A pile foundation response test method under a double-line tunnel shield side-penetrating working condition

Abstract

The present application relates to the technical field of tunnel construction, and particularly relates to a pile foundation response test method under a double-line tunnel shield side-penetration working condition. Residual strain is obtained after the first tunneling body passes and rests until the end, and the stiffness attenuation rate at each depth is calculated according to the attenuation linkage ratio; when the second tunneling body passes from the other side, the cumulative axial strain and the cumulative hoop strain are obtained by merging the stiffness attenuation rate as the weight, the real-time axial and hoop strain and the residual strain at each depth, and the cumulative plastic strain, the cumulative settlement and the bottom interface stiffness are calculated accordingly, so that the quantitative characterization of the pile body deformation and the internal force distribution evolution law in the whole double-line construction process is realized.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a test method for pile foundation response under the condition of a double-track tunnel shield tunneling side-passing. Background Technology

[0002] When large-diameter shield tunnels pass through the core urban areas, they often need to pass alongside existing bridge pile foundations. The ground disturbance caused by shield tunneling alters the interaction between the pile foundation and the soil, leading to additional deformation and redistribution of internal forces in the pile body. In severe cases, this can affect the normal service safety of the bridge foundation. Furthermore, when two tunnels pass sideways sequentially, the disturbances already generated by the later tunnel on the earlier tunnel have a cumulative effect.

[0003] In the prior art, such as Chinese invention patent with publication number CN121805017A, a test method and device for responding soil deformation and tunnel stress during foundation pit excavation are disclosed. Based on the deformation-stress coupling prediction model and the excavation disturbance quantification model, a dynamic coupling response model is constructed, and the dynamic coupling curve of soil deformation and tunnel stress is output to capture the dynamic coupling law and provide technical support for underground engineering construction safety assessment and parameter optimization.

[0004] However, the existing technologies still have the following shortcomings: 1. They do not address the superimposed impact of the dual-track construction sequence on the pile foundation response, and lack simulation and quantification of the accumulation of residual strain and stiffness attenuation process in the pile body, resulting in unclear superimposed effects and evolution laws of the impact of dual-track tunnel lateral penetration on the pile foundation. 2. They do not adequately reflect the dynamic changes between pile top settlement and pile bottom bearing capacity, making it difficult to quantify the degree of interaction between the pile foundation and the soil caused by shield tunnel lateral penetration, thus failing to provide a basis for timely detection of abnormal states such as pile bottom voids or loss of bearing capacity. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a test method for pile foundation response under the condition of side-passing of a double-track tunnel shield.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a pile foundation response test method under the condition of double-track tunnel shield tunneling, including the following steps: applying bidirectional load to the pile foundation model to obtain the initial axial and circumferential strain, top settlement and bottom support force at each depth of the pile body.

[0007] The tunnel body passes through from one side. Based on the real-time and initial top settlement and bottom support force, the settlement difference and support force difference are obtained, and the attenuation linkage ratio is calculated accordingly.

[0008] After the tunnel body passes through, it is left to stand until the end. The residual strain is obtained based on the real-time and initial axial and circumferential strains. The attenuation linkage ratio is used as the overall control factor, and the stiffness attenuation rate at each depth is calculated in combination with the residual strain.

[0009] The tunnel body 2 passes through from the other side. Based on the stiffness attenuation rate, residual strain, and real-time axial and circumferential strain, the cumulative axial strain and cumulative circumferential strain are obtained by merging them at each depth. Based on this, the cumulative plastic strain, cumulative settlement, and bottom interface stiffness are calculated.

[0010] Additional plastic strain and additional circumferential stiffness reduction rate are obtained based on cumulative plastic strain, residual strain, and initial circumferential strain; additional settlement is calculated from cumulative settlement and settlement difference, and additional interface stiffness is calculated from bottom interface stiffness and bearing force difference.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention obtains the residual strain after the first tunnel body passes through and is left to stand until the end of the project. The attenuation linkage ratio is used as the overall control factor, and the stiffness attenuation rate at each depth is calculated in combination with the residual strain. When the second tunnel body passes through from the other side, the stiffness attenuation rate is used as the weight. Based on the real-time axial and circumferential strain and residual strain, the cumulative axial strain and cumulative circumferential strain are merged at each depth to obtain the cumulative plastic strain, cumulative settlement and bottom interface stiffness. This realizes the quantitative characterization of the deformation and internal force distribution evolution law of the pile body during the entire process of double-line construction.

[0012] 2. This invention quantifies the dynamic changes between pile top settlement and pile bottom support force by calculating the attenuation linkage ratio based on real-time and initial top settlement and bottom support force during the lateral passage of the tunnel body. This provides a basis for timely detection of abnormal states such as pile bottom void or loss of bearing capacity.

[0013] 3. This invention obtains additional plastic strain and additional circumferential stiffness reduction rate based on cumulative plastic strain, residual strain, and initial circumferential strain; additional settlement is calculated from cumulative settlement and settlement difference, and additional interface stiffness is calculated from bottom interface stiffness and bearing force difference, thereby revealing the superimposed effect law of subsequent tunnel construction on the already disturbed pile foundation of the preceding tunnel, and providing data support for clarifying the process of residual strain accumulation and stiffness attenuation of pile body caused by the dual-track construction sequence. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the test method of the present invention.

[0016] Figure 2 This is a schematic diagram of the process for calculating the attenuation linkage ratio according to the present invention.

[0017] Figure 3This is a schematic diagram illustrating the process of calculating the stiffness attenuation rate at various depths according to the present invention.

[0018] Figure 4 This is a schematic diagram of the process for calculating cumulative settlement and bottom interface stiffness according to the present invention.

[0019] Figure 5 This is a top view of the pile foundation model.

[0020] Figure 6 This is a schematic diagram showing the arrangement of strain gauges and strain-type micro earth pressure cells on a single pile foundation model.

[0021] Figure 7 This is a curve showing the axial strain change of the front side of the No. 1 pile foundation model during the tunneling process from one side.

[0022] In the diagram: LT, left tunnel; RT, right tunnel; ED, excavation direction; P1, pile model 1; P2, pile model 2; P3, pile model 3; VL, vertical load; SG, strain gauge; EPC, strain-type micro earth pressure cell; d, fixed spacing; PSS, axial strain; PED, depth; PS, pile model; ISF, initial shield face; SPF, shield penetration face; SE1, reference section of pile model 1; SE2, reference section of pile model 2; SE3, reference section of pile model 3. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. Furthermore, it should be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale.

[0024] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification.

[0025] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] The following describes in detail, with reference to the accompanying drawings, the specific scheme of the pile foundation response test method under the condition of side-passing of a double-track tunnel shield provided by the present invention.

[0028] Please see Figure 1 , Figure 5 and Figure 6 The present invention provides a flowchart of a pile foundation response test method under the condition of a double-track tunnel shield tunneling, which includes the following steps: Step S1, apply bidirectional load to the pile foundation model to obtain the initial axial and circumferential strain, top settlement and bottom support force at each depth of the pile body.

[0029] In practice, the plane at the top of the pile foundation model is used as the zero-depth reference, and the length and diameter of the pile foundation model are measured. To avoid data redundancy and layout difficulties due to excessively dense measuring points, one-seventh of the pile foundation model's length is used as a fixed interval. Starting from the top of the pile foundation model, the depth position is marked segment by segment along the pile axis downwards at fixed intervals. Each marked position corresponds to a depth layer (e.g., ...). Figure 6 (As shown).

[0030] Two orientations are selected in the circumferential direction at each depth layer; one orientation is the side facing the excavation direction, defined as the front; the other orientation is the side adjacent to the side facing the excavation direction, defined as the side. On the front, axial measuring points are arranged in a direction parallel to the pile axis, and circumferential measuring points are arranged in a direction perpendicular to the pile axis. On the side, axial and circumferential measuring points are arranged in the same manner.

[0031] Then attach strain gauges (such as) to each axial and circumferential measuring point. Figure 6 As shown in the diagram, the output end of each strain gauge is connected to a static strain gauge. Specifically, the sensitive grid direction of the strain gauge at the axial measuring point is parallel to the pile axis; the sensitive grid direction of the strain gauge at the circumferential measuring point is perpendicular to the pile axis.

[0032] After completing the layout of measuring points and the bonding of strain gauges, according to the pre-installation position of the pile foundation model in the model box, the strain gauge micro earth pressure cell is buried in the model box filled with soil with the bearing surface facing upward. Then, the pile foundation model is buried in the model box so that the bottom end face of the pile is directly opposite and in direct contact with the bearing surface of the strain gauge micro earth pressure cell; the pressure cell is used as the bearing force measuring point.

[0033] After the pile foundation model is installed, an adjustable special steel frame is set up directly above the pile foundation model. The non-contact laser displacement sensor is fixed on the steel frame. The height of the steel frame is adjusted so that the laser beam emission direction is perpendicular to the pile top surface and points from above to the pile top surface. This allows the change in the vertical straight distance (hereinafter referred to as distance) obtained by subsequent measurements to directly reflect the vertical settlement of the pile top. The laser displacement sensor is used as the settlement measuring point.

[0034] Then, bidirectional loads (vertical and horizontal) are simultaneously applied to the pile foundation model using existing loading devices, and voltage signals at each moment are collected using static strain gauges and converted into resistance values. Starting from the moment the bidirectional load reaches the target value, the real-time distance output from settlement measuring points is continuously collected. The standard deviation of the real-time distance over the ten consecutive moments preceding the current moment is calculated; the repeatability accuracy from the product specifications of the non-contact laser displacement sensor is read. When the standard deviation is less than the repeatability accuracy, the deformation is considered stable; otherwise, the deformation is considered unstable, and data is collected for the next moment, repeating the above calculation and judgment process. The time period from the moment the load reaches the target value to the moment the deformation stabilizes is defined as the load holding period.

[0035] After applying bidirectional load to the target value to the pile foundation model, the resistance time series output from the axial measuring points on the front and side of the same depth layer are extracted. The two resistance time series are aligned according to time. At each time step, the resistance value of the axial measuring point on the front is subtracted from the resistance value of the axial measuring point on the side. The subtraction results are arranged in chronological order to obtain the axial resistance difference time series. Based on the resistance time series output from the circumferential measuring points on the front and side of the same depth layer, the circumferential resistance difference time series is calculated similarly.

[0036] Subsequently, all values ​​of the axial resistance difference time series within the load-bearing period are extracted, and the arithmetic mean of all extracted values ​​is calculated as the axial resistance reference after pressure is applied. Similarly, all values ​​of the circumferential resistance difference time series within the load-bearing period are extracted, and the arithmetic mean of all extracted values ​​is calculated as the circumferential resistance reference after pressure is applied.

[0037] Next, the axial resistance reference at the last sampling moment before the application of bidirectional load on the pile foundation model is used as the axial reference, and the circumferential resistance reference is used as the circumferential reference. The difference between the axial resistance reference and the axial reference after the application of load is calculated, and the difference is divided by the sensitivity coefficient of the strain gauge to obtain the initial axial strain; the difference between the circumferential resistance reference and the circumferential reference after the application of load is calculated, and the difference is multiplied by the preset strain conversion coefficient to obtain the initial circumferential strain.

[0038] The sensitivity coefficient of the strain gauge is provided by the strain gauge manufacturer. The strain conversion coefficient is obtained experimentally: the strain gauge is attached to a specimen made of the same material as the pile foundation model; the specimen is mounted on a universal testing machine, a known strain is applied to the specimen, the change in resistance of the strain gauge is measured, and the ratio of the relative rate of change of resistance to the known strain is calculated. The obtained ratio is used as the strain conversion coefficient. The specific experimental procedure is existing technology and will not be described in detail here.

[0039] After applying bidirectional load to the pile foundation model to the target value, the distance time series output by the settlement measuring points during the load-bearing period is extracted, and the arithmetic mean of all values ​​in the distance time series is calculated as the initial top settlement. The pressure time series output by the support force measuring points during the load-bearing period is extracted, and the arithmetic mean of all values ​​in the pressure time series is calculated as the initial bottom support force.

[0040] The calculation process for the aforementioned target value is as follows: The standard value of the pile top reaction force and the diameter of the prototype pile foundation are read from the engineering design drawings; the diameter of the pile foundation model is divided by the diameter of the prototype pile foundation to obtain the length similarity ratio; the elastic modulus of the pile foundation model is divided by the elastic modulus of the prototype pile foundation to obtain the elastic modulus similarity ratio; the standard value of the pile top reaction force, the square of the length similarity ratio, and the elastic modulus similarity ratio are multiplied together to obtain the target value of the vertical load. The elastic modulus is determined through existing material tensile tests, which will not be elaborated upon here.

[0041] The density of the soil filled in the model box was measured using the ring cutter method. The density value was multiplied by the gravitational acceleration to obtain the soil weight. The internal friction angle of the soil filled in the model box was determined by a direct shear test. The specific measurement and testing process is existing technology and will not be described in detail here. The coefficient of earth pressure at rest was obtained by subtracting the sine of the internal friction angle from the given value. The target value of the horizontal load was obtained by multiplying the soil weight, the length of the pile foundation model, and the coefficient of earth pressure at rest by the pile foundation model diameter.

[0042] Please see Figure 2 and Figure 5 Step S2: Pass the tunnel body through from one side. Based on the real-time and initial top settlement and bottom support force, obtain the settlement difference and support force difference, and calculate the attenuation linkage ratio accordingly.

[0043] In practice, the propulsion system in the tunnel boring machine (TBM) propels the cutterhead of the tunnel boring machine (TBM) horizontally through the side area of ​​the pile foundation model, while a rotation system controls the rotation of the shaft and cutterhead to carry out tunnel boring machine (TBM) construction. For example... Figure 5 As shown, three pile foundation models are arranged sequentially along the tunneling direction inside the model box. One pile foundation model is set between the left tunnel and the right tunnel, on one side of the left tunnel, and on one side of the right tunnel. Tunneling body one and tunneling body two excavate the left tunnel and the right tunnel respectively, with the left tunnel being constructed before the right tunnel.

[0044] Using the vertical plane containing the pile axis as the reference section (e.g.) Figure 5(As shown by the red dashed line in the middle), the reference section is perpendicular to the tunneling direction; during the process of the tunnel body passing through one side, the time when the front end of the cutterhead of the tunnel body one reaches the reference section is recorded as the start time, and the time when the tail end of the cutterhead of the tunnel body one leaves the reference section is recorded as the end time. The time period between the start time and the end time is the time period when the cutterhead passes through the pile axis. This time period is taken as the time interval, which represents the time period when the construction of the tunnel body one causes the most concentrated disturbance to the pile foundation model.

[0045] like Figure 5 As shown, during the advance of the tunnel body from the initial shield face to the shield penetration face, the cutterhead front end reaches the initial shield face, each reference section, and the shield penetration face respectively. During this process, the axial strain data of the front face of each pile foundation model is acquired in real time. The axial strain data of the front face of pile foundation model No. 1 is shown below. Figure 7 As shown. The initial shield face is the vertical end face when the soil of the model box initially contacts the front end of the cutterhead, and the shield penetration face is the vertical end face when the soil of the model box is completely penetrated by the front end of the cutterhead.

[0046] Next, based on the real-time settlement time series output by the settlement measuring points and the real-time support force time series output by the support force measuring points, the arithmetic mean of all real-time settlement values ​​within the time interval is subtracted from the initial top settlement to obtain the settlement difference; the arithmetic mean of all real-time support force values ​​within the time interval is subtracted from the initial bottom support force to obtain the support force difference.

[0047] Then, the ratio of settlement difference to bearing force difference is used as the benchmark ratio, which represents the average proportional relationship between the pile top settlement change and the pile bottom bearing force change within the time interval. Based on the real-time settlement time series and the real-time bearing force time series, the ratio of real-time settlement value to real-time bearing force value at each moment from the end of the time interval to the moment when the tunnel body stops advancing is calculated as the real-time ratio. The real-time ratio represents the proportional relationship between the current settlement and the current bearing force at each moment after the cutterhead passes through the pile axis.

[0048] Then, the difference between the real-time ratio and the baseline ratio is taken as the response deviation; the sum of all response deviations is divided by the number of all times after the end of the time interval to obtain the attenuation linkage ratio.

[0049] Please see Figure 3 and Figure 7 Step S3: After the tunnel body passes through, it is left to stand until the end. Based on the real-time and initial axial and circumferential strains, the residual strain is obtained. The residual strain includes axial residual strain and circumferential residual strain. The attenuation linkage ratio is used as the overall control factor, and the stiffness attenuation rate at each depth is calculated in combination with the residual strain.

[0050] In practice, after the tunnel body has completely passed through the pile foundation model, all tunneling operations are stopped and this moment is recorded as the start time of static settling. The state of the soil and pile foundation model within the model box remains unchanged, and the output data of all measuring points is continuously monitored. The difference between the maximum and minimum values ​​of the output data of the measuring points within the ten consecutive sampling moments prior to the current moment is calculated. When the difference is less than a set threshold, the deformation is determined to be stable; otherwise, data is collected at the next moment, and the above calculation and judgment are repeated. The moment when the deformation is determined to be stable is recorded as the end time of static settling.

[0051] The process of setting the threshold is as follows: Before the pile foundation response test begins, for each measuring point, the output value is continuously collected for no less than 100 sampling times under static conditions. The standard deviation of the output value is calculated and denoted as N, where N follows a normal distribution. The statistical upper limit of the difference between the maximum and minimum values ​​of ten consecutive sampling times is 6 times N. Therefore, 6 times N is used as the set threshold.

[0052] Then, based on the calculation process of the axial resistance reference and circumferential resistance reference after pressure is applied in step S1, and based on the resistance timing sequence output by the axial measuring points on the front and side of each depth layer, as well as the resistance timing sequence output by the circumferential measuring points and the resting period, the axial resistance reference and circumferential resistance reference at the end of the resting period of each depth layer are calculated in the same way.

[0053] For the same depth layer, based on the calculation process of the initial axial strain and initial circumferential strain in step S1, and using the difference between the axial resistance reference at the end of static settling and the axial resistance reference after pressure application, as well as the difference between the circumferential resistance reference at the end of static settling and the circumferential resistance reference after pressure application, the axial residual strain and circumferential residual strain are calculated similarly. The axial residual strain characterizes the amount of irreversible axial plastic deformation of the pile body after the tunnel body has passed through. The circumferential residual strain characterizes the amount of irreversible circumferential plastic deformation of the pile body after the tunnel body has passed through.

[0054] To quantify the degree of attenuation of the pile's resistance to deformation at various depths after the tunnel body has passed, relative to the initial state, the stiffness attenuation rate at each depth is calculated based on the attenuation linkage ratio and residual strain. Specifically, the depth at the top of the pile foundation model is taken as the starting depth (depth value is zero), and the depth at the bottom of the pile foundation model is taken as the ending depth (depth value is equal to the length of the pile foundation model). Considering that the pile foundation response usually gradually propagates downwards from the pile top, the depth layers are arranged in ascending order along the pile axis, and the initial axial strain of each depth layer is arranged in depth order to form a benchmark distribution sequence.

[0055] Furthermore, considering that the attenuation linkage ratio characterizes the overall shift in the proportional relationship between settlement and bearing force after the tunnel body passes through, and indirectly reflects the degradation level of the overall stiffness of the pile body, and that the degradation effect is transferable along the depth direction, the attenuation linkage ratio is used as the overall control factor in the depth direction. For each depth layer, the product of the initial axial strain in the benchmark distribution sequence and the overall control factor is used as the attenuation base, which characterizes the benchmark strain level of that depth layer after considering stiffness degradation.

[0056] Subsequently, the ratio of the axial residual strain at the same depth layer to the overall control factor is used as the stiffness retention rate. The closer the stiffness retention rate is to 1, the better the stiffness retention. To quantify the degree of stiffness degradation that has occurred in the pile body, value 1 is used as the initial stiffness value before the tunnel body passes through, and the result of subtracting the stiffness retention rate from value 1 is used as the stiffness decay rate.

[0057] Please see Figure 4 Step S4: Allow the tunnel body two to pass through from the other side. Based on the stiffness attenuation rate, residual strain, and real-time axial and circumferential strain, the cumulative axial strain and cumulative circumferential strain are merged at each depth to obtain the cumulative plastic strain, cumulative settlement, and bottom interface stiffness.

[0058] In practice, the propulsion system in the tunnel boring machine (TBM) causes the cutterhead of the second tunneling body to pass horizontally through the other side of the pile foundation model. The tunneling direction of the second tunneling body is parallel to but opposite to that of the first tunneling body. The axis of the second tunneling body and the axis of the first tunneling body are located on opposite sides of the pile foundation model. The rotation system controls the rotation of the shaft and the cutterhead to carry out tunnel shield construction, simulating the working condition of two tunnels passing through the pile foundation side by side in sequence.

[0059] During the passage of the tunnel body from the other side, based on the real-time resistance time sequence output by the axial measuring points on the front and side of each depth layer, the real-time resistance time sequence output by the circumferential measuring points, and the load holding period, the real-time axial resistance reference and real-time circumferential resistance reference of each depth layer are calculated similarly according to the calculation process of the axial resistance reference and circumferential resistance reference after pressure is applied in step S1.

[0060] Next, the difference between the real-time axial resistance reference and the axial resistance reference after pressure is calculated for each depth layer, as well as the difference between the real-time circumferential resistance reference and the circumferential resistance reference after pressure for each depth layer. Based on the obtained differences, the real-time circumferential strain and real-time axial strain are calculated similarly according to the calculation process of the initial axial strain and initial circumferential strain in step S1.

[0061] In a preferred embodiment of the present invention, tunneling pressure and shield friction are introduced to correct the real-time circumferential strain and real-time axial strain obtained above, so as to reflect the real-time influence of construction parameters during the passage of the second tunnel body. Specifically: during the passage of the second tunnel body from the other side, the tunneling pressure is collected at each moment by a pressure sensor installed on the shield equipment; by installing both the propulsion system and the rotation system on the support plates on the slide rail, with each of the two independent support plates equipped with a slider, and a slider installed at the bottom of the propulsion system, the friction force generated by the shield shell during shield construction is simulated; by installing a force sensor on the slide rail, the friction force during the movement of the slider is directly measured as the shield shell friction force.

[0062] Divide the tunneling pressure and shield friction by their respective maximum values ​​during the entire passage process to obtain the tunneling pressure coefficient and shield friction coefficient; use the sum of the tunneling pressure coefficient and shield friction coefficient as a correction factor; if the correction factor is greater than 1, then take 1 as the correction factor, otherwise directly use the calculated correction factor; multiply the correction factor by the real-time axial strain and real-time circumferential strain at the current moment to obtain the corrected real-time axial strain and corrected real-time circumferential strain, respectively.

[0063] Considering that the passage of tunnel body 2 will superimpose new deformation on the residual deformation already caused by tunnel body 1, and that the stiffness attenuation caused by tunnel body 1 has already occurred before tunnel body 2 passes, the value of stiffness attenuation rate is used as a weight.

[0064] For each depth layer, the corrected real-time axial strain is multiplied by the sum of the weight of this depth layer and a factor of 1, and then added to the axial residual strain to obtain the cumulative axial strain. The cumulative axial strain characterizes the total axial strain after considering stiffness attenuation during the passage of the tunnel body. Similarly, the corrected real-time circumferential strain is multiplied by the sum of the weight of this depth layer and a factor of 1, and then added to the circumferential residual strain to obtain the cumulative circumferential strain. The cumulative circumferential strain characterizes the total circumferential strain after considering stiffness attenuation during the passage of the tunnel body. The introduction of the value 1 is to convert the stiffness attenuation rate into a strain amplification factor, so as to reflect the physical process of strain superposition even in the extreme case of no attenuation.

[0065] Furthermore, in order to quantify the pile foundation response after the tunnel body passes through from four dimensions—plastic deformation, stiffness variation along depth, settlement distribution, and pile bottom bearing characteristics—the cumulative plastic strain is calculated for each depth layer using the following method.

[0066] Specifically, after the second tunnel body completely passes through the pile foundation model, the static settling time corresponding to the second tunnel body is obtained by similarly determining the stabilization of deformation according to step S2. After static settling, the cumulative axial strain at each depth layer at this time is recorded as the cumulative axial strain before unloading. Then, the vertical load at the top of the pile foundation model is removed, and after determining the stabilization of deformation again according to step S2, the cumulative axial strain after unloading is obtained by similarly following the process of obtaining the cumulative axial strain described above. The cumulative plastic strain is obtained by subtracting the cumulative axial strain after unloading from the cumulative axial strain before unloading. The cumulative plastic strain characterizes the degree of accumulated plastic deformation of the pile material during the passage of the second tunnel body.

[0067] In a preferred embodiment of the present invention, the depth layers are arranged in order from shallow to deep along the pile axis, the depth value of each depth layer in the direction of the pile axis is measured, and the depth value of the lower depth layer in the adjacent depth layer is subtracted from the depth value of the upper depth layer to obtain the depth difference between adjacent depth layers, and the depth difference is used as the step size.

[0068] The difference between the cumulative plastic strain of the upper depth layer and the cumulative plastic strain of the lower depth layer is calculated and then divided by the step size to obtain the piecewise gradient between adjacent depth layers. The piecewise gradient represents the rate of change of the cumulative plastic strain between adjacent depth layers. The absolute values ​​of all piecewise gradients are then summed sequentially along the depth and divided by the number of depth layers to obtain the stiffness gradient.

[0069] The stiffness gradient characterizes the overall variation of cumulative plastic strain along the pile depth, and it is an important indicator for evaluating the degree of uneven distribution of plastic damage in the pile. The larger the stiffness gradient value, the more drastic the change in plastic strain from the pile top to the pile bottom, the more uneven the pile damage, and the greater the differential damage to the pile caused by subsequent tunnel construction.

[0070] As another preferred embodiment of the present invention, considering that the change of the bending moment of the pile body along the depth will cause additional bending stiffness, a bending moment gradient is introduced to correct the stiffness gradient, so as to comprehensively reflect the coupling effect of bending deformation and stiffness degradation of the pile body when the tunnel body passes through.

[0071] Specifically, for each depth layer, the cumulative axial strain is multiplied by the elastic modulus of the pile foundation model to obtain the stress. Based on mechanics of materials, for a pile foundation model with a circular cross-section, pi is multiplied by the cube of the diameter and divided by 32 to obtain the bending section modulus. The stress is then multiplied by the bending section modulus of the pile foundation model to obtain the bending moment. The difference between the bending moment of the previous depth layer and the bending moment of the next depth layer is divided by the step size to obtain the bending moment gradient between adjacent depth layers. The bending moment gradient is added to the stiffness gradient to obtain the corrected stiffness gradient.

[0072] Next, using the depth difference between adjacent depth layers as the integration step size, and taking the depth layer where the top of the pile foundation model is located as the first layer, the cumulative axial strain of the first layer is added to the cumulative axial strain of the second layer, divided by two, and then multiplied by the corresponding integration step size to obtain the settlement increment from the first layer to the second layer. Since the cumulative settlement of the first layer is zero, the cumulative settlement of the second layer is the settlement increment obtained above. The cumulative axial strain of the second layer is added to the cumulative axial strain of the third layer, divided by two, and then multiplied by the corresponding integration step size to obtain the settlement increment from the second layer to the third layer. The cumulative settlement of the second layer is added to the obtained settlement increment to obtain the cumulative settlement of the third layer. This process is repeated until the depth layer where the bottom of the pile foundation model is located is calculated.

[0073] Subsequently, the cumulative settlement of the layer at the depth where the bottom of the pile foundation model is located is taken as the cumulative bottom settlement. During the passage of the second tunnel body, the real-time bottom support force at each moment is extracted and subtracted from the initial bottom support force to obtain the real-time change in bottom support force. The real-time change in bottom support force is divided by the real-time value of the cumulative bottom settlement to obtain the bottom interface stiffness. The bottom interface stiffness characterizes the ability of the soil at the pile bottom to resist settlement during the passage of the second tunnel body, i.e., the pile bottom support stiffness.

[0074] Step S5: Obtain the additional plastic strain and additional circumferential stiffness reduction rate based on the cumulative plastic strain, residual strain, and initial circumferential strain; calculate the additional settlement from the cumulative settlement and settlement difference, and calculate the additional interface stiffness from the bottom interface stiffness and bearing force difference.

[0075] To separate the additional response caused by tunnel section two from the response already caused by tunnel section one, and to obtain the additional pile foundation effect caused solely by the later tunnel excavation during the construction of the twin-track tunnel, for each depth layer, the cumulative plastic strain is subtracted from the axial residual strain. If the difference is positive, it is taken as the additional plastic strain; if the difference is negative, the additional plastic strain is taken as zero.

[0076] Additional plastic strain characterizes the extra plastic deformation that occurs during the passage of tunnel body two relative to the residual deformation of tunnel body one. The larger the value of additional plastic strain, the more severe the additional plastic deformation caused by tunnel body two.

[0077] Next, for each depth layer, the ratio of the circumferential residual strain to the initial circumferential strain is taken as the circumferential strain residual ratio. According to the stiffness degradation theory in material damage mechanics, the current stiffness of a material can be expressed as the initial stiffness multiplied by the stiffness retention rate, where the stiffness retention rate ranges from 0 to 1, with a value of 1 indicating no stiffness degradation and a value of 0 indicating complete stiffness loss. Based on this, in this invention, the additional circumferential stiffness reduction rate (dimensionless) is obtained by subtracting the circumferential strain residual ratio from 1. The larger the value of the additional circumferential stiffness reduction rate, the more significant the circumferential stiffness degradation caused by the tunnel body.

[0078] Meanwhile, for each depth layer, the cumulative settlement is subtracted from the settlement difference to obtain the additional settlement; the additional settlement characterizes the amount of settlement that increases in proportion to the settlement caused by tunnel body two during its passage relative to the settlement caused by tunnel body one. The larger the additional settlement value, the greater the amount of additional settlement caused by tunnel body two.

[0079] The ratio of the bearing force difference to the cumulative settlement at the bottom is calculated, and this ratio is added to the bottom interface stiffness to obtain the additional interface stiffness. The additional interface stiffness characterizes the extra interface stiffness caused by the change in bearing force relative to that caused by the first tunnel body during the passage of the second tunnel body. A larger additional interface stiffness value indicates a greater additional interface stiffness caused by the second tunnel body.

[0080] Finally, the additional plastic strain, corrected stiffness gradient, additional circumferential stiffness reduction rate, additional settlement, and additional interface stiffness obtained from the above calculations are used as the output results of the pile foundation response under the condition of shield tunneling in a double-track tunnel, so as to provide a quantitative basis for the adjustment of construction parameters and pile foundation reinforcement design of the double-track tunnel.

[0081] Specifically, when the additional settlement exceeds the allowable settlement value specified in the technical code for building pile foundations, the excavation speed of the second excavation body should be reduced, and the grouting pressure should be increased to reduce the disturbance to the soil around the pile; otherwise, the existing excavation speed and grouting pressure should be maintained.

[0082] When the additional interface stiffness is negative, it indicates that the pile bottom support stiffness decreases after the subsequent tunnel passes through. In this case, the pile bottom should be reinforced by grouting before the subsequent tunnel passes through; otherwise, there is no need to reinforce the pile bottom by grouting.

[0083] When the additional plastic strain at a certain depth layer is greater than zero, it indicates that irreversible additional plastic deformation has occurred at this depth layer, and this depth layer is marked as a plastic damage layer. When the corrected stiffness gradient monotonically increases or decreases for three consecutive depth layers along the depth direction, the region formed by the corresponding depth layers is marked as a stiffness abrupt change segment. When the value of the additional circumferential stiffness reduction rate at a certain depth layer is greater than that of its adjacent depth layers, the region formed by this depth layer and its upper and lower adjacent depth layers is marked as a stiffness reduction segment.

[0084] Reinforcement measures should be taken for stiffness reduction zones, plastic damage layers, and stiffness abrupt change zones. These measures include, but are not limited to, increasing pile reinforcement, using steel sleeves to reinforce the piles, or grouting the soil around the piles. Unmarked depth layers do not require reinforcement.

[0085] In addition, by Figure 7It is evident that the increase in positive axial strain is greatest during the process of advancing from the reference section of pile foundation model 1 to the reference section of pile foundation model 2, indicating the most intense soil disturbance. During the process of advancing from the reference section of pile foundation model 3 to the shield tunneling face, the strain increase significantly decreases. Based on this pattern, when the cutterhead is between the reference sections of pile foundation model 1 and 2, the tunneling speed should be reduced and the grouting pressure increased to minimize disturbance to the pile foundations. After the cutterhead passes the reference section of pile foundation model 3, the tunneling speed and grouting pressure should be gradually restored to their pre-adjustment levels.

[0086] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product.

[0087] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0088] In addition, the functional modules in the various embodiments of the present invention can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0089] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0090] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A test method for pile foundation response under the condition of dual-track tunnel shield tunneling, characterized in that, Includes the following steps: A bidirectional load was applied to the pile foundation model to obtain the initial axial and circumferential strain, top settlement, and bottom bearing force at each depth of the pile. The tunnel body passes through from one side. Based on the real-time and initial top settlement and bottom support force, the settlement difference and support force difference are obtained, and the attenuation linkage ratio is calculated accordingly. After the tunnel body passes through, it is left to stand until the end. The residual strain is obtained based on the real-time and initial axial and circumferential strains. The attenuation linkage ratio is used as the overall control factor, and the stiffness attenuation rate at each depth is calculated in combination with the residual strain. The tunnel body 2 passes through from the other side. Based on the stiffness attenuation rate, residual strain, real-time axial and circumferential strain, the cumulative axial strain and cumulative circumferential strain are merged at each depth to obtain the cumulative plastic strain, cumulative settlement and bottom interface stiffness. Additional plastic strain and additional circumferential stiffness reduction rate are obtained based on cumulative plastic strain, residual strain, and initial circumferential strain; additional settlement is calculated from cumulative settlement and settlement difference, and additional interface stiffness is calculated from bottom interface stiffness and bearing force difference.

2. The method for testing the pile foundation response under the condition of a double-track tunnel shield tunneling side-passing as described in claim 1, characterized in that, The initial axial and circumferential strains are obtained as follows: Multiple depth layers are divided along the axial direction on the outer wall of the pile foundation model. In each depth layer, axial measuring points are set up in different directions along the direction parallel to the pile axis, and circumferential measuring points are set up in the direction perpendicular to the pile axis. After applying bidirectional load to the target value to the pile foundation model, the axial resistance difference time series is calculated based on the resistance time series output by axial measuring points at different orientations in the same depth layer; the circumferential resistance difference time series is calculated based on the resistance time series output by circumferential measuring points at different orientations in the same depth layer. Based on the axial resistance difference timing sequence and the circumferential resistance difference timing sequence, the axial resistance reference and the circumferential resistance reference after pressure are obtained respectively; The axial resistance benchmark when the pile foundation model is not subjected to bidirectional ballast is used as the axial reference, and the circumferential resistance benchmark is used as the circumferential reference. The difference between the axial resistance reference and the axial reference after applying pressure is converted into the initial axial strain; the difference between the circumferential resistance reference and the circumferential reference after applying pressure is converted into the initial circumferential strain.

3. The method for testing the pile foundation response under the condition of a double-track tunnel shield tunneling side-passing, as described in claim 1, is characterized in that... The initial process of obtaining the top settlement and bottom support force is as follows: Settlement measuring points are set above the top of the pile foundation model, with the sensing direction of the settlement measuring points pointing towards the top surface of the pile; bearing force measuring points are set at the bottom of the pile foundation model. After applying bidirectional load to the target value to the pile foundation model, the initial top settlement is calculated based on the distance time series output by the settlement measuring points during the load holding period. The initial bottom support force is calculated based on the pressure time sequence output by the support force measuring point during the load holding period.

4. The method for testing the pile foundation response under the condition of a double-track tunnel shield tunneling side-passing as described in claim 1, characterized in that, The process of calculating the attenuation linkage ratio is as follows: During the process of the tunnel body passing through one side, the time interval during which the cutterhead of the tunnel body passes through the axis of the pile body is taken as the time interval; Based on the real-time settlement time series output from the settlement measuring points and the real-time support force time series output from the support force measuring points, the settlement difference is obtained by subtracting the initial top settlement from the average of all real-time settlement values ​​within the time interval; the support force difference is obtained by subtracting the initial bottom support force from the average of all real-time support force values ​​within the time interval. The ratio of settlement difference to bearing force difference is used as the benchmark ratio. Based on the real-time settlement time series and the real-time bearing force time series, the ratio of real-time settlement value to real-time bearing force value is calculated at each moment from the end of the time interval to the point where the tunnel body stops advancing, and is used as the real-time ratio. The difference between the real-time ratio and the baseline ratio is taken as the response deviation; the sum of all response deviations is divided by the number of all times after the end of the time interval to obtain the attenuation linkage ratio.

5. The method for testing the pile foundation response under the condition of a double-track tunnel shield tunneling side-passing, as described in claim 1, is characterized in that... The residual strain includes axial residual strain and circumferential residual strain; After the tunnel body passes through and is left to stand until the end, the axial resistance reference and circumferential resistance reference at the end of the standing period are obtained based on the resistance timing sequence output from the axial measuring points at different orientations of each depth layer and the resistance timing sequence output from the circumferential measuring points. For the same depth layer, the difference between the axial resistance reference at the end of the settling period and the axial resistance reference after pressure is converted into axial residual strain, and the difference between the circumferential resistance reference at the end of the settling period and the circumferential resistance reference after pressure is converted into circumferential residual strain.

6. The method for testing the pile foundation response under the side-passing condition of a double-track tunnel shield as described in claim 4, characterized in that, The process of calculating the stiffness attenuation rate at each depth is as follows: Starting from the depth at the top of the pile foundation model and ending from the depth at the bottom of the pile foundation model, the depth layers are arranged in order from shallow to deep along the axis of the pile body. The attenuation linkage ratio is used as the overall control factor in the depth direction; the initial axial strain of each depth layer is arranged in depth order to form a reference distribution sequence; For each depth layer, the product of the initial axial strain in the reference distribution sequence and the overall control factor is used as the attenuation base; the ratio of the axial residual strain of the same depth layer to the overall control factor is used as the stiffness retention rate; and the result of subtracting the stiffness retention rate is used as the stiffness attenuation rate.

7. The method for testing the pile foundation response under the condition of a double-track tunnel shield tunneling side-passing as described in claim 1, characterized in that, The process of obtaining the cumulative axial strain and cumulative circumferential strain is as follows: During the passage of the second tunnel body from the other side, the real-time axial resistance reference and real-time circumferential resistance reference of each depth layer are obtained based on the real-time resistance time sequence output by the axial measuring points at different orientations of each depth layer and the real-time resistance time sequence output by the circumferential measuring points. The difference between the real-time axial resistance reference and the axial resistance reference after pressure application for each depth layer is converted into real-time axial strain; the difference between the real-time circumferential resistance reference and the circumferential resistance reference after pressure application for each depth layer is converted into real-time circumferential strain. For each depth layer, the corresponding stiffness attenuation rate is used as the weight. The real-time axial strain is multiplied by the weight of this depth layer and the sum of 1, and then added to the axial residual strain to obtain the cumulative axial strain. The cumulative circumferential strain is calculated similarly based on the real-time circumferential strain and the circumferential residual strain.

8. The method for testing the pile foundation response under the condition of a double-track tunnel shield tunneling side-passing, as described in claim 7, is characterized in that... The process of calculating cumulative plastic strain is as follows: For each depth layer, after the tunnel body passes through and is left to stand still, the ballast at the top of the pile foundation model is removed, and the cumulative plastic strain is obtained based on the difference in cumulative axial strain before and after removal.

9. The method for testing the pile foundation response under the side-passing condition of a double-track tunnel shield as described in claim 7, characterized in that, The process of calculating cumulative settlement and bottom interface stiffness is as follows: Arrange the depth layers along the pile axis in order from shallow to deep, take the depth layer where the top of the pile foundation model is located as the first layer, and take the depth difference between adjacent depth layers as the integration step size. Integrate the cumulative axial strain of each depth layer along the depth to obtain the cumulative settlement. The cumulative settlement of the layer at the depth where the bottom of the pile foundation model is located is taken as the cumulative settlement at the bottom. During the passage of the second tunnel body, the ratio of the real-time change of the bottom support force to the real-time value of the cumulative settlement at the bottom is calculated to obtain the stiffness of the bottom interface.

10. The method for testing the pile foundation response under the condition of a double-track tunnel shield tunneling side-passing, as described in claim 5, is characterized in that... The calculation process for additional plastic strain, additional circumferential stiffness reduction rate, additional settlement, and additional interface stiffness is as follows: For each depth layer: the net increment of the cumulative plastic strain and the axial residual strain is taken as the additional plastic strain; the ratio of the circumferential residual strain to the initial circumferential strain is taken as the circumferential strain residual ratio, and the additional circumferential stiffness reduction rate is obtained by subtracting the circumferential strain residual ratio from one. The difference between the cumulative settlement and the settlement difference is taken as the additional settlement; The additional interface stiffness is obtained by superimposing the ratio of the bearing force difference to the cumulative settlement at the bottom end and the interface stiffness at the bottom end.

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