A method for predicting safety of a grout-stopping wall during roof falling of weak surrounding rock in a tunnel

Abstract

The present application relates to the field of tunnel construction, in particular to a safety prediction method for a tunnel soft surrounding rock roof fall when the grout retaining wall, comprising: obtaining the size of the tunnel cross section and the specific gravity of the mud body behind the grout retaining wall when the soft surrounding rock is not roof fall, so as to determine the initial thrust of the grout retaining wall by the mud body behind it; obtaining the impact pressure when the overburden above the cavity falls to the bottom of the cavity when the soft surrounding rock roof falls, and then determining the thrust acting on the grout retaining wall when the overburden above the cavity collapses based on the size of the tunnel cross section and the specific gravity of the mud body; calculating the total thrust on the grout retaining wall, and comparing the total thrust on the grout retaining wall with the resistance thrust of the grout retaining wall to judge the safety of the grout retaining wall. The present application has the advantages of strong process and reliable results, and can comprehensively master the safety performance of the grout retaining wall, providing protection for the safety of tunnel construction.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to a method for predicting the safety of the grout-stopping wall when the surrounding rock of a tunnel collapses. Background Technology

[0002] When tunnel excavation encounters weak surrounding rock and abundant groundwater, sudden water and mud inrush disasters are likely to occur. Once such a disaster occurs, cavities will appear above the tunnel arch. To prevent further damage, construction workers build concrete grout stop walls in front of the inrush. However, once these cavities form, the overlying layer loses its support, and the surface soil gradually loosens over time. During heavy rainfall or earthquakes, the overlying layer may collapse, leading to a tunnel roof collapse. The landslide material exerts a tremendous impact on the underlying rock and soil, further impacting the grout stop wall. If the collapse force is too great, the grout stop wall may be pushed away, thus losing its safety and its ability to prevent sudden water and mud inrushes. However, the safety of grout stop walls in the event of a surface roof collapse is largely based on engineering experience, and no relevant theoretical guidance for prediction is currently available.

[0003] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting the safety of the grout-stopping wall when the tunnel roof collapses due to weak surrounding rock, so as to solve or alleviate the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for predicting the safety of a grout-stopping wall when a tunnel experiences roof collapse due to weak surrounding rock, comprising the following steps:

[0007] Step S1: Obtain the dimensions of the tunnel cross section and the density of the mud-bursting body behind the grout stop wall when the weak surrounding rock has not collapsed, so as to determine the initial thrust of the grout stop wall on the mud-bursting body behind it.

[0008] Step S2: Obtain the impact pressure of the overburden layer above the cavity falling to the bottom of the cavity when the weak surrounding rock collapses; then determine the thrust acting on the grout stop wall when the overburden layer above the cavity collapses based on the dimensions of the tunnel cross section and the density of the mudslide.

[0009] Step S3: Calculate the total thrust on the grout-stopping wall and compare the total thrust with the thrust resistance of the grout-stopping wall itself to determine the safety of the grout-stopping wall.

[0010] Furthermore, in step S1, the dimensions of the tunnel cross-section are based on the height and width of the tunnel cross-section.

[0011] Furthermore, in step S1, the density of the mud mass is obtained and combined with the gravitational acceleration to determine the specific weight of the mud mass.

[0012] Furthermore, in step S2, the impact pressure when the cover layer falls to the bottom of the cavity is based on the mass of the cover layer soil, the height of the cavity, and the area of ​​the cavity in the horizontal plane.

[0013] Furthermore, the thickness of the cover layer, the area of ​​the voids in the horizontal plane, and the soil density of the cover layer are obtained to determine the mass of the cover layer soil.

[0014] Furthermore, in step S3, the resistance to thrust of the grout stop wall itself is based on the shear strength between the grout stop wall and the bottom of the tunnel, the length of the grout stop wall along the longitudinal direction of the tunnel, and the width of the tunnel cross section.

[0015] Beneficial effects: This invention provides a method for predicting the safety of a grout stop wall when the surrounding rock of a tunnel collapses. It can predict all the horizontal thrusts acting on the grout stop wall and the grout stop wall's own resistance to horizontal thrust when the overburden above the tunnel's surrounding rock cavity collapses. By comparing the magnitude of the total horizontal thrust and the grout stop wall's resistance to horizontal thrust, the stability of the grout stop wall can be determined. This method has the advantages of strong process flow and reliable results, thus ensuring the safety of the grout stop wall and providing a guarantee for the safety of tunnel construction. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art are within the scope of protection of the present invention.

[0017] This invention provides a method for predicting the safety of a grout-stopping wall when a tunnel experiences roof collapse due to weak surrounding rock, comprising the following steps:

[0018] Step S1: Obtain the dimensions of the tunnel cross section and the density of the mud mass protruding behind the grout stop wall when the weak surrounding rock has not collapsed, so as to determine the initial thrust of the grout stop wall on the mud mass protruding behind it.

[0019] Step S1.1: Determine the height of the tunnel cross section based on the tunnel design data. and the width of the cross section .

[0020] Step S1.2: Determine the unit weight of the mud protruding behind the grout-stopping wall. Drilling was conducted behind the grout stop wall using a drilling rig. The undisturbed soil mass behind the grout stop wall was removed and transported back to the laboratory. Density testing was performed using the ring cutter method. After obtaining the density, it was multiplied by the acceleration due to gravity to obtain its unit weight. .

[0021] Step S1.3: Determine the initial horizontal thrust on the grout-stopping wall when the overburden above the cavity has not collapsed. The calculation method is as follows:

[0022] .

[0023] Step S2: Obtain the impact pressure of the overburden layer above the cavity falling to the bottom of the cavity when the weak surrounding rock collapses. Then, based on the dimensions of the tunnel cross section and the density of the mudslide, determine the thrust acting on the grout stop wall when the overburden layer above the cavity collapses.

[0024] Step S2.1: Determine the area of ​​the tunnel surrounding rock cavities on the horizontal plane. Using geophysical methods, the boundary of the cavity on the horizontal plane was determined. A benchmark point was established near the center of the boundary. Using this benchmark point as the center, the distances from each boundary point to the benchmark point were measured with a ruler, and the azimuth of each boundary point was measured with a compass. The boundary of the cavity was drawn in AutoCAD software, and the area of ​​the cavity on the horizontal plane was determined using the area lookup function of AutoCAD software. .

[0025] Step S2.2: Soil samples are extracted from the overburden using a drilling rig and transported back to the laboratory for density testing using the ring cutter method to determine the density of the overburden soil. Used to calculate the mass of the overburden soil above the cavities in the surrounding rock of a tunnel. .

[0026] Step S2.3: Calculate the mass of the overburden soil above the cavity. The calculation method is as follows:

[0027] .

[0028] Step S2.4: Determine the gravitational acceleration of the overburden layer above the tunnel cavity as it falls to the bottom of the cavity. Impact time of the overburden falling This is used to calculate the impact pressure when the overburden above a tunnel cavity falls to the bottom of the cavity. .

[0029] Step S2.5: Calculate the impact pressure when the overburden above the cavity falls to the bottom of the cavity in the surrounding rock of the tunnel. The calculation method is as follows:

[0030] .

[0031] Step S2.6: Determine the horizontal thrust acting on the grout stop wall when the overburden above the cavity collapses. The calculation method is as follows:

[0032] ,in, This is the reduction factor.

[0033] Step S3: Calculate the total thrust on the grout-stopping wall and compare it with the thrust resisting force of the grout-stopping wall itself to determine the safety of the grout-stopping wall.

[0034] Step S3.1: Determine the total horizontal thrust acting on the grout-stopping wall. The calculation method is as follows:

[0035] .

[0036] Step S3.2: Obtain the unit weight of the grout-stopping wall Obtain the length of the grout-stopping wall along the longitudinal direction of the tunnel. The design and construction plan for the tunnel grout stop wall shall be determined accordingly.

[0037] Step S3.3: Determine the gravity of the grout-stopping wall. The calculation method is as follows:

[0038] .

[0039] Step S3.4: Determine the shear strength between the grout-stopping wall and the tunnel bottom. Small grout-stopping wall test blocks were cast at the bottom of the tunnel, and the shear strength was determined using a large-scale direct shear test with the normal stress set to zero. .

[0040] Step S3.5: Determine the horizontal thrust resisted by the grout-stopping wall. The calculation method is as follows:

[0041] .

[0042] Step S3.6: Determine the safety of the grout-stopping wall; by comparing the total horizontal thrust acting on the grout-stopping wall. Resistance of the grout-stopping wall to horizontal thrust The size of the grout-stopping wall is used to determine its safety. If the grout-stopping wall is not in good condition, it loses its safety and becomes unsafe; conversely, if... If so, the grout-stopping wall is in a safe state.

[0043] Example

[0044] During the construction of a water conveyance tunnel in Tong'an District, Xiamen City, Fujian Province, a sudden water and mud inrush occurred when the surrounding rock reached level 5, resulting in a cavity above the arch. The construction team immediately built a grout-stopping wall to prevent further expansion of the water and mud inrush. To determine the safety of the grout-stopping wall should a collapse occur in the overburden above the cavity, the method of this invention was used for prediction.

[0045] The height of the tunnel cross section was determined based on the tunnel design data. The width of the tunnel cross-section is 4.2m. The depth is 3.4m. A drilling rig was used to drill behind the grout stop wall to collect undisturbed soil samples of the mudslide. These samples were transported back to the laboratory, where the density was tested using the ring cutter method. The density was then multiplied by the acceleration due to gravity to obtain the final density.

[0046] Heavy mud mass protruding behind the grout stop wall 16.4 kN / m 3 ; through calculation formula Determined to exit the tunnel

[0047] The initial horizontal thrust on the grout stop wall when the overburden above the cavity in the surrounding rock has not collapsed. It is 491.8 kN.

[0048] Drilling was conducted directly above the cavity in the surrounding rock of the tunnel to determine the thickness of the overburden layer above the cavity. The height of the cavity in the surrounding rock of the tunnel is 5.7m. The depth is 13.6m. Using geophysical methods, the boundary of the cavity on the horizontal plane was determined. A benchmark point was established near the center of the boundary. Using this benchmark point as the center, the distances from each boundary point to the benchmark were measured with a ruler, and the azimuth of each boundary point was measured with a compass. The boundary of the cavity was drawn in AutoCAD software, and the area of ​​the cavity on the horizontal plane was determined using the area lookup function of AutoCAD software. It is 21.3m 2 Soil samples were extracted from the overburden using a drilling rig and transported back to the laboratory for density testing using the ring cutter method to determine the density of the overburden soil above the tunnel cavities. 1840 kg / m 3 ; through calculation formula Determine the mass of the overburden soil above the cavity. The weight is 223394.4 kg; obtain the gravitational acceleration of the overlying layer above the cavity as it falls to the bottom of the cavity. And the impact time of the falling overburden. Through calculation formula Determine the impact pressure of the overburden falling from the top of the cavity to the bottom of the cavity. The value is 11415.6 kPa.

[0049] Obtain the reduction factor The value is 0.75, calculated using the formula. Determine the exit from the tunnel

[0050] The horizontal thrust acting on the grout stop wall when the overburden above the cavity in the surrounding rock collapses. It is 122630kN, and according to the formula Calculate the total horizontal thrust on the grout-stopping wall. The value is 123121.8 kN.

[0051] The total horizontal thrust on the tunnel grout stop wall was calculated based on the design and construction schemes. The value is 123121.8 kN, calculated using the formula. Determine the gravity of the grout-stopping wall. It is 1249.5 kN, of which, The unit weight of the grout-stopping wall is taken as 25 kN / m. 3 Small grout-stopping wall test blocks were poured at the bottom of the tunnel. Using a large-scale direct shear test, with the normal stress set to zero, the shear strength between the grout-stopping wall and the tunnel bottom was determined to be 9506 kPa. This was then calculated using the formula... Determine the horizontal thrust resistance of the grout-stopping wall. The value is 113121.4 kN.

[0052] The total horizontal thrust on the grout-stopping wall 123121.8kN and the resistance of the grout-stopping wall to horizontal thrust The results were compared with those of 113121.4 kN. The grout-stopping wall loses its safety.

[0053] In this embodiment, the initial horizontal thrust on the grout stop wall when the overburden above the tunnel surrounding rock cavity has not collapsed and the horizontal thrust acting on the grout stop wall when the overburden collapses are predicted. The total horizontal thrust on the grout stop wall is calculated, and the stability of the grout stop wall can be judged by comparing the total horizontal thrust on the grout stop wall with the magnitude of the grout stop wall's resistance to horizontal thrust. This method has the advantages of strong process and reliable results, so as to fully grasp the safety performance of the grout stop wall and provide a guarantee for the construction safety of the tunnel.

[0054] It is understood that the above description is merely exemplary and the embodiments of this application do not limit the scope of the application.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for predicting the safety of a grout retaining wall during tunnel roof fall in weak surrounding rock, characterized by, The method comprises the following steps: Step S1: Obtain the size of the tunnel cross section and the specific gravity of the mud body behind the grout stop wall when the soft surrounding rock does not cave in, to determine the initial thrust of the grout stop wall by the mud body behind it; determine the height of the tunnel cross section according to the tunnel design data and the width of the cross section , determine the specific gravity of the mud body behind the grout stop wall , determine the initial horizontal thrust of the grout stop wall when the overburden above the cavity does not collapse , the calculation method is as follows: ； Step S2: obtaining the impact pressure when the overburden above the space collapses to the bottom of the space, and determining the horizontal thrust acting on the stop wall based on the size of the tunnel cross section and the specific gravity of the mud body , determining the density of the overburden soil , calculating the mass of the overburden soil above the space , determining the gravitational acceleration when the overburden above the tunnel surrounding rock collapses to the bottom of the space and the impact time of the overburden collapse , for calculating the impact pressure when the overburden above the tunnel surrounding rock collapses to the bottom of the tunnel surrounding rock , determining the horizontal thrust acting on the stop wall when the overburden above the space collapses , the calculation method is as follows: wherein, is the reduction factor; Step S3: calculating the total pushing force on the grout-stop wall and comparing the total pushing force on the grout-stop wall with the pushing resistance of the grout-stop wall to determine the safety of the grout-stop wall; determining the total horizontal pushing force on the grout-stop wall The calculation method is as follows: ； acquiring the length of the spigot wall along the longitudinal direction of the tunnel determining the shear strength between the spigot wall and the tunnel bottom determining the resistance of the spigot wall to horizontal thrust The calculation method is as follows: 。 2. The method according to claim 1, wherein, In the step S1, the size of the tunnel cross section is based on the height and width of the tunnel cross section.

3. The method according to claim 1, wherein the method is characterized by, In the step S1, the density of the soil body is obtained and combined with the gravity acceleration to determine the specific weight of the soil body.

4. The method according to claim 1, wherein the method is characterized by, In the step S2, the impact pressure of the falling of the overburden layer to the bottom of the cavity is based on the mass of the overburden layer, the height of the cavity and the area of the cavity in the horizontal plane.

5. The method for predicting the safety of a tunnel weak surrounding rock roof fall stop-sluice wall according to claim 1, characterized in that, The thickness of the overburden layer, the area of the cavity in the horizontal plane and the density of the soil body of the overburden layer are obtained to determine the mass of the soil body of the overburden layer.

6. The method according to claim 1, wherein the method is characterized by, In the step S3, the resistance of the thrust of the wall is based on the shear resistance between the wall and the tunnel bottom, the length of the wall along the longitudinal direction of the tunnel and the width of the tunnel cross section.

7. The method according to claim 5, wherein the tunnel weak surrounding rock roof fall is stopped by the grout wall safety prediction method. The thickness of the overburden layer is determined by the drilling method.

8. The method according to claim 1, wherein the method is characterized by, The gravity acceleration is generated in the time period of the falling of the overburden layer to the bottom of the cavity.

9. The method according to claim 5, wherein the method is characterized by, The density of the soil body of the overburden layer is tested by the cutting ring method to determine the density of the soil body of the overburden layer.

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