A large deformation control system and construction method for tunnels in high ground stress soft rock strata

Abstract

A large deformation control system and construction method for tunnels in high geostress soft rock strata, which can give full play to the self-bearing capacity of surrounding rocks, solve technical problems such as difficult control of large deformations in tunnels in high geostress soft rock strata, large engineering investment, and low construction efficiency, and at the same time need to have characteristics such as general applicability, construction convenience, and good economy. The large deformation control system for tunnels includes a rock mass active stripping area, a surface support, and an anchor injection system. The surface support is constructed on the tunnel wall. The rock mass active stripping area is located between the surface support and the deep bearing area of the surrounding rock. In this area, rock mass excavation holes are arranged longitudinally or radially along the tunnel to dynamically and actively eliminate a certain volume of rock mass expansion in the rock mass active stripping area. The anchor injection system is constructed in the rock mass active stripping area to reinforce and transform it into a tunnel peripheral reinforcement area, and jointly control the formation of the deep bearing area of the surrounding rock with the surface support.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel and underground engineering, and relates to a control system and construction method for underground engineering construction in high in-situ stress soft rock strata to solve large deformation disasters. More specifically, the present invention relates to a control system and construction method for large deformation of tunnels in high in-situ stress soft rock strata. Background Art

[0002] With the development of China's economy and the progress of technology, the transportation industry is developing rapidly, and infrastructure construction work is also in full swing. Depending on China's special topographical features, a large number of tunnel and underground engineering constructions have been carried out in the country, which has greatly promoted the high-quality development of China's underground engineering technology, and at the same time brought new challenges to construction and operation. In the construction of tunnel projects in the difficult and dangerous mountainous areas of southwest China, complex geological conditions and special environmental conditions are faced. Among them, large deformation of high in-situ stress soft rock is known as the "cancer" in the tunnel engineering field, and its treatment difficulty is so great that it has caused great difficulties to design, construction and operation.

[0003] Regarding the treatment of large deformation of high in-situ stress soft rock, scholars at home and abroad have carried out a large amount of research work and proposed some large deformation control methods and measures. From the perspective of support measures, they are mainly divided into three types: timely strong support, layered support and yielding support. However, at present, these support measures all have certain limitations. Timely strong support restricts the deformation of the surrounding rock too early, and the stress of the surrounding rock is not released, resulting in the failure of the support structure due to the force exceeding its bearing capacity. At the same time, blindly increasing the support strength is uneconomical. The timing of layered support is uncertain and the construction efficiency is low, which is prone to engineering accidents. The yielding support is also not satisfactory in terms of "yielding".

[0004] For example, in the specification of the invention patent application with publication number CN111852505A, a yielding primary support system for controlling large deformation of high in-situ stress soft rock tunnels is disclosed. The yielding primary support system includes: a plurality of deformation joints, which are arranged on the shotcrete layer of the tunnel and arranged longitudinally along the tunnel; a plurality of square steel pipes, which are respectively clamped in the deformation joints; a plurality of steel arch frames arranged in parallel along the transverse direction of the tunnel. Each steel arch frame includes: a plurality of arch frames one and arch frames two; a plurality of arch frame joints, which are respectively arranged between the arch frames one and arch frames two and used to connect the arch frames one and arch frames two. The distance between the ends of the arch frames one and arch frames two is adjustable, and the arch frame joints are fixed to the square steel pipes. It can ensure that the concrete shot layer and the square steel pipes do not undergo torsional damage during the convergence deformation process of the surrounding rock, and after deformation, grouting can be carried out through the reserved grouting holes to further improve the stability of the primary support system. However, the construction accuracy requirements for the steel pipe joints of this yielding primary support system are high, and it is difficult for the joints to slide along the preset groove after the steel frame deforms, so the deformation control effect is greatly reduced.

[0005] For another example, the invention patent application specification with publication number CN111706355A discloses a tunnel structure suitable for large deformation surrounding rock and a method for controlling large deformation of tunnel surrounding rock. The tunnel structure of large deformation surrounding rock includes an outer layer of initial support and an inner layer of secondary lining along its radial direction. A plurality of deformation release holes are arranged on the outer periphery of the tunnel along the longitudinal direction of the tunnel. There are N deformation release holes in each group, and the N deformation release holes in each group are arranged circumferentially around the tunnel. Each deformation release hole is drilled from the initial support into the tunnel surrounding rock along the radial direction of the tunnel. By setting the deformation release hole, deformation space is reserved for the tunnel surrounding rock, and part of the surrounding rock pressure is released, thereby reducing the pressure on the initial support and reducing the deformation of the initial support. By continuously monitoring deformation and other related data and providing feedback to guide the construction, the deformation release hole is dynamically adjusted to match the surrounding rock deformation, so as to achieve the purpose of reasonably and effectively releasing the surrounding rock deformation pressure. This tunnel surrounding rock large deformation control method is based on high-accuracy estimation, but the deformation of each section of the tunnel varies greatly, making it inconvenient to implement. In addition, a large number of radial stress release holes are set at one time based on the estimated deformation, which seriously damages the integrity of the surrounding rock and affects its self-bearing capacity.

[0006] For another example, the invention patent specification with authorization announcement number CN109779654A discloses an initial support system and construction method for a high-ground stress and large-deformation tunnel that combines release and resistance. The initial support system includes an initial support body, which is a steel arch frame and an anchor-net spraying combined support system that matches the steel arch frame, wherein the initial support body is provided with multiple stress release windows in the tunnel side wall section, and multiple stress release windows located on each side of the initial support body are arranged at intervals along the longitudinal direction of the tunnel. It can achieve asynchronous deformation of the surrounding rock and the initial support body, effectively reduce the deformation of the maximum deformation part of the initial support body before the initial support body forms a ring, and avoid the beneficial effect of the initial support body being destroyed before the ring is formed. However, this initial support system only solves the high-ground stress situation where the maximum principal stress is in the horizontal direction and is nearly perpendicular to the tunnel axis, and is not suitable for large deformation control under complex ground stress.

[0007] In addition, there are also measures such as increasing the reserved deformation and constructing an advanced pilot tunnel. The setting size of the reserved deformation of the former is uncertain. A small reserved deformation will result in a large intrusion of the initial support deformation, while a large reserved deformation increases the tunnel excavation area and the secondary lining masonry backfill volume, which is poor in economy. Although the latter releases the stress, the stress release time is too long due to secondary disturbance and process reasons, which increases the loose load of the surrounding rock, causing the support structure to deform greatly and be damaged due to insufficient bearing capacity.

[0008] Although scholars at home and abroad realize that simply improving the resistance of the support structure is feasible under high ground stress, the cost is high and not worth it, and therefore the self-bearing capacity of the surrounding rock must be brought into play, how to give full play to the self-bearing capacity of the surrounding rock to control the large deformation of tunnels in soft rock strata with high ground stress has never been formed into a reasonable, feasible and effective control system and construction method. Summary of the invention

[0009] The purpose of the present invention is to provide a large deformation control system for tunnels in high-ground stress soft rock formations, so as to give full play to the self-bearing capacity of the surrounding rock, solve the technical problems of difficult large deformation control of tunnels in high-ground stress soft rock formations, large engineering investment, low construction efficiency, etc., and at the same time, it should have the characteristics of universal applicability, convenient construction, good economy, etc.

[0010] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0011] The invention discloses a large deformation control system for a tunnel in a soft rock formation with high ground stress, which is characterized by comprising a rock active stripping zone, a surface support and an anchor injection system, wherein the surface support is applied on the tunnel wall; the rock active stripping zone is located between the surface support and the surrounding rock deep bearing zone, and rock excavation holes are arranged in the tunnel longitudinally or radially in the zone to dynamically and actively eliminate a certain amount of rock expansion volume in the rock active stripping zone; the anchor injection system is applied in the rock active stripping zone to transform its reinforcement into a tunnel periphery reinforcement zone, and jointly controls the formation of the surrounding rock deep bearing zone with the surface support;

[0012] The rock removal holes are constructed by using active soil-cutting equipment such as small spiral drilling machines or small high-pressure cutting machines. The range of rock removal is no more than 2.5m from the tunnel wall, and the allowable volume of rock expansion is V 消 Calculate as follows:

[0013] V 消 =6.28×R×(0.5-S)+0.79×n×L×D 2

[0014] Wherein, n is the number of rock excavation holes set per meter of tunnel cross section, which should not be more than 10 holes; D is the diameter of the rock excavation hole, unit: m; L is the length of the rock excavation hole, when it is radially arranged, L≤2.5m; S is the allowable unilateral convergence deformation of the tunnel, unit: m; R is the equivalent radius of the tunnel clearance, unit: m.

[0015] Another technical problem to be solved by the present invention is to provide a construction method for the above-mentioned large deformation control system of a tunnel in a high-stress soft rock formation.

[0016] The construction method comprises the following steps:

[0017] S01. After tunnel excavation and slag removal, timely implement surface support for the excavated section;

[0018] S02. Drill rock excavation holes evenly along the surface support, and the rock excavation volume is V ki ;

[0019] S03. Conduct deformation monitoring and measurement on the surface support. If the deformation rate exceeds 1 cm / d, use active soil cutting equipment to extract the rock mass within the active rock mass stripping area of the rock mass through the rock mass excavation holes, add rock mass excavation holes to the parts with large surface support deformation, and actively strip the rock mass of this part. The total excavated volume of the rock mass this time is recorded as V ti , the cumulative volume V 消 ’ of the stripped rock mass in the active rock mass stripping area 10 at the current time point = ΣV ki + ΣV ti ;

[0020] S04. Repeat the above steps until the surface support forms a ring. At this time, ensure that V 消 ’ / V 消 ≤ 0.75;

[0021] S05. Drill the rock mass excavation holes at the locations where bolts, cables, and surrounding rock grouting are to be constructed to the design depth again to form bolt or cable installation holes and grouting holes. After installing the steel sleeve 7 on the surface support and installing bolts and cables, grout and reinforce the rock mass from the deep bearing area of the surrounding rock to the excavated area through the grouting holes;

[0022] S06. When the deformation rate of the surface support is less than 1 mm / d, construct the waterproof and drainage system and carry out the casting of the secondary lining.

[0023] The beneficial effects of the present invention are mainly reflected in the following aspects:

[0024] First, by setting the active rock mass stripping area, the volume expansion that inevitably occurs after the surrounding rock is squeezed by high in-situ stress is actively eliminated in a restricted manner, the internal pressure of the surrounding rock is released, and the self-bearing capacity of the surrounding rock is fully exerted, which can effectively solve the problem of large deformation of tunnels in high in-situ stress soft rock strata;

[0025] Second, the project cost of large deformation tunnels is reasonably controlled, and the project investment is effectively saved. Through the dynamic adjustment of the excavated volume of the rock mass, on the one hand, the engineering quantity of raw materials required to improve the strength of the support structure system is greatly reduced; on the other hand, the amount of waste slag from the early excavation of a large amount of rock mass and the masonry backfill volume increased for the secondary lining to reach the design contour are effectively controlled;

[0026] Third, the construction is convenient and meets the "dual carbon" goal. Compared with the current construction process of the mine method tunnel, only the rock mass excavation is added, and the implementation space range of this process can be from the tunnel excavation face to the end of the secondary lining. The position is flexible, and the impact on the on-site construction process is small, which can ensure the tunnel excavation progress. At the same time, using the rock mass excavation holes as bolt installation holes and grouting holes reduces the investment in repeated projects and reflects the green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] This specification includes the following seven drawings:

[0028] Figure 1 It is a schematic cross-sectional view of the zoned surrounding rock of the tunnel during the surface support of the tunnel section

[0029] Figure 2 It is a schematic cross-sectional view of the zoned surrounding rock of the tunnel when the surface support forms a ring

[0030] Figure 3 It is a schematic cross-sectional view of the zoned surrounding rock and the structural system of the tunnel after the tunnel construction is completed

[0031] Figure 4 It is a partial schematic cross-sectional view of the structural system of the tunnel after the tunnel construction is completed

[0032] Figure 5 It is a partial schematic longitudinal section of the structural system of the tunnel after the tunnel construction is completed

[0033] Figure 6 It is a partial schematic view of the surface layout of the structural system of the tunnel after the tunnel construction is completed

[0034] Figure 7 It is a cross-sectional view of the installation position of the anchor rod or cable

[0035] The figure shows the meanings of the markings: the active rock stripping area 10, the tunnel surrounding rock reinforcement area 20, the deep surrounding rock bearing area 30, the rock excavation holes 40, the anchor injection system 50, the anchor rods 51, the cables 52, the installation holes 53, the grouting holes 54, the surface support 60, the shotcrete layer 61, the steel skeleton 62, the steel sleeve 70, the waterproof and drainage system 80, and the secondary lining 90. Detailed implementation manners

[0036] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0037] Refer to Figures 1 to 3 , A large deformation control system for tunnels in high in-situ stress soft rock strata of the present invention is characterized in that: it includes an active rock stripping area 10, a surface support 60, and an anchor injection system 50, the surface support 60 is constructed on the tunnel wall; the active rock stripping area 10 is located between the surface support 60 and the deep surrounding rock bearing area 30, and a certain amount of rock expansion volume in the active rock stripping area 10 is dynamically and actively eliminated by arranging rock excavation holes 40 longitudinally or radially along the tunnel in this area; the anchor injection system 50 is constructed in the active rock stripping area 10, and it is reinforced and transformed into the tunnel surrounding rock reinforcement area 20, and jointly controls the formation of the deep surrounding rock bearing area 30 with the surface support 60.

[0038] First, the basic phenomena of tunnel excavation in high in-situ stress soft rock strata are explained. After the tunnel excavation in high in-situ stress soft rock strata, without the action of a support structure, the tunnel will surely collapse. However, the collapse generally does not affect an infinitely long distance, and the strata outside the collapse influence range remain undisturbed. Due to the reduction of the rock mass volume caused by tunnel excavation, the rock mass within the collapse influence range becomes loose, while the undisturbed strata remain in their original state. Therefore, there must be a deep surrounding rock bearing area 30 between the loose rock mass and the undisturbed strata, and it has reached a stable stress state. Its function is to support the load of the external original state strata even after the internal rock mass becomes loose.

[0039] Theoretically, in high in-situ stress soft rock strata, the closer the position of the deep surrounding rock bearing area 30 is to the excavation wall, the better the control of strata deformation. However, a high-strength and large-rigidity surface support 60 is required to support the stress stability of the deep surrounding rock bearing area 30, which is costly and has poor economy. In addition, with the current material technology and construction level, it is difficult to form a surface support 60 that matches the high in-situ stress level in the original unexcavated state. This is bound to break the stress balance of the strata, resulting in the dilation deformation of the rock mass under high in-situ stress and squeezing towards the weak part, namely the surface support 60, causing the deformation and failure of the surface support 60.

[0040] Therefore, the present invention provides a large deformation control system for tunnels in high in-situ stress soft rock strata. A rock mass active stripping area 10 is arranged along the tunnel perimeter. On the condition of maintaining small deformation of the primary support, after dynamically and actively eliminating a certain amount of rock mass dilation volume within the rock mass active stripping area 10, an anchor injection system 50 is constructed to form a tunnel perimeter reinforcement 20 area, which jointly controls the formation of the deep surrounding rock bearing area 3 with the surface support 60. The rock mass active stripping area 10 is located between the surface support 60 and the deep surrounding rock bearing area 30. After the surface support 60 is formed into a ring, it is reinforced by the anchor injection system 50, and the loose rock mass within the rock mass active stripping area 10 is improved and transformed into the tunnel perimeter reinforcement area 20.

[0041] The rock mass active stripping area 10 consists of rock mass excavation holes 40. The hole layout form can be arranged longitudinally or radially along the tunnel. Limited by the current equipment technology and construction level, the hole positions are preferably arranged radially.

[0042] In the rock mass active stripping area 10, active soil cutting equipment and technologies such as small screw drills and small high-pressure cutting machines can be used to actively strip the rock mass whose volume has dilated within the rock mass active stripping area 10, so as to reduce the deformation load of the rock mass on the surface support and control the surface support 60 from undergoing large deformation.

[0043] Set the active rock mass stripping area 10 by means of the rock mass excavation holes 40. It should not be too long to avoid affecting the stress stability of the deep bearing area 30 of the surrounding rock. According to on-site test experiments, the deep bearing area 30 of the surrounding rock is generally at a position of 5 - 8 m. To achieve better results, the rock mass elimination range of the active rock mass stripping area 10 is set to be no more than 2.5 m from the tunnel wall. The allowable value V of the expanded volume of the eliminated rock mass 消 is calculated according to the following formula:

[0044] V 消 = 6.28×R×(0.5 - S)+0.79×n×L×D 2

[0045] In the formula, n is the number of rock mass excavation holes set in the cross-section per meter of the tunnel extension, and it should not be more than 10 holes; D is the diameter of the rock mass excavation hole 40, unit: m; L is the length of the rock mass excavation hole 40. When arranged radially, L ≤ 2.5 m; S is the allowable unilateral convergence deformation of the tunnel, unit: m; R is the equivalent radius of the tunnel clearance, unit: m.

[0046] The expanded volume of the eliminated rock mass mainly includes the volume of the rock and soil mass due to the construction of the rock mass excavation holes and the volume eliminated due to the active stripping of the rock and soil mass. The calculation formula for the former is n×single-hole volume = n×1 / 4×π×L×D 2 = 0.79×n×L×D 2 ; for the volume eliminated due to the active stripping of the rock and soil mass, it is necessary to determine the deformation amount when the "surrounding rock - support" system reaches stability under different stratum lithologies and in-situ stress levels. According to a large amount of tunnel large deformation research data at present, the final deformation in the large deformation section of the tunnel under conventional support measures is basically 30 - 50 cm. After reconstructing the support, the large deformation can basically be controlled. Therefore, the unilateral convergence deformation of the tunnel is taken as 50 cm as the limit value when the support structure reaches stability, and considering the allowable unilateral convergence deformation of the tunnel, the volume eliminated due to the active stripping of the rock and soil mass is calculated as: π[(R + 0.5 - S) 2 -(R) 2 = π[2R(0.5 - S)+(0.5 - S) 2 ≈6.28×R×(0.5 - S). In the formula, π(0.5 - S) 2 The maximum value is 0.79 m 3 and is a small value compared to 6.28×R×(0.5 - S), so it is omitted.

[0047] In the active rock mass stripping area 10, the stripping of the rock mass should not be unrestricted. When the surface support 60 is formed into a ring and can fully exert its bearing capacity, the outward expansion of the deep bearing area 30 of the surrounding rock should be controlled as soon as possible. At this time, with the help of the anchor grouting system 50, the loose rock mass in the active rock mass stripping area 10 is reinforced and improved to provide the bearing force for the deep bearing area 30 of the surrounding rock. The depth of the anchor bolt 51 is within the deep bearing area 30 of the surrounding rock, and the depth of the cable bolt 52 is outside the deep bearing area 30 of the surrounding rock.

[0048] Refer to Figures 4 to 7 The anchor grouting system 50 is jointly formed by the anchor bolt 51, the cable bolt 52 and the surrounding rock grouting. The layout spacing of the anchor bolt 51 or the cable bolt 52 is arranged in a plum blossom shape at 1.0 m × 1.0 m. The installation holes 53 and grouting holes 54 of the anchor bolt or the cable bolt both utilize the rock mass excavation holes 40. The outer ends of the anchor bolt 51 and the cable bolt 52 are anchored and connected to the surface support 60. The main body of the anchor bolt 51 is located within the tunnel peripheral reinforcement area 20, and the rear part of the cable bolt 52 passes through the deep bearing area 30 of the surrounding rock. The surrounding rock grouting is to grout and reinforce the rock mass from the deep bearing area 30 of the surrounding rock to the excavation range through the grouting holes 54.

[0049] Refer to Figures 4 to 7 The surface support 60 is composed of a shotcrete layer 61 and a steel skeleton 62 in combination. To restrain the deformation of the shotcrete 61 under the triaxial stress state and further improve the bearing capacity of the shotcrete layer 61, steel sleeves 70 are arranged at the corresponding positions of the anchor bolt 51 and the cable bolt 52 on the surface support 60, and the outer ends of the anchor bolt 51 and the cable bolt 52 are anchored on the steel sleeves 70.

[0050] Refer to Figures 1 to 7 The construction method of a large deformation control system for a tunnel in a high in-situ stress soft rock formation according to the present invention includes the following steps:

[0051] S01. After the tunnel excavation and mucking, the surface support 60 of the excavation section is constructed in a timely manner;

[0052] S02. Rock mass excavation holes 40 are evenly arranged and drilled along the surface support 60, and the excavated rock mass volume is V ki ;

[0053] S03. The deformation of the surface support 60 is monitored and measured. If the deformation rate exceeds 1 cm / d, the rock mass within the active rock mass stripping area 10 is extracted through the rock mass excavation holes 40 by using an active soil cutting device, and additional rock mass excavation holes 40 are added to the part with large deformation of the surface support 60 and the rock mass of this part is actively stripped. The total excavated rock mass volume this time is counted as V ti At the current time point, the cumulative volume V 消 ’ of the stripped rock mass in the active rock mass stripping area 10 = ΣV ki + ΣV ti ;

[0054] S04. Repeat the above steps until the surface support 60 forms a ring. At this time, ensure that V 消 ’ / V 消 ≤0.75;

[0055] S05. For the rock mass where the rock bolts 51, cable bolts 52 need to be installed and the surrounding rock needs to be grouted, redrill the rock removal holes 40 to the design depth to form the rock bolt or cable bolt installation holes 53 and grouting holes 54. After installing the steel sleeves 7 on the surface support 60, install the rock bolts 51 and cable bolts 52, and grout and reinforce the rock mass in the deep bearing area 30 of the surrounding rock to the rock mass within the excavation range through the grouting holes 54;

[0056] S06. When the deformation rate of the surface support 60 is less than 1 mm / d, construct the waterproof and drainage system 80 and pour the secondary lining 90.

[0057] If V 消 ’ / V 消 >0.5 before the surface support 60 forms a ring, accelerate the construction process of the surface support 60 forming a ring to avoid the deep bearing area 30 of the surrounding rock expanding too far outwards, which will deteriorate the stress stability of the surface support 60 and increase the construction difficulty of the anchor grouting system 50.

[0058] By setting the active rock mass stripping area, the present invention actively and restrictedly eliminates the inevitable volume expansion of the surrounding rock after being squeezed by high in-situ stress, releases the internal pressure of the surrounding rock, and gives full play to the self-bearing capacity of the surrounding rock, which can effectively solve the large deformation problem of tunnels in high in-situ stress soft rock strata. Compared with the traditional stress release method, through the dynamically adjustable volume of the rock mass removal, on the one hand, it greatly reduces the engineering quantity of raw materials required to improve the strength of the support structure system; on the other hand, it effectively controls the amount of waste slag from the early removal of a large amount of rock mass and the amount of masonry backfill increased for the secondary lining to reach the design contour. Compared with the current construction process of the mine method tunnel, only the rock mass removal is increased, and the implementation space range of this process can be from the tunnel excavation face to the end of the secondary lining, with a flexible position and little impact on the on-site construction process, which can ensure the tunnel excavation progress. At the same time, using the rock removal holes as the rock bolt installation holes and grouting holes reduces the investment in repeated projects and reflects the green environmental protection.

[0059] Generally speaking, while effectively solving the large deformation of tunnels in high in-situ stress soft rock strata, the present invention reasonably controls the project cost of large deformation tunnels, effectively saves project investment, is convenient for construction, and meets the "dual carbon" goal.

[0060] The above is only to illustrate some principles of a large deformation control system and construction method for tunnels in high in-situ stress soft rock strata of the present invention by means of diagrams, and it is not intended to limit the present invention to the specific structures and application scopes shown and described. Therefore, all possible corresponding modifications and equivalents that can be utilized belong to the scope of the patent applied for by the present invention.

Claims

1. A large deformation control system for tunnels in soft rock formations with high ground stress. Its characteristics are: The invention comprises a rock mass active stripping zone (10), a surface support (60) and an anchoring and grouting system (50), wherein the surface support (60) is applied on the tunnel wall; the rock mass active stripping zone (10) is located between the surface support (60) and the surrounding rock deep bearing zone (30), and rock mass excavation holes (40) are arranged in the tunnel longitudinally or radially in the zone to dynamically and actively eliminate a certain amount of rock mass expansion volume in the rock mass active stripping zone (10); the anchoring and grouting system (50) is applied in the rock mass active stripping zone (10), and the rock mass reinforcement is converted into a tunnel periphery reinforcement zone (20), and the anchoring and grouting system (50) is combined with the surface support (60) to control the formation of the surrounding rock deep bearing zone (30); The rock mass excavation holes (40) are constructed by using active soil cutting equipment such as small spiral drill rigs or small high-pressure cutting machines. The range of the eliminated rock mass is not more than 2.5 m from the tunnel wall, and the allowable value V of the expanded volume of the eliminated rock mass 消 is calculated according to the following formula: V 消 = 6.28 × R × (0.5 - S) + 0.79 × n × L × D 2 Where n is the number of rock removal holes set per meter of tunnel cross section, which should not be more than 10 holes; D is the diameter of the rock removal hole (40), unit: m; L is the length of the rock removal hole (40), and when it is radially arranged, L≤2.5m; S is the allowable unilateral convergence deformation of the tunnel, unit: m; R is the tunnel clearance equivalent radius, unit: m.

2. A large deformation control system for a tunnel in a high ground stress soft rock formation as claimed in claim 1, Its characteristics are: The anchoring system (50) is formed by the combination of an anchor rod (51), an anchor cable (52) and surrounding rock grouting. The anchor rod or anchor cable installation hole (53) and the grouting hole (54) are both made from a hole (40) excavated from the rock mass. The outer ends of the anchor rod (51) and the anchor cable (52) are anchored and connected to the surface support (60). The main body of the anchor rod (51) is located in the tunnel periphery reinforcement area (20), and the rear part of the anchor cable (52) passes through the surrounding rock deep bearing area (30). The surrounding rock grouting is to grout and reinforce the rock mass from the surrounding rock deep bearing area (30) to the excavation range through the grouting hole (54).

3. A large deformation control system for a tunnel in a high ground stress soft rock formation as claimed in claim 2, Its characteristics are: The surface support (60) is composed of a sprayed concrete layer (61) and a steel frame (62). The surface support (60) is provided with a steel sleeve (70) at the position corresponding to the anchor rod (51) and the anchor cable (52). The outer ends of the anchor rod (51) and the anchor cable (52) are anchored on the steel sleeve (70).

4. A construction method for a large deformation control system for a tunnel in a high ground stress soft rock formation according to any one of claims 1 to 3, comprising the following steps: S01. After tunnel excavation and slag removal, timely implementation of surface support for the excavated section (60); S02. Uniformly arrange and drill rock mass excavation holes (40) along the surface support (60), and the excavated volume of the rock mass is V ki ; S03. Monitor and measure the deformation of the surface support (60). If the deformation rate exceeds 1 cm / d, use active soil-cutting equipment to extract the rock mass within the active rock mass stripping area (10) through the rock mass excavation holes (40). Add rock mass excavation holes (40) to the parts with large deformation of the surface support (60) and actively strip the rock mass of this part. The total volume of rock mass excavated this time is recorded as V ti , and the cumulative volume V 消 ’ of the stripped rock mass in the active rock mass stripping area (10) at the current time point is ΣV ki + ΣV ti ; S04. Repeat the above steps until the surface support (60) forms a ring. At this time, ensure that V 消 ’ / V 消 ≤0.75; S05. The rock mass excavation hole (40) where the anchor rod (51), anchor cable (52) and surrounding rock grouting are required is drilled again to the designed depth to form the anchor rod or anchor cable installation hole (53) and the grouting hole (54), and after the steel sleeve (70) is installed on the surface support (60), the anchor rod (51), anchor cable (52) and the grouting hole (54) are installed, the rock mass from the deep bearing area (30) of the surrounding rock to the excavation range is grout-reinforced; S06. When the deformation rate of the surface support (60) is less than 1 mm / d, the drainage system (80) is constructed and the secondary lining (90) is poured.

5. The construction method of a large deformation control system for tunnels in high in-situ stress soft rock strata as described in claim 4, characterized in that: at If V before the surface support (60) is not formed into a loop 消 ’ / V 消 > 0.5, the construction process of forming the loop of the surface support (60) shall be accelerated to avoid the deep bearing area (30) of the surrounding rock from expanding too far outwards, deteriorating the stress stability of the surface support (60) and increasing the construction difficulty of the grouting and anchoring system (50).

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