A construction timing determination method for anti-floating anchor rods based on a reserved soil layer counterpressure condition

Abstract

The application provides a construction timing determination method for anti-floating anchor rods based on reserved soil layer counterpressure conditions, and relates to the technical field of deep foundation pit engineering. The method comprises the following steps: obtaining hydrological and anchor rod design parameters of a foundation pit, and extracting the thickness variable of the reserved soil layer and the total effective uplift resistance variable of the locked anchor rod in the excavation process; setting the uplift resistance variable to zero in the initial stage to obtain a first critical reserved soil layer thickness; calculating the total effective uplift resistance value of each subsequent stage based on the batch construction plan, and substituting the value into the model to obtain a second critical reserved soil layer thickness set. Finally, the first critical thickness is taken as the stop limit triggered by the first batch of construction, and the second critical thickness set is taken as the soil layer stripping control limit of each subsequent stage, so as to determine the collaborative construction timing of the excavation and anchoring alternately executed. The application effectively prevents the uplift and gushing risks caused by the unloading of the foundation pit, and optimizes the construction timing and cost under the premise of ensuring the anti-floating safety.

Description

Technical Field

[0001] This invention relates to the field of deep foundation pit engineering technology, and in particular to a method for determining the construction sequence of anti-buoyancy anchors based on the back pressure conditions of reserved soil layers. Background Technology

[0002] As underground space development extends into deep confined aquifers, the impact of groundwater uplift pressure on the stability of deep foundation pit bottoms and underground structures is becoming increasingly prominent. Traditional anti-buoyancy anchor construction often employs a process of full excavation to the design elevation of the foundation before anchor drilling and tensioning. This full-section unloading mode causes a rapid release of the initial in-situ stress in the foundation soil. Under the influence of the confined water head at the bottom layer, the foundation is highly susceptible to excessive rebound deformation, which can induce engineering disasters such as foundation heave, piping, or even sudden surge.

[0003] To control foundation deformation and prevent water inrush risks, current research and practice in geotechnical engineering are gradually incorporating the theory of spatiotemporal effects, adopting a construction strategy that combines pre-reserved soil layers with counter-pressure and phased excavation. The core of this technical approach lies in utilizing the self-weight of the natural soil in the unexcavated strata as a temporary passive counterweight to resist the upward buoyancy of the still water at the bottom of the pit. This transforms the instantaneous and complete unloading of the foundation pit into a gradual unloading transition, and during this mechanical transformation process, a permanent anti-buoyancy system is gradually constructed.

[0004] However, existing methods for constructing pre-reserved soil layers for counter-pressure mainly rely on static mechanical design and qualitative engineering experience, resulting in significant arbitrariness in determining the thickness of the pre-reserved soil layer and the timing of its stripping. Current technology has not yet established a dynamic mechanical coupling analysis mechanism between the excavation and unloading of the pre-reserved soil layer and the tensioning and resistance increase of the anti-buoyancy anchor. If the pre-reserved soil layer is too thin or stripped too early, it will lead to a transient breakdown of the anti-buoyancy mechanical equilibrium, causing instability and failure of the foundation pit floor. If the pre-reserved soil layer is too thick, it will cause a surge in the ineffective drilling depth of the anti-buoyancy anchor penetrating the non-anchored soil layer, leading not only to difficulties in drilling and material waste but also making it difficult to achieve the optimal construction schedule. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of the reserved soil layer. This invention solves the problem of lack of quantitative dynamic mechanical coordination control between the excavation and unloading of the reserved soil layer and the tensioning and locking of the anti-buoyancy anchor in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: A method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers includes: The design still water buoyancy of the foundation pit bottom slab, the design pull-out force of a single anti-buoyancy anchor, and the phased construction plan of the anti-buoyancy anchor are obtained. The phased construction plan is divided into the first construction phase and each subsequent construction phase. The thickness of the reserved soil layer during the foundation pit excavation process is extracted as the reserved soil layer thickness variable, and the total pull-out force provided by the locked anti-buoyancy anchor is extracted as the total effective pull-out force variable; Based on the reserved soil layer thickness variable, the total effective pull-out force variable and the design static buoyancy force, a dynamic anti-buoyancy mechanical equilibrium model is constructed. In the initial excavation stage before the anti-buoyancy anchor is installed, the total effective pull-out force variable is assigned to zero, and the total effective pull-out force variable with the value of zero is substituted into the dynamic anti-buoyancy mechanical equilibrium model to determine the lower limit value of the reserved soil layer thickness variable and obtain the first critical reserved soil layer thickness. Based on the phased construction plan and the single-strand design pull-out force, calculate the value of the total effective pull-out force variable that is incrementally accumulated in each subsequent construction stage; Substitute the values ​​of the total effective pull-out force variables of each subsequent construction stage into the dynamic anti-buoyancy mechanical equilibrium model, solve for the extreme value set of the reserved soil layer thickness variables that satisfy the dynamic anti-buoyancy mechanical equilibrium model, and obtain the second critical reserved soil layer thickness set. The first critical reserved soil layer thickness is used as the excavation stop limit before the first construction stage is triggered, and the second critical reserved soil layer thickness set is used as the soil stripping control limit corresponding to each subsequent construction stage, so as to determine the coordinated construction sequence.

[0007] The present invention discloses the following technical effects: This invention provides a method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of the reserved soil layer. By constructing a dynamic mechanical equilibrium model that integrates the back pressure of the reserved soil layer and the effective pull-out resistance of the anchor, this invention accurately and quantitatively calculates the critical reserved soil layer thickness at each stage, generating a coordinated control sequence for alternating excavation and anchoring. This invention completely eliminates the blindness of traditional engineering experience-based approaches, effectively preventing foundation heave and sudden surge damage caused by excessively rapid unloading, and avoiding the surge in ineffective anchor drilling and material waste due to excessively thick soil layers. It achieves the optimal configuration of construction period and economic cost while ensuring the absolute safety of the foundation pit against buoyancy. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A flowchart illustrating a method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of a reserved soil layer, provided for an embodiment of the present invention. Detailed Implementation

[0010] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0011] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0012] like Figure 1 As shown, this invention provides a method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers, including: Step 100: Obtain the design still water buoyancy of the foundation pit bottom slab, the design pull-out force of a single anti-buoyancy anchor, and the phased construction plan of the anti-buoyancy anchor, wherein the phased construction plan is divided into the first phase of construction and each subsequent phase of construction. Step 200: Extract the thickness of the reserved soil layer during the foundation pit excavation process as the reserved soil layer thickness variable, and extract the total pull-out resistance provided by the locked anti-buoyancy anchor as the total effective pull-out resistance variable; Step 300: Based on the reserved soil layer thickness variable, the total effective pull-out force variable, and the design static buoyancy force, construct a dynamic anti-buoyancy mechanical equilibrium model; Step 400: In the initial excavation stage before the anti-buoyancy anchor is constructed, the total effective pull-out force variable is assigned to zero, and the total effective pull-out force variable with the value of zero is substituted into the dynamic anti-buoyancy mechanical equilibrium model to determine the lower limit value of the reserved soil layer thickness variable and obtain the first critical reserved soil layer thickness. Step 500: Based on the batch construction plan and the single-strand design pull-out force, calculate the value of the total effective pull-out force variable that is incrementally accumulated in each subsequent construction stage; Step 600: Substitute the values ​​of the total effective pull-out force variables of each subsequent construction stage into the dynamic anti-buoyancy mechanical equilibrium model, solve for the extreme value set of the reserved soil layer thickness variables that satisfy the dynamic anti-buoyancy mechanical equilibrium model, and obtain the second critical reserved soil layer thickness set. Step 700: Use the first critical reserved soil layer thickness as the excavation stop limit before the first construction stage is triggered, and use the second critical reserved soil layer thickness set as the soil stripping control limit corresponding to each subsequent construction stage, so as to determine the coordinated construction sequence.

[0013] Furthermore, the specific implementation process of step 100 is as follows: In this embodiment, when obtaining the design static water buoyancy force faced by the foundation pit bottom slab, the following steps are taken: first, the anti-buoyancy design water level elevation, the design bottom elevation of the foundation pit bottom slab, and the projected area of ​​the foundation pit bottom slab are extracted. Based on the height difference between the anti-buoyancy design water level elevation and the design bottom elevation, the confined water head height faced by the foundation pit bottom slab is calculated. Then, the confined water head height, the specific weight of water, and the projected area are multiplied to quantify the design static water buoyancy force. This process materializes the site's hydrogeological parameters into an upward lifting force directly acting on the bottom surface of the foundation pit bottom slab, accurately identifying the ultimate driving force source for the bottom slab heave failure induced by groundwater unloading in deep foundation pits. This establishes an absolute benchmark thrust boundary for determining the dynamic stress of the entire anti-buoyancy system.

[0014] To determine the design pull-out force of a single anti-buoyancy anchor, this embodiment extracts the geotechnical physical and mechanical parameters of the target site, as well as the design parameters of a single anti-buoyancy anchor, including the diameter of the anchor body and the design anchor length. Based on these geotechnical physical and mechanical parameters, this embodiment determines the standard value of the ultimate lateral resistance between the anchor body and the deep soil-rock interface, and derives the design pull-out force of a single anchor by combining the design parameters and a preset pull-out safety factor. This mechanical derivation process essentially physically characterizes the tensile bearing potential of the cylindrical friction-slip interface between the grouted anchor body and the surrounding stable strata, clarifying the reliable downward resistance that the smallest stress unit in the structural anti-buoyancy system can provide, thereby ensuring that a single tension member has a safety reserve to resist disaster-causing deformation during actual engineering operation.

[0015] When generating the phased construction plan for anti-buoyancy anchors, this embodiment obtains the overall construction organization scheme of the foundation pit. Based on the total excavation depth of the foundation pit and the excavation sequence of layered unloading of the reserved soil layers, the overall anti-buoyancy anchor construction task of the foundation pit is divided into multiple physical operation batches that unfold sequentially along the depth direction. In this embodiment, the shallow soil layer batch in which the drilling and tensioning locking operations are performed first is defined as the first construction stage, and the deep soil layer batches that are subsequently stripped and performed in the top-down excavation sequence are defined as each subsequent construction stage. Through this spatial dimensionality reduction and temporal segmentation technique, this embodiment materializes the traditional one-time full-section unloading abrupt change process of the foundation pit into a controlled step-like spatiotemporal stripping operation step, laying the foundation time series framework for the subsequent introduction of soil self-weight counterpressure to participate in the dynamic equilibrium evolution of the foundation pit's anti-buoyancy.

[0016] Specifically, the expression for the confined water head height is: ; in, This refers to the height of the confined water head. A waterproof level is set to prevent buoyancy. Design the bottom elevation of the foundation pit slab.

[0017] The expression for the buoyancy force in still water is: ; in, The foundation pit bottom slab is designed with static water buoyancy. The specific gravity of water; This refers to the height of the confined water head. This represents the projected area of ​​the foundation pit bottom slab.

[0018] The expression for the pull-out resistance of a single root is: ; in, The design pull-out force of a single anti-buoyancy anchor rod; The diameter of the anchor body; To design the anchorage length; This represents the standard value of the ultimate lateral resistance between the anchor body and the soil-rock interface; This is the pull-out safety factor.

[0019] Furthermore, the specific implementation process of step 200 is as follows: In this embodiment, when extracting the reserved soil layer thickness variable, the design bottom elevation of the foundation pit slab determined in the foundation pit construction drawings is first obtained, and the actual excavation surface elevation of the current construction stage during the foundation pit excavation is extracted in real time. The physical thickness of the unloaded reserved soil layer is obtained by calculating the vertical soil height difference between the two. This operation accurately maps the dynamically changing construction excavation boundary into quantifiable three-dimensional geometric parameters, precisely locking the natural soil layer entity above the foundation that has not yet been removed. This embodiment uses this physical thickness as the core dynamic calculation parameter input to extract the reserved soil layer thickness variable, directly physically representing the self-weight counterpressure potential energy reserve of the pressure zone at the bottom of the foundation pit that continuously decreases as the soil is peeled off layer by layer. This establishes a real transient physical spatial boundary for subsequent quantitative evaluation of the gravity pressure barrier against unloading heave of the foundation.

[0020] Regarding the assessment of the effectiveness of anti-buoyancy anchors, this embodiment strictly tracks the actual process flow nodes of each batch of components during the alternating excavation and anchoring operation cycle. Anti-buoyancy anchors that simultaneously meet the requirements of completed drilling and grouting, the anchor body reaching its design strength, and complete tensioning and locking are considered locked. This determination mechanism abandons the idealistic assumption of traditional calculations that rely solely on anchoring length or the number of anchors to determine resistance. It visualizes the hidden stress transmission path within deep soil and rock masses as a physically binding entity with constraint capabilities. This embodiment clarifies that only when the prestressed tendons and the grouting consolidation body jointly complete frictional engagement with the surrounding strata, and initial prestress is applied to the base plate through the tensioning lock, does the anchor truly transform from a dormant component into a force-bearing fulcrum with downward active tensile resistance, ensuring that the pull-out force subsequently introduced into the equilibrium system has an absolutely reliable engineering physical basis for effectiveness.

[0021] In the step of extracting the total effective pull-out force variable, this embodiment accurately counts the effective number of all anti-buoyancy anchors determined to be locked within the current construction stage. This effective number, the design pull-out force of a single anchor, and a preset group anchor effect reduction coefficient are multiplied to calculate the total effective pull-out force in the current stage. By introducing a group anchor effect reduction coefficient, this embodiment realistically recreates the phenomenon of overall bearing capacity attenuation caused by the overlapping and penetration of stress bubbles within densely deployed underground anchor groups in deep soil and rock. This calculation step transforms the solid integral of discretely distributed single tension members into a downward constraint force of the overall group anchors that collaboratively suppress the upward deformation of the base. This not only eliminates the potentially dangerous excess force values ​​in theoretical superposition calculations but also scientifically aggregates the batch-formed hidden resistance network into a macroscopic structural pull-out physical measure that dynamically increases with construction milestones.

[0022] Specifically, the expression for the reserved soil layer thickness variable is: ; in, To allow for variations in soil layer thickness; This represents the actual excavation elevation at the current construction stage. Design the bottom elevation of the foundation pit slab.

[0023] The expression for the total pull-out force (total effective pull-out force) is: ; in, This represents the total effective pull-out resistance during the current construction phase. This is the reduction factor for the group anchoring effect; This refers to the effective number of anti-buoyancy anchor bolts that have been locked in and are under stress during the current construction phase. This refers to the design pull-out resistance of a single anti-buoyancy anchor rod.

[0024] Furthermore, the specific implementation process of step 300 is as follows: In calculating the self-weight counterpressure of the reserved soil layer, this embodiment first obtains the weighted average unit weight of the reserved soil layer and the stress-bearing area of ​​the foundation pit bottom slab from the site survey report. This embodiment multiplies the dynamically obtained reserved soil layer thickness variable, weighted average unit weight, and stress-bearing area to accurately calculate the self-weight counterpressure of the reserved soil layer corresponding to the current construction unloading stage. This calculation process materializes the geometric dimensions and geomechanical properties of the unexcavated physical soil at the bottom of the foundation pit into a gravity load directly acting on the pressure-bearing isolation body. It physically characterizes the passive pressure barrier constructed by the natural soil self-weight above the foundation pit bottom slab, thereby effectively quantifying the engineering resistance potential to suppress the rise failure of the underlying confined water head during the unloading transition period.

[0025] To determine the total resistance to buoyancy during the current construction phase, this embodiment performs a mechanical superposition calculation by combining the calculated self-weight counterpressure of the reserved soil layer with the total effective pull-out force variable extracted in the previous steps. Through this superposition and integration mechanism, this embodiment materializes the passive self-weight load of the natural soil and the active deep anchoring constraint into a synergistic resistance combination. This operation physically breaks the isolated state of soil stripping and unloading versus structural buoyancy resistance enhancement in traditional foundation pit engineering. Within the dynamically changing construction period, it establishes a macroscopic mechanical interlocking network where the soil overburden and the group anchor resistance mutually compensate, thus realizing the physical embodiment of the comprehensive pull-out resistance of the foundation.

[0026] In constructing the final dynamic anti-buoyancy mechanical equilibrium model, this embodiment obtains the preset anti-buoyancy safety factor defined in the deep foundation pit engineering specifications, and uses the logical judgment relationship that the calculated total anti-buoyancy resistance is not less than the product of the design still water buoyancy force and the anti-buoyancy safety factor as the core mechanical boundary condition. This criterion model established in this embodiment not only sets the disaster evolution boundary that the anti-buoyancy resistance end of the foundation pit must encompass the water buoyancy thrust end, but also materializes the static game process between groundwater overburden damage and the resistance of the engineering structure into a dynamic early warning red line that progresses over time. This model transforms the transient soil-water imbalance risk, which is highly susceptible to inducing sudden instability of the foundation, into a quantifiable and step-by-step adjustable physical and mechanical control criterion, providing a solid physical decision-making foundation for subsequent triggering of layered stripping and alternating drilling operations.

[0027] Specifically, the expression for the self-weight reaction pressure of the reserved soil layer is: ; in, To allow for the self-weight reaction pressure of the soil layer; The average unit weight of the reserved soil layer; To allow for variations in soil layer thickness; This represents the projected area of ​​the foundation pit bottom slab.

[0028] The expression for the total resistance to buoyancy is: ; in, This represents the total resistance to buoyancy during the current construction phase. To allow for the self-weight reaction pressure of the soil layer; This represents the total effective pull-out resistance during the current construction phase.

[0029] The expression for the dynamic anti-buoyancy mechanical equilibrium model (boundary conditions) is as follows: ; in, This represents the total resistance to buoyancy during the current construction phase. The safety factor for buoyancy resistance; The static buoyancy of the foundation pit bottom slab is designed.

[0030] Furthermore, the specific implementation process of step 400 is as follows: In this embodiment, during the initial excavation stage before the installation of anti-buoyancy anchors, the total effective pull-out force variable is strictly assigned to zero to eliminate the structural resistance bonus. Simultaneously, the pre-set anti-buoyancy safety factor in the dynamic anti-buoyancy mechanical equilibrium model, as well as the effective area of ​​the foundation pit bottom slab and the soil weight parameters of the reserved soil layer, are obtained. This embodiment multiplies the design still water buoyancy force faced by the foundation with the anti-buoyancy safety factor to accurately calculate the total anti-buoyancy requirement force in the initial stage. This calculation process physically materializes the extreme water buoyancy thrust of the foundation pit without any anchor support into a total disaster load that must be fully offset, establishing an insurmountable safety redundancy stress baseline in the pure soil calculation stage. This provides an extreme stress boundary environment for subsequent suppression of groundwater activity purely by the weight of the natural strata.

[0031] To deduce the geometric indices for satisfying the mechanical equilibrium state, this embodiment uses the total initial anti-buoyancy requirement force calculated above as the divisor in the mechanical calculation. Simultaneously, it uses the product of the effective area of ​​the foundation pit bottom slab and the soil weight parameter as the divisor for reverse division, scientifically determining the minimum soil layer thickness required to satisfy dynamic anti-buoyancy mechanical equilibrium. This calculation logic materializes the abstract total tonnage of the anti-buoyancy mechanical requirement into a three-dimensional soil geometric barrier that must be preserved above the foundation pit bottom. It precisely marks the critical resistance line in physical space where the gravitational potential energy of the natural undisturbed strata can overwhelm the pressure head and cause collapse, completely eliminating the potential for water and soil imbalance and collapse induced by traditional blind excavation to the foundation.

[0032] After completing the quantitative deduction of the thickness of the pure soil mass at the base, this embodiment extracts the minimum soil layer thickness value obtained from the above calculation as the absolute lower limit value of the reserved soil layer thickness variable, and explicitly determines this lower limit value as the first critical reserved soil layer thickness. Through this threshold calibration and variable locking technique, this embodiment physically visualizes the analytical results of the complex rock and soil groundwater equilibrium equation as an absolute elevation red line that large earthmoving machinery must unconditionally prohibit and stop excavation at the construction site. This critical thickness limit not only serves as the endpoint benchmark for the initial large-area unloading stage of the soil mass, but also materializes as the command switch that directly triggers the first batch of anti-buoyancy anchor penetration operations, perfectly bridging the engineering fault between the large unloading of pure soil stripping and the implantation of the bottom group anchor structure in the macroscopic temporal flow.

[0033] Specifically, the expression for the total force required to resist buoyancy in the initial stage is: ; in, This represents the total force required for buoyancy resistance in the initial stage. The safety factor for buoyancy resistance; The static buoyancy of the foundation pit bottom slab is designed.

[0034] The expression for calculating the minimum soil layer thickness is as follows: ; in, The first critical reserved soil layer thickness; This represents the total force required for buoyancy resistance in the initial stage. The average unit weight of the reserved soil layer; This represents the projected area of ​​the foundation pit bottom slab.

[0035] Furthermore, the specific implementation process of step 500 is as follows: In this embodiment, when dynamically tracking the staged stress increments of anti-buoyancy components, the batch quantity of newly locked and effective anti-buoyancy anchors is extracted sequentially according to the phased construction plan. This extraction process precisely delves into each micro-level independent excavation step, physically locking the anchor component entity group that has actually completed grouting consolidation and tension stress conversion at the current unloading elevation. By sequentially tracking the number of newly locked and effective anchors, this embodiment realistically recreates the spatiotemporal evolution trajectory of the deep ties system from point to surface and from sparse to dense during the advancement of deep foundation pit engineering, thereby establishing an absolutely objective entity increment benchmark for the subsequent incrementally loaded anti-buoyancy resistance pool.

[0036] To accurately quantify the added structural resistance, this embodiment obtains a pre-set group anchor reduction coefficient and multiplies the extracted batch quantity, single-strand design pull-out force, and group anchor reduction coefficient to scientifically calculate the added batch pull-out force corresponding to each subsequent construction stage. This calculation step does not employ the ideal mechanical assumption of pure linear superposition, but rather uses the group anchor reduction coefficient to physically visualize the stress bubble overlap and soil disturbance loss generated within the densely distributed anchor body in the soil layer. This embodiment transforms discretely distributed single tensile entities into a staged group anchor resultant force increment with synergistic force characteristics, accurately measuring the additional effective downward tensile potential that the current batch of components can provide after rigid implantation into the stratum, completely eliminating potentially dangerous false bearing capacity surpluses in engineering safety calculations.

[0037] After calculating the incremental resistance of a single batch, this embodiment physically adds the newly added pull-out force of the current subsequent construction stage to the total effective pull-out force variable of the adjacent previous construction stage to calculate the cumulative pull-out force value of the current subsequent construction stage. Subsequently, this embodiment extracts the cumulative pull-out force value as the value of the total effective pull-out force variable for each subsequent construction stage. This incremental data processing mechanism perfectly fits the dynamic interaction process of unloading the foundation pit layer by layer from top to bottom and stabilizing it batch by batch from bottom to top in physical space. By changing the total effective resistance value in stages, this embodiment materializes the scattered tie-and-restraint network embedded in the deep strata at each stage into a dynamic pull-out resistance array that grows and expands with the excavation depth. Thus, during the long and dangerous layer-by-layer stripping and unloading cycle of the foundation pit, a real-time dynamic resistance base capable of resisting the sudden surge of pressurized water head is always maintained.

[0038] Specifically, the pull-out strength of the newly added batch (the first batch) The expression for the subsequent stage is: ; in, For the first The pull-out resistance of additional batches added in subsequent construction phases; This is the reduction factor for the group anchoring effect; For the first The number of anchor bolts that are newly locked and effective in subsequent construction phases; The design pull-out force of a single anti-buoyancy anchor rod; This is the sequence number for subsequent construction stages. Cumulative pull-out force value (stage number...) The expression for the subsequent stage is: ; in, For the first Total effective pull-out resistance accumulated in each subsequent construction phase; For the first Total effective pull-out resistance accumulated across all construction phases; For the first The pull-out resistance of additional batches added in subsequent construction phases; This is the sequence number for the subsequent construction phases.

[0039] Furthermore, the specific implementation process of step 600 is as follows: In this embodiment, when solving for the thickness extremum that satisfies the dynamic anti-buoyancy mechanical equilibrium model, the pre-set anti-buoyancy safety factor, the effective area of ​​the foundation pit bottom slab, and the soil weight parameters of the reserved soil layer are first accurately obtained. This embodiment multiplies the design static water buoyancy force faced by the foundation with the anti-buoyancy safety factor to calculate the total anti-buoyancy demand force under extreme conditions. This calculation process materializes the maximum potential for jacking failure that a deep foundation pit may encounter under unfavorable fluctuations in groundwater level into a constant benchmark resistance target, providing an insurmountable absolute force ceiling for the subsequent dynamic allocation and force transfer of the multiple resistance system, completely eliminating the hidden dangers of foundation pit heave and structural instability induced by insufficient resistance estimation.

[0040] To address the dynamically changing structural resistance configuration at each construction stage, this embodiment subtracts the constant total anti-buoyancy demand from the total effective pull-out force variable corresponding to each subsequent construction stage, accurately calculating the soil back pressure demand that must be borne by the undisturbed soil at each subsequent construction stage. This subtraction perfectly visualizes, at the physical and mechanical level, the dynamic stress replacement mechanism where the constraint of downward pressure and buoyancy is gradually transferred from the self-weight of the natural undisturbed soil to the deep artificial anchor group structure during the unloading process of deep foundation pit excavation. Through this precise mechanical stripping calculation, this embodiment ensures that the increase in tensile force contributed by each batch of anti-buoyancy anchors after rigid implantation and locking into the strata is instantly converted into an equivalent deductible natural soil gravity load, achieving seamless coordination between unloading of underground concealed works and increasing structural resistance.

[0041] After establishing the gravity counterpressure index that must be retained at each stage, this embodiment uses the soil counterpressure demand of each subsequent construction stage as the divisor and the product of the area of ​​action and the soil weight parameter as the divisor for reverse spatial dimension calculation, rigorously deriving the lower limit of the allowable remaining soil thickness for each subsequent construction stage. This embodiment further merges and extracts the lower limit of the allowable remaining soil thickness for each subsequent construction stage into an extreme value set of the reserved soil thickness variable, and explicitly labels this extreme value set as the second critical reserved soil thickness set. This division operation and set extraction mechanism reverses the abstract remaining anti-buoyancy mechanical tonnage requirement into a three-dimensional soil retention geometric barrier distributed at each stepped excavation node, providing an extremely accurate physical elevation warning matrix for on-site earthmoving stripping machinery and anchoring drilling equipment. This maximizes the release of the reduced-dimensional excavation working face at each stage while completely sealing the potential for sudden water and soil imbalance.

[0042] Specifically, the formula for calculating the required soil back pressure is as follows: ; in, For the first The soil counterpressure demand in the subsequent construction phase; The safety factor for buoyancy resistance; The foundation pit bottom slab is designed with static water buoyancy. For the first Total effective pull-out resistance accumulated in each subsequent construction phase; This is the sequence number for the subsequent construction phases.

[0043] Permissible minimum thickness of remaining soil layer (the first) The expression for the subsequent stage is: ; in, For the first The minimum allowable thickness of the remaining soil layer in each subsequent construction stage; For the first The soil counterpressure demand in the subsequent construction phase; The average unit weight of the reserved soil layer; The projected area of ​​the foundation pit bottom slab; To select the larger of the functions; This is the sequence number for the subsequent construction phases.

[0044] Furthermore, the specific implementation process of step 700 is as follows: In this embodiment, when initiating the initial earthwork unloading control, the elevation data of the excavation face at the working surface of the foundation pit is acquired in real time, the remaining thickness of the current reserved soil layer is dynamically calculated, and the current remaining thickness of the reserved soil layer is continuously and frequently compared with the theoretically derived first critical reserved soil layer thickness. When the current remaining thickness of the reserved soil layer precisely decays to equal the first critical reserved soil layer thickness, this embodiment immediately generates and issues an initial excavation stop command, forcibly cutting off the earthwork stripping action, and directly triggering the drilling and tensioning locking operations of the first batch of construction phases of anti-buoyancy anchors based on the initial excavation stop command. This monitoring and command issuance mechanism physically materializes the macroscopic mechanical anti-surge bottom line into a spatial physical elevation red line that the excavator tracks must not traverse, completely abandoning the blindness of traditional disorderly over-excavation of foundation pits. At the absolute safety boundary where the gravity counter-pressure potential energy of the natural undisturbed soil is about to be exhausted, the rigid implantation and stress loading action of the underground structure anti-buoyancy components are forcibly introduced.

[0045] To confirm and guide the handover of the anti-buoyancy resistance system, this embodiment rigorously acquires the locking status data of the anti-buoyancy anchors in the current construction stage. When the locking status data fully meets the preset stress activation conditions, it is confirmed that the bottom anti-pull-out tie network has truly formed a substantial downward rigid constraint. Subsequently, this embodiment accurately extracts the critical thickness value corresponding to the next subsequent construction stage from the second critical reserved soil layer thickness set calculated in the previous stage, and directly establishes it as the target soil layer stripping boundary to guide the next round of earthwork unloading. This extraction and establishment process physically materializes the actual frictional tensile force generated by the prestressed tendons and grouting consolidation body in the concealed works into a safe authorization pass for the next stage of unloading and excavation. This ensures that before the bottom of the foundation pit experiences the next round of intense unloading stress release, it must have an equivalent increase in structural anchoring resistance to replace the weight of the excavated soil, realizing a seamless dynamic handover of natural soil gravity overburden and artificial anchor tie anti-buoyancy at the physical stress level.

[0046] After establishing the unloading space target for each stage, this embodiment generates an excavation recovery command to guide the large machinery on site to safely peel and excavate the reserved soil layer downwards to the target soil layer peeling boundary. Upon precisely reaching the target soil layer peeling boundary at the work face, an excavation stop command is instantly generated, triggering the drilling and tensioning of anti-buoyancy anchor bolts for the corresponding subsequent construction stage. This embodiment strictly follows the spatial depth stage division sequence of the batch construction plan, constructing a closed-loop control matrix by acquiring locking status data, extracting the target soil layer peeling boundary, and triggering excavation and locking operations. This matrix alternately and cyclically executes the work face control flow within the aforementioned physical space until all deep-level anti-buoyancy anchor bolt construction is completed and the foundation reserved soil layer is completely peeled to the design bottom elevation. This alternating cyclical technique completely stitches together the originally fragmented large-scale unloading and peeling of earthwork with the deep underground support penetration operation, generating a complete collaborative construction sequence. Under the premise of suppressing the deformation caused by pressurized water jacking throughout the process, it safely and efficiently presents the ultimate evolution process of deep foundation pit excavation from top to bottom.

[0047] Specifically, the calculation expression for the remaining thickness of the reserved soil layer is as follows: ; in, To allow for the remaining thickness of the soil layer in real time; This represents the actual excavation elevation at the current construction stage. Design the bottom elevation of the foundation pit slab.

[0048] More specifically, in determining the preset stress-effectiveness conditions, this embodiment first obtains the measured strength of the grout in the anti-buoyancy anchor during the current construction stage, and then precisely compares this measured strength with the pre-set anchor body design strength threshold. This comparison process physically visualizes the microscopic hydration reaction process of cement grout transforming from a fluid plastic state to a consolidated hardened state in underground concealed works as a macroscopic entity generating node of frictional interlocking force between the pull-out structure and the deep stable rock and soil. By ensuring that the measured strength of the grout is greater than or equal to the anchor body design strength threshold, this embodiment completely eliminates the risk of anchor body slippage and loss of ground grip caused by blindly applying force before the grout reaches the standard, thus constructing a solid physical material foundation for subsequent components to bear the extreme buoyancy force of upward lifting.

[0049] To confirm the active constraint force applied to the anti-buoyancy anchor, this embodiment collects the measured tension force of the anchor head in real time and compares it dynamically with the tension locking threshold determined based on the single-strand design pull-out force. This comparison and verification mechanism physically materializes the pull-out mechanical indicators abstracted on the structural design drawings into a downward rigid pulling force directly applied to the prestressed steel strand entity by on-site tensioning equipment. This embodiment strictly limits the measured tension force of the anchor head to be greater than or equal to the tension locking threshold, thereby instantly activating the passively tensioned members that were originally in a relaxed dormant state into a rigid load-bearing entity with the ability to actively suppress the kinetic energy of the foundation surge, accurately measuring and storing the true initial stress reserve of the structural system to resist the heave deformation of the foundation pit floor.

[0050] Under the premise of ensuring that the strength of the grouting material and the tension of the rod meet the standards, this embodiment closely monitors and confirms that the anti-buoyancy anchor has completely completed the final anchor locking operation, and then outputs a judgment command that the conditions for the force to take effect have been fully met. This operation confirmation step physically materializes the transient prestress transfer process when the tensioning equipment is unloaded into the mechanical locking action of the high-strength anchor clamp on the tensioned steel strand, which declares the complete physical closure of the rigid connection network between the deep stable soil layer, the anti-buoyancy anchor body and the pressure bottom plate of the foundation pit. By completing the anchor locking operation, this embodiment permanently transforms the temporarily applied external tension force into a long-term effective pull-out force that resists the overthrow of groundwater within the structural system, completely locking the engineering loophole of prestress shrinkage and loss, and issuing the only reliable physical resistance replacement certificate for the safe stripping and excavation of the large-area reserved soil layer in the macroscopic coordinated alternating time flow.

[0051] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0052] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers, characterized in that, include: The design still water buoyancy of the foundation pit bottom slab, the design pull-out force of a single anti-buoyancy anchor, and the phased construction plan of the anti-buoyancy anchor are obtained. The phased construction plan is divided into the first construction phase and each subsequent construction phase. The thickness of the reserved soil layer during the foundation pit excavation process is extracted as the reserved soil layer thickness variable, and the total pull-out force provided by the locked anti-buoyancy anchor is extracted as the total effective pull-out force variable; Based on the reserved soil layer thickness variable, the total effective pull-out force variable and the design static buoyancy force, a dynamic anti-buoyancy mechanical equilibrium model is constructed. In the initial excavation stage before the anti-buoyancy anchor is installed, the total effective pull-out force variable is assigned to zero, and the total effective pull-out force variable with the value of zero is substituted into the dynamic anti-buoyancy mechanical equilibrium model to determine the lower limit value of the reserved soil layer thickness variable and obtain the first critical reserved soil layer thickness. Based on the phased construction plan and the single-strand design pull-out force, calculate the value of the total effective pull-out force variable that is incrementally accumulated in each subsequent construction stage; Substitute the values ​​of the total effective pull-out force variables of each subsequent construction stage into the dynamic anti-buoyancy mechanical equilibrium model, solve for the extreme value set of the reserved soil layer thickness variables that satisfy the dynamic anti-buoyancy mechanical equilibrium model, and obtain the second critical reserved soil layer thickness set. The first critical reserved soil layer thickness is used as the excavation stop limit before the first construction stage is triggered, and the second critical reserved soil layer thickness set is used as the soil stripping control limit corresponding to each subsequent construction stage, so as to determine the coordinated construction sequence.

2. The method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers according to claim 1, characterized in that, Obtain the design still water buoyancy of the foundation pit bottom slab, the design pull-out force of a single anti-buoyancy anchor, and the phased construction plan for the anti-buoyancy anchor, including: Extract the anti-buoyancy design water level elevation of the foundation pit site, the design bottom elevation of the foundation pit bottom slab, and the projected area of ​​the foundation pit bottom slab; The height of the pressure head faced by the foundation pit bottom slab is calculated based on the height difference between the anti-buoyancy design water level and the design bottom elevation. The design still water buoyancy force is calculated by multiplying the pressure head height, the weight of water, and the projected area. Extract the geophysical and mechanical parameters of the target site and the design parameters of a single anti-buoyancy anchor, wherein the design parameters include: the diameter of the anchor body and the design anchor length; Based on the aforementioned geotechnical physical and mechanical parameters, the standard value of the ultimate lateral resistance between the anchor body and the soil-rock interface is determined, and combined with the aforementioned design parameters and the preset pull-out safety factor, the design pull-out force of a single anchor is calculated. Obtain the overall construction organization plan for the foundation pit; Based on the overall construction organization plan of the foundation pit, according to the total excavation depth of the foundation pit and the excavation steps of layered unloading of the reserved soil layer, the construction task of the anti-buoyancy anchor rod of the foundation pit is divided into multiple batches to be carried out sequentially along the depth direction, thus obtaining the batch construction plan. Based on the phased construction plan, the first batch to perform hole drilling and tensioning locking operations is defined as the first construction phase, and each subsequent batch executed in sequence according to the excavation steps is defined as the subsequent construction phase.

3. The method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers according to claim 1, characterized in that, The thickness of the reserved soil layer during the excavation process is extracted as the reserved soil layer thickness variable, and the sum of the pull-out resistance provided by the locked anti-buoyancy anchors is extracted as the total effective pull-out resistance variable, including: Obtain the design bottom elevation of the foundation pit slab as determined in the foundation pit construction drawings, and obtain the actual excavation surface elevation of the current construction stage during the foundation pit excavation process in real time; The physical thickness of the unloaded reserved soil layer is obtained based on the vertical soil height difference between the actual excavation surface elevation and the design bottom elevation. The physical thickness is used as a dynamic calculation parameter to determine the variable of the reserved soil layer thickness. During the excavation of the foundation pit, the anti-buoyancy anchor rods that meet the requirements of completed hole drilling and grouting, the anchor body reaching the design strength, and the tensioning and locking process are determined to be the locked anti-buoyancy anchor rods. The effective number of all the anti-buoyancy anchors that are determined to be locked during the current construction phase is counted, and the effective number, the single anchor design pull-out force, and the preset group anchor effect reduction coefficient are multiplied to calculate the total pull-out force that is actually effective during the current construction phase. The sum of the pull-out forces is extracted as the total effective pull-out force variable.

4. The method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers according to claim 1, characterized in that, The dynamic anti-buoyancy mechanical equilibrium model is constructed based on the reserved soil layer thickness variable, the total effective pull-out force variable, and the design still water buoyancy force, including: Obtain the weighted average unit weight of the reserved soil layer and the effective area of ​​the foundation pit bottom slab; calculate the self-weight reaction pressure of the reserved soil layer based on the reserved soil layer thickness variable, the weighted average unit weight, and the effective area. The total anti-buoyancy resistance of the current construction stage is obtained by superimposing the self-weight reaction pressure of the reserved soil layer with the total effective pull-out force variable. Obtain the preset anti-buoyancy safety factor; The dynamic anti-buoyancy mechanical equilibrium model is constructed by using the product of the total anti-buoyancy resistance being no less than the design still water buoyancy force and the anti-buoyancy safety factor as the mechanical boundary condition.

5. The method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers according to claim 1, characterized in that, In the initial excavation stage before the anti-buoyancy anchor is installed, the total effective pull-out force variable is assigned a value of zero, and the total effective pull-out force variable with a value of zero is substituted into the dynamic anti-buoyancy mechanical equilibrium model to determine the lower limit value of the reserved soil layer thickness variable, thereby obtaining the first critical reserved soil layer thickness, including: Obtain the preset anti-buoyancy safety factor in the dynamic anti-buoyancy mechanical equilibrium model, as well as the effective area of ​​the foundation pit bottom plate and the soil weight parameters of the reserved soil layer; Multiply the designed still water buoyancy force by the anti-buoyancy safety factor to calculate the total anti-buoyancy force required in the initial stage; The total anti-buoyancy requirement in the initial stage is used as the divisor, and the product of the effective area and the soil weight parameter is used as the divisor. The ratio of the two is calculated to obtain the minimum soil layer thickness value that satisfies mechanical equilibrium. The minimum soil layer thickness value is extracted as the lower limit value of the reserved soil layer thickness variable, and the lower limit value is determined as the first critical reserved soil layer thickness.

6. The method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers according to claim 1, characterized in that, Based on the phased construction plan and the single-strand design pull-out force, the values ​​of the total effective pull-out force variable, which are incrementally accumulated in each subsequent construction stage, are calculated, including: According to the phased construction plan, the batch quantity of the anti-buoyancy anchor bolts that are newly locked and effective in each subsequent construction stage is extracted sequentially; Obtain the preset group anchor reduction coefficient, multiply the batch quantity, the single anchor design pull-out force and the group anchor reduction coefficient, and calculate the new batch pull-out force corresponding to each subsequent construction stage; The cumulative pull-out force value of the current subsequent construction stage is calculated by adding the newly added batch pull-out force of the current subsequent construction stage to the total effective pull-out force variable of the adjacent previous construction stage. The cumulative pull-out force values ​​of each subsequent construction stage are extracted as the values ​​of the total effective pull-out force variable corresponding to each subsequent construction stage.

7. The method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers according to claim 1, characterized in that, The steps involve substituting the values ​​of the total effective pull-out force variables for each subsequent construction stage into the dynamic anti-buoyancy mechanical equilibrium model, solving for the extreme value set of the reserved soil layer thickness variables that satisfy the dynamic anti-buoyancy mechanical equilibrium model, and obtaining the second critical reserved soil layer thickness set, including: Obtain the preset anti-buoyancy safety factor, the effective area of ​​the foundation pit bottom plate, and the soil weight parameters of the reserved soil layer in the dynamic anti-buoyancy mechanical equilibrium model; Multiply the designed still water buoyancy force by the anti-buoyancy safety factor to obtain the total anti-buoyancy demand force. Subtract the total anti-buoyancy demand force from the value of the total effective pull-out force variable corresponding to each subsequent construction stage to calculate the soil counterpressure demand force corresponding to each subsequent construction stage. The soil counterpressure demand for each subsequent construction stage is used as the divisor, and the product of the effective area and the soil weight parameter is used as the divisor to calculate the lower limit of the allowable remaining soil thickness for each subsequent construction stage. The lower limit of the allowable remaining soil layer thickness for each subsequent construction stage is merged and extracted into the extreme value set of the reserved soil layer thickness variable, and the extreme value set is determined as the second critical reserved soil layer thickness set.

8. The method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers according to claim 1, characterized in that, The step of using the first critical reserved soil layer thickness as the excavation stop limit before the first construction stage is triggered, and using the second critical reserved soil layer thickness set as the soil stripping control limit corresponding to each subsequent construction stage, to determine the coordinated construction sequence, includes: Real-time acquisition of excavation surface elevation data of the foundation pit, and calculation of the remaining thickness of the current reserved soil layer; Compare the remaining thickness of the current reserved soil layer with the thickness of the first critical reserved soil layer. When the remaining thickness of the current reserved soil layer is equal to the thickness of the first critical reserved soil layer, an initial excavation stop command is generated, and the drilling and tensioning locking operations of the anti-buoyancy anchor rods in the first construction phase are triggered based on the initial excavation stop command. Obtain the locking status data of the anti-buoyancy anchor in the current construction stage. When the locking status data meets the preset stress activation conditions, extract the critical thickness value corresponding to the next subsequent construction stage from the second critical reserved soil layer thickness set, and use it as the target soil layer stripping boundary. Generate an excavation recovery command to guide the reserved soil layer to be stripped downwards to the target soil layer stripping boundary, and after reaching the target soil layer stripping boundary, generate a stage excavation stop command to trigger the execution of the anti-buoyancy anchor drilling and tensioning locking operations for the corresponding subsequent construction stage. According to the phase division sequence of the batch construction plan, the acquisition of the locking status data, the extraction of the target soil layer stripping boundary, and the triggering command of the excavation and locking operation are executed alternately and cyclically until the construction of anti-buoyancy anchors in all stages is completed and the reserved soil layer is stripped to the design bottom elevation, thus generating the complete collaborative construction sequence.

9. The method for determining the construction sequence of anti-buoyancy anchors based on the back pressure condition of reserved soil layers according to claim 8, characterized in that, The preset force activation conditions include: During the current construction phase, the measured strength of the grout of the anti-buoyancy anchor is greater than or equal to the preset anchor body design strength threshold, and the measured tension force of the anchor head of the anti-buoyancy anchor is greater than or equal to the tension locking threshold determined based on the single-strand design pull-out force, and the anchor locking operation is completed.

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