Method for rapid evaluation of liquefaction potential of tunnel underlying sand layer based on vibration inversion

Abstract

This invention relates to the field of liquefaction assessment technology for saturated sandy soil, specifically to a rapid assessment method for the liquefaction potential of sandy soil layers beneath subway train shield tunnels based on vibration inversion. This method addresses the problem of the inability to assess the liquefaction of sandy soils induced by subway train vibration loads, enabling rapid and reliable assessment of the liquefaction probability of sandy soils at a target site under subway train operation. This meets the early warning requirements for liquefaction risks caused by subway vibration in railway underpass shield tunnel projects. The method is based on soil shear wave velocity... V s Determine the cyclic resistance ratio of the soil layer CRR By inverting vibration loads, the equivalent cyclic shear stress ratio of the underlying soil layer was determined. CSR When the equivalent cyclic shear stress ratio CSR greater than Comparison of soil cyclic resistance ratio CRR hour ， The underlying layer of a tunnel is at risk of liquefaction; conversely, the underlying layer of a tunnel is not at risk of liquefaction.

Description

Technical Field

[0001] This invention relates to the field of site saturated sand liquefaction discrimination technology, specifically to a rapid assessment method for the liquefaction potential of sand layers underlying subway train shield tunnels based on vibration inversion. Background Technology

[0002] The long-term cyclic vibration load generated by subway train operation in shield tunnels may induce the accumulation of excess pore water pressure and reduction of effective stress in the sandy soil layer beneath the tunnel, leading to soil liquefaction. This can affect the deformation and stability of the shield tunnel structure and may result in major tunnel engineering accidents. Therefore, the assessment of sandy soil liquefaction damage has become an important aspect.

[0003] Currently, representative methods for assessing the liquefaction potential of sandy soils can be categorized into three types: empirical discrimination, laboratory test discrimination, and machine learning discrimination. Empirical discrimination methods obtain corresponding indicators through standard penetration tests, static cone penetration tests, and shear wave velocity tests, and then determine the liquefaction probability based on empirical formulas. Laboratory tests calculate the liquefaction resistance shear stress by inputting equivalent sinusoidal waves into the soil layer, or directly input seismic waves for liquefaction experiments, using the pore pressure ratio to determine the soil's liquefaction resistance strength. Machine learning discrimination methods generate predictive models by learning the sample characteristics of known liquefaction and non-liquefaction data and then using the training results for new samples. However, the practical engineering applications of sandy soil liquefaction potential assessment methods, both domestically and internationally, are mostly focused on seismic liquefaction, while research and applications for sandy soil liquefaction induced by subway train vibration loads are limited. In-situ testing or borehole sampling is often difficult to conduct on-site, and relevant data on the liquefaction behavior of sandy soil strata under subway train loads are scarce. Therefore, a rapid assessment method for the liquefaction potential of sandy soil layers beneath tunnels based on vibration inversion is urgently needed to address the situation of sandy soil liquefaction induced by subway train vibration loads. Summary of the Invention

[0004] This invention provides a rapid assessment method for the liquefaction potential of sandy soil layers beneath tunnels based on vibration inversion. This method addresses the problem of the inability to assess the liquefaction of sandy soil caused by the vibration load of subway trains. It provides a rapid and reliable assessment of the liquefaction potential of sandy soil at the target site under the operation of subway trains, thereby meeting the early warning requirements for liquefaction risks caused by subway vibration in shield tunnel projects under railways.

[0005] This invention is achieved through the following technical solution:

[0006] A rapid assessment method for the liquefaction potential of underlying sandy soil layers in tunnels based on vibration inversion includes the following steps:

[0007] S10. Determine the soil characteristics of the underlying layer of the tunnel;

[0008] S20. Calculation of shear wave velocity based on soil characteristics V s ;

[0009] S30, Based on soil shear wave velocity V s Determine the cyclic resistance ratio of the soil layer CRR ;

[0010] S40. Determine the equivalent cyclic shear stress ratio of the underlying soil layer through vibration load inversion. CSR ;

[0011] S50, Comparison with the soil cyclic resistance ratio obtained in step S30 CRR The equivalent cyclic shear stress ratio obtained in step S40 CSR The magnitude of the vibration was assessed to evaluate the likelihood of liquefaction in the underlying strata of the tunnel.

[0012] When the equivalent cyclic shear stress ratio CSR is greater than Comparison of soil cyclic resistance ratio CRR hour ， The underlying layer of a tunnel is at risk of liquefaction; conversely, the underlying layer of a tunnel is not at risk of liquefaction.

[0013] Furthermore, step S20 also includes the following steps:

[0014] S201. Calculation of initial small-strain shear modulus of soil layer based on soil characteristics G 0;

[0015] S202, Based on initial small strain shear modulus G 0. Calculate the soil shear wave velocity using the following formula. V s :

[0016]

[0017] in, r This represents the soil density.

[0018] Furthermore, in step S10, the soil characteristics include the target soil layer void ratio. e Minimum void ratio is e min , soil layer unit weight c and the average vertical effective stress of the corresponding soil layer s 1´.

[0019] Furthermore, step S30 includes the following steps:

[0020] S301. Considering the anisotropic stress conditions on site, calculate the reference stress according to the following formula. p a Equivalent site wave velocity at an effective overburden pressure of 100 kPa V s1-field ,

[0021]

[0022] in, m The modulus stress level is related to the power exponent. s ´ represents the average effective stress of the soil.

[0023] S302, combined with earthquake magnitude M w The evaluation curve for liquefaction triggering at magnitude 7.5 is used to calculate the cyclic resistance ratio of the soil layer under an earthquake magnitude of 7.5 using the following formula. CRR 7.5 ;

[0024]

[0025] in, C r It is a correction constant. F ( e min The porosity ratio is calculated based on the following function:

[0026] ;

[0027] In step S40, the equivalent cyclic shear stress ratio of the underlying soil layer of the tunnel is determined by vibration load inversion under an earthquake magnitude of 7.5. CSR 7.5 ;

[0028] In step S50, the following calculation formula is used to determine whether there is a risk of liquefaction in the underlying layer of the tunnel:

[0029]

[0030] when F When the value is less than 1, there is no risk of liquefaction in the underlying layer of the tunnel; conversely, there is a risk of liquefaction in the underlying layer of the tunnel.

[0031] Furthermore, in step S302, the correction constant is... C r It is calculated using the following formula:

[0032]

[0033] in, K 0 is the initial static lateral pressure coefficient.

[0034] Furthermore, the initial static lateral pressure coefficient K 0 is calculated using the following formula:

[0035] .

[0036] Furthermore, in step S40, the equivalent cyclic shear stress ratio of the underlying soil layer under the tunnel is determined by vibration load inversion under an earthquake magnitude of 7.5. CSR 7.5 Specifically, it includes the following steps:

[0037] S401. Conduct field measurements of ground surface vibration caused by subway operation and obtain the response at the measuring points;

[0038] S402. Establish a tunnel-foundation finite element model and invert the optimal vibration source. The calculation process is as follows:

[0039]

[0040]

[0041]

[0042] In the formula, For the first i Vibration response spectrum at each measuring point For the first i Vibration transfer function at each measuring point For the first i Vibration load spectrum acting on the tunnel floor at each measuring point; n The number of measurement points participating in the inversion, n≥2, The optimal vibration source time history;

[0043] S403. Apply the vibration source obtained from the inversion as an input load to the finite element model to obtain the shear stress time history curve of the soil layer under the tunnel.

[0044] S404. Convert the shear stress time history curve of the soil layer beneath the tunnel into an equivalent cyclic shear stress ratio. CSR The calculation formula is as follows:

[0045]

[0046]

[0047] in, The maximum value in the time history curve of the shear stress of the target soil layer. To correspond to the equivalent cyclic shear stress, This represents the average effective overburden stress of the corresponding soil layer;

[0048] S405. Determine the equivalent cyclic shear stress ratio of the soil layer beneath the tunnel under an earthquake magnitude of 7.5. CSR 7.5 The calculation method is as follows:

[0049]

[0050]

[0051] in, MSF This is the magnitude scaling factor. M w The magnitude of the earthquake at the scene.

[0052] Furthermore, in step S404,

[0053] s v ´= s 1´.

[0054] Furthermore, in step S201, the initial small-strain shear modulus of the soil layer is calculated based on the soil characteristics. G The process of 0 is as follows:

[0055] First, calculate the initial dynamic shear modulus of the soil layer using the following formula. G 0 ref ,

[0056]

[0057] Then, the initial static lateral pressure coefficient is calculated using the following formula. K 0,

[0058]

[0059] Finally, the initial small strain shear modulus of the soil layer was calculated. G 0,

[0060]

[0061] in, s 3´ represents the effective horizontal confining pressure of the soil, and K 0= s 3´ / s 1´.

[0062] Furthermore, in step S201, the modulus stress level is related to the power exponent. m The value is 0.70; in step S301, the modulus stress level is related to the power exponent. m The value is 0.125.

[0063] The beneficial effects achieved by this invention compared with the prior art are as follows:

[0064] 1. To address the problem of assessing the liquefaction potential of sandy soil induced by subway train vibration loads, this invention provides a rapid assessment method for the liquefaction potential of sandy soil layers beneath tunnels based on vibration inversion. Through vibration load inversion, the equivalent cyclic shear stress ratio of the soil layers beneath the tunnel is determined. CSR ; Comparison layer cyclic resistance ratio CRR and equivalent cyclic shear stress ratio CSR The magnitude of the vibration is used to assess the liquefaction potential of the underlying soil in the tunnel. This invention can quickly and reliably assess the liquefaction potential of sandy soil in the target site under the operation of subway trains, so as to meet the early warning requirements for liquefaction risk caused by subway vibration in the shield tunnel project under the railway.

[0065] This invention rapidly and rationally determines the liquefaction resistance of sandy soil layers and accurately inverts the vibration intensity of subways through theoretical analysis, assesses the risk of soil liquefaction, overcomes the limitations of test conditions in traditional discrimination methods, provides fast assessment speed and eliminates the need for soil sampling to conduct tests, saving test costs and time.

[0066] 2. This invention fully utilizes known survey report information, combined with theoretical calculation methods and finite element simulation, to accurately determine the vibration load of subway trains. Furthermore, through vibration load inversion, it can determine the equivalent cyclic shear stress ratio of the underlying soil layer of the tunnel. CSR ;

[0067] 3. Compared with existing technologies, this invention, through thorough analysis of geological survey report data, theoretically calculates the soil layer's liquefaction resistance by estimating soil layer shear wave velocity, and accurately determines the soil layer's stress level by combining reliable inversion of subway vibration loads to assess the liquefaction potential of the underlying sandy soil layer. This overcomes the shortcomings of traditional discrimination methods under subway vibration load conditions, offers fast prediction speed without requiring target soil samples, saves experimental and computational resources, and features a simple and comprehensive discrimination formula suitable for practical engineering use. It can provide a reference for the construction of shield tunnels under railways and the safety assessment of tunnel structures. Attached Figure Description

[0068] Figure 1 This is a flowchart of the rapid assessment method for liquefaction potential of underlying sandy soil layer in tunnel based on vibration inversion described in this embodiment.

[0069] Figure 2 This is a flowchart of the subway vibration load inversion process described in this embodiment;

[0070] Figure 3 A 1 / 3 octave band comparison chart for inverting subway vibration loads;

[0071] Figure 4 The time history curve of the corresponding soil layer obtained from the inversion vibration source calculation;

[0072] Figure 5This is a diagram showing the layout of the measuring points for on-site vibration testing. Detailed Implementation

[0073] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0074] Taking a shield-tunneled sewage tunnel passing beneath a subway tunnel in Shanghai as an example, it is necessary to first assess the liquefaction potential of the underlying sand layer. This embodiment discloses a rapid assessment method for the liquefaction potential of the underlying sand layer based on vibration inversion. The basic process is as follows: Figure 1 As shown, the main steps include:

[0075] S10. Determine the soil characteristics of the underlying layer of the tunnel;

[0076] Specifically: Based on the engineering geological profile, all underlying sandy soil layers of tunnels affected by the subway line underpass are identified. In this embodiment, the underlying sandy soil layers are mainly sandy soil containing silty sand. Based on the detailed geological survey report, the soil characteristics can be directly determined, including the porosity of the target soil layer. e The minimum porosity is e min unit weight of soil layer c The average vertical effective stress of the corresponding soil layer s 1´;

[0077] S20. Calculation of shear wave velocity based on soil characteristics V s ;

[0078] This step specifically includes the following steps:

[0079] S201. Calculation of initial small-strain shear modulus of soil layer based on soil characteristics G 0;

[0080] The initial small-strain shear modulus of the soil layer was calculated based on the parameter selection method of the Shanghai Soil HSS model. The effective internal friction angle of sandy and silty soils was calculated based on the fitting formula of the Shanghai Municipal Foundation Code data below. f ´,

[0081]

[0082] The effective cohesion of sandy and silty soils is calculated using the fitting formula based on the data from the Shanghai Municipal Foundation Code. c ´,

[0083]

[0084] Based on the above soil characteristics, the initial small strain shear modulus of the soil layer is calculated. G The process of 0 is as follows:

[0085] First, calculate the initial dynamic shear modulus of the soil layer using the following formula. G 0 ref ,

[0086]

[0087] Then, the initial static lateral pressure coefficient is calculated using the following formula. K 0,

[0088]

[0089] Finally, the initial small strain shear modulus of the soil layer was calculated. G 0,

[0090]

[0091] in, m The modulus stress level is related to the power exponent; in this embodiment, m is taken as 0.70 in this step. s 3´ represents the effective horizontal confining pressure of the soil, and K 0= s 3´ / s 1´;

[0092] S202, Based on initial small strain shear modulus G 0. Calculate the soil shear wave velocity using the following formula. V s :

[0093]

[0094] in, r The density of the soil, i.e. c / g ;

[0095] S30, Based on soil shear wave velocity V s Determine the cyclic resistance ratio of the soil layer (soil layer liquefaction resistance strength). CRR ;

[0096] In this embodiment, the earthquake magnitude is set to 7.5, a commonly used magnitude value in studies of seismic liquefaction of saturated sand, and the cyclic resistance ratio of the soil layer under the earthquake magnitude of 7.5 is calculated. CRR 7.5 ;

[0097] Specifically, the following steps are included:

[0098] S301. Taking into account the anisotropic stress conditions on site, calculate the reference stress according to the following formula. p a The equivalent site wave velocity when the effective overburden pressure is equal to 100 kPa. V s1-field ,

[0099]

[0100] in, m The modulus stress level is related to the power exponent; in this embodiment, m is taken as 0.125 in this step. s ´ represents the average effective stress of the soil.

[0101] S302. In this embodiment, the earthquake magnitude is taken into account. M w The evaluation curve for liquefaction triggering at magnitude 7.5 is used to calculate the cyclic resistance ratio of the soil layer under an earthquake magnitude of 7.5 using the following formula. CRR 7.5 ;

[0102]

[0103] in, F ( e min The porosity ratio is calculated based on the following function:

[0104] ;

[0105] C r It is a correction constant, and is calculated using the following formula:

[0106] ;

[0107] S40. Determine the equivalent cyclic shear stress ratio of the underlying soil layer through vibration load inversion. CSR ;

[0108] For effective comparison, it is necessary to determine the equivalent cyclic shear stress ratio of the soil layer beneath the tunnel under an earthquake magnitude of 7.5. CSR 7.5 This embodiment employs a vibration source inversion method that combines on-site measurements and finite element simulation, specifically including the following steps:

[0109] S401. Conduct field measurements of ground surface vibration caused by subway operation and obtain the response at the measuring points;

[0110] First, conduct on-site vibration measurements caused by subway operation. For example... Figure 5 As shown, the shield-tunneled sewage tunnel has a burial depth of 27.65m, while the bottom burial depths of the subway tunnels for both directions are 13.38m and 13.75m, respectively. Two measuring points (measuring point 1 and measuring point 2) are arranged inside the shield tunnel. Measuring point 1 is located at the 100th ring, and measuring point 2 is located at the 119th ring. The two measuring points are located directly below the subway tunnels for both directions, and are used to record the vibration response.

[0111] Data acquisition was performed using a micro-vibration tester, simultaneously recording the velocity and acceleration time histories of the ground surface in three mutually perpendicular directions caused by subway operation. The test was conducted during the evening rush hour, lasting 20 minutes, with a sampling frequency of 512 Hz, recording a total of 8 complete waveforms including the passage of both upward and downward trains. Fourier transforms were performed on the obtained on-site measured vibration time histories to obtain the... i Vibration response spectrum at each measuring point P i ( oh ),like Figure 2 As shown;

[0112] S402. Establish a tunnel-foundation finite element model and invert the optimal vibration source;

[0113] A finite element model of a subway tunnel (both directions), a shield tunnel, and a layered foundation was established, and a white noise vibration load was applied to the subway tunnel floor. According to vibration transfer function theory, under the assumptions of zero initial conditions and linearity, the transfer function of a linear system is equal to the ratio of the Laplace transform of the system response to the excitation. For the vibration propagation system caused by subway operation, it is assumed that the Fourier transform of the white noise source force sequence is known. F w ( oh (The spectrum of the vibration load acting on the tunnel floor) and the Fourier transform of the vibration acceleration at the measuring point. P wi ( oh (Measurement point response spectrum), then the vibration transfer function of the linear system C i ( oh )for:

[0114]

[0115] Based on this, time history data of the vibration at the measuring point caused by subway operation has been obtained through on-site measurements, namely the [data missing]. i Vibration response spectrum at each measuring point If the transfer function of the system is known, the th can be obtained by inversion using the following formula. i Vibration source load spectrum acting on the tunnel floor at each measuring point :

[0116]

[0117] A finite element model of a subway tunnel-layered foundation-shield tunnel was established, and a unit amplitude white noise load was applied to the subway tunnel lining to calculate the system's transfer function. Two measuring points were used in the inversion, resulting in two vibration sources. The least squares method was employed to calculate and obtain the optimal vibration source. It was assumed that the optimal vibration source and the inverted vibration sources at each measuring point... The cumulative error between them is:

[0118]

[0119] In the formula, n The number of measurement points participating in the inversion is set to 2. When y When it is at its minimum, the corresponding This represents the optimal vibration source spectrum. Furthermore, for... By performing an inverse Fourier transform, the optimal vibration source time history of the subway vibration load can be reconstructed. :

[0120]

[0121] S403. Apply the vibration source obtained from the inversion as an input load to the finite element model to obtain the shear stress time history curve of the soil layer under the tunnel.

[0122] The inverted vibration source obtained in the previous step is applied as the input load to the finite element model, and the vibrations at the two corresponding measurement points are calculated. Z The vibration magnitude was determined and compared with the field measurement results. A schematic diagram of some inversion results is shown below. Figure 3 As shown. After verification, using the above finite element numerical model, based on the inverted vibration source, the shear stress time history curve of the soil layer beneath the tunnel was calculated and obtained, as shown. Figure 4 As shown;

[0123] S404. Convert the shear stress time history curve of the soil layer beneath the tunnel into an equivalent cyclic shear stress ratio. CSR ;

[0124] Based on the obtained shear stress time history curve, determine the corresponding equivalent cyclic shear stress level. CSR According to the Palmgren-Miner assumption, the energy in each stress cycle has a cumulative destructive effect on the material, which is proportional to the magnitude of the energy in that cycle and independent of the actual stress wave sequence. Therefore, the effect of stress over a period of time can be equivalent to the effect of a certain value of uniform stress, as calculated by the following formula:

[0125]

[0126] in, The maximum value in the time history curve of the shear stress of the target soil layer. This corresponds to the equivalent cyclic shear stress;

[0127] The corresponding equivalent cyclic shear stress ratio is calculated as follows:

[0128]

[0129] in, s v ´ represents the average effective overburden stress of the corresponding soil layer. s v ´= s 1´;

[0130] S405. Determine the equivalent cyclic shear stress ratio of the soil layer beneath the tunnel under an earthquake magnitude of 7.5. CSR 7.5 The calculation method is as follows:

[0131]

[0132]

[0133] in, MSF This is the magnitude scaling factor. M w The magnitude of the earthquake at the site is given. However, the magnitude of the earthquake caused by the subway load in the soil layer beneath the tunnel must be less than 7.5. Therefore:

[0134]

[0135] S50, Comparison with the soil cyclic resistance ratio obtained in step S30 CRR The equivalent cyclic shear stress ratio obtained in step S40 CSR The magnitude of the vibration was assessed to evaluate the likelihood of liquefaction in the underlying strata of the tunnel.

[0136] In this embodiment, the equivalent cyclic shear stress ratio of the soil layer beneath the tunnel under an earthquake magnitude of 7.5 is determined by comparing step S30. CSR 7.5 Step S40 determines the equivalent cyclic shear stress ratio of the soil layer beneath the tunnel under an earthquake magnitude of 7.5. CSR 7.5 Assess the potential impact of vibration on the liquefaction of the underlying strata of the tunnel;

[0137] The following formula can be used to determine whether there is a risk of liquefaction in the underlying layer of a tunnel:

[0138]

[0139] when FWhen the value is less than 1, there is no risk of liquefaction in the underlying layer of the tunnel; conversely, there is a risk of liquefaction in the underlying layer of the tunnel.

[0140] Using the above scheme, the equivalent cyclic shear stress ratio of the underlying soil layer of the tunnel is determined through vibration load inversion. CSR ; Comparison layer cyclic resistance ratio CRR and equivalent cyclic shear stress ratio CSR The invention assesses the liquefaction potential of sandy soil under a tunnel by evaluating the magnitude of vibration. It can quickly and reliably assess the liquefaction potential of sandy soil at a target site under the operation of a subway train, meeting the early warning requirements for liquefaction risk caused by subway vibration in shield tunnel projects under railways. By rapidly and reasonably determining the liquefaction resistance of sandy soil layers and accurately inverting the intensity of subway vibration, the invention assesses the liquefaction risk of the soil, overcoming the limitations of test conditions in traditional discrimination methods. The assessment is fast and does not require soil sampling for testing, saving test costs and time.

Claims

1. A method for rapid evaluation of liquefaction potential of sand layer underlying a tunnel based on vibration inversion, characterized in that, The method comprises the following steps: S10, determining the soil characteristics of the tunnel underlayer; S20, calculating the shear wave velocity based on the soil characteristics V s ; S30, determining the soil layer shear wave velocity V s , determining the soil layer cyclic resistance ratio CRR ; The step S30 comprises the following steps: S301、Consider the anisotropic stress condition of the site, calculate the reference stress according to the following formula p a Effective overburden pressure for 100 kPa V s1-field , wherein, m is the power exponent related to the modulus stress level, σ is the average effective stress of the soil. S302, combining the earthquake magnitude M w =7.5 under the field liquefaction trigger evaluation curve, the soil cyclic resistance ratio under the condition of earthquake magnitude of 7.5 is calculated by the following formula CRR 7.5 ; wherein C r is a correction number, F ( e min ) is calculated according to the following void ratio function: ； S40, determine the equivalent cyclic shear stress ratio of the underlying soil layer of the tunnel by vibration load inversion CSR ; In step S40, the equivalent cyclic shear stress ratio of the underlying soil layer of the tunnel under the condition of a seismic magnitude of 7.5 is determined by vibration load inversion CSR 7.5 ; specifically comprising the following steps: S401, performing field surface vibration measurement caused by subway operation to obtain the response of the measuring point; S402, establishing a tunnel-foundation finite element model, and inverting the optimal vibration source, and the calculation process is as follows: wherein, is the vibration response spectrum at the i th measurement point, is the vibration transfer function at the i th measurement point, is the vibration load spectrum acting on the tunnel floor at the i th measurement point; n is the number of measurement points participating in the inversion, n≥2, is the optimal vibration source time history; S403, applying the inverted vibration source as an input load to the finite element model to obtain the time-history curve of the shearing stress of the underlayer soil under the tunnel; S404, convert the tunnel underlying soil shear stress time history curve into equivalent cyclic shear stress ratio CSR The calculation formula is as follows: wherein, is the maximum value in the time history curve of the shear stress of the target soil layer, is the equivalent cyclic shear stress corresponding to the average overburden effective stress of the soil layer, and is the average overburden effective stress of the soil layer. S405、Determine the equivalent cyclic shear stress ratio of the tunnel underlying soil layer under the condition of earthquake magnitude of 7.5 CSR 7.5 The calculation method is as follows: wherein, MSF is a magnitude scaling factor, M w is the local earthquake magnitude; S50, the ratio of the cyclic resistance of the soil layer obtained in step S30 to the ratio of the equivalent cyclic shear stress obtained in step S40 CRR CSR the size of the ratio of the cyclic resistance of the soil layer obtained in step S30 to the ratio of the equivalent cyclic shear stress obtained in step S40, to evaluate the possibility of liquefaction of the underlying layer of the tunnel by vibration;​ When the equivalent cyclic shear stress ratio CSR is greater than The contrast soil cyclic resistance ratio CRR When ， The tunnel underlying layer has liquefaction risk; otherwise, the tunnel underlying layer has no liquefaction risk.

2. The method for rapid evaluation of the liquefaction potential of a sand layer underlying a tunnel according to claim 1, characterized in that, The step S20 further comprises the following steps: S201、based on the soil characteristics, calculate the initial small strain shear modulus of the soil layer G 0; S202、based on the initial small strain shear modulus G 0, the soil layer shear wave velocity is calculated according to the following formula V s : wherein, ρ is the density of the soil.

3. The method for rapid evaluation of the potential of liquefaction of a sand layer underlying a tunnel according to claim 2, characterized in that, In step S10, the soil characteristics include the target soil layer void ratio e , the minimum void ratio is e min , the soil layer unit weight γ , and the average vertical effective stress of the corresponding soil layer σ 1´.

4. The method for rapid evaluation of the potential of liquefaction of a sand layer underlying a tunnel according to claim 3, characterized in that, In step S50, whether the tunnel underlayer has a liquefaction risk is determined by using the following calculation formula: When F <1, the tunnel underlayer has no liquefaction risk; otherwise, the tunnel underlayer has liquefaction risk.

5. The method for rapid evaluation of the potential of liquefaction of a sand layer underlying a tunnel according to claim 4, characterized in that, In step S302, the constant is corrected C r is calculated by the following equation: wherein K 0 is the initial static side pressure coefficient.

6. The method for rapid evaluation of the potential of liquefaction of a sand layer underlying a tunnel according to claim 5, characterized in that, initial static side pressure coefficient K 0 is calculated by the following equation: 。 7. The method for rapid evaluation of the potential of liquefaction of a sand layer underlying a tunnel according to claim 4, characterized in that, In step S404, σ v ´= σ 1´。 8. The method for rapid evaluation of the liquefaction potential of a sand layer underlying a tunnel according to any one of claims 4 to 7, characterized in that, In step S201, the initial small-strain shear modulus of the soil layer is calculated based on the soil characteristics G The process of 0 is as follows: First, the dynamic shear initial modulus of the soil layer is calculated by the following equation G 0 ref , Then, the initial static side pressure coefficient is calculated by the following equation K 0, Finally, the initial small-strain shear modulus of the soil layer is calculated G 0, wherein, σ 3' is the horizontal effective confining pressure of the soil mass, and K 0 = 3' / 1' σ 3' / 1' σ 1'.

9. The method for rapid evaluation of the potential of liquefaction of a sand layer underlying a tunnel according to claim 8, characterized in that, In step S201, the modulus stress level dependent power exponent m with a value of 0.70; In step S301, the modulus stress level dependent power exponent m is taken as 0.125.

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