Analysis of key points of tunnel lining construction in tunnel engineering
Tunnel lining construction is a key construction content of tunnel engineering, which is related to construction quality and construction safety. So what are the common causes of common problems in tunnel lining construction? What control measures can ensure the quality of tunnel lining construction? The following is an analysis of the main points of tunnel lining construction in tunnel engineering, so that you can easily avoid common problems in tunnel lining construction.
Quality issues and phenomena
1.There are holes behind the lining;
2.The lining is obviously wrong, the slurry is leaking, the quicksand is serious, and the appearance quality is poor;
3.The thickness of the lining does not meet the design requirements;
4. Leakage of lining;
5.Cracking of lining concrete;
6.The appearance quality of the cable trench is poor;
7. Drainage ditch is not smooth.
Cause analysis of cavities behind the lining
1.The construction of backfilling was not carried out according to the specifications;
2. When the lining is filled with concrete, the arch is not full, and the vibration is not enough;
3. Pumping concrete is hollow at the far end of the conveying pipe due to pressure loss, slope and other reasons;
4. The looseness control of the waterproof board is not in place.
The prevention of cavities behind the lining
1. The excavation surface of the tunnel is inevitably uneven. For pits caused by over-excavation in a small area, the backfill of lining concrete is generally used during construction. Pay attention to the fact that the waterproof board should be closely attached to the rock surface, and the tightness is suitable; Deep subsidence pits should be backfilled smoothly before the second lining construction;
2. General lining formwork trolleys have one reserved pumping hole before and after the top of the arch. If the formwork trolley is longer, additional reserved holes can be added in the middle to prevent the pouring concrete from being in place when the longitudinal slope of the tunnel is large. Backfill grouting after construction;
3. The new lining formwork trolley is equipped with an attached vibrator on the side wall and arch waist. At the same time, two plug-in vibrators are provided on each side of the trolley during concrete pouring. Layer vibration, these can effectively solve the vibration problem.
Analysis of the cause of poor apparent lining quality
1. The rigidity of the lining trolley is insufficient, and the formwork is not properly repaired;
2. The lining concrete is not easy to work with, and the bleeding is serious;
3.No symmetrical pouring on both sides;
4. The pouring speed is too fast, the trolley floats up;
5. The template is too oiled, and fish scale clouds are formed after the mold is removed;
6. The partial template is not cleaned up, and the phenomenon of “skinning” and falling off is formed after the mold is removed.
Preventive measures for poor lining apparent quality
1. The lining trolleys are processed by regular manufacturers, and they have been checked for strength and stiffness before processing. Check the check data when purchasing;
2. If the lining formwork trolley overlaps less than 0.5m during lining construction, generally no misplacement will occur. Therefore, it is necessary to plan the mileage of the trolley in place before lining construction to avoid long overlaps. At the same time, surveyors should have certain construction experience, the lining center line and elevation should be well controlled, and the distance between the two sides of the formwork trolley should be properly controlled to prevent excessive and small influences from affecting the next set of trolleys in place;
3. The lining concrete is constructed strictly according to the designed mix ratio. Pumping concrete and workability requirements should be considered when designing the mix ratio. At the same time, the formwork trolley should be coated with a mold release agent. It is best to use a special mold release agent for uniform application. Moderate dosage can improve the quality of lining surface;
4. When placing the lining, it should be layered symmetrically on both sides, and the self-fall height of the concrete should be controlled within 2m to prevent segregation;
5. If there is some concrete on the formwork trolley, remove it before the next pouring, and then apply mold release agent, otherwise it will affect the surface finish of the next group of linings;
6. Due to problems such as the pressure of the cast-in-place concrete at the foot of the side wall will rise, and the end pressure will move longitudinally, the template-bed trolley is strengthened firmly before the lining construction. The lead screw is reinforced again to prevent the trolley from being displaced due to the loosened part of the lead screw.
Cause analysis of insufficient lining thickness
1. The contractor’s quality awareness is not strict, and the process monitoring is not in place;
2. Or the reserved settlement is insufficient;
3. The undercut site is not treated.
Measures to ensure lining thickness
1. The thickness of the lining should be ensured, and the initial support section should be inspected before the lining construction.
2. For some tunnels with large settlements, it is necessary to pay attention to the settlement observations. If the designed settlements do not meet the requirements, the reserve can be appropriately enlarged according to the actual situation, but it cannot be too large to prevent artificial overdigging. Waste lining hoe.
Cause analysis of lining leakage
1. Cracking of the lining;
2.Insufficient waterproofing, drainage and diversion facilities;
3. There are quality defects in the treatment of circumferential construction joints and deformation joints, and the installation of water stop strips and water stop zones is not standardized;
4. The waterproof board is damaged, perforated, and the weld is not tight
5. The lining is not compacted and there are holes or honeycombs;
6.The waterproof material is unqualified;
7. Insufficient number of drain holes or inaccessible drainage.
Prevention measures for lining seepage
The lining seepage is generally caused by the inadequate drainage and drainage construction and the lining itself is not dense. To strengthen the on-site management to ensure that the drainage and drainage measures are in place and the lining concrete is compacted, the following aspects should be done:
1. The blind pipe is installed in place. Before construction of the waterproof board, it is necessary to ensure that the blind pipe is installed according to the design requirements. The local section has a large amount of water to increase the number of blind pipes. The blind pipe and the vertical drainage pipe are well connected to ensure the drainage effect.
2. Waterproof board construction is the key link of lining waterproofing. At present, there are many types of waterproof boards on the market, and the waterproof boards must be qualified. The waterproof board connection is best to be welded. During the construction process, a quality supervisor will inspect the site and find the problem in time. deal with. Strengthen inspections on some uneven areas to prevent leakage; for reinforced concrete linings to prevent damage to the waterproofing board during the construction of the steel bar, if there is any damage, notify the waterproofing board builder to repair it; if the waterproofing board is installed, it must be close to the rock surface. , Moderate tightness to prevent tearing of the waterproof board due to pressure during pouring;
3. Treatment of construction joints and settlement joints: General construction joints and settlement joints are designed with pre-buried and buried buried waterstops or waterstops, and some have back-attached waterstops. The waterproof board can be fixed with a baffle board. When the middle-buried water-proof strip is used for construction, a small-sized cao (half the thickness of the water-stop) must be reserved in the middle of the lining end. In, fixed firmly. The construction of the middle buried waterstop requires the layered construction of the headboard, which is divided into two layers from the position of the waterstop to ensure that the waterstop is reserved and cannot be destroyed. This seriously affects the construction of the headboard, so it is often not in place. Strengthen the management on site to ensure the construction of the middle buried waterstop;
4. The horizontal drainage pipe shall be reserved according to the design, and a three-way connection shall be used to ensure that the drainage can smoothly flow into the ditch; the vertical drainage pipe is generally a perforated corrugated pipe, which is wrapped with geotextile to prevent the sediment from entering and affecting the drainage effect;
5. The lining concrete can not be stopped for a long time during the pouring process, so the site materials and generators must be fully prepared to prevent stoppages because the concrete poured twice is prone to gaps, causing the lining to leak; the only solution is to punch and grout. Water, but the holes should be shallow to prevent damage to the waterproof board;
6. The lining concrete must have a waterproof effect. Generally, it is designed as a waterproof concrete. When cooperating with the design, it must be considered from multiple aspects. It must ensure the workability and water resistance.
7. Control the self-falling height of the concrete when pouring the lining concrete, ensure the layered pouring, the layer vibration is in place, the formwork trolley window template is closed tightly to prevent slurry leakage, etc., to ensure that the concrete lining is dense and the construction concrete is waterproof.
Cause analysis of lining cracking
1. Temperature difference and dry shrinkage;
2. Alkali aggregate chemical reaction;
3.The side wall foundation sinks;
5.Cracking of the arch and side wall due to stress concentration;
6.Cracking caused by difficulty or interrupted pouring of concrete in the arch;
7. The demolding time is too early, the lining strength is not enough to support its own weight and crack.
Crack prevention measures
1. High-grade concrete hydration heat is increased, and water conservation should be carried out after construction, not less than 14d, to prevent the surface from drying and causing cracks;
2. Select qualified materials for lining concrete, and strictly follow the mix ratio construction;
3. The lining generally does not crack. Generally, the lining cracks due to bias or topographical movement at the entrance of the cave. Therefore, when backfilling the cave top, pay attention to symmetrical backfilling on both sides. For tunnels with bias, strengthen the lining strength or decompress;
4. The joint of the overhead arch and the side wall is prone to stress concentration. During the construction, ensure that the side wall foot excavation is in place, and there must be no under-excavation, which causes the lining to crack;
5. Control the lining demolding time, and formulate the corresponding demolding time and curing time according to the tunnel temperature in different seasons, to prevent the occurrence of cracking and cracking;
6. The lining concrete is guaranteed to be put in place at one time, and it cannot be stopped halfway, which is not conducive to waterproofing and easy to cause cracks and reduce the strength of the lining. Therefore, sufficient material reserves and good equipment and equipment are available before construction. Deformation, loose bolts, welding off, etc., prevent problems during the construction process, resulting in the lining cannot be properly constructed.
Cause analysis of poor appearance quality of cable trenches
1. The vertical mold is not detailed and not firm, and the outer edge of the groove is not controlled according to the center line of the line;
2.The cover plate is prefabricated and the installation quality is poor;
3. Construction in other processes, which was broken by repeated lifting, moving and collision.
Appearance quality control measures
The cable trench of the ditch is the surface engineering of the tunnel. The quality of the surface construction affects the overall image of the tunnel. Therefore, the linearity and straightness must be ensured, and there must be no wrong platforms and smooth surfaces.
1. The cable trench of the ditch is controlled for measuring and laying out, the curve is controlled according to the radius, 10m or 20m center line elevation control, and the straight line 50m control. The template adopts the overall steel template to ensure one-time pouring molding, and the template is coated with a mold release agent to ensure the appearance quality. After the template is installed, the technician checks the installation of the template, whether the linearity is up to standard, and whether the reinforcement is firm;
2. The prefabrication of the cover plate is centralized prefabrication in the prefabrication field, and the shaped steel-plastic template is used, with marks on the top and bottom for easy installation.
3. After the prefabricated cover is prefabricated, store it in the prefabricated yard. After the tunnel trench construction is completed, it will be placed in a concentrated way when there are no other processes affected. Mortar is used to fill the gap between the cover and the foundation.
Cause analysis of poor drainage ditch
1. The vertical slope of the ditch bottom is not standardized, there are deviations, and the control is not accurate. The bottom of the ditch is “wavy”;
2. The longitudinal slope of the ditch bottom is small;
3. There are debris in the ditch, and the flow path is blocked;
4. The groove bottom is uneven.
Prevention and control measures for poor drainage of drainage ditch
1. Trench excavation is in place, to ensure linearity and straightness when pouring concrete, to ensure smooth trench and prevent water accumulation;
2. There are many sundries in the hole during working hours, and it is easy to block the trench. It must be cleaned regularly to facilitate drainage in the hole.
3. Drainage Because the formwork is installed straight during the ditch pouring, the reinforcement is firm, and the compaction is used when pouring the concrete.