High-crustal-stress phyllite sand-included slate interaction stratum tunnel water inrush prevention construction method

Abstract

The invention belongs to the technical field of tunnel construction and underground engineering, and particularly relates to a high-ground-stress phyllite and sand slate interaction stratum tunnel water inrush prevention construction method which comprises the following steps that S1, a tunnel face is excavated in an upper step of a tunnel, a drainage hole is drilled, and a drainage steel pipe is buried for pressure relief; s2, a steel pipe is constructed to compact the weak rock mass, and the connecting tension of the net spraying concrete is increased; s3, constructing a self-drilling pipe shed at the arch part, and grouting to form a forepoling system; s4, core soil is reserved for mechanical excavation, and a crushing head is adopted for auxiliary excavation; s5, an upper step temporary inverted arch is constructed in time after excavation, reinforcing locking feet are constructed on arch feet on the two sides and side walls, and grouting is conducted; s6, the left side and the right side of the lower step are staggered and asymmetrically excavated and supported, and the excavation circulation footage is not larger than 2 m; and finally, the inverted arch is formed through one-time excavation, and the excavation circulation footage is not larger than 3 m. The pressure of large rheological deformation formed by water inrush is reduced, large rheological deformation of the soft rock non-uniform interaction stratum is controlled, and the construction efficiency and progress are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction and underground engineering, and in particular to a construction method for preventing sudden water inrush in a tunnel in a high-stress phyllite-sandstone alternating stratum. Background Art

[0002] According to the national standard for geotechnical engineering investigation, high geostress refers to the phenomenon of rock or structure damage caused by stress concentration. The stress concentration coefficient is generally between 2 and 3, that is, the surrounding rock strength stress ratio at which high geostress occurs should be between 2 and 3. Moreover, strata with high geostress show significant stress during the exploration period, and the high geostress phenomenon tends to intensify as the construction period progresses. High geostress can lead to large convergence and deformation of the surrounding rock, extrusion of weak interlayers, water seepage, and other problems. In extreme cases, there will be rock bursts and peeling of the surrounding rock.

[0003] The geotechnical engineering investigation specification stipulates that the definition of geostress is mainly the magnitude of the geostress measurement value. For example, if the first principal stress is greater than 20MPa, it is high geostress, and if it is greater than 30MPa or 40MPa, it is extremely high geostress. The technical regulations for engineering geological investigation of underground buildings in hydropower and water conservancy projects stipulate that the initial geostress classification scheme is: the geostress classification scheme based on the strength-stress ratio, formula (1): δ1 = UCS 饱和 / σ s1 ;Formula (2): δ2=UCS 饱和 / σ1. δ1=20~40MPa, δ2=2~4 is high ground stress, δ1≥40, δ2<2 is extremely high ground stress.

[0004] With the continuous advancement of the western development, a large number of transportation projects such as the Sichuan-Tibet Railway and the Sichuan-Tibet Highway have been started. A large number of tunnel projects need to be built, which inevitably cross high mountain canyons and active faults such as the Longmen Mountain and Xianshui River. They face major engineering and technical problems such as large deformation of soft rocks under high ground stress and large deformation control of soft and hard alternating strata, which seriously restrict the construction of transportation projects in western Sichuan.

[0005] The existing tunnels in high-in-situ stress phyllite-sandstone alternating strata are very difficult to control deformation due to sudden water inrush. Usually, the three-step seven-step method after advanced curtain grouting is used for excavation and construction. It is difficult to control the deformation problem of sudden water inrush in tunnels in high-in-situ stress phyllite-sandstone alternating strata. The construction progress is about 20m per month, which seriously restricts the construction. Therefore, the deformation of high-in-situ stress soft rock tunnels in plateau areas is a serious obstacle to tunnel construction. Although there are many existing technologies for tunnel water inrush control, they lack pertinence for the special scenarios of high-in-situ stress soft rock tunnels.

[0006] For example, the Chinese invention patent application with the publication number CN115045688A discloses a method for treating sudden water inrush in a high-buried deep tunnel by blocking first and draining later. Two rows of grouting holes are arranged in front of the face and on the side. The grouting holes are divided into grouting sections and non-grouting sections. The non-grouting sections are drilled to the top of the grouting sections, and casing is lowered into the non-grouting sections. After all the casings are lowered, they are fixed and cast with thick slurry. The grouting sections are drilled and grouted in sections from top to bottom. 14 days after the grouting and water blocking construction is completed, the drainage construction in the tunnel begins. The branch tunnel uses a submersible pump to alternately move forward for drainage, and the main tunnel uses a centrifugal pump to drain water through a fixed pump station.

[0007] This patented method uses a method of blocking water, pressurizing water, and fully draining water. However, soft rock tunnels with high ground stress phyllite and sandstone are very prone to rock slippage. After the grouting holes are injected with slurry to increase the pressure, the soft rock strata are more prone to serious slippage accidents, so it is not applicable.

[0008] Another example is the Chinese invention patent application with publication number CN116181369A, which discloses a method for quickly and safely implementing grouting reinforcement for face collapse in a hard rock, broken and water-rich tunnel section. The method mainly includes the steps of backfilling with counter pressure, pouring a grouting stop wall, diversion and decompression, grouting and later operation and maintenance delivery. Backfilling with counter pressure is carried out on the virtual slag in the collapse area, and pre-buried grouting pipes and drainage pipes are poured with concrete or shotcrete grouting stop walls. 4-5 rings of holes are drilled on the top and waist of the arch with a ring spacing of 1.5 meters and a hole spacing of 30-50 centimeters. Grouting is circulated in the holes to ensure that the grouting is dense and a reinforcement ring is formed to ensure that the surrounding rock is solid and meet the safety of later excavation.

[0009] This patented method aims at the treatment of landslides at the face of a broken and water-rich tunnel section, and mainly achieves the reinforcement effect by solidifying the water-rich layer through circulating grouting. However, for soft rock tunnels with high geostress phyllite and sandstone, the internal stability is poor, and there may be groundwater systems in the phyllite interlayers. Circulating grouting often fails to achieve a sufficient reinforcement effect, and the grouting pressure may further aggravate the stratum stress and cause structural instability. Therefore, the above patented method is not applicable to high geostress phyllite and sandstone interlayers. Summary of the invention

[0010] The purpose of the present invention is to provide a construction method for preventing sudden water inrush in tunnels in high-in-situ stress phyllite-sandstone-interlaced strata, aiming at the problem of excessive deformation control of sudden water inrush in tunnels in high-in-situ stress phyllite-sandstone-interlaced strata. According to the stratum structural characteristics of high-in-situ stress phyllite-sandstone-interlaced strata, a targeted treatment method is adopted to solve the interlayer ground stress, fully relieve pressure, stably complete tunnel excavation construction, and avoid sliding and collapse accidents of weak phyllite in the interlayer.

[0011] The method of the present invention can effectively control the deformation problem of sudden water inrush in tunnels in high-stress phyllite-sandstone alternating strata, reduce the delay in project progress caused by sudden water inrush accidents, greatly speed up construction speed, and save construction costs.

[0012] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0013] A method for preventing sudden water inrush from tunnels in high-stress phyllite-sandstone alternating strata, comprising the following steps:

[0014] S1. Drilling pressure relief: Drill drainage holes in the middle and lower part of the tunnel face in the upper step excavation of the tunnel, and bury drainage steel pipes for pressure relief; the hard rock part is the sandstone in the alternating strata of phyllite and sandstone;

[0015] S2, face reinforcement: the first steel pipe is installed on the face to compact the soft rock mass, and mesh shotcrete reinforcement is constructed on the face; the first steel pipe is installed in the soft rock part of phyllite;

[0016] S3. Construction of advance support for the arch: self-advanced pipe shed is used to construct a self-drilling pipe shed in the tunnel arch, and grouting is used to form an advance support system. The longitudinal overlap length of each cycle shall not be less than 4m;

[0017] S4, upper step construction: The core soil is mechanically excavated at the phyllite part of the tunnel face, and the sandstone part is excavated with the assistance of a crusher; the core soil area is not less than 55% of the upper step excavation area, and the upper step excavation height is controlled within 7.5m;

[0018] Construction of temporary invert: After the upper step is excavated, a temporary invert is constructed for the upper step; then, reinforced locking feet are constructed and grouting is performed on the arch feet and side walls on both sides of the tunnel.

[0019] Construction of lower steps and invert arches: staggered asymmetric excavation supports are used on the left and right sides of the lower steps to control the excavation cycle advance of the lower steps to no more than 2m.

[0020] The invert is excavated once, and the excavation cycle advance is no more than 3m;

[0021] S5. Repeat the above S1-S4 until the construction of the tunnel in the high-stress phyllite-sandstone alternating strata is completed.

[0022] The tunnel anti-surge water construction method of the present invention is a control method for sudden water inrush in high-ground stress phyllite-sandstone-interchange strata, which can effectively solve the safe construction of tunnel sudden water inrush scenes in high-ground stress phyllite-sandstone-interchange strata and ensure the construction progress. First, according to the results of the study on the rheological characteristics of sudden water inrush in high-ground stress phyllite-sandstone-interchange strata, a drainage hole is drilled on the step of the heading face to reduce the sudden water pressure. Then, the heading face is sealed with the first steel pipe and steel mesh sprayed concrete, and the tunnel arch is constructed with a self-drilling pipe shed advance support system to improve the stability of the top stratum in front of the heading face. The two-step method is used for excavation construction, and the core soil of the upper step is retained at least 55%, and the core soil is used to maintain the pressure stability of the stratum to prevent the stratum from becoming unstable. After excavation, a temporary inverted arch of the upper step is constructed in time, and the arch feet and side wall parts on both sides of the tunnel are reinforced with locking feet and grouting, and the anchor locking feet of the arch feet and side wall parts on both sides of the upper step are used for grouting reinforcement to stabilize the rock stratum at the excavation side wall of the tunnel. Finally, the left and right sides of the lower step are staggered and excavated asymmetrically to support the arch, and the arch is formed in one go.

[0023] The tunnel water inrush prevention construction method of the present invention realizes water inrush control by dividing the water inrush from the high-stress phyllite-sandstone alternating strata into multiple blocks for treatment. On the one hand, drainage and pressure relief are carried out according to the characteristics of the phyllite-sandstone alternating strata to reduce the water inrush pressure, so that the phyllite and sandstone at the water inrush location can be restored to a closed state to prevent further development of water inrush. On the other hand, self-drilling pipe-roof advance support is adopted to improve the stability of the bottom layer in front of the tunnel face, and then it is divided into upper step excavation, left and right staggered asymmetric excavation support, and one-time excavation and forming of the invert arch. The amount of excavation each time is controlled within a small range, and coordinated with the advance pipe-roof support and the means of stabilizing the pressure of the core soil layer.

[0024] Therefore, the method of the present invention has achieved effective control of sudden water inrush in the high-stress phyllite-sandstone alternating strata through comprehensive measures in multiple aspects. Although there is no pumping treatment or cyclic grouting reinforcement treatment after blocking for 14 days, it combines the structural characteristics of the high-stress phyllite-sandstone alternating strata itself, and preliminarily stabilizes this complex structure by combining the pressure reduction through drilling drainage holes and advanced pipe-roof support. Then, during the excavation process, excavation is carried out in stages to avoid excessive disturbance, improve the safety of construction, and coordinate multiple factors to ensure safe and efficient construction.

[0025] Among them, mesh shotcrete is to arrange the steel mesh first, and then spray concrete on the surface of the steel mesh. Different from plain shotcrete (spraying concrete on the surface without steel mesh), it is generally high-strength cement slurry, or added with medium sand, coarse sand and crushed stone particles not larger than 15mm, which is convenient for spraying. Mesh shotcrete plays a role in wall protection on the face of the tunnel, preventing scouring and landslides, and ensuring the stability of the face structure during the drainage and pressure reduction of the drainage holes.

[0026] Furthermore, in S1, the rheological characteristics of sudden water in the high-stress phyllite-sandstone interbedded strata are first determined, and then drainage holes are drilled and drainage steel pipes are buried in the sandstone-slate hard rock area of ​​the tunnel face to reduce the pressure of the sudden water.

[0027] Preferably, the drain hole is For example, Weep holes. Drain hole.

[0028] The alternating strata of water-rich phyllite and sandstone are more likely to produce large rheological deformation under the action of water pressure. By reducing the water pressure through the drainage holes, the alternating strata of water-rich phyllite and sandstone can be restored to the stable state with less water content before the tunnel construction.

[0029] Furthermore, in S1, the number of drainage holes drilled is 1-4, and the length of each drainage hole is 8-20m.

[0030] Through multiple drainage holes, water is drained synchronously to better keep the formation water between the rock layers inside the face fully discharged, reduce the pressure of sudden water in front of the face, and ensure structural stability.

[0031] Further, in S2, a first steel pipe is used to compact the soft rock mass. The first steel pipe used is 5 to 15 m in length. Steel pipe.

[0032] Preferably, the first steel pipe is used to compact the soft rock mass, and the first steel pipe used is 8 to 12 meters in length. Steel pipe.

[0033] Preferably, the first steel pipes are arranged in the phyllite soft rock area, and the distance between adjacent first steel pipes is 1 to 2 m.

[0034] Further, in S2, the tunnel face is sealed with sprayed concrete, and the thickness of the concrete is 10-30 cm.

[0035] Preferably, the concrete thickness is 15-25 cm.

[0036] Preferably, C25 concrete is used for shotcrete.

[0037] Furthermore, in S2, when the tunnel face is still unstable after mesh spraying concrete reinforcement, a fine wire mesh is laid on the tunnel face with a wire diameter of 3 to 5 mm and a mesh spacing of 5 to 8 cm. C25 concrete is then sprayed to seal the tunnel face. The spraying thickness is determined according to the stability of the tunnel face and is 15 to 30 cm.

[0038] Furthermore, in S2, when the tunnel face was still unstable, the tunnel face was sealed by backfilling with ton bags and sprayed with concrete. Then, the second steel pipe was used to press in cement-water-glass double liquid slurry to backfill the voids formed by the lost phyllite.

[0039] Preferably, the backfill ton bags are sand bags, earth bags, etc. International standard ton bags are also called bulk bags / space bags / flexible containers / ton bags / ton bags / space bags / mother-child bags, which are flexible transport packaging containers. They have the advantages of being moisture-proof, dust-proof, radiation-resistant, firm and safe, and have sufficient structural strength. In tunnel construction, it is convenient to use the mining slag or small gravel or soil on site for rapid backfilling and plugging, reinforce the face, and avoid the chain reaction of face slip / collapse.

[0040] Preferably, a second steel pipe with a diameter of 30-80 mm is used to press cement slurry or cement-water-glass double-liquid slurry to backfill the voids formed by the lost phyllite.

[0041] Furthermore, in S3, the self-propelled pipe shed adopts T76 self-propelled pipe shed, and the length of the pipe shed is 12 to 20 meters. The longitudinal overlap length of the self-propelled pipe shed in each cycle is not less than 4 meters, which means that the tunnel construction adopts cyclic operation, and the support structure formed by the previous T76 self-propelled pipe shed and the support structure formed by the next T76 self-propelled pipe shed overlap at least 4 meters in the tunnel extension direction.

[0042] The surrounding rock of the alternating phyllite and sandstone strata is relatively broken. Under the high ground stress, it is difficult to drill holes for advance support. A self-propelled pipe shed is used to form an advance support system after grouting, and a scaffolding is formed in the arch to create conditions for tunnel excavation. This provides for the instability problem that may occur in the early stage of mechanical crushing and excavation disturbance on the upper step. Because there is a cyclic overlap support of the pipe shed, the stability of a small amount of crushing and excavation on the upper step is better.

[0043] Furthermore, in S4, the core soil length of the face is no more than 4m. This is to facilitate the timely closure of the temporary invert and the initial support into a ring. The longitudinal length is no more than 4m. The stability of the phyllite-sandstone structure is poor. The core soil of the face provides pressure balance. Considering the stability of the pipe-roof support, the longitudinal length should not exceed 4m.

[0044] Furthermore, in S5, the temporary invert of the upper step is cast with C20 concrete.

[0045] Furthermore, in S5, the reinforcing locking feet are formed by using T76 self-advancing anchor pipes, and 2-5 rows of reinforcing locking feet are applied and grouting is performed.

[0046] Preferably, the locking foot length L = 4-7 m. Preferably, the locking foot length L = 5.5 m.

[0047] Preferably, the locking foot anchor rod adopts a T76 self-propelled anchor pipe with a length of 5m and grouting, with a row spacing of 50cm.

[0048] Preferably, the holes of the bottom locking foot anchor rods are angled downward by 45°, and the holes of the upper row of locking foot anchor rods are angled downward by 18°.

[0049] Furthermore, in S5, the locking foot anchor rod adopts a 5m long T76 self-drilling anchor pipe and is grouted.

[0050] Furthermore, in S6, the left and right sides of the lower step are staggered by 4m for asymmetrical excavation support.

[0051] Furthermore, in S6, the left and right sides of the lower step are staggered with asymmetric excavation supports, and the advance of each excavation cycle on both sides is not more than 2m.

[0052] Furthermore, in S6, the distance between the initial support of the invert and the closed ring and the tunnel face was controlled within 28m.

[0053] Furthermore, in S6, the invert is excavated once, the excavation cycle advance is no more than 3m, and the distance from the initial support ring of the invert to the tunnel face is controlled within 28m.

[0054] The present invention adopts the above technical solution to achieve the following technical effects:

[0055] 1. The tunnel sudden water control method of the present invention adopts drainage holes to reduce water pressure and reduce the large deformation pressure of sudden water flow, adopts self-propelled pipe shed to improve the efficiency and quality of advanced support construction, and the auxiliary reinforcement of the heading face and the temporary invert create the initial support and timely closure ring conditions for the step method excavation. The large locking feet of the side wall suppress the continuous large deformation of high ground stress, water-rich, soft and hard uneven alternating strata, and the two-step method excavation improves the construction progress.

[0056] 2. The method for controlling sudden water inrush in the tunnel of the present invention uses a variety of means and seven levels of progressive steps to carry out tunnel construction of high-stress phyllite-interbedded sandstone through pressure relief in drilling holes + local grouting of the face, steel pipes, mesh sprayed concrete sealing + advance self-advanced pipe shed for the arch + mechanical excavation of reserved core soil on the upper step + temporary steel invert + side walls and large locking feet for the arch feet, effectively preventing and controlling sudden water inrush in the tunnel under such geological conditions, controlling large deformation of soft rock uneven alternating strata rheological type, improving tunnel construction efficiency, accelerating construction progress, and effectively ensuring that the construction period is completed on time. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 The invention discloses a construction process flow chart of the tunnel sudden water inrush control method.

[0058] Figure 2 It is a cross-sectional diagram of sudden water inrush in a tunnel in high-stress phyllite-sandstone alternating strata.

[0059] Figure 3 It is a longitudinal section diagram of the construction method for preventing sudden water inrush in tunnels in high-stress phyllite-sandstone alternating strata.

[0060] Figure 4 This is a sketch of the phyllite and slate surfaces detected by geological drilling in the ZGS tunnel.

[0061] Figure 5 It is the displacement cloud diagram in the z direction.

[0062] Figure 6 It is the displacement cloud diagram in the x direction.

[0063] Figure 7 This is the displacement cloud diagram of the tunnel face using the three-step method.

[0064] Figure 8 It is the displacement cloud diagram of the tunnel face with three-step reserved core soil method.

[0065] Markings in the figure: 1-T76 large locking foot, 2-temporary invert arch on the upper step, 3-drainage hole, 4-face reinforcement steel bars, 5-T76 self-propelled pipe shed, 6-invert arch, 7-core soil. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0067] Unless otherwise specified, in the description of the specific embodiments of the present invention, the terms indicating the orientation or position relationship such as "up", "down", "left", "right", "center", "inside", "outside", etc. are all expressions based on the orientation or position relationship shown in the drawings, or are the orientation or position relationship when the invented product / equipment / device is usually used. These terms of orientation or position relationship are only for the convenience of describing the scheme of the present invention or simplifying the description in the specific embodiments, so as to facilitate the technicians to quickly understand the scheme, and do not indicate or imply that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific position relationship, and therefore cannot be understood as a limitation on the present invention.

[0068] In addition, if the terms "horizontal", "vertical", "overhanging", "parallel" and the like appear, it does not mean that the corresponding devices / components / elements are required to be absolutely horizontal or vertical or overhanging or parallel, but may be slightly tilted or have deviations. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but may be slightly tilted. Alternatively, it can be simplified to mean that the corresponding devices / components / elements are set in directions such as "horizontal", "vertical", "overhanging", "parallel", etc., and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably an error / deviation within ±8%, more preferably an error / deviation within ±6%, more preferably an error / deviation within ±5%, and more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its role in the scheme of the present invention.

[0069] In addition, the expressions “first”, “second”, “third”, etc., which appear in the terms, are merely used to distinguish the description of the same or similar components and should not be understood as emphasizing or implying the relative importance of specific components.

[0070] In addition, in the description of the embodiments of the present invention, "several", "plurality" and "a number" represent at least 2. It can be any number such as 2, 3, 4, 5, 6, 7, 8, 9, and even more than 9.

[0071] In addition, in the description of the technical solution of the present invention, unless otherwise clearly specified / defined / restricted, the terms "set", "install", "connect", "connected", "provided with", "laid", and "arranged" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection, and can be welding, riveting, bolting, threading, and other commonly used connection means in the field. This connection can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be the internal connection of two elements.

[0072] Example 1

[0073] The ZGS tunnel site is located at the northern end of the QL Mountains in the northeast of the CX Plateau. It is an eroded deep mountain canyon landform with transition from high mountains to plateaus. The ground elevation of the tunnel site is 3050m to 4623.8m. The terrain of the whole area is steep and the mountains are majestic. ZGS is the watershed between the SM River of the DDH water system and the LS River of the MJ River water system. The overall trend of the ridgeline is nearly north-south, and the peak elevation is mostly above 4200m above sea level, with a height difference of 1000m to 1600m. ZGS is a tectonic erosion mountain composed of shallow metamorphic rock systems in the middle and upper Triassic systems. The tunnel and the ridgeline are obliquely intersected at a large angle. The mountain is thick, the peaks are towering, the canyons are vertical, and the slopes are steep.

[0074] The exposed strata in the tunnel site are mainly the Quaternary Holocene (Q4), the Quaternary Upper Pleistocene glacial water accumulation layer (Q3 fgl ), Xinduqiao Formation of the Upper Triassic (T 3x ), the Upper Triassic Zhuwo Formation (T 3zh ) and the Zagunao Formation of the Middle Triassic (T 2z The Xinduqiao Formation of the Upper Triassic (T 3x ), for example, the lithology is dark gray to black gray carbonaceous phyllite, carbonaceous phyllite, silty phyllite or slate, phyllite-like sericite slate with gray, dark gray thin to medium layers, a few thick layers of metamorphic fine sandstone, siltstone and tuffaceous sandstone, and local gray thin layers of sandy crystalline limestone. The thickness is greater than 509-784 meters. Phyllite: gray to dark gray, the main mineral components are sericite and quartz, followed by feldspar, a small amount of chlorite, scaly metamorphic structure, phyllite structure. The composition is uneven, and the sericite phyllite and carbonaceous phyllite are formed under the influence of mineral composition. Carbonaceous phyllite: gray to dark gray, the main mineral components are sericite and quartz, followed by feldspar, a small amount of chlorite and some carbonaceous, scaly metamorphic structure, phyllite structure. The composition is uneven, and the sericite phyllite and carbonaceous phyllite are formed under the influence of mineral composition. The structure is uneven, with interlayers of slate and sandstone. The slate and sandstone are both thin-layered and the rock is relatively hard. The thickness ratio of phyllite to slate sandstone is 7:1 to 10:1.

[0075] The ZGS tunnel site area on the north side of the structure is dominated by tight linear arc folds, large and medium-sized fault structures are not developed, and there are folds and faults in the tunnel area, resulting in very complex tunnel geology. In addition, the tunnel has high ground stress rock bursts and large deformations, and the weak rock burst section is expected to be 600m long.

[0076] The advanced geological drilling analysis of the geological adjustment of the ZGS tunnel revealed that the surrounding rock at the ZK18x+549 face of the tunnel is mainly composed of medium to thin layers of phyllite and slate, with metamorphic sandstone in some parts, poor interlayer bonding, thin slate layer thickness, easy to flak, carbonaceous phyllite and carbonaceous phyllite, which have hydrocarbon generation conditions. Due to the cutting effect of joints and fissures, the overall rock mass at the face has a fragmented structure to a mosaic structure. The overall layer thickness of the surrounding rock is thin, and it is strongly squeezed by the structure, with poor strength and poor self-stabilization ability. In particular, phyllite is easily softened when it comes into contact with water, which can easily cause structural instability of the face. Fissure water is generally developed, and there are several places where water seeps and drips on the face; the quality of the rock mass is poor, and the overall stability of the surrounding rock is poor. See the geological sketch of the advanced geological drilling face. Figure 4 shown.

[0077] Taking the three-step method of core soil excavation as an example, the model is established and simulated. First, it is assumed that the surrounding rock is a continuous, uniform, isotropic ideal material. The physical and mechanical parameters of the surrounding rock are determined according to the "Highway Tunnel Design Code".

[0078] The excavation and construction of ZGS Mountain Tunnel revealed that the surrounding rock is mainly composed of phyllite and slate, and this calculation is for Class V surrounding rock. The surrounding rock material parameters are selected according to the relevant chapters of the "Highway Tunnel Design Code".

[0079] Because the steel arch frame and shotcrete are combined into a whole to bear the surrounding rock pressure, according to the principle of material mechanics, the effect of the steel arch frame can be converted into a certain value of elastic modulus, which is added to the elastic modulus of shotcrete for equivalent consideration. The conversion formula is:

[0080]

[0081] Where: E h ' is the elastic modulus of the initial support after conversion, E h 0 is the elastic modulus of the shotcrete itself, A g is the cross-sectional area of ​​the shotcrete, E g is the elastic modulus of the steel arch, A h is the cross-sectional area of ​​the steel arch. The shotcrete is C20 with a thickness of 26 cm, and the steel arch is I20b with a spacing of 0.6 m. The initial support physical and mechanical parameters calculated using formula (1) are shown in the following table.

[0082] Surrounding rock and structural material parameters

[0083]

[0084] The construction sequence of the three-bench method construction model numerical simulation is as follows: ① excavation of the upper step ② initial support of the upper step arch ③ excavation of the left and right jumps of the middle step ④ initial support of the middle step ⑤ excavation of the left and right jumps of the lower step ⑥ initial support of the side wall of the lower step ⑦ excavation of the invert ⑧ initial support and filling of the invert ⑨ integral casting of the secondary lining. During the calculation process, the tunnel excavation distance is 50m, the invert is 20m away from the tunnel face, the step length is 2m, and the secondary lining is 30m away from the tunnel face.

[0085] The construction sequence of this model numerical simulation is as follows: ① circular excavation of the upper step; ② initial support of the upper step arch; ③ excavation of the core soil of the upper step; ④ left and right jump excavation of the middle step; ⑤ initial support of the middle step; ⑥ excavation of the core soil of the middle step; ⑦ left and right jump excavation of the lower step; ⑧ initial support of the side wall of the lower step; ⑨ excavation of the core soil of the lower step, base and initial support; ⑩ integral pouring of the secondary lining. During the calculation process, the tunnel excavation distance is 50m, the distance between the invert and the face is 20m, the step length is 2m, and the distance between the second lining and the face is 30m.

[0086] The surrounding rock displacement cloud diagram of the three-bench method and the three-bench reserved core soil method is as follows Figure 5 to Figure 6As shown in Figure 2, it can be seen that the maximum vertical (z-direction) displacement is concentrated at the top and bottom of the arch, the maximum horizontal (x-direction) displacement is concentrated near the waist of the arch, and the influence decreases with the increase of distance.

[0087] Monitoring point displacement data

[0088] construction method Vault settlement(mm) Arch bottom horizontal convergence value (mm) Bottom plate displacement value (mm) Three-step method 6.75 11.89 17.39 Reserve core soil method 5.74 10.56 5.7

[0089] The control of the horizontal convergence value of the arch bottom is not much different, and the three-step reserved core soil method is relatively small. The three-step reserved core soil method has obvious advantages in controlling the displacement of the tunnel floor, because the existence of the core soil can control the uplift of the floor.

[0090] like Figure 7 and Figure 8 As shown in the figure, the displacement cloud diagram of the extrusion (y direction) of the tunnel face by the three-step method and the three-step reserved core soil method. The maximum displacement in the y direction is concentrated near the tunnel face. The tunnel face displacement caused by the three-step method is 16.61mm, and the displacement of the three-step reserved core soil method is 9.92mm. Since the existence of the core soil in the three-step reserved core soil method has a restraining effect on the tunnel face, it controls the extrusion of the tunnel face to a certain extent. Therefore, compared with the three-step method, the three-step reserved core soil method has obvious advantages in controlling the extrusion of the tunnel face.

[0091] Analysis shows that for the influence of ground stress during the construction of tunnels with high ground stress phyllite and sandstone, the core soil retention method is preferred. Although the three-step method is divided into three steps, the core soil mainly solves the ground stress balance of the upper step. From the perspective of construction safety and speeding up construction, it is more appropriate to use two steps. In conjunction with the two-step construction, self-drilling pipe shed advance support is necessary. In addition, combined with the characteristics that the maximum horizontal displacement of tunnels with high ground stress phyllite and sandstone is concentrated near the arch waist, four rows of reinforced lock feet are applied and grouting is performed on the arch feet and side walls on both sides of the tunnel. It is also very important to reinforce the lock feet of the arch feet and side walls of the tunnel.

[0092] Based on the above analysis, it can be seen that the surrounding rock hydrogeology and deformation characteristics of the phyllite and slate alternating strata have poor stability and are difficult to construct. Leaving core soil in the surrounding rock is of great help to the stability of the structure. Therefore, for the tunnel construction with complex geological conditions, a tunnel construction method of high-stress phyllite intercalated with sand and slate is proposed.

[0093] like Figure 1 As shown, the main flow chart of the construction method of the sudden water tunnel in the high-stress phyllite-sandstone alternating strata is shown. The specific construction process includes the following steps.

[0094] First, the rheological characteristics of sudden water inrush in the high-stress phyllite-sandstone interbedded strata were studied, and the sandstone-slate hard rock part of the tunnel face was drilled. Drain holes are built and steel drainage pipes are buried to reduce the pressure of sudden water surges.

[0095] Then, a single 8m long steel bar was used at the face. The steel pipe is used as a drainage steel pipe, and then a steel mesh is set to spray concrete to seal the tunnel face. If the tunnel face is still unstable after the sprayed concrete is sealed, cement-water-glass double liquid slurry is pressed into the water-rich phyllite part to backfill and seal it, and the gaps formed by the lost phyllite are backfilled with cement-water-glass double liquid slurry.

[0096] After the cement-water-glass double slurry backfilling and plugging is completed, a single 12m-long T76 self-drilling pipe-roof advance support system is constructed in the tunnel arch, with a longitudinal overlap length of not less than 4m. If it is the latter stage of cyclic construction, pay attention to maintaining an overlap of not less than 4m between the T76 self-drilling pipe-roof advance support and the self-drilling pipe-roof advance support of the previous round of construction. When constructing the T76 self-drilling pipe-roof advance support, face the outside direction of the tunnel excavation extension direction so that the self-drilling pipe-roof advance supports of the two sections before and after can be arranged in an overlapping manner.

[0097] After the T76 self-drilling pipe shed advance support is completed, core soil is left in the phyllite part of the face and mechanical excavation is carried out. Among them, the sandstone part is excavated with a crusher to reduce the disturbance to the uneven soft rock strata. The length of the core soil is not more than 4m (the length along the extension direction of the tunnel, that is, the longitudinal direction), and the core soil area is not less than 55% of the excavation area of ​​the upper step. The core soil makes the stratum pressure inside the upper platform face more stable and less disturbed.

[0098] After the upper step is excavated, a temporary invert arch is constructed in time and C20 concrete is poured to form a preliminary invert arch to protect the structural stability.

[0099] Then, four rows of reinforced locking feet were constructed and grouted at the arch feet and side walls on both sides of the tunnel. The locking foot anchors used 5m long T76 self-drilling anchor pipes and were grouted with a row spacing of 50cm. The locking foot anchors were used to reinforce the side walls to improve the structural stability on both sides of the high-stress phyllite-sandstone alternating strata and prevent lateral sliding and collapse.

[0100] Finally, if Figure 3 As shown, the left and right sides of the lower step are staggered by 4m with asymmetrical excavation support, and the invert arch is excavated and formed in one step.

[0101] Repeat the above process steps and carry out tunnel excavation construction in a cycle until the construction of the tunnel in the high-stress phyllite-sandstone alternating stratum is completed. In this way, the tunnel can be safely passed through the high-stress phyllite-sandstone alternating stratum, avoiding tunnel collapse accidents caused by sudden water inrush that affect the construction progress.

[0102] Example 2

[0103] like Figures 1 to 3 The construction method for preventing sudden water inrush in a tunnel in the high-stress phyllite-sandstone alternating strata shown in the figure is carried out in the following steps.

[0104] (1) Drilling pressure relief in hard rock areas of phyllite and sandstone face

[0105] After preliminary investigation, it was found that the alternating strata of water-rich phyllite and sandstone are more likely to produce large rheological deformation under the action of water pressure. Drain hole and bury Drainage steel pipe, with 1 to 3 drainage holes and a single hole length of 8 to 20m, to reduce the pressure of sudden water inflow in front of the face.

[0106] Because in the alternating strata of phyllite and sandstone, sandstone is hard rock and phyllite is soft rock; phyllite (soft rock) is very slippery under the action of groundwater, and drilling holes in the hard rock strata to relieve pressure and reduce groundwater pressure is helpful to prevent phyllite collapse at the face. Conventional drainage holes are not drilled according to the hard and soft rock bodies. Drilling holes in soft rock is more likely to cause stratum structure instability, leading to local collapse / slippage, which in turn triggers a chain reaction and causes tunnel excavation structure safety accidents.

[0107] (2) Face reinforcement

[0108] The tunnel face in the water-rich stratum with alternating phyllite and sandstone is very prone to collapse. Phyllite is very easy to soften when it comes into contact with water. If it is not properly handled, the rapid collapse of phyllite fragments can easily cause collapse. The tunnel face reinforcement treatment is divided into the following four sub-stages.

[0109] ① Apply a single length of 8 to 12m on the face of the tunnel. The first steel pipe compacts the soft rock mass and increases the tension of the mesh shotcrete connection. The first steel pipe is set in the soft rock part of the phyllite with a spacing of 1 to 2 meters.

[0110] ② Spray concrete to seal the tunnel face. According to the tunnel face stability analysis and test results, determine the reasonable spray concrete thickness to seal the tunnel face. Usually, the thickness of spray concrete in water-rich strata with alternating phyllite and sandstone is 15cm to 25cm.

[0111] After the above two measures are basically completed, the tunnel face can be stabilized and the next stage of construction can be carried out. If the tunnel face is not stable, the following two stages of treatment will be carried out in sequence according to the situation until the tunnel face is completely reinforced.

[0112] ③ When the tunnel face is still unstable after taking the above two measures, a fine wire mesh (wire diameter 3-5mm, grid spacing 5-8cm) is laid on the tunnel face, and then C25 concrete is sprayed to seal the face. The spraying thickness is determined according to the stability of the face, usually 15-30cm.

[0113] ④ When the tunnel face is still unstable, the tunnel face is sealed by backfilling with ton bags (sand bags, earth bags, etc.). After sealing with shotcrete, the second steel pipe with a diameter of 50 mm constructed on the tunnel face is used to press in cement slurry and cement-water glass double liquid slurry to backfill the gaps formed by the lost phyllite.

[0114] Control measures are taken step by step for the stability of the tunnel face in the water-rich strata of the alternating phyllite and sandstone, and measures are taken in three situations. In the existing technology, there is a lack of comprehensive analysis of the tunnel face treatment method, and the treatment measures are not gradually adopted according to the structural characteristics of the tunnel face in the alternating phyllite and sandstone strata, which cannot achieve the lowest cost and high efficiency tunnel face reinforcement.

[0115] (3) Construction of the arch advance support system

[0116] The surrounding rock of the alternating phyllite and sandstone strata is relatively broken. Under the high ground stress, it is difficult to drill holes for advance support, so a self-propelled pipe shed is used. Therefore, a single T76 self-propelled pipe shed with a length of 12 to 20m is constructed in the tunnel arch, and an advance support system is formed after grouting. In the next cycle, the newly constructed T76 self-propelled pipe shed and the self-propelled pipe shed advance support of the previous cycle should maintain a certain longitudinal overlap. The longitudinal overlap length of each cycle is not less than 4.5m, and the arch forms a scaffolding to create conditions for tunnel excavation.

[0117] (4) Mechanical excavation of two steps + temporary invert

[0118] The core soil is mechanically excavated in the phyllite part of the tunnel face, and the crusher is used to assist the excavation in the sandstone and slate part to reduce the disturbance to the uneven soft rock strata. The length of the core soil left in the face is not more than 4m, so that the temporary invert and the initial support can be closed into a ring in time. The core soil area is not less than 55% of the upper step excavation area, and the upper step excavation height is controlled within 7.5m.

[0119] After excavation, the temporary inverted arch of the upper step was constructed in time and C20 concrete was poured. Then, 4 rows of T76 reinforced lock feet were constructed and grouting was carried out at the arch feet and side walls on both sides of the tunnel. The lock foot length L = 5.5m, and the lock foot anchor rods used 5m long T76 self-propelled anchor pipes and grouting, with a row spacing of 50cm, and the bottom 2 rows of holes were angled downward at 45°, and the upper 2 rows of holes were angled downward at 18°.

[0120] Then, carry out the excavation of the lower steps, such as Figure 3 As shown, the left and right sides of the lower step are staggered by 4m for asymmetrical excavation support, and the excavation cycle advance is no more than 2m.

[0121] The invert is constructed behind the lower bench excavation (behind the longitudinal direction, away from the tunnel face). The invert is excavated once, and the excavation cycle advance is no more than 3m. The distance from the tunnel face to the closed ring of the initial support of the invert is controlled within 28m.

[0122] In the prior art, it has not been found that the up-and-down step method is used to excavate and construct a large-section tunnel in the high-stress phyllite and sandstone alternating strata, mainly because the up-and-down step excavation construction has the risk of stratum pressure damage between the two steps. The method of the present invention adopts up-and-down step excavation construction, combined with self-propelled pipe shed advance support + face reinforcement, so that the stratum structure in front of the tunnel construction is stable, and then the two sides are reinforced and locked after excavation and grouting is performed to achieve the stability of the tunnel excavation structure in the high-stress phyllite and sandstone alternating strata.

[0123] This embodiment uses the above-mentioned two-step method in conjunction with the sealing and reinforcement construction method to realize the construction of the upper and lower step method in the high-stress phyllite-sandstone alternating strata, and then uses the upper and lower step method to assist large-scale mechanical equipment in performing advanced support and initial support, thereby improving construction efficiency and achieving faster excavation and initial support to form an overall closed loop.

[0124] Mechanical excavation is carried out, and crushing heads are used to assist in excavation in the sandstone and slate areas to reduce disturbance to the uneven soft rock interlaced strata. After excavation, a temporary invert arch is constructed on the upper step in a timely manner. The temporary invert arch on the upper step is used to enhance the structural stability of the tunnel and ensure the stability of the stratum sidewalls. Then, 4 rows of reinforced self-propelled anchor bolts are constructed and grouting is performed on the arch feet and side walls on both sides of the upper step, and the tunnel structure is reinforced from top to bottom. Finally, the left and right sides of the lower step are staggered by 4m for asymmetrical excavation and support, and the invert arch is excavated and formed at one time. The tunnel excavation is decomposed according to the longitudinal direction of the tunnel, which improves the safety of construction and overcomes the safe construction of the extreme working conditions of the high-stress phyllite-sandstone interlaced strata.

[0125] In summary, the above-mentioned method for preventing sudden water inrush in tunnels in high-in-situ stress phyllite-sandstone alternating strata is adopted. The drainage holes reduce the water pressure and reduce the pressure of sudden water to form large rheological deformation. The self-propelled pipe shed is adopted to improve the efficiency and quality of advance support construction. The auxiliary reinforcement measures of the heading face create favorable conditions for smooth excavation. The large locking feet of the side walls suppress the continuous large rheological deformation of high-in-situ stress and uneven soft and hard strata. The two-bench excavation method improves the construction progress.

Claims

1. A method for preventing sudden water inrush from tunnels in high-stress phyllite-sandstone alternating strata, characterized in that: The following steps are involved: S1. Drilling pressure relief: Drill drainage holes in the middle and lower part of the tunnel face in the upper step excavation of the tunnel, and bury drainage steel pipes for pressure relief; the hard rock part is the sandstone in the alternating strata of phyllite and sandstone; S2. Face reinforcement: construct a first steel pipe on the face and reinforce the face with mesh shotcrete; the first steel pipe is set in the soft rock part of phyllite; S3. Construction of advance support for the arch: self-advanced pipe shed is used to construct a self-drilling pipe shed in the tunnel arch, and grouting is used to form an advance support system. The longitudinal overlap length of each cycle shall not be less than 4m; S4, upper step construction: The core soil is mechanically excavated at the phyllite part of the tunnel face, and the sandstone part is excavated with the assistance of a crusher; the core soil area is not less than 55% of the upper step excavation area, and the upper step excavation height is controlled within 7.5m; Construction of temporary inverted arch: After the upper step is excavated, a temporary inverted arch is constructed for the upper step; then, reinforced locking feet are constructed and grouting is performed on the arch feet and side walls on both sides of the tunnel; Construction of lower steps and inverts: staggered asymmetric excavation support is carried out on the left and right sides of the lower steps, and the excavation cycle advance of the lower steps is controlled to be no more than 2m; The invert is excavated once, and the excavation cycle advance is no more than 3m; S5. Repeat the above S1-S4 until the construction of the tunnel in the high-stress phyllite-sandstone alternating strata is completed.

2. According to claim 1, a method for preventing sudden water inrush from tunnels in high-stress phyllite-sandstone alternating strata, characterized in that: In S1, the rheological characteristics of sudden water in the high-stress phyllite-sandstone interbedded strata are first determined, and then drainage holes are drilled and drainage steel pipes are buried in the sandstone-slate hard rock area of ​​the tunnel face to reduce the pressure of the sudden water; the drainage holes are φ60-150mm drainage holes.

3. According to claim 1, a method for preventing sudden water inrush from tunnels in high-stress phyllite-sandstone alternating strata, characterized in that: In S1, the number of drainage holes drilled is 1-4, and the length of each drainage hole is 8-20m.

4. According to claim 1, a method for preventing sudden water inrush from tunnels in high-stress phyllite-sandstone alternating strata, characterized in that: In S2, the first steel pipe is constructed to compact the soft rock mass. The first steel pipe used is a φ30-90mm steel pipe with a length of 5 to 15m.

5. The method for preventing sudden water inrush from tunnels in high-stress phyllite-sandstone alternating strata according to claim 1, characterized in that: In S2, the tunnel face is sealed with sprayed concrete, with a concrete thickness of 10-30 cm.

6. A method for preventing sudden water inrush from tunnels in high-in-situ stress phyllite-sandstone alternating strata according to claim 5, characterized in that: In S2, when the tunnel face is still unstable, a fine wire mesh is laid on the tunnel face with a wire diameter of 3 to 5 mm and a grid spacing of 5 to 8 cm. C25 concrete is then sprayed to seal the tunnel face. The spraying thickness is determined according to the stability of the tunnel face and is 15 to 30 cm.

7. A method for preventing sudden water inrush from tunnels in high-stress phyllite-sandstone alternating strata according to claim 6, characterized in that: In S2, when the tunnel face was still unstable, the tunnel face was sealed by backfilling with ton bags. After the face was sealed with shotcrete, a second steel pipe was used to press in cement-water-glass double liquid slurry to backfill the voids formed by the lost phyllite.

8. The method for preventing sudden water inrush from tunnels in high-stress phyllite-sandstone alternating strata according to claim 1, characterized in that: In S3, the self-propelled pipe rack adopts T76 self-propelled pipe rack with a length of 12 to 20 meters.

9. The method for preventing sudden water inrush from tunnels in high-in-situ stress phyllite-sandstone alternating strata according to claim 1, characterized in that: In S4, the length of core soil left at the tunnel face is not more than 4m.

10. The method for preventing sudden water inrush from tunnels in high-in-situ stress phyllite-sandstone alternating strata according to claim 1, characterized in that: In S5, the reinforcing lock feet are formed by using T76 self-advancing anchor pipes, and 2-5 rows of reinforcing lock feet are constructed and grouting is performed.

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