Today’s tunnel construction requires not only high quality but also fast speed. In order to ensure the quality and construction speed of the tunnel’s lining, a full-section and integral translational trolley is used in the lining construction to ensure the “inside real and outside beauty” of the lining The construction progress of the tunnel.
First, design of lining trolley
The formwork trolley used in tunnel construction is a translational lining trolley. The trolley and formwork are a complete system. The formwork is formed by laying steel plates on the profile steel as the framework to form a shell, and is equipped with a retractable mechanism.
The overall rigidity, strength and stability of the trolley under the construction load of one-time concrete pouring were considered during the design of the trolley. At the same time, it should be considered that the template can be easily and quickly replaced when lining different end faces. There must be enough passing section under the trolley to facilitate the smooth passage of construction machinery.
1, trolley template part
The formwork trolley used in the tunnel has a total length of 12m and consists of 8 splicing sections with a length of 1.5m. Among them, it is mainly composed of vault widening block, arch waist template, arch foot and side wall template, and curved wall lining side wall template. The arch foot and the side wall template are designed as a whole, which is hinged with the arch waist template, and the other modules are connected by bolts. The dome widening block can be replaced according to different widening requirements of the curve. The arch waist template is hinged with the arch foot side wall template, and the side wall template is opened and closed by 6 lateral hydraulic cylinders on the trolley. The whole set of templates are vertically raised and lowered by four hydraulic cylinders on the top of the trolley. There are 32 windows on the arch waist and side wall formwork for concrete pouring and vibrating. An attached vibrator is installed on the arch waist mold board. The end of the trolley is equipped with a plug steel plate to facilitate the concrete plugging of the lining end.
2, the overall part of the lining trolley:
The trolley is a truss structure as a whole, the beams are all made of box-shaped cross-section structure, and the other parts are of steel composite structure. The trolley is divided into upper and lower platforms, and 1500mm air ducts can pass between the platforms. The lower part of the trolley is equipped with a wheel-rail walking mechanism, which is driven by two 7.5kw three-phase asynchronous motors for short-distance movement.
3, electric hydraulic system:
a. Hydraulic system: It consists of 4 vertical oil cylinders for lifting the template, 6 lateral oil cylinders for opening and closing the side template, and high-pressure oil pump, one-way valve, overflow valve, oil pipe, etc.
b. The electricity used on the trolley is divided into lighting and power electricity. The lighting must meet the requirements of safe electricity use, and be used for lighting after being reduced to 36V by a low-voltage transformer. The power consumption is 380V, which is mainly used for trolley walking, hydraulic oil pump and vibrating rod. The power line must be equipped with electric leakage protector and knife box and other safe power equipment.
Second, main performance of trolley
|Length * width
|Clearance under the trolley
|Length * width
|Trolley track center distance
|Vertical cylinder adjustment
|Number of vertical cylinders
|Number of lateral cylinders
|Number of screw jacks
|12 up and down, 30 left and right
Third, the use of template trolley
1. Move the trolley into place:
a. Laying the track before the trolley moves, the requirements are as follows:
Trolley track laying requirements
|Allowable error of gauge
|Allowable offset between track center and tunnel center
|Height from the top surface of the track to the bottom surface
|Rail surface difference on the left and right sides of the same cross section
|Track longitudinal slope
|Consistent with the tunnel longitudinal slope
|Sleeper specifications (length * width * height)
b. Use the traveling mechanism of the trolley to move the trolley to the section to be lined, and fix the traveling part of the trolley;
c. Descaling, derusting, and brushing release agent on the template.
2. Trolley positioning and moulding:
a. When positioning the standing formwork, the back end of the formwork should be based on the concrete surface of the lined section, and the back end of the formwork should be raised against the top surface of the concrete vault of the lined section, and the slab seams should be aligned;
b. Raise the front end of the template to the design elevation (plus reserve);
c. Use a horizontal jack to align the vertical line of the front end of the template with the center of the ground. The curve segment should make the center line of the template coincide with the black line of the curve of the group of lining segments;
d. Spread the side board and stick to the low side wall. It is required that the distance from the bottom of the formwork to the centerline of the tunnel and the distance from the formwork to the centerline at the arch line must meet the design net width requirements.
e. Matters needing attention:
①The overlapping length between the trolley formwork and the lining ≤5cm can effectively control the staggered concrete platform;
②The sleepers under the trolley should not be too high, and it is necessary to ensure that there is enough room for contraction after the template is raised to the design elevation to ensure that the trolley can pass through the lining section smoothly after being folded;
③In the pouring lining concrete, when there is a large or small avoidance hole, all the templates of the avoidance hole should be installed first, and then the formwork of the formwork trolley shall be carried out;
④For the specific operation method of the trolley, please refer to the manual of the template trolley.
3. Reinforcement of template:
a. After the above process is completed, a sponge strip is inserted at the overlapping part of the formwork and concrete to prevent leakage;
b. Fasten the support jacks on the upper and lower parts, and the plug plates can be installed at the same time;
c. Tighten the horizontal jacks on both sides of the trolley, requiring the jacks to be perpendicular to the template and the support;
d. Matters needing attention:
①The wall waist part of the overlapping end with the lining must be reinforced with a jack to make it close to the concrete surface;
② At least 6 supports shall be used to reinforce the side of the overlap between the lower part of the trolley and the side wall foundation;
③The position of the screw must be horizontally supported and perpendicular to the template. It must not be added to the screw base, but must be added to the column;
④The screw at the wall waist of the front end of the formwork trolley (near the face of the hand) cannot be reinforced too tightly, and no support can be added to ensure that the formwork can be closely attached to the concrete when the next set of linings are laid;
⑤The car shelter model can be made of wood, steel or steel-wood according to the actual situation. The model is required to have sufficient rigidity, and the surface is flat and free of errors. It is best to use an integrally formed steel mold. The connecting seam between the avoiding hole and the formwork trolley should be tightly sealed.
4. Concrete pouring
a. The automatic metering concrete mixing station can ensure the accuracy of various concrete parameters and the uniform mixing. Transported by a concrete tanker and poured by a pump to ensure the quality of concrete construction;
b. Pumping concrete must be mixed with pumping agent, the slump of concrete is 8cm~15cm, and the water-cement ratio is not more than 0.7. Check the slump after opening and adjust according to the situation;
c. Before pumping the concrete, pump the mortar with the same mark as the concrete to lubricate the pipe wall. The pumping of concrete should be carried out continuously, and the interruption time should generally not exceed 20 minutes;
d. The concrete of the side wall and the arch foot part can be poured by the window on the mold board, and vibrated with the plug-in vibrating rod;
e. The concrete of the arch is injected into the mould by the sprinkler port on the top mould board. When the first section of concrete lining is poured by the trolley, the concrete pumping pipe presses the concrete into the model from the spray nozzle in the middle, so that the concrete is squeezed from the middle forward and the rear ends to achieve the purpose of capping.
When overlapping with the lining concrete, the concrete is pressed in from the sprinkler nozzle at the overlapping end, so that the concrete gradually moves outward to achieve the purpose of capping. If hopped and segmented pouring is used, vent holes should be punched at both ends of the lining vault of the trolley during the concrete construction of the sealing section to prevent the air from being removed during pouring. The concrete of the arch can be vibrated with the attached vibrator on the trolley, or the plug-in vibrator can be used to vibrate the inner surface of the die plate;
f. Matters needing attention:
①The height difference between the left and right sides of the concrete pouring is not more than 50cm, and the pipes fall frequently to prevent bias;
②When the side wall concrete is poured, the front end of the pump pipe should be a rubber conveying pipe and extend into the window, and the pipe mouth should not exceed 2 meters from the concrete surface;
③For the part with over-excavation greater than 30cm, it can be backfilled with rubble concrete or grout rubble;
④Concrete construction is carried out strictly in accordance with the “Concrete Construction Code”.
5. Demoulding and maintenance:
a. The demoulding time of concrete meets the following requirements:
①The concrete strength of the arch wall that is not subject to external load reaches 5Mpa, or the concrete surface and edges and corners will not be damaged when the form is removed, and it can bear its own weight;
②The arch wall concrete with less surrounding rock pressure reaches 70% of the design strength.
b. Trolley demoulding:
① Loosen the upper and lower side mold screw jacks;
②Loosen the upper and lower middle supporting screw jacks;
③ Use the side form hydraulic jack to pull the side wall form towards the center of the tunnel and shrink it by 15-20cm to separate the side form from the concrete surface;
④ Use the side mold hydraulic jack to lower the arch formwork 10~15cm to separate the arch formwork from the concrete surface.
C. Concrete curing:
①Cure the concrete immediately after 10-20 hours of pouring, and the curing time shall not be less than 7 days;
②For the lining and open tunnel near the tunnel portal, the maintenance should be strengthened due to the greater impact from outside the tunnel, and the maintenance time should not be less than 14 days.
Fourth, the restructuring of the die pull trolley
The tunnel lining section includes: 30cm widened and 50cm widened curved wall integral lining, 30cm, 50cm and unwidened straight wall integral lining, so the formwork should be replaced in different lining sections.
1. Replacement of side panels: The replacement of side wall templates needs to be done outside the hole. After moving the formwork trolley to the outside of the hole, first remove the connecting bolts between the formwork and between the formwork and the longitudinal beam, and then hang the side plate with a crane, remove the latch between the side plate and the arched waist formwork, and set the formwork Lift off the trolley. Replace the curved or straight wall template, hoist the template with a crane, the process: the opposite of the disassembly. After replacement, push the template trolley to the designated position for construction.
2. Replacement of widening module: Considering the need for widening when designing the trolley, a replaceable die plate is designed in the center of the vault. When the dome is not widened, the center of the dome is 35cm wide, when it is 30cm widened, it is 65cm wide, and when 50cm widened, it is 85cm wide. The widening template and the arch-waist template are connected by bolts. When replacing, it can be replaced manually in the hole. Remove the longitudinal connecting bolts between the mold plates, and then remove the connecting bolts between the center template and the arch-waist template, and replace them with widened ones. Tighten the bolts after the template.
During the construction, it was found that the wall waist of the overlapping part of the trolley and the lining cannot be closely attached to the concrete surface after the screw is tightened, and the expansion mode will appear during the pouring process, until the wall waist at the lining connection is staggered by 5 ~8mm or so. In order to ensure the apparent quality of the concrete and reduce the misalignment, a 2m-long vertical channel steel is added to the back of the formwork and a screw is installed between the vertical channel and the column at the wall waist part of the lap end of the formwork and the concrete. Tighten the lead screw before construction, so that the formwork can be closely attached to the concrete surface. After treatment, the misalignment can be reduced to about 2mm.
Five, formwork trolley entry and exit organization
1. Lay the track before the trolley moves, and the laying of the track must meet the requirements.
2. Mobile trolley:
a. For trackless transportation, a forklift can be used to drag the trolley, move about 25 meters to remove the rear track of the trolley and move it to the front of the trolley for connection, and then drag the trolley to the designated position;
b. The trolley can be driven by a battery car when transporting on rails. When the transport track is in the center of the line, the trolley track will not affect each other. If the line track is on the bottom side, the trolley rail on the same side as the line track can be directly laid on the sleepers of the transportation line, and the battery car can be towed in front;
c. When moving in a short distance, the traveling mechanism of the trolley can be used to move, but the power supply plug must be connected for the traveling motor of the trolley;
3. The method of trolley entering and exiting the hole is the same. It should be noted that when the track is laid, it overlaps with the center of the line as much as possible to prevent the trolley from shifting and scratching the concrete surface. The moving speed cannot be too fast, and it can be stopped at any time when an accident occurs. When stopping moving, a stop wedge should be added to the wheels to prevent accidental sliding of the trolley.