The secondary lining can only be supported by how much the tunnel has to be bored

Reasons (1) The smooth blasting of the tunnel is not good, the surface treatment is not smooth after the initial support or the waterproof membrane is laid too tightly, and the huge impact force when pouring concrete acts on the waterproof board, causing the waterproof board to puncture and crack, so that the waterproof board loses its waterproof effect. (2) The concrete pouring is not compact, and the waterproof measures taken at the construction joint are not in place, so that the free water behind the lining can seep out smoothly. (3) The spacing of the drain holes is too large or the protection of the drain pipe is not effective and the drain pipe is blocked when pouring concrete, so that the seepage water of the surrounding rock cannot be smoothly removed from the drain pipe, and the back accumulates to form a hydrostatic pressure and seeps out.

According to past experience, seepage water mostly occurs in places with weak structures and high water pressure. Water seepage can occur in concrete cracks caused by various reasons, such as concrete additive dosage, improper maintenance, temperature and uneven settlement. The tunnel is lined with anti-drainage structure, which involves the arch tunnel structure of tunnel construction, and is especially suitable for drainage structure.

It is characterized in that the arch blind pipe is fixed along the arch outer side of the arch at the longitudinal two ends of the arch hole body of each section of secondary lining concrete layer, and the horizontal blind pipe is fixed along the horizontal outer side of the lower end of the secondary lining concrete layer, and the arch blind pipe is connected with the horizontal blind pipe with tee, and the other outlet of the tee is communicated with the ditch. The advantage is that the structure that combines prevention and drainage is implemented, and the water leakage and seepage caused by the construction are discharged to the ditch from the blind pipe structure in time.

The length of the second lining time is related to the grade of the surrounding rock, the better the surrounding rock, the longer the excavation distance, on the contrary, the second lining must be constructed as soon as possible and closed into a ring. The surrounding rock is graded differently on roads and railways, but they are all classified into 6 or 6 categories, with specific reference to the technical specifications for tunnel construction of roads or railways.

In tunnel construction, the primary lining is also called initial support, and the concept is that the tunnel is a combination of surrounding rock and supporting structure. Tunnel excavation destroys the initial stress balance of the formation, resulting in stress release of the surrounding rock and deformation of the cavern, and excessive deformation will lead to loosening or even collapse of the surrounding rock.

In the periphery of the cavern after excavation, steel, concrete and other supports are applied to provide resistance to the periphery of the cavern and control the deformation of the surrounding rock. In order to control the appropriate amount of stress release and deformation of the surrounding rock, increase the structural safety and facilitate construction, the structural layer with low stiffness and as a part of the long-standing bearing structure is constructed immediately after tunnel excavation, which is called initial support.

Under normal circumstances, the initial support is spray anchor support, composed of anchors, steel mesh, steel frame, sprayed concrete, and tunnel excavation after the slag is discharged, a layer of 3 4cm concrete is sprayed on the rock surface at the beginning to prevent the weathering of the surrounding rock, and then the hollow anchor is applied in the tunnel arch, and the mortar anchor is applied on the side wall, and there must be an anchor backing plate, a steel mesh is hung, and the steel frame is supported (there must be a lock foot anchor or anchor pipe during the construction of the step method), and then the concrete is sprayed, which must conform to the thickness of the design. After the initial construction, it becomes a part of the permanent bearing structure, which together with the surrounding rock constitutes a permanent bearing system of the tunnel structure.

The secondary lining is molded concrete, formwork trolley pouring, depending on the design situation, some parts of the reinforced concrete, some parts are plain concrete.

According to the actual situation of the construction site and the monitoring and measurement results of the surrounding rock, the application time of the second lining is selected to make the structure in the best stress state.

Another way is that the first lining is the shotcrete in the initial support, and the second lining is the molded concrete.

A lining refers to the initial support of the steel arch and other after completion, shotcrete cover, that is, the layer of concrete that is close to the surrounding rock.

The second lining refers to the layer of concrete that is close to the first lining, usually tied to the steel skeleton, and then poured with an integral formwork.

Answers]: a, c, e

The application of the second royal side lining should be carried out when the following requirements are met:

1) The horizontal clearance velocity of the tunnel and the vertical displacement velocity of the vault or floor decrease significantly.

2) The relative value of the displacement per mu of the tunnel has reached more than 90% of the relative displacement.

For special sections such as shallow burial, weakness, and high geostress surrounding rock, the number of towns should be determined according to the site conditions.

Answer] Sharp lead bucket: a

The secondary lining is basically not stressed, so it needs to be carried out after the deformation of the surrounding rock and bolt support is basically stable. Silver mill.

Answer]: B, only bend C

The center of the caulking at the end of the deformation joint should coincide with the position of the initial support deformation joint, and the end template should be supported vertically and firmly. The silver should be poured from the bottom to the top, and each part should be poured symmetrically and vibrated densely, and the vibrator does not refer to the finger so stuffy that it touches the waterproof layer. The removal of the rectangular section roof formwork should reach 100%.