The self-propelled hydraulic inverting bridge formwork adopts mechatronics and hydraulic integration design, equipped with multi-functional automatic walking device, front support, rear lateral movement mechanism, hydraulic self-balancing system, which can realize automatic vertical movement, rise and fall, and automatic horizontal movement, with a high degree of automation , Can adapt to a variety of construction work environment.

The self-propelled hydraulic inverting bridge formwork is composed of the main body of the trestle bridge, hydraulic system, electrical control system, and walking system.

The main structure of the main bridge: 8 40b# I-beams are arranged in parallel along the longitudinal direction of the tunnel at the bottom of the bridge, 4 20# channel steels and 6 20b# I-beams are arranged horizontally along the tunnel on the bottom of the bridge, with box-shaped structures on both sides and the middle 25# I-shaped steel support connection. The hydraulic system includes various lifting cylinders and related hydraulic pump stations and pipelines; the electrical system is responsible for controlling the operation of each system, mainly composed of various relays, switches, circuit breakers, etc.

The traveling system is composed of a motor reducer, a transmission chain, a box body, a traveling wheel, etc. There are 4 groups, which are respectively placed on both sides of the end of the trestle body to realize the automatic walking of the trestle body. The walking device can realize horizontal and vertical walking, which is flexible and convenient.

Hydraulic inverting bridge formwork walking principle

In order to meet the requirements of movement, a mobile walking mechanism is set at both ends of the trestle bridge, and a limit warning device is set; when walking, the lifting and lowering of the slope bridge at both ends of the trestle bridge is completed by the hydraulic system actuator. The self-propelled hydraulic inverting bridge formwork is mainly composed of the main bridge, traveling device, hydraulic system, electrical system, limit device and alarm system. The trestle bridge is moved. When moving, it is driven by a motor and driven by a gear pinion to drive the walking wheel to move on the walking track. The working steps are as follows:

Start the main bridge lifting cylinder installed at the end of the trestle bridge to make the trestle bridge slope off the ground, and then with the cooperation of workers, drag the trestle bridge walking track forward. After the track is dragged to the end, shrink the main bridge lifting cylinder to start the traveling motor. The trestle moves forward on the track, after moving to the end of the track, repeat the above steps until the trestle is in place (the trestle’s lateral movement is the same as this). After the trestle bridge is in place, the main bridge lifting cylinder is lifted up, so that the running wheels are not stressed. After being fixed, the front and rear slope bridges are put down.

Hydraulic inverting bridge formwork construction technology

According to the requirements of the construction schedule, the construction of the tunnel entering the invert position, in order to ensure that the invert construction continues and the slag from the tunnel excavation and the transportation of materials in the tunnel are not affected by the invert excavation, so the invert excavation slot is installed the trestle bridge will be constructed. After the strength of the poured invert concrete meets the traffic strength requirements, the trestle bridge can be pushed forward to the excavation groove at the bottom of the next tunnel, and then recycled. So as to realize the rapid and safe progress of tunnel construction.

Trestle installation and positioning

Plan ahead of time the personnel, materials and machinery required for processing. The installation of the trestle is carried out by professional and technical personnel. When the hydraulic inverting bridge formwork is erected, the bottom slag of the front platform of the trestle must be removed before the trestle is advanced, and the foundation must have a certain bearing capacity. The back end is laid on the top surface of the filling; the front ramp of the trestle bridge should be firmly connected with the trestle platform to ensure the safety of erection. After the trestle bridge is erected and installed in place, safety nets must be hung outside the guardrails on both sides of the trestle bridge to prevent the falling of gravel from hurting the operators of the inverted arch construction below; obvious slow-moving warning signs should be set at the front and rear of the trestle bridge, and the trestle bridge surface should have anti-skid measures.

Trestle inspection

Before the trestle bridge is moved, erected and installed, the welding parts of the trestle bridge shall not have the phenomenon of welding seam falling off or welding seam cracking, and the supporting system shall be inspected to check whether the main beam and auxiliary components of the trestle bridge are cracked and deformed. If problems are found, the trestle shall not be carried out. Moving and erecting, the trestle can be moved and erected only after the processing is completed and the inspection is qualified.

Trestle move

Use an excavator or loader to set it in place, and walk on its own after it is in place: the inverted arch can only be moved after the strength of the filled concrete reaches the design requirements and the necessary protective measures must be taken. The movement must be slow to avoid damage to the quality of the finished concrete: trestle bridge When moving, full-time personnel must be assigned to uniformly command, and no one is allowed to stand in the trestle work area.

Invert excavation

(1) The invert excavation is divided into left and right parts, and half of the excavation is carried out first.

(2) In the first cycle, first excavate the left or right inverted arch, and park the trestle on the side where there is no excavation: park the slag truck on the trestle, and excavate the excavator on the surface to be excavated When excavating from the front to the rear of the trestle bridge, the excavator has been parked on the elevation surface of the inverted arch, so as to ensure that the excavator can load the slag into the slag truck.

(3) After excavating one side, operate the trestle bridge to move the trestle bridge to the side that has been excavated, and also park the slag truck on the trestle bridge, and the excavator will excavate on the surface to be excavated. When excavating from the front end to the back end of the trestle bridge, the excavator has been stopped on the elevation surface of the invert, so as to ensure that the excavator can load the slag into the slag truck; at this time, the invert excavation and the invert lining can be carried out simultaneously.

(4) Repeat the above process to complete the next cycle of invert construction.

Advantages of hydraulic trestle

(1) Through the application of the trestle bridge in the tunnel, the materials and tools for the construction of the tunnel face can pass from the upper part of the trestle bridge, reducing the interference between excavation construction and invert construction: at the same time, the trestle bridge has a large span and is an inverted arch The construction provides a streamlined work surface: the trestle itself is convenient and quick to install, walks more flexible, and has a high level of mechanization. These are conducive to speeding up the tunnel construction speed and solving the schedule problem, especially for the long tunnel and the tight construction period, the benefit of ensuring the schedule is very obvious.

(2) Compared with the simple trestle bridge, the use of movable hydraulic inverting bridge formwork, although the cost of manufacturing or purchase increases, but because it provides enough space for inverting operations, it can effectively organize flow construction. Improve production efficiency and speed up, especially in the case of long tunnels, which will play a role in reducing engineering costs.

(3) Ensure the safety of construction workers under the trestle bridge. The hydraulic inverting bridge formwork made of section steel is stable in structure, safe and reliable; the mobile trestle reduces the interference between working procedures, and the structural safety is improved compared with the simple trestle.

(4) It is beneficial to ensure the quality of tunnel construction. Due to the use of the trestle bridge, it is guaranteed that the invert is poured in one time, which is beneficial to ensure the quality of the invert.

Precautions when using self-propelled hydraulic inverting bridge formwork

(1) Personnel operating the trestle bridge must be trained and qualified before they can carry out operations.

(2) When the hydraulic inverting bridge formwork is in place, pay attention to the flatness of the installation and the width of the installation to meet the design requirements to ensure the safety of the vehicle and the normal passage of vehicles with different wheel bases.

(3) The speed limit for vehicles passing through the trestle bridge should be determined according to the actual situation on site to ensure the stability and safety of the hydraulic inverting bridge formwork during work: construction personnel are prohibited from passing vehicles when working under the trestle bridge to ensure the safety of operators.

(4) Lay safety nets on the outside of the trusses on both sides of the trestle bridge to prevent the falling of gravel from hurting the construction operators below. The concrete and debris on the self-propelled hydraulic inverting bridge formwork should be cleaned up in time to keep the upper part of the trestle clean.

Concluding remarks

The application of hydraulic trestle has changed the existing tunnel invert construction organization mode. Under the premise of not affecting the tunnel face construction, the tunnel invert excavation, reinforcement binding, invert pouring and other operations are carried out at the same time to realize the excavation and invert the parallel operation of arch construction greatly saves construction time and improves the overall efficiency of tunnel construction.

Due to the automatic walking device, the trouble of manually moving the trestle bridge is reduced, the automation level of tunnel construction is improved, and the safety is enhanced. Become the technical basis for ensuring the quality, schedule, and cost control of the tunnel invert construction, and the technical basis for realizing the standardization of tunnel construction and the construction of humanized and civilized construction sites.

Introduction

As the development of road traffic brings rapid economic development, the construction of roads and tunnels is becoming more and more common. Under normal circumstances, during the tunnel lining construction, concrete often has problems and defects such as leaking bars, pitting and cracks. Although it has no direct impact on the actual use of the structure and the internal quality, due to its relatively high probability of occurrence, the lining The aesthetic appearance is affected to a certain extent, and the overall quality of the lining is reduced.

The factors affecting the tunnel lining concrete

(1) Freeze-thaw damage of concrete

Concrete has certain pores and expands after freezing. When the water retention of the concrete is high and the volume in the pores is small, the problem of excessive pressure will occur, and during the freezing and thawing process, the moisture on the surface of the concrete will be affected by the osmotic pressure, resulting in damage to the concrete.

(2) Constituent materials of concrete

In the process of on-site concrete mixing, the use of different materials directly affects the durability of the concrete. In some specific processes, the diameter of the cement particles will become thinner and thinner. Under such conditions, high heat of hydration will be generated. At the same time, the problems of high temperature difference and high shrinkage rate, concrete collapse is increasing, and the particle size of the aggregate is reduced to increase its workability. The addition of cement and admixtures also exacerbates the problem of heat of hydration, which directly leads to more serious problems of shrinkage and deformation of concrete.

(3) Rebar corrosion

If the concrete is in a highly alkaline environment for a long time, the surface of the steel will be oxidized to form a passivation film, which will not be damaged by rust. If the protective layer of concrete reinforcement is carbonized, it will cause a decrease in alkalinity, resulting in some air and moisture inside the concrete, which will lead to corrosion of the reinforcement.

Defect analysis of tunnel lining concrete

The defects of tunnel lining concrete construction mainly include leaking bars, pitted surfaces, holes, etc., and the solutions to these defects. For details, please see “TREATMENT AND PREVENTION OF TUNNEL LINING CONCRETE DEFECTS”

Treatment measures for defects in tunnel lining concrete

(1) Conduct a detailed site survey

In order to make the tunnel construction proceed more smoothly, and to further ensure that the repaired concrete pavement is stronger, it is necessary to carry out certain surveys on the local construction road sections and determine the construction plans in different areas before the repair, which is difficult for the construction Obtained, the region chooses the construction plan that is most suitable for it. This is the preparation work before construction. This can to a certain extent promote the concrete to be completed within a fixed period of time, and can further consolidate the quality of the road section. During the process of topographic survey In the process, it is necessary to investigate the soil moisture content and settlement of the soil, which will further make the later construction more perfect. When the survey is completed, all factors need to be more comprehensively improved, based on the relevant influencing factors. More suitable for construction.

(2) Choose the right concrete material

When the material is artificial, it is necessary to carry out certain experiments to verify the performance of the material before using it, and in order to make the material can be connected with the concrete and other interface materials: it has better adhesion, so it needs to ensure that its edges and corners are clear. The mud content of related materials has clear requirements, that is, the mud content cannot exceed 1%. When the mud content in the material is high, the concrete structure composed of it will not be able to withstand high bending resistance. And when the wall surface is dry, due to the difference in temperature, it is easy to cause large deformation. Therefore, the actual relevant content needs to be more clearly defined. In the selection of raw materials, especially for the first stone, etc. More clear management of materials, etc.

(3) Choose the right gravel gradation

In the selection of crushed stone, the following judgments need to be made: the gradation of crushed stone needs to be guaranteed. When the particle size of the stones is large, since the gaps between the stones cannot be completely filled with concrete, it is likely to cause many gaps between them, which will greatly reduce the bearing capacity of the concrete, and when the particle size is small Because it requires a large amount of bonding material to bond it, when the particle size of the stone is small, the amount of cement will be greatly increased, which will increase the cost of the project.

(4) Ensure the quality of lining concrete pouring

At present, concrete transportation is mainly carried out by concrete trucks. During the transportation process, it is necessary to pay attention to the control of the water in the concrete, so that the water content of the concrete is within a certain range. When the concrete truck needs to be transported as much as possible Reduce the number of times of parking, and reduce the time spent on the road as much as possible, so that concrete can enter the link of people’s pouring faster, so that the quality of concrete is guaranteed to a certain extent.

Conclusion

In summary, in the actual construction process of tunnel lining concrete, it needs to be based on prevention. If problems occur, they should be resolved at the first time, and the experience and lessons of specific defects should be continuously summarized. At the same time, it is necessary to strengthen the emphasis on process control, combine the requirements and standards of coagulation and construction, scientifically implement the relevant work quality, and use scientific methods to promote the overall improvement of the construction quality of tunnel lining concrete.

Hydraulic inverting bridge formwork is one of the main components of the tunnel structure, it is the foundation of the tunnel structure. On the one hand, it is necessary to effectively transmit the formation pressure of the upper part of the tunnel to the underground through the tunnel side wall structure or the load on the road surface, and also effectively resist the reaction force from the lower layer of the tunnel. In fact, it is a kind of foundation beam (slab) that can bear the permanent load of the ground and the temporary load of the road (dynamic load).

For this reason, the stress state of the back arch is more complicated. Judging from the examples of traffic tunnel engineering diseases at home and abroad, due to the design and construction of the tunnel arch structure, the tunnel structure is unstable, the road surface settlement is cracked, and there are many examples of the disease caused by mud and mud. For this reason, it must be fine when applying the inverted arch structure, and its structure must meet the specifications and design requirements.

1. Processing of Hydraulic inverting bridge formwork

Each Hydraulic inverting bridge formwork is composed of two beam plates, each beam plate is welded by four I36b I-beams, the length of the I-beam is 12m, the distance between the I-beams is 20 cm, and there are 8 groups of intermediate connections with a spacing of 1. 5 m, every two I36b I-beams are welded with I16 I-beams to form a whole. The top of the beam is welded with ￠22 steel bars, the distance between the steel bars is 20cmm, and the bottom uses l5 cm wide and 10 mm thick steel plates to weld the four I36b I-beams into a whole.

2. The number of Hydraulic inverting bridge formwork is determined

The curing time of the concrete was determined to be 4 days to meet the driving requirements. The cycle time of the upward arch construction operation was 2 days, each cycle of construction was 9 m, and each hydraulic inverting bridge formwork was 54 meters per month. The average monthly advance of the palm face excavation is 120m. To match the progress of the excavation and the palm face excavation, at least 2 (4 pieces) Hydraulic inverting bridge formwork are required to meet the requirements.

3. Construction points of Hydraulic inverting bridge formwork

1. The trestle processing is carried out in strict accordance with technical disclosure, and the welding seam is full.

2. When the Hydraulic inverting bridge formwork is in place, pay attention to the flatness and width of the installation to meet the design requirements, to ensure that the vehicle traffic safety and vehicles with different wheelbases can pass the Hydraulic inverting bridge formwork.

3. The muddy water and residual concrete on the upper part of Hydraulic inverting bridge formwork should be removed in time to keep the upper part of the trestle clean.

4. The speed limit of vehicles passing through the trestle is 5 km/h. Construction under the trestle is strictly forbidden to ensure safe construction.

The secondary lining is carried out after the surrounding rock and the initial support deformation are basically stabilized according to the measurement situation, and it closely follows the excavation surface to meet the safety distance requirements for excavation and lining. The secondary lining uses a 12m formwork trolley, and the concrete is transported to the construction site by a concrete transport truck, and pumped into the mold. The concrete adopts the vibrating method with the attached vibrator as the main insertion vibrator and the auxiliary. Reinforced concrete lining section, the steel bar is cut and formed outside the hole, and the hole is installed in the hole using a multi-functional operation platform.

Construction process of tunnel secondary lining

1. Steel bar production and installation

The main lining and stirrup of the lining are processed by the steel bar processing plant. The processing and manufacturing process of the steel bar should meet the design and specification requirements.

In order to ensure the accurate positioning of the second lining steel bar, the thickness of the steel bar protective layer meets the requirements. specific methods:

(1) First, the surveyors use the coordinates to stake out the center points of the two front and rear rebars within the range of the self-made trolley on the leveling layer and the tarpaulin, determine the normal direction, and ensure the verticality and elevation of the rebar The accuracy of the rebar connection in the arch. The verticality of the steel bar binding is determined by the three-point hanging ball method.

(2) Measure the elevation of the center point of the reinforcing steel bar on the filling surface of the invert arch with a level gauge, calculate the difference in height between the center of the circle and the upper center of the invert arch, and use a self-made tripod to determine the center of the circle.

(3) After the center of the circle is determined, use the ruler method to check whether the size of the positioning rebar meets the design requirements, readjust the position that does not meet the requirements, and fix the rebar after all the requirements are met. The fixing of the steel bar is controlled by an adjustable supporting rod welded by steel pipes on a self-made trolley.

(4) After the positioning reinforcement is fixed, mark the location of the circumferential main reinforcement with chalk on the support bar according to the design reinforcement spacing, and mark the installation position of the longitudinal distribution reinforcement on the positioning reinforcement, and then start binding the reinforcement within this section. All steel bar intersections should be tied.

2. The second-line trolley is in place

The heavy-duty steel rail is used for the lining trolley track, and the bottom surface is directly placed on the concrete surface filled with the construction invert arch to ensure the stability of the trolley. Track layout control standards: first, the track center distance is 6m, and the allowable error is ±25px; second, the track surface elevation is 375px above the center of the tunnel filling surface, and the allowable error is ±25px. The center line of the formwork should be adjusted to coincide with the center of the trolley beam as much as possible, so that the trolley is in a good state of stress during the concrete pouring process.

The positioning of the trolley in the curved section should consider the change of the length of the left and right overlap caused by the difference between the length of the inner and outer arcs, so that the arc is smooth, and the joints are reduced.

The lining trolley travels to the position of the vertical mold, adjusts to the accurate position with the lateral jack, and performs the positioning and re-testing until it is adjusted to the accurate position. After the trolley is stretched into place, check whether the connection of each node of the trolley is firm and there is no misalignment and displacement. The five-point positioning method is used to check whether the template is warped or twisted, whether the position is accurate, to ensure the lining clearance, and at the same time it is easy to overcome the stagger at the joint of the lining ring. In order to prevent the trolley from floating when pouring the side wall concrete, it is necessary to add wooden braces or jacks on the top of the trolley. Also check whether the working window is in good condition. When measuring the pay-off, the design reserves should be considered.

3. Treatment of construction joints and deformation joints

The tunnel circumferential construction joint is provided with a composite waterproof structure of a mid-buried rubber water stop belt and a back-attached water stop belt, and the longitudinal construction joint is made of a composite waterproof structure of a mid-buried steel edge rubber water stop belt and a water-swelling rubber water stop bar . During construction, the waterstop is installed in the center of the plug template of the lining trolley, and is fixed by a U-shaped card to ensure that the location of the waterstop is accurately installed, and the ring and longitudinal construction joints are waterproof.

Construction joint construction should be smooth, straight, clean and free of water seepage on both sides. Construction joints shall be cut with cement mortar and loose layer on the concrete surface. Chiselling makes exposed fresh concrete area no less than 75%.
The deformation joints of the tunnel are set at the place where the stratum changes significantly, the light and dark boundary and the section where the section changes obviously. The deformation joint adopts the compound waterproof structure of middle buried rubber waterstop, externally attached waterstop and caulking material.
The position, width and structural type of the deformed joint should meet the design requirements; both sides of the joint should be flat, clean and free of water seepage; the back of the joint should be set with a backing material that has no adhesion to the joint material; the joint is dense.

4. Construction of second lining concrete

(1) Concrete pouring

The concrete is poured in layers and alternately symmetrically. The thickness of each layer should be less than 0.5m. The height difference on both sides should be controlled within 1.5m. The vertical distance from the hose nozzle to the pouring surface should be controlled within 2.0m to prevent the concrete from segregating. The pouring process should be continuous to avoid “cold joints” caused by the stop. If the intermittent time exceeds 1h, it will be treated as construction joints.

When the concrete is poured to 50cm under the working window, the dirt near the window should be scraped off, and the mold release agent should be applied. Putty should be applied at the joint between the window and the panel to ensure a close combination and no leakage.

(2) Concrete vibration

Vibration and tamping should be fixed by inserting the vibrator to ensure the compactness of the concrete; the arching line is supplemented by external hammering of the wooden hammer mold and tamping of the inserting vibrator to suppress the generation of air bubbles on the concrete surface. During the pouring process, it is strictly prohibited to drag the concrete with a vibrating rod.

(3) Lining concrete capping

When the tunnel lining is capped, the steel pipe injection method is used to select the appropriate concrete slump, and the injection is capped from the injection port of the arch. In order to ensure that the top concrete is tightly attached to the surrounding rock, the concrete should be pumped back one by one from the top sealing port. The concrete pump should be continuously operated, the conveying pipe should be straight, the turning should be slow, the joints are tight, and the pipeline is lubricated before pumping. In the top lining, the plastic grouting pipe is pre-buried every 20 meters in the longitudinal direction, and the grouting treatment is carried out after the lining.

(4) Demoulding

According to the construction specification, the strength of the on-site pressure test of the last capped concrete test piece shall be used to control. In general, the concrete strength shall reach more than 8.0MPa. The initial support is not stable, and the concrete strength should be more than 70% of the design strength when the secondary lining is applied in advance. Under special circumstances, the demolding time should be determined according to the test and monitoring measurement results.

(5) Concrete curing

Wash the outer surface of the template with water before removing the mold, and spray the concrete surface with high-pressure water after removing the mold to reduce the heat of hydration. The curing period is not less than 14 days.

With the rapid development of transportation, tunnels, as important buildings on highway lines, have undergone tremendous changes in terms of tunnel length and construction technology. Tunnel lining is a permanent support structure built with reinforced concrete and other materials along the periphery of the tunnel body to prevent deformation or collapse of the surrounding rock. After the tunnel is excavated, in order to maintain the stability of the surrounding rock, support (lining) is generally required. The structure of the tunnel lining is closely related to the level and construction method of the surrounding rock. The choice of support type should depend on the surrounding rock geological conditions, construction conditions and use requirements.

1. Tunnel lining type

(1) Spray anchor support (lining)

Shotcrete support refers to the use of shotcrete and anchor as the main support means, and through the monitoring and measurement of the surrounding rock to guide the design and construction, so that the surrounding rock becomes a part of the support system, so as to rationally use the ground Carrying capacity to ensure the stability of the surrounding rock tunnel construction method. The bearing structure formed by bolts, shotcrete and surrounding rock can effectively limit the free development of the deformation of surrounding rock and adjust the stress distribution of surrounding rock to prevent the rock mass from falling loosely. It can be used as a temporary support during the construction process, and in some cases it may not be necessary to do long-time support or lining.

Depending on the geological conditions of the surrounding rock, a variety of support forms can be used:

A. Anchor rods used alone are generally only used locally;

B. Shotcrete is used alone, sometimes only for local use;

C. Anchor rods combined with shotcrete are mostly used for the top arch and side walls of underground caves;

D. Anchor rods and shotcrete, the addition of single-layer or double-layer reinforced mesh can improve the tensile strength and crack resistance of the sprayed layer, thereby improving the support ability;

E. Anchor spraying is added with metal mesh, and rib-shaped support made of I-beam and other shaped steel is added in the spray layer.

The above-mentioned various forms of anchor spraying support, the number of anchor rods used, the depth, the thickness of the spacing spray layer, and the size of the metal mesh and rib support, etc., should be determined according to the actual situation. In order to do a good job of support, it is also necessary to carry out on-site measurement work such as wall rock displacement and deformation. The anchor and shotcrete support often follows the parallel operation of excavation and excavation, especially when tunneling or underground powerhouse construction adopts partial excavation. As the excavation section expands, it can be digged and sprayed until the entire section is completed.

For modern highway tunnels, the excavation width is generally 10m ~ 20m, and the excavation section is 80m2 ~ 150m2. For such a large cross-section construction, the construction support mainly with shotcrete support plays a decisive role in preventing the surrounding rock deformation, bearing the surrounding rock pressure and protecting the construction safety in the initial stage of the tunnel.

(2) Integral lining

Integral lining refers to cast-in-place concrete or reinforced concrete lining, also known as formwork concrete lining. The technological process is as follows: standing mould, pouring, curing, and removing mould. The advantages of integral lining are: strong adaptability to geological conditions, easy to form as required, good integrity and strong impermeability, and can be suitable for a variety of construction conditions (such as available wooden formwork, steel formwork or formwork car, etc.)

According to different geological conditions or surrounding rock levels, the integral lining has two styles of straight wall and curved wall. Straight wall lining is suitable for the situation where the geological conditions are better and the vertical surrounding rock pressure is the main, while the horizontal surrounding rock pressure is smaller. Mainly suitable for the second and third grade surrounding rocks. When in a tunnel, most of the surrounding rock is below grade 4, and only a few sections are grade IV wall rock, straight wall lining can also be used. Straight wall lining is composed of three parts: upper arch ring, vertical side walls on both sides and bottom bottom.

Curved wall lining is suitable for surrounding rock of grade IV and above with good geological conditions and large horizontal surrounding rock pressure. It consists of a top arch ring, side curved side walls and a bottom arch. The function of the invert arch is to resist the surrounding rock pressure at the bottom and prevent the lining from settling, so that the lining forms a ring-shaped closed overall structure to improve the bearing capacity of the lining.

(3) Compound lining

The compound lining divides the lining structure into two or more layers, and the lining of each layer may be of the same form and material, or may be of different forms and materials. At present, the outer layer and the inner layer are mostly used. The most commonly used outer lining is spray anchor support, and the inner lining is integral concrete lining.

The compound lining is applied in combination with spray anchor support and new Austrian construction. A layer of concrete is first sprayed on the surface of the cave wall, and sometimes anchors are also arranged at the same time. After the country is solidified, a thin layer of flexible supporting structure (called initial support) is formed. It can not only allow a certain change in the surrounding rock, but also limit the excessive deformation of the surrounding rock. During construction, regularly measure the deformation of the support, and feed back these deformation information to the construction and structural design, to determine the best time to apply the liner and the appropriate thickness of the liner. After the deformation of the outer lining is terminated or basically stabilized, the inner lining is applied.

The initial support of the composite lining is timely and closely combined with the surrounding rock, so as to protect and strengthen the surrounding rock and give full play to the self-supporting ability of the surrounding rock. After the secondary lining is completed, the inner surface of the lining is smooth and flat, which can decorate the inner wall and enhance the sense of security. It is an ideal structural form and is currently widely used.

2. Choose

Among the three types of spray anchor support (lining), integral lining and complex table lining, the type of boron lining used in highway tunnels should depend on the surrounding rock geological conditions, construction conditions and use requirements. Compound linings should be used for highways, first-grade highways, and second-grade highway tunnels; for third-grade and below highway tunnels, under the conditions of I, Ⅱ, and Ⅲ surrounding rocks, the tunnel opening section should be composite lining or integral lining other sections Spray anchor lining can be used.