and the length is greater than 5m: the arch cracks are meshed, and the lining is peeled off.

The damage of the tunnel lining surface is an important reference data for the safe operation of the tunnel. Therefore, once the tunnel is found to be cracked during the daily inspection of the tunnel, it means that the structural stress level of the tunnel lining has changed, and there is a hidden safety hazard. Therefore, it is necessary to make detailed records and descriptions of the cracked part of the tunnel lining, mark the crack location and changes, and increase the inspection of the crack location to support the later repair and reinforcement of the tunnel and ensure the safe operation of the tunnel.