Earth pressure balance shield construction micro-deformation control method

Abstract

The invention discloses a micro-deformation control method for earth pressure balance shield construction. Micro-deformation control over the whole earth pressure balance shield construction process is achieved through precise pressure maintaining, shield body mud injection, synchronous double-liquid slurry injection and repeated slurry supplementing. According to the method, accurate pressure maintaining control over the excavation face of the existing peripheral circular-arc-shaped cutter head is achieved through a foam and low-concentration polyacrylamide water solution comprehensive muck improvement method and a soil pressure calculation method; by means of the method that plastic mud is synchronously injected into the two mud injection points of the middle shield and the two mud injection points of the shield tail along with shield tunneling, balance between a shield body and an excavation forming face is achieved, and meanwhile the problems that the upper portion of the shield body settles, synchronous slurry losses, the shield body is prone to wrapping, and spewing is prone to occurring during shield tunneling are solved. The double-liquid slurry is injected synchronously along with shield tunneling, so that balance between the duct piece separated from the shield tail and an excavation forming face is achieved, and the problem that the duct piece floats upwards is solved; multiple times of slurry supplementing and filling synchronize the slurry water loss volume, and balance between the pipe piece and the excavation forming face is achieved.

Description

Technical Field

[0001] The invention relates to shield construction, in particular to a micro-deformation control method for earth pressure balance shield construction. Background Art

[0002] As the cutting-edge equipment in the field of international tunnel construction today, the shield machine has become the first choice in urban rail transit construction with its significant advantages - low safety risk, excellent tunnel forming quality, and efficient construction progress. In particular, the earth pressure balance shield is used in urban tunnel construction with its many advantages such as small footprint, small construction impact, and low cost. When the earth pressure balance shield travels underground, it will inevitably pass through subways, high-speed railways, roads, buildings, underground important pipelines and other large-scale dangerous projects, and has high requirements for the settlement of nearby buildings (structures). If the settlement of shield construction is not well controlled, large or even major safety accidents are prone to occur. The surface uplift and settlement specifications of shield construction require control between -30 and +10mm, and crossing the subway requires control within 10mm. The uplift and settlement requirements of high-speed railways are even higher, which requires that the shield construction has little impact on nearby buildings (structures), and it is best to achieve micro deformation or even zero deformation. Due to the deep burial depth of shield construction and the high bearing capacity of the stratum, the deformation of shield construction is generally reflected as settlement.

[0003] The settlement of the ground surface and nearby buildings (structures) during EPB shield construction is a continuous process (e.g. Figure 1 ), which mainly occurs during the shield cutter excavation process, the shield body passing through the process and a long time after the shield passes through. This requires finding the settlement mechanism of the whole process of shield construction and taking corresponding measures to control it, so as to achieve the goal of micro-deformation or even zero deformation of shield construction. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and construction methods, and to provide a method for controlling micro-deformation of earth pressure balance shield construction. By innovating precise pressure maintenance, shield body mud injection, synchronous dual-liquid slurry injection and multiple grouting, the whole process of shield construction can be balanced and controlled, so as to achieve the goal of micro-deformation or even zero deformation of shield construction.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The micro-deformation control method of earth pressure balance shield construction includes: controlling the micro-deformation of earth pressure balance shield construction through precise pressure maintenance, shield body mud injection, synchronous double-liquid slurry injection and multiple grouting.

[0007] As a preferred method, the comprehensive slag improvement method using foam and low-concentration polyacrylamide aqueous solution includes: using different slag improver ratios in different strata; injecting foam through the foam pipeline in front of the cutterhead, and injecting low-concentration polyacrylamide aqueous solution in the center in front of the cutterhead, the center of the soil bin and above the soil bin, with the injection amount mainly in the center in front of the cutterhead and the center of the soil bin, and the injection amount is adjustable and visible, so as to prevent shield excavation gushing and mud cake formation in the center of the soil bin to the greatest extent, thereby achieving the goal of precise pressure maintenance of the soil bin.

[0008] Mixing ratio of soil conditioner in different strata

[0009]

[0010] As a preferred embodiment, the present invention also includes a method for accurately maintaining soil bin pressure, wherein the pressure of the surrounding arc-shaped cutterhead shield soil bin should be between the active balance pressure and the passive balance pressure, and when the pressure of the top soil bin is at the original soil self-weight stress, the stratum above the excavation surface can achieve micro-deformation or even zero deformation.

[0011] As a preferred embodiment, the present invention also includes a synchronous mud injection method for the middle shield and the shield tail, which injects plastic mud at two middle shield injection points at the upper part of the middle shield and two shield tail injection points at the lower part of the shield tail to fill the upper gap of the shield body and the lower gap of the shield tail. The plastic mud mix ratio is a mass ratio of calcium-based bentonite: water: water glass of 15:12:1. The design of the two shield tail injection points at the lower part of the shield tail can effectively prevent the synchronous slurry from flowing to the lower part of the suspended shield tail and prevent the lower part of the shield tail from being wrapped by the synchronous slurry.

[0012] As a preferred embodiment, the present invention also includes a synchronous dual-liquid slurry injection method, which uses a synchronous dual-liquid slurry injection technology with a thickener polyacrylamide aqueous solution as B liquid, and A liquid is a settable fluid slurry mixed with cement, fly ash, dry fine sand, sodium-based bentonite and water as the main materials. As the shield advances forward, liquid A and liquid B are mixed in a volume ratio of 10:1 in front of the shield tail grouting pipe. In the shield tail grouting pipe, the synchronous slurry is thickened from a fluid to a plastic body, and injected into the gap between the outer surface of the segment that has escaped from the shield tail and the excavation molding surface, so as to achieve a balance between the outer surface of the segment and the excavation molding surface and prevent settlement at the shield tail. The synchronous dual-liquid slurry formulation is shown in Table 2;

[0013] Table 2 Double liquid slurry mix ratio

[0014]

[0015] As a preferred mode, the present invention also includes a multiple grouting method, which takes multiple grouting for the unsaturated area caused by water loss during the solidification process of the synchronous slurry. At regular intervals (such as 6 to 8 hours), holes are opened at the grouting holes on the top of the segments within the shield trolley range to add grout (either single-liquid slurry or double-liquid slurry) to supplement the volume shrinkage caused by water loss of the synchronous slurry, ensure the balance between the outer surface of the segment and the excavation molding surface, control the surface settlement, and achieve the goal of controlling micro-deformation during shield excavation.

[0016] The present invention has at least the following beneficial effects: the present invention realizes the precise pressure-maintaining control of the current peripheral arc-shaped cutter disc excavation surface, and can achieve the water-soil pressure balance between the earth bin slag and the original soil of the shield excavation surface; by the method of injecting plastic mud synchronously at two mud injection points in the middle shield and two mud injection points at the shield tail as the shield advances, the balance between the shield body and the excavation forming surface is achieved, and at the same time, many difficult problems such as settlement above the shield body, loss of synchronous slurry, easy wrapping of the shield body, and easy gushing during shield excavation are solved; by the synchronous double-liquid slurry injection technology, the slurry is thickened from a single-liquid slurry fluid to a double-liquid slurry plastic body, and the balance between the outer surface of the segment and the excavation forming surface is achieved when the shield excavation segment is out of the shield tail, and at the same time, the difficult problems of segment floating, easy loss of slurry, low stone rate, and high grouting cost are solved; by replenishing slurry multiple times behind the segment on the shield trolley, the water loss part of the synchronous slurry during the solidification process is compensated, and the balance between the outer surface of the segment and the excavation forming surface is continuously achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only illustrate embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 This is a schematic diagram of the shield host;

[0019] Figure 2 This is a schematic diagram of single-point surface settlement during shield construction;

[0020] Figure 3 This is a flow chart of the micro-deformation control method for earth pressure balance shield construction;

[0021] Figure 4 This is the force analysis diagram of the tiny unit at the arc of the excavation surface;

[0022] Figure 5 This is a schematic diagram of the active balance pressure analysis of a small unit at the arc of the excavation surface;

[0023] Figure 6 It is a schematic diagram of passive balance pressure analysis of a small unit at the arc of the excavation surface;

[0024] Figure 7 This is a schematic diagram of soil bin pressure balance;

[0025] Figure 8 This is a schematic diagram of the mud injection position of Zhongdun;

[0026] Fig. 9 This is a schematic diagram of the shield tail mud injection position.

[0027] In the figure, 1-cutter disc, 2-center in front of the cutter disc, 3-center of the soil bin, 4-front shield, 5-above the soil bin, 6-middle shield, 7-shield tail, 8-segment assembler, 9-shield tail brush, 10-segment, 11-screw conveyor, 12-rear gate of screw conveyor, 13-belt, 14-settlement in front of the cutter disc, 15-settlement at the excavation of the cutter disc, 16-settlement above the shield, 17-settlement at the rear of the shield tail, 18-settlement behind the shield tail, 19-continuous settlement, 20-soil bin, 21-active balancing pressure, 22-soil bin pressure, 23-passive balancing pressure, 24-excavation forming surface, 25-plastic mud, 26-mud injection point in the middle shield, 27-mud injection point at the shield tail. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0029] Hereinafter, different embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that the present disclosure is not limited to the specific form disclosed herein, but rather, the present disclosure should be interpreted as covering different changes, equivalents and / or replacements of the embodiments of the present disclosure. When describing the accompanying drawings, similar reference numerals may be used to indicate similar components.

[0030] In the present disclosure, if there is a statement "A or B", "at least one of A and / or B", or "one or more of A and / or B", it can include all possible combinations of the listed items. For example, the statement "A or B", "at least one of A and B", or "at least one of A or B" refers to all of the following situations: (1) including at least one A, (2) including at least one B, or (3) including both at least one A and at least one B.

[0031] The expressions used in different embodiments of the present disclosure, if there is "first", "second", "the first" or "the second" can modify different elements, regardless of order and / or importance, without limiting the corresponding elements. For example, a first user device and a second user device refer to different user devices, although both of them are user devices. For example, a first element can be referred to as a second element, and similarly, a second element can be referred to as a first element without departing from the scope of the present disclosure.

[0032] It will be understood that when an element (e.g., a first element) is referred to as being (operably or communicatively) "connected to" or "coupled to" another element (e.g., a second element), the element may be directly connected or coupled to the other element, or any other element (e.g., a third element) may be interposed therebetween. Conversely, when an element (e.g., a first element) is referred to as being "directly connected" or "directly coupled to" another element (the second element), no element (e.g., a third element) is interposed therebetween.

[0033] In the present disclosure, the terms are used to describe specific embodiments and do not limit the present disclosure. As used herein, the singular form is intended to also include the plural form, unless the content clearly indicates otherwise. In the specification, it should be understood that the term "including" or "having" represents the presence of a feature, number, step, operation, structural element, component or combination thereof, without excluding in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, structural elements, components or combinations thereof.

[0034] It should be understood that certain details are provided in the following description to facilitate a complete understanding of the example embodiments. However, one of ordinary skill in the art should understand that the example embodiments can be implemented without these specific details. For example, the system can be shown in a block diagram to avoid obscuring the example with unnecessary details. In other examples, well-known processes, structures, and techniques may not be shown in unnecessary details to avoid obscuring the example.

[0035] Settlement mechanism of earth pressure balance shield construction and difficulties in shield construction

[0036] like Figure 1 , Figure 2 , Figure 7 to Figure 9 As shown, the main machine of the earth pressure balance shield and its supporting parts include a cutterhead 1, a front shield 4, a middle shield 6, a shield tail 7, a segment assembler 8, a shield tail brush 9, a screw conveyor 11, a screw conveyor rear gate 12, a belt 13 and other components. The shield construction process is that the cutterhead 1 rotates, the thrust cylinder pushes forward on the front end surface of the segment 10, and the tool on the cutterhead 1 cuts the soil on the front face. The soil enters the soil bin 20 after being improved, and is transported to the hopper car in the trolley through the screw conveyor 11, the screw conveyor rear gate 12, and the belt 13, and then transported away. When the shield advances about a ring of segments 10, it stops advancing, and the segment assembler 8 is used to assemble multiple segments 10 into a ring in the shield tail 7 in sequence, and the segments 10 are fixed to the previous ring of segments 10 with the segment 10 bolts. The shield tail brush 9 is used to seal the segment 10 and the shield tail 7, and the shield tail sealing grease is filled between the multiple rows of shield tail brushes 9.

[0037] like Figure 1 , Figure 2As shown, the shield cutter head 1 excavates the soil to form a tunnel, the shield moves forward in this tunnel, and the multi-ring segments 10 form a shaped tunnel and finally stay in the excavated tunnel. The slag excavated by the cutter head 1 and the original soil in front of the excavation face are in two states. In order to prevent the original soil from deforming, the excavated slag must have equal support pressure. This is the balance of the excavation face. If the slag pressure is lower than the water and soil pressure of the original soil, it will cause settlement 15 at the cutter head excavation and settlement 14 in front of the cutter head. The shield body moves forward in the excavation tunnel, and the shield excavation diameter must be larger than the shield body diameter. At the same time, the diameters of the front shield 4, the middle shield 6, and the shield tail 7 become smaller in sequence. Due to the effect of gravity, the lower parts of the front shield 4 and the middle shield 6 are in contact with the excavation forming surface 24, and there are gaps between the shield body and the left and right and upper parts of the excavation forming surface 24. If the excavated stratum does not form an arch, the nearby stratum will deform (settle), forming a settlement 16 above the shield body. In order to prevent settlement, it is necessary to take measures to fill the gap and ensure the balance between the shield body and the excavation molding surface 24. As the shield body moves forward, there is a gap between the outer diameter of the segment 10 and the excavation molding surface 24 after the segment 10 escapes from the shield tail 7. The conventional practice is to inject a coagulated single liquid slurry simultaneously. However, due to the reasons that the single liquid slurry is easy to lose and easy to flow into the soil bin 20 through the shield body, the upper part behind the segment 10 that escapes from the shield tail 7 is not fully filled, and the balance between the segment 10 and the excavation molding surface 24 is not formed, which causes the surface to settle behind the shield tail 17. During the solidification process of the synchronous slurry, due to the effect of the formation pressure or the slurry pressure, part of the water in the synchronous slurry will be lost before the synchronous slurry is completely solidified. For the formation with high permeability (such as sand layer, sand and gravel formation), the water loss rate is higher, which leads to settlement behind the shield tail 18. In order to avoid the settlement behind the shield tail 18, the volume of water loss must be supplemented during the synchronous slurry water loss process to achieve a balance between the back of the segment 10 and the excavation profile 24. During the shield tunneling process, the nearby strata are disturbed, and the disturbed strata will continue to change under the action of gravity, forming a continuous settlement 19, but this settlement value is generally very small. In summary, if the balance of the excavation surface is achieved, the settlement in front of the cutterhead 14 and the settlement at the cutterhead excavation 15 can be controlled; if the balance between the shield body and the excavation profile 24 is achieved, the settlement above the shield body 16 can be controlled; if the balance between the segment 10 and the excavation profile 24 is achieved, the settlement at the rear of the shield tail 17 and the settlement behind the shield tail 18 can be controlled; if the entire shield construction process is balanced, there will be no continuous settlement 19.

[0038] like Figure 3 As shown in the figure, the method for controlling micro-deformation of earth pressure balance shield construction includes: controlling micro-deformation of earth pressure balance shield construction through precise pressure maintenance, mud injection of shield body, synchronous double-liquid slurry injection and multiple grouting.

[0039] In a preferred embodiment, the comprehensive slag improvement method using foam and low-concentration polyacrylamide aqueous solution includes: a good slag state is a necessary condition, by combining one or more slag improvers such as foam, bentonite slurry, polyacrylamide aqueous solution, sodium polyacrylate aqueous solution, and sodium carboxymethyl cellulose aqueous solution, using slump measurement, direct shear test, slag permeability test, water dispersibility test, and water retention test, it is finally determined that the ideal slag for the earth pressure balance shield should be in a plastic state with appropriate internal friction angle, low permeability, high water dispersibility, and high water retention rate. The comprehensive slag improvement method using foam and low-concentration polyacrylamide aqueous solution (polyacrylamide's high thickening properties can convert free water in the slag into weakly bound water) is the easiest to achieve the ideal slag state, and proposes the slag improver ratios for different strata. Figure 1 As shown, in order to achieve the ideal slag state for preventing gushing and mud cake formation in the earth pressure balance shield, in addition to injecting foam through the foam pipeline in front of the cutter head 1, a low-concentration polyacrylamide aqueous solution is injected into the center 2 in front of the cutter head, the center 3 of the soil bin and the top 5 of the soil bin. The injection amount is mainly in the center 2 in front of the cutter head and the center 3 of the soil bin. The injection amount is adjustable and visible, which can prevent gushing during shield excavation and mud cake formation in the center 3 of the soil bin to the greatest extent.

[0040] Mixing ratio of soil conditioner in different strata

[0041]

[0042] In a preferred embodiment, it also includes a method for accurately maintaining the pressure of the soil bin 20, such as Figure 4 to Figure 7 As shown in the figure, based on the anisotropic characteristics of the soil skeleton, the stratum above the excavation surface of the currently commonly used peripheral arc-shaped cutterhead 1 does not deform (when the pressure of the soil bin 20 is lower than the active balance pressure 21, the stratum above the excavation surface will settle, and when the pressure of the soil bin 20 is higher than the passive balance pressure 23, the stratum above the excavation surface will bulge), the forces on the soil body cut by the micro-unit are analyzed, and the balance pressure value and balance pressure range of any point on the excavation surface of the cutterhead 1 under the dynamic conditions of shield excavation are derived. Finally, the pressure of the shield soil bin 20 of the peripheral arc-shaped cutterhead 1 should be between the active balance pressure 21 and the passive balance pressure 23, and when the pressure 22 of the top soil bin is at the original soil self-weight stress, the stratum above the excavation surface can achieve a micro-deformation or even zero deformation effect.

[0043] The active balance pressure 21 refers to the minimum soil bin pressure 22 at which the original soil outside the excavation surface does not sink downward. The passive balance pressure 23 refers to the maximum soil bin pressure 22 at which the original soil outside the excavation surface does not rise upward. Figure 7It can be seen that the balance pressure at the opening above the excavation surface of the cutter disc 1 is the self-weight stress of the stratum, and the soil bin pressure 22 is lower than the self-weight stress settlement and higher than the self-weight stress uplift. The active balance pressure 21 in front of the excavation surface of the cutter disc 1 is the static lateral soil pressure (self-weight stress multiplied by the lateral pressure coefficient), and the passive balance pressure 23 in front of the excavation surface of the cutter disc 1 is the self-weight stress divided by the lateral pressure coefficient. The active balance pressure 21 below the excavation surface of the cutter disc 1 is the self-weight stress multiplied by the square of the lateral pressure coefficient. The passive balance pressure 23 below the excavation surface of the cutter disc 1 is the self-weight stress divided by the square of the lateral pressure coefficient. Since the size of the soil bin pressure 22 mainly depends on the top soil bin pressure 22, when the top soil bin pressure 22 is at the original soil self-weight stress, the stratum above the excavation surface can achieve micro-deformation or even zero deformation.

[0044] In a preferred embodiment, in order to prevent the shield from being stuck, the shield excavation diameter is larger than the shield diameter, and the diameters of the front shield 4, the middle shield 6 and the shield tail 7 are successively reduced, and there is a gap here when the shield passes through the excavated tunnel. This shield design defect can cause the upper part of the shield to sink 16, the synchronous slurry to flow to the soil bin 20, the shield to be wrapped, and the shield to gush.

[0045] like Figure 8 , Fig. 9 As shown, the present invention also includes a synchronous mud injection method for the middle shield 6 and the shield tail 7, which injects plastic mud 25 at two middle shield 6 mud injection points at the upper part of the middle shield 6 and two shield tail 7 mud injection points at the lower part of the shield tail 7 to fill the upper gap of the shield body and the lower gap of the shield tail 7, thereby solving the above-mentioned problem. The plastic mud 25 is a calcium-based bentonite: water: water glass with a mass ratio of 15:12:1. The design of the two shield tail 7 mud injection points at the lower part of the shield tail 7 can effectively prevent the synchronous slurry from flowing to the lower part of the suspended shield tail 7, and prevent the lower part of the shield tail 7 from being wrapped by the synchronous slurry.

[0046] Design of mud injection point on the upper part of Zhongdun 6:

[0047] Position selection: Select the symmetrical position of the upper center of the middle shield 6 to ensure uniform filling. The distance should be suitable for the overall structure of the shield, usually 1-2 meters apart.

[0048] Mud injection port structure: an adjustable valve is used to control the amount of mud injection, and a pressure sensor is equipped for real-time monitoring. Design of mud injection point at the bottom of shield tail 7:

[0049] Position selection: The mud injection point at the lower part of the shield tail 7 should be set at the edge of the shield tail 7 to prevent affecting the assembly of the pipe segment 10 in the shield tail 7.

[0050] Anti-backflow design: A reverse valve is designed to prevent mud from flowing back to the injection port and maintain a stable injection pressure.

[0051] In a preferred embodiment, a method of synchronously injecting dual-liquid slurry is also included. Based on the problem that the settable single-liquid slurry easily causes the pipe segment 10 to float up and the ground to settle, a technology of synchronously injecting dual-liquid slurry is adopted with a thickener polyacrylamide aqueous solution as liquid B. Through seven comparative tests of single-liquid slurry and dual-liquid slurry on expansion, consistency, compressive and flexural strength, initial and final setting time, water resistance, water-land strength ratio, and water loss rate, dual-liquid slurry has the advantages of not easy to block the grouting pipe, no buoyancy, strong water resistance, and good water retention. It can improve the quality of the formed tunnel, reduce the cost of shield construction, and improve the construction progress. The synchronous dual-liquid slurry formula is shown in Table 2;

[0052] Table 2 Double liquid slurry mix ratio

[0053]

[0054] In a preferred embodiment, the solidification of the synchronous slurry of the shield is a continuous process, with an initial setting time of about 8 hours and a final setting time of 40 hours. During the solidification process, water will be lost due to the rock and soil pressure around the tunnel. For strata with high permeability (such as gravel strata and sand strata), the water loss is more serious, and the volume of the synchronous slurry will shrink. If the lost part is not replenished in time, the stratum will settle. Therefore, in addition to improving the filling rate of synchronous grouting, it is also necessary to take multiple grouting measures for the unsaturated areas caused by water loss during the solidification of the synchronous slurry. At regular intervals (such as 6 to 8 hours), the grouting holes at the top of the segment 10 in the shield trolley range are opened for grouting (it can be single liquid slurry or double liquid slurry) to supplement the volume shrinkage caused by water loss of the synchronous slurry, ensure the balance between the segment 10 and the excavation molding surface 24, control the surface settlement, and achieve the goal of controlling micro-deformation during shield excavation.

[0055] The present invention combines shield body mud injection, synchronous dual-liquid slurry injection and multiple grouting schemes to achieve the filling of gaps in the entire shield construction process and effectively control surface settlement. The shield body mud injection volume can be injected according to 105% of the theoretical volume (the volume of the gap between the shield excavation diameter and the outer surface of the shield tail). Although the permeability of the synchronous dual-liquid slurry injection is much lower than that of the single-liquid slurry, it is still necessary to determine the reasonable synchronous grouting volume based on geological conditions and other factors. According to the geological exploration situation, understand the surrounding rock and soil properties, permeability, density and other information. Adjustment of grouting volume for different strata, case one, strata with high permeability (such as sand layers, gravel layers). In view of the high permeability and severe early water loss, it is recommended to increase the grouting volume. Adjustment factor: increase the grouting volume by 20%-30%. Example: If the calculated theoretical grouting volume is 10m 3 , then considering the infiltration and water loss, adjust to 12-13m 3 Case 2: Ordinary strata (such as clay layers). The synchronous grouting volume can be adjusted based on the theoretical calculation results. Adjustment factor: The theoretical grouting volume remains unchanged, or is slightly increased by 5%-10%. Example: The theoretical grouting volume is 10m 3, then adjust to 10.5-11m 3 In the multiple grouting scheme, grouting is carried out every 6-8 hours according to the water loss rate, and adjusted according to the geological conditions. Generally, the grouting frequency is higher (such as 4-5 times) in the strata with high permeability (such as sand layer, gravel layer), and lower (such as 1-2 times) in the ordinary strata (such as clay layer). The amount of grouting each time should be based on the injection pressure. The maximum pressure should not exceed the bearing capacity of the pipe segment, generally not exceeding 3bar. Monitor the pressure in the tunnel and the displacement of the surrounding strata in real time, and increase the grouting frequency or adjust the grouting amount when necessary.

[0056] like Figure 3 As shown in the figure, the surface settlement of shield construction occurs during the shield excavation process, the shield body passing through and the shield tail coming out. The micro-deformation control of the whole shield construction process is achieved through precise pressure maintenance of the soil bin, mud injection of the shield body, synchronous injection of double liquid slurry and multiple grouting. Through a detailed analysis of the settlement mechanism of the whole shield construction process, it is proposed that only when the shield excavation surface is balanced, the shield body and the excavation forming surface 24 are balanced, and the pipe segment 10 and the excavation forming surface 24 are balanced, can the shield construction be truly micro-deformed or even zero deformed. Through the comprehensive slag improvement method of foam plus low-concentration polyacrylamide aqueous solution and the precise pressure maintenance of the soil bin 20, the precise pressure maintenance control of the current peripheral arc-shaped cutter head 1 excavation surface is achieved, and the water and soil pressure balance between the slag in the soil bin 20 of the shield excavation surface and the original soil can be achieved; through the method of synchronously injecting plastic mud 25 at the two mud injection points of the middle shield 6 and the two mud injection points of the shield tail 7 as the shield advances, the balance between the shield body and the excavation forming surface 24 is achieved, and at the same time, the settlement 16 above the shield body, the loss of synchronous slurry, and the easy wrapping of the shield body are solved. The many problems of easy gushing during shield tunneling are solved; through the synchronous injection of double-liquid slurry technology, the slurry is thickened from a single-liquid slurry fluid to a plastic body, thereby achieving a balance between the segment 10 and the excavation forming surface 24 when the shield tunneling segment 10 is out of the shield tail 7, and at the same time solving the problems of floating of the segment 10, easy loss of slurry, low stone rate and high grouting cost; by replenishing the slurry behind the segment 10 on the shield trolley for many times, compensating for the water loss of the synchronous slurry during the solidification process, the balance between the segment 10 and the excavation forming surface 24 is continuously achieved.

[0057] Some advantages and precautions of the present invention

[0058] (1) The shield construction achieves the whole process balance of the shield excavation surface, the shield body and the excavation forming surface 24, and the segment 10 and the excavation forming surface 24 through precise pressure maintenance of the soil bin 20, mud injection of the shield body, simultaneous injection of dual-liquid slurry and multiple grouting, thus achieving micro-deformation control of the shield construction.

[0059] (2) It is proposed that the ideal slag for earth pressure balance shield should have a plastic state with appropriate internal friction angle, low permeability, high water dispersion resistance and high water retention rate. Through multiple tests, it is determined that the comprehensive slag improvement method of foam plus low-concentration polyacrylamide aqueous solution is the easiest to achieve the ideal slag state, which can prevent gushing and mud cake formation and is more suitable for precise pressure maintenance.

[0060] (3) The shield mud injection technology solves the difficulties in shield construction, such as the settlement of the stratum above the shield, the easy flow of synchronous slurry into the soil bin 20, and the shield being easily wrapped.

[0061] (4) The invented simultaneous injection of thickened plastic dual-liquid slurry technology solves the problem of the pipe segment 10 floating up, improves the quality of the formed tunnel, speeds up the shield construction progress, and reduces the shield construction cost.

[0062] (5) Multiple grouting and filling behind the segments 10 simultaneously reduces the water loss during the solidification process of the slurry, effectively controlling the settlement of the shield tail 18.

[0063] (6) Each process of the present invention solves its own shield construction problem and effectively controls the deformation of the shield construction. Each process is indispensable and can be promoted and applied as a general technology of earth pressure balance shield.

[0064] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for controlling micro-deformation during construction of an earth pressure balance shield, characterized in that: include: Micro-deformation control of earth pressure balance shield construction is achieved through precise pressure maintenance, shield mud injection, simultaneous dual-liquid slurry injection and multiple grouting.

2. The method for controlling micro-deformation during construction of an earth pressure balance shield according to claim 1, characterized in that: The comprehensive soil improvement method using foam and low-concentration polyacrylamide aqueous solution includes: using different soil improver ratios for different strata; injecting foam through the foam pipeline in front of the cutter head, and injecting low-concentration polyacrylamide aqueous solution in the center in front of the cutter head, the center of the soil bin and above the soil bin, so as to achieve the goal of precise pressure maintenance.

3. The method for controlling micro-deformation during construction of an earth pressure balance shield according to claim 1, characterized in that: Mixing ratio of soil conditioner in different strata 4. The method for controlling micro-deformation during construction of an earth pressure balance shield according to claim 1, characterized in that: It also includes a precise soil bin pressure-maintaining method, in which the soil bin pressure of the surrounding arc-shaped cutterhead shield should be between the active balance pressure and the passive balance pressure.

5. The method for controlling micro-deformation during construction of an earth pressure balance shield according to claim 1, characterized in that: It also includes a synchronous mud injection method for the middle shield and the shield tail, which injects plastic mud at two middle shield mud injection points on the upper part of the middle shield and two shield tail mud injection points on the lower part of the shield tail to fill the upper gap of the shield body and the lower gap of the shield tail.

6. The method for controlling micro-deformation during construction of an earth pressure balance shield according to claim 1, characterized in that: It also includes a synchronous double-liquid slurry injection method, which uses a thickener polyacrylamide aqueous solution as liquid B. The synchronous double-liquid slurry formulation is shown in Table 2; Table 2 Double liquid slurry mix ratio 7. The method for controlling micro-deformation during construction of an earth pressure balance shield according to claim 1, characterized in that: It also includes multiple grouting methods, which take multiple grouting measures for the incomplete areas caused by water loss during the solidification process of the synchronous slurry; at regular intervals, holes are opened at the grouting holes on the top of the segments within the shield trolley range to replenish the volume shrinkage caused by water loss of the synchronous slurry, thereby ensuring the balance between the segments and the excavation forming surface.

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