Targeted precise grouting method for three areas at top of tunnel in sand-gravel locking stratum

Abstract

The invention discloses a targeted precise grouting method for locking three areas at the top of a sandy gravel stratum tunnel, which comprises the following steps of: constructing a mathematical physical model of the three areas at the top of the tunnel, deducing an instability criterion and a stability analysis mechanical model of a tunnel face of the sandy gravel stratum tunnel, locking the positions of the three areas of the sandy gravel stratum tunnel, and verifying through a simulation experiment table. And the locked three-area position of the sandy gravel stratum tunnel is reinforced through a spatial vertical crossing targeted accurate advanced grouting reinforcement method, and the three-area position of the sandy gravel stratum tunnel comprises a caving area, a key control area and a sinking area from bottom to top. According to the technical scheme provided by the invention, technical support is provided for solving the problem of collapse engineering induced by sand-gravel stratum tunnel construction, the mechanism of water and mud bursting and collapse evolution of the tunnel can be revealed, pre-judgment and corresponding grouting, supporting and other measures can be taken, surface collapse and damage to the surface environment are avoided, and thus safe tunneling construction of the tunnel is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of advanced grouting reinforcement for tunnels, and particularly to a method for targeted and precise grouting in three zones at the top of a tunnel in a sandy cobble stratum. Background Art

[0003] In a sandy gravel stratum, there is no cementation, the structure is loose, and each single stone has a relatively high strength, but the overall self-stabilizing ability is poor, the permeability coefficient is high, the cohesion is small, and the voids between particles are large. Therefore, after the sandy gravel stratum is disturbed by excavation, the face of the tunnel heading will become unstable, which will not only seriously threaten the safety of on-site construction personnel, but also affect the later use of the tunnel, and even break the self-balance of the original ecosystem, damage the ecological environment, and cause secondary environmental disasters such as water resource depletion and ground settlement around the tunnel. Using grouting reinforcement is an effective means to solve the difficulty of tunnel excavation in a sandy gravel stratum, which can enhance the bearing capacity and stability of the stratum and provide guarantee for the smooth excavation and long-term operation of the tunnel. However, if the layout position of the grouting holes is unreasonable, it will not only cause waste of grouting materials, but also result in poor grouting effect and it is difficult to achieve a reliable reinforcement effect.

[0004] It should be specifically noted that the above technical information is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of implication that the above technical information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0005] Aiming at the deficiencies in the above background art, the present invention proposes a method for targeted and precise grouting in three zones at the top of a tunnel in a sandy cobble stratum, which solves the technical problem that the existing grouting reinforcement method cannot reliably reinforce the tunnel in a sandy cobble stratum.

[0006] The technical solution of the present application is as follows:

[0007] A method for targeted and precise grouting in three zones at the top of a tunnel in a sandy cobble stratum, which constructs a mathematical and physical model of three zones at the top of the tunnel, deduces the instability criterion and the mechanical model for stability analysis of the face of the tunnel in a sandy cobble stratum, locates the positions of three zones at the top of the tunnel in the sandy cobble stratum, and uses a spatial three-dimensional cross-targeted and precise advanced grouting reinforcement method to reinforce the located positions of three zones at the top of the tunnel. The three zones at the top of the tunnel include the caving zone, the key control zone, and the subsidence zone from bottom to top in the tunnel in a sandy cobble stratum.

[0008] On the basis of the above technical solution, as a preferred technical solution of the method for targeted and precise grouting in three zones at the top of a tunnel in a sandy cobble stratum, the mathematical and physical model is:

[0009] H1 + H2 + H3 = H (1);

[0010] In formula (1), H is the total height of the overlying rock above the tunnel in the sandy cobble stratum; H1 is the height of the caving area; H2 is the height of the key control area; H3 is the height of the subsidence area;

[0011] The expression of the instability criterion is derived from the above formula (1):

[0012] H1 + H3 ≥ H (2).

[0013] Based on the above technical solution, as an optimized technical solution of the three - zone targeted precise grouting method for locking the top of the tunnel in the sandy cobble stratum, the spatial three - dimensional cross - targeted precise advanced grouting reinforcement method includes using long holes to lock the key control area for advanced targeted precise grouting reinforcement, and also includes using short holes to inject foamed filling materials to seal the caving area. The reinforcement holes in the key control area and the sealing holes in the caving area form a spatial three - dimensional cross tunnel collapse prevention and control system.

[0014] Based on the above technical solution, as an optimized technical solution of the three - zone targeted precise grouting method for locking the top of the tunnel in the sandy cobble stratum, the spatial three - dimensional cross - targeted precise advanced grouting reinforcement method also includes using ground grouting reinforcement to reinforce the subsidence area and tunnel lining support measures.

[0015] Based on the above technical solution, as an optimized technical solution of the three - zone targeted precise grouting method for locking the top of the tunnel in the sandy cobble stratum, the ground settlement empirical formula derived by Peck can be used to obtain the ground settlement amount H3 during shield construction.

[0016]

[0017] In formula (3): H3 - the surface settlement value at a distance of X from the tunnel center axis, unit: m;

[0018] i - the ground settlement trough width coefficient, unit: m;

[0019] S - the maximum ground settlement amount at the tunnel center line, unit: m;

[0020]

[0021] In formula (4): i - the ground settlement trough width coefficient, unit: m;

[0022] V i - the ground loss per unit length of the tunnel caused by construction, unit: m 3 / m;

[0023]

[0024] In formula (5): - the angle of internal friction of the soil, unit: °;

[0025] H——Total height of overlying rock above the top of the tunnel in sandy cobble stratum, unit: m;

[0026] V i ——Stratum loss per unit length of the tunnel caused by construction, unit: m 3 / m;

[0027] Then the ground settlement can be obtained

[0028] On the basis of the above technical solution, as an optimized technical solution for the targeted precise grouting method in the three areas at the top of the tunnel in sandy cobble stratum, a face stability analysis model is established by combining the ellipsoid theory and the logarithmic spiral model of the limit equilibrium method. An origin O is established on the upper side of the excavated part of the tunnel, and the angle between the bottom end of the slip surface and the horizontal plane is θ; D is the tunnel diameter; l n is the horizontal distance from the origin O to the face; l i is the horizontal distance from the face to the center of the ellipsoid; l m is the horizontal distance from the origin O to the center of the ellipsoid; σ t is the ultimate support force to maintain the face stability; h s is the height from the lowest point of the ellipsoid to the tunnel crown; the initial radius of the logarithmic spiral is r0: the radius of the logarithmic spiral corresponding to the bottom end of the slip surface is r a ; a is the short semi-axis of the ellipsoid: b is the long semi-axis of the ellipsoid; r a The included angle with r0 is α; According to the geometric relationship, it can be known that:

[0029] r = r0exp(θtanφ);

[0030]

[0031] In the formula, L = 2l i is the width of the sliding soil mass in front of the face; ε is the eccentricity; Assuming that the axis ratio of the ellipsoid is equal to the lateral pressure coefficient, then 1 - ε 2 = a 2 / b 2 ; Among them, The geometric parameters of the ellipsoid are: short axis length Long axis length And H1 + h s = 2b;

[0032] From H1 + H2 + H3 = H, substituting H1 and H3 into equation (1) gives H2:

[0033]

[0034] On the basis of the above technical solution, as an optimized technical solution for the targeted precise grouting method in the three zones at the top of the tunnel in sandy cobble strata, a simulation test bench for the spatio-temporal evolution law of the three zones at the top of the tunnel in sandy cobble strata is designed, and the simulation test bench is used to verify the instability criterion of the tunnel face in sandy cobble strata and the mechanical model for stability analysis derived from the mathematical and physical model.

[0035] On the basis of the above technical solution, as an optimized technical solution for the targeted precise grouting method in the three zones at the top of the tunnel in sandy cobble strata, the simulation test bench includes a rectangular test box storing sandy cobble strata, a rainfall system, and a multi-information detection system. The shield excavation is simulated for the prepared strata in the rectangular test box, and the multi-information detection system is used to monitor the changes in soil temperature, soil pressure, surface and settlement of the strata above the tunnel, and stress and strain changes around the tunnel during the excavation process inside the rectangular test box, so as to obtain the settlement evolution law of the three zones at the top of the tunnel during the construction of the sandy cobble strata tunnel. The multi-information detection system is used to measure the specific heights of the three zones at the top of the tunnel outside the rectangular test box to determine the positions of the three zones at the top of the tunnel.

[0036] On the basis of the above technical solution, as an optimized technical solution for the targeted precise grouting method in the three zones at the top of the tunnel in sandy cobble strata, the rectangular test box includes a high-strength steel structure and a transparent acrylic board. The water seepage and deformation conditions inside the rectangular test box are observed through the transparent acrylic board, and the images taken by the camera outside the rectangular test box are compared and analyzed.

[0037] On the basis of the above technical solution, as an optimized technical solution for the targeted precise grouting method in the three zones at the top of the tunnel in sandy cobble strata, the rainfall system controls the rainfall intensity by precisely adjusting the water output of the nozzle and the water output of the water tank, and the nozzle is an irrigation micro-spray atomizing copper nozzle.

[0038] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0039] The technical solution provided by the present invention realizes the targeted precise grouting of the three zones at the top of the tunnel in sandy cobble strata by constructing a mathematical and physical model for the excavation of the three zones of the tunnel in sandy cobble strata, an instability criterion for the tunnel face, and locking the positions of the three zones of the tunnel in sandy cobble strata. In the tunnel, plugging holes are used for filling in the caving area, reinforcement holes in the key control area are grouted for reinforcement, and ground grouting is used for reinforcement in the surface subsidence area. Finally, a three-dimensional spatial cross tunnel prevention and control system for collapse is formed by the cooperation of the reinforcement holes and plugging holes in the tunnel and surface grouting. The technical solution provided by the present invention provides technical support for solving the engineering problem of tunnel collapse induced by the construction of sandy cobble strata tunnels, thus ensuring the safe tunneling construction of the tunnels.

[0040] The technical solution provided by the present invention constructs a three-zone model for tunnels in sandy pebble strata, deduces the instability criterion for the tunnel face, reveals the mechanisms of water and mud inrush and collapse evolution in the tunnel, and combines the pressure manifestation characteristics of the overlying rock strata of the tunnel to enable early prediction and take corresponding measures such as grouting and support to avoid surface collapse and damage to the surface environment.

[0041] Due to the loose strata of the tunnel in gravel strata, there are risks of difficult construction and high risks during the tunnel construction process. The present invention proposes a three-zone collapse model of a falling area, a key control area, and a sinking area that appears from bottom to top during the excavation of a tunnel in sandy pebble strata according to the imbalance characteristics of the sandy pebble strata, and studies the seepage distribution and strata deformation laws in the sandy pebble strata, as well as the mechanisms of water and mud inrush and collapse in water-rich tunnels.

[0042] The technical solution provided by the present invention can determine the positions of the three zones at the top of the tunnel according to the parameters in the relational expression of the key control area, lock the key control area for advanced targeted precision grouting reinforcement, and use plugging holes to inject foaming filling materials to plug the falling area, forming a three-dimensional cross tunnel prevention and control collapse system with long-hole reinforcement and short-hole plugging. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0044] Figure 1 It is a mathematical and physical model of the three zones of a tunnel in sandy pebble strata;

[0045] Figure 2 It is a schematic diagram for strengthening the locked positions of the three zones of a tunnel in sandy pebble strata;

[0046] Figure 3 It is a mechanical model for the stability analysis of the tunnel face of a tunnel in sandy pebble strata;

[0047] Figure 4 It is a front view of the simulation test bench;

[0048] Figure 5 It is a sectional view of the simulation test bench. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the core concept of the present invention and the following embodiments, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0050] These embodiments are provided in this application to make this application thorough and complete, and to fully convey the scope of this application to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the compositions of materials, numerical expressions and values described in these embodiments should be construed as merely exemplary, rather than as limitations.

[0051] It should be noted that in the description of this application, unless otherwise specified, the meaning of "several" is greater than or equal to two; the orientation or positional relationships indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", "axial", "radial", etc. are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of this application. When the absolute position of the object being described changes, then this relative position relationship may also change accordingly.

[0052] In addition, the "first", "second" and similar terms used in this application do not denote any order, quantity or importance, but are only used to distinguish different parts. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range. Terms such as "including" or "comprising" mean that the elements before this term cover the elements listed after this term, and do not exclude the possibility of also covering other elements.

[0053] It should also be noted that in the description of this application, unless otherwise clearly specified and limited, the terms "mounted", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations. When it is described that a specific device is located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0054] All terms used in this application have the same meanings as those understood by ordinary technicians in the field to which this application belongs, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such here.

[0055] Technologies, methods, and devices known to ordinary technicians in the relevant field may not be discussed in detail, but where appropriate, the technologies, methods, and devices should be regarded as part of the specification.

[0056] The present invention provides a method for targeted and precise grouting in three zones at the top of a tunnel in a sandy cobble stratum. The positions of the three zones at the top of the tunnel in the sandy cobble stratum are determined according to the parameters in the key control zone relationship expression. Long holes are used to lock the key control zone for advanced targeted and precise grouting reinforcement, and short holes are used to inject foamed filling materials to seal the caving zone, forming a three-dimensional cross tunnel prevention and control collapse system with long hole reinforcement and short hole sealing.

[0057] The object of the present invention can be achieved by the following technical solutions:

[0058] A method for targeted and precise grouting in three zones at the top of a tunnel in a sandy cobble stratum constructs a three-zone stratum settlement model of a caving zone, a key control zone, and a subsidence zone that appears from bottom to top during the excavation of a tunnel in a sandy cobble stratum. The spatio-temporal evolution law of the three zones at the top of the tunnel in the sandy cobble stratum is studied. As the tunnel is excavated, the stratum cavity in the caving zone moves upward, the shear failure zone of the tunnel face develops from bottom to top, the collapse zone increases, and the rainfall infiltration sandy cobble ground subsidence zone develops from top to bottom. When the subsidence zone and the collapse zone are connected and the key control zone approaches 0, a stratum collapse accident occurs.

[0059] Therefore, a mathematical and physical model of the three zones at the top of the tunnel in the sandy cobble stratum, a criterion for the instability of the tunnel face, and a mechanical analysis equation are constructed, and the positions of the three zones of the tunnel in the sandy cobble stratum are locked. A three-dimensional cross-targeted and precise advanced grouting reinforcement method with long hole reinforcement and short hole sealing is adopted. According to the mathematical and physical model of the three zones at the top of the tunnel, the criterion for the instability of the tunnel face is deduced, the mechanism of water and mud inrush and collapse evolution of the tunnel is revealed, and combined with the pressure manifestation characteristics of the overlying rock stratum of the tunnel, early prediction is carried out, and corresponding grouting, support and other measures are taken to avoid causing surface collapse and damaging the surface environment.

[0060] Furthermore, since the sandy cobble stratum is formed by mixing cobble particles of different sizes and shapes with sandy soil, the structure of the stratum is relatively loose, the particle gaps are relatively large, and the cohesion between particles is basically zero. When water and sand gush out due to the instability of the tunnel face, a cavity caving zone is formed. The sandy cobbles form an arch key control zone through force chain transmission in a point contact manner, and a large amount of sand particles are lost to form a subsidence zone of surface subsidence.

[0061] A three - zone ground settlement model is constructed for the excavation process of a tunnel in sandy pebble stratum, which shows a caving zone (with a height of H1), a key control zone (with a height of H2), and a subsidence zone (with a height of H3) from bottom to top. Among them, the soil layer in the key control zone will transfer along the subsidence zone and the caving zone due to inappropriate support force. Therefore, the thickness of the soil layer in the key control zone plays a crucial role in ground settlement.

[0062] As Figure 1 shown, the total thickness H of the overlying rock above the tunnel roof is expressed as follows:

[0063] H1 + H2 + H3 = H (1)

[0064] In the formula, H is the total height of the overlying rock above the tunnel roof, m; H1 is the height of the loosening zone, m; H2 is the key control zone, m; H3 is the height of the subsidence zone, m.

[0065] Furthermore, the theoretical basis for the instability criterion of the tunnel face is as follows: As the tunnel is excavated, the void in the caving zone of the stratum moves upward, the shear failure zone of the tunnel face develops from bottom to top, H1 in the caving zone increases, the ground subsidence zone develops from top to bottom, H3 increases. When the subsidence zone and the caving zone are connected, H2 decreases accordingly. When the key control zone approaches 0, a ground collapse accident occurs.

[0066] The above formula (1) is transformed into the tunnel ground collapse criterion expression as:

[0067] H1 + H3 ≥ H (2).

[0068] Furthermore, when water and sand gushing occur due to the instability of the tunnel face, a void caving zone is formed. To prevent the void in the caving zone of the stratum from moving upward and damaging the key control zone, resulting in a delayed ground collapse accident. According to the parameters in the key control zone relationship expression, the positions of the three zones at the tunnel roof are determined. Long holes are used to lock the key control zone for advanced targeted precision grouting reinforcement, and short holes are used to inject foaming filling materials to seal the caving zone, forming a three - dimensional cross - tunnel prevention and control collapse system of reinforcement holes and sealing holes, so as to enable the key control zone to play a key role in sandy pebble stratum.

[0069] Taking the construction of a water diversion tunnel in sandy pebble stratum in Luoyang area as the background, aiming at the stability problems in tunnel construction, the particle composition and hydrogeological conditions of the sandy pebble stratum are studied. According to the parameters in the key control zone relationship expression, the positions of the three zones at the tunnel roof are determined, and through the three - dimensional cross - targeted precision advanced grouting reinforcement of reinforcement holes and sealing holes, the grouting cost is reduced, and a theoretical and experimental basis is provided for the prevention and control of ground settlement during the construction process.

[0070] As a preferred implementation method, the ground settlement empirical formula derived by Peck can be used to obtain the ground settlement amount in shield construction projects.

[0071]

[0072] Where: H3—the ground settlement value (m) at a distance of X from the center axis of the tunnel;

[0073] i—the width coefficient of the ground settlement trough (m);

[0074] S—the maximum ground settlement at the center line of the tunnel (m)

[0075]

[0076] Where: —the internal friction angle of the soil (°);

[0077] H—the buried depth of the tunnel axis (m);

[0078] V i —the ground loss per unit length of the tunnel caused by construction (m 3 / m).

[0079] Combined with Figure 1 , the ground settlement can be sorted out Combined with the maximum propulsion speed of the shield machine of 80 mm / min, the maximum settlement H3≈5.1 m is calculated.

[0080] As a preferred implementation mode, a simplified mechanical model for the collapse area is as Figure 3 , a face stability analysis model is established by combining the ellipsoid theory and the logarithmic spiral model of the limit equilibrium method. An origin O is established on the upper side of the excavated part of the tunnel; the angle between the bottom of the slip surface and the horizontal plane is θ; H1 is the height of the upper collapsed body; D is the tunnel diameter; l n is the horizontal distance from the origin O to the face; l j is the horizontal distance from the face to the center of the ellipsoid; l m is the horizontal distance from the origin O to the center of the ellipsoid; σ t is the limit support force to maintain the face stability; h s is the height from the lowest point of the ellipsoid to the tunnel crown; the initial radius of the logarithmic spiral is r0: the radius of the logarithmic spiral corresponding to the bottom of the slip surface is r a ; a is the short semi-axis of the ellipsoid: b is the long semi-axis of the ellipsoid; the angle between r a and r0 is α; this model can better simulate the situation of the sliding soil mass in front of the face caused by the excavation of the shield tunnel in the sandy cobble stratum.

[0081] The following conclusions can be drawn according to the geometric relationship:

[0082]

[0083]

[0084] where; L = 2l i is the width of the sliding soil mass in front of the heading face; ε is the eccentricity; assuming the axis ratio of the ellipsoid is equal to the lateral pressure coefficient, then 1 - ε 2 = a 2 / b 2 . From the geometric relationship, the geometric parameters of the ellipsoid are further obtained as: the length of the minor axis the length of the major axis and H1 + hs = 2b. It is calculated that H1max ≈ 7.5m;

[0085] Then, substituting H1 and H3 into Equation (1) by H1 + H2 + H3 = H, the following equation can be obtained

[0086]

[0087] Therefore, the specific thickness positions of the three zones are determined as: the height of the collapse zone is H1 = 7.5m, the height of the key control zone is H2 = 48m, and the height of the subsidence zone is H3 = 5.1m. In the tunnel, the collapse zone is filled with plugging holes, the key control zone is grouted and reinforced with reinforcement holes, and the ground subsidence zone is grouted and reinforced on the ground. Finally, the targeted precise grouting of the three zones at the top of the tunnel in the cobble and pebble stratum is realized, and a collaborative spatial three-dimensional cross tunnel collapse prevention system of tunnel reinforcement hole reinforcement, plugging hole filling and surface grouting is formed

[0088] Furthermore, a simulation test bench for the spatio-temporal evolution law of the three zones at the top of the tunnel in the cobble and pebble stratum is designed, and the simulation test bench is used to verify the instability criterion and stability analysis mechanical model of the heading face of the tunnel in the cobble and pebble stratum derived from the mathematical and physical model

[0089] Specifically, as Figure 4 and Figure 5 shown, the simulation test bench includes a rectangular test box 1 storing the cobble and pebble stratum, a rainfall system 2, and a multi-information detection system 3. The shield excavation simulation is carried out on the prepared stratum in the rectangular test box 1, and the multi-information detection system 3 is used to monitor the changes in soil temperature, soil pressure, surface and settlement of the upper stratum of the tunnel, and stress and strain changes around the tunnel during the excavation process inside the rectangular test box 1, so as to obtain the settlement evolution law of the three zones at the top of the tunnel during the construction of the tunnel in the cobble and pebble stratum. The multi-information detection system 3 is used to measure the specific heights of the three zones at the top of the tunnel outside the rectangular test box 1 to determine the positions of the three zones at the top of the tunnel

[0090] Preferably, the rectangular test box 1 includes a high-strength steel structure and a transparent acrylic plate 101. The water seepage and deformation conditions inside the rectangular test box 1 are observed through the transparent acrylic plate 101, and the images taken by the camera 301 outside the rectangular test box 1 are compared and analyzed

[0091] Preferably, the rainfall system 2 controls the intensity of rainfall by precisely adjusting the water output of the sprinkler head and the water output of the water tank. The sprinkler head is an irrigation micro-spray atomizing copper sprinkler head.

[0092] Preferably, the simulation test bench mainly consists of a rectangular experimental box 1 for preparing the formation, a rainfall system 2, a multi-information detection system 3, etc.

[0093] The external dimensions of the rectangular experimental box 1 are 1500 mm in length × 1000 mm in width × 1500 mm in height. The main body is made of high-strength steel structure and transparent acrylic plate 101. The high-strength steel structure provides sufficient lateral stiffness to prevent soil collapse, ensure the controllability of the experiment, and the seepage and deformation conditions inside the rectangular experimental box 1 can be observed through the front transparent acrylic plate 101.

[0094] The rainfall system 2 includes a water storage tank 201, a water supply pipeline 202, and a rainfall sprinkler head 203. There are also drainage holes 204 for drainage at the bottom of the rectangular experimental box 1. By precisely adjusting the water output of the sprinkler head and the water output of the water storage tank, the intensity of rainfall can be effectively controlled. The rainfall sprinkler head used is an irrigation micro-spray atomizing copper sprinkler head, and the water it sprays is in a delicate water mist shape, and the water output can be flexibly adjusted according to specific needs, so as to achieve precise control of the rainfall intensity. The water supply pipeline of the rainfall system 2 is a black explosion-proof pipeline with an inner diameter of 8 mm. The water storage tank of the rainfall system 2 is a special thick horizontal plastic water tank made of high-density polyethylene raw material, and the flow rate can be adjusted through the main switch. To ensure uniform and controllable rainfall effect, a one-to-four splitter is used, and the water flow rate can be controlled through the branch switches of each line, so as to control the amount of rainfall.

[0095] The multi-information detection system 3 can collect various parameters such as temperature, displacement, earth pressure, and strain in real time. By comparing and analyzing the images taken by the camera 301, the movement law of gravel and egg particles in the formation when the tunnel is unstable and the corresponding deformation field and strain field are obtained. Preferably, an LED light source 302 is arranged outside the rectangular experimental box 1 to assist the camera 301 in taking pictures. Through this device and the supporting test technology, the spatio-temporal evolution of the three zones at the top of the tunnel is intuitively realized, and the settlement mechanism of the damaged part at the top of the tunnel and the top of the tunnel in the sand and gravel formation and the spatio-temporal evolution law between the two are revealed.

[0096] During each excavation process, the data changes of soil pressure sensors, pore water pressure sensors, displacement gauges, and strain gauges are recorded in real time. Once water seepage or sand and water gushing phenomena occur, excavation shall be immediately stopped, and the experimental phenomena shall be observed in a timely manner and the experimental data shall be collected and recorded. Given the difficulty in controlling the excavation footage and the requirements for test accuracy, the excavation footage for each excavation shall be strictly controlled throughout the entire test process. Under the combined action of rainfall and construction disturbance, as the tunnel is excavated, the face of the tunnel becomes unstable and collapses to form a cavity. The cavity in the stratum moves upward, and the cavity in the shear failure zone of the tunnel face develops from bottom to top. Since the sandy cobble stratum is formed by the mixture of cobble particles of different sizes and shapes and sandy soil, the structure of the stratum is relatively loose, the particle gaps are relatively large, and the cohesion between particles is basically zero. The rainfall infiltration causes the surface subsidence area of the sandy cobble to develop from top to bottom. The sandy cobbles form an arch key control area through force chain transmission in a point-contact manner. The excavation destroys the stability of the original soil layer, and the rainfall runoff begins to carry loose sandy soil, breaking through the key control area, and the subsidence area and the collapse area are connected, resulting in a stratum collapse accident.

[0097] That is, the entire experimental device includes a model box, a shield excavation system, a soil pressure monitoring system, a strain monitoring system, a soil layer settlement monitoring system, and a data acquisition and analysis system. The similar material proportioning technology is adopted to reproduce the heterogeneity and low cohesion characteristics of the sandy cobbles, ensuring a high similarity between the physical model and the prototype geomechanical behavior. By controlling the particle size distribution and porosity, the permeability and structural differences of the real stratum are simulated. Subsequently, the shield excavation simulation of the tunnel is carried out. Inside the model box, by monitoring the changes in soil pressure, surface settlement, and the settlement of the stratum above the tunnel during the excavation process, as well as the stress and strain changes around the tunnel, the settlement evolution law of the three zones at the top of the tunnel during the construction of the tunnel in the sandy cobble stratum is obtained. Outside the model box, the specific heights of the three zones are measured through an external endurance transparent plate, and the positions of the three zones are captured by the camera 301. Then, the positions of the three zones of the tunnel are determined. The three-dimensional cross-targeted precise advanced grouting reinforcement with long-hole reinforcement and short-hole plugging reduces the grouting cost and provides a theoretical and experimental basis for the prevention and control of stratum settlement during the construction process.

[0098] The details not elaborated in the present invention are all conventional technical means well known to those skilled in the art.

[0099] The above content shows and describes the basic principles, main features, and beneficial effects 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. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for targeted precise grouting in three zones at the top of a tunnel in a sandy pebble stratum, characterized in that: Construct a mathematical and physical model for the three zones at the top of the tunnel, derive the instability criterion and the mechanical model for the stability analysis of the tunnel face in sandy pebble strata, lock the positions of the three zones at the top of the tunnel in sandy pebble strata, and use the spatial three-dimensional cross-targeted precise advanced grouting reinforcement method to reinforce the locked positions of the three zones at the top of the tunnel. The three zones at the top of the tunnel include the caving zone, the key control zone, and the subsidence zone from bottom to top in the tunnel in sandy pebble strata.

2. The targeted precise grouting method for the top three zones of a tunnel in a locked sandy pebble stratum according to claim 1, wherein: The mathematical and physical model is as follows: H1 + H2 + H3 = H (1); In formula (1), H is the total height of the overlying rock at the top of the tunnel in sandy pebble strata; H1 is the height of the caving zone; H2 is the height of the key control zone; H3 is the height of the subsidence zone; The expression of the instability criterion is derived from the above formula (1): H1 + H3 ≥ H (2).

3. The targeted and precise grouting method for the top three zones of a tunnel in a locked sandy pebble stratum according to claim 2, characterized in that: The spatial three-dimensional cross-targeted precise advanced grouting reinforcement method includes using long holes to lock the key control zone for advanced targeted precise grouting reinforcement, and also includes using short holes to inject foamed filling materials to block the caving zone. The reinforcement holes in the key control zone and the blocking holes in the caving zone form a spatial three-dimensional tunnel anti-collapse prevention system.

4. The targeted precise grouting method for the top three zones of a tunnel in a locked sandy pebble stratum according to claim 3, characterized in that: The spatial three-dimensional cross-targeted precise advanced grouting reinforcement method also includes using ground grouting reinforcement to reinforce the subsidence zone and tunnel support measures.

5. The targeted precise grouting method for the top three zones of a tunnel in a locked sandy pebble stratum according to any one of claims 1-4, characterized in that: The ground settlement amount H3 in the shield construction project can be obtained from the empirical formula of ground settlement derived by Peck; In formula (3): H3 - the surface settlement value at a distance X from the tunnel center axis, unit: m; i - the ground settlement trough width coefficient, unit: m; S - the maximum ground settlement amount at the tunnel center line, unit: m; In formula (4): i - the ground settlement trough width coefficient, unit: m; V i —— Ground loss per unit length of tunnel caused by construction, unit: m 3 / m; In formula (5): —— The angle of internal friction of the soil, in °; H - the total height of the overlying rock at the top of the tunnel in sandy pebble strata, unit: m; V i ——Ground loss per unit length of tunnel caused by construction, unit: m 3 / m; Then the ground settlement can be obtained 6. The targeted and precise grouting method for the top three zones of a tunnel in a locked sandy pebble stratum according to claim 5, characterized in that: Establish a face stability analysis model by combining the ellipsoid theory with the logarithmic spiral model of the limit equilibrium method. Set the origin O on the upper side of the excavated part of the tunnel, and the angle between the bottom of the slip surface and the horizontal plane is θ; D is the tunnel diameter; l n is the horizontal distance from the origin O to the face; l i is the horizontal distance from the face to the center of the ellipsoid; l m is the horizontal distance from the origin O to the center of the ellipsoid; σ t is the ultimate support force to maintain the face stability; h s is the height from the lowest point of the ellipsoid to the tunnel crown; the initial radius of the logarithmic spiral is r0: the radius of the logarithmic spiral corresponding to the bottom of the slip surface is r a ; a is the short semi-axis of the ellipsoid: b is the semi-major axis of the ellipsoid; r a The included angle with r0 is α; According to the geometric relationship, it can be known that: r = r0exp(θtanφ); where L = 2l i is the width of the sliding soil mass in front of the heading face; ε is the eccentricity; assuming that the axis ratio of the ellipsoid is equal to the coefficient of lateral pressure, then 1 - ε 2 = a 2 / b 2 ; where the geometric parameters of the ellipsoid are: the length of the minor axis the length of the major axis and H1 + h s = 2b; From H1 + H2 + H3 = H, substituting H1 and H3 into formula (1), H2 can be obtained:

7. The targeted precise grouting method for the top three zones of a tunnel in a locked sandy pebble stratum according to claim 6, characterized in that: Design a simulation test bench for the spatio-temporal evolution law of the three zones at the top of the tunnel in sandy pebble strata, and use the simulation test bench to verify the instability criterion and the mechanical model for the stability analysis of the tunnel face in sandy pebble strata derived from the above mathematical and physical model.

8. The targeted precise grouting method for the top three zones of a tunnel in a locked sandy pebble stratum according to claim 7, characterized in that: The simulation test bench includes a rectangular test box (1) storing sandy pebble strata, a rainfall system (2), and a multi-information detection system (3). Simulate shield excavation on the prepared strata in the rectangular test box (1), and use the multi-information detection system (3) to monitor the changes in soil temperature, soil pressure, surface and subsidence of the strata above the tunnel, and stress and strain changes around the tunnel during the excavation process inside the rectangular test box (1) to obtain the settlement evolution law of the three zones at the top of the tunnel during the construction of the tunnel in sandy pebble strata. Use the multi-information detection system (3) to measure the specific heights of the three zones at the top of the tunnel outside the rectangular test box (1) to determine the positions of the three zones at the top of the tunnel.

9. The targeted precise grouting method for the top three zones of a tunnel in a sandy pebble stratum according to claim 8, characterized in that: The rectangular test box (1) includes a high-strength steel structure and a transparent acrylic plate (101). Observe the water seepage and deformation conditions inside the rectangular test box (1) through the transparent acrylic plate (101), and conduct comparative analysis on the images taken by the camera (301) outside the rectangular test box (1).

10. The targeted precise grouting method for the top three zones of a tunnel in a locked sandy pebble stratum according to claim 8 or 9, characterized in that: The rainfall system (2) controls the intensity of rainfall by precisely adjusting the water output of the sprinkler head and the water output of the water tank, and the sprinkler head is an irrigation micro-spray atomizing copper sprinkler head.

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