Construction method for shield to underpass heavy and extra-large risk source active underpinning stratum

Abstract

The invention relates to the technical field of tunnel construction, in particular to a construction method for a shield to underpass a heavy and extra-large risk source active underpinning stratum, which comprises the following steps: S1, analyzing and determining a construction scheme through software modeling; s2, selecting and designing a shield machine type and a duct piece; s3, in the tunneling process, a sulphoaluminate cement grouting technology is adopted for grouting; s4, in the tunneling process, a gap between the shield body and the soil body is filled with the anti-mud-effect advanced radial grouting technology; s5, during shutdown, soil body replacement is carried out by adopting a bentonite soil bin replacement shutdown pressure maintaining technology; and S6, grout supplementing measures are taken after tunneling is completed. According to the construction method, stress compensation of the front part, the middle part and the tail part of the shield tunneling machine and behind the tunnel wall can be comprehensively realized; high-precision control over deformation of the heavy and extra-large risk source is achieved when the shield penetrates through the heavy and extra-large risk source downwards; the problems that in the prior art, an existing grouting technology cannot restrain deformation of soil around a shield body, and the stability of surrounding rock of a tunnel face during shutdown cannot be guaranteed are solved.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to a construction method for actively underpinning strata when a shield machine passes through a heavy or extremely large risk source. Background Art

[0002] With the continuous development of urban rail transit and the continuous improvement of operating lines, the design of routes crossing existing buildings in the early line planning of my country's subway, light rail, urban rail and other rail transit projects has become more and more diversified. For example, shield tunneling under residential buildings, lakes and rivers, highways, bridges and roadbeds are common. At the same time, domestic experts and scholars have also conducted some research on shield tunneling under high-speed railways in recent years, but most of them focus on shield tunneling under high-speed railway bridges and roadbeds; while there are still very few engineering cases and scientific research results on major risk sources such as subway shield tunnels under high-speed railway tunnels. When the shield tunnel passes under major risk sources, it is necessary not only to ensure that the shield machine passes under the major risk sources safely and efficiently, but also to ensure that the structure and track of the major risk sources meet the requirements of high-precision deformation control. Therefore, in the process of shield tunneling, it is necessary to adopt the construction technology of "actively replacing the stratum" to achieve "near zero settlement" control of shield tunneling under major risk sources.

[0003] At present, the commonly used grouting methods in the shield tunneling construction process include synchronous grouting and secondary synchronous double-liquid grouting. The construction process of synchronous grouting is simple, easy to control, low in cost, and the slurry spreads evenly; however, the injection point of the synchronous slurry is behind the shield tail, which cannot fill the gap between the shield body and the soil in time, and cannot suppress the deformation of the soil around the shield body; it is also impossible to compensate the stress of the front of the shield machine during the shutdown and re-pushing process, and cannot ensure the stability of the surrounding rock of the face during the shutdown period; when the synchronous grouting technology is applied to the construction projects of shield tunneling under heavy and major hazardous sources, such as shield tunneling under high-speed railway tunnels, it cannot solve the problem of stress compensation of the soil around the shield body and the rock formation around the face in front of the shield, and then cannot suppress the deformation of the high-speed railway tunnel structure and track. Secondary synchronous double-liquid grouting is a supplementary grouting operation performed after the shield is advanced. It is mainly used to deal with problem areas after synchronous grouting, such as pipe segment floating, tunnel settlement, etc., by injecting double-liquid grout to reinforce and correct these problems; therefore, the secondary synchronous double-liquid grouting is also applied to the construction project of shield tunneling under heavy and large dangerous sources. It is also unable to suppress the deformation of the shield body and the surrounding soil in front of the shield. Therefore, there is an urgent need for a construction method that can simultaneously suppress the deformation of the soil around the front, middle and tail of the shield machine.

[0004] The present invention provides a construction method for actively underpinning strata when a shield machine is passing through a heavy or extremely large risk source, so as to solve the problems existing in the prior art that the existing grouting technology cannot fill the gap between the shield body and the soil body in time and cannot suppress the deformation of the soil body around the shield body, and cannot ensure the stability of the surrounding rock of the face during shutdown. Summary of the invention

[0005] The purpose of the present invention is to provide a construction method for actively underpinning the strata when a shield machine passes through a heavy or extremely large risk source, so as to solve the problems existing in the prior art that the existing grouting technology cannot fill the gap between the shield body and the soil body in time and cannot suppress the deformation of the soil body around the shield body, and cannot ensure the stability of the surrounding rock of the face during shutdown.

[0006] The technical solution of the present invention is: a construction method for actively underpinning the ground when a shield machine passes through a heavy or extremely large risk source, comprising the following steps:

[0007] S1. Analyze and clarify the construction plan through software modeling;

[0008] According to the geological conditions of the shield tunnel under the existing major risk source intersection, the FLAC3D software modeling theory was used to analyze and calculate the construction plan, and the stress compensation amount, stress compensation method and stress compensation location in the actual construction process were clarified;

[0009] S2. Selection and design of shield machine type and segments;

[0010] Several radial grouting holes and a double-liquid grouting system are added to the middle shield of the shield machine; several of the radial grouting holes are respectively provided with single-way valves, and the ports of the single-way valves are all connected with three-way pipes; 1-1.5m wide segments are used, and grouting holes are added to the segments;

[0011] S3. During the excavation process, sulphoaluminate cement grouting technology is used to perform grouting to achieve stress compensation of the surrounding rock from the tail to the rear of the shield machine; the specific implementation process of sulphoaluminate cement grouting technology is as follows:

[0012] (1) Synchronous grouting;

[0013] Through the synchronous grouting system and the grouting pipe at the shield tail, grouting is carried out into the gap while the shield machine is moving forward to form a gap at the shield tail. The slurry for synchronous grouting is sulphoaluminate cement mortar. During synchronous grouting, the grouting pressure is not less than 5 bar, and the grouting speed must match the excavation speed.

[0014] (2) Grouting in the tunnel

[0015] After the segment is out of the shield tail, radial grouting is carried out in time through the grouting holes added to the segment; the grouting range of the segment is 0.8-1.2m in the upper radial direction of the segment and 0-1.2m in the lower radial direction of the segment; the grouting slurry used in the segment is a single-liquid slurry formed by sulphoaluminate cement and water, and the mass ratio of sulphoaluminate cement to water in the single-liquid slurry is 1:(0.6-1); during the grouting process in the segment, the grouting pressure is not less than 1Mpa;

[0016] S4. During the excavation process, the gap between the shield and the soil is filled with mud-effective advanced radial grouting technology to achieve stress compensation in the middle of the shield machine;

[0017] During the tunneling process of the shield machine, a double-liquid grouting system is used to inject mud-killing slurry into the shield shell through the radial grouting holes added on the middle shield to fill the gap between the shield and the soil in time to maintain the stability of the rock formation and inhibit rock settlement.

[0018] The slurry comprises liquid A and liquid B; liquid A is a special bentonite liquid, and the mass ratio of bentonite to water in the special bentonite liquid is (35-45): (80-85); liquid B is a mixture of water glass and water, and the volume ratio of water glass to water in liquid B is (0.8-1.1): 1; in the process of injecting the slurry into the shield shell, the volume ratio of liquid A to liquid B in the slurry is (11-14): 1, and the flow rate of liquid A is 0.8-1m 3 / h;

[0019] S5. When the machine is shut down, the bentonite soil bin replacement and shutdown pressure maintenance technology is used to replace the soil to achieve stress compensation for the front part of the shield machine;

[0020] The skylight point construction mode is adopted, and multiple shutdowns and re-pushing are carried out during the whole process of crossing the existing major risk source intersection section; when waiting for the shutdown, the pressure in the bin is maintained and bentonite slurry is injected into the soil bin, and the slag in the soil bin is discharged through the screw conveyor to replace the soil to ensure the stability of the surrounding rock of the tunnel face during the shutdown period; the bentonite slurry includes bentonite, sand and water, and the ratio of bentonite, sand and water in the bentonite slurry is 4:5:12.5; during the replacement process, the pressure in the soil bin is 1.7-1.9 bar, and after the replacement is completed, the pressure in the soil bin is 1.9 bar;

[0021] S6. Grouting measures after excavation is completed;

[0022] (1) Secondary or multiple grouting measures;

[0023] After the segment is out of the shield tail 2-4 rings, secondary or multiple grouting measures are immediately carried out to meet the engineering quality requirements; and the grouting volume for each ring of secondary or multiple grouting is 0.3-0.7m 3 , grouting pressure shall not be less than 1Mpa;

[0024] The secondary / multiple grouting measures use ordinary cement paste as the slurry, and the mass ratio of water to ash in the slurry is (0.6-1):1;

[0025] (2) Grouting measures for water stop ring;

[0026] After the second or multiple grouting measures are implemented, a water stop ring is made every 3-5 rings by using the water stop ring grouting measures to block the rear water collection channel and ensure the grouting effect;

[0027] The water stop ring grouting measure uses cement and water glass double liquid slurry as the slurry, and the volume ratio of cement slurry to water glass slurry in the slurry is 1:1.

[0028] Preferably, the theoretical analysis modeling using FLAC3D software described in S1 specifically includes analyzing the stability of the surrounding rock in the bare hole state of the shield tunnel, analyzing the deformation of existing major and heavy risk sources and interval tunnels under different surrounding rock stress compensation rates, and analyzing the sensitivity of the physical and mechanical parameters of the surrounding rock to the influence of existing major and heavy risk sources and shield tunnel deformation.

[0029] Preferably, the sulphoaluminate cement mortar in S2 comprises sulphoaluminate cement, water, fly ash, fine aggregate and bentonite, and the mass ratio of water, fly ash, fine aggregate, bentonite and sulphoaluminate cement in the sulphoaluminate cement mortar is (44-47):(30-39):(69-72):(11-16):(16-20).

[0030] Preferably, the dual-liquid grouting system in S2 includes a water glass box, a bentonite box, a double-layer stirring tank, and several sections of slurry conveying pipelines; the water glass box and the bentonite box are respectively equipped with a stirring pump and a grouting pump; the water glass box and the bentonite box are respectively connected to the three-way pipe through the slurry conveying pipeline.

[0031] Preferably, during the soil replacement process described in S5, the cutter head speed is set to 0.6-0.8r / min; when the slag content in the soil bin is 70%-100%, the speed of the screw conveyor is set to 16-20r; when the slag content in the soil bin is 40%-70%, the speed of the screw conveyor is set to 10-16r; when the slag content in the soil bin is 0%-40%, the speed of the screw conveyor is set to 0-10r.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] (1) The present invention provides a construction method for actively underpinning the ground when a shield machine is passing through a heavy or extremely large risk source. The construction method uses a combination of construction technologies such as micro-shrinkage and early-strength sulphoaluminate cement grouting technology, mud-killing effect advanced radial grouting technology, and bentonite soil bin replacement shutdown pressure maintenance technology to perform early grouting, early pressure increase, and excellent pressure maintenance during the construction period when the shield machine is passing through a heavy or extremely large risk source, thereby achieving the effect of timely and active underpinning of the ground pressure, and then achieving the purpose of compensating the stress of the surrounding rock during excavation, and ensuring that stress compensation is fully achieved at the front, middle, and rear of the shield machine and behind the tunnel wall; achieving high-precision control of the deformation of the heavy or extremely large risk source when the shield machine is passing through the heavy or extremely large risk source; and solving the problems in the prior art that the existing grouting technology cannot timely fill the gap between the shield body and the soil body, cannot suppress the deformation of the soil body around the shield body, and cannot ensure the stability of the surrounding rock of the face during shutdown.

[0034] (2) The present invention provides a construction method for actively underpinning the ground when a shield machine passes through a heavy or extremely large risk source. The construction method adopts sulphoaluminate cement grouting technology, performs synchronous grouting during the excavation process, and performs in-tunnel grouting after the excavation is completed, making full use of its fast hardening and early strength characteristics to quickly fill the gap behind the segment wall, and can increase pressure early to achieve stress compensation for the surrounding rock from the tail to the rear of the shield machine, thereby achieving the purpose of actively underpinning the ground and avoiding the risk of delayed settlement.

[0035] (3) The present invention provides a construction method for actively underpinning strata when a shield machine is under a heavy or extremely large risk source. The construction method adopts a mud-reducing effect advanced radial grouting technology. During the excavation process, mud-reducing effect slurry is radially injected into the outside of the shield shell through grouting holes on both sides of the radial direction of the shield in the shield machine, forming a layer of fluid plastic colloid outside the shield shell, and supporting the surrounding rock pressure together with the shield shell, thereby compensating for the stress in the middle of the shield machine and achieving the purpose of actively underpinning the strata. At the same time, the mud-reducing effect slurry used in the mud-reducing effect advanced radial grouting technology has plasticity, which can ensure that the assembly of the segments is basically unaffected by it.

[0036] (4) The present invention provides a construction method for actively underpinning the ground when a shield machine is passing through a heavy or extremely large risk source. The construction method adopts a bentonite silo replacement and shutdown pressure maintenance technology to maintain the pressure in the silo and inject bentonite slurry. The slag is discharged through a screw conveyor to replace the soil, thereby compensating for the stress in the front of the shield machine and achieving the purpose of actively underpinning the ground. At the same time, it can avoid the phenomenon of difficulty in re-pushing caused by the slag losing water and the formation of mud cake after the soil solidifies under high temperature in the silo. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0038] Figure 1 It is a structural schematic diagram of the grouting reinforcement range of the interval tunnel according to the present invention;

[0039] Figure 2 It is a cross-sectional schematic diagram of the grouting reinforcement range of the interval tunnel according to the present invention;

[0040] Figure 3 This is a comparison chart of the gelling properties of the grouting slurry in the hole according to the present invention;

[0041] Among them: 1. In-tunnel reinforcement scope; 11. Upper segment reinforcement scope; 12. Lower segment reinforcement scope; 2. Segment; 3. Section tunnel. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with specific embodiments:

[0043] The present invention takes the project of a subway tunnel passing under an existing high-speed railway tunnel as an example; since the safe operation of the high-speed railway has extremely high requirements on the stability and smoothness of the high-speed railway track, during the construction process of the shield machine passing under the high-speed railway tunnel, it is necessary not only to ensure that the shield machine can pass under the high-speed railway tunnel safely and efficiently, but also to ensure that the high-speed railway tunnel structure and track meet the requirements of high-precision deformation control; therefore, in the project of the shield machine passing under the existing high-speed railway tunnel, it is necessary to adopt a construction method that can better suppress the deformation and settlement of the soil around the high-speed railway tunnel.

[0044] A construction method for actively replacing the ground layer by shield tunneling under heavy and extremely large risk sources, wherein the construction method is used to implement the shield tunneling under the existing high-speed railway tunnel project, specifically comprising the following steps:

[0045] S1. Analyze and clarify the construction plan through software modeling;

[0046] Through a full survey and evaluation of the geology of the crossing section of the shield tunnel under the high-speed railway, and the use of FLAC3D software modeling to simulate the impact of the shield tunnel under the high-speed railway tunnel construction, a construction plan was made, and the stress compensation amount, stress compensation method and stress compensation location in the actual construction process were clarified. Among them, during the survey and evaluation, the elastic modulus and Poisson's ratio of the medium-weathered mudstone strata and the strongly weathered mudstone strata were focused on the influence of the surrounding rock disturbance; at the same time, through the FLAC3D software modeling, the surrounding rock stability in the bare hole state of the shield tunnel, the deformation of the existing railway tunnel and the interval tunnel under different surrounding rock stress compensation rates, and the sensitivity of the physical and mechanical parameters of the surrounding rock to the deformation of the existing railway line and the shield tunnel were specifically analyzed; thus, relevant conclusions on the impact of the shield construction process on the existing railway were drawn, and a reasonable and feasible construction plan was made.

[0047] S2. Selection and design of shield machine type and segments;

[0048] In this construction method, the shield machine No. 556 of China Railway Equipment is used for shield tunneling, and several radial grouting holes and a double-liquid grouting system are added to the middle shield of the shield machine. Single valves are respectively set on several radial grouting holes, and the ports of the single valves are connected to three-way pipes; the double-liquid grouting system includes a water glass box, a bentonite box, a double-layer mixing tank, and several sections of slurry delivery pipelines; the water glass box and the bentonite box are respectively equipped with a mixing pump and a grouting pump; the water glass box and the bentonite box are respectively connected to the three-way pipe connected to the valve through the slurry delivery pipeline. In this construction method, a pipe segment with an outer diameter of 6.7m, an inner diameter of 6m, a ring width of 1.5m, and a model of c50p10 is used, and grouting holes are added on the pipe segment for grouting into the gap between the pipe segment and the soil. In other construction methods, the selection and design of shield machine type and segments need to be determined according to actual construction needs; the shield machine can be an earth pressure balance shield machine, a slurry balance shield machine, etc.

[0049] S3. During the excavation process, sulphoaluminate cement grouting technology is used to achieve grouting to compensate for the stress of the surrounding rock from the tail to the rear of the shield machine; the specific implementation process of sulphoaluminate cement grouting technology includes two parts: synchronous grouting and in-tunnel grouting.

[0050] (1) Synchronous grouting

[0051] During the synchronous grouting process, it is first necessary to screen out the synchronous grouting slurry whose performance meets the use requirements through on-site trial mixing; secondly, through the synchronous grouting system and the grouting pipe at the shield tail, grouting is carried out into the gap while the shield machine moves forward to form a gap at the shield tail.

[0052] In this construction method, the main mechanical properties of the synchronous grouting slurry meet the following requirements:

[0053] (1) Gel time: 3-5h;

[0054] (2) Strength: 1-day strength ≥ 0.3 MPa, 28-day strength ≥ 1 MPa;

[0055] (3) Stone rate: ≥98%;

[0056] (4) Stability: good workability, no stratification or segregation.

[0057] Since sulphoaluminate cement is a hydraulic cementitious material obtained by calcining aluminum raw materials (aluminum), lime raw materials (limestone) and gypsum after proper combination to form clinker containing an appropriate amount of anhydrous calcium sulphoaluminate, and then grinding with an appropriate amount of gypsum, it has good early strength and anti-seepage capabilities; in this construction method, sulphoaluminate cement is selected as the raw material to prepare the synchronous grouting slurry; at the same time, the raw materials for preparing the synchronous grouting slurry also include fly ash, fine aggregate, bentonite, etc.

[0058] Multiple groups of synchronous grouting slurries are trial-mixed on site, and the performance of each group of synchronous grouting slurries is tested to select the slurry with the best mix ratio parameters as the synchronous grouting slurry for this construction method. The mix ratio parameters and performance of multiple groups of synchronous grouting slurries trial-mixed on site are shown in Table 1.

[0059] Table 1. Synchronous grouting slurry test parameters and properties

[0060]

[0061] As shown in Table 1, the stone setting rates of the synchronous grouting slurries prepared in Test 1 and Test 2 can meet the use requirements, but the synchronous grouting slurry prepared in Test 1 has a shorter initial setting time, which means that the time required for gelling is shorter and the gelling effect is better; therefore, this construction method preferably prepares the synchronous grouting slurry according to the specific ratio provided in Test 1. In other construction methods, the synchronous grouting slurry that meets the requirements can be screened out by adjusting the ratio of raw materials such as water, fly ash, fine aggregate, bentonite, and sulphoaluminate cement.

[0062] During the excavation process, synchronous grouting needs to adopt the control standard of volume and pressure dual control, and the grouting volume control is mainly used to ensure that the filling behind the pipe segment is dense and avoid soil disturbance. Through on-site survey, software modeling and calculation, it can be deduced that during the synchronous grouting process, the synchronous grouting volume of each ring should be no less than 7m 3 , and the grouting volume also needs to be dynamically adjusted according to the groundwater conditions, shield slag conditions, etc.; at the same time, the grouting pressure needs to be controlled to be no less than 5bar during the synchronous grouting process; the grouting speed during the synchronous grouting process needs to be basically consistent with the excavation speed, that is, sufficient grouting is carried out while the shield machine is advancing. In addition, during synchronous grouting, it is necessary to ensure that six grouting pipes are grouted at the same time, and the shield operator pays attention to the synchronous grouting volume after each 100mm of forward excavation, and promptly controls and adjusts the grouting speed; prevent grouting too fast or too slow, causing gaps to form behind the pipe segments, causing ground settlement and damaging the waterproof function. In other construction methods, the synchronous grouting volume and grouting pressure of each ring need to be calculated and adjusted according to the surveyed geological conditions, shield slag conditions, etc.

[0063] By selecting synchronous grouting slurry with excellent mechanical properties and controlling parameters such as grouting volume, grouting pressure, and grouting speed, it is possible to ensure that the gaps behind the segment wall are fully filled to achieve the purpose of timely replacing the strata and controlling the deformation of the high-speed railway; and the grouting effect can be verified by opening holes in the segment hoisting holes every other ring.

[0064] (2) Grouting in the tunnel

[0065] During the grouting process in the tunnel, it is also necessary to first select the synchronous grouting slurry with slurry performance that meets the use requirements through on-site trial mixing; secondly, after the pipe segment 2 is removed from the shield tail, radial grouting in the tunnel is carried out in time through the grouting holes added to the pipe segment 2. Figure 1 , Figure 2 As shown, the tunnel reinforcement range 1 in the interval tunnel 3 is 0-1.2m radially outside the segment 2; wherein, the segment upper reinforcement range 11 is 0.8-1.2m radially, and the segment lower reinforcement range 12 can be grouting according to the surveyed geological conditions and the monitored synchronous grouting conditions, and the segment lower reinforcement range 12 is preferably 0-1.2m radially. At the same time, during the tunnel grouting process, the grouting pressure needs to be controlled to be not less than 1MPa.

[0066] Sulphoaluminate cement, ordinary Portland cement and other cements are selected as raw materials, mixed with water in a certain proportion to prepare multiple groups of single-liquid slurries as in-tunnel grouting slurries, and the performance of each group of in-tunnel grouting slurries is tested to select the slurry with the best ratio parameters as the in-tunnel grouting slurry for this construction method. Based on the grouting construction experience, ordinary Portland cement (model: P.O42.5) and sulphoaluminate cement (model: R.SAC42.5) are selected in this construction method. Sulphoaluminate cement single-liquid slurry and ordinary Portland cement single-liquid slurry are prepared according to three ratios of water:ash ratio of 0.6:1, 0.8:1 and 1:1, respectively, and indoor tests are carried out to test their relevant performance. Figure 3 As shown in the figure, the single-liquid slurry obtained by mixing sulphoaluminate cement and water is used as the grouting slurry for in-tunnel grouting, and its gelling time is significantly lower than the gelling time of the single-liquid slurry obtained by mixing ordinary silicate cement and water as the grouting slurry for in-tunnel grouting, which further indicates that the single-liquid slurry of sulphoaluminate cement used as the grouting slurry for in-tunnel grouting has better coagulation performance; at the same time, the slurry gel time curve shows that when the water-cement ratio is between (0.6-1):1, the slurry gel time gradually increases with the increase of the water-cement ratio; however, the slurry with a water-cement ratio of 0.6:1 is too viscous and is not suitable for stirring and grouting; the slurries with water-cement ratios of 0.8:1 and 1:1 have good workability and are more operable in on-site construction; therefore, the single-liquid slurry of sulphoaluminate cement with a water-cement ratio of 0.8-1:1 is preferred for in-tunnel grouting. In addition, according to the GB20472-2006 sulphoaluminate cement specification, the early strength of fast-hardening sulphoaluminate cement is very high, with a one-day compressive strength reaching 70% of the standard strength and a three-day compressive strength reaching 100% of the standard strength, and there is still an increasing trend in the later period; therefore, fast-hardening sulphoaluminate cement is selected as the raw material for preparing the in-hole grouting slurry in this construction method.

[0067] S4. During the excavation process, the mud-killing effect advanced radial grouting technology is used to fill the gap between the shield and the soil, so as to realize the stress compensation of the middle part of the shield machine. The injection point of the above-mentioned synchronous slurry is behind the shield tail, and there are defects such as failure to fill the gap between the shield and the soil in time, and failure to suppress the deformation of the soil around the shield. However, this construction method is to construct a subway tunnel under a high-speed railway tunnel. As a shield tunneling project under a heavy and major hazardous source, ensuring that the high-speed railway tunnel structure and track meet the high-precision deformation control requirements is a top priority, and solving the stress compensation of the soil around the shield is an important part of controlling its deformation. Therefore, the mud-killing effect advanced radial grouting technology is used. During the excavation process, slurry is injected into the outside of the shield shell through the double-liquid grouting system and the radial grouting holes added on the middle shield to fill the gap between the shield and the soil in time, so as to actively support the formation and maintain the stability of the rock formation, so as to achieve the purpose of controlling the deformation of the high-speed railway tunnel.

[0068] The shield machine No. 556 of China Railway Equipment used in this construction method has a cutter diameter of 6.98m, a front shield diameter of 6.95m, a middle shield diameter of 6.94m, and a shield tail diameter of 6.93m. During the tunneling process of the shield machine, there will be a gap of 30-50mm between the shield and the soil. At the same time, due to the large deadweight of the shield, the lower part of the shield is in close contact with the soil, and the gap between the upper part of the shield and the soil will be larger. Assuming that each ring is 1.5m wide, it can be theoretically calculated that each ring excavated will generate 0.66m around the front shield. 3 In this construction method, the mud-effective advanced radial grouting technology is used to fill the gaps in time, thereby effectively inhibiting the settlement of the rock formation.

[0069] Similarly, the use of the mud-effect advanced radial grouting technology to fill the gap between the shield and the soil requires firstly to screen out the mud-effect slurry whose slurry properties meet the use requirements through on-site trial mixing, and secondly, to implement the mud-effect grouting process for grouting; and before grouting, the operating personnel need to test the injection according to the process, fully familiarize themselves with the operating process, and fully debug the equipment performance.

[0070] (1) Proportion of slurry with gram-effect effect

[0071] The slurry with good effect includes liquid A and liquid B, and liquid A is a special bentonite liquid, and liquid B is a mixture of water glass and water. According to the grouting construction experience and the experimental verification of multiple groups of slurries, the mass ratio of bentonite to water in liquid A is preferably (35-45): (80-85), and the volume ratio of water glass to water in liquid B is preferably (0.8-1.1): 1; at the same time, in the process of injecting the slurry with good effect into the shield shell, the volume ratio of liquid A to liquid B in the slurry with good effect is (11-14): 1, and the flow rate of liquid A is 0.8-1m 3 / h. According to the geological conditions surveyed on site, this construction method uses liquid A with a mass ratio of bentonite to water of 16:33 and liquid B with a volume ratio of water glass to water of 1:1. In the process of injecting the mud-effect slurry outside the shield shell, the volume ratio of liquid A to liquid B in the mud-effect slurry is 12.5:1, and the flow rate of liquid A is controlled at 0.9m 3 / h. In order to control the settlement of high-speed railway tunnels, combined with theoretical calculations, it is known that during the tunneling process of the shield machine, 0.8m of grouting fluid is injected into each ring of the shield shell through the double-liquid grouting system and the radial grouting holes added on the middle shield. 3 The gram-effect slurry of each ring, that is, 121% of the theoretical value of gram-effect slurry is injected into each ring to fill the gap between the shield and the soil. In other construction methods, the amount of gram-effect slurry to be injected into each ring can be determined according to geological conditions and actual needs, but the amount of gram-effect slurry injected into each ring should not be less than the calculated theoretical value.

[0072] (2) Mud-killing grouting construction technology

[0073] First, weigh water glass and water in a volume ratio of 1:1, put the water glass and water into a double-layer mixing tank and mix them thoroughly to form a mixed liquid, store it in a water glass box, and stir it at a low speed as liquid B; then, weigh bentonite and water in a mass ratio of 16:33, put the weighed bentonite and water into a double-layer mixing tank and mix them thoroughly to form a mixed liquid, store it in a bentonite box, and stir it at a low speed as liquid A; secondly, adjust the injection rate of liquid A to 20L / min and the injection rate of liquid B to 1L / min, monitor the flow meter data throughout the process, and control the slurry ratio; then, after each ring of grouting is completed, stop the grouting of liquid B first, and stop the grouting of liquid A after 30s. Finally, disconnect the connection between the slurry delivery pipeline and the tee pipe, and inject clean water into the slurry delivery pipeline to wash the pipe, preparing for the next ring of grouting operation. Among them, the one-way valve on the radial grouting hole has a pre-processed three-way pipe connected to its port, one of which is connected to the slurry delivery pipeline of liquid A, one is connected to the slurry delivery pipeline of liquid B, and the other is used as a slurry inspection port. In addition, since the injection amount of gram-effective slurry per ring is small, considering the economic cost and convenient operation factors, a double-layer mixing tank can be used to fully mix the bentonite slurry in the upper tank body and then put it into the lower tank body for storage as liquid A. According to the excavation speed of 35-40min / ring, the injection amount per ring can be calculated to be 735-840L. In the actual excavation process, the excavation time of each ring is different. The grouting amount is controlled by adjusting the grouting pumps installed on the water glass box and the bentonite box to ensure that the grouting amount is 0.8m 3 During the grouting process, the grouting volume of each ring should be kept consistent, and the grouting rate should be matched with the excavation to ensure uniform grouting.

[0074] S5. When the machine is shut down, the bentonite soil bin replacement and shutdown pressure maintenance technology is used to replace the soil to achieve stress compensation for the front part of the shield machine;

[0075] During the construction of the shield machine under the high-speed railway tunnel crossing section, the skylight point construction mode is adopted; the shield machine will be shut down and pushed repeatedly during the whole process of crossing the high-speed railway. If the slag soil pressure maintenance method is adopted, the cutterhead at the front of the shield machine is prone to mud cake; and the cutterhead needs to be rotated continuously during the shutdown period to prevent consolidation, which will disturb the rock layer soil many times and cannot ensure the stability of the surrounding rock of the face. In order to ensure the stability of the surrounding rock of the face during the shutdown period, the bentonite soil bin replacement shutdown pressure maintenance technology is adopted. Bentonite mortar is injected into the soil bin and the slag in the soil bin is replaced. The bentonite mortar pressure maintenance is adopted, and the cutterhead is wrapped by the bentonite slurry, which can not only avoid the formation of mud cakes, but also achieve the purpose of pressure maintenance, thereby realizing the stress compensation of the face and ensuring the stability of the rock formation.

[0076] Before using the bentonite silo replacement shutdown pressure maintenance technology to replace the slag, it is also necessary to prepare a bentonite slurry whose slurry performance meets the use requirements. In this construction method, combined with the surveyed geological conditions, a bentonite mortar prepared from raw materials such as bentonite and sand is used, and the mass ratio of bentonite, sand and water in the bentonite mortar is 8:10:25; at the same time, the bentonite mortar needs to be fully mixed with the slurry through the shield mixing station to ensure uniform mixing.

[0077] The slurry tank containing bentonite mortar is transported to the cave by an electric vehicle, and the bentonite mortar is stored in the bentonite box. When the machine is to be shut down, the pressure in the silo is maintained and bentonite mortar is injected into the soil silo. At the same time, the slag in the soil silo is discharged through a screw conveyor to replace the soil. During the soil replacement process, the cutter head speed is set to 0.6-0.8r / min; when the slag content in the soil silo is 70%-100%, the speed of the screw conveyor is set to 16-20r; when the slag content in the soil silo is 40%-70%, the speed of the screw conveyor is set to 10-16r; when the slag content in the soil silo is 0%-40%, the speed of the screw conveyor is set to 0-10r. In addition, during the soil replacement process, the amount of slag discharged by the screw machine needs to be kept consistent with the amount of bentonite injected; at the same time, the pressure in the soil bin needs to be kept within the range of 1.7-1.9 bar, and the pressure in the soil bin is 1.9 bar at the end of the soil replacement. If necessary, the pressure in the soil bin can be balanced by controlling the air pressure in the soil bin. According to test verification statistics, about 24 cubic meters of bentonite mortar need to be injected during each skylight period. Through soil replacement, the stress compensation of the front part of the shield machine is realized, and the purpose of actively underpinning the formation is achieved.

[0078] S6. Grouting measures after excavation is completed: To meet the quality requirements of the project, it is necessary to carry out grouting behind the segment wall through secondary grouting and water stop ring grouting measures to effectively fill and compact the gap behind the segment wall, so as to achieve the effect of timely and active replacement of the stratum and control of the floating of the segment.

[0079] (1) Secondary or multiple grouting measures;

[0080] After the segment is out of the shield tail 2-4 rings, secondary or multiple grouting measures are immediately carried out to meet the engineering quality requirements; and in the process of secondary or multiple grouting, the grouting volume for each ring is 0.3-0.7m 3 , the grouting pressure is not less than 1Mpa; in addition, during the grouting process, the grouting volume of each ring is not less than the designed volume, and the grouting can only be stopped when the final pressure value is reached to ensure that the grouting is full; at the same time, a dedicated person is required to monitor the grouting pump pressure gauge to ensure that the grouting pressure is not less than the planned value and not greater than the final pressure value. The secondary / multiple grouting measures use ordinary cement slurry as the slurry, and the mass ratio of water to ash in the slurry is (0.6-1):1;

[0081] (2) Grouting measures for water stop ring;

[0082] After the second or multiple grouting measures are implemented, a water stop ring is made every 3-5 rings by using the water stop ring grouting measures to block the water collection channel at the rear and ensure the grouting effect. The water stop ring grouting measures use a double liquid slurry containing cement slurry and water glass slurry as the slurry, and the volume ratio of cement slurry to water glass slurry in the slurry is 1:1.

[0083] The main materials and material specifications used in this construction method are shown in Table 2.

[0084] Table 2. Main materials and their specifications

[0085] Material Name Specification Sand Fine sand cement Sulphoaluminate cement cement Ordinary Portland Cement Fly ash Level II Bentonite Calcium Steel flower pipe DN50 Water Glass 35be

[0086] This construction method adopts comprehensive construction technologies including the above-mentioned sulphoaluminate cement grouting technology, mud-killing effect advanced radial grouting technology, bentonite soil bin replacement shutdown pressure maintenance technology, etc. During the construction of the shield subway tunnel under the high-speed railway tunnel, early grouting, early pressure increase, and excellent pressure maintenance are carried out to achieve the effect of timely and active replacement of stratum pressure, thereby achieving the purpose of compensating the stress of the surrounding rock during excavation and ensuring that the front, middle, tail and rear of the shield machine and the tunnel wall are fully compensated for stress; finally, the "near zero settlement" control of the shield under the high-speed railway tunnel is achieved. Chengdu Rail Transit Line 9 passes through the Chenggui High-speed Railway Tunnel, which is the first project in China to pass under a high-speed railway tunnel. It was constructed using this construction method; at the same time, this construction method is also suitable for circular section TBM (full section tunneling) in mudstone and sandstone formations or shield construction under other major and extremely dangerous sources or other similar projects.

[0087] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description, and it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A construction method for actively replacing ground layers by shield tunneling through a heavy or extremely large risk source, characterized in that: The steps include: S1. Analyze and clarify the construction plan through software modeling; According to the geological conditions of the shield tunnel under the existing major risk source intersection, the FLAC3D software modeling theory was used to analyze and calculate the construction plan, and the stress compensation amount, stress compensation method and stress compensation location in the actual construction process were clarified; S2. Selection and design of shield machine type and segments; Several radial grouting holes and a double-liquid grouting system are added to the middle shield of the shield machine; several of the radial grouting holes are respectively provided with single-way valves, and the ports of the single-way valves are all connected with three-way pipes; 1-1.5m wide segments are used, and grouting holes are added to the segments; S3. During the excavation process, sulphoaluminate cement grouting technology is used to compensate for the stress of the surrounding rock from the tail to the rear of the shield machine. The specific implementation process of sulphoaluminate cement grouting technology is as follows: (1) Synchronous grouting; Through the synchronous grouting system and the grouting pipe at the shield tail, grouting is carried out into the gap while the shield machine is moving forward to form a gap at the shield tail. The slurry for synchronous grouting is sulphoaluminate cement mortar. During synchronous grouting, the grouting pressure is not less than 5 bar, and the grouting speed must match the excavation speed. (2) Grouting in the tunnel After the segment is out of the shield tail, radial grouting is promptly carried out in the tunnel through the grouting holes added to the segment; the grouting range of the tunnel is 0.8-1.2m radially on the upper part of the segment and 0-1.2m radially on the lower part of the segment; the slurry used for the tunnel grouting is a single-liquid slurry composed of sulphoaluminate cement and water, and the mass ratio of sulphoaluminate cement to water in the single-liquid slurry is 1:(0.6-1); during the tunnel grouting process, the grouting pressure is not less than 1Mpa; S4. During the excavation process, the gap between the shield and the soil is filled with mud-effective advanced radial grouting technology to achieve stress compensation in the middle of the shield machine; During the tunneling process of the shield machine, a double-liquid grouting system is used to inject mud-killing slurry into the shield shell through the radial grouting holes added on the middle shield to fill the gap between the shield and the soil in time to maintain the stability of the rock formation and inhibit rock settlement. The slurry comprises liquid A and liquid B; liquid A is a special bentonite liquid, and the mass ratio of bentonite to water in the special bentonite liquid is (35-45): (80-85); liquid B is a mixture of water glass and water, and the volume ratio of water glass to water in liquid B is (0.8-1.1): 1; in the process of injecting the slurry into the shield shell, the volume ratio of liquid A to liquid B in the slurry is (11-14): 1, and the flow rate of liquid A is 0.8-1m 3 / h; S5. When the machine is shut down, the bentonite soil bin replacement and shutdown pressure maintenance technology is used to replace the soil to achieve stress compensation for the front part of the shield machine; The skylight point construction mode is adopted, and multiple shutdowns and re-pushing are carried out during the whole process of crossing the existing major risk source intersection section; when waiting for the shutdown, the pressure in the bin is maintained and bentonite slurry is injected into the soil bin, and the slag in the soil bin is discharged through the screw conveyor to replace the soil to ensure the stability of the surrounding rock of the tunnel face during the shutdown period; the bentonite slurry includes bentonite, sand and water, and the ratio of bentonite, sand and water in the bentonite slurry is 4:5:12.5; during the replacement process, the pressure in the soil bin is 1.7-1.9 bar, and after the replacement is completed, the pressure in the soil bin is 1.9 bar; S6. Grouting measures after excavation is completed; (1) Secondary or multiple grouting measures; After the segment is out of the shield tail 2-4 rings, secondary or multiple grouting measures are immediately carried out to meet the engineering quality requirements; and the grouting volume for each ring of secondary or multiple grouting is 0.3-0.7m 3 , grouting pressure is not less than 1Mpa; The secondary / multiple grouting measures use ordinary cement paste as the slurry, and the mass ratio of water to ash in the slurry is (0.6-1):1; (2) Grouting measures for water stop ring; After the second or multiple grouting measures are implemented, a water stop ring is made every 3-5 rings by using the water stop ring grouting measures to block the rear water collection channel and ensure the grouting effect; The water stop ring grouting measure uses cement and water glass double liquid slurry as the slurry, and the volume ratio of cement slurry to water glass slurry in the slurry is 1:

1.

2. According to claim 1, a construction method for actively underpinning strata by a shield machine passing through a heavy or extremely large risk source, characterized in that: The theoretical analysis modeled using FLAC3D software as described in S1 specifically includes analyzing the stability of the surrounding rock in the bare hole state of the shield tunnel, analyzing the deformation of existing major risk sources and interval tunnels under different surrounding rock stress compensation rates, and analyzing the sensitivity of the physical and mechanical parameters of the surrounding rock to the influence of existing major risk sources and shield tunnel deformation.

3. The construction method of a shield tunneling under a heavy or extremely large risk source and actively underpinning the stratum according to claim 2 is characterized by: The sulphoaluminate cement mortar in S2 includes sulphoaluminate cement, water, fly ash, fine aggregate and bentonite, and the mass ratio of water, fly ash, fine aggregate, bentonite and sulphoaluminate cement in the sulphoaluminate cement mortar is (44-47):(30-39):(69-72):(11-16):(16-20).

4. The construction method of a shield tunneling under a heavy or extremely large risk source to actively underpin the stratum according to claim 2 is characterized by: The double-liquid grouting system described in S2 includes a water glass box, a bentonite box, a double-layer stirring tank, and several sections of slurry conveying pipelines; the water glass box and the bentonite box are respectively equipped with a stirring pump and a grouting pump; the water glass box and the bentonite box are respectively connected to the three-way pipe through the slurry conveying pipeline.

5. The construction method of a shield tunneling under a heavy or extremely large risk source and actively underpinning the ground according to claim 2 is characterized by: During the soil replacement process described in S5, the cutter head speed is set to 0.6-0.8r / min; when the slag content in the soil bin is 70%-100%, the speed of the screw conveyor is set to 16-20r; when the slag content in the soil bin is 40%-70%, the speed of the screw conveyor is set to 10-16r; when the slag content in the soil bin is 0%-40%, the speed of the screw conveyor is set to 0-10r.

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