Optimization Layout Method for Row Spacing of Double-Row NT-CEP Pile Foundation Pit Support System

Abstract

This invention relates to the field of pile foundation support technology, specifically to a method for optimizing the spacing of double-row NT-CEP pile foundation pit support systems. The invention first divides the soil between the front and rear rows of piles into several soil layers and determines the pressure transmission range of each layer. Then, it extracts the tangential stress within the pressure transmission range and at the elevations of the upper and lower bearing plates to obtain the interlayer load transfer. Next, it determines the boundary soil layers and the upper limit elevation. Using the upper limit elevation as the boundary, the interlayer load transfer is accumulated layer by layer in both the positive and negative directions along the pit depth, resulting in bearing set one and bearing set two. Within bearing set one and bearing set two, based on the normal stress of the pile walls of the front and rear rows of piles, the load ratio on the arch and the load ratio at the end of the bearing plate are obtained respectively. This allows for layered analysis and processing of the soil between piles according to differences in the stress mechanism, rather than treating the soil between piles as a whole along the depth direction in the stress analysis. This avoids the unbalanced load distribution between the front and rear rows of piles, which could affect the overall bearing capacity and stability of the support system.

Description

Technical Field

[0001] This invention relates to the field of pile foundation support technology, specifically to a method for optimizing the spacing of rows in a double-row NT-CEP pile foundation pit support system. Background Technology

[0002] NT-CEP piles are variable cross-section expanded-diameter piles, specifically referring to reinforced concrete cast-in-place piles in which one or more bearing plates with a diameter larger than the pile body are formed at a set elevation through specific construction methods (such as extrusion expansion or rotary expansion). The bearing plate and the pile body are an integral structure used to improve the vertical and horizontal bearing capacity of a single pile.

[0003] In the design of double-row pile support systems, the spacing between the front and rear rows of piles affects the formation of the soil arching effect between piles, the stress in the soil between piles, and the transmission of end bearing resistance of the bearing plate. Existing methods for determining the spacing between double-row piles, such as using the elastic foundation beam method or the finite element method for trial calculations, typically treat the soil between the front and rear rows of piles as a whole along the depth direction, participating in the stress. However, they do not perform layered analysis and treatment of the soil between piles according to the differences in stress mechanisms. This results in an uneven load distribution between the front and rear rows of piles under the determined spacing value, which in turn affects the overall bearing capacity and stability of the support system.

[0004] Furthermore, when the spacing between rows of piles is adjusted, the stress diffusion range of the front and rear rows of piles changes accordingly, which in turn causes a change in the load sharing ratio of the front and rear rows of piles. However, existing methods lack quantitative analysis of the relationship between changes in row spacing and changes in the load sharing ratio of the front and rear rows of piles, so as to use quantitative analysis as a convergence criterion for adjusting the row spacing. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for optimizing the spacing of the double-row NT-CEP pile foundation pit support system, including the following steps: dividing the soil between the front and rear rows of piles into several soil layers according to the cantilever diameter and elevation of the bearing plate of the front and rear rows of piles.

[0006] Based on the current row spacing and cantilever diameter, the pressure transmission range of each soil layer is determined, and the tangential stress within the pressure transmission range and at the elevation of the upper and lower bearing plates is extracted to obtain the interlayer load transfer.

[0007] The difference in load transfer between adjacent soil layers is compared to determine the boundary soil layer, and the elevation of the boundary soil layer is used as the upper limit elevation.

[0008] Using the upper limit elevation as the boundary, the interlayer load transfer amount is accumulated layer by layer in both the positive and negative directions along the depth of the foundation pit until the difference between adjacent accumulated values ​​is less than the difference between the previous accumulated values. The soil layers corresponding to the accumulated interlayer load transfer amount are then included in bearing set one and bearing set two, respectively.

[0009] Based on the normal stress of the pile wall of the front and rear piles in load set one and load set two, the load ratio on the arch and the load ratio at the disk end are obtained respectively, and the current load difference is obtained from this.

[0010] The current row spacing is corrected based on the comparison between the load difference obtained by superimposing the cantilever diameter on the current row spacing and the current load difference.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention first divides the soil between the front and rear rows of piles into several soil layers and determines the pressure transmission range of each soil layer. Then, it extracts the tangential stress at the elevation of the upper and lower surfaces of the bearing plate within the pressure transmission range to obtain the interlayer load transfer. Then, it determines the boundary soil layer and the upper limit elevation. With the upper limit elevation as the boundary, the interlayer load transfer is accumulated layer by layer in both the positive and negative directions along the depth of the foundation pit to obtain bearing set one and bearing set two. Based on the normal stress of the pile wall of the front and rear rows of piles in bearing set one and bearing set two, the load ratio on the arch and the load ratio at the end of the plate are obtained respectively. In this way, the soil between the piles is analyzed and processed in layers according to the difference in the force mechanism, instead of treating the soil between the piles as a whole along the depth direction to participate in the force analysis. This avoids the impact on the overall bearing performance and stability of the support system due to the uneven load distribution of the front and rear rows of piles.

[0012] 2. This invention obtains the current load difference based on the load ratio on the arch and the load ratio at the end of the plate. It compares the comparative load difference obtained by superimposing the cantilever diameter on the current row spacing with the current load difference. The stopping condition for row spacing iteration is whether the comparative load difference is greater than or equal to the current load difference. This establishes a quantitative correlation between row spacing and the load sharing ratio of the front and rear rows of piles. Attached Figure Description

[0013] 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.

[0014] Figure 1 This is a schematic diagram of the deployment method of the present invention;

[0015] Figure 2 This is a schematic diagram of the process for dividing soil layers according to the present invention;

[0016] Figure 3 This is a flowchart illustrating the process of determining the pressure transmission range of each soil layer in this invention.

[0017] Figure 4 This is a schematic diagram of the process for obtaining interlayer load transfer in this invention;

[0018] Figure 5 This is a flowchart illustrating the process of determining the boundary soil layer and upper limit elevation for this invention.

[0019] Figure 6 This is a structural schematic diagram of an NT-CEP pile.

[0020] In the diagram: BD, load-bearing plate; R, cantilever diameter. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The following description, in conjunction with the accompanying drawings, details the specific scheme of the optimized layout method for the row spacing of the double-row NT-CEP pile foundation pit support system provided by this invention.

[0026] Please see Figure 1 , Figure 2 and Figure 6 The flowchart shows the optimized layout method of the double-row NT-CEP pile foundation pit support system provided by the present invention, which specifically includes the following steps: Step S1, according to the bearing plate cantilever diameter and plate elevation of the front and rear piles, the soil between the front and rear piles is divided into several soil layers.

[0027] In the double-row NT-CEP pile foundation pit support system, the soil stress mechanism differs at different depths. The shallow soil mainly achieves coordinated stress distribution between the front and rear rows of piles through the soil arching effect between piles, while the deep soil mainly shares the load through the independent end-bearing effect of each pile's bearing plate. To extract the stress information of different sections in the shallow and deep layers respectively, a soil layer division operation is performed.

[0028] Furthermore, since the elevation of the bearing plate determines the vertical position of the bearing plate in the soil, and the cantilever diameter determines the radial range of the bearing plate end on the soil, using the cantilever diameter and the elevation of the bearing plate as the basis for division can ensure that the formed soil layer corresponds to the position of the bearing plate, thereby ensuring that the stress data extracted later reflects the end bearing effect at the surface of each bearing plate.

[0029] In practice, the cantilever diameter of the bearing plate for the front and rear rows of piles is read from the pile foundation design drawings. The cantilever diameter is the length by which the outer edge of the bearing plate cantilevers radially outward relative to the outer wall of the pile body. The cantilever diameter of all bearing plates in the same project is a uniform design parameter. At the same time, using the bottom of the foundation pit as the reference plane, the vertical distance from the center point of the upper surface of the bearing plate to the reference plane is read from the pile foundation design drawings and used as the elevation of the upper surface of the bearing plate. The elevation of the lower surface of the bearing plate is obtained in the same way.

[0030] Based on this, along the vertical direction (i.e. the direction of the gravity line of action), the horizontal plane where the upper plate elevation of each bearing plate of the front row pile and the horizontal plane where the lower plate elevation of each bearing plate of the rear row pile are located are all taken as the initial dividing interface. All the initial dividing interfaces divide the soil between the outer walls of the front and rear rows of piles into multiple initial vertical soil segments.

[0031] It should be noted that when the number of bearing plates on the front and rear rows of piles is the same and the plate elevations correspond one-to-one, each initial interface appears in pairs. When the number of bearing plates or the plate elevations on the front and rear rows of piles are inconsistent, the horizontal plane containing the upper plate elevation and the horizontal plane containing the lower plate elevation of each pile are used independently as initial interfaces to divide the soil between the piles.

[0032] Then, since the outer edge of the bearing plate is the farthest boundary of the radial extension of the bearing plate, the interaction between the bearing plate end and the soil is transmitted outward through this boundary. In order to determine the vertical influence range of the bearing plate end bearing effect on the soil between piles, the outer boundary of the upper surface of the bearing plate and the outer boundary of the lower surface of the bearing plate are first determined.

[0033] The process for determining the outer boundary of the upper and lower surfaces of the bearing plate is the same. Taking the determination of the outer boundary of the upper surface as an example: On a horizontal plane at the elevation of the upper surface of the bearing plate, with the projection point of the pile axis onto the horizontal plane as the center point, add the cantilever diameter of the bearing plate to the radius of the pile to obtain the outer radius of the bearing plate; draw a circle on the horizontal plane using the outer radius of the bearing plate, and the resulting circumference is the outer boundary of the upper surface of the bearing plate. The pile axis and pile radius are obtained from the pile foundation design drawings.

[0034] Next, for each initial vertical soil segment, the outer boundary of the upper plate of the bearing plate at its upper horizontal plane is vertically orthographically projected downwards to its lower horizontal plane, forming a vertical projection cylinder of the upper plate. Simultaneously, the outer boundary of the lower plate of the bearing plate at its lower horizontal plane is vertically orthographically projected upwards to its upper horizontal plane, forming a vertical projection cylinder of the lower plate. Vertical orthographic projection refers to the operation of projecting geometric boundaries in space along the vertical direction onto a horizontal plane; the specific process is existing technology and will not be elaborated here.

[0035] If there is no outer boundary of the upper plate of the bearing plate at the upper horizontal plane of an initial vertical soil segment, or no outer boundary of the lower plate of the bearing plate at the lower horizontal plane, then the formation operation of the upper vertical projection column surface will not be performed on this initial vertical soil segment, and this initial vertical soil segment will be regarded as an independent soil layer.

[0036] Subsequently, the vertical projection surfaces of the upper plate and the lower plate are used as dividing surfaces. Within the initial vertical soil section, the soil within the area enclosed by the dividing surfaces is designated as the inner core soil, and the remaining soil is designated as the outer ring soil.

[0037] In addition, if the vertical projection areas of the upper plate and the lower plate overlap on the horizontal plane due to the dense arrangement of the bearing plates, the vertical column soil segment corresponding to the overlapping area is separated from the outer ring soil and the inner core soil and treated as the column core soil to avoid the stress state of the overlapping area being confused or averaged in subsequent calculations.

[0038] Subsequently, the outer ring soil, inner core soil, and column core soil were treated as independent soil layers. After the soil layers were divided, for any soil layer, three non-collinear measurement points were selected on the top surface of the soil layer, and the vertical height of each measurement point relative to the bottom of the foundation pit was measured. The arithmetic mean of the three measurements was taken as the elevation of the horizontal plane where the top surface of the soil layer was located. The elevation of the horizontal plane where the bottom surface of the soil layer was located was obtained in the same way. The specific measurement process is existing technology and will not be described in detail here.

[0039] For ease of description, the elevation of the horizontal plane containing the top surface of the soil layer is recorded as the top elevation, and the elevation of the horizontal plane containing the bottom surface of the soil layer is recorded as the bottom elevation. Furthermore, the arithmetic mean of the top and bottom elevations is calculated and used as the center elevation of the soil layer.

[0040] Please see Figure 3 and Figure 4 Step S2: Determine the pressure transmission range of each soil layer based on the current row spacing and cantilever diameter, extract the tangential stress within the pressure transmission range and at the elevation of the upper and lower bearing plates, and obtain the interlayer load transfer amount accordingly.

[0041] In order to quantify the spatial area in which the soil in each soil layer participates in the load transfer between the front and rear rows of piles, the ratio of the current row spacing to the cantilever diameter is rounded up as the extension segment number, since the cantilever diameter is the basic unit of measurement for the radial influence of the bearing plate end bearing effect, so that the pressure transmission range formed later completely covers the soil between the piles corresponding to the row spacing.

[0042] Then, because the front row of piles bears the main anti-overturning role, its back side (i.e. the side of the pile body facing away from the inside of the foundation pit) is the main force-bearing surface for the earth pressure to be transmitted to the pile body; the rear row of piles receives the load transmitted by the front row of piles through the soil between the piles, and its front side (i.e. the side of the pile body facing the inside of the foundation pit) is the main force-bearing surface for receiving the earth pressure. Therefore, the back side of the front row of piles and the front side of the rear row of piles are selected as the reference side for determining the pressure transmission boundary.

[0043] Specifically, starting from the pile wall on the back side of the front row of piles at the center elevation of each soil layer, the process extends horizontally away from the front row of piles, segment by segment according to the cantilever diameter. This ensures that the subsequent pressure transmission range is directly related to the geometric parameters of the bearing plate. During each extension, the end point of the current segment is used as the starting point of the next segment. This extension operation is repeated until the required number of segments is reached. The area between the starting point and the end point of the last segment is defined as the pressure transmission zone of the front row of piles. The direction away from the front row of piles specifically refers to the horizontal direction from the pile wall on the back side of the front row of piles towards the rear row of piles.

[0044] Simultaneously, starting from the soil-facing pile wall of the rear row of piles at the center elevation of each soil layer, the cantilever diameter is extended horizontally towards the front row of piles segment by segment. At the end of each segment, the starting point of the next segment is used. This extension operation is repeated until the required number of segments is reached. The area between the starting point and the end point of the last segment is designated as the soil-facing pressure transmission zone of the rear row of piles. Specifically, the direction away from the front row of piles refers to the horizontal direction from the soil-facing pile wall of the rear row of piles towards the front row of piles.

[0045] Next, the area where the front back soil pressure transmission zone and the rear front soil pressure transmission zone intersect and overlap is taken as the pressure transmission range of the corresponding soil layer. If the front back soil pressure transmission zone and the rear front soil pressure transmission zone do not intersect and overlap, it indicates that the current soil layer has failed to form an effective stress transmission path. The pressure transmission range of the current soil layer is recorded as an empty set, and the current soil layer does not participate in the subsequent calculation of interlayer load transfer.

[0046] The pressure transmission range reflects the size of the spatial area in which the soil between piles participates in stress transmission. The larger the range, the greater the overlap of the stress diffusion range between the front and rear rows in the soil between piles after the row spacing increases, and the stronger the load transmission capacity of the soil between piles.

[0047] To further illustrate the process of determining the pressure transmission range, data from four soil layers are used as an example, as shown in Table 1 below. The specific values ​​in Table 1 are for illustrative purposes only and do not constitute a limitation on the protection scope.

[0048] Table 1. Data for determining the pressure transmission range of each soil layer

[0049]

[0050] As shown in Table 1, soil layer 1 has two extension segments. The pressure transmission zone of the front back soil is 0–0.6 m, and the pressure transmission zone of the rear front soil is 1.2–1.8 m. There is a 0.6 m gap between the two, and they do not form an overlapping area. Soil layer 4 has six extension segments. The pressure transmission zone of the front back soil is 0–1.8 m, and the pressure transmission zone of the rear front soil is 0–1.8 m. The two completely overlap within the 0–1.8 m range, so the pressure transmission range is 0–1.8 m. This indicates that the stress diffusion range of the front and rear piles in soil layer 4 covers the entire soil between the piles.

[0051] As can be seen from the above data, the larger the number of extension segments, the wider the overlap between the front back soil pressure transmission zone and the rear soil pressure transmission zone, and the larger the pressure transmission range. This indicates that the spatial area in which the soil between piles participates in stress transfer is wider, and the load transmission capacity is stronger. Therefore, by comparing the front back soil pressure transmission zone and the rear soil pressure transmission zone, the pressure transmission range can be determined, which can provide a basis for the calculation of subsequent inter-layer load transfer.

[0052] In Table 1, the number 0 in the two items, "front back soil pressure transmission zone" and "rear soil pressure transmission zone", indicates the starting position of the corresponding pressure transmission zone extension. That is, the starting position is recorded as 0, not that the value is zero.

[0053] After determining the pressure transmission range, since the essence of interlayer load transfer is the transfer of load through shear deformation of the soil in the horizontal direction, and tangential stress is a direct physical quantity characterizing shear action, the tangential stress within the pressure transmission range and at the elevations of the upper and lower surfaces of the bearing plate is first extracted.

[0054] Specifically, since the stress transfer path of the soil between the double rows of piles is mainly horizontal, from the back side of the front piles to the front side of the rear piles, stress measurement lines for the back soil of the front row are laid out horizontally from the pile wall on the back soil side of the front piles to the pressure transmission zone of the front back soil at the center elevation of each soil layer. At the same time, stress measurement lines for the front soil of the rear row are laid out horizontally from the pile wall on the front soil side of the rear piles to the pressure transmission zone of the rear front soil, so that the stress data extracted later can reflect the characteristics of the load transfer path in the horizontal direction.

[0055] The layout process of the back soil stress measurement line and the front soil stress measurement line is the same. Taking the layout process of the front soil stress measurement line as an example, specifically: in the horizontal plane where the center elevation of each soil layer is located, the intersection of the outer surface of the pile wall on the back soil side of the front pile with the horizontal plane is taken as the starting point of the measurement line, and the intersection of the boundary of the pressure transmission zone of the front soil with the horizontal plane is taken as the ending point of the measurement line; along the straight path from the starting point of the measurement line to the ending point of the measurement line, N measurement points are evenly inserted between the starting point and the ending point. Each measurement point together with the starting point and the ending point of the measurement line constitutes the front soil stress measurement line.

[0056] To avoid an excessive number of stress sensors resulting in too many measuring points, which would increase costs and installation difficulty, and to avoid an insufficient number of measuring points leading to excessive spacing between them and loss of stress change information between adjacent measuring points, this invention uses N equal to 3. Based on this, to control the number of stress sensors and reduce installation costs and workload, stress sensors are installed at the starting and ending points of the front back soil stress measuring line, as well as at measuring points located in the middle, to obtain the tangential stress at the corresponding locations. The tangential stress at the remaining two measuring points is obtained by taking the arithmetic mean of the tangential stresses at the adjacent two sides.

[0057] If there are measuring points on the rear soil stress measuring line and the front soil stress measuring line that are level with the elevation of the upper plate of the bearing plate, then the tangential stress at these measuring points is directly selected and the arithmetic mean is taken as the tangential stress at the position level with the elevation of the upper plate of the bearing plate (hereinafter briefly described as the upper plate candidate tangential stress), thus obtaining two upper plate candidate tangential stresses. Otherwise, on the front soil stress measuring line, two adjacent measuring points on the left and right sides of the position where the elevation of the upper plate of the bearing plate is located are selected, and the arithmetic mean of the tangential stress values ​​at the two selected measuring points is taken as the upper plate candidate tangential stress. Based on the rear soil stress measuring line, the upper plate candidate tangential stress is obtained in the same way.

[0058] The larger of the two candidate tangential stresses obtained is taken as the tangential stress at the upper surface of the bearing plate. The greater the tangential stress at the upper surface of the bearing plate, the greater the vertical load component transmitted from the soil above the upper surface of the bearing plate to the plate surface through friction, which will result in uneven vertical settlement between the front and rear piles.

[0059] Simultaneously, based on the stress measurement lines of the front row of back soil and the stress measurement lines of the rear row of front soil, the tangential stress at the bottom surface of the bearing plate is obtained by the same operation as above. The greater the tangential stress at the bottom surface of the bearing plate, the greater the vertical load component transmitted from the soil above the bottom surface of the bearing plate to the plate surface through friction, and uneven vertical settlement will occur between the front and rear rows of piles.

[0060] Next, the tangential stress at all measuring points on the front row back soil stress measuring line and the rear row front soil stress measuring line is extracted. The arithmetic mean of all extracted tangential stresses is taken as the tangential stress within the pressure transmission range. This comprehensively reflects the average level of the overall soil between piles participating in shear transmission, avoiding deviations in the calculation of subsequent interlayer load transfer due to single-point outliers.

[0061] Because the dominant roles of the overall load transfer between piles, the end-bearing effect of the upper bearing plate, and the end-bearing effect of the lower bearing plate differ in different soil layers, this invention adopts a comparative value rule to determine the inter-layer load transfer amount, so that the inter-layer load transfer amount reflects the actual dominant load transfer in the current soil layer.

[0062] Specifically, for each soil layer, the tangential stress at the upper surface of the bearing plate is taken as the upper limit parameter, and the tangential stress at the lower surface of the bearing plate is taken as the lower limit parameter. The upper and lower limit parameters constitute the bearing effect range of the bearing plate. The tangential stress within the pressure transmission range is then taken as an intermediate reference value.

[0063] When the intermediate reference value is less than the upper limit parameter but greater than the lower limit parameter, it indicates that the overall load transfer between piles plays a dominant role in the current soil layer. Therefore, the intermediate reference value is taken as the interlayer load transfer value.

[0064] When the intermediate reference value is greater than the upper limit parameter, it indicates that the end bearing effect of the bearing plate on the upper plate plays a dominant role in the current soil layer. Therefore, the upper limit parameter is taken as the interlayer load transfer value.

[0065] When the intermediate reference value is less than the lower limit value, it indicates that the end-bearing effect of the lower plate of the load-bearing plate plays a dominant role in the current soil layer. Therefore, the lower limit value is taken as the interlayer load transfer value. The interlayer load transfer value is used for lateral comparison of the load transfer capacity between soil layers, not the absolute total amount of load transferred by the soil layers.

[0066] Interlayer load transfer reflects the load transferred by the horizontal shear deformation of the soil between piles in the soil layer. The larger the interlayer load transfer, the higher the degree of soil layer participation in load transfer, which is beneficial to the coordinated work of double-row NT-CEP pile foundations.

[0067] Please see Figure 5 Step S3: Compare the difference in load transfer between adjacent soil layers to determine the boundary soil layer, and use the elevation of the boundary soil layer as the upper limit elevation.

[0068] Specifically, all soil layers are arranged in descending order of top elevation, and the difference in load transfer between adjacent soil layers is calculated sequentially. The larger the difference, the greater the variation in load transfer between adjacent soil layers, and the greater the discontinuity in load transfer capacity between the two soil layers. This discontinuity corresponds to the transition boundary between the shallow soil arching effect and the deep soil end bearing effect. Therefore, the two adjacent soil layers with the largest difference are selected as candidate soil layer pairs. In order to locate the boundary at the starting point of the discontinuous change in interlayer load transfer, the top elevation of the lower soil layer in the candidate soil layer pair is selected as the candidate boundary elevation.

[0069] Then, using the candidate boundary elevation as the boundary, calculate the total inter-layer load transfer of all soil layers above the candidate boundary elevation, denoted as the upper inter-layer load transfer total. Simultaneously, calculate the total inter-layer load transfer of all soil layers below the candidate boundary elevation, denoted as the lower inter-layer load transfer total. For both the upper and lower inter-layer load transfer totals, the region consisting of all soil layers corresponding to the smaller value is designated as the low-load side, and the region consisting of all soil layers corresponding to the larger value is designated as the high-load side.

[0070] Because the load transfer on the low-load side is relatively small, the fluctuation of the load transfer between layers within it does not affect the final determination of the boundary soil layer. Therefore, a layer-by-layer comparison operation is performed on the high-load side rather than the low-load side.

[0071] Specifically, within the high-load side, starting from the candidate boundary elevation, the difference in load transfer between adjacent layers is compared layer by layer in the direction away from the low-load side. The direction away from the low-load side specifically refers to the direction from the candidate boundary elevation towards the interior of the high-load side, away from the low-load side. When the first occurrence of a difference in load transfer between adjacent layers being less than the difference in load transfer between layers corresponding to the candidate boundary elevation, the upper soil layer of the two corresponding soil layers is designated as the boundary soil layer; otherwise, the comparison continues layer by layer.

[0072] Then, the top elevation of the boundary soil layer is taken as the upper limit elevation. In addition, if there is no soil layer above or below the candidate boundary elevation, the candidate boundary elevation is directly taken as the upper limit elevation.

[0073] If, after traversing to the end of the high-load side, no inter-layer load transfer difference is found that is less than the inter-layer load transfer difference corresponding to the candidate boundary elevation, then the top elevation of the soil layer at the end of the traversal will be taken as the top elevation of the boundary soil layer.

[0074] Step S4: Using the upper limit elevation as the boundary, accumulate the interlayer load in both the positive and negative directions along the depth of the foundation pit, until the difference between adjacent accumulated values ​​is less than the difference between the previous accumulated values. Then, include the soil layers corresponding to the accumulated interlayer loads into bearing set one and bearing set two, respectively.

[0075] Specifically, the direction perpendicular to and pointing towards the bottom of the excavation pit is denoted as the depth direction of the excavation pit. The positive direction of the depth direction is defined as the direction from the top of the excavation pit to the bottom, and the negative direction of the depth direction is defined as the direction from the bottom of the excavation pit to the top.

[0076] Based on this, taking the upper limit elevation as the boundary, the interlayer load transfer of each soil layer is accumulated layer by layer downwards along the positive direction of the foundation pit depth. After each layer is accumulated, the difference between the current accumulated value and the previous accumulated value is calculated. When the difference is less than the difference between the previous adjacent accumulated values, continuing to accumulate will further reduce the difference of the accumulated values, which may cause the calculation result of the subsequent arch load ratio to deviate from the true value. Therefore, the downward accumulation is stopped. For ease of description, the set of soil layers corresponding to the accumulated interlayer load transfer is denoted as bearing set one.

[0077] Meanwhile, taking the upper limit elevation as the boundary, the interlayer load transfer of each soil layer is accumulated layer by layer in the opposite direction of the foundation pit depth. After each layer is accumulated, the difference between the current accumulated value and the previous accumulated value is calculated. When the difference is less than the difference of the previous adjacent accumulated value, the upward accumulation is stopped. For ease of description, the set of soil layers corresponding to the accumulated interlayer load transfer is denoted as bearing set two.

[0078] In the initial accumulation, there is no difference between the previous adjacent accumulated value. The current accumulated value is used as the starting base value, and the next layer is accumulated. The difference comparison is performed after at least two adjacent accumulated values ​​are obtained.

[0079] Step S5: Based on the normal stress of the pile wall of the front and rear piles in bearing set one and bearing set two, obtain the load ratio on the arch and the load ratio at the end of the disk, and thus obtain the current load difference.

[0080] Considering that in the double-row NT-CEP pile foundation pit support system, the load transfer between the front and rear rows of piles is mainly achieved through the direct compression of the pile wall by the soil between the piles, and that normal stress is the direct physical quantity characterizing the compression effect, normal stress rather than tangential stress is selected as the basis for the load ratio.

[0081] In practice, at the center elevation of each soil layer contained in the bearing set 2, earth pressure cells are installed on the outer surface of the pile wall on the back side of the front row of piles and the outer surface of the pile wall on the front side of the rear row of piles. The frequency or voltage signal of each earth pressure cell is read by the strain acquisition instrument on the ground and then converted into normal stress (the specific process is existing technology and will not be described in detail).

[0082] The normal stress of the pile wall on the back side of the front row piles and the front side of the pile wall on the back side of the rear row piles are extracted separately. The arithmetic mean of the extracted normal stress of the pile wall on the back side of the front row piles is recorded as the average front force. The arithmetic mean of the extracted normal stress of the pile wall on the front side of the rear row piles is recorded as the average rear force. The ratio of the average front force to the average rear force is taken as the load ratio on the arch. The larger the load ratio on the arch, the greater the bending moment and shear force borne by the front row piles in the bearing capacity group, which is prone to overturning risk, while the bearing capacity of the rear piles is not fully utilized.

[0083] Based on the soil layers included in bearing set 1, the end load ratio is obtained in the same way as described above. A larger end load ratio indicates that the front row of piles in bearing set 1 bears a larger end bearing reaction force, which is prone to vertical settlement risk, while the bearing capacity of the rear row of piles is also not fully utilized.

[0084] Then, the absolute value of the difference between the load ratio on the arch and the load ratio at the end of the plate is taken as the current load difference. The larger the current load difference, the greater the difference in the load sharing ratio between the front and rear rows of piles in bearing group one and bearing group two. When the vertical load borne by the front and rear rows of piles exceeds the vertical bearing capacity of the pile body, the front row of piles is prone to overturning or vertical settlement failure, while the rear row of piles is prone to pile body crushing or buckling failure.

[0085] It should be added that the determination of the front back soil pressure transmission zone and the rear soil pressure transmission zone in step S1, the establishment of the rear soil stress measurement line and the front back soil stress measurement line in step S2, and the extraction of the pile wall normal stress in step S5 are all based on the soil layer center elevation. This is to avoid the influence of stress abrupt changes at the interface of adjacent soil layers when taking values ​​near the top or bottom surface of the soil layer.

[0086] Step S6: Based on the comparison between the load difference obtained after superimposing the cantilever diameter on the current row spacing and the current load difference, correct the current row spacing.

[0087] In a double-row NT-CEP pile foundation pit support system, the spacing between rows directly affects the load transfer path and load-sharing ratio between the front and rear rows of piles. If the spacing is too small, the stress diffusion areas of the front and rear rows of piles overlap excessively, leading to stress concentration in the soil between the piles; if the spacing is too large, the stress diffusion areas of the front and rear rows of piles separate, and the soil between the piles cannot effectively transfer the load. Therefore, this invention uses load difference analysis to correct the current row spacing.

[0088] Since the cantilever diameter is the basic unit of measurement for the radial influence of the bearing plate end bearing effect, using the cantilever diameter as the step size for adjusting the row spacing ensures that each adjustment will cause a change in the interaction state between the bearing plate and the soil between the piles. Therefore, the sum of the current row spacing and the cantilever diameter is used as the comparison row spacing. Based on the comparison row spacing, steps S1 to S5 are re-executed to obtain the comparison load difference corresponding to the comparison row spacing.

[0089] When the load difference is greater than or equal to the current load difference, it indicates that the load difference has not decreased after increasing the row spacing. Continuing to increase the row spacing may cause the load difference to increase further, resulting in the vertical load borne by the front and rear rows of piles exceeding the vertical bearing capacity of the pile body. Therefore, the iteration is stopped, the current row spacing is kept unchanged, and the current row spacing is used as the layout row spacing.

[0090] When the comparison load difference is less than the current load difference, the current row spacing is replaced by the comparison row spacing, the pressure transmission range is redefined, and the current load difference is updated. This iterative process is repeated until either of the following termination conditions is met: 1) The comparison load difference is greater than or equal to the current load difference; 2) The current row spacing is greater than or equal to the preset minimum row spacing limit. The current row spacing at the time of stopping the iteration is taken as the layout row spacing.

[0091] The process for determining the minimum pre-set spacing between rows is as follows: According to the technical specifications for building pile foundations, in unsaturated soil and saturated non-cohesive soil, the larger of 2.0 times the design diameter of the bearing plate and 3.5 times the pile diameter is taken as the minimum center-to-center distance between drilled and expanded cast-in-place piles (NT-CEP pile category); in saturated cohesive soil, the larger of 2.2 times the design diameter of the bearing plate and 4.5 times the pile diameter is taken as the minimum center-to-center distance between drilled and expanded cast-in-place piles. Based on this, according to the actual soil layer category at the engineering site, the corresponding minimum center-to-center distance between piles is selected as the minimum pre-set spacing between rows. The design diameter of the bearing plate and the pile diameter are directly read from the pile foundation design drawings.

[0092] It should be added that when the initial row spacing is greater than or equal to the preset minimum row spacing limit, the above termination condition 2) will not be triggered during the iteration process. The iteration process determines whether to terminate based solely on the comparison result between the load difference and the current load difference.

[0093] After obtaining the spacing between the rows, the spacing between the rows is used as the design spacing between the front and rear rows of piles in the double-row NT-CEP pile foundation pit support system. It is used to guide the on-site construction layout and pile position arrangement. For example, during the construction phase, the surveyors use a total station or steel ruler on-site to lay out the pile positions according to the design spacing. Using the already constructed pile positions of the front row of piles as the reference point, the design spacing is measured along the direction perpendicular to the side wall of the foundation pit on the horizontal plane (i.e., from the inside of the foundation pit to the outside of the foundation pit), and the center point of the pile position of the rear row of piles is marked.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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 method for optimizing the spacing of rows in a double-row NT-CEP pile foundation pit support system, characterized in that, Includes the following steps: Based on the cantilever diameter and elevation of the bearing plate of the front and rear piles, the soil between the front and rear piles is divided into several soil layers. Based on the current row spacing and cantilever diameter, determine the pressure transmission range of each soil layer, extract the tangential stress within the pressure transmission range and at the elevation of the upper and lower surfaces of the bearing plate, and obtain the interlayer load transfer amount accordingly. The difference in load transfer between adjacent soil layers is compared to determine the boundary soil layer, and the elevation of the boundary soil layer is used as the upper limit elevation. Using the upper limit elevation as the boundary, the interlayer load is accumulated layer by layer in both the positive and negative directions along the depth of the foundation pit until the difference between adjacent accumulated values ​​is less than the difference between the previous accumulated values. The soil layers corresponding to the accumulated interlayer load are then included in bearing set one and bearing set two, respectively. Based on the normal stress of the pile wall of the front and rear piles in load-bearing set one and load-bearing set two, the load ratio on the arch and the load ratio at the end of the disk are obtained respectively, and the current load difference is obtained from this. The current row spacing is corrected based on the comparison between the load difference obtained by superimposing the cantilever diameter on the current row spacing and the current load difference.

2. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 1, characterized in that, The process of dividing soil layers is as follows: Along the vertical direction, the horizontal plane where the upper plate elevation of each bearing plate of the front and rear piles is located and the horizontal plane where the lower plate elevation is located are both taken as the initial dividing interface. All the initial dividing interfaces divide the soil between the outer walls of the front and rear piles into multiple initial vertical soil segments. For each initial vertical soil segment, the outer boundary of the upper plate of the bearing plate at its upper horizontal plane is vertically projected downwards to its lower horizontal plane to form a vertical projection cylinder of the upper plate; at the same time, the outer boundary of the lower plate of the bearing plate at its lower horizontal plane is vertically projected upwards to its upper horizontal plane to form a vertical projection cylinder of the lower plate. Using the vertical projection columns of the upper plate and the lower plate as dividing columns, within the initial vertical soil section, the soil within the area enclosed by the dividing columns is designated as the inner core soil, and the remaining soil is designated as the outer ring soil. When the projection areas of the upper vertical projection column and the lower vertical projection column overlap on the horizontal plane, the vertical column soil segment corresponding to the overlapping area is separated from the outer ring soil and the inner core soil and used as the column core soil. The outer ring soil, inner core soil, and column core soil are treated as independent soil layers.

3. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 1, characterized in that, The elevation of the horizontal plane containing the top surface of the soil layer is taken as the top elevation, and the elevation of the horizontal plane containing the bottom surface of the soil layer is taken as the bottom elevation; the elevation of the center of the soil layer is the arithmetic mean of the top elevation and the bottom elevation.

4. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 3, characterized in that, The process of determining the pressure transmission range of each soil layer is as follows: The number of extension segments is the integer part of the ratio of the current row spacing to the cantilever diameter. Starting from the pile wall of the back soil side of the front row of piles at the center elevation of each soil layer, extend horizontally away from the front row of piles in sections according to the cantilever diameter, and the range between the starting point and the end point of the last section is taken as the pressure transmission zone of the back soil of the front row. Starting from the soil-facing pile wall of the rear row of piles at the center elevation of each soil layer, extend horizontally towards the front row of piles according to the cantilever diameter, and take the range between the starting point and the end point of the last section as the soil-facing pressure transmission zone of the rear row. The area where the front back soil pressure transmission zone and the rear front soil pressure transmission zone intersect and overlap is taken as the pressure transmission range of the corresponding soil layer.

5. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 3, characterized in that, The process for extracting tangential stress is as follows: At the center elevation of each soil layer, stress measurement lines for the back soil of the front row are laid out horizontally from the pile wall on the back soil side of the front row pile to the pressure transmission zone of the back soil of the front row pile, and stress measurement lines for the front soil side of the rear row pile are laid out horizontally from the pile wall on the front soil side of the rear row pile to the pressure transmission zone of the front soil side of the rear row pile. On the front row back soil stress measuring line and the rear row front soil stress measuring line, select the tangential stress at the position level with the elevation of the upper plate of the bearing plate, and take the larger one as the tangential stress at the upper plate of the bearing plate; at the same time, select the tangential stress at the position level with the elevation of the lower plate of the bearing plate, and take the larger one as the tangential stress at the lower plate of the bearing plate. The arithmetic mean of all tangential stress values ​​on the front back soil stress measurement line and the rear front soil stress measurement line is taken as the tangential stress within the pressure transmission range.

6. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 1, characterized in that, The process of obtaining the interlayer load transfer is as follows: For each soil layer, the tangential stress at the upper surface of the bearing plate is taken as the upper limit parameter, the tangential stress at the lower surface of the bearing plate is taken as the lower limit parameter, and the tangential stress within the pressure transmission range is taken as the intermediate reference value. When the intermediate reference value is less than the upper limit parameter but greater than the lower limit parameter, the intermediate reference value is used as the interlayer load transfer value. When the intermediate reference value is greater than the upper limit parameter, the upper limit parameter is used as the inter-layer load transfer value; when the intermediate reference value is less than the lower limit parameter, the lower limit parameter is used as the inter-layer load transfer value.

7. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 3, characterized in that, The process of determining the boundary soil layer and upper limit elevation is as follows: Arrange all soil layers in order of top elevation from top to bottom, calculate the difference in load transfer between adjacent soil layers, and take the top elevation of the lower soil layer in the adjacent soil layer with the largest difference as the candidate boundary elevation. Calculate the total interlayer load transfer of all soil layers above the candidate boundary elevation and the total interlayer load transfer of all soil layers below the candidate boundary elevation respectively. Take the area corresponding to the smaller value of the two as the low load side and the area corresponding to the larger value as the high load side. On the high-load side, starting from the candidate boundary elevation, compare the load transfer difference between adjacent layers in the direction away from the low-load side. When the first occurrence of the load transfer difference between adjacent layers being less than the load transfer difference between layers corresponding to the candidate boundary elevation, the upper soil layer of the two corresponding soil layers is taken as the boundary soil layer; the top elevation of the boundary soil layer is taken as the upper limit elevation.

8. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 1, characterized in that, The process of constructing bearer set one and bearer set two is as follows: Using the upper limit elevation as the boundary, the interlayer load transfer of each soil layer is accumulated layer by layer downward along the positive direction of the foundation pit depth. After each layer is accumulated, the difference between the current accumulated value and the previous accumulated value is calculated. When the difference is less than the difference of the previous adjacent accumulated value, the downward accumulation is stopped, and the soil layer corresponding to the accumulated interlayer load transfer is included in the bearing set 1. Using the upper limit elevation as the boundary, the interlayer load transfer of each soil layer is accumulated layer by layer upwards in the opposite direction of the foundation pit depth. After each layer is accumulated, the difference between the current accumulated value and the previous accumulated value is calculated. When the difference is less than the difference between the previous adjacent accumulated value, the upward accumulation is stopped, and the soil layer corresponding to the accumulated interlayer load transfer is included in the bearing set two.

9. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 4, characterized in that, The process of obtaining the current load difference is as follows: At the center elevation of each soil layer contained in the bearing set 2, the normal stress of the pile wall on the back side of the front row piles and the front side of the rear row piles are extracted respectively; the average value of the extracted normal stress of the pile wall on the back side of the front row piles is recorded as the average value of the front row force; the average value of the extracted normal stress of the pile wall on the front side of the rear row piles is recorded as the average value of the rear row force; the ratio of the average value of the front row force to the average value of the rear row force is used as the load ratio on the arch. Based on each soil layer included in the bearing set, the plate end load ratio is obtained in the same way; the absolute value of the difference between the arch load ratio and the plate end load ratio is taken as the current load difference.

10. The method for optimizing the spacing of rows in the double-row NT-CEP pile foundation pit support system according to claim 1, characterized in that, The process of correcting the current row spacing is as follows: The sum of the current row spacing and the cantilever diameter is used as the comparison row spacing, and the comparison load difference corresponding to the comparison row spacing is obtained based on this. When the comparison load difference is greater than or equal to the current load difference, stop the iteration and use the current row spacing as the layout row spacing; When the comparison load difference is less than the current load difference, replace the current row spacing with the comparison row spacing, redetermine the pressure transmission range, update the current load difference, until the comparison load difference is greater than or equal to the current load difference.

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