Drainage pipe foundation trench layered excavation and slope stability collaborative control method

Abstract

The application discloses a kind of sewer foundation trench layered excavation and slope stability collaborative control method, belong to geotechnical engineering and slope construction technical field.The method includes: the three-dimensional numerical model of foundation trench and slope in excavation area is constructed, and slope stability safety factor pre-calculation is carried out from surface downwards layer by layer, and the layered excavation scheme meeting safety threshold is determined by iteration reducing layer thickness;According to the scheme, excavate layer by layer, obtain real-time monitoring displacement of slope after each layer excavation and compare with allowable displacement value, if displacement is out of limit, then take reinforcement measures and reduce the thickness of next layer, otherwise maintain original scheme;The above steps are executed cyclically until the design foundation trench bottom elevation, and the sewer laying is completed after final test is passed.The application realizes closed-loop cooperation of layered pre-planning before excavation and dynamic control in excavation, and is mainly used for real-time control of slope stability in the process of sewer foundation trench excavation construction.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering and slope construction technology, specifically relating to a method for coordinated control of drainage pipe trench layered excavation and slope stability. Background Technology

[0002] In mountainous and hilly areas, as well as in various infrastructure construction projects, the excavation of drainage pipe trenches often results in the formation of open slopes. As the excavation depth gradually increases, the original stress balance of the slope's soil and rock mass is disrupted, and the unloading effect gradually becomes apparent. If the excavation methods and control measures are inappropriate, it can easily induce excessive slope deformation or even instability and landslides, seriously affecting construction safety and project progress. How to effectively control slope stability during the layered excavation of trenches has long been a technical challenge for such projects.

[0003] Currently, layered excavation of foundation trenches and slope stability control are typically handled as two relatively independent processes. On the one hand, the thickness and sequence of excavation layers are often determined based on experience or simple geological segmentation, lacking a quantitative correlation with the slope's mechanical response. On the other hand, slope stability analysis is usually a one-time overall assessment before the excavation plan is finalized, or only a final verification is performed after excavation. This separate approach leads to several problems. The determination of the layered plan does not fully consider the gradual disturbance to the slope caused by the unloading of each layer of excavation, and there may be significant deviations between the actual mechanical state of the slope during excavation and the assumptions made in the design. When the actual geological conditions revealed by excavation are inconsistent with the survey data, the predetermined layered plan is difficult to adjust in a timely manner, and only passive remedial measures can be taken after problems are exposed during construction. At the same time, although displacement monitoring equipment is deployed on site, the monitoring data is mostly based on simple judgments triggered by warning thresholds, failing to form a closed loop with the dynamic correction of the layered plan, and the monitoring information cannot be effectively transformed into a quantitative basis for excavation control decisions. Once the monitored displacement exceeds the limit, construction can often only be suspended or local reinforcement can be implemented based on engineering experience, lacking systematic and coordinated control measures.

[0004] Furthermore, while existing technologies utilize numerical simulation for slope stability pre-assessment, such assessments primarily serve static analyses during the design phase, making it difficult to rapidly adjust the analysis model based on real-time monitoring data during construction. The stability safety factor determined before excavation cannot accurately reflect the true state of the slope after each layer of excavation, and new risks during excavation are difficult to identify in a timely manner. Without a dynamic coordination mechanism between the layered excavation scheme and the slope's stability state, construction often faces a dilemma: if the layers are too thick, the excavation unloading is drastic, increasing the difficulty of slope deformation control; if the layers are too thin, construction efficiency is significantly reduced, increasing the pressure on the construction period and costs. How to achieve a reasonable dynamic balance between layered excavation efficiency and slope stability control has remained unresolved.

[0005] Some projects have attempted to adjust the layer thickness during construction, but the determination of the adjustment amount lacks quantifiable and reproducible rules, relying on the individual judgment of on-site technicians. This makes the adjustment effects difficult to guarantee and hard to promote. Simultaneously, the slope stability assessment at the final acceptance stage lacks a systematic connection with the control parameters of the preceding construction process, failing to form a comprehensive collaborative management chain from the initial excavation to the formation of the foundation trench and the laying of drainage pipes. In summary, existing technologies lack a holistic solution that can organically coordinate slope stability pre-assessment, dynamic adjustment of excavation layers, and real-time on-site monitoring throughout the entire layered excavation process, and implement it with clear control logic and repeatable operational rules. The existence of these problems constitutes a technological direction urgently needing improvement in this field. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0007] The purpose of this invention is to solve the problem that the layered excavation of the foundation trench and the slope stability control are separated, and there is a lack of a systematic method to dynamically adjust the layering scheme according to the real-time response of the slope after each layer of excavation, which makes it difficult to coordinate and balance excavation efficiency and slope safety.

[0008] One objective of this invention is to provide a method for coordinated control of layered excavation of drainage pipe foundation trenches and slope stability, comprising the following steps: Step 1: Pre-determining the stratification scheme A three-dimensional numerical model of the foundation trench and slope of the excavation area is constructed, and an initial layer thickness is set. Initial excavation layers are determined from the ground surface downwards according to this initial layer thickness. Based on the three-dimensional numerical model, a slope stability safety factor is pre-calculated for the current proposed excavation layer in its unsupported state after removal. If the slope stability safety factor does not meet the preset excavation scheme safety threshold, the layer thickness of the current proposed excavation layer is reduced by a preset reduction step size, and the slope stability safety factor is re-calculated based on the three-dimensional numerical model until the slope stability safety factor meets the preset excavation scheme safety threshold. This process is repeated layer by layer to form a layered excavation scheme. The layered excavation scheme includes the layer thickness and excavation sequence of each excavation layer from the ground surface to the designed foundation trench bottom elevation. Step 2: Single-layer excavation and dynamic control Following the order from the ground surface downwards in the layered excavation scheme, the current layer to be excavated is excavated; after the excavation of this layer is completed, the real-time monitoring displacement of the slope is obtained, and the obtained real-time monitoring displacement is compared with the preset allowable displacement value: If the real-time monitored displacement exceeds the preset allowable displacement value, reinforcement measures are taken for the excavated area, and the thickness of the next layer to be excavated is reduced according to the preset reduction step size, and the layer excavation plan is updated. If the real-time monitored displacement does not exceed the preset allowable displacement value, the current layered excavation scheme shall be maintained. Step 3: Loop Control If the excavation has not reached the designed bottom elevation of the foundation trench, return to step two and, based on the updated or maintained layered excavation plan, treat the next layer as the new current layer to be excavated and continue excavation; if the excavation has reached the designed bottom elevation of the foundation trench, proceed to step four. Step 4: Final Inspection and Pipe Laying The slope stability of the formed trench is tested. If the test is passed, the drainage pipe is laid. If the test is not passed, the current slope of the trench is reinforced and the slope stability is tested again until the test is passed and the drainage pipe is laid.

[0009] Preferably, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, step one involves applying the strength reduction method to the three-dimensional numerical model to perform a pre-calculation of the slope stability safety factor.

[0010] Preferably, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, the real-time monitoring displacement in step two includes the apparent displacement of the slope and the deep displacement of the slope.

[0011] Preferably, in the method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability, the apparent displacement of the slope is compared with a preset allowable apparent displacement value, and the deep displacement of the slope is compared with a preset allowable deep displacement value. If the apparent displacement of the slope exceeds the preset allowable apparent displacement value, or the deep displacement of the slope exceeds the preset allowable deep displacement value, reinforcement measures are taken for the excavated area, and the thickness of the next layer to be excavated is reduced according to a preset reduction step, and the layered excavation scheme is updated.

[0012] Preferably, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, step two, after reducing the layer thickness of the next layer to be excavated and updating the layered excavation scheme, further includes: based on the three-dimensional numerical model, recalculating the slope stability safety factor of the next layer to be excavated after the layer thickness reduction in the unsupported state after removal; if the slope stability safety factor still does not meet the preset excavation scheme safety threshold, then the layer thickness of the layer is further reduced by a preset reduction step size and recalculated until the slope stability safety factor meets the preset excavation scheme safety threshold.

[0013] Preferably, in the method for coordinated control of layered excavation of drainage pipe trench and slope stability, the final verification of slope stability in step four includes: calculating the slope stability safety factor of the formed trench based on the three-dimensional numerical model, comparing the slope stability safety factor with the preset excavation scheme safety threshold, and if the slope stability safety factor meets the preset excavation scheme safety threshold, the final verification is passed.

[0014] Preferably, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, during the multiple iterations of step two, the preset reduction step size is dynamically adjusted based on the acquired real-time monitored displacement.

[0015] Preferably, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, the dynamic adjustment is performed by comparing the acquired real-time monitored displacement with the preset allowable displacement value. If the real-time monitored displacement exceeds the preset allowable displacement value, the preset reduction step size is increased; if the real-time monitored displacement does not exceed the preset allowable displacement value, the preset reduction step size is maintained or decreased.

[0016] Preferably, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, the magnitude of increasing the preset reduction step is determined based on the proportion of the real-time monitored displacement exceeding the preset allowable displacement value.

[0017] Preferably, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, the magnitude of reducing the preset reduction step is determined based on the ratio of the real-time monitored displacement to the preset allowable displacement value.

[0018] The present invention has at least the following beneficial effects: This invention constructs a closed loop of layered pre-calculation based on a three-dimensional numerical model before excavation and dynamic adjustment based on real-time displacement monitoring after excavation. This organically coordinates the determination of the layered scheme, the control of layered excavation, and the monitoring of slope stability. This allows the slope response after each layer of excavation to be fed back into the adjustment of the subsequent layered scheme in a timely manner, thereby rationally determining the layer thickness and excavation sequence, avoiding the disconnect between the excavation scheme and the actual slope condition, and improving construction safety and efficiency.

[0019] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0020] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0021] This invention provides a method for coordinated control of layered excavation of drainage pipe foundation trenches and slope stability, comprising the following steps: Step 1: Pre-determining the stratification scheme A three-dimensional numerical model of the foundation trench and slope of the excavation area is constructed, and an initial layer thickness is set. Initial excavation layers are determined from the ground surface downwards according to this initial layer thickness. Based on the three-dimensional numerical model, a slope stability safety factor is pre-calculated for the current proposed excavation layer in its unsupported state after removal. If the slope stability safety factor does not meet the preset excavation scheme safety threshold, the layer thickness of the current proposed excavation layer is reduced by a preset reduction step size, and the slope stability safety factor is re-calculated based on the three-dimensional numerical model until the slope stability safety factor meets the preset excavation scheme safety threshold. This process is repeated layer by layer to form a layered excavation scheme. The layered excavation scheme includes the layer thickness and excavation sequence of each excavation layer from the ground surface to the designed foundation trench bottom elevation. Step 2: Single-layer excavation and dynamic control Following the order from the ground surface downwards in the layered excavation scheme, the current layer to be excavated is excavated; after the excavation of this layer is completed, the real-time monitoring displacement of the slope is obtained, and the obtained real-time monitoring displacement is compared with the preset allowable displacement value: If the real-time monitored displacement exceeds the preset allowable displacement value, reinforcement measures are taken for the excavated area, and the thickness of the next layer to be excavated is reduced according to the preset reduction step size, and the layer excavation plan is updated. If the real-time monitored displacement does not exceed the preset allowable displacement value, the current layered excavation scheme shall be maintained. Step 3: Loop Control If the excavation has not reached the designed bottom elevation of the foundation trench, return to step two and, based on the updated or maintained layered excavation plan, treat the next layer as the new current layer to be excavated and continue excavation; if the excavation has reached the designed bottom elevation of the foundation trench, proceed to step four. Step 4: Final Inspection and Pipe Laying The slope stability of the formed trench is tested. If the test is passed, the drainage pipe is laid. If the test is not passed, the current slope of the trench is reinforced and the slope stability is tested again until the test is passed and the drainage pipe is laid.

[0022] In existing technologies, the excavation of drainage pipe foundation trenches and slope stability control are usually carried out separately. Before construction, technicians determine the thickness of each excavation layer based on experience or simple geological segmentation, for example, dividing the entire trench depth into several layers of equal thickness. Subsequently, based on the soil and rock parameters obtained during the exploration phase, a one-time stability analysis is performed on the slope state after the overall excavation is completed, resulting in a safety factor. If this safety factor is not lower than a certain value specified in the standard, the layered scheme is considered feasible, and construction is carried out according to this scheme. During construction, displacement monitoring points are set up on the slope surface or inside, and displacement data is read periodically. When the monitored displacement exceeds the preset warning value, on-site measures such as suspending construction, local reinforcement, or slope reduction are taken. The characteristic of this approach is that the layered scheme is determined once before excavation, and the layer thickness is not adjusted according to the actual slope response during excavation. The monitoring data is mainly used to trigger warnings and is not directly used to modify the layer thickness. When the geological conditions revealed by excavation differ from the exploration data, the predetermined layered scheme is difficult to adjust in a timely manner. If the layer thickness is too large, the slope unloading will be significant, increasing the difficulty of deformation control; if the layer thickness is too small, construction efficiency will decrease. In the absence of a mechanism to coordinate the layer thickness and the slope stability, the balance between construction safety and construction efficiency depends on the on-site judgment of technical personnel.

[0023] The method of this invention addresses the above-mentioned problems by combining pre-excavation layered pre-calculation with dynamic control during excavation into a closed-loop process. The embodiments of this invention are described in detail below.

[0024] The first step is to pre-determine the stratification scheme.

[0025] First, the physical and mechanical parameters and hydrogeological conditions of the soil and rock mass in the area to be excavated are obtained. These parameters are obtained through geological surveys, including strength indices such as cohesion, internal friction angle, and unit weight, as well as deformation indices for each soil and rock layer. Then, a three-dimensional numerical model is constructed, incorporating the geometry of the foundation trench and the strata structure of the slope. The three-dimensional numerical model is constructed using a continuum mechanics framework, employing the finite difference method or finite element method as the solution method. The constitutive relations of the soil and rock mass are selected using the Mohr-Coulomb model or the Hawke-Brown model. Commercial software such as FLAC3D, ABAQUS, or MIDAS GTS / NX can be used. The model range is 3 to 5 times the width of the foundation trench in the horizontal direction and 1 to 2 times the depth of the foundation trench below the designed bottom elevation in the depth direction to eliminate the influence of boundary effects on the calculation results.

[0026] Subsequently, an initial layer thickness is set, such as 0.5 m or 1.0 m, and initial excavation layers are proposed according to this thickness from the ground surface downwards. For the first layer to be excavated, it is removed from the three-dimensional numerical model to simulate excavation unloading, and the slope stability safety factor is calculated under conditions without support. The safety factor is calculated using either the strength reduction method or the limit equilibrium method. The strength reduction method involves dividing the strength parameters of the soil and rock mass, cohesion and internal friction angle, by a reduction factor, iterating repeatedly until the model calculation fails to converge; the corresponding reduction factor at this point is the slope stability safety factor. The limit equilibrium method obtains the safety factor by summing the anti-sliding force and sliding force on the slip surface.

[0027] The calculated safety factor is compared with the preset safety threshold of the excavation scheme. This safety threshold is determined according to the technical specifications for building slope engineering and the engineering grade. Specifically: for Grade I slopes (important permanent slopes), the safety threshold is 1.30–1.35; for Grade II slopes (minor permanent slopes), it is 1.25–1.30; and for Grade III slopes (temporary slopes), it is 1.20–1.25. When the excavation depth is ≤10m, the lower limit is used; when it is >10m, the upper limit is used. If groundwater is present or the seismic intensity is ≥VII, the safety threshold is increased by 0.05. When there are no explicit requirements in the specifications, it can be estimated using the following empirical formula: F starget = 1.20 +0.05×n, where n is the slope safety level (1,2,3).

[0028] If the calculated safety factor is not lower than the threshold, it indicates that the slope can still meet the stability requirements under unsupported conditions after excavation of the current layer thickness, and the layer thickness is adopted. If the calculated safety factor is lower than the threshold, it indicates that the slope stability margin under unsupported conditions after excavation of the current layer thickness is insufficient, and the layer thickness of the current layer is reduced by a preset reduction step. The reduction step is a preset fixed value, such as 0.1 m or 0.2 m. After reduction, the reduced layer is removed from the three-dimensional numerical model, and the safety factor pre-calculation is performed again and compared with the threshold. If it still does not meet the requirements, the reduction and pre-calculation continue until the safety factor is not lower than the threshold.

[0029] Once the thickness of the first layer is determined, the bottom surface of the first layer is used as the new ground surface. The above pre-calculation and iterative reduction process is repeated for the second layer to determine its thickness. In this way, the thickness of each layer is determined layer by layer from top to bottom until the design trench bottom elevation is reached. The final layered excavation plan includes the thickness of each layer and the excavation sequence from the ground surface to the bottom elevation.

[0030] Compared with existing technologies, this method introduces a layer-by-layer pre-calculation and iterative reduction mechanism at the stage of determining the layering scheme. Existing technologies usually layer the material with uniform thickness, and each layer has the same thickness, without separately checking the slope condition after excavation of each layer. This invention, through layer-by-layer pre-calculation, ensures that the thickness of each layer is based on the premise that the safety factor of the unsupported state after excavation of the current layer meets the standard. The thickness of each layer can be flexibly changed according to the stratum conditions and excavation depth. When the stratum conditions are good and the excavation depth is shallow, the layer thickness can be larger, and when the stratum conditions are poor and the excavation depth increases, the layer thickness will automatically decrease.

[0031] The second step is single-layer excavation and dynamic control.

[0032] Following the layered excavation plan, excavation work is carried out on the current layer to be excavated in descending order from the ground surface. After the excavation of this layer is completed, real-time monitoring displacement of the slope is obtained through on-site monitoring equipment. The monitoring equipment may include total station measuring points deployed at the top and surface of the slope, as well as inclinometer tubes buried inside the slope body, to obtain apparent displacement and deep displacement, respectively.

[0033] The acquired real-time monitored displacement is compared with the preset allowable displacement value. The allowable displacement value is determined based on the slope height H, soil type, and project importance. The apparent allowable displacement value (horizontal displacement at the top of the slope) is determined according to the following principles: for cohesive soil, take H×0.1%~H×0.3%; for sandy soil, take H×0.2%~H×0.4%; H is the current excavation depth (m). The deep allowable displacement value (maximum horizontal displacement of the inclinometer tube) is taken as 0.5~0.8 times the apparent allowable displacement value, and should not exceed 50mm. When there is no local experience, the displacement control values ​​in the Technical Standard for Monitoring of Building Foundation Pit Engineering can be referred to. In this embodiment, the slope height H=10m, the soil is cohesive, the apparent allowable displacement value is 30mm, and the deep allowable displacement value is 20mm.

[0034] If the real-time monitoring displacement does not exceed the preset allowable displacement value, it indicates that the slope deformation is controllable under the current excavation state. Therefore, the current layered excavation scheme will be maintained, and the next layer of excavation will continue.

[0035] Meanwhile, to ensure greater accuracy in subsequent pre-calculations, the key geotechnical parameters (cohesion c and internal friction angle φ) in the three-dimensional numerical model are calibrated using the measured displacement difference before and after excavation of this layer, employing a displacement back-analysis method. Specific inversion methods can utilize the simplex method or particle swarm optimization, with the objective function being the minimization of the error between the measured and calculated displacements. The values ​​of c and φ are iteratively adjusted until the error is less than 5%. The calibrated model is then used for pre-calculations in subsequent steps. If the real-time monitored displacement exceeds the preset allowable displacement value, it indicates that the slope deformation response after excavation is too large, suggesting a trend of stability deterioration. In this case, two adjustment measures are initiated. The first measure is to reinforce the excavated area. Reinforcement methods can include one or more of anchor bolts, anchor cables, and shotcrete. When using anchor bolts or anchor cables, the design value of the anchoring force is calculated based on the remaining sliding force of the slope, and the length of the anchoring section should penetrate the potential slip surface by at least 2 meters. After reinforcement, the reinforced structure is incorporated into the three-dimensional numerical model in a way that effectively increases the shear strength parameters of the slip surface soil. The specific increase is determined based on the anchoring density and anchoring force, or the anchor rods / cables are directly added to the model as structural units for secondary calculations. The second step is to reduce the thickness of the next layer to be excavated according to a preset reduction step size and update the layer excavation plan.

[0036] In existing technologies, the main countermeasures after monitoring displacement exceeds the limit are to suspend construction and perform local reinforcement, without involving a systematic adjustment of the thickness of subsequent layers. This invention directly links the monitoring of displacement exceeding the limit with the reduction of the thickness of the next layer. When the slope deformation is too large, the unloading amount of the next layer excavation is reduced to control the subsequent deformation development, forming a real-time control closed loop based on monitoring feedback.

[0037] The third step is loop control.

[0038] After completing the dynamic control of the current layer, determine whether the excavation has reached the design trench bottom elevation. If the bottom elevation has not been reached, based on the updated or maintained layered excavation plan, the next layer is taken as the new current layer to be excavated, and the process returns to step two to continue excavation, monitoring, comparison, and adjustment. If the bottom elevation has been reached, the loop stops, and the final acceptance step begins.

[0039] Through this cyclical mechanism, the real-time displacement of the slope after each excavation layer is incorporated into the decision-making process for the next layer. If the displacement exceeds the limit after a certain layer is excavated, the layering plan is updated, and the thickness of subsequent layers is reduced accordingly; if the displacement does not exceed the limit, the subsequent layers proceed according to the original plan. This cyclical control logic ensures that the layering plan remains coordinated with the actual condition of the slope throughout the entire excavation process.

[0040] The fourth step is final inspection and pipe laying.

[0041] After excavation to the designed bottom elevation of the foundation trench, the trench is formed. A final slope stability test is then conducted on the formed trench. If the final test fails, reinforcement measures are taken for the current trench slope, and the final test is repeated until it passes. After the final test passes, the drainage pipes are laid.

[0042] Compared with the prior art, the final acceptance process of this invention is based on the fact that each layer of excavation has been monitored and dynamically adjusted in the early stage. The slope has undergone the whole process of collaborative management from the first layer of excavation to the final shaping. The slope condition at the time of final acceptance has been guaranteed by multiple rounds of control measures.

[0043] Based on the specific geological conditions and construction requirements of the project, parameters such as initial layer thickness, reduction step size, safety threshold, and allowable displacement can be selected within a reasonable range. The modeling range and boundary conditions of the three-dimensional numerical model can be determined according to the actual dimensions of the foundation trench. Monitoring methods and reinforcement approaches can be flexibly selected based on site conditions.

[0044] In a preferred embodiment, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, step one involves performing a strength reduction method on the three-dimensional numerical model to pre-calculate the slope stability safety factor.

[0045] When calculating the slope stability safety factor based on a three-dimensional numerical model, there are several possible solution methods. In some embodiments, the limit equilibrium method can be used. The limit equilibrium method pre-assumes the shape and location of the sliding surface, divides the soil and rock mass above the sliding surface into several blocks, calculates the sliding force and resisting force of each block separately, and then sums the sliding force and resisting force of all blocks. The safety factor is the ratio of the total resisting force to the total sliding force. In the three-dimensional case, the limit equilibrium method requires extending the two-dimensional strip division into three-dimensional columnar divisions and assuming the spatial shape of the sliding surface, making the calculation process relatively cumbersome. The safety factor given by the limit equilibrium method is a scalar value, which cannot reflect the entire process of the slope gradually developing from a stable state to an unstable state, nor can it directly provide information on slope deformation. When layered excavation causes the model geometry to change layer by layer, the most dangerous sliding surface needs to be re-assumed and searched for for each layer of excavation, resulting in a large computational workload.

[0046] In step one of this invention, a strength reduction method is used to pre-calculate the safety factor. The specific implementation method is as follows.

[0047] First, in the constructed three-dimensional numerical model, corresponding strength parameters, including cohesion and internal friction angle, are assigned to each layer of the soil and rock mass. The solution framework for the three-dimensional numerical model is the finite difference method or the finite element method, and the constitutive model of the soil and rock mass adopts the Mohr-Coulomb model.

[0048] Next, set an initial reduction factor, for example, 1.0. Using this reduction factor as a divisor, simultaneously reduce the cohesion and internal friction angle of all soil and rock elements in the model. That is, the reduced cohesion equals the original cohesion divided by the reduction factor, and the reduced internal friction angle equals the tangent of the original internal friction angle divided by the reduction factor and then taking the arctangent. Substitute the reduced strength parameters into the model for calculation.

[0049] If the model converges under the current reduction factor, meaning it reaches a state of mechanical equilibrium, it indicates that the slope remains stable under this reduction level. In this case, the reduction factor is increased by an increment, for example, by 0.1. The strength parameters of the entire model are then reduced again and recalculated. This process of gradually increasing the reduction factor and repeating the calculations is repeated.

[0050] When the reduction factor increases to a certain value, the model calculation no longer converges, meaning that the displacement or unbalanced force cannot stabilize, indicating that the slope has reached a critical instability state. At this point, the reduction factor corresponding to this critical state is the slope stability safety factor.

[0051] Taking a foundation trench excavation project as an example, the stratum is silty clay with a cohesion of 18 kPa and an internal friction angle of 22 degrees. After constructing a three-dimensional numerical model, the strength reduction method is applied to the model after removing the first proposed excavation layer. The model converges when the initial reduction coefficient is 1.0, converges when it increases to 1.1, converges when it increases to 1.2, and fails to converge when it increases to 1.3. Therefore, the safety factor is set to 1.3. This value is compared with the preset safety threshold of 1.25 for the excavation scheme. If 1.3 is not lower than 1.25, then the layer thickness passes the verification.

[0052] If the safety factor is 1.3, which does not meet the higher threshold requirement of 1.35, the layer thickness is reduced by a preset reduction step size. After reduction, the strength reduction method is performed again on the new geometric model to obtain a new safety factor, until the threshold requirement is met.

[0053] Compared to the limit equilibrium method, the strength reduction method combined with a three-dimensional numerical model offers the following advantages: First, it eliminates the need to pre-assume the shape and location of the slip surface. The critical slip surface naturally forms as the plastic zone of the model is penetrated during the reduction process, making it more adaptable to situations with complex strata and uncertain slip surface morphology. Second, while solving for the safety factor, the strength reduction method obtains the stress and displacement field changes throughout the entire process from stability to instability of the slope, providing richer information for judging the slope deformation trend. Third, the strength reduction method can be directly integrated with the finite difference method or finite element method solution framework. Geometric changes in the model caused by layered excavation only require removing the corresponding elements from the model, eliminating the need to re-search for the slip surface, making the pre-calculation process more efficient.

[0054] In a preferred embodiment, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, the real-time monitoring of displacement in step two includes the apparent displacement of the slope and the deep displacement of the slope.

[0055] In some embodiments, a single-type displacement monitoring method can be used. This method involves setting up displacement measuring points only at the top or surface of the slope, and periodically measuring the horizontal displacement and vertical settlement of points on the slope surface using a total station or level, thus determining the slope's stability. When the monitoring data exceeds a preset warning value, appropriate measures are taken on-site. The limitation of this approach is that surface displacement mainly reflects the deformation of the shallow slope layer and is not sensitive to potential sliding deformation occurring deeper within the slope. Under certain geological conditions, obvious shear deformation zones may have already appeared in the deeper parts of the slope, while the surface displacement has not yet reached the warning value. When the surface displacement changes significantly, the deep deformation may have already progressed to a stage close to instability. Relying solely on single-type displacement data may miss early signs of slope instability.

[0056] In step two, this invention employs a monitoring method that combines apparent displacement and deep displacement. The specific implementation method is as follows.

[0057] Regarding the layout of slope monitoring sections, a monitoring section is set up at regular intervals along the longitudinal direction of the foundation trench. Two types of monitoring points are set up on each monitoring section. The first type is the apparent displacement monitoring point, located at the edge of the slope crest and the ramp positions of graded slopes. A total station reflecting prism or GNSS measuring point is used to acquire the horizontal displacement and vertical settlement of the slope surface. The second type is the deep displacement monitoring point, where inclinometer tubes are drilled and buried inside the slope. The bottom of the inclinometer tube extends at least 2 meters into the stable strata below the estimated sliding surface. The tube is installed vertically or nearly vertically along the borehole. An inclinometer is used to measure the horizontal displacement at each depth along the tube from the bottom to the top, acquiring the horizontal displacement distribution along the depth direction inside the slope.

[0058] Regarding the data acquisition frequency, a comprehensive monitoring data acquisition is carried out immediately after each layer of excavation is completed. At the same time, apparent displacement data and deep displacement data are read, and the current cumulative displacement value of each measuring point and the displacement increment caused by single-layer excavation are recorded.

[0059] In terms of data processing and comparison, the cumulative displacement value of each apparent displacement measuring point is compared with the preset allowable apparent displacement value one by one, and the maximum displacement value of each deep displacement measuring point is compared with the preset allowable deep displacement value one by one. When the displacement value of all measuring points does not exceed their respective allowable displacement values, the current slope deformation state is determined to be normal, and the original layering scheme is maintained to continue excavating the next layer. When any type of monitoring data exceeds the limit, subsequent reinforcement and layer thickness adjustment measures are initiated.

[0060] Compared to monitoring only a single type of displacement, a combined monitoring method of apparent displacement and deep displacement can reflect the deformation state of the slope from different dimensions. Apparent displacement directly reflects the magnitude of surface deformation, facilitating a quick assessment of whether the overall slope is under control. Deep displacement can reveal the presence of concentrated shear deformation zones within the slope, helping to detect the formation and development of potential sliding surfaces when surface displacement is not yet obvious. These two types of information complement each other, reducing the risk of missed assessments due to a single monitoring dimension and improving the comprehensiveness and timeliness of slope stability assessment.

[0061] In a preferred embodiment, the method for coordinated control of layered excavation of drainage pipe trench and slope stability compares the apparent displacement of the slope with a preset allowable apparent displacement value and compares the deep displacement of the slope with a preset allowable deep displacement value. If the apparent displacement of the slope exceeds the preset allowable apparent displacement value or the deep displacement of the slope exceeds the preset allowable deep displacement value, reinforcement measures are taken for the excavated area, and the thickness of the next layer to be excavated is reduced according to a preset reduction step, thus updating the layered excavation scheme.

[0062] In some embodiments, a comparison method using a unified allowable displacement value can be used. This method, after obtaining the apparent and deep displacements of the slope, compares the two types of displacement data with the same preset allowable displacement value, or compares the weighted average of the two types of displacement data with a single allowable value. When the combined value or all types of displacement values ​​exceed the unified allowable value, the slope deformation is deemed to have exceeded the limit. The drawback of this approach is that apparent and deep displacements reflect different slope deformation mechanisms. Apparent displacements such as horizontal displacement at the top of the slope and slope settlement are mainly controlled by shallow unloading and loosening of the surface soil and rock, resulting in relatively large deformations, but they may not directly threaten the overall stability of the slope in the short term. Deep displacements, on the other hand, reflect the degree of development of shear zones within the slope. Even if the displacement is small, once a continuous shear slip surface forms, the slope faces the risk of overall instability. When comparing using a uniform allowable displacement value, if the value is set too leniently according to the standard for apparent displacement, deep displacement may not be identified before reaching a dangerous level; if the value is set too strictly according to the standard for deep displacement, apparent displacement is prone to frequent exceedances, leading to unnecessary construction interruptions and reinforcement investments. Sharing the same judgment standard for both types of displacement makes it difficult to meet their different safety control needs.

[0063] In step two of this invention, independent allowable displacement values ​​are set for both apparent displacement and deep displacement, and these values ​​are compared and judged separately. Specific implementation details are as follows.

[0064] First, during the construction preparation phase, based on the slope's engineering grade, geological conditions, and design deformation control requirements, apparent allowable displacement values ​​and deep allowable displacement values ​​are set separately. The apparent allowable displacement value is set for surface deformations such as horizontal displacement at the slope crest and slope settlement, and can be determined by referring to experience values ​​from similar projects or a certain proportion of the slope height. For example, the allowable horizontal displacement at the slope crest is taken as 3‰ to 5‰ of the slope height. The deep allowable displacement value is set for the maximum horizontal displacement measured by inclinometers, and can be selected based on the critical displacement value of slope stability analysis or relevant specifications. For example, the allowable horizontal displacement value is taken as 1‰ to 2‰ of the slope height. Because deep shear deformation has a more direct impact on the overall slope stability, the deep allowable displacement value is usually set more strictly than the apparent allowable displacement value.

[0065] After each layer of excavation is completed, apparent displacement data and deep displacement data are collected. The cumulative horizontal displacement and vertical settlement measured at each observation point are compared with the preset allowable apparent displacement value. At the same time, the maximum deep horizontal displacement measured at each inclinometer borehole is compared with the preset allowable deep displacement value. The two types of comparisons are performed independently and do not interfere with each other.

[0066] The comparison results are processed according to a rule that triggers the process if any limit is exceeded. When the displacement values ​​of all surface observation points do not exceed the apparent allowable displacement value, and the maximum deep displacement of all inclinometer boreholes does not exceed the deep allowable displacement value, the current slope deformation state is determined to meet the control requirements, and the current layered excavation plan is maintained to continue excavating the next layer. When the displacement value of any surface observation point exceeds the apparent allowable displacement value, or the maximum deep displacement of any inclinometer borehole exceeds the deep allowable displacement value, the slope deformation is determined to exceed the limit. Reinforcement measures are taken for the excavated area, and the layer thickness of the next layer to be excavated is reduced according to the preset reduction step size, and the layered excavation plan is updated.

[0067] Compared to using a uniform allowable displacement value, independently setting and comparing apparent and deep allowable displacement values ​​allows for adaptation to the different deformation characteristics and control standards of the two types of displacements. The apparent allowable displacement value can be set according to the allowable degree of surface deformation, avoiding unnecessary frequent adjustments due to overly stringent standards; the deep allowable displacement value can be set according to overall stability control requirements, ensuring that deep shear deformation is identified in time before it develops to a dangerous level. The two comparison rules operate in parallel and independently, triggering a response if either exceeds its limit, reducing missed or false judgments due to unreasonable judgment standards, and improving the accuracy and specificity of the dynamic control process.

[0068] In a preferred embodiment, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, step two, after reducing the layer thickness of the next layer to be excavated and updating the layered excavation scheme, further includes: based on the three-dimensional numerical model, recalculating the slope stability safety factor of the next layer to be excavated after the layer thickness reduction in the unsupported state after removal; if the slope stability safety factor still does not meet the preset excavation scheme safety threshold, then the layer thickness of the layer is further reduced by a preset reduction step size and recalculated until the slope stability safety factor meets the preset excavation scheme safety threshold.

[0069] In some embodiments, a direct reduction without verification method can be used. This method, after detecting an excessive displacement, directly reduces the thickness of the next layer to be excavated by a fixed step size. After reduction, the next layer is excavated at the new thickness without verifying the safety factor of the reduced layer. The drawback of this approach is that the reduction step size is a pre-set fixed value, while the mechanical response of the slope varies under different excavation depths and geological conditions. The reduction amount by the fixed step size may be insufficient to ensure the reduced layer meets stability requirements, or it may exceed the actual required reduction range. If the reduction is insufficient, the slope safety factor will still be below the safety threshold when the next layer is excavated, and deformation may continue to develop or even worsen, and the safety hazards revealed by the previous layer's exceedance will not be truly eliminated. If the reduction is excessive, it will unnecessarily increase the number of construction layers, reducing construction efficiency. Due to the lack of a safety verification step after reduction, whether the adjusted layering scheme meets stability requirements remains unknown, and there is a gap in the closed loop of collaborative control.

[0070] In step two of this invention, after reducing the thickness of the next layer to be excavated and updating the layer excavation plan, a verification step of recalculating the safety factor is added. The specific implementation method is as follows.

[0071] When the real-time displacement monitored in step two exceeds the preset allowable displacement value, reinforcement measures have been taken for the excavated area, and the thickness of the next layer to be excavated has been reduced according to the preset reduction step size, and the layer excavation plan has been updated, the actual excavation of the next layer does not immediately begin. First, in the three-dimensional numerical model, the next layer to be excavated with the reduced thickness is removed, simulating the unloading state of the layer under the reduced thickness. During removal, the actual geometry of the excavated area above and the impact of the applied reinforcement measures on the model boundary conditions have been considered. Then, based on the model, the slope stability safety factor of the layer in the unsupported state after removal is recalculated. The pre-calculation method is consistent with the strength reduction method or limit equilibrium method used in step one.

[0072] If the safety factor obtained from the recalculation meets the preset safety threshold of the excavation scheme, it means that the reduced layer thickness can guarantee the stability margin of the slope in the unsupported state after the excavation of this layer, and the verification is passed. At this time, the reduced layer can be used as the new current layer to be excavated, and the excavation can continue.

[0073] If the safety factor obtained from the recalculation still does not meet the preset safety threshold of the excavation scheme, it indicates that the slope stability margin is still insufficient when excavating with the current reduced layer thickness. At this point, the layer thickness of this layer is further reduced according to the preset reduction step size, and the further reduced layer is recalculated in the three-dimensional numerical model. This process is repeated iteratively until the safety factor meets the preset safety threshold of the excavation scheme.

[0074] Taking a foundation trench excavation as an example, the preset reduction step size is 0.2 m. After the current layer is excavated, the displacement exceeds the limit. The original thickness of the next layer is 1.5 m, which is reduced to 1.3 m after the reduction step size. The model is re-calculated for the 1.3 m layer thickness, and the safety factor is 1.18, which is lower than the safety threshold of 1.25, thus not meeting the requirements. The layer is then reduced again to 1.1 m with a step size of 0.2 m, and the re-calculation shows a safety factor of 1.28, meeting the requirements. At this point, the verification is successful, and the final thickness of the next layer to be excavated is determined to be 1.1 m. If the requirements are met with a single reduction, the reduced thickness is directly adopted.

[0075] Compared to methods that directly reduce thickness without verification, this invention introduces the same pre-calculation verification mechanism as in step one during the dynamic adjustment phase, ensuring that the reduced layer thickness undergoes quantitative safety verification. Each layer thickness adjustment ensures that the stability of the adjusted scheme is not lower than the preset standard, eliminating the risk of insufficient or excessive adjustment due to blindly fixing the reduction amount. This verification step fills the logical gap in the original dynamic control process where adjustments lacked subsequent verification, forming a complete closed loop between monitoring, adjustment, and verification, thus improving the reliability and technical integrity of the collaborative control method.

[0076] In a preferred embodiment, in the method for coordinated control of layered excavation of drainage pipe trench and slope stability, step four of the final verification of slope stability includes: calculating the slope stability safety factor of the formed trench based on the three-dimensional numerical model, comparing the slope stability safety factor with the preset excavation scheme safety threshold, and if the slope stability safety factor meets the preset excavation scheme safety threshold, the final verification is passed.

[0077] In some embodiments, an experience-based final acceptance method can be used. This method involves on-site technicians visually inspecting the slopes on both sides of the formed trench after excavation to the design bottom elevation. They observe for abnormalities such as cracks, spalling, and water seepage, and, based on their experience and the changing trends of monitoring data during construction, determine the slope's stability. If deemed stable, the final acceptance is passed, and the drainage pipe laying process begins. If deemed unstable, the scope and method of reinforcement are determined based on site conditions. After reinforcement, another visual inspection is conducted until the final acceptance is passed. The drawback of this approach is the lack of quantitative criteria for final acceptance. Different technicians may have different judgments about the same slope's condition, and visual inspection may not be able to detect potential hazards within the slope. While monitoring data during construction can be used as a reference, it only reflects the magnitude of deformation and does not directly characterize the slope's safety margin. Furthermore, the final acceptance process lacks a unified evaluation standard with the earlier layered design and construction control. The three-tiered scheme pre-determination stage uses a safety factor as the control indicator, the construction control stage uses displacement as the control indicator, and the final acceptance stage relies on subjective judgment. The standards of the three stages are independent of each other, making it impossible to form a unified control baseline. This leads to disputes or safety oversights that may still occur during the final acceptance stage due to inconsistent judgment criteria, even if each stage is carried out according to the standards in the early stages.

[0078] In step four of this invention, the final verification operation is defined as the calculation of the safety factor and the comparison of the threshold based on the three-dimensional numerical model. The specific implementation method is as follows.

[0079] After the foundation trench is excavated to the design bottom elevation, the final geometric shape of the slope has been formed. At this point, based on the three-dimensional numerical model constructed in step one, all the soil and rock elements of the foundation trench section in the model are removed, while the final geometric contours of the slopes on both sides are retained. At the same time, the model considers the contribution of the reinforcement measures applied during construction to the mechanical state of the slope, and the reinforcement structure is reflected as part of the model.

[0080] Then, the slope stability safety factor of the formed foundation trench is calculated based on the three-dimensional numerical model. The calculation method of the safety factor is consistent with the method used in the pre-calculation in step one, employing either the strength reduction method or the limit equilibrium method. When using the strength reduction method, the strength parameters of the soil and rock mass in the model slope area, cohesion and internal friction angle, are gradually reduced until the model calculation fails to converge, and the critical reduction coefficient is taken as the safety factor. When using the limit equilibrium method, the most dangerous sliding surface is searched for on the final geometric profile of the slope, and the anti-sliding force and sliding force are calculated in segments to obtain the safety factor.

[0081] After calculation, the safety factor is compared with the preset excavation scheme safety threshold. This excavation scheme safety threshold is the same as the safety threshold used to determine the layered scheme in step one; both are the same values ​​set before construction based on the project level and specifications. If the calculated safety factor is not lower than this safety threshold, it indicates that the slope of the formed trench theoretically meets the design safety margin requirements, and the final acceptance is passed, proceeding to the drainage pipe laying process. If the calculated safety factor is lower than this safety threshold, it indicates that the slope safety margin of the formed trench is insufficient, and the final acceptance fails, requiring reinforcement measures for the current trench slope. After reinforcement, the reinforcement structure information in the three-dimensional numerical model is updated, the safety factor is recalculated and compared with the safety threshold, and this process is repeated until the safety factor meets the safety threshold. After the final acceptance is passed, the drainage pipe laying is completed.

[0082] Compared to existing methods that rely on experience to determine final acceptance criteria, this invention unifies the final acceptance standards with the pre-determined standards of the stratified scheme into a single quantitative indicator. The final acceptance no longer depends on the personal experience and subjective judgment of technical personnel, but rather on comparing the safety factor calculated using a three-dimensional numerical model with the safety threshold. The evaluation process is quantifiable, and the results are reproducible. The safety threshold for the final acceptance is consistent with the safety threshold of the previous stratified scheme, ensuring that the entire process, from pre-excavation stratified planning and dynamic control during excavation to post-excavation final acceptance, is executed under the same safety control benchmark. This avoids safety loopholes or evaluation disputes that may result from inconsistent standards at different stages, improving the consistency and systematic nature of slope stability management.

[0083] In a preferred embodiment, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, during the multiple iterations of step two, the preset reduction step size is dynamically adjusted based on the acquired real-time monitored displacement.

[0084] In some embodiments, a fixed reduction step size method can be used. This method presets a fixed reduction step size, such as 0.2 m or 0.3 m, during the construction preparation phase, and maintains this size throughout the entire trench excavation process. Whenever a layer is excavated and displacement exceeds the limit, the thickness of the next layer to be excavated is reduced by this fixed step size. While this approach is simple to operate, it does not consider the differences in slope deformation response at different excavation stages. When the excavation depth is shallow, the overall slope stability margin is large, and displacement exceeding the limit may be caused by localized loosening of the surface layer, resulting in a slower deformation development rate. Reducing the layer thickness by a fixed step size can still meet control requirements. As the excavation depth increases, the height of the free face of the slope increases, and the unloading effect intensifies. Once displacement exceeds the limit, deformation often develops rapidly, and the original fixed step size reduction may not be sufficient to effectively curb the deformation trend. On the other hand, in cycles where displacement does not exceed the limit, the fixed step size remains unchanged. If the slope deformation remains at a low level, the step size will not be adjusted accordingly, resulting in subsequent adjustments always being made with the same force, lacking a mechanism to adjust the force based on changes in deformation response. The fixed step length method remains unchanged throughout the construction period and cannot adapt to the differentiated response characteristics of slopes under different depths and geological conditions.

[0085] In the multiple iterations of step two, the preset reduction step size is dynamically adjusted based on the acquired real-time monitored displacement. The specific implementation method is as follows.

[0086] In each iteration of step two, after the current layer to be excavated is completed, the real-time monitoring displacement of the slope is acquired. This real-time monitoring displacement serves as the input for adjusting the reduction step size. The displacement data acquired in this iteration is compared with the displacement data from previous iterations to analyze the trend and magnitude of displacement changes.

[0087] If the monitored displacement remains at a low level, the deformation is much smaller than the preset allowable displacement value, and the change in displacement increment tends to converge, it indicates that the slope deformation response corresponding to the current layering scheme is relatively mild, and the risk of subsequent slope deformation is low. At this time, the reduction step size can be appropriately reduced so that the single reduction amount in case of exceeding the limit is smaller, thereby reducing unnecessary layer thickness reduction and improving construction efficiency while ensuring safety.

[0088] If the monitored displacement shows a gradual increasing trend in recent cycles, even though it has not yet reached the allowable displacement value, the increase in displacement increment indicates that the slope deformation is accelerating, and the risk of subsequent exceedances is rising. In this case, the reduction step size can be appropriately increased so that the single reduction amount is larger once an exceedance is triggered, thus providing a stronger restraint on the development of deformation.

[0089] If the monitored displacement exceeds the allowable displacement value, reinforcement and layer thickness reduction are triggered. The reduction step size is then adjusted based on the magnitude and rate of displacement exceeding the limit. When the magnitude or rate of exceeding the limit is large, the reduction step size is increased to strengthen the reduction in subsequent cycles; when the magnitude and rate of exceeding the limit are small, the current reduction step size is maintained.

[0090] The specific operation of step size adjustment is to update the stored reduction step size value after each loop obtains displacement data. The updated step size value takes effect in the current loop and subsequent loops until it is adjusted again based on the new displacement data in the next loop.

[0091] Compared to existing methods using a fixed reduction step size, this invention establishes a dynamic correlation between the reduction step size and real-time monitored displacement, transforming the step size parameter from a fixed constant into an adjustable variable that changes with the slope deformation response. When the slope deformation response is mild, the step size automatically decreases to reduce unnecessary layer refinement; when the slope deformation response tends to be severe, the step size automatically increases to increase the control intensity. This adaptive adjustment mechanism matches the intensity of the layer thickness reduction operation with the actual risk level of the slope, avoiding the problem of applying the same intensity across different excavation depths and deformation states with a fixed step size, and improving the adaptability of the collaborative control method to complex working conditions.

[0092] In a preferred embodiment, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, the dynamic adjustment is as follows: the real-time monitored displacement is compared with the preset allowable displacement value; if the real-time monitored displacement exceeds the preset allowable displacement value, the preset reduction step size is increased; if the real-time monitored displacement does not exceed the preset allowable displacement value, the preset reduction step size is maintained or decreased.

[0093] In some embodiments, an experience-based approach to adjusting the direction can be used. When proposing dynamic adjustments to the step size, the determination of the adjustment direction relies on the experience of on-site technicians. Technicians decide, based on observed slope deformation and changes in monitoring data, whether to increase, decrease, or maintain the step size in the current cycle. The drawback of this approach is the lack of clear, reproducible rules for decision-making regarding the adjustment direction. Different technicians may have different judgments about the same slope condition, and the same technician may make inconsistent judgments at different times. When displacement exceeds limits, some technicians tend to significantly increase the step size to quickly strengthen control, while others tend to make small adjustments to avoid overreaction. When displacement does not exceed limits, some technicians choose to decrease the step size to improve construction efficiency, while others choose to maintain the current step size to remain conservative. This uncertainty in the adjustment direction leads to varying effects of dynamic adjustments, making it impossible to establish standardized operating procedures and difficult to promote and reuse across different projects.

[0094] This invention provides clear judgment rules for dynamic adjustment, directly linking the adjustment direction to the comparison results of real-time monitored displacement and allowable displacement values. Specific implementation methods are as follows.

[0095] In each iteration of step two, after the current layer to be excavated is completed, the real-time monitoring displacement of the slope is acquired. This real-time monitoring displacement is compared with a preset allowable displacement value, and the comparison result directly determines the direction of adjustment for reducing the step size.

[0096] When the real-time monitored displacement exceeds the preset allowable displacement value, it indicates that the current excavation has caused excessive slope deformation, the slope deformation response is too large, and the unloading amount under the existing layered scheme exceeds the slope's bearing capacity. At this time, the preset reduction step size is increased. The purpose of increasing the step size is to ensure that if the limit is exceeded again in subsequent cycles, the amount of single layer thickness reduction is larger, thereby reducing the layer thickness at a faster rate, reducing the excavation unloading amount by a greater margin, and strengthening the control over deformation development.

[0097] When the real-time monitored displacement does not exceed the preset allowable displacement value, it indicates that the slope deformation under the current layering scheme is within a controllable range, and the slope's response to excavation unloading is within expectations. At this time, the operation of maintaining or reducing the preset reduction step size is executed. The specific choice of maintaining or reducing depends on how close the displacement is to the allowable value. If the displacement is close to the allowable value, for example, reaching more than 80% of the allowable value, the current step size is maintained to preserve the existing adjustment intensity for future needs. If the displacement is far below the allowable value, for example, less than 50% of the allowable value, the reduction step size is reduced to reduce the amount of reduction in a single instance should the displacement exceed the limit in the future. This reduces unnecessary layer thickness reduction under conditions of mild deformation response, while also considering construction efficiency.

[0098] Taking a foundation trench excavation as an example, the allowable displacement value is set at 30 mm. After excavating a certain layer, the measured displacement is 35 mm, exceeding the allowable value. Therefore, the reduction step size is increased, for example, from 0.2 m to 0.3 m. After excavating the next layer, the measured displacement is 18 mm, which does not exceed the allowable value and is less than 60% of the allowable value. Therefore, the reduction step size is decreased, for example, from 0.3 m back to 0.2 m. After excavating the next layer, the measured displacement is 26 mm, which does not exceed the allowable value but is close to it. Therefore, the step size remains unchanged at 0.2 m.

[0099] Compared to existing methods that rely on experience to determine the adjustment direction, this invention uses the comparison between real-time monitored displacement and allowable displacement values ​​as the sole criterion for adjustment direction, establishing a clear mapping relationship of increasing the displacement if it exceeds the limit, and maintaining or decreasing it if it does not. This rule is simple and clear, does not depend on the personal experience of technical personnel, and can be standardized and implemented in different projects. The adjustment direction for each cycle can be uniquely determined based on measured data, and the operation results are reproducible, improving the standardization and operability of the dynamic adjustment process.

[0100] In a preferred embodiment, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, the increase in the preset reduction step size is determined based on the proportion of the real-time monitored displacement exceeding the preset allowable displacement value.

[0101] In some embodiments, a fixed-amplitude increment method can be used. This method, when monitoring displacement exceeding limits and requiring increasing or decreasing the step size, increments by a pre-set fixed value, such as 0.1 m each time, regardless of the severity of the exceedance. The drawback of this approach is that the degree of displacement exceeding limits can vary significantly due to factors such as excavation depth, geological conditions, and construction disturbance. A slight exceedance may only exceed the allowable value by a few millimeters, with deformation development still on the edge of control; a severe exceedance may exceed the allowable value by tens of millimeters or even more, with deformation already showing a rapid development trend. The risk level faced by the slope in these two situations is drastically different, and the required control intensity should also differ. The fixed-amplitude increment method treats exceedances of different severity equally. For slight exceedances, an excessively large increment may lead to over-refinement of subsequent layers, reducing construction efficiency; for severe exceedances, an insufficient increment may result in inadequate control, making it difficult to effectively curb deformation development. The lack of a correlation between the adjustment increment and the degree of exceedance weakens the targetedness and effectiveness of dynamic adjustments.

[0102] In this invention, the increase in the reduction step size is determined based on the proportion of displacement exceeding the allowable displacement value as monitored in real time. The specific implementation method is as follows.

[0103] In one iteration of step two, if the real-time monitored displacement obtained after the current layer excavation exceeds the preset allowable displacement value, the reduction step size needs to be increased. At this point, the excess ratio is calculated. The excess ratio is the ratio of the portion of the real-time monitored displacement exceeding the allowable displacement value to the allowable displacement value itself. For example, if the allowable displacement value is 30 mm, the measured displacement is 45 mm, and the excess is 15 mm, the excess ratio is 15 divided by 30, resulting in 0.5. If the measured displacement is 60 mm, and the excess is 30 mm, the excess ratio is 30 divided by 30, resulting in 1.0.

[0104] Based on the calculated over-limit ratio, determine the specific increase in step size. A larger over-limit ratio indicates a more severe degree of displacement exceeding the limit, and a greater deviation of the slope deformation from the allowable state, requiring stronger control measures; therefore, the step size should be increased accordingly. Conversely, a smaller over-limit ratio indicates a minor degree of over-limit, with the slope deformation just exceeding the allowable limit; a moderate increase in step size is sufficient, and the increase should be relatively small.

[0105] The specific method for determining the increment can be based on corresponding increments. When the over-limit ratio is between 0 and 0.3, the increment increases by 0.05 m. When the over-limit ratio is between 0.3 and 0.6, the increment increases by 0.10 m. When the over-limit ratio is between 0.6 and 1.0, the increment increases by 0.15 m. When the over-limit ratio is greater than 1.0, the increment increases by 0.20 m. The above values ​​are for illustrative purposes only; in actual operation, the increment corresponding to each increment can be preset according to the specific circumstances of the project.

[0106] Taking a foundation trench excavation as an example, the allowable displacement is 30 mm, and the current reduction step size is 0.2 m. After excavation of a certain layer, the measured displacement is 36 mm, exceeding the limit by 0.2, which falls within the 0 to 0.3 range. The step size is increased by 0.05 m, and the adjusted reduction step size is 0.25 m. After excavation of another layer, the measured displacement is 54 mm, exceeding the limit by 0.8, which falls within the 0.6 to 1.0 range. The step size is increased by 0.15 m, and the adjusted reduction step size is 0.35 m.

[0107] The increment of the step size can be determined according to the following rules: New step size = Original step size × (1 + k·η), where η is the over-limit ratio (measured displacement / allowable displacement - 1), and k is the adjustment coefficient (which can be 0.5 to 1.0). When decreasing the step size, the new step size = Original step size × (1 - k'·μ), where μ is the ratio of measured displacement to allowable displacement, and k' is the adjustment coefficient (which can be 0.3 to 0.6). To prevent the step size from being too small or too large, a lower limit of 0.1m and an upper limit of 0.5m are set. The above coefficients can be set on-site according to the actual engineering situation and are not limited to fixed values.

[0108] Compared to existing methods that use a fixed increment, this invention correlates the increment of the step size with the proportion of exceeding the limit, establishing a quantitative correspondence between the degree of exceeding the limit and the adjustment intensity. When the exceedance is minor, the step size is increased slightly; when the exceedance is severe, the step size is increased significantly, ensuring that the intensity of the control measures matches the degree of slope deformation risk. This approach avoids the efficiency loss caused by over-adjustment in cases of minor exceedance and the safety risks caused by insufficient adjustment in cases of severe exceedance, thus improving the targeting and precision of dynamic step size adjustment.

[0109] In a preferred embodiment, in the method for coordinated control of drainage pipe trench layered excavation and slope stability, the magnitude of reducing the preset reduction step is determined based on the ratio of the real-time monitored displacement to the preset allowable displacement value.

[0110] In some embodiments, a fixed-amplitude reduction method can be used. This method, when monitoring displacement and finding it necessary to reduce the reduction step size when it has not exceeded the allowable displacement value, reduces the step size by a pre-set fixed value each time, for example, 0.05m each time. The reduction magnitude remains constant regardless of the current displacement level. The drawback of this approach is that the displacement not exceeding the limit covers a wide range, from near zero to near the allowable value. When the displacement is far below the allowable value, it indicates that the slope deformation response is very weak, and the safety margin under the existing layered scheme is sufficient. In this case, reducing the step size by a larger magnitude will not affect safety and can more effectively reduce unnecessary layer thickness reduction, improving construction efficiency. When the displacement is close to the allowable value, the slope deformation, although not exceeding the limit, is already in a critical state. If the step size is still reduced by a fixed magnitude at this time, it may lead to insufficient reduction force when the limit is exceeded again after the step size is reduced, increasing the risk of further deformation development. The fixed-amplitude reduction method uses the same reduction force for different levels of displacement not exceeding the limit, failing to fully release efficiency potential when the safety margin is sufficient, and also failing to maintain sufficient control reserves in critical states.

[0111] In this invention, the reduction step size is determined based on the ratio of the real-time monitored displacement to the allowable displacement value. The specific implementation method is as follows.

[0112] In a certain iteration of step two, if the real-time monitored displacement obtained after the current layer excavation is completed does not exceed the preset allowable displacement value, it is necessary to maintain or reduce the reduction step size. When deciding to reduce the step size, the displacement ratio is calculated. The displacement ratio is the ratio of the real-time monitored displacement to the allowable displacement value. For example, if the allowable displacement value is 30 mm and the measured displacement is 6 mm, the ratio is 0.2. If the measured displacement is 24 mm, the ratio is 0.8.

[0113] Based on the calculated displacement ratio, determine the specific amount by which the step size is reduced. The smaller the displacement ratio, the farther the current displacement is from the allowable limit, the weaker the slope deformation response, and the more sufficient the safety margin. In this case, the step size can be reduced by a larger margin. The larger the displacement ratio, the closer the current displacement is to the allowable limit. Although the slope deformation has not exceeded the limit, the safety margin is limited. In this case, the step size should be reduced by a smaller margin, or even kept unchanged.

[0114] The specific method for determining the reduction range can be based on corresponding increments. When the displacement ratio is between 0 and 0.3, the step size is reduced by 0.10 m. When the displacement ratio is between 0.3 and 0.6, the step size is reduced by 0.05 m. When the displacement ratio is between 0.6 and 0.8, the step size is reduced by 0.02 m. When the displacement ratio is greater than 0.8, the current step size remains unchanged, and no reduction adjustment is made. The above values ​​are only examples; in actual operation, the reduction range corresponding to each increment can be preset according to the specific engineering conditions.

[0115] Taking a foundation trench excavation as an example, the allowable displacement is 30 mm, and the current reduction step size is 0.3 m. After excavating a certain layer, the measured displacement is 6 mm, with a displacement ratio of 0.2, which falls within the range of 0 to 0.3. The step size is reduced by 0.10 m, and the adjusted reduction step size is 0.20 m. After excavating another layer, the measured displacement is 21 mm, with a displacement ratio of 0.7, which falls within the range of 0.6 to 0.8. The step size is reduced by 0.02 m, and the adjusted reduction step size is 0.28 m. After excavating yet another layer, the measured displacement is 27 mm, with a displacement ratio of 0.9, which is greater than 0.8. Therefore, the current step size of 0.28 m is maintained.

[0116] Compared to existing methods that use a fixed reduction step size, this invention correlates the reduction step size with the displacement ratio, establishing a correspondence between safety margin and pullback force. When the displacement is far below the allowable value, the safety margin is sufficient, and the step size is pulled back by a large margin to fully release the construction efficiency potential. When the displacement is close to the allowable value, the safety margin is limited, and the step size is pulled back by a small margin or remains unchanged to maintain sufficient control reserves to cope with possible subsequent deformation development. This approach ensures that the step size reduction operation is neither overly conservative to the point of sacrificing efficiency, nor overly aggressive to the point of weakening safety control, achieving a reasonable balance between safety and efficiency.

[0117] It should be noted that soil and rock parameters are inherently discrete, and numerical simulation results may differ from actual slope responses. Therefore, this invention recommends conducting sensitivity analysis on key parameters (c, φ, elastic modulus) and calculating safety factors using interval values ​​or probabilistic methods (e.g., taking the parameter mean minus one standard deviation as a conservative value). When the deviation between the monitored displacement and the pre-calculated displacement exceeds 30%, construction should be suspended, geological parameters re-verified, and the model updated. These measures have been verified as feasible in numerous engineering practices.

[0118] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily implemented by those skilled in the art. Therefore, the present invention is not limited to the specific details without departing from the general concept defined by the claims and their equivalents.

Claims

1. A method for coordinated control of layered excavation of drainage pipe foundation trenches and slope stability, characterized in that, Includes the following steps: Step 1: Pre-determining the stratification scheme Construct a three-dimensional numerical model of the foundation trench and slope of the excavation area, set the initial layer thickness, and determine the initial excavation layers from the ground surface downwards according to the initial layer thickness; Based on the three-dimensional numerical model, the slope stability safety factor is pre-calculated for the current proposed excavation layer in the unsupported state after removal. If the slope stability safety factor does not meet the preset excavation scheme safety threshold, the layer thickness of the current proposed excavation layer is reduced by a preset reduction step size, and the slope stability safety factor is pre-calculated again based on the three-dimensional numerical model until the slope stability safety factor meets the preset excavation scheme safety threshold. The layered excavation scheme is determined layer by layer. The layered excavation scheme includes the layer thickness and excavation sequence of each excavation layer from the ground surface to the designed foundation trench bottom elevation; Step 2: Single-layer excavation and dynamic control Following the order from the ground surface downwards in the layered excavation scheme, the current layer to be excavated is excavated; after the excavation of this layer is completed, the real-time monitoring displacement of the slope is obtained, and the obtained real-time monitoring displacement is compared with the preset allowable displacement value: If the real-time monitored displacement exceeds the preset allowable displacement value, reinforcement measures are taken for the excavated area, and the thickness of the next layer to be excavated is reduced according to the preset reduction step size, and the layer excavation plan is updated. If the real-time monitored displacement does not exceed the preset allowable displacement value, the current layered excavation scheme shall be maintained. Step 3: Loop Control If the excavation has not reached the designed bottom elevation of the foundation trench, return to step two and, based on the updated or maintained layered excavation plan, treat the next layer as the new current layer to be excavated and continue excavation; if the excavation has reached the designed bottom elevation of the foundation trench, proceed to step four. Step 4: Final Inspection and Pipe Laying The slope stability of the formed trench is tested. If the test is passed, the drainage pipe is laid. If the test is not passed, the current slope of the trench is reinforced and the slope stability is tested again until the test is passed and the drainage pipe is laid.

2. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 1, characterized in that, In step one, the strength reduction method is applied to the three-dimensional numerical model to perform a pre-calculation of the slope stability safety factor.

3. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 1, characterized in that, The real-time monitoring of displacement mentioned in step two includes the apparent displacement of the slope and the deep displacement of the slope.

4. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 3, characterized in that, The apparent displacement of the slope is compared with a preset allowable apparent displacement value, and the deep displacement of the slope is compared with a preset allowable deep displacement value. If the apparent displacement of the slope exceeds the preset allowable apparent displacement value, or the deep displacement of the slope exceeds the preset allowable deep displacement value, reinforcement measures are taken for the excavated area, and the thickness of the next layer to be excavated is reduced according to a preset reduction step, and the layered excavation plan is updated.

5. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 1, characterized in that, In step two, after reducing the thickness of the next layer to be excavated and updating the layer excavation scheme, the method further includes: based on the three-dimensional numerical model, recalculating the slope stability safety factor of the next layer to be excavated after the layer thickness reduction in the unsupported state after removal. If the slope stability safety factor still does not meet the preset excavation scheme safety threshold, the layer thickness of the layer is further reduced by the preset reduction step size and the recalculation is performed until the slope stability safety factor meets the preset excavation scheme safety threshold.

6. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 1, characterized in that, Step four, the final acceptance of slope stability, includes: calculating the slope stability safety factor of the formed trench based on the three-dimensional numerical model, comparing the slope stability safety factor with the preset excavation scheme safety threshold, and if the slope stability safety factor meets the preset excavation scheme safety threshold, the final acceptance is passed.

7. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 1, characterized in that, During the multiple iterations of step two, the preset reduction step size is dynamically adjusted based on the acquired real-time monitored displacement.

8. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 7, characterized in that, The dynamic adjustment method is as follows: the real-time monitored displacement is compared with the preset allowable displacement value. If the real-time monitored displacement exceeds the preset allowable displacement value, the preset reduction step size is increased; if the real-time monitored displacement does not exceed the preset allowable displacement value, the preset reduction step size is maintained or decreased.

9. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 8, characterized in that, The increase in the preset reduction step size is determined based on the proportion of the real-time monitored displacement exceeding the preset allowable displacement value.

10. The method for coordinated control of layered excavation of drainage pipe foundation trench and slope stability according to claim 8, characterized in that, The magnitude of the reduction in the preset reduction step size is determined based on the ratio of the real-time monitored displacement to the preset allowable displacement value.