Method for evaluating stability of fully-weathered granite tunnel

Abstract

The invention relates to the technical field of tunnel construction, in particular to a method for evaluating the stability of a fully-weathered granite tunnel. According to the evaluation method, the critical water content of the completely weathered granite is solved by combining indoor geotechnical experiments and numerical simulation; and comparing the moisture content of the advanced drilling soil sample according to the critical moisture content, and analyzing the stability of the fully weathered granite tunnel in real time. According to the evaluation method, the underground water condition of the stratum can be concerned in real time in the construction process, the tunnel construction safety is evaluated in real time, and a new guarantee measure is provided for safe excavation of the fully-weathered water-containing granite tunnel.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to a stability evaluation method for a fully weathered granite tunnel. Background Art

[0002] With the development of the national economy, people's demand for transportation has gradually increased, and the number of railways being built has also increased. The curve radius of high-speed railway lines is often large, and the ability to bypass unfavorable geology during line selection is weak. Due to various factors, the entrance and exit sections of tunnels are often in shallow buried sections, and they may encounter unfavorable geology such as weak surrounding rock and rich water.

[0003] Completely weathered granite is widely distributed on the surface of hilly and mountainous areas in my country. It has a high degree of weathering, poor mechanical structure, and is easily softened when exposed to water, resulting in a significant decrease in its bearing capacity. Therefore, when constructing tunnel projects in completely weathered granite strata, the stability of tunnel excavation is difficult to guarantee.

[0004] The Chinese invention patent application number 201410684155.1 shows that groundwater has a great influence on the mechanical properties of fully weathered granite. Therefore, it is necessary to pay attention to the groundwater situation in the stratum in real time during construction to ensure construction safety. Based on this, there is an urgent need for a technical method that can evaluate the stability of the tunnel in real time and is suitable for tunnel construction in granite strata. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a stability evaluation method for a fully weathered granite tunnel.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for evaluating the stability of a fully weathered granite tunnel, comprising the following steps: Step 1: Test the mechanical parameters of fully decomposed granite soil samples at different moisture contents; Step 2: Based on the mechanical parameters obtained in step 1, calculate the maximum extrusion displacement of the tunnel face under different water contents, and obtain the critical water content for stable tunnel excavation; Step 3: Based on the critical moisture content, compare the moisture content of the advance drilling soil samples and analyze the stability of the fully weathered granite tunnel in real time.

[0007] The beneficial effects of the present invention are as follows: the stability evaluation method of the fully weathered granite tunnel of the present invention calculates the critical moisture content of the fully weathered granite by combining indoor geotechnical experiments and numerical simulations; based on the critical moisture content, the moisture content of the advanced drilling soil samples is compared to analyze the stability of the fully weathered granite tunnel in real time. The method can pay attention to the groundwater conditions of the strata in real time during construction, realize the real-time evaluation of the safety of tunnel construction, and provide new safeguards for the safe excavation of fully weathered water-containing granite tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a flow chart of the evaluation method in Embodiment 1 of the present invention; Figure 2 is a curve diagram showing the change of the maximum extrusion displacement of the tunnel face at different water contents in the first embodiment of the present invention; Figure 3 The figure is a curve diagram of the change of the vault settlement under different moisture contents in the first embodiment of the present invention. DETAILED DESCRIPTION

[0009] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0010] A method for evaluating the stability of a fully weathered granite tunnel comprises the following steps: Step 1: Test the mechanical parameters of fully decomposed granite soil samples at different moisture contents; Step 2: Based on the mechanical parameters obtained in step 1, calculate the maximum extrusion displacement of the tunnel face under different water contents, and obtain the critical water content for stable tunnel excavation; Step 3: Based on the critical moisture content, compare the moisture content of the advance drilling soil samples and analyze the stability of the fully weathered granite tunnel in real time.

[0011] From the above description, it can be seen that the beneficial effects of the present invention are as follows: the present invention first tests and obtains the physical and mechanical parameters of fully weathered granite under different moisture contents, then selects the above physical and mechanical parameters, and performs numerical simulation on the tunnel excavation of fully weathered granite under different moisture content conditions; based on the principle of the novel method, the extrusion displacement of the tunnel excavation face is used as a quantitative indicator for evaluating the stability of the tunnel, and the critical moisture content when the tunnel excavation is unstable is obtained. By comparing the critical moisture content and the moisture content of the advance drilling soil sample, the safety of the construction can be analyzed and evaluated in real time, and the operation is simple and convenient.

[0012] Furthermore, the method for preparing the fully weathered granite soil sample in step 1 comprises the following steps: taking the fully weathered granite soil sample on site and drying it, and then preparing fully weathered granite with different moisture contents.

[0013] Furthermore, the different moisture contents in step 1 are a series of moisture contents that vary evenly, such as the moisture contents are 15%, 20%, 25% and 30% in sequence, or the moisture contents are 15%, 17%, 19% and 21% in sequence, or the moisture contents are 20%, 26%, 32% and 38% in sequence.

[0014] From the above description, it can be seen that the simulation effect is better if a series of moisture contents with uniform variations are used as reference data.

[0015] Furthermore, step 1 also includes determining the maximum moisture content and the minimum moisture content that may occur in the project based on the on-site geological survey data combined with literature research; the moisture content selected in the test in step 1 is between the maximum moisture content and the minimum moisture content.

[0016] From the above description, it can be seen that the moisture content selected in the test in step 1 is between the maximum moisture content and the minimum moisture content, and the simulated value is more consistent with the on-site situation.

[0017] Furthermore, in step 1, a static triaxial compression test is used to test the mechanical parameters of fully weathered granite soil samples at different water contents.

[0018] Furthermore, the mechanical parameters include cohesion and internal friction angle.

[0019] Furthermore, step 2 includes the following steps: according to the mechanical parameters obtained in step 1, a tunnel excavation model is established using finite difference software, and the maximum extrusion displacement of the face under different moisture contents is simulated and calculated to obtain the critical moisture content for stable tunnel excavation.

[0020] From the above description, it can be seen that the present invention performs geotechnical experiments and numerical simulation calculations on soil samples during the evaluation process, which increases the scientificity and professionalism.

[0021] Furthermore, in step 2, the water content before the maximum extrusion displacement of the face changes suddenly is used as the critical water content for stable tunnel excavation.

[0022] Furthermore, step 3 also includes ensuring that the moisture content of the soil sample is dynamically stable during on-site construction.

[0023] Furthermore, step 3 includes the following steps: during on-site construction, the moisture content of the advance drilling soil samples is measured in real time, and compared with the critical moisture content to achieve real-time evaluation of the safety of tunnel construction; when the moisture content of the advance drilling soil samples exceeds the critical moisture content, precipitation treatment or other advance reinforcement measures are taken in time to ensure construction safety.

[0024] The following embodiments take a double-track high-speed railway tunnel line as an example, where the tunnel exit section is buried at a shallow depth, and the soil around the tunnel is fully weathered granite and is rich in water.

[0025] Please refer to Figure 1 The first embodiment of the present invention is: a method for evaluating the stability of a fully weathered granite tunnel, the steps are as follows: Step 1: Based on the on-site geological survey data and literature research, determine that the maximum moisture content that may occur in the project is 30% and the minimum moisture content is 15%; Step 2: Take the fully decomposed granite soil sample on site and dry it, then prepare soil samples with moisture contents of 15%, 20%, 25% and 30% respectively; Step 3: In the laboratory, a static triaxial compression test is performed on the granite with different water contents in step 2 using a static triaxial apparatus, and the mechanical parameters of the fully weathered granite with different water contents are calculated, as shown in Table 1; Table 1

[0026] Step 4: According to the mechanical parameters in Table 1, the tunnel excavation model is established using the finite difference software FLAC3D, and numerical simulation calculations are performed. The results are collated and a curve diagram is drawn as shown in FIG. Figure 2 , Figure 3 As shown; Step 5: Based on the principle of the new method, the stability of the tunnel is judged according to the maximum extrusion displacement of the tunnel face under different water contents obtained by numerical calculation. When the water content increases from 25% to 30%, Figure 2 It can be found that the maximum extrusion displacement of the tunnel face changes suddenly, and Figure 3 It can be found that the tunnel vault settlement also changes suddenly, so the water content of 25% is selected as the critical water content; Step 6: Based on the critical moisture content, during on-site construction, the moisture content of the advance drilling soil samples is measured in real time and compared with the critical moisture content of stable excavation to achieve real-time evaluation of the safety of tunnel construction; when the moisture content exceeds the critical moisture content, timely precipitation treatment or other advance reinforcement measures are taken to ensure construction safety.

[0027] In summary, the stability evaluation method for fully weathered granite tunnel based on the moisture content of advance-drilled soil samples provided by the present invention has the following advantages: 1. Geotechnical experiments and numerical simulation calculations were carried out on soil samples during the evaluation process, which increased its scientificity and professionalism; 2. The present invention is based on the principle of the novel method. The critical moisture content for stable excavation is determined according to the sudden change of the extrusion displacement of the face. Then, during construction, the moisture content of the on-site soil samples is ensured not to exceed the critical state to maintain the stability of the tunnel excavation, thereby ensuring safety during construction.

[0028] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for evaluating the stability of a fully weathered granite tunnel, characterized in that: The following steps are involved: Step 1: Test the mechanical parameters of fully decomposed granite soil samples at different moisture contents; Step 2: Based on the mechanical parameters obtained in step 1, calculate the maximum extrusion displacement of the tunnel face under different water contents, and obtain the critical water content for stable tunnel excavation; Step 3: Based on the critical moisture content, compare the moisture content of the advance drilling soil samples and analyze the stability of the fully weathered granite tunnel in real time.

2. The method for evaluating the stability of a fully weathered granite tunnel according to claim 1, characterized in that: The method for preparing the fully weathered granite soil sample in step 1 comprises the following steps: taking the fully weathered granite soil sample on site and drying it, and then preparing fully weathered granite with different moisture contents.

3. The method for evaluating the stability of a fully weathered granite tunnel according to claim 1, characterized in that: The different moisture contents in step 1 are a series of moisture contents that vary evenly.

4. The method for evaluating the stability of a fully weathered granite tunnel according to claim 1, characterized in that: The step 1 also includes determining the maximum moisture content and the minimum moisture content that may occur in the project based on the on-site geological survey data combined with literature research; the moisture content selected in the test in the step 1 is between the maximum moisture content and the minimum moisture content.

5. The method for evaluating the stability of a fully weathered granite tunnel according to claim 1, characterized in that: In step 1, a static triaxial compression test is used to test the mechanical parameters of fully weathered granite soil samples at different water contents.

6. The method for evaluating the stability of a fully weathered granite tunnel according to claim 1, characterized in that: The mechanical parameters include cohesion and internal friction angle.

7. The method for evaluating the stability of a fully weathered granite tunnel according to claim 1, characterized in that: The step 2 comprises the following steps: according to the mechanical parameters obtained in step 1, a tunnel excavation model is established using finite difference software, the maximum extrusion displacement of the tunnel face under different moisture contents is simulated and calculated, and the critical moisture content for stable tunnel excavation is obtained.

8. The method for evaluating the stability of a fully weathered granite tunnel according to claim 1, characterized in that: In step 2, the moisture content before the maximum extrusion displacement of the face changes suddenly is used as the critical moisture content for stable tunnel excavation.

9. The method for evaluating the stability of a fully weathered granite tunnel according to claim 1, characterized in that: The step 3 also includes ensuring the dynamic stability of the moisture content of the soil sample during on-site construction.

10. The method for evaluating the stability of a fully weathered granite tunnel according to claim 9, characterized in that: The step 3 comprises the following steps: during on-site construction, the moisture content of the advance-drilled soil sample is measured in real time, and compared with the critical moisture content, so as to achieve a real-time evaluation of the safety of the tunnel construction; when the moisture content of the advance-drilled soil sample exceeds the critical moisture content, precipitation treatment or other advance reinforcement measures are taken in time to ensure construction safety.

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