Comprehensive treatment method for tunnel vault collapse based on collapse grading evaluation

Abstract

The application discloses a comprehensive treatment method for tunnel vault collapse based on a collapse grading evaluation. The method comprises the following steps: according to the geometric parameters of the collapse, the scale of the collapse is divided into four grades, and the scale of the collapse in the four grades increases successively; a grading treatment measure is taken for the collapse; the construction process of the treatment of the fourth-grade collapse comprises the following steps: a, back pressure backfilling treatment is performed, a pre-buried concrete backfilling pipe and an exhaust pipe are arranged in the back pressure backfilling process; b, a set thickness of concrete is backfilled in the collapse through the backfilling pipe, and the collapse is closed; c, an advanced grouting large pipe shed is constructed at the vault range at a distance away from the collapse tunnel section; d, multi-step short footage excavation is performed; e, systematic support closely follows the tunnel face, a steel mesh is hung, a steel arch is erected, and shotcrete is sprayed; and f, an outer octagonal mortar anchor rod is punched towards the collapse direction, and the mortar anchor rod is anchored into the stable surrounding rock through the backfilled concrete in the collapse area. The application provides a four-grade classification treatment method, solves the problem of the fuzziness in the treatment of the collapse according to the traditional experience, and guarantees the construction quality and safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel engineering safety construction, in particular to a comprehensive treatment method for tunnel vault collapse cavity based on collapse cavity grading evaluation. BACKGROUND

[0002] In the process of tunnel engineering excavation construction, due to the adverse geological conditions such as gently inclined weak rock stratum, karst cave, fault fracture zone, etc., collapse often occurs in the range of arch top, forming cavities of different scales, and the surrounding rock in the cavity is unstable, which has the risk of continuous collapse, causing construction safety hazards; and the cavity also has adverse effects on the overall stress performance of the supporting and lining structure. Therefore, effective methods need to be taken to treat cavities of different grades.

[0003] The commonly used cavity treatment method at present is: for small-scale cavities, spray concrete backfill is adopted, and for larger-scale cavities, reinforced support is adopted, and after being closed, materials such as mortar are backfilled.

[0004] However, the existing tunnel cavity treatment method has the following technical problems:

[0005] Firstly, there is no reference standard after the collapse occurs, and the treatment measures prepared are of different strengths. If the backfill amount (thickness) of the collapse is too large, on the one hand, the initial support system may bear too much load, causing the initial support to be damaged, and on the other hand, the economy is not high; if the backfill amount (thickness) of the collapse is too small, there is a quality and safety hazard;

[0006] Secondly, when a single treatment measure is adopted, it is difficult to adapt to complex geological conditions and disaster situations; when different support measures are adopted for treatment, the coordination of the support structure and the safety factor after treatment are rarely considered, and the scheme is prepared only by experience, which is too extensive, and improper treatment may lead to the risk of damage to the support structure and secondary collapse. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a comprehensive treatment method for tunnel vault collapse cavity based on collapse cavity grading evaluation, which solves the problem of ambiguity in the preparation of treatment methods for cavities according to traditional experience in the construction process, ensures the construction quality and safety, improves the construction efficiency, and has strong operability and good economy.

[0008] To achieve the above-mentioned purpose, the comprehensive treatment method for tunnel vault collapse cavity based on collapse cavity grading evaluation designed by the present application has the following special features:

[0009] S1) Measure the geometric parameters of the cavity, divide the cavity size into grades I-IV according to the geometric parameters of the cavity, and the cavity size of grades I-IV increases in turn;

[0010] S2) Take grading treatment measures for the cavity;

[0011] The construction process of the grade II collapse cavity treatment includes a, initial spraying of concrete on the collapse cavity; b, hanging of steel mesh on the tunnel vault and erection of steel arch; c, pre-reserving concrete backfill pipes and exhaust pipes in the collapse cavity; d, spraying of concrete on the outside of the steel arch to form a protective shell; e, backfilling of concrete through the backfill pipes to densely backfill the collapse cavity, and real-time monitoring of the exhaust state during the backfilling process; f, setting of system mortar anchor rods towards the direction of the collapse cavity, and the mortar anchor rods are vertically arranged and anchored into the stable surrounding rock through the backfilled concrete in the collapse cavity area.

[0012] The construction process of the grade III collapse cavity treatment includes a, initial spraying of concrete on the collapse cavity; b, hanging of steel mesh on the tunnel vault and erection of steel arch, and the spacing of the steel arch is increased; c, pre-reserving concrete backfill pipes and exhaust pipes in the collapse cavity; d, spraying of concrete on the outside of the steel arch to form a protective shell; e, backfilling of concrete through the backfill pipes to densely backfill the collapse cavity, and real-time monitoring of the exhaust state during the backfilling process; f, setting of mortar anchor rods towards the direction of the collapse cavity, and the mortar anchor rods are in the shape of an outer octagon and anchored into the stable surrounding rock through the backfilled concrete in the collapse cavity area.

[0013] The construction process of the grade IV collapse cavity treatment includes a, reverse pressure backfilling treatment, and pre-embedding of concrete backfill pipes and exhaust pipes during the reverse pressure backfilling process; b, backfilling of concrete of a set thickness through the backfill pipes and closing of the collapse cavity; c, construction of an advanced grouting large pipe shed at a distance away from the collapse section at the vault range; d, multi-step short footage excavation; e, system support following the working face, hanging of steel mesh, erection of steel arch, and spraying of concrete; f, setting of mortar anchor rods towards the direction of the collapse cavity, and the mortar anchor rods are in the shape of an outer octagon and anchored into the stable surrounding rock through the backfilled concrete in the collapse cavity area.

[0014] Further, in S1), according to the height of the collapse cavity, the size of the collapse cavity is divided into grades I-IV, wherein when the height of the collapse cavity is <0.5 m, the size of the collapse cavity is grade I; when the height of the collapse cavity is ≥0.5 m and <2.5 m, the size of the collapse cavity is grade II; when the height of the collapse cavity is ≥2.5 m and <5 m, the size of the collapse cavity is grade III; and when the height of the collapse cavity is >5 m, the size of the collapse cavity is grade IV.

[0015] Further, in S2), the grade I collapse cavity treatment further includes a, multi-layer spraying of concrete backfilling and closing of the collapse cavity; b, hanging of steel mesh on the tunnel vault and spraying of concrete; and c, arrangement of radial system mortar anchor rods towards the direction of the collapse cavity.

[0016] Further, in the grade II collapse cavity treatment in S2), the backfill pipe port is 30-50 cm away from the bottom of the collapse cavity, and the exhaust pipe is arranged at the geometric highest point of the collapse cavity and is always higher than the backfill pipe outlet in the spatial position.

[0017] Further, the grade II collapse cavity treatment in S2) is provided with system mortar anchor rod with diameter of Φ22~Φ28, interval spacing of 1.2~1.5m×1.2~1.5m, and length of L2≥max(H+2, R p +2), wherein R p is the plastic zone radius of the tunnel surrounding rock, and H is the collapse cavity height.

[0018] Further, the grade II collapse cavity treatment in S2) is provided with system mortar anchor rod, steel arch, and hanging net shotcrete, which need to resist the sliding force generated by backfill concrete, and have a set safety margin, which is expressed by the following formula

[0019] KG≤F c +F s +F ss +F m；

[0020] F c =0.7·β h ·f t ·u m ·T 2；

[0021] F s =0.8·f yv ·A s；

[0022] F ss =n ss ·V ss；

[0023] V ss =f sv ·A ss；

[0024] F m =n m ·π·d 2 ·f y / 4;

[0025] In the formula,

[0026] K is the safety factor after collapse backfill treatment, K is 1.5~2.0,

[0027] G is the self-weight of backfill concrete,

[0028] F c is the anti-cutting capacity of hanging net shotcrete,

[0029] F s is the contribution of the steel mesh to the anti-cutting bearing capacity,

[0030] F ssContribution of steel arch to punching shear bearing capacity,

[0031] F m Contribution of system mortar anchor to bearing capacity,

[0032] β h Factor of influence of shotcrete section height,

[0033] f t Design value of tensile strength of shotcrete,

[0034] u m Perimeter length of excavation profile line of exposed collapse cavity,

[0035] f yv Tensile strength of steel mesh,

[0036] A s Area of steel mesh,

[0037] n ss Number of steel bars in punching failure cone,

[0038] V ss Shear bearing capacity of single steel bar,

[0039] f sv Shear strength,

[0040] A ss Cross-sectional area of single steel bar,

[0041] n m Number of anchors in punching failure cone,

[0042] f y Design value of tensile strength,

[0043] d is the diameter of the mortar anchor.

[0044] Further, in S2), the III-grade collapse cavity is treated by mortar anchors with a diameter of Φ22~Φ28 and an interval of 1.0~1.2m x 1.0~1.2m, and the length of the mortar anchor is determined according to the depth of the cavity, and the anchor into the stable surrounding rock is required to be not less than 2m.

[0045] Further, in S2), the III-grade collapse cavity is treated by mortar anchors with a diameter of Φ22~Φ28 and an interval of 1.0~1.2m x 1.0~1.2m, and the length of the mortar anchor is determined according to the depth of the cavity, and the anchor into the stable surrounding rock is required to be not less than 2m.

[0046] KG≤F c +F s +F ss +F m；

[0047] F c =0.7·β h ·f t ·u m ·T 2；

[0048] F s =0.8·f yv ·A s；

[0049] F ss =n ss ·V ss；

[0050] V ss =f sv ·A ss；

[0051] F m =n m ·π·d 2 ·f y ·cosα / 4;

[0052] In the formula,

[0053] K is the safety factor after the collapse backfill treatment, K is 1.5-2.0,

[0054] G is the self-weight of backfill concrete,

[0055] F c is the impact shear resistance of the hanging net shotcrete,

[0056] F s is the contribution of the steel mesh to the impact shear resistance,

[0057] F ss is the contribution of the steel arch to the impact shear resistance,

[0058] F m is the contribution of the outer octagonal mortar anchor rod to the bearing capacity,

[0059] β h is the shotcrete section height influence coefficient,

[0060] f t is the tensile strength design value of the shotcrete,

[0061] u m is the peripheral length of the collapse cavity exposed excavation design contour line,

[0062] f yv is the tensile strength of the steel mesh,

[0063] A s is the steel mesh area,

[0064] n ss Number of steel bars in the punching failure cone,

[0065] V ss Shear capacity of a single steel bar,

[0066] f sv Shear strength,

[0067] A ss Cross-sectional area of a single steel bar,

[0068] n m Number of anchor rods in the punching failure cone,

[0069] f y Tensile strength design value,

[0070] d is the diameter of the mortar anchor rod,

[0071] α is the angle between the outer octagonal mortar anchor rod and the vertical direction.

[0072] Further, in S2), the IV-grade collapse cavity treatment, the backfill pipe is arranged from the backfill face to the upper slope, and the pipe opening is 50-100 cm away from the cavity bottom; the exhaust pipe is arranged from the backfill face to the upper slope, and is always higher than the backfill pipe outlet in space position.

[0073] Further, in S2), the IV-grade collapse cavity treatment, the super-advanced grouting large pipe shed, the outer octagonal mortar anchor rod, the densely arranged steel arch, and the supporting strength provided by the hanging net sprayed concrete need to be able to resist the sliding force generated by the backfill concrete, and have a set safety margin, which is represented by the following formula,

[0074] KG≤F c +F s +F ss +F m +F g；

[0075] F c =0.7·β h ·f t ·u m ·T 2；

[0076] F s =0.8·f yv ·A s；

[0077] F ss =n ss ·V ss；

[0078] V ss =fsv ·A ss；

[0079] F m =n m ·π·d 2 ·f y ·cosα / 4;

[0080] F g =n g ·V g；

[0081] V g = f sv ·(π·(D g 2 -(D g -2T g ) 2 / 4+A g );

[0082] In the formula,

[0083] K is the safety factor after the collapse backfill treatment, K is 1.5-2.0,

[0084] G is the self-weight of backfill concrete,

[0085] F c is the impact shear resistance of the sprayed concrete,

[0086] F s is the contribution of the steel mesh to the impact shear resistance,

[0087] F ss is the contribution of the steel arch to the impact shear resistance,

[0088] F m is the contribution of the outer octagonal mortar anchor rod to the bearing capacity,

[0089] F g is the contribution of the advanced grouting large pipe shed to the bearing capacity,

[0090] β h is the influence coefficient of the sprayed concrete section height,

[0091] f t is the design value of the tensile strength of the sprayed concrete,

[0092] u m is the peripheral length of the collapse cavity exposed excavation design contour line,

[0093] f yv is the tensile strength of the steel mesh,

[0094] A sN is the number of steel bars,

[0095] n ss N is the number of steel bars,

[0096] V ss N is the number of steel bars,

[0097] f sv N is the number of steel bars,

[0098] A ss N is the number of steel bars,

[0099] n m N is the number of steel bars,

[0100] f y N is the number of steel bars,

[0101] d is the diameter of the mortar anchor,

[0102] α is the angle between the outer octagonal mortar anchor and the vertical direction,

[0103] n g N is the number of steel bars,

[0104] V g N is the number of steel bars,

[0105] D g N is the number of steel bars,

[0106] T g N is the number of steel bars,

[0107] A g N is the number of steel bars,

[0108] The advantages of the present application are:

[0109] 1. The present application establishes a collapse cavity size classification standard, and then adopts a differentiated combination management scheme for different levels, and provides a safety factor calculation method for the collapse cavity management scheme of different levels. The method can quantitatively and efficiently handle the collapse problem of the arch top range caused by adverse geological reasons such as gently inclined soft rock stratum, dissolved cave, fracture zone or fault during the excavation of the tunnel project.

[0110] 2. The tunnel arch top collapse cavity comprehensive management method based on the collapse cavity classification evaluation provides a four-level classification management method, solves the fuzziness problem of managing the collapse cavity according to the traditional experience, ensures the construction quality and safety, improves the construction efficiency, and has strong operability and good economy. BRIEF DESCRIPTION OF DRAWINGS

[0111] Figure 1 is a flowchart of the present application;

[0112] Figure 2 A cross-sectional view for treating a grade I collapsed cavity in the present application;

[0113] Figure 3 A cross-sectional view for treating a grade II collapsed cavity in the present application;

[0114] Figure 4 A cross-sectional view for treating a grade III collapsed cavity in the present application;

[0115] Figure 5 A cross-sectional view for treating a grade IV collapsed cavity in the present application;

[0116] Figure 6 A longitudinal cross-sectional view of a large pipe shed for treating a grade IV collapsed cavity in the present application;

[0117] Figure 7 A structure diagram of a steel bar bundle inserted in a large pipe shed for treating a grade IV collapsed cavity in the present application. DETAILED DESCRIPTION

[0118] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0119] In the description of the present application, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application.

[0120] As shown in Figure 1 A comprehensive treatment method for tunnel vault collapse based on collapsed cavity grading evaluation, characterized in that it comprises the following steps:

[0121] S1) Measure the geometric parameters of the collapsed cavity, and divide the collapsed cavity size into grades I-IV according to the geometric parameters of the collapsed cavity, and the sizes of the grades I-IV collapsed cavities increase in turn.

[0122] The geometric parameters (height H, span B, axis direction length L, and volume V) of the collapsed cavity are measured by three-dimensional laser scanning, and the load of the collapsed cavity backfill is mainly related to the height of the collapsed cavity.

[0123] Specifically, according to the collapse height, the collapse scale is divided into levels I-IV, wherein when the collapse height is <0.5 m, the collapse scale is level I; when the collapse height is ≥0.5 m and <2.5 m, the collapse scale is level II; when the collapse height is ≥2.5 m and <5 m, the collapse scale is level III; and when the collapse height is >5 m, the collapse scale is level IV. See Table 1 for details.

[0124] Table 1 Collapse scale grading standard

[0125]

[0126] S2) Take grading control measures for the collapse.

[0127] Level I collapse control (collapse height H <0.5 m), the construction process includes: a. Multi-layer shotcrete backfilling and sealing of the collapse; b. Hanging steel mesh on the tunnel vault and spraying concrete; c. Laying radial system mortar anchor rods towards the collapse direction.

[0128] Specifically, after the risk is eliminated and the collapse site is stable, the collapse is backfilled and sealed by multi-layer shotcrete; the shotcrete is backfilled in layers to the original design excavation contour line, system anchor and shotcrete support measures are used, Φ8.0@15cm×15cm steel mesh is hung, the shotcrete thickness T1 is sprayed, radial system mortar anchor rods with a diameter of d (generally Φ22-Φ28) are laid out at an interval of 1.5-2.0m×1.5-2.0m, and the system anchor rod length L1 ≥max(H+2, R p +2), wherein R p is the plastic zone radius of the tunnel surrounding rock, and H is the collapse height. As shown in FIG. 1, it is a cross-sectional view of level I collapse control in the present application. Figure 2

[0129] Considering that the collapse backfilling height is small and the shotcrete and surrounding rock interface has good adhesion, at this time, the force acting on the shotcrete and system anchor rod is mainly the surrounding rock deformation pressure. Considering that the interaction process of support stiffness and surrounding rock deformation pressure is considered in the original primary support parameter design process, and a certain safety margin is left, the level I collapse control does not need to calculate the collapse control safety factor.

[0130] Level II collapse control (0.5 m≤H<2.5 m), the construction process includes: a. Initial shotcrete of the collapse; b. Hanging steel mesh on the tunnel vault and erecting steel arch; c. Preparing concrete backfilling pipes and exhaust pipes in the collapse; d. Spraying concrete on the outside of the steel arch to form a protective shell; e. Backfilling concrete through the backfilling pipes to densely fill the collapse, and monitoring the exhaust state in real time during the backfilling process; f. Laying system mortar anchor rods towards the collapse direction, which are vertically arranged and anchored into the stable surrounding rock through the backfilled concrete in the collapse area.

[0131] ​Specifically, after the risk is eliminated, the initial concrete is sprayed to the collapse cavity after the collapse position is stable, and the sprayed concrete thickness is generally 5-10 cm to prevent rock block from falling. The collapse cavity hole section system support is strengthened, the steel arch is used, the height F2, the frame distance D2, the Φ8.0@15 cm*15 cm steel mesh is hung, the sprayed concrete thickness T2, the steel needs to be completely wrapped by the concrete, the protection layer thickness is not less than 2 cm, that is, T2≥F2+2, the unit is cm. After the sprayed concrete reaches the design strength, the C25 concrete is backfilled through the backfill pipe to densely backfill the collapse, and the exhaust state is monitored in real time during the backfilling process. If the concrete backflow occurs, it should be closed immediately and the quick-setting mortar is injected for sealing.

[0132] The backfill pipe adopts a seamless steel pipe with a diameter of Φ100 mm-Φ200 mm, the pipe diameter needs to meet the concrete flow degree requirement, and the pipe opening is 30-50 cm away from the collapse cavity bottom. The exhaust pipe adopts a PVC pipe with a diameter of Φ50 mm-Φ150 mm, which is arranged at the geometric highest point of the collapse cavity and is always higher than the backfill pipe outlet in space position. The exhaust pipe opening is additionally provided with a blocking filter screen (mesh ≤5 mm) to prevent the concrete from flowing in.

[0133] The system mortar anchor rod is anchored into the stable surrounding rock by more than 2.0 m through the backfilled concrete in the collapse cavity area. The vertical system mortar anchor rod has a diameter d (generally Φ22-Φ28), an interval of 1.2-1.5 m*1.2-1.5 m, and a length L2≥max(H+2,R p +2), wherein R p is the radius of the plastic zone of the surrounding rock of the tunnel, and H is the height of the collapse cavity. As shown in FIG. 2, it is a cross section schematic view of the treatment of the II-grade collapse cavity in the present application. Figure 3

[0134] Preferably, the support strength provided by the system mortar anchor rod, the steel arch and the net hanging sprayed concrete needs to be able to resist the sliding force generated by the backfilled concrete and has a set safety margin, which is represented by the following formula

[0135] KG≤F c +F s +F ss +F m；

[0136] F c =0.7·β h ·f t ·u m ·T 2；

[0137] F s =0.8·f yv ·A s；

[0138] F ss =n ss ​·V ss；

[0139] V ss =f sv ·A ss；

[0140] F m =n m ·π·d 2 ·f y / 4;

[0141] wherein,

[0142] K is the safety factor after the collapse backfill treatment, K is 1.5~2.0,

[0143] G is the self weight of backfill concrete (kN),

[0144] F c is the impact shear resistance of the hanging net shotcrete, calculated according to the Code for Design of Concrete Structures (GB 50010),

[0145] F s is the contribution of the steel mesh to the impact shear resistance, calculated according to (GB 50010),

[0146] F ss is the contribution of the steel arch to the impact shear resistance,

[0147] F m is the contribution of the system mortar anchor rod to the bearing capacity,

[0148] β h is the shotcrete section height influence coefficient, considering that its general thickness is not greater than 80cm, β h is 1.0,

[0149] f t is the tensile strength design value of shotcrete (MPa),

[0150] u m is the peripheral length of the collapse cavity exposed excavation design contour line (m),

[0151] f yv is the tensile strength of steel mesh (MPa),

[0152] A s is the steel mesh area,

[0153] n ss is the number of steel arches in the impact shear failure cone, n ss =[L / D2], wherein [ ] is the integral symbol, L is the length of the collapse cavity along the axis of the tunnel, and D2 is the arch distance,

[0154] V ss is the shear capacity of the single steel,

[0155] f sv is the shear strength of the steel (MPa),

[0156] A ss is the cross-sectional area of the single steel,

[0157] n m is the number of anchor rods in the punch failure cone,

[0158] f y is the tensile strength design value (MPa),

[0159] d is the diameter of the mortar anchor.

[0160] The construction process of the third-grade collapse cavity treatment includes: a, initial spraying of concrete on the collapse cavity; b, hanging steel mesh on the tunnel vault, erecting steel arch, and the spacing of the steel arch is densified; c, reserving concrete backfill pipes and exhaust pipes in the collapse cavity; d, spraying concrete on the outside of the steel arch to form a protective shell; e, backfilling concrete through the backfill pipes to densely backfill the collapse cavity, and monitoring the exhaust state in real time during the backfilling process; f, setting mortar anchors towards the collapse cavity direction, and the mortar anchors are in the shape of an outer octagon, and are anchored into the stable surrounding rock through the backfilled concrete in the collapse cavity area.

[0161] Specifically, after the risk is eliminated and the collapse site is stable, initial spraying of concrete is performed on the collapse cavity, and the sprayed concrete thickness is generally 5-10 cm to prevent rock blocks from falling. The collapse cavity hole section system support is strengthened, the steel arch specifications are strengthened, and the spacing is densified, i.e., the height F3 is greater than or equal to F2, and the spacing D3 is less than or equal to D2; Φ8.0@15 cm*15 cm steel mesh is hung, the sprayed concrete thickness T3 is sprayed, the steel arch needs to be completely wrapped by concrete, and the protective layer thickness is not less than 2 cm, i.e., T3 is greater than or equal to F3+2, and the unit is cm; the locking foot anchor is strengthened or a locking foot anchor pipe is used.

[0162] The backfill pipe adopts a seamless steel pipe with a diameter of Φ100mm-Φ200mm, the pipe diameter needs to meet the concrete flow degree requirement, and the pipe opening is 30-50 cm away from the cavity bottom; the exhaust pipe adopts a PVC pipe with a diameter of Φ50mm-Φ150mm, the exhaust pipe can be arranged at the geometric highest point of the collapse cavity, and the spatial position is always higher than the outlet of the backfill pipe, a blocking filter screen (mesh ≤5mm) is installed at the exhaust pipe opening to prevent concrete from flowing in. After the sprayed concrete reaches the design strength, C25 concrete is backfilled through the backfill pipe to densely backfill the collapse cavity, and the exhaust state is monitored in real time during the backfilling process. If concrete backflow occurs, it should be closed immediately and injected with quick-setting mortar to block.

[0163] The mortar anchor rod is encrypted, the diameter is d (generally Φ22~Φ28), the interval is 1.0~1.2m*1.0~1.2m, considering that the cavity collapse scale is relatively large, in order to facilitate the anchor rod to pass through the backfilling concrete in the cavity collapse area and anchor into the stable surrounding rock, the anchor rod in the cavity collapse range adopts an outer octagon arrangement form, the length of the anchor rod is determined according to the cavity depth, and the outer octagonal mortar anchor rod passing through the backfilling concrete in the cavity collapse area and anchoring into the stable surrounding rock is not less than 2.0m. Figure 4 As shown in the figure, it is a section schematic view of the treatment of the III-grade cavity collapse in the application.

[0164] Preferably, the support strength provided by the outer octagonal mortar anchor rod, the encryption arrangement of the steel arch and the shotcrete with a hanging net can resist the sliding force generated by the backfilling concrete, and has a set safety margin, which is represented by the following formula,

[0165] KG≤F c +F s +F ss +F m；

[0166] F c =0.7·β h ·f t ·u m ·T 2；

[0167] F s =0.8·f yv ·A s；

[0168] F ss =n ss ·V ss；

[0169] V ss =f sv ·A ss；

[0170] F m =n m ·π·d 2 ·f y ·cosα / 4;

[0171] In the formula,

[0172] K is a safety factor after the cavity collapse backfilling treatment, K is 1.5~2.0,

[0173] G is the self weight of the backfilling concrete (kN),

[0174] F c is the impact cutting resistance of the shotcrete with a hanging net, which is calculated according to the Code for Design of Concrete Structures (GB 50010),

[0175] F s The contribution of steel mesh to the punching shear resistance is calculated according to (GB 50010),

[0176] F ss The contribution of steel arch to the punching shear resistance is calculated according to (GB 50010),

[0177] F m The contribution of the outer octagonal mortar anchor to the bearing capacity is calculated according to (GB 50010),

[0178] β h β is the influence coefficient of the shotcrete section height, considering that its general thickness is not greater than 80 cm, h Take 1.0,

[0179] f t f is the tensile strength design value of shotcrete (MPa),

[0180] u m u is the peripheral length (m) of the excavation design contour line exposed by the collapse cavity,

[0181] f yv f is the tensile strength of steel mesh (MPa),

[0182] A s A is the area of steel mesh,

[0183] n ss n is the number of steel bars in the punching failure cone, ss =[L / D3], where [ ] is the integer symbol, L is the length of the collapse cavity along the axis of the tunnel, and D3 is the distance between the bars,

[0184] V ss V is the shear resistance of a single steel bar,

[0185] f sv f is the shear strength of steel (MPa),

[0186] A ss A is the cross-sectional area of a single steel bar,

[0187] n m n is the number of anchor bars in the punching failure cone,

[0188] f y f is the tensile strength design value (MPa),

[0189] d is the diameter of the mortar anchor,

[0190] α is the angle between the outer octagonal mortar anchor and the vertical direction.

[0191] The construction process for treating a Class IV collapse cavity includes: a) performing counter-pressure backfilling, during which concrete backfill pipes and vent pipes are pre-embedded; b) backfilling with concrete of a set thickness through the backfill pipes and sealing the collapse cavity; c) constructing a pre-grouting large pipe shed in the arch area at a distance back from the collapsed tunnel section; d) multi-step short-advance excavation; e) system support closely following the tunnel face, hanging steel mesh, erecting steel arch frames, and spraying concrete; f) driving mortar anchors in the direction of the collapse cavity, with the mortar anchors in an outward octagonal shape, and anchoring them into the stable surrounding rock through the backfilled concrete in the collapse cavity area.

[0192] Specifically, the backfilling process begins with crushed stone and cavitary debris, during which concrete backfill pipes and vent pipes are pre-embedded. Considering the large collapse height, the high cost of backfilling the entire cavity with concrete, and the significant additional pressure on the support structure, the concrete backfill thickness is set at 5-8m. The backfill pipes can be seamless steel pipes with diameters ranging from 100mm to 200mm, ensuring the pipe diameter meets the concrete flow requirements. The backfill pipes are positioned diagonally upwards from the backfilling face, with the pipe opening 50-100cm from the bottom of the cavity. The vent pipes are PVC pipes with diameters ranging from 50mm to 150mm, positioned diagonally upwards from the backfilling face, always higher than the backfill pipe outlet, and with the pipe opening 0.5-1.0m above the final backfill surface. C25 concrete is then backfilled through the backfill pipes, with a backfill thickness of 5-8m.

[0193] After backfilling is completed, retreat 2-3 steel arch frames from the collapsed section, and construct a pre-grouting pipe roof within a 120-150° range of the top arch (range depending on the width of the collapsed cavity). The outer diameter D of the pipe roof is... g Wall thickness T g Spacing S p To increase the rigidity of the pipe roof, steel reinforcement bundles are added in the middle. Multi-step, short-advance excavation is employed, with each cycle typically extending at the arch frame spacing. The system support closely follows the working face, with steel mesh installed, steel arch frames erected, and shotcrete applied. After the shotcrete reaches its design strength, outward-facing octagonal mortar anchors are installed, penetrating the backfilled concrete in the collapsed cavity area and anchoring into the stable surrounding rock for at least 2.0m. For example... Figure 5 The diagram shown is a cross-sectional schematic of the Class IV cavity treatment in this invention (backfilling is done by pressing against the working face, within the excavation outline area, and is not shown in the diagram). Figure 6 The image shown is a schematic longitudinal section of the advanced large pipe shed used for the treatment of Level IV cavity collapse in this invention. Figure 7 The diagram shown is a structural diagram of the steel reinforcement bundle inserted into the pre-construction large pipe shed of the Class IV collapsed cavity in this invention.

[0194] Preferably, the support strength provided by the pre-grouting large pipe shed, the outward-facing octagonal mortar anchors, the densely arranged steel arch frames, and the shotcrete with wire mesh must be able to resist the sliding force generated by the backfill concrete, and have a set safety margin, expressed by the following formula:

[0195] KG≤F c+F s +F ss +F m +F g；

[0196] F c =0.7·β h ·f t ·u m ·T 2；

[0197] F s =0.8·f yv ·A s；

[0198] F ss =n ss ·V ss；

[0199] V ss =f sv ·A ss；

[0200] F m =n m ·π·d 2 ·f y ·cosα / 4;

[0201] F g =n g ·V g；

[0202] V g = f sv ·(π·(D g 2 -(D g -2T g ) 2 / 4+A g );

[0203] In the formula,

[0204] K is the safety factor after the collapse backfill treatment, K is 1.5-2.0,

[0205] G is the self weight of backfill concrete (kN),

[0206] F c is the resistance to impact cutting of the hanging net shotcrete, which is calculated according to the Code for Design of Concrete Structures (GB 50010),

[0207] F s is the contribution of the steel mesh to the resistance to impact cutting, which is calculated according to (GB 50010),

[0208] Fss contribution of the steel arch to the punching shear bearing capacity,

[0209] F m contribution of the outer octagon mortar anchor to the bearing capacity,

[0210] F g contribution of the super-long pipe roof to the bearing capacity,

[0211] β h β is the influence coefficient of the shotcrete section height, considering that its general thickness is not greater than 80 cm, h β = 1.0,

[0212] f t f is the tensile strength design value of the shotcrete (MPa),

[0213] u m u is the peripheral length of the collapse cavity exposed excavation design contour line (m),

[0214] f yv f is the tensile strength of the steel mesh (MPa),

[0215] A s A is the area of the steel mesh,

[0216] n ss n is the number of steel bars in the punching failure cone, ss n = [L / D4], where [ ] is the rounding symbol, L is the length of the collapse cavity along the axis of the tunnel, and D4 is the pitch,

[0217] V ss V is the shear bearing capacity of a single steel bar,

[0218] f sv f is the shear strength of steel (MPa),

[0219] A ss A is the cross-sectional area of a single steel bar,

[0220] n m n is the number of anchor bars in the punching failure cone,

[0221] f y f is the tensile strength design value,

[0222] d is the diameter of the mortar anchor,

[0223] α is the angle between the outer octagonal mortar anchor and the vertical direction,

[0224] n g n is the number of pipe roofs in the collapse cavity range, ss n = [B / S p ], where [ ] is the rounding symbol, B is the span of the collapse cavity, and Sp for pipe roof spacing,

[0225] V g for single pipe roof shear capacity,

[0226] D g for pipe roof outer diameter,

[0227] T g for pipe roof wall thickness,

[0228] A g for steel bar section area.

[0229] Example 1

[0230] In this embodiment, the tunnel section type adopts a horseshoe shape, and the section size (width m x height m) is 9.40 x 9.40. When excavating to a certain stake number, the arch crown collapses, and after comprehensive measurement, the maximum height of the collapsed cavity is about 2.4 m, the maximum along the tunnel axis direction is about 2 m, and the maximum width is about 4 m. According to the classification of the collapsed cavity size, it belongs to a II-level collapsed cavity, and the following treatment scheme is adopted:

[0231] (1) After the risk is eliminated, the cavity is initially sprayed with C25 polypropylene coarse fiber concrete protection, the initial spraying thickness is 5 cm to 10 cm, and the rock blocks are prevented from falling.

[0232] (2) A Φ8.0@15 cm x 15 cm steel mesh is hung, an I18 type steel arch is erected with a spacing of 2.0 m, and a Φ127 mm x 6 mm seamless steel pipe is pre-buried as a concrete backfill pipe, and a Φ110 mm x 3.2 mm PVC pipe is pre-buried as an exhaust pipe.

[0233] (3) A 20 cm thick C25 polypropylene coarse fiber concrete is sprayed to form a protective shell.

[0234] (4) The collapsed cavity is backfilled and compacted by backfilling C25 concrete through the backfill pipe.

[0235] (5) System mortar anchor rods are punched, the mortar anchor rods are arranged radially, the spacing and row distance is 1.5 m x 1.5 m, and the anchor rod passes through the backfilled concrete in the collapsed cavity area and is anchored into the stable surrounding rock by not less than 2.0 m.

[0236] (6) Through calculation, the safety factor K = 3.84, which is greater than the required range of 1.5~2.0. The support strength provided by the system anchor rod, steel arch and net sprayed concrete is sufficient to resist the sliding force generated by the backfilled concrete.

[0237] Example 2

[0238] In this embodiment, the tunnel section type adopts a horseshoe shape, and the section size (width m x height m) is 9.40 x 9.40. When excavated to a certain stake, the arch crown collapses. After comprehensive measurement, the maximum height of the collapsed cavity is about 4.3 m, the maximum along the tunnel axis direction is about 3.6 m, and the maximum width is about 5.4 m. According to the classification of the collapsed cavity size, it belongs to a class III collapsed cavity, and the following treatment scheme is adopted:

[0239] (1) After the risk is eliminated, the cavity is initially sprayed with C25 polypropylene coarse fiber concrete protection, and the initial spraying thickness is 5 cm to 10 cm to prevent rock blocks from falling.

[0240] (2) A Φ8.0@15 cm x 15 cm steel mesh is hung, an I20a type steel arch is erected with a spacing of 1.0 m, and 2 Φ127 mm x 6 mm seamless steel pipes with a length of 2.5 m are pre-buried as concrete backfill pipes, and a Φ110 mm x 3.2 mm PVC pipe is used as an exhaust pipe.

[0241] (3) A 22 cm thick C25 polypropylene coarse fiber concrete protection shell is sprayed.

[0242] (4) The collapsed cavity is backfilled and compacted by backfilling C25 concrete through the backfill pipe.

[0243] (5) The mortar anchor is punched, the mortar anchor is arranged in an octagon outside the collapsed cavity range, the spacing and row spacing are 1.2 m x 1.2 m, the included angle with the vertical direction is 19°, and the concrete backfilled through the collapsed cavity area is anchored into the stable surrounding rock by not less than 2.0 m.

[0244] (6) Through calculation, the safety factor K = 2.02, which is greater than the value K of 1.5~2.0. The supporting strength provided by the outer octagonal mortar anchor, the reinforced and densified steel arch, and the sprayed concrete with the hanging mesh is sufficient to resist the sliding force generated by the backfilled concrete.

[0245] The present application establishes a four-level quantitative classification standard based on the size of the collapsed cavity, adopts a differentiated combination management scheme for different levels, and provides a safety factor calculation method for the collapsed cavity management scheme of different levels. As known from the above embodiment, the method can efficiently handle the collapse problem of the arch crown range caused by the poor geology such as gently inclined soft rock, dissolved cave, broken zone, or fault during the excavation of the tunnel engineering, solves the ambiguity problem of the traditional experience management method for the collapsed cavity during the construction process, ensures the construction quality and safety, improves the construction efficiency, and has strong operability and good economy.

[0246] The above embodiment is a preferred embodiment of the present application, but the embodiment of the present application is not limited to the above embodiment, and any change, modification, substitution, combination, simplification made without departing from the spirit and principle of the present application should be an equivalent replacement method, and all are included in the protection scope of the present application.

Claims

1. A comprehensive treatment method for tunnel vault collapse based on the collapse grading evaluation, characterized in that, Comprising the following steps: S1) measuring the collapse cavity geometric parameters, and classifying the collapse cavity scale into levels I-IV according to the collapse cavity geometric parameters, the collapse cavity scale of the levels I-IV increasing in turn; S2) taking classified treatment measures for the collapse cavity; The construction process of the level II collapse cavity treatment includes a, initial spraying of concrete on the collapse cavity; b, hanging steel mesh on the tunnel vault and erecting steel arch; c, reserving concrete backfill pipes and exhaust pipes in the collapse cavity; d, spraying concrete outside the steel arch to form a protective shell; e, backfilling concrete through the backfill pipes to densely backfill the collapse cavity, and monitoring the exhaust state in real time during the backfilling process; f, setting system mortar anchor rods towards the collapse cavity direction, the mortar anchor rods being vertically arranged and anchored into the stable surrounding rock through the backfilled concrete in the collapse cavity area; The construction process of the level III collapse cavity treatment includes a, initial spraying of concrete on the collapse cavity; b, hanging steel mesh on the tunnel vault and erecting steel arch, and the spacing of the steel arch being densified; c, reserving concrete backfill pipes and exhaust pipes in the collapse cavity; d, spraying concrete outside the steel arch to form a protective shell; e, backfilling concrete through the backfill pipes to densely backfill the collapse cavity, and monitoring the exhaust state in real time during the backfilling process; f, setting mortar anchor rods towards the collapse cavity direction, and the mortar anchor rods being in an outer octagon shape and anchored into the stable surrounding rock through the backfilled concrete in the collapse cavity area; The construction process of the level IV collapse cavity treatment includes a, reverse pressure backfilling treatment, and reserving concrete backfill pipes and exhaust pipes during the reverse pressure backfilling process; b, backfilling concrete of a set thickness through the backfill pipes in the collapse cavity and closing the collapse cavity; c, erecting an advanced grouting large pipe shed at a distance behind the collapse section at the vault range; d, multi-step short footage excavation; e, system support closely following the working face, hanging steel mesh, erecting steel arch, and spraying concrete; f, setting mortar anchor rods towards the collapse cavity direction, and the mortar anchor rods being in an outer octagon shape and anchored into the stable surrounding rock through the backfilled concrete in the collapse cavity area; The support strength provided by the system mortar anchor rods, steel arch, and hanging net spraying concrete in the level II collapse cavity treatment in S2) needs to be able to resist the sliding force generated by the backfilled concrete, and has a set safety margin, which is represented by the following formula KG≤ F c +F s +F ss +F m； F c = 0.7 · β h · f t · u m · T 2； F s = 0.8 f yv · A s； F ss =n ss ·V ss； V ss =f sv ·A ss； F m =n m ·π·d 2 ·f y / 4; In the formula, K is the safety factor after the collapse cavity backfilling treatment, K taking a value of 1.5-2.0, G is the self-weight of the backfilled concrete, F c For the resistance of the shotcrete to the cutting, F s The contribution of the reinforcement grid to the punching shear capacity, F ss The contribution of the steel arch to the punching shear capacity, F m The load bearing contribution provided by the system of mortar-anchored rock bolts, β h β is the height of the shotcrete section, f t For sprayed concrete tensile strength design value, u m The length of the perimeter of the profile line is designed for the open excavation of the collapsed cavity, f yv For the tensile strength of the reinforcement mesh, A s for the area of the reinforcement mesh, n ss To punch the number of steel pieces in the damage cone, V ss For single steel shear capacity, f sv For steel shear strength, A ss A is the cross-sectional area of the single steel bar, n m To punch the number of anchor rods in the failure cone, f y for the tensile strength design value, d is the diameter of the mortar anchor rod.

2. The comprehensive treatment method for tunnel vault collapse based on the collapse classification evaluation according to claim 1, characterized in that: In S1), according to the collapse cavity height, the collapse cavity scale is classified into levels I-IV, wherein the collapse cavity scale is level I when the collapse cavity height is <0.5 m; the collapse cavity scale is level II when the collapse cavity height is ≥0.5 m and <2.5 m; the collapse cavity scale is level III when the collapse cavity height is ≥2.5 m and <5 m; and the collapse cavity scale is level IV when the collapse cavity height is >5 m.

3. The comprehensive treatment method for tunnel vault collapse based on the collapse classification evaluation according to claim 1, characterized in that: The level I collapse cavity treatment in S2) includes the following construction processes: a, multi-layer spraying of concrete backfilling and closing of the collapse cavity; b, hanging steel mesh on the tunnel vault and spraying concrete; and c, laying radial system mortar anchor rods.

4. The comprehensive treatment method for tunnel vault collapse based on the collapse classification evaluation according to claim 1, characterized in that: In the level II collapse cavity treatment in S2), the backfill pipe port is 30-50 cm away from the collapse cavity bottom; and the exhaust pipe is arranged at the geometric highest point of the collapse cavity and is always higher than the backfill pipe outlet in spatial position.

5. The comprehensive treatment method for tunnel vault collapse based on the collapse classification evaluation according to claim 4, characterized in that: The diameter of the system mortar anchor rod is Φ22~Φ28, the interval spacing is 1.2~1.5m*1.2~1.5m, and the length is L2≥max(H+2, R p +2), wherein R p is the plastic zone radius of the tunnel surrounding rock, and H is the height of the collapse cavity.

6. The comprehensive treatment method for tunnel vault collapse based on the collapse classification evaluation according to claim 1, characterized in that: The diameter of the mortar anchor rod in the III-grade collapse cavity treatment in S2 is Φ22~Φ28, the interval and row distance is 1.0~1.2m x 1.0~1.2m, the length of the mortar anchor rod is determined according to the cavity depth, and the anchor into the stable surrounding rock is required to be not less than 2m.

7. The comprehensive treatment method for tunnel vault collapse based on the collapse classification evaluation according to claim 6, characterized in that: The supporting strength provided by the outer-octagonal mortar anchor rod, the densely arranged steel arch, and the shotcrete with mesh in the III-grade collapse cavity treatment in S2 needs to be able to resist the sliding force generated by the backfill concrete, and has a set safety margin, which is expressed by the following formula, KG≤ F c +F s +F ss +F m； F c = 0.7 · β h · f t · u m · T 2； F s = 0.8 f yv · A s； F ss =n ss ·V ss； V ss =f sv ·A ss； F m =n m ·π·d 2 ·f y ·cosα / 4; In the formula, K is the safety factor after the collapse backfill treatment, K is 1.5~2.0, G is the self-weight of the backfill concrete, F c For the resistance of the shotcrete to the cutting, F s The contribution of the reinforcement grid to the punching shear capacity, F ss The contribution of the steel arch to the punching shear capacity, F m The load bearing contribution provided for the outer octagon mortar anchor, β h K = 1.0 for shotcrete section height f t For sprayed concrete tensile strength design value, u m The length of the perimeter of the profile line is designed for the open excavation of the collapsed cavity, f yv for the tensile strength of the reinforcement mesh, A s for the area of the reinforcement mesh, n ss To punch the number of steel pieces in the damage cone, V ss For single steel shear capacity, f sv For steel shear strength, A ss A is the cross-sectional area of the single steel bar, n m To punch the number of anchor rods in the failure cone, f y for the tensile strength design value, d is the diameter of the mortar anchor rod, α is the angle between the outer-octagonal mortar anchor rod and the vertical direction.

8. The comprehensive treatment method for tunnel vault collapse based on the collapse classification evaluation according to claim 1, characterized in that: The backfill pipe in the IV-grade collapse cavity treatment in S2 is arranged from the backfill face to the obliquely upward, and the pipe opening is 50~100cm away from the cavity bottom; the exhaust pipe is arranged from the backfill face to the obliquely upward, and is always higher than the backfill pipe outlet in the spatial position.

9. The comprehensive treatment method for tunnel vault collapse based on the collapse grading evaluation according to claim 8, characterized in that: The supporting strength provided by the advanced grouting large pipe shed, the outer-octagonal mortar anchor rod, the densely arranged steel arch, and the shotcrete with mesh in the IV-grade collapse cavity treatment in S2 needs to be able to resist the sliding force generated by the backfill concrete, and has a set safety margin, which is expressed by the following formula, KG≤ F c +F s +F ss +F m +F g； F c = 0.7 · β h · f t · u m · T 2； F s =0.8·f yv ·A s； F ss =n ss ·V ss； V ss =f sv ·A ss； F m =n m ·π·d 2 ·f y ·cosα / 4; F g =n g ·V g； V g = f sv ·(π·(D g 2 -(D g -2T g ) 2 / 4+A g ) In the formula, K is the safety factor after the collapse backfill treatment, K is 1.5~2.0, G is the self-weight of the backfill concrete, F c For the hanging net shotcrete impact cut ability, F s The contribution of the reinforcement grid to the punching shear capacity, F ss The contribution of the steel arch to the punching shear capacity, F m The load bearing contribution provided for the outer octagon mortar anchor, F g The bearing capacity contribution provided for the super-advanced grouting large pipe shed, β h is the height of the shotcrete section, and β is the height of the shotcrete section, and β is the height of the shotcrete section, and f t For sprayed concrete tensile strength design value, u m The length of the perimeter of the profile line is designed for the open excavation of the collapsed cavity, f yv for the tensile strength of the reinforcement mesh, A s for the area of the reinforcement mesh, n ss To punch the number of steel pieces in the damage cone, V ss For single steel shear capacity, f sv For steel shear strength, A ss A is the cross-sectional area of the single steel bar, n m To punch the number of anchor rods in the failure cone, f y for the tensile strength design value, d is the diameter of the mortar anchor rod, α is the angle between the outer-octagonal mortar anchor rod and the vertical direction, n g for the number of pipe roofs in the collapsed cavity range, V g For single pipe shed shear capacity, D g D is the outer diameter of the tube tent, T g For pipe roof wall thickness, A g A is the cross-sectional area of the tendon.

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