What are the types of tunnel lining formwork?

Tunnel lining formwork

The tunnel lining trolley is an indispensable non-standard product for the secondary lining during tunnel construction. It mainly consists of simple lining trolley, full hydraulic automatic walking lining trolley and grid lining trolley. The fully hydraulic lining trolley can be divided into a side arch type, a full round needle beam type, a bottom mold needle beam type, a full circle walking type and the like. Lifting slipforms, jacking slipforms and overturning are also commonly used in hydraulic tunnels and bridge construction. Full-round lining trolleys are often used in hydraulic tunnel construction. Vertical tunnel joints are not allowed in tunnels. Full-circle walk-through type is generally used when the span of hydraulic tunnels is large; the application of side-arched lining trolleys is common. It is commonly used in the secondary lining construction of roads, railway tunnels and underground caverns.

1. Simple lining trolley

The simple lining trolley is generally designed as a steel arch type. It uses a standard composite steel formwork. It can be used without external walking. It is driven by external power. The detaching formwork is all manual operation and labor intensive. This type of lining trolley is generally used for short tunnel construction, especially for tunnel lining construction with complex plane and space geometry, frequent process conversion and strict process requirements, and its superiority is more obvious.

For example, a double-arch tunnel of a highway is 200m long, and the plane is at a circular curve of R=300m. The cross slope in the tunnel changes from i=±2% to +5%, and the tunnel is also at R=3000m. On the vertical curve, the tunnel shape is in a “hyperbolic” state, while the middle wall is a straight wall design. The outlet 15m is gradual from R=5.5m to R=7.5m. The tunnel reinforced concrete is lined with a simple arch. The trolley design is a good solution to these problems, and the engineering cost is low.

Most of the simple trolleys use artificial perfusion rafts, and the simple lining trolleys are filled with sputum pump trucks, so the rigidity of the trolleys should be particularly strengthened. Some simple lining trolleys also use integral steel formwork, but the detachment die still uses the screw rods, and there is no automatic walking. This type of trolley is generally filled with a sputum pump. Simple lining trolleys generally use composite steel formwork. The combined steel formwork is generally made of thin plate. The rigidity of the steel formwork should be considered in the design process, so the spacing of the steel arches should not be too large.

If the length of the steel formwork is 1.5m, the mean spacing of the steel arches should be no more than 0.75m, and the longitudinal joints of the steel formwork should be placed between the concrete and the concrete to facilitate the installation of the formwork fasteners and the formwork hooks. If the pump is used for perfusion, the filling speed should not be too fast, otherwise the combined steel formwork will be deformed, especially when the thickness of the lining is more than 500mm. Care should be taken when filling the cap, and the filling condition of the cockroach should be paid attention to at any time to prevent the cockroach from being forced to fill after filling. Otherwise, the explosion mode or the trolley will be deformed and damaged.

2. Fully hydraulic automatic walking lining trolley

It is mainly used in the construction of medium and long tunnels, and has high requirements on construction progress and surface quality of concrete. This type of lining trolley is designed as an integral steel formwork and a hydraulic cylinder to take off the vertical die. The construction is supported by a screw rod. The electric reducer is automatically driven or the cylinder is stepped automatically. All of them are filled with a pump. Most lining trolleys are such trolleys.

When designing such a lining trolley, in the case of meeting the clearance requirements, the lower installation position of the diagonal support on the inside of the gantry should be considered, as close as possible to the lower part of the column, so that it is well stressed. The gantry beam should be high enough that the conventional railway tunnel is not less than 400mm and the road tunnel is not less than 5500mm. The small distance between the end face of the template and the gantry is not less than 250mm, otherwise the front and back lining sections will be difficult to overlap.

When lining the trolley with this type, it should be noted that the paving height difference between the two sides of the traveling rail is not more than 1%, otherwise the screw jack and the jacking cylinder will be deformed. When lining a tunnel with a ramp, in order to adjust the lining elevation, the height difference between the front and rear ends of the trolley and the end face of the stencil are not parallel with the end face of the gantry, which will cause a large horizontal component between the stencil and the gantry, resulting in a large horizontal component. The support screw between the template and the door frame is misplaced, resulting in damage to the cylinder and the cylinder.

Therefore, in the design, the constraint structure or adjustment system that causes the horizontal component of the front and rear height differences should be fully considered. When positioning the vertical mold, the rail clamp must be installed, tighten the basic screw jack, the top of the gantry and the top of the formwork. If necessary, other measures can be used to reinforce the position of the lower arch, so that the gantry is exhausted. It may be small to prevent deformation of the running mold and the gantry.

3. Net frame lining trolley

The truss lining trolley has been structurally modified compared to conventional lining trolleys. In the construction of the traditional lining trolley, the trolley frame is a force-bearing member. It receives a large side pressure and varies with the stiffness of the gantry. It is not suitable for direct operation in tunnels with large cross slopes and longitudinal slopes. The requirements for the working environment are high, otherwise the overall deformation and damage of the trolley will be caused.

The truss lining trolley frame is unstressed during construction, and the support member of the stencil is the top screw of the side arch, and the gantry is only stressed during the process of taking off the mold and walking, and The force is vertically downward, there is no side pressure, and the gantry is designed to be rigid enough to be deformed according to the weight of the trolley. When constructing or walking in a tunnel with ramps, whether it is a horizontal slope or a vertical slope, the height can be adjusted through the jacking cylinder at the lower part of the gantry, so that the whole trolley is in a horizontal state, and there is no front tilting force in the whole trolley. And the side force ensures the overall stability of the trolley.

Because the trolley completely cancels the screw for support, the trolley is easy to position and can be adjusted to the geometric position of the lining very quickly, saving a lot of manpower and material resources, improving work efficiency, shortening the work cycle, and saving engineering accordingly. cost. In order to ensure the rigidity and strength of the top arch formwork, the upper frame is designed as a grid-type bar structure, so that the force is good, and the template will not be deformed and displaced during the lining process. The weak link in the whole trolley is the lower template and the lower mold supporting the diagonal rod. Therefore, when designing the lower template, the force of the lower mold should be fully calculated, and the width and thickness of the curved plate should be widened as much as possible. The rod is stable and calculated to ensure that the slanting rod has sufficient rigidity and strength to prevent deformation and bending during use, resulting in running the mold. In the calculation process, the influence of the lining thickness, slump, perfusion speed, aggregate size and whether it is reinforced concrete or not should be fully considered.

The screw of the lower arch is the main force-bearing part. When the whole formwork is below the centerline of the center of the lining, it is supported by it. Therefore, the structural form and rigidity should be considered in the design. In use, the jack must be firmly pressed against the ground, no looseness is allowed, and if necessary, it can be reinforced with other parts as an auxiliary support to prevent the running mold and the trolley from shifting downward.

It should be noted that the rails as the longitudinal positioning of the trolley and the basic screw jacks must be tightened, stuck and secured to the rails, especially when lining the ramp. This type of lining trolley is mainly used for the construction of large-span tunnels and underground caverns.

If the traditional full-hydraulic lining trolley is used, the gantry design is difficult to meet the requirements of use, resulting in deformation and damage of the gantry. First, the truss beam is distorted and deformed, eventually leading to running the mold. If the beam is raised, the cross section of the vertical sill, the side sill and the end face are increased, which causes unnecessary waste, and the lining lining trolley can overcome the above difficulties. Since this type of lining trolley is a large-span construction, its operability should be considered in design, and its working ladder and working aisle should be able to reach every working position conveniently.