Sensor-based monitoring method for deep foundation pit combined steel pipe inclined support

Abstract

The application discloses a sensor-based deep foundation pit combined steel pipe inclined support monitoring method, relates to the steel pipe inclined support monitoring field, and comprises the following steps: the actual center coordinates of the embedded steel plates of the upper support pier and the lower support pier are measured, the actual inclination angle of the inclined support is calculated, and the sensor is installed by taking the qualified actual angle as the stress reference direction; while collecting the axial pressure of the inclined support, stress measuring points are arranged at equal intervals along the length direction of the waist beam surface, the real-time stress distribution of the waist beam surface is synchronously collected, the stress gradient is calculated, and the stress concentration area is circled; the under-stressed member is positioned by calculating the difference between the axial force of each inclined support and the average axial force in the group, the elongation hinge head compensation operation is performed, and the hinge head of the adjacent inclined support is retracted according to the overload amplitude of the stress concentration area to release the local stress; the combined diagnosis of the under-load of the support member and the local overload of the waist beam is realized, and the safety and stress balance of the deep foundation pit support system are improved.

Description

Technical Field

[0001] This invention belongs to the field of steel pipe inclined support monitoring technology, and relates to a sensor-based monitoring method for combined steel pipe inclined supports in deep foundation pits. Background Technology

[0002] Composite steel pipe diagonal bracing is widely used in deep foundation pit support projects due to its advantages such as convenient construction, small space occupation, and recyclability. During foundation pit construction, it is necessary to monitor the stress state of the diagonal bracing in real time and adjust the support to ensure the safety of the foundation pit and the stability of the surrounding environment.

[0003] Currently, there are existing technologies that propose solutions to the problem of deep foundation pit monitoring. For example, patent application CN110258497A discloses an intelligent monitoring system for the safety of deep foundation pits. This system collects foundation pit monitoring data, sets the power supply status of abnormal monitoring sensors, transmits data remotely, and uses regression analysis to model and calculate the monitoring data to obtain the expected data monitoring values ​​for the future, thereby realizing foundation pit safety monitoring and early warning.

[0004] However, the above-mentioned existing technologies still have the following shortcomings in practical applications: First, the support posture in the design drawings is used as the installation benchmark by default. However, due to the deviation in the positioning of the pre-embedded components at the construction site, the actual spatial posture of the support is not completely consistent with the design drawings. Installing the sensor according to the drawings will cause the measurement direction to deviate from the actual force direction of the support. As a result, the collected values ​​are not the actual axial load borne by the support, but data distorted due to the directional deviation, which makes it difficult to truly reflect the stress state of the support.

[0005] Secondly, in the bracing system, the stress distribution of the lumbar beam reflects the uniformity of load transfer. Existing technology cannot determine whether there is excessive local stress in the lumbar beam based solely on the axial force values ​​of each brace. When the actual load of a certain brace is too small, the load it should bear will automatically transfer to the adjacent brace, causing the lumbar beam in the adjacent brace's action zone to bear additional stress. The lumbar beam may be under excessive stress for a long time without being detected, posing a risk of structural damage.

[0006] Finally, existing technologies mainly rely on trend prediction through regression analysis, and the output results are used to assist in manual early warning. When an anomaly is detected, manual intervention is required for judgment, which makes it difficult for operators to determine the location of local overload, and adjustments rely on experience, making it difficult to accurately control the force balance. Summary of the Invention

[0007] In view of this, in order to solve the problems mentioned in the background art, the present invention provides a sensor-based monitoring method for combined steel pipe inclined supports in deep foundation pits.

[0008] The objective of this invention can be achieved through the following technical solution: a sensor-based monitoring method for combined steel pipe inclined supports in deep foundation pits, comprising: S1, calculating the theoretical inclination angle of the inclined support according to the support construction drawing, measuring the actual center coordinates of the embedded steel plates of the upper and lower supports, and calculating the actual inclination angle and support length of the inclined support;

[0009] S2. If the deviation between the actual tilt angle and the theoretical tilt angle exceeds the limit, adjust the angle of the diagonal brace until the deviation is within acceptable limits, and use the adjusted actual tilt angle as the reference direction for force application.

[0010] S3. Based on the stress of the diagonal braces in the support, divide the monitoring group and collect the real-time axial pressure of each diagonal brace and the real-time stress on the surface of the waist beam under the stress reference direction.

[0011] S4. Calculate the difference between the real-time axial pressure of each brace and the average axial force of all braces in the monitoring group, and locate the understressed support members in combination with the design axial force value of the brace.

[0012] S5. Calculate the stress gradient based on the rate of change of real-time stress along the surface of the waist beam to delineate the stress concentration area;

[0013] S6. Adjust the hinge at the end of the understressed support member to compensate for axial pressure according to the support length. Adjust the hinge of the adjacent diagonal brace according to the stress overload amplitude of the stress concentration area until the balance control is met.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention calculates the actual tilt angle of the bracing by measuring the actual center coordinates of the pre-embedded steel plates of the upper and lower supports, and installs the sensor with the actual angle after adjustment as the force reference direction, so that the data collected by the sensor truly reflects the actual load of the bracing, suppresses the measurement direction error caused by the installation deviation, and reduces the deviation of the collected axial pressure data from the force direction to within the allowable range of the project.

[0015] (2) While collecting the axial pressure of the diagonal brace, the present invention arranges stress measuring points at equal intervals along the length direction of the waist beam surface, simultaneously collects the real-time stress distribution on the waist beam surface, and calculates the stress gradient to delineate the stress accumulation area. This overcomes the limitation that the local stress of the waist beam cannot be judged by the axial force value alone, and can promptly detect the local overload of the waist beam caused by load transfer, avoiding the risk of structural damage to the waist beam being under excessive stress for a long time without being detected.

[0016] (3) This invention locates understressed members by calculating the difference between the axial force of each diagonal brace and the average axial force within the group, performs the extension of the flexible head compensation operation, and releases local stress by retracting the flexible head of the adjacent diagonal brace according to the overload amplitude of the stress accumulation area. This overcomes the defect of relying on manual experience judgment, which makes it difficult to accurately control the force balance and improves the timeliness of regulation. Attached Figure Description

[0017] 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.

[0018] Figure 1 This is a diagram illustrating the implementation steps of the method of the present invention;

[0019] Figure 2 This is a flowchart of the deviation calibration process of the present invention;

[0020] Figure 3 This is a flowchart illustrating the process of identifying stress concentration areas in the waist beam according to the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figure 1 As shown, the present invention provides a sensor-based monitoring method for combined steel pipe inclined supports in deep foundation pits, including: S1, calculating the theoretical inclination angle of the inclined support according to the support construction drawing, measuring the actual center coordinates of the embedded steel plates of the upper and lower supports, and calculating the actual inclination angle and support length of the inclined support.

[0023] In step S1 above, the theoretical inclination angle of the diagonal brace is calculated based on the design coordinates of the upper and lower supports in the support construction drawing, and then calculated using the Pythagorean theorem.

[0024] Considering that in actual construction, if the actual angle is not calculated and the diagonal brace is installed directly according to the theoretical angle, the two ends of the diagonal brace will not make a tight contact with the steel plate, resulting in initial eccentric compression. This will not only change the actual stress state of the diagonal brace, causing errors in the measured axial pressure, but will also turn it into a complex force with bending moment.

[0025] Based on this, the calculation of the actual tilt angle and support length of the diagonal brace includes: S1-1, selecting four edge corner points on the surface of the pre-embedded steel plates of the upper and lower supports respectively, using a total station to aim at the edge corner points respectively, and recording the three-dimensional spatial coordinates of each corner point.

[0026] S1-2. Connect the two edge corners on the diagonal of each embedded steel plate to form two spatial diagonals on the surface of the corresponding embedded steel plate. Extract the coordinates of the intersection of the two spatial diagonals on each embedded steel plate as the center coordinates of the upper and lower supports.

[0027] S1-3. Connect the center coordinates of the upper pier and the center coordinates of the lower pier to construct a spatial vector, calculate the angle between the spatial vector and the horizontal plane, and output the actual tilt angle.

[0028] S1-4 Calculate the Euclidean distance of the spatial vector and output the actual support length.

[0029] In step S1-1 above, the four edge corner points are selected as follows: For a rectangular steel plate, measure its edges along both the length and width directions, and determine the intersection of two adjacent edges as the corner point. If the steel plate edge has a chamfer or rounded transition, the tangent point between the chamfer arc and the straight edge is taken as the corner point, or the intersection along the extension of the straight edge is taken as the virtual edge corner point.

[0030] Using the center of the total station as the origin, and two mutually perpendicular directions in the horizontal plane as the X and Y axes respectively, with the vertical direction as the Z axis, the three-dimensional coordinates of the four corner points on the embedded steel plate need to be obtained simultaneously in the X, Y, and Z directions. If a level and steel tape combination is used, elevation and horizontal position need to be measured step by step, which is not only cumbersome but also introduces accumulated errors from multiple centering and leveling operations. The total station, however, can directly measure the three-dimensional coordinates of each corner point with a single setup, and uses infrared laser non-contact aiming, eliminating the need to climb support piers and ensuring safe operation. During measurement, the total station is set up on a stable station, and after orientation at a known backsight point, the reflectors at each corner point are aimed sequentially. The instrument automatically calculates and records the three-dimensional coordinates of each point.

[0031] In steps S1-2 above, the principle behind obtaining the center coordinates of the upper and lower supports is as follows: When the end of the diagonal brace is tightened against the steel plate through the hinge, if the steel plate is uniformly compressed, the point of application of the resultant force of the contact pressure should theoretically be located at the geometric center of the steel plate. The geometric center of the rectangular embedded steel plate is the intersection of the two diagonals. The four edge corners are the most easily identifiable and measurable feature points on the steel plate profile. Constructing diagonals and finding their intersection can offset the random errors in measuring individual corner points. Simultaneously, the upper and lower supports use the exact same method for obtaining their center coordinates, ensuring consistent measurement benchmarks and eliminating systematic deviations introduced by different methods. The line connecting the geometric centers of the upper and lower supports serves as the spatial axis of the diagonal brace, conforming to the actual stress state of the diagonal brace under axial compression.

[0032] In practice, if the intersection of the two diagonals does not coincide completely, the average of the coordinates of the two intersection points is taken as the final center coordinates to eliminate the influence of the steel plate's own processing error on the center positioning.

[0033] In step S1-3, when calculating the actual tilt angle, the vertical height difference between the center points of the upper and lower supports is divided by the straight-line distance between the two points to obtain a ratio. The actual tilt angle is then calculated using the arcsine of this ratio. Here, the straight-line distance is the actual support length, and the vertical height difference is obtained by subtracting the elevation coordinates of the two points. The sine of the actual tilt angle is equal to the ratio of the vertical height difference to the support length.

[0034] S2. If the deviation between the actual tilt angle and the theoretical tilt angle exceeds the limit, adjust the angle of the diagonal brace until the deviation is within acceptable limits, and use the adjusted actual tilt angle as the reference direction for force application.

[0035] Because angular deviations can cause the end of the diagonal brace to contact the steel plate line, generating eccentric moments and additional bending moments, this can lead to brace bending and distorted axial force measurements. Therefore, it is necessary to adjust the angle to ensure uniform contact between the end faces, eliminate eccentricity, and ensure pure axial compression. (Refer to...) Figure 2 As shown, adjust the angle of the diagonal brace until the deviation is acceptable, including: S2-1, using the center point of the embedded steel plate of the lower support as the benchmark and the horizontal plane as the reference, calculate the horizontal and height coordinates of the theoretical center point of the upper support according to the construction drawings; specifically, use the Pythagorean theorem to calculate the horizontal and height coordinates of the theoretical center point of the upper support.

[0036] S2-2. Measure the horizontal and vertical coordinates of the actual center point of the upper support using a total station, and calculate the deviations between the actual and theoretical values ​​in the left-right, front-back, and vertical directions, respectively.

[0037] S2-3. If the height deviation is positive, reduce the suspension height of the upper support pier of the diagonal brace; if it is negative, increase the height.

[0038] S2-4. If there is a deviation in the left-right or front-back direction, apply traction force in the opposite direction.

[0039] S2-5. During the adjustment process, monitor the deviation values ​​in each direction in real time, and repeatedly adjust the height and horizontal traction. When the absolute value of the deviation in each direction is not greater than the corresponding installation allowable deviation, fix the two ends of the diagonal brace to the pre-embedded steel plates of the upper and lower supports.

[0040] In step S2-2, when measuring the horizontal and height coordinates of the actual center point of the upper support pier using a total station, since the actual center point is a virtual intersection point, the aforementioned diagonal intersection method is required. The horizontal and height coordinates of the actual center point of the upper support pier are calculated by measuring the coordinates of the four edge corner points.

[0041] The deviations in the left-right, front-back, and height directions represent the differences between the actual center point coordinates and the theoretical center point coordinates in the X-axis (left-right), Y-axis (front-back), and Z-axis (height) directions, respectively.

[0042] In step S2-3, a positive height deviation indicates that the actual center point of the upper support is higher than the theoretical center point. In this case, the actual tilt angle of the brace is too large, with the end contacting the upper side of the steel plate and being suspended below, generating an eccentric moment that causes the brace to tilt backward, making it prone to bending and instability. A negative height deviation indicates that the actual center point is lower than the theoretical center point, with the actual tilt angle of the brace being too small, and the end contacting the lower side of the steel plate and being suspended above. Therefore, the adjustment direction should be opposite to the deviation direction: for a positive deviation, lower the suspension height; for a negative deviation, raise the height, so that the center point of the upper support returns to the theoretical position, ensuring that the end face of the brace is evenly fitted with the steel plate.

[0043] During adjustment, a manual chain hoist is used in conjunction with a wire rope to suspend the upper support of the diagonal brace. The lifting and lowering are precisely controlled by pulling the chain of the manual chain hoist. For heavy diagonal braces, a truck crane is first used to lift the upper support of the diagonal brace to keep the height deviation within ±3 cm. Then, the lifting force of the truck crane is removed, and the adjustment is carried out by pulling the chain hoist. Each pull of the chain hoist results in a lifting or lowering of approximately 2 to 3 cm, and the height deviation is gradually adjusted to within ±1 cm.

[0044] In step S2-4, a deviation in the left-right or front-back direction indicates that the actual center point of the upper support has shifted relative to the theoretical center point on the horizontal plane. At this time, the end of the diagonal brace contacts the edge of the steel plate, generating a horizontal eccentric moment, which poses a risk of slippage. Therefore, it is necessary to apply a traction force in the opposite direction to pull the end of the upper support back to its theoretical position horizontally.

[0045] Apply traction to set up anchor points on the opposite side of the offset direction, connect the anchor points to the ends of the diagonal braces by pulling the chain, and apply horizontal traction by pulling the chain to correct the deviation.

[0046] In steps S2-5, height adjustment and horizontal traction are not entirely independent. When adjusting the suspension height of the diagonal brace, the brace will swing around the support pier, potentially causing a change in its horizontal position. Similarly, when applying horizontal traction, the inclination angle of the diagonal brace will also change slightly, thus affecting the deviation in the height direction. Therefore, these steps must be repeated alternately, with the deviation in each direction remeasured after each adjustment. The new deviation values ​​will then determine whether to continue adjusting the height or continuing horizontal traction.

[0047] The specific values ​​of the allowable deviations for installation in step S2-5 are determined according to the requirements of the design drawings or with reference to the provisions in the Code for Acceptance of Construction Quality of Steel Structure Engineering. For example, the allowable deviation in the height direction is ±5 mm and the allowable deviation in the horizontal direction is ±10 mm.

[0048] The actual tilt angle after adjustment in step S2 above is used as the force reference direction of the diagonal brace. This direction is used as the reference for the installation and positioning of all subsequent monitoring sensors, the direction of data acquisition, and the adjustment of the flexible head. This ensures that the measurement data truly reflects the axial force state of the diagonal brace, and the adjustment operation is carried out along the axial direction to avoid generating additional bending moment.

[0049] S3. Based on the stress of the diagonal braces in the support, divide the monitoring group and collect the real-time axial pressure of each diagonal brace and the real-time stress on the surface of the waist beam under the stress reference direction.

[0050] Due to the uneven soil conditions during the excavation of the foundation pit, the axial forces actually borne by different diagonal braces on the same layer of the wainscoting are often not equal. As a result, when the axial force of a certain diagonal brace is lower than that of the surrounding diagonal braces, the diagonal brace basically does not participate in the load-bearing. Furthermore, since the surrounding diagonal braces bear the load shared by this diagonal brace, the actual load they bear is close to or exceeds the design value, posing a risk of overload.

[0051] Therefore, the monitoring group is divided according to the stress of the diagonal bracing in the support. All combined steel pipe diagonal bracing in the deep foundation pit that is at the same excavation depth and connected to the waist beam of the same layer is classified into one monitoring group.

[0052] The axial forces of the inclined braces at the same excavation depth are similar and comparable; the inclined braces connected to the waist beam at the same level are coupled to each other through the waist beam, and their forces are related. Therefore, inclined braces that simultaneously meet both conditions are grouped into the same monitoring group, and lateral comparisons are made based on the average axial force within the group.

[0053] When there is a corner in the same-floor wainscoting, and the main reinforcing bar of the wainscoting at the corner is broken or there is a structural expansion joint, the diagonal bracing in the same-floor wainscoting is divided into multiple monitoring groups with the corner as the boundary. This is because if the main reinforcing bar at the corner of the wainscoting is broken or there is a structural expansion joint, the wainscoting on both sides of the corner is structurally independent, and the load applied by the diagonal bracing on one side cannot be transferred to the other side through the corner. The axial forces of the diagonal bracing on both sides are not comparable laterally.

[0054] Otherwise, if the wainscoting at the corner is cast as a whole and the main reinforcing bars pass through continuously, the diagonal bracing crossing the corner will still be classified into the same monitoring group; ensuring that the number of diagonal bracing within the group is sufficient and that their stress states are interconnected.

[0055] Since the force reference direction determines the measurement direction of the axial force sensor, thus avoiding component force errors, and also determines the stress distribution location of the lumbar beam to ensure correct measurement point placement, all monitoring data must be collected under this reference direction; otherwise, subsequent diagnostics will lose accuracy. Therefore, collecting the real-time axial pressure of each diagonal brace and the real-time stress on the lumbar beam surface under the force reference direction includes: installing axial force sensors on each composite steel pipe diagonal brace to obtain the real-time axial pressure of each diagonal brace.

[0056] It should be added that the axial force sensor uses a vibrating wire axial force gauge. During installation, ensure that the sensor axis coincides with the force reference direction of the diagonal brace. Alignment is achieved through a positioning ring. After installation, the initial value is read as the zero-point reference. The real-time axial pressure is obtained by subtracting the initial value from the acquired value and multiplying it by a calibration coefficient. This calibration coefficient is set by the manufacturer at the time of manufacture and is used to convert the frequency change output by the sensor into an axial pressure value. The specific value is determined according to the calibration certificate provided by the manufacturer.

[0057] Stress measuring points are arranged at equal intervals along the length of the waist beam surface. The real-time stress value and its corresponding position of each measuring point are collected synchronously by stress sensors to form a stress value sequence along the length of the waist beam.

[0058] Stress measuring points are evenly spaced along the length of the lumbar beam, with a spacing of 1 / 3 to 1 / 2 of the spacing between the diagonal braces. The section within 1 meter on either side of the connection point between the diagonal brace and the lumbar beam is defined as the critical section, where the spacing between stress measuring points is increased to 0.5 meters. In other non-critical sections, the spacing between measuring points remains at 1.5 meters. The measuring points are placed on the load-bearing surface of the lumbar beam, i.e., the side where the diagonal brace presses against the lumbar beam, arranged in a straight line along the length of the lumbar beam. All measuring points are at the same height. Vibrating wire surface strain gauges are used as stress sensors, with the sensor axis parallel to the length of the lumbar beam. After installation, the initial strain value is read as the zero-point reference. All measuring points are simultaneously monitored, recording the real-time stress value and mileage coordinates of each point, arranged in ascending order of mileage coordinates to form a stress value sequence along the length of the lumbar beam. Temperature compensation plates are also placed near each measuring point to eliminate the influence of temperature changes on the measurement results.

[0059] All axial force and stress data were collected at a consistent frequency: once every 10 to 30 minutes under normal operating conditions, and once every 5 minutes under critical operating conditions.

[0060] S4. Calculate the difference between the real-time axial pressure of each diagonal brace and the average axial force of all diagonal braces in the monitoring group, and locate the understressed support members in combination with the design axial force value of the diagonal brace.

[0061] Considering that the stress on each diagonal brace is not completely uniform, some diagonal braces may have lower actual axial forces due to installation errors or insufficient preload. If these underloaded members are not identified in time, the load that should be borne by them will automatically transfer to the adjacent diagonal braces, causing the adjacent diagonal braces to be overloaded for a long time and posing a risk of instability.

[0062] Therefore, the determination process for the understressed support members is as follows: sum the real-time axial pressure of each diagonal brace in each monitoring group and divide it by the total number of diagonal braces in each monitoring group to obtain the real-time average axial force of each monitoring group; the total number of diagonal braces in the monitoring group is the actual number of diagonal braces included in the corresponding monitoring group, which is determined by the construction drawings and on-site inventory verification.

[0063] The difference between the real-time axial pressure of each diagonal brace in each monitoring group and the real-time average axial force is calculated. Diagonal braces with negative difference results are selected, and the real-time axial pressure of the selected diagonal braces is compared with the corresponding design axial force of the diagonal brace.

[0064] If the difference between the real-time axial pressure and the average axial force of each diagonal brace is negative, it indicates that the load borne by the diagonal brace is less than its theoretical share, and the missing load has been transferred to other diagonal braces in the same group, which is considered a relative under-stress. However, relative under-stress does not necessarily require compensation: if the axial force of all diagonal braces in the group is higher than the design value, the absolute axial force of the diagonal brace with the negative difference may still meet the safety requirements and no compensation is needed.

[0065] Therefore, the real-time axial force of the negative difference brace needs to be compared with its design axial force. The design axial force of the brace is obtained as follows: treating the brace as a two-force member, calculating the internal forces for each working condition according to the construction sequence of layered excavation and bracing, taking the maximum envelope value of the calculated axial force of the brace, and multiplying it by the load partial factor to obtain the design bearing capacity value. The load partial factor is taken as 1.25 according to the relevant technical specifications for foundation pit engineering. In the project implementation, the design axial force value is directly marked on the support plan layout drawing or the support component list in the foundation pit support design and construction drawings.

[0066] Braces whose real-time axial pressure is lower than the average real-time axial force within the group and lower than their own design axial force are marked as understressed support members.

[0067] According to force balance, the average axial force within a group represents the ideal, evenly distributed value of the total earth pressure. A axial force below the average indicates that the actual load borne by the brace is less than its corresponding share, with the missing load transferred to adjacent braces, indicating relative understress. The design axial force, on the other hand, is the lower limit of safe bearing capacity determined based on earth pressure calculations and code requirements. A axial force below the design force indicates that the absolute bearing capacity of the brace does not meet design requirements, posing a safety hazard. The intersection of these two factors represents an understressed support member that must be compensated for.

[0068] S5. Calculate the stress gradient based on the rate of change of real-time stress along the surface of the waist beam to delineate the stress concentration area.

[0069] When a diagonal brace is underloaded, the load it should bear will be transferred to the adjacent diagonal brace through the lateral beam. This causes a sharp increase in stress in the lateral beam section near the point of action of the adjacent diagonal brace, forming a local stress peak. Local overload of the lateral beam may cause concrete cracking or steel yielding, disrupting the force transmission path. Without delineating the concentrated area, it is impossible to distinguish between normal load peaks and abnormal overloads, and it is also impossible to determine which adjacent diagonal brace should be adjusted.

[0070] refer to Figure 3 As shown, delineating the stress concentration area includes: obtaining the real-time stress and corresponding mileage coordinates of each measuring point laid out along the length direction on the surface of the waist beam.

[0071] Calculate the absolute value of the difference in real-time stress between two adjacent measuring points and divide it by the actual spacing between the two adjacent measuring points to obtain the stress gradient in the adjacent measuring point section. The calculation of the absolute value of the difference in real-time stress between two adjacent measuring points is carried out sequentially from the end with a smaller mileage to the end with a larger mileage on the waist beam, subtracting the stress value of the previous measuring point from the stress value of the later measuring point.

[0072] Calculate the average stress gradient of all adjacent measuring point sections, and the average real-time stress value of all measuring points.

[0073] The adjacent measuring point sections where the stress gradient is greater than the average stress gradient are marked as high stress change sections, and the measuring points where the real-time stress value is greater than the real-time average stress value are marked as high stress measuring points.

[0074] The stress gradient represents the change in stress per unit length. The average stress gradient reflects the overall average drastic degree of stress change along the entire length of the beam. When the stress gradient in a certain section is greater than the average stress gradient, it indicates that the rate of stress change in that section exceeds the average level of the beam, meaning that the stress in that section has experienced a relatively more rapid rise or fall. In continuous elastic beams, rapid changes in stress usually correspond to local abrupt changes in bending moment, which are often caused by concentrated load application points or changes in cross-sectional stiffness.

[0075] The real-time average stress represents the arithmetic average level of stress at all measuring points along the entire length of the chord beam, reflecting the overall stress benchmark of the chord beam under the current load. When the stress value at a certain measuring point is greater than the real-time average stress, it indicates that the stress at that point is higher than the overall average stress level of the chord beam, meaning that this location is a local high-stress point.

[0076] The length range of the wainscoting containing multiple consecutive high-stress variation sections, and where the proportion of high-stress measuring points exceeds the proportional threshold, is defined as the stress concentration area.

[0077] Stress concentration areas on the chord beam manifest as a continuous length with large stress differences between adjacent measuring points, and the stress values ​​at most measuring points within this section are higher than the overall average level of the chord beam. Therefore, multiple consecutive high-stress variation sections ensure spatial continuity, eliminating isolated abrupt changes; and a high proportion of high-stress measuring points exceeding a threshold ensures high stress within this section, eliminating low-stress fluctuations. When both conditions are met simultaneously, the section can be accurately identified as the stress concentration area requiring intervention.

[0078] The continuous high-stress variation zones are usually divided into 2 to 3 zones, so as to avoid a single isolated zone being misjudged as stress accumulation due to measurement noise or local random fluctuations.

[0079] Before the foundation pit is excavated, simulated design loads are applied to the test girders using measured data from similar projects. The maximum value of the proportion of high-stress measuring points under normal working conditions is used as the proportion threshold. When no test conditions are available, the proportion threshold is taken as 0.6.

[0080] S6. Adjust the hinge at the end of the understressed support member to compensate for axial pressure according to the support length. Adjust the hinge of the adjacent diagonal brace according to the stress overload amplitude of the stress concentration area until the balance control is met.

[0081] Considering that the understressed diagonal brace is equivalent to a reduction in the stiffness of the elastic support at this point, the vertical constraint of the lumbar beam at this support point is weakened, causing the lumbar beam to undergo greater flexural deformation between adjacent support points. This results in an additional bending moment inside the lumbar beam, leading to cracking or yielding of the lumbar beam. Specifically, adjusting the hinge at the end of the understressed support member to compensate for axial pressure according to the support length includes: operating the hinge thread at the end of the understressed support member, extending the hinge by rotating the thread and tightening it against the support block; using a special wrench to rotate the hinge thread, gradually extending the hinge in a clockwise direction, so that the end of the diagonal brace is tightened against the support block until the axial force sensor reading rises and there is no gap at the end.

[0082] The system synchronously acquires the real-time axial pressure corresponding to the diagonal brace during the threading process of the rotating hinge head. When the real-time axial pressure rises to a point where the absolute value of the difference between it and the average axial force within the group is less than the preset allowable deviation range, and the real-time axial pressure does not exceed the design axial force of the diagonal brace, the rotation of the hinge head is stopped and the thread limit device is locked. The preset allowable deviation range is taken as 5% to 10% of the design axial force value based on engineering experience.

[0083] The goal of increasing the axial force in underloaded members is to restore the axial force to a level close to the average value. When the absolute value of the difference is less than the allowable deviation range, it indicates that the stress on the diagonal brace is basically consistent with the average level within the group, and the diagonal brace is no longer underloaded, so no further compensation is needed. The design axial force is the safety boundary of the diagonal brace's bearing capacity. During the compensation process, even if the axial force has not yet reached the average value, if it has reached the design axial force, it must be stopped to prevent the diagonal brace from becoming unstable due to overload.

[0084] The formation of stress concentration zones is usually due to excessive axial force on adjacent diagonal braces, leading to a significant increase in local bending moment and stress in the lumbar beam at that location. While compensating only the underloaded members can reduce the load on adjacent diagonal braces, stress concentration may not be completely eliminated due to material nonlinearity or localized damage, and the compensation process is delayed. Therefore, adjusting the adjacent diagonal braces based on the stress overload amplitude of the stress concentration zone involves: extracting the maximum real-time stress value on the lumbar beam surface within the stress concentration zone and obtaining the design allowable stress of the lumbar beam material.

[0085] The allowable design stress refers to the maximum stress value that the chord beam material is allowed to withstand under safe use conditions. It is directly adopted from the value marked on the support construction drawing. If it is not marked on the construction drawing, the axial compressive design value shall be obtained from the concrete structure design standard.

[0086] If the maximum real-time stress value exceeds the design allowable stress, then at least one adjacent diagonal brace shall be selected from the diagonal braces supporting the corresponding waist beam segment in the stress concentration area.

[0087] When the maximum real-time stress in the stress concentration area exceeds the design allowable stress of the lintel material, it indicates that the area is under excessive stress. Continued stress may lead to local cracking or yielding failure of the lintel. Based on the force transmission path, the stress concentration in the stress concentration area is mainly caused by the excessive axial force of adjacent diagonal braces. Therefore, it is necessary to start with the adjacent diagonal braces and release the axial force by retracting their flexible ends to directly reduce the load transmitted to the lintel in this area, allowing the stress to fall back within the safe limit. Selecting at least one adjacent diagonal brace ensures redundancy in adjustment.

[0088] The adjacent diagonal braces are selected in order of increasing distance from the stress concentration area. The diagonal braces whose real-time axial pressure is not lower than the lower limit of their own design axial force are selected. The screw threads at the ends of the braces are retracted and the support length is shortened until the maximum real-time stress value of the stress concentration area on the surface of the waist beam falls back to the design stress limit range.

[0089] The distance to the stress concentration area refers to the arc distance from the center of the connection point between the diagonal brace and the lumbar beam along the length of the lumbar beam to the geometric center of the stress concentration area; the lower limit of the self-designed axial force is taken as 30% to 50% of the corresponding diagonal brace design axial force value.

[0090] During the retraction of the adjustable head thread, the real-time axial pressure of the diagonal brace and the maximum real-time stress value of the stress accumulation area on the surface of the waist beam are monitored. If the real-time axial pressure of the diagonal brace drops below its own design axial force lower limit and the stress accumulation area is not eliminated, the retraction of the diagonal brace is stopped, and the operation is switched to the next adjacent diagonal brace in sequence according to distance. If the real-time axial pressure of all selected adjacent diagonal braces is lower than its own design axial force lower limit, the retraction operation is stopped and an alarm is issued to prompt the on-site engineer to check.

[0091] The upper limit of the design stress limit range is the control value, which is the material strength design value. It is obtained by referring to the steel structure design standard according to the grade of the steel girders. If the allowable stress has been marked on the construction drawings, it can be directly adopted. The lower limit is 0.

[0092] During the adjustment process, the number of understressed support members and the number of stress accumulation areas are recorded after each round of adjustment. If the number of understressed support members or the number of stress accumulation areas do not decrease after two consecutive rounds of adjustment, the adjustment is terminated and an alarm is issued to prompt the on-site engineer to intervene and check; otherwise, the adjustment operation continues until the balance control is met.

[0093] To ensure that there are no understressed members or stress accumulation areas in the support system, and to avoid over-adjustment or under-adjustment.

[0094] Based on this, the judgment process for satisfying the equilibrium control is as follows: continuously acquire the real-time axial pressure of all diagonal braces in each monitoring group and the real-time stress gradient along the surface of the waist beam.

[0095] When the difference between the real-time axial pressure of all understressed support members in each monitoring group and the average axial force in the group is less than the allowable axial force deviation value, and the maximum stress gradient in all detected stress accumulation areas on the surface of the waist beam is less than the gradient safety threshold, the deep foundation pit combined steel pipe inclined support system is determined to have reached a state of stress equilibrium, and the current round of monitoring and adjustment operations ends.

[0096] Within the same monitoring group, all diagonal bracing members should have similar axial compressive forces under balanced stress. A difference in axial force between an understressed member and the group's average axial force exceeding the allowable range indicates uneven load distribution. Simultaneously, a stress gradient on the lumbar beam surface exceeding the safety threshold reflects abrupt changes in the local force transmission path or stress concentration. Therefore, a balanced stress state is considered achieved only when the stress deviation between members and the local stress variation in the lumbar beam are both controlled within the preset allowable range.

[0097] The allowable axial force deviation value is taken as 10% of the design axial force value of the diagonal brace, and the gradient safety threshold is taken as 1.5 to 2.0 times the average stress gradient of all adjacent measuring point sections, and is determined according to the material properties of the waist beam.

[0098] The gradient safety threshold is taken as 1.5 to 2.0 times the average stress gradient of all adjacent measuring point sections, and the multiple is determined according to the material properties of the wainscoting. For steel wainscoting, it is taken as 2.0.

[0099] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0100] 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 implementation should not be considered beyond the scope of this application.

[0101] In addition, the functional modules in the various embodiments of this application 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.

[0102] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0103] 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 sensor-based monitoring method for combined steel pipe inclined supports in deep foundation pits, characterized in that: include: Calculate the theoretical inclination angle of the diagonal brace based on the support construction drawings, measure the actual center coordinates of the embedded steel plates of the upper and lower supports, and calculate the actual inclination angle and support length of the diagonal brace. If the deviation between the actual tilt angle and the theoretical tilt angle exceeds the limit, adjust the angle of the diagonal brace until the deviation is within acceptable limits, and use the adjusted actual tilt angle as the reference direction for force application. Based on the stress of the diagonal braces in the support, the monitoring group is divided, and the real-time axial pressure of each diagonal brace and the real-time stress on the surface of the waist beam are collected under the stress reference direction. Calculate the difference between the real-time axial pressure of each diagonal brace and the average axial force of all diagonal braces in the monitoring group, and locate the understressed support members in combination with the design axial force value of the diagonal brace; The stress gradient is calculated based on the rate of change of real-time stress along the surface of the waist beam to delineate the stress concentration area; Adjust the hinge at the end of the understressed support member according to the support length to compensate for axial pressure, and adjust the hinge of the adjacent diagonal brace according to the stress overload amplitude of the stress concentration area until balanced control is achieved.

2. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The calculation of the actual tilt angle and support length of the diagonal brace includes: Four edge corner points were selected on the surface of the embedded steel plates of the upper and lower supports, and the three-dimensional spatial coordinates of each corner point were recorded by using a total station to aim at the edge corner points. Connect the two edge corners on the diagonal of each embedded steel plate to form two spatial diagonals on the surface of the corresponding embedded steel plate. Extract the coordinates of the intersection of the two spatial diagonals on each embedded steel plate as the center coordinates of the upper and lower supports. Connect the center coordinates of the upper pier and the center coordinates of the lower pier to construct a spatial vector, calculate the angle between the spatial vector and the horizontal plane, and output the actual tilt angle; Calculate the Euclidean distance of the spatial vector and output the actual support length.

3. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The adjustment of the diagonal brace angle until the deviation is within acceptable limits includes: Using the center point of the embedded steel plate of the lower support as the benchmark and the horizontal plane as the reference, calculate the horizontal and height coordinates of the theoretical center point of the upper support according to the construction drawings. The horizontal and vertical coordinates of the actual center point of the upper support pier were measured using a total station, and the deviations between the actual and theoretical values ​​in the left-right, front-back, and vertical directions were calculated respectively. If the height deviation is positive, the suspension height of the upper support pier of the diagonal brace is reduced; if it is negative, the height is increased. If there is a deviation in the left-right or front-back direction, apply traction in the opposite direction; During the adjustment process, the deviation values ​​in each direction are monitored in real time, and the height and horizontal traction adjustments are repeated. When the absolute value of the deviation in each direction is not greater than the corresponding installation allowable deviation, the two ends of the diagonal brace are fixed to the pre-embedded steel plates of the upper and lower supports.

4. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The monitoring groups are divided according to the stress of the diagonal bracing in the support, including: All combined steel pipe diagonal supports in the deep foundation pit that are at the same excavation depth and connected to the waist beam at the same level are classified into one monitoring group; When there is a corner in the same layer of the wainscoting, and the main reinforcing bar of the wainscoting at the corner is broken or a structural deformation joint is provided, the diagonal bracing in the same layer is divided into multiple monitoring groups with the corner as the boundary. Otherwise, if the wainscoting at the corner is cast as a whole and the main reinforcing bars pass through continuously, the diagonal bracing that crosses the corner will still be classified into the same monitoring group.

5. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The real-time axial pressure of each diagonal brace and the real-time stress on the surface of the waist beam, collected under the force reference direction, include: An axial force sensor is installed on each of the combined steel pipe diagonal supports to obtain the real-time axial pressure of each diagonal support; Stress measuring points are arranged at equal intervals along the length of the waist beam surface. The real-time stress value and its corresponding position of each measuring point are collected synchronously by stress sensors to form a stress value sequence along the length of the waist beam.

6. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The determination process for the understressed positioning support member is as follows: The real-time axial pressure of each diagonal brace in each monitoring group is summed and divided by the total number of diagonal braces in each monitoring group to obtain the real-time average axial force of each monitoring group. The difference between the real-time axial pressure of each diagonal brace in each monitoring group and the real-time average axial force is calculated. Diagonal braces with negative difference results are selected, and the real-time axial pressure of the selected diagonal braces is compared with the corresponding design axial force of the diagonal brace. Braces whose real-time axial pressure is lower than the average real-time axial force within the group and lower than their own design axial force are marked as understressed support members.

7. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The process of delineating the stress concentration region is as follows: Obtain the real-time stress and corresponding mileage coordinates of each measuring point laid out along the length direction on the surface of the waist beam. Calculate the absolute value of the difference in real-time stress between two adjacent measuring points, and divide it by the actual spacing between the two adjacent measuring points to obtain the stress gradient in the adjacent measuring point section. Calculate the average stress gradient of all adjacent measuring point sections, and the average real-time stress value of all measuring points; The adjacent measuring point sections with stress gradients greater than the average stress gradient are marked as high stress change sections, and the measuring points with real-time stress values ​​greater than the real-time average stress value are marked as high stress measuring points. The length range of the wainscoting containing multiple consecutive high-stress variation sections, and where the proportion of high-stress measuring points exceeds the proportional threshold, is defined as the stress concentration area.

8. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The method of adjusting the hinge at the end of the understressed support member to compensate for axial pressure according to the support length includes: Operate the hinge thread at the end of the understressed support member, and extend the hinge by rotating the thread to tighten it against the support block; The real-time axial pressure corresponding to the diagonal brace during the rotation of the hinge head threading process is simultaneously acquired. When the real-time axial pressure rises to the point where the absolute value of the difference between it and the average axial force in the group is less than the preset allowable deviation range, and the real-time axial pressure does not exceed the design axial force of the diagonal brace, the rotation of the hinge head is stopped and the thread limit device is locked.

9. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The adjustable head for adjusting the stress overload amplitude of adjacent diagonal braces based on the stress concentration region includes: Extract the maximum real-time stress value on the surface of the wainscoting within the stress concentration area, and obtain the design allowable stress of the wainscoting material; If the maximum real-time stress value exceeds the design allowable stress, then at least one adjacent diagonal brace shall be selected from the diagonal braces supporting the corresponding waist beam segment in the stress concentration area. The adjacent diagonal braces are selected in order of increasing distance from the stress concentration area. The diagonal braces whose real-time axial pressure is not lower than the lower limit of their own design axial force are selected. The screw threads at the ends of the braces are retracted and the support length is shortened until the maximum real-time stress value of the stress concentration area on the surface of the waist beam falls back to the design stress limit range.

10. The sensor-based monitoring method for deep foundation pit combined steel pipe inclined support according to claim 1, characterized in that: The determination process for satisfying the equilibrium control is as follows: Continuously acquire the real-time axial pressure of all diagonal braces in each monitoring group and the real-time stress gradient along the surface of the waist beam; When the difference between the real-time axial pressure of all understressed support members in each monitoring group and the average axial force in the group is less than the allowable axial force deviation value, and the maximum stress gradient in all detected stress accumulation areas on the surface of the waist beam is less than the gradient safety threshold, the deep foundation pit combined steel pipe inclined support system is determined to have reached a state of stress equilibrium, and the current round of monitoring and adjustment operations ends.

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