A method for evaluating stability of a fully weathered granite tunnel

Abstract

The present application relates to the technical field of tunnel construction, in particular to a kind of full weathered granite tunnel stability evaluation method.The evaluation method is obtained by combining indoor geotechnical experiment, numerical simulation, the critical moisture content of full weathered granite;Again, the moisture content of the soil sample is compared with the critical moisture content, and the stability of the full weathered granite tunnel is analyzed in real time.The evaluation method can pay attention to the formation groundwater condition in construction, realize the real-time evaluation of the safety of tunnel construction, and provide new protection measures for the safe excavation of full weathered water-bearing granite tunnel.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a method for evaluating the stability of a completely weathered granite tunnel. Background Technology

[0002] With the development of the national economy, people's demand for transportation is gradually increasing, and the number of railways being built is also increasing. High-speed railway lines often have large curve radii, and their ability to avoid adverse geological conditions during route selection is relatively weak. Due to various limitations, tunnel entrance and exit sections are often located in shallow buried sections, where they may encounter adverse geological conditions such as weak surrounding rock and water-rich areas.

[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 bearing capacity. Therefore, it is difficult to guarantee the stability of tunnel excavation when constructing tunnels in completely weathered granite strata.

[0004] Chinese invention patent application number 201410684155.1 indicates that groundwater has a significant impact on the mechanical properties of completely weathered granite. Therefore, it is necessary to monitor the groundwater situation in real time during construction to ensure construction safety. Based on this, there is an urgent need for a technical method suitable for tunnel construction in granite strata that can evaluate tunnel stability in real time. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for evaluating the stability of a completely weathered granite tunnel.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for evaluating the stability of a completely weathered granite tunnel, comprising the following steps:

[0007] Step 1: Test the mechanical parameters of completely weathered granite soil samples at different moisture contents;

[0008] Step 2: Based on the mechanical parameters obtained in Step 1, calculate the maximum extrusion displacement of the tunnel face under different moisture contents, and obtain the critical moisture content for tunnel excavation stability.

[0009] Step 3: Based on the critical moisture content, compare the moisture content of the advanced drilling soil samples to analyze the stability of the completely weathered granite tunnel in real time.

[0010] The beneficial effects of this invention are as follows: The stability evaluation method for completely weathered granite tunnels of this invention, by combining indoor geotechnical experiments and numerical simulations, determines the critical moisture content of completely weathered granite; then, based on the critical moisture content, it compares the moisture content of soil samples obtained from advance drilling to analyze the stability of the completely weathered granite tunnel in real time. This method can monitor the groundwater situation in the strata in real time during construction, enabling real-time evaluation of tunnel construction safety and providing new safeguards for the safe excavation of completely weathered water-bearing granite tunnels. Attached Figure Description

[0011] Figure 1 This is a flowchart of the evaluation method in Embodiment 1 of the present invention;

[0012] Figure 2 This is a graph showing the variation of the maximum extrusion displacement of the tunnel face under different moisture contents in Embodiment 1 of the present invention.

[0013] Figure 3 This is a graph showing the variation of arch settlement under different moisture contents in Embodiment 1 of the present invention. Detailed Implementation

[0014] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0015] A method for evaluating the stability of a completely weathered granite tunnel includes the following steps:

[0016] Step 1: Test the mechanical parameters of completely weathered granite soil samples at different moisture contents;

[0017] Step 2: Based on the mechanical parameters obtained in Step 1, calculate the maximum extrusion displacement of the tunnel face under different moisture contents, and obtain the critical moisture content for tunnel excavation stability.

[0018] Step 3: Based on the critical moisture content, compare the moisture content of the advanced drilling soil samples to analyze the stability of the completely weathered granite tunnel in real time.

[0019] As can be seen from the above description, the beneficial effects of the present invention are as follows: The present invention first tests and obtains the physical and mechanical parameters of completely weathered granite under different moisture contents, and then selects the above physical and mechanical parameters to conduct numerical simulation of the excavation of completely weathered granite tunnels under different moisture contents; based on the principle of STMicroelectronics, the extrusion displacement of the tunnel excavation face is used as a quantitative index for evaluating the stability of the tunnel, and the critical moisture content when the tunnel excavation becomes unstable is obtained. By comparing the critical moisture content with the moisture content of the advanced drilling soil sample, the safety of the construction can be analyzed and evaluated in real time, and the operation is simple and convenient.

[0020] Furthermore, the preparation method of the completely weathered granite soil sample in step 1 includes the following steps: take the completely weathered granite soil sample from the site, dry it, and then prepare it into completely weathered granite with different moisture contents.

[0021] Furthermore, the different moisture contents in step 1 are a series of uniformly varying moisture contents. For example, the moisture contents are 15%, 20%, 25% and 30% in sequence, or 15%, 17%, 19% and 21% in sequence, or 20%, 26%, 32% and 38% in sequence.

[0022] As can be seen from the above description, using a series of uniformly varying moisture contents as reference data results in better simulation effects.

[0023] Furthermore, step 1 also includes determining the maximum and minimum moisture content that may occur in the project based on on-site geological survey data and literature review; the moisture content selected for testing in step 1 is between the maximum and minimum moisture content.

[0024] As can be seen from the above description, the moisture content selected for testing in step 1 is between the maximum and minimum moisture content, and the simulated values ​​are more consistent with the actual situation on site.

[0025] Furthermore, in step 1, a static triaxial compression test was used to test the mechanical parameters of completely weathered granite soil samples under different moisture contents.

[0026] Furthermore, the mechanical parameters include cohesion and internal friction angle.

[0027] Furthermore, step 2 includes the following steps: based on the mechanical parameters obtained in step 1, a tunnel excavation model is established using finite difference software, and the maximum extrusion displacement of the tunnel face under different moisture contents is simulated and calculated to obtain the critical moisture content for tunnel excavation stability.

[0028] As can be seen from the above description, the present invention conducts geotechnical experiments and numerical simulation calculations on soil samples during the evaluation process, thereby increasing the scientific rigor and professionalism.

[0029] Furthermore, in step 2, the moisture content before the maximum extrusion displacement at the tunnel face is used as the critical moisture content for tunnel excavation stability.

[0030] Furthermore, step 3 also includes ensuring the dynamic stability of soil moisture content during on-site construction.

[0031] Furthermore, step 3 includes the following steps: during on-site construction, the moisture content of the pre-drilled soil sample is measured in real time and compared with the critical moisture content to achieve real-time evaluation of tunnel construction safety; when the moisture content of the pre-drilled soil sample exceeds the critical moisture content, dewatering treatment or other pre-reinforcement measures are taken in a timely manner to ensure construction safety.

[0032] The following example uses a double-track high-speed railway tunnel as an example. The tunnel exit section is shallow, and the soil around the tunnel is completely weathered granite and rich in water.

[0033] Please refer to Figure 1 Embodiment 1 of the present invention is: a method for evaluating the stability of a completely weathered granite tunnel, the steps of which are as follows:

[0034] Step 1: Based on on-site geological survey data and literature review, the maximum possible moisture content in this project is 30%, and the minimum moisture content is 15%.

[0035] Step 2: After drying the completely weathered granite soil samples taken from the site, prepare soil samples with moisture contents of 15%, 20%, 25% and 30% respectively;

[0036] Step 3: In the laboratory, a static triaxial apparatus was used to conduct static triaxial compression tests on the granite with different moisture contents in Step 2, and the mechanical parameters of the completely weathered granite under different moisture contents were calculated, as shown in Table 1.

[0037] Table 1

[0038]

[0039] Step 4: Based on the mechanical parameters in Table 1, establish a tunnel excavation model using the finite difference software FLAC3D, perform numerical simulation calculations, organize the results, and plot the curves as shown below. Figure 2 , Figure 3 As shown;

[0040] Step 5: Based on the principles of STMicroelectronics, the stability of the tunnel is determined by the maximum extrusion displacement at the tunnel face under different moisture contents calculated numerically. When the moisture content increases from 25% to 30%, the stability is determined by… Figure 2 It can be observed that the maximum extrusion displacement at the tunnel face undergoes a sudden change, and from... Figure 3 It can be observed that the settlement of the tunnel arch also undergoes abrupt changes, therefore a moisture content of 25% is selected as the critical moisture content;

[0041] Step 6: Based on the critical moisture content, measure the moisture content of the pre-drilled soil samples in real time during on-site construction and compare it with the critical moisture content for excavation stability to achieve real-time evaluation of tunnel construction safety; when the moisture content exceeds the critical moisture content, take timely dewatering treatment or other pre-reinforcement measures to ensure construction safety.

[0042] In summary, the stability evaluation method for completely weathered granite tunnels based on the water content of soil samples obtained from advance drilling provided by this invention has the following advantages:

[0043] 1. Geotechnical experiments and numerical simulations were conducted on the soil samples during the evaluation process, which increased its scientific rigor and professionalism;

[0044] 2. Based on the principles of STMicroelectronics, this invention determines the critical moisture content for excavation stability according to the abrupt change in the extrusion displacement of the tunnel face. Thus, by ensuring that the moisture content of the soil sample at the construction site does not exceed the critical state, the stability of tunnel excavation can be maintained, thereby ensuring the safety of construction.

[0045] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for evaluating the stability of a completely weathered granite tunnel, characterized in that, Includes the following steps: Step 1: Test the mechanical parameters of completely weathered granite soil samples at different moisture contents; the mechanical parameters include cohesion and internal friction angle. Step 2: Based on the mechanical parameters obtained in Step 1, a tunnel excavation model is established using finite difference software to simulate and calculate the maximum extrusion displacement of the tunnel face under different moisture contents. The moisture content before the sudden change of the maximum extrusion displacement of the tunnel face is taken as the critical moisture content for tunnel excavation stability. Step 3: Based on the critical moisture content, compare the moisture content of the pre-drilled soil samples to analyze the stability of the completely weathered granite tunnel in real time; during on-site construction, measure the moisture content of the pre-drilled soil samples in real time and compare it with the critical moisture content to achieve real-time evaluation of tunnel construction safety; when the moisture content of the pre-drilled soil samples exceeds the critical moisture content, take timely dewatering treatment or other pre-reinforcement measures to ensure the dynamic stability of the soil sample moisture content and guarantee construction safety.

2. The method for evaluating the stability of a completely weathered granite tunnel according to claim 1, characterized in that, The preparation method of the completely weathered granite soil sample in step 1 includes the following steps: take the completely weathered granite soil sample from the site, dry it, and then prepare it into completely weathered granite with different moisture contents.

3. The method for evaluating the stability of a completely weathered granite tunnel according to claim 1, characterized in that, The different moisture contents in step 1 are a series of uniformly varying moisture contents.

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

5. The method for evaluating the stability of a completely 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 completely weathered granite soil samples with different moisture contents.

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