A method for evaluating and preventing the collapse risk level of a tunnel heading face

Abstract

The present invention provides a method for evaluating and preventing the risk level of tunnel face collapse, with the emphasis on "prevention". That is, it fully considers multi-source geological information such as in-situ stress, lithology, rock mass integrity, groundwater and structure. Through the analysis of this information, the risk level of collapse can be preliminarily evaluated at the exploration stage. Since more information is available during the construction process, the preliminary evaluation results can be corrected according to geophysical exploration, drilling and surrounding rock deformation conditions. Relying on the evaluation results of the risk level of collapse in the exploration and construction stages, corresponding construction and support measures are selected, which can minimize the probability of the occurrence of collapse disasters to the greatest extent. Even if a collapse occurs after taking certain measures, it will be handled at the lowest cost, which can save costs to the greatest extent and ensure safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel face collapse treatment, and particularly relates to a method for evaluating and preventing tunnel face collapse risks. Background Art

[0002] The in-situ stress level near the tunnel face is high and mostly under un-supported or weakly supported conditions. When the geological conditions change greatly, such as the rock mass grade is low and the water inflow is large, especially when the support measures do not match when passing through the tectonic area, collapse accidents are likely to occur. Face collapse is a common engineering geological disaster during tunnel construction, which brings great potential safety hazards to the lives of on-site construction workers and causes damage to the tunnel structure, extension of the construction period, and increase in costs.

[0003] Currently, there is no complete method for risk level assessment, prevention, and treatment system of tunnel face collapse disasters. Many beneficial explorations have been carried out on the treatment of collapse disasters in engineering practice. For example, Chinese Patent CN 104060999A proposes a method of excavating a bypass tunnel to pass through the collapse area; Chinese Patent CN 105673020A proposes a method of treating collapse by grouting from the top of the mountain; Chinese Patent CN 112228082A proposes a grouting method combining pipe shed and advanced small pipe. These measures have treated the collapse disasters to a certain extent, but there are problems of too high costs, and in complex geological conditions such as high in-situ stress level and poor surrounding rock integrity, good control effects are often not achieved. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for evaluating and preventing tunnel face collapse risks in view of the deficiencies in the prior art.

[0005] To achieve the above object, the following technical solutions are adopted for the present invention:

[0006] A method for evaluating and preventing tunnel face collapse risks, characterized in that: the method for evaluating and preventing tunnel face collapse risks includes collapse risk level assessment, collapse disaster prevention, and collapse disaster treatment;

[0007] Among them, the collapse risk level assessment includes the following steps:

[0008] S101: Obtain the maximum in-situ stress data of the tunnel site area;

[0009] S102: Obtain the lithology and rock mass integrity data of the tunnel site area;

[0010] S103: Obtain the groundwater and geological structure conditions of the tunnel site area;

[0011] S104: Based on the data obtained in steps S101 - S103, preliminarily evaluate the collapse risk level according to the preliminary evaluation system for the tunnel face collapse risk level;

[0012] S105: During the construction period, re - evaluate the collapse risk level according to the construction situation;

[0013] In step S104, the preliminary evaluation system for the tunnel face collapse risk level is constructed as follows:

[0014]

[0015] Note: “—” indicates no collapse; I, II, and III are collapse risk levels with increasing severity in sequence;

[0016] The softer the lithology and the poorer the integrity, the higher the risk of collapse. The description of the rock hardness and rock mass integrity refers to the "National Industry Standard of the People's Republic of China: Standard for Engineering Rock Mass Classification" (GB / T50218 - 2014); the higher the in - situ stress level, the higher the risk of collapse. The in - situ stress must be obtained through a combination of two methods: borehole measurement and numerical back - analysis of in - situ stress. If there is no measured data, it can be estimated according to the "National Industry Standard of the People's Republic of China: Standard for Engineering Rock Mass Classification" (GB / T50218 - 2014); in areas where structures and groundwater are relatively developed, the rock mass quality is poor and the rock mass strength parameters are low, and collapse is likely to occur.

[0017] In step S105, re - evaluate the collapse risk level according to the following table. When the situations in this table occur, adjust the collapse risk level in the above table to "III" level; because more geological information is available during the construction period, a more intuitive judgment of the rock mass quality can be made;

[0018]

[0019] Note: a Here, the anomaly refers to broken rock mass or water - rich;

[0020] b Indicates that the rock mass is broken and the surrounding rock quality is poor;

[0021] Among them, the prevention of tunnel face collapse disasters includes the following steps:

[0022] S201: According to the evaluation result of the tunnel face collapse risk level, select the excavation method based on the prevention measures system for tunnel face collapse disasters; reduce the disturbance to the surrounding rock and prevent the excessive reduction of the surrounding rock quality caused by excavation activities;

[0023] S202: According to the evaluation result of the tunnel face collapse risk level, select the support method based on the tunnel face collapse disaster prevention measure system; before excavation, pre-reinforce the surrounding rock in advance to improve the integrity of the rock mass at the tunnel face; after excavation, quickly support the surrounding rock to reduce the deterioration of the surrounding rock, and improve the integrity of the rock mass near the tunnel face through grouting;

[0024] In steps S201 and S202, the tunnel face collapse disaster prevention measure system is constructed as follows:

[0025]

[0026] Among them, the treatment of the tunnel face collapse disaster includes the following steps:

[0027] S301: Spray concrete to construct a grout stop wall, that is, spray quick-setting concrete into the collapse area to cover the entire tunnel section, and the thickness of the concrete is not less than 5 cm;

[0028] S302: Construct boreholes, that is, construct high-level boreholes and low-level boreholes in the collapse area, and insert pipes and seal the holes;

[0029] S303: Targeted grouting, that is, first inject a quick-setting material with a low water-cement ratio into the high-level borehole, and then inject a quick-setting material with a high water-cement ratio into the low-level borehole; using quick-setting materials with different water-cement ratios reduces the material consumption and enables the collapsed rock blocks to solidify quickly;

[0030] S304: Construct pipe roofs, steel frames and clean up the slag. In the collapse area, construct pipe roofs, steel arch frames in sequence and clean up the waste slag until passing through the collapse area.

[0031] While adopting the above technical solutions, the present invention can also adopt or combine the following technical solutions:

[0032] As a preferred technical solution of the present invention: in the prevention of tunnel face collapse disasters, for the prevention of grade III collapse risks, high-strength grouting materials should be selected for the advanced large pipe roof grouting; in the advanced deep-hole targeted grouting, according to the geophysical exploration results, boreholes should be drilled and grouted into the abnormal area of the rock mass in front of the tunnel face, and grouting materials with good fluidity and long setting time should be selected; the grouting position is the abnormal area in front of the tunnel face, and the grouting is more targeted, reducing the blindness of construction, and using materials with good fluidity and long setting time enables the grouting materials to fully penetrate into the micro-cracks.

[0033] As a preferred technical solution of the present invention: for the treatment of the collapse disaster of the tunnel face, in step S302, during the drilling construction, if problems such as drill jamming or drill dropping occur, the drill needs to be withdrawn and a quick-setting grouting material is injected into the drill hole through the drill pipe and the grouting pump to reinforce the loosened and broken area. After the grouting material solidifies, the drilling continues. The quick-setting grouting material can solidify quickly and reach a relatively high strength rapidly, reducing the construction waiting time and improving the construction efficiency.

[0034] As a preferred technical solution of the present invention: for the treatment of the collapse disaster of the tunnel face, in the targeted grouting process of step S303, for the high-position drill hole grouting, a quick-setting grouting material with a low water-cement ratio is required, and the grouting pressure is 2 - 5 MPa; for the low-position drill hole, a quick-setting grouting material with a relatively high water-cement ratio is required, and the grouting pressure is lower than 2 MPa.

[0035] The present invention provides a method for evaluating and preventing the collapse risk level of a tunnel face, with the emphasis on "prevention", that is, fully considering multi-source geological information such as in-situ stress, lithology, rock mass integrity, groundwater, and structure; through the analysis of this information, the collapse risk level can be initially evaluated at the exploration stage; since more information is obtained during the construction stage, the preliminary evaluation results can be corrected according to the geophysical exploration, drilling, and surrounding rock deformation conditions; relying on the evaluation results of the collapse risk level in the exploration and construction stages, corresponding construction and support measures are selected, which can minimize the probability of the occurrence of the collapse disaster as much as possible. Even if a collapse occurs after taking certain measures, it will be handled at the lowest cost, which can save costs to the greatest extent and ensure safety. The method provided by the present invention includes three main parts: the evaluation of the collapse risk level of the tunnel face, the prevention of the collapse disaster, and the treatment of the collapse disaster. This method can effectively reduce the probability of the occurrence of the collapse disaster of the tunnel face; and even after the collapse accident occurs, it has the advantages of simple treatment technology, good safety, good safety for workers without having to enter the collapse area for operation, small amount of waste residue to be cleaned, small material consumption, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a layout diagram of the grouting stop wall and drill holes for the tunnel face collapse.

[0037] In the figure: 1 - grouting stop wall; 2 - low-position drill hole; 3 - high-position drill hole. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

[0039] A method for evaluating and preventing the collapse risk level of a tunnel face includes the evaluation of the collapse risk level, the prevention of the collapse disaster, and the treatment of the collapse disaster;

[0040] (1), Evaluation of the collapse risk level:

[0041] S101: Obtain the maximum in-situ stress data of the tunnel site area;

[0042] S102: Obtain the lithology and rock mass integrity data of the tunnel site area;

[0043] S103: Obtain the groundwater and geological structure conditions of the tunnel site area;

[0044] S104: Based on the data obtained in steps S101 - S103, conduct a preliminary assessment of the collapse risk level according to Table 1;

[0045] S105: During the construction period, conduct a re-assessment of the collapse risk level according to Table 2;

[0046] Table 1 Preliminary assessment system for the collapse risk level of the tunnel heading face

[0047]

[0048] Note: “—” indicates no collapse occurs; I, II, and III are the collapse risk levels with the severity increasing in sequence;

[0049] Table 2 Revision system for the collapse risk level of the tunnel heading face

[0050] Geophysical prospecting situation Drilling and surrounding rock deformation situation Anomaly of rock mass in front of the tunnel face Drilling anomalies, such as sticking of drill pipe and dropping of drill; radial deformation of surrounding rock near the tunnel face does not converge and shows an accelerating deformation trend

[0051] Note: In case of the situations in Table 2, adjust the collapse risk level in Table 1 to “III” level;

[0052] (2) Collapse disaster prevention

[0053] S201: According to the assessment result of the collapse risk level of the tunnel heading face, select the excavation method based on Table 3;

[0054] S202: According to the assessment result of the collapse risk level of the tunnel heading face, select the support method based on Table 3;

[0055] Table 3 Prevention measure system for the collapse disaster of the tunnel heading face

[0056]

[0057] For the prevention of the collapse risk of level III, high-strength grouting materials shall be selected for the advanced large-diameter pipe shed grouting; in the deep-hole targeted grouting, according to the geophysical exploration results, drill holes and grout into the abnormal rock mass area in front of the heading face, and grouting materials with good fluidity and long setting time shall be selected.

[0058] (3) Collapse disaster treatment

[0059] S301: Spray concrete to construct a grout stop wall 1, that is, spray quick-setting concrete into the collapse area to cover the entire tunnel section, and the concrete thickness shall not be less than 5 cm;

[0060] S302: Construction of boreholes, that is, constructing high-level borehole 2 and low-level borehole 3 towards the collapse area, and inserting pipes and sealing the holes; during the process of borehole drilling, abnormal phenomena such as sticking of the drill may occur. The method of combining grouting and drilling can be adopted. That is, when abnormal phenomena such as sticking of the drill occur, the drill should be immediately withdrawn and grouting should be carried out. The grouting material should be a quick-setting and early-strength grouting material with a low water-cement ratio to quickly reinforce the loose gangue in the broken area. After half an hour, re-drill the hole to enlarge it. When drilling abnormalities occur again, repeat the grouting and hole-enlarging process until the hole depth reaches the designed depth.

[0061] S303: Targeted grouting, that is, first grouting into the high-level borehole, a quick-setting grouting material with a low water-cement ratio (less than 1.0:1) should be used, and the grouting pressure is 2 - 5 MPa; then grouting into the low-level borehole, a quick-setting grouting material with a higher water-cement ratio (greater than 3.0:1) should be used, and the grouting pressure is lower than 2 MPa.

[0062] S304: Construction of pipe roofs, steel frames and slag cleaning, successively construct pipe roofs and steel arch frames in the collapse area and clean up the waste slag until passing through the collapse area.

[0063] In the prevention of face collapse disasters, for the prevention of grade III collapse risks, high-strength grouting materials should be selected for the advanced large pipe roof grouting; in the advanced deep-hole targeted grouting, according to the geophysical exploration results, boreholes should be drilled and grouted into the abnormal areas of the rock mass in front of the face. The grouting materials should be grouting materials with good fluidity and long setting time; the grouting position is the abnormal area in front of the face, and the grouting is more targeted, reducing the blindness of construction. Moreover, using grouting materials with good fluidity and long setting time enables the grouting materials to fully penetrate into the micro-cracks.

[0064] During the process of borehole construction, if problems such as sticking of the drill and dropping of the drill occur, the drill should be withdrawn and a quick-setting type of grouting material should be injected into the borehole through the drill pipe and grouting pump to reinforce the loose and broken area. After the grouting material solidifies, continue drilling. The quick-setting grouting material can solidify quickly and reach a relatively high strength quickly, reducing the construction waiting time and improving construction efficiency.

[0065] In the targeted grouting process, for the high-level borehole grouting, a quick-setting grouting material with a low water-cement ratio should be used, and the grouting pressure is 2 - 5 MPa; for the low-level borehole, a quick-setting grouting material with a higher water-cement ratio should be used, and the grouting pressure is lower than 2 MPa.

[0066] The above specific implementation manners are used to explain and illustrate the present invention, which are only the preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and scope of the protection of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A method for evaluating and preventing the risk level of tunnel face collapse, characterized in that: The method for evaluating and preventing the collapse risk of the tunnel face includes collapse risk level assessment, collapse disaster prevention, and collapse disaster treatment; Among them, the collapse risk level assessment includes the following steps: S101: Obtain the maximum in-situ stress data of the tunnel site area; S102: Obtain the lithology and rock mass integrity data of the tunnel site area; S103: Obtain the groundwater and geological structure conditions of the tunnel site area; S104: Based on the data obtained in steps S101 to S103, preliminarily evaluate the collapse risk level according to the preliminary evaluation system of the tunnel face collapse risk level; S105: During the construction period, re-evaluate the collapse risk level according to the construction situation; In step S104, the preliminary evaluation system of the tunnel face collapse risk level is constructed as follows: Note: "-" indicates no collapse; I, II, and III are the collapse risk levels, and the severity increases in turn; Among them, the prevention of the collapse disaster of the tunnel face includes the following steps: S201: According to the evaluation results of the tunnel face collapse risk level, select the excavation method based on the prevention measures system of the tunnel face collapse disaster; S202: According to the evaluation results of the tunnel face collapse risk level, select the support method based on the prevention measures system of the tunnel face collapse disaster; In steps S201 and S202, the prevention measures system of the tunnel face collapse disaster is constructed as follows: Among them, the treatment of the collapse disaster of the tunnel face includes the following steps: S301: Spray concrete to construct a grout stop wall, that is, spray quick-setting concrete into the collapse area to cover the entire tunnel section, and the concrete thickness is not less than 5 cm; S302: Drill holes, that is, construct high-level holes and low-level holes in the collapse area, and insert pipes and seal the holes; S303: Targeted grouting, that is, first inject a quick-setting material with a low water-cement ratio into the high-level holes, and then inject a quick-setting material with a high water-cement ratio into the low-level holes; S304: Construct pipe roofs, steel frames and remove slag. In the collapse area, construct pipe roofs, steel arch frames in sequence and clean up the waste slag until passing through the collapse area.

2. The method for evaluating and preventing the risk level of tunnel face collapse according to claim 1, characterized in that: In the prevention of the collapse disaster of the tunnel face, for the prevention of the collapse risk of grade III, high-strength grouting materials should be selected for the grouting of the advanced large pipe roof; in the advanced deep-hole targeted grouting, according to the geophysical exploration results, drill holes and grout into the abnormal area of the rock mass in front of the tunnel face, and the grouting materials should be selected with good fluidity and long setting time; the grouting position is the abnormal area in front of the tunnel face, and materials with good fluidity and long setting time are used to make the grouting materials fully penetrate into the micro-cracks.

3. The method for evaluating and preventing the risk level of tunnel face collapse according to claim 1, characterized in that: In the treatment of the collapse disaster of the tunnel face, in step S302, during the drilling construction, if problems such as drill sticking and drill dropping occur, it is necessary to withdraw the drill and inject quick-setting grouting materials into the drill hole through the drill pipe and grout pump to reinforce the loose and broken area. After the grouting materials are solidified, continue drilling.

4. The method for evaluating and preventing the risk level of tunnel face collapse according to claim 1, characterized in that: In the treatment of the collapse disaster of the tunnel face, in the targeted grouting process of step S303, the high-level hole grouting needs to use a quick-setting grouting material with a low water-cement ratio, and the grouting pressure is 2 - 5 MPa; the low-level hole needs to use a quick-setting grouting material with a higher water-cement ratio, and the grouting pressure is lower than 2 MPa.

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