What are the technical standards for tunnel lining

During the construction of the tunnel lining, the midline, elevation, section and clearance dimensions shall meet the design requirements. The standards, specifications and requirements of the lining materials shall comply with the regulations of the Ministry of Railways’ current “Railway Tunnel Design Regulations”.

1. The lining shall not invade the boundary of the tunnel construction. When setting out the lining construction, the designed contour line can be expanded by 5cm. When using spray anchor lining, it should be handled according to the design requirements.

2. During the lining construction, closely cooperate with the design unit. For the section where the lining is completed, continue to observe and monitor the stable state of the tunnel, pay attention to the deformation, cracking, and intrusion of the lining, and make long-term stability evaluation.

3. The sundries in the formwork and the oil on the steel bars should be removed before pouring concrete.

4. Before and during concrete pouring, check the formwork, support, steel frame, embedded parts, etc. Any problems should be dealt with in a timely manner and recorded.

5. When pouring integral lining, choose lining formwork trolley and mobile formwork according to different construction methods, and be equipped with concrete pump and concrete tanker.

(1) The arch frame and wall frame template should be processed and manufactured with a shaped metal structure, and the position of the ventilation pipe should be reserved;

(2) The spacing of the arch wall frame should be determined according to the surrounding rock conditions of the lining section, the width of the tunnel, the thickness of the lining and the length of the formwork, and should be 1.0~1.5m;

(3) The erection of the arch wall frame and the formwork should be accurate, firmly connected, and strictly prevent walking, and should be based on the centerline and elevation of the tunnel, combined with the allowable construction error and the reserved settlement value of the arch, and the excavation section should be reviewed and checked. Trim;

(4) The vertical arch should be based on the center line of the tunnel and erected vertically according to the line direction;

(5) When erecting the wall frame, the position of the wall frame should be determined according to the center line of the line, and the height of the wall foundation should be checked. When erecting the curved wall frame, the horizontal control position of the off-track surface should be marked;

6. The construction joints and deformation joints of the lining should be waterproofed.

Composite lining

1. When the composite lining adopts the inverted arch, the construction time of the secondary lining should be determined according to the deformation law of the surrounding rock and support measurement.

2. The waterproof layer should be laid without nails and carried out before the secondary lining is poured.

3. Under normal circumstances, the secondary lining should be constructed after the surrounding rock and the initial support deformation are basically stable. The basic stability of the deformation should conform to the obvious slowing down trend of the displacement velocity around the tunnel. The relative clearance speed of the arch toe level is less than 0.2mm/d, and the relative sinking speed of the vault is less than 0.15mm/d.

4. For tunnels built under special conditions (such as loose accumulations, shallow buried sections, etc.), the secondary lining should be constructed in time.

5. For the secondary lining, it is advisable to use the full-section primary or wall-first-arch method to fill concrete. The following requirements should be met during construction:

(1) Execute according to the roofing process to ensure the concrete of the vault is dense;

(2) Before pouring, the dust on the surface of the spray layer or waterproof layer should be removed and sprinkled with water to wet it;

(3) The perfusion concrete should be vibrated and compacted to prevent shrinkage and cracking, and the ring waterproof layer should not be broken during vibrating;

6. When demoulding the secondary lining, the concrete strength should reach 2.5Mpa.

Integral lining

1. The side wall construction should meet the following requirements:

(1) The wall foundation scum, sludge, and stagnant water should be removed;

(2) The side wall in the perfusion should be stable, and the backfilling of the over-excavated part should be carried out according to the design requirements;

(3) The enlarged part of the foundation of the side wall and the arch table of the invert should be completed at one time in combination with construction.

2. The arch construction should meet the following requirements:

(1) The length of the arch ring link should be determined according to the stability of the surrounding rock and the construction method;

(2) The pouring sequence should be symmetrical from the arch feet on both sides to the vault, and the intermittent and capping layers should be radial;

(3) The arch ring closure of the segmented construction should be selected in a better place of the surrounding rock;

(4) Grouting holes should be reserved for the arch, and the air conditioner should be backfilled and grouted to ensure that the arch is dense.

3. The demoulding time of the lining should meet the following requirements:

(1) Arch wall that does not bear external load, concrete: soil strength shall not be less than 2.5Mpa;

(2) For arch walls that bear greater pressure from surrounding rock, the strength of the top and seal concrete should reach 100% of the design strength.

(3) For arch walls with less surrounding rock pressure, the strength of the top and seal concrete should reach 70% of the design strength.

4. The lining concrete is cured after the lining is poured, and the curing time is 7 to 14 days.

Reinforced concrete lining

1. The steel bars should be straightened before processing and bending, and meet the following requirements:

(1) The oil stains, cement paste and floating skin rust on the surface of the steel bars should be removed;

(2) The surface of the processed steel bar should not have scars that weaken the cross-section of the steel bar;

(3) When using the cold drawing method to straighten the elongation: Class I steel bars shall not exceed 2%, and Class II steel bars shall not exceed 1%.

2. When installing steel bars, the position of the steel bars and the thickness of the concrete protective layer should meet the design requirements.

The above is the relevant introduction about the tunnel lining technical standards. During the construction process, strict technical inspections must be carried out to ensure the quality and safety of the tunnel.