Method for predicting force on secondary lining of soft rock tunnel with large deformation

Abstract

Disclosed in the present invention is a method for predicting the force on a secondary lining of a soft rock tunnel with large deformation, comprising: firstly, acquiring tunnel section dimensions and surrounding rock parameters; acquiring a surrounding rock pressure P1; during tunnel excavation, monitoring the deformation of a tunnel section; on the basis of deformation monitoring data, using an exponential function to perform fitting to obtain a deformation-time fitting function of the tunnel section and a final deformation amount; assuming a secondary lining construction time t, and on the basis of the deformation-time fitting function of the tunnel section and the final deformation amount, calculating a corresponding residual deformation amount after the secondary lining is constructed at the time t; on the basis of an elastic theoretical pull-tight solution of deformation U21 of the inner wall of a primary support under the action of the surrounding rock pressure P1 and the contact pressure P2 between the primary support and the secondary lining in a thick-walled cylinder theory, calculating the contact pressure P2 between the primary support and the secondary lining after the secondary lining is constructed at the time t; and finally, checking whether the obtained contact pressure P2 between the primary support and the secondary lining is reasonable, if not, re-determining a secondary lining construction time until P2 is reasonable, and finally determining a proper secondary lining construction time.

Description

A method for predicting stress of secondary lining of large deformation tunnel in soft rock TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical engineering, and particularly relates to a method for predicting stress of secondary lining of large deformation tunnel in soft rock. BACKGROUND

[0002] The most prominent feature of the large deformation tunnel in soft rock is large deformation, which causes the primary support to be unstable, and the secondary lining to crack, thereby causing great difficulties in construction. The main reason is that the data is incomplete during design, which leads to poor matching between the structure and the stratum, and the construction progress and quality control are not matched. In the 1970s, the concept of dynamic design of tunnel was introduced in China, and the realization of the concept is mainly combined with monitoring and support informationization, so as to realize the information completion input of construction design and improve the related design. However, from the construction process of some large deformation tunnels in soft rock, it can be seen that the adjustment and field test of construction technology are mainly focused on.

[0003] Overall, the dynamic design of the large deformation tunnel in soft rock mainly focuses on the experience and technology. The dynamic design of the structure stress of the large deformation tunnel in soft rock is related to the problems in design and construction. First, what form of structure is adopted; second, when the structure is constructed. At present, whether the experience design or the technical design, the first problem, that is, what form is adopted, is mainly focused on. However, the second problem is less studied. Due to the poor stability of the primary support of the large deformation tunnel in soft rock, the secondary lining also needs to be part of the bearing structure. If the secondary lining is constructed too early, the stress of the secondary lining is too large, and the secondary lining is easy to crack. If the secondary lining is constructed too late, the primary support is deformed too much, and the primary support is easy to be unstable.

[0004] Therefore, a method for predicting the stress of the secondary lining of the large deformation tunnel in soft rock needs to be proposed, which provides a basis for dynamic design calculation, and thereby provides guidance for determining the appropriate construction time of the secondary lining. SUMMARY

[0005] The present application aims at solving the problems in the prior art, and provides a method for predicting stress of secondary lining of large deformation tunnel in soft rock.

[0006] In order to achieve the purpose of the present application, the technical scheme adopted is:

[0007] A method for predicting stress of secondary lining of large deformation tunnel in soft rock, comprising the following steps:

[0008] Step 1, obtaining the tunnel section size and surrounding rock parameters;

[0009] The tunnel section size includes a tunnel excavation radius r1 and a tunnel primary support radius r2;

[0010] The surrounding rock parameters include a surrounding rock elastic modulus E1 and a Poisson's ratio μ1;

[0011] Step 2: Obtain the surrounding rock pressure P1;

[0012] Step 3: During the tunnel excavation, deformation monitoring points are arranged on the tunnel section to perform deformation monitoring;

[0013] Step 4: According to the deformation monitoring data of Step 3, a deformation-time fitting function of the tunnel section and the final deformation are obtained by drawing a deformation-time curve of the tunnel section and fitting the curve with an exponential function .

[0014] Step 5: Assuming the secondary lining construction time t, the residual deformation U of the secondary lining after the secondary lining is applied at the t moment is calculated according to the deformation-time fitting function of the tunnel section and the final deformation obtained in Step 2 c , ,U t is the deformation of the tunnel section at the t moment;

[0015] Step 6: According to the elastic theory Lami solution formula of the deformation U 21 of the inner wall of the primary lining under the action of the surrounding rock pressure P1 and the contact pressure P2 between the primary lining and the secondary lining, the contact pressure P2 between the primary lining and the secondary lining after the secondary lining is applied at the t moment is calculated;

[0016] U 21 The elastic theory Lami solution formula of U

[0017] ,

[0018] The U 21 is equal to the residual deformation U c obtained in Step 5;

[0019] Step 7, check whether the contact pressure P2 between the primary lining and the secondary lining obtained in Step 6 is reasonable, if it is reasonable, stop calculation, if it is not reasonable, re-determine the secondary lining construction time, repeat Step 5-Step 7, until P2 is reasonable.

[0020] In the above technical solution, in Step 1, when the tunnel is a non-circular section, the tunnel excavation radius r1 and the tunnel primary lining radius r2 are calculated according to the equivalent radius, and the calculation formula is as follows:

[0021]

[0022] B1 is the tunnel excavation span, and h1 is the tunnel excavation height;

[0023]

[0024] B2 is the tunnel primary lining span, and h1 is the tunnel primary lining height.

[0025] In the technical scheme, the total station is used to monitor the deformation of the monitoring points of the tunnel section.

[0026] In the technical scheme, the deformation-time fitting function expression of the tunnel section is as follows:

[0027] , wherein, U t is the deformation of the tunnel section at time t, and A is a fitting parameter.

[0028] In the technical scheme, in step 7, whether P2 is reasonable is judged according to whether the load sharing ratio G0 of the tunnel primary support and the secondary lining is suitable for the tunnel surrounding rock grade.

[0029] ;

[0030] The relationship between the tunnel surrounding rock of different grades and the suitable G0 is as follows:

[0031] When the tunnel surrounding rock grade is III, the suitable G0 is 0-0.2.

[0032] When the tunnel surrounding rock grade is IV, the suitable G0 is 0.1-0.5.

[0033] When the tunnel surrounding rock grade is V, the suitable G0 is 0.1-0.7.

[0034] When the tunnel surrounding rock grade is VI, the suitable G0 is 0.3-0.9.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] The present application combines the thick-walled cylinder theory stress model of the tunnel and the residual deformation of the tunnel primary support, and pre-fits the deformation-time fitting function of the tunnel section and the final deformation according to the deformation monitoring data by using an exponential function; then, the residual deformation corresponding to the time t when the secondary lining is applied is calculated according to the deformation-time fitting function of the tunnel section and the final deformation; then, the contact pressure P2 between the primary support and the secondary lining after the secondary lining is applied at time t is calculated according to the elastic theory Lami solution formula of the deformation U 21 of the inner wall of the primary support under the action of the surrounding rock pressure P1 and the contact pressure P2 between the primary support and the secondary lining; finally, whether the obtained contact pressure P2 between the primary support and the secondary lining is reasonable is checked, and if not, the time t when the secondary lining is applied is re-determined until P2 is reasonable.

[0037] The method proposed by the present application is particularly suitable for dynamic design of a soft rock large deformation tunnel, and the contact pressure P2 between the primary support and the secondary lining corresponding to the time t when the secondary lining is applied can be accurately predicted through the method, the rationality of the predicted P2 is evaluated, and then the suitable time t when the secondary lining is applied is determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is a flow chart of the method for predicting the secondary lining stress of a soft rock large deformation tunnel according to the present invention.

[0039] Figure 2 is the layout of monitoring points on the tunnel section.

[0040] FIG3 is a graph showing the deformation of each section changing with time.

[0041] Figure 4 is the theoretical stress model of a thick-walled cylinder in a tunnel.

[0042] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] A method for predicting the stress of the secondary lining of a soft rock large deformation tunnel, as shown in FIG1 , comprises the following steps:

[0045] Step 1: Obtain tunnel section dimensions and surrounding rock parameters.

[0046] The tunnel cross-sectional dimensions include the tunnel excavation radius r1 and the tunnel initial support radius r2; the surrounding rock parameters include the surrounding rock elastic modulus E1 and Poisson's ratio μ1.

[0047] It should be noted that when the tunnel has a non-circular cross-section, the tunnel excavation radius r1 and the tunnel initial support radius r2 are calculated according to the equivalent radius. The calculation formula is as follows:

[0048]

[0049] B1 is the tunnel excavation span, h1 is the tunnel excavation height;

[0050]

[0051] B2 is the span of the tunnel's primary support, and h1 is the height of the tunnel's primary support.

[0052] Step 2: Obtain the surrounding rock pressure P1 through ground stress measurement or soil mechanics methods.

[0053] Step 3: During the tunnel excavation process, deformation monitoring points are set up on the tunnel section to carry out deformation monitoring.

[0054] In the present embodiment, as shown in Fig. 2, preferably, deformation monitoring points are arranged at 10 adjacent tunnel sections, and 10 monitoring points are arranged at each section, and the deformation of each monitoring point is monitored by using a total station to monitor the settlement data of each monitoring point.

[0055] Step 4: According to the deformation monitoring data of step 3, the deformation-time curve of the 10 sections is drawn, as shown in Fig. 3, wherein the deformation of each section is the average value of the settlement of all monitoring points of the section; then, the deformation-time fitting function of the tunnel section and the final deformation are obtained by using an exponential function to fit the curve. It should be noted that when fitting, the data of the 10 sections is averaged to obtain a fitting function.

[0056] The expression of the obtained deformation-time fitting function of the tunnel section is as follows:

[0057] , wherein U t is the deformation of the tunnel section at time t, and A is a fitting parameter. In the present embodiment, = 527.87 mm, and A = 5.17.

[0058] Step 5: Assuming that the time t of applying the secondary lining, according to the deformation-time fitting function of the tunnel section and the final deformation of step 2, the residual deformation U c of the secondary lining applied at time t is calculated. , U t is the deformation of the tunnel section at time t.

[0059] Step 6: According to the elastic theory Lami solution of the deformation U 21 of the inner wall of the primary lining under the action of the surrounding rock pressure P1 and the contact pressure P2 between the primary lining and the secondary lining, the contact pressure P2 between the primary lining and the secondary lining after the secondary lining is applied at time t is calculated.

[0060] Referring to Fig. 4, which is a thick-walled cylinder theory stress model of the tunnel, the elastic theory Lami solution of the deformation U 21 is as follows:

[0061] ,

[0062] The deformation U 21 is equal to the residual deformation U c obtained in step 5, and since P1, E1, μ1, r1 and r2 are known, the value of P2 can be obtained according to the above formula.

[0063] Step 7, check if the contact pressure P2 between the primary support and the secondary lining obtained in step 6 is reasonable, if yes, stop the calculation, if not, re-determine the secondary lining construction time, repeat step 5-step 7, until P2 is reasonable.

[0064] Further, whether P2 is reasonable can be judged according to whether the tunnel primary support and secondary lining load sharing ratio G0 is suitable for the tunnel surrounding rock grade.

[0065]

[0066] The relationship between different grades of tunnel surrounding rock and the suitable G0 is shown in the following table (recommended in combination with the current specification and construction technology system and other comprehensive factors):

[0067]

[0068] The tunnel surrounding rock grade is divided into I to VI according to the Railway Tunnel Design Specification (TB10003-2005), and the specific grade division rules are conventional technology in the art, which will not be described here.

[0069] The above has made an exemplary description of the present application, it should be explained that, without departing from the core of the present application, any simple modification, modification or other equivalent replacement which can not cost the creative labor of the person skilled in the art falls within the protection scope of the present application.

Claims

1. A method for predicting the secondary lining stress of a soft rock large deformation tunnel, characterized by: The following steps are involved: Step 1: Obtain tunnel section dimensions and surrounding rock parameters; The tunnel cross-sectional dimensions include the tunnel excavation radius r1 and the tunnel initial support radius r2; The surrounding rock parameters include the surrounding rock elastic modulus E1 and Poisson's ratio μ1; Step 2: Obtain surrounding rock pressure P1; Step 3: During tunnel excavation, deformation monitoring points are set up on the tunnel section to monitor deformation; Step 4: Draw the deformation curve of the tunnel section over time based on the deformation monitoring data in step 3, and use the exponential function to fit the deformation-time fitting function of the tunnel section and the final deformation. ； Step 5: Assuming the second lining construction time t, according to the deformation-time fitting function and final deformation of the tunnel section obtained in step 4 Calculate the residual deformation U corresponding to the application of the second lining at time t c , , U t is the tunnel section deformation at time t; Step 6: Based on the thick-walled cylinder theory, the deformation U of the inner wall of the primary support under the surrounding rock pressure P1 and the contact pressure P2 between the primary support and the secondary lining is calculated. 21 The contact pressure P2 between the primary support and the secondary lining after the secondary lining is applied at time t is calculated using the Lamme solution of elastic theory. U 21 The Lammite solution of elastic theory is as follows: ， The U 21 Equal to the residual deformation U obtained in step 5 c ; Step 7: Check whether the contact pressure P2 between the primary support and the secondary lining obtained in step 6 is reasonable. If it is reasonable, stop the calculation. If it is unreasonable, redetermine the secondary lining application time and repeat steps 5 to 7 until P2 is reasonable.

2. The method for predicting the secondary lining stress of a soft rock large deformation tunnel according to claim 1 is characterized by: In step 1, when the tunnel has a non-circular cross-section, the tunnel excavation radius r1 and the tunnel initial support radius r2 are calculated according to the equivalent radius. The calculation formula is as follows: ， B1 is the tunnel excavation span, h1 is the tunnel excavation height; ， B2 is the span of the tunnel's primary support, and h2 is the height of the tunnel's primary support.

3. The method for predicting the secondary lining stress of a soft rock large deformation tunnel according to claim 1 is characterized by: The deformation of monitoring points on the tunnel section is monitored using a total station.

4. The method for predicting the secondary lining stress of a soft rock large deformation tunnel according to claim 1 is characterized by: The deformation-time fitting function expression of the tunnel section is as follows: , where U t is the tunnel section deformation at time t, and A is the fitting parameter.

5. The method for predicting the secondary lining stress of a soft rock large deformation tunnel according to claim 1 is characterized by: In step 7, the rationality of P2 is determined based on whether the load sharing ratio G0 of the primary support and secondary lining of the tunnel is suitable for the tunnel surrounding rock level; ； The relationship between different levels of tunnel surrounding rock and suitable G0 is as follows: When the tunnel surrounding rock grade is III, the appropriate G0 is 0~0.2; When the tunnel surrounding rock grade is IV, the appropriate G0 is 0.1~0.5; When the tunnel surrounding rock grade is V, the appropriate G0 is 0.1~0.7; When the tunnel surrounding rock grade is VI, the suitable G0 is 0.3~0.9.

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