154 results about "Friction angle" patented technology

The invention relates to the field of geological exploration and geotechnical engineering, provides a rock mass dynamic mechanical parameter sensing method and system based on while-drilling parameters in order to dynamically obtain rock mass dynamic mechanical parameter characteristics in situ in real time in the drilling process, and provides a rock mass dynamic mechanical parameter sensing method and system based on while-drilling parameters by using multi-modal signals such as vibration, acoustic emission, torque and bit pressure through uniform characteristic engineering and multi-task learning. The instantaneous elastic modulus, the dynamic Poisson's ratio, the transient uniaxial compressive strength, the cohesive force and the internal friction angle can be synchronously and dynamically predicted in single drilling, and the limitation that only a single static parameter is estimated in a traditional method is broken through; a rock mass dynamic mechanical parameter acquisition model constructed on the basis of a multi-modal adaptive graph attention sequential network can effectively couple the physical proximity and the statistical association relationship of a sensor, and integrates expansion sequential convolution and a time perception Transform module, so that the characterization capability of emergencies (such as jamming / friction resistance) and long-term trends is considered on the premise of low time delay; therefore, the prediction accuracy is improved.

The invention relates to the field of peak friction angle calculation, in particular to a peak friction angle calculation method and system based on a static sounding experiment. The method comprises the steps that a static sounding experiment is conducted on a seabed, and the conical tip resistance, the side friction resistance, the seabed penetration depth, the seawater unit weight and the seawater depth of a seabed soil body are obtained; the conical tip resistance is corrected through the seawater depth, the seabed penetration depth and the seawater unit weight, and corrected conical tip resistance is obtained; calculating the friction resistance ratio of the opposite sides of the seabed soil body by using the corrected conical tip resistance and the side friction resistance; determining the soil layer type of the seabed soil body by utilizing the friction resistance ratio of the opposite sides and the corrected conical tip resistance; and calculating a peak friction angle estimated value based on the soil layer type. According to the method, the problem that the calculation of the peak friction angle is not accurate and scientific enough due to complex and changeable environments for estimating the peak friction angle in the prior art is solved, and the accuracy and scientificity of estimating the peak friction angle are greatly improved.

The invention discloses a method for predicting dynamic mechanical properties of a tough difficult-to-machine material based on milling. The method comprises the following steps: firstly, optimizing and solving a normal shear angle of an oblique angle cutting shear plane through an iterative method: (a) setting an initial value of the normal shear angle; (b) calculating an undeformed chip thickness, a cutter instantaneous invasion angle, a cutting force component and a normal friction angle based on the normal shear angle initial value; (c) updating a normal shear angle calculation value; (d) calculating the error between the initial value and the calculated value of the normal shear angle, if the error is not within the allowable range, repeating the steps (a)-(d) until the error is within the allowable range, and outputting the final calculated value as the optimized normal shear angle; then, parameters such as the optimized normal shear angle are substituted into a related equation containing fracture toughness, yield strength and viscous toughness to solve the fracture toughness Gc of a workpiece material at a tool nose in the milling process, the yield stress sigma Y in a shear plane and the viscous toughness Ga of chip slippage at a tool-chip contact interface.

The invention relates to the technical field of geotechnical engineering, in particular to a slip crack surface calculation method for a limited-width soil body in an active non-limit state. Comprising the following steps: step 1, determining a gradual exertion rule of a limited soil body internal friction angle and cohesion between the rigid gravity type retaining wall and an existing bedrock, a wall-soil external friction angle and wall-soil interface cohesion developing along with the displacement of the retaining wall, and establishing mathematical characterization of limited soil body non-limit state strength parameters developing along with the displacement of the retaining wall; step 2, establishing a relationship among the horizontal stress, the interlayer shear stress and the average vertical stress; step 3, establishing a balance equation of the rectangular area and the triangular area in the horizontal and vertical directions; 4, solving the slip crack surface inclination angle meeting the plastic upper limit theorem by adopting a numerical method; and 5, calculating the resultant force of the horizontal active soil pressure and the upsetting moment of the horizontal active soil pressure on the wall heel. The method provides a theoretical calculation basis for the design of the soil retaining structure under the working condition of the limited-width soil body.

This invention discloses a logging method for rapidly predicting collapse pressure in mudstone / shale formations, obtaining the formation depth h, formation pore fluid pressure gradient (FPG), formation lithology density (DEN), and formation clay content (V) of the target formation. sh The drilling fluid system used – the system influence coefficient ε and the clay influence coefficient ξ are determined based on the drilling fluid system – using the formula PCG=(0.1×DEN×g+FPG+ξ×V) sh The formation collapse pressure gradient PCG is calculated using the formula P(ε) / 2-1, where ε is the system influence coefficient of the drilling fluid system. c =0.01×PCG×h to calculate the formation collapse pressure P c It effectively overcomes the complex experimental process required by traditional methods to determine parameters such as the internal friction angle, cohesion, and Biot coefficient of the rock; it also overcomes the drawbacks of relying on personal experience for calculation, which involves many subjective factors, and avoids random interference that is difficult to quantify, program, and maintain stability.

The invention discloses a gravel pile composite foundation reinforcement effect evaluation method based on dynamic sounding. The method comprises the steps that a target area is selected; the dynamic penetration hammering number N, the dynamic penetration resistance F and the composite foundation bearing capacity data are obtained; the unconfined compressive strength Cu of soil between piles and the friction angle delta p in the piles are obtained; on the basis of the unconfined compressive strength Cu of the soil between the piles and the friction angle delta p in the pile body, the theoretical ultimate bearing capacity fef of the gravel pile is obtained; and based on the ultimate bearing capacity fef of the gravel pile theory, the bearing capacity fsp, d of the composite foundation is obtained. The method can establish an empirical relationship between the dynamic penetration hammering number or the dynamic penetration resistance and the bearing capacity of the composite foundation on a semi-infinite foundation, is used for evaluating the bearing capacity of the composite foundation, solves the problem of insufficient number of existing load plate tests, can be used for reinforcing effect evaluation and bearing capacity estimation of the gravel pile composite foundation, and also can be used for evaluating the bearing capacity of the composite foundation. And the method can also be widely applied to reinforcing effect evaluation and bearing capacity estimation of discrete material pile composite foundations such as sand piles.

The invention discloses a plane sliding type rock slope seismic stability analysis model considering rough structural surface strength degradation. Aiming at the important defect that an existing structural surface strength vibration degradation model exaggerates the influence degree of a vibration wear effect influence coefficient and a relative movement speed effect influence coefficient on structural surface strength vibration degradation, the model is improved on the basis of a Barton criterion; therefore, a novel plane sliding type rock slope seismic stability analysis model considering the shear strength degradation of the rough structural surface is provided; parameter sensitivity analysis is adopted to research the influence rule of the seismic wave peak acceleration, the structural plane basic friction angle and roughness coefficient and the structural plane shear strength degradation factor influence parameters m and P0 on the slope seismic stability, and beneficial reference can be provided for slope seismic stability analysis.

The invention relates to the technical field of tunnel monitoring, and discloses an advanced monitoring method and system based on an existing tunnel, and the method comprises the steps: obtaining a proper hole measurement position, depth and direction according to an analysis result; monitoring the displacement and stress change of the surrounding rock in real time, and analyzing according to the monitored surrounding rock data to obtain surrounding rock parameters such as elastic modulus, Poisson's ratio, friction angle and cohesive force of the surrounding rock; and the geological analysis system analyzes the unfavorable geologic body, and starts the advanced horizontal equipment for detection and verification. The system comprises an existing tunnel data acquisition module, an existing tunnel data calculation module and a geological forecast scheme module. Through the combination of the geological analysis system and the detection equipment, the state of the unfavorable geologic body can be more accurately judged, and the reliability of geological forecast is improved; early warning is given out in time, the construction scheme is adjusted, collapse, water burst and other disasters caused by unfavorable geologic bodies are effectively avoided, and construction safety is ensured.

The invention discloses a rock anisotropy index determination method based on indoor drilling and multi-parameter fusion, and relates to the technical field of geotechnical engineering. The method comprises the following steps: S1, carrying out digital drilling experiments on a rock sample in different directions to obtain drilling parameters of the rock in different directions; s2, feed force and torque force are calculated according to the drilling parameters, and the ratio of the feed force and the torque force is calibrated based on a linear fitting equation of the feed force and the torque force; s3, calculating internal friction angles of the rock in different drilling directions on the basis of the force balance analysis model; s4, calculating unit grinding energy of the rock in different drilling directions; and S5, calculating the comprehensive anisotropy index of the rock based on the variable coefficient. The rock anisotropy index can effectively quantify the directivity difference of the rock, can directly serve rock mass stability analysis, drilling scheme optimization and support design decision of an engineering site, and effectively connects indoor test and field engineering application.

The invention relates to the technical field of side slope safety, and provides a safety detection method and related equipment for an existing side slope, and the method comprises the steps: obtaining a plurality of side slope parameters of a target side slope; constructing a relational expression between the total strain of the target slope soil and the time, and calculating the total strain of the target slope soil based on all the slope parameters and the relational expression; the current anchor rod prestress of the target slope is calculated according to the total strain of the target slope soil body; the current soil cohesive force and the current internal friction angle of the target slope are obtained through inversion based on slope monitoring data; finally, the safety coefficient of the target slope is calculated according to the current anchor rod prestress, the soil cohesive force and the internal friction angle which are obtained through calculation. According to the method, the reliability of safety detection of the existing side slope can be improved while disturbance to the existing side slope is avoided.

The invention discloses a foundation pit construction method and system based on BIM, and relates to foundation pit monitoring. The foundation pit construction method comprises the steps that a foundation pit BIM model is established; parameter distribution is initialized, the elastic modulus, the cohesive force and the internal friction angle of the soil body unit and the contact rigidity parameter of the contact surface unit serve as parameters to be updated, and when n is equal to 1, initial prior distribution of the parameters to be updated is established according to engineering geological survey parameters; when ngt; when 1 is greater than 1, taking the posterior distribution of the parameters obtained in the (n-1) th excavation step as the prior distribution of the nth excavation step; for the nth excavation step, according to the parameter expected value in the prior distribution, iteratively calculating the soil pressure distribution and the support structure deformation through the foundation pit BIM model, and obtaining a foundation pit deformation predicted value of the nth excavation step; constructing a comprehensive likelihood function according to the accumulated foundation pit deformation measured values of the first excavation step to the nth excavation step, and obtaining posterior distribution of to-be-updated parameters through Bayesian updating; the deep foundation pit deformation monitoring precision is improved.

The invention discloses a rock dynamic pressure-torsion experimental device and method based on a Hopkinson pressure bar, and belongs to the technical field of rock mechanics dynamic testing. The device mainly comprises a split Hopkinson pressure bar system and a spiral conversion mechanism, wherein the spiral conversion mechanism consists of a spiral (4) and a screw sleeve (5) which are meshed with each other; the screw (4) is fixedly connected with the incident rod (2), the screw sleeve (5) is fixedly connected with one end of a cylindrical rock sample (6), and the other end of the sample is fixedly connected with the transmission rod (7). The core is that the lead angle of the screw pair is greater than the equivalent friction angle of the screw pair under the impact load, so that the screw pair is ensured to be non-self-locked; and the sample (6) is of a hollow thin-wall cylinder structure. The method comprises the following steps: driving the spiral (4) to advance by utilizing axial stress waves generated by the split Hopkinson pressure bar, and driving the hollow sample to rotate by the screw sleeve in a forced constraint state, so as to synchronously apply dynamic axial compression and torsional shear combined load.

The invention provides a mining ground fracture erosion prediction method, device and equipment under a freeze-thaw condition, and belongs to the field of geological research, and the method comprises the steps: obtaining the related data of a target mining ground fracture; calculating a frost heaving stress field and a mining-induced tensile stress field based on the related data, and performing superposition to obtain a total tensile stress field; when the total tensile stress field is greater than the tensile strength of the soil, calculating the coupling damage degree; based on the coupling damage degree, the effective cohesion and the effective internal friction angle of the soil are determined, and then the critical starting shear stress of the crack and the average flow velocity of the scouring critical state are determined; based on the critical starting shear stress and the average flow velocity, total energy consumed for erosion and collapse of the soil body in unit area is determined, and actual water flow power is calculated; and calculating the ratio of the total energy to the actual water flow power to obtain a physical index of the anti-erosion comprehensive capability of the soil so as to judge the erosion risk state of the soil crack. Therefore, space-time prediction and accurate early warning of the erosion risk can be realized.

The present invention relates to a method for calculating the anti-uplift stability coefficient taking into account the shear strength of the soil above the caisson blade foot, and the method comprises the following steps: (1) determining calculation parameters, which mainly include the thickness, density, internal friction angle, cohesion, ground overload, soil plug height in the well, and geometric dimensions of the caisson; (2) determining the type of the caisson according to the width and sinking depth of the caisson; (3) according to the determined different caisson types, substituting the calculation parameters into a calculation expression to calculate the anti-uplift stability coefficient of the caisson structure; the method for calculating the anti-uplift stability coefficient taking into account the shear strength of the soil above the caisson blade foot proposed by the present invention can quickly and accurately analyze the anti-uplift stability of the caisson in actual engineering, and provide theoretical support for design and construction.

This invention relates to a design method for reinforcing rock mass structures with small-diameter piles under post-load conditions in the field of slope protection. The method first obtains the inclination angle θ of the outward-dipping structural surface, the internal friction angle and cohesion c, the sliding mass weight γ, the sliding mass height H, the stress ratio n between the pile and the rock mass at the structural surface, the vertical load q applied to the upper part of the sliding mass after the construction of a single deeply embedded small-diameter anti-slide pile, the sliding mass width b, and the horizontal extension length l. Then, using these parameters, it calculates the initial axial force of the deeply embedded small-diameter anti-slide pile before sliding, the deflection angle of the deeply embedded small-diameter anti-slide pile when the anti-slide force is at its maximum, the minimum compressive stiffness of the small-diameter anti-slide pile, and the axial force and anchorage length of the deeply embedded small-diameter anti-slide pile caused by compression after minor deflection deformation at the structural surface. This invention saves resources compared to empirical design methods.

The utility model discloses a rock mass structural plane friction angle detection device which comprises a base and an upper cover, the upper cover is located above the base, a multi-dimensional force sensor is installed between the base and the upper cover, an anti-skid pad is installed at the bottom of the base, and the upper cover and the multi-dimensional force sensor are connected through a first fixing bolt. The base and the multi-dimensional force sensor are connected through a second fixing bolt. The device is simple in structure, small in size and convenient to carry and use.

The application discloses a plane sliding type rock slope seismic stability analysis model considering rough structure surface strength degradation. In view of the important deficiency of the current structure surface strength vibration degradation model, that is, exaggerating the influence degree of the vibration wear effect influence coefficient and the relative movement speed effect influence coefficient on the structure surface strength vibration degradation, the application improves the above model based on the Barton criterion, thereby proposing a new plane sliding type rock slope seismic stability analysis model considering rough structure surface shear strength degradation, and adopts parameter sensitivity analysis to study the influence law of the peak ground acceleration of the earthquake, the basic friction angle and the roughness coefficient of the structure surface, the influence parameter m of the structure surface shear strength degradation factor and P0 on the slope seismic stability, so as to provide beneficial reference for the slope seismic stability analysis.

The present invention discloses a method for determining the constant m in the Hoek-Brown criterion based on digital drill parameters. i The cutting force F is obtained by using the Hoek-Brown criterion and the relationship between the digital drill parameters. t With thrust F n The relationship curve of the drill bit rake angle α and the rock contact friction angle θ between the drill bit cutting surface and the end face are calculated; the friction angle between the compression zone and the intact rock #imgabs0# and the internal friction angle of the rock #imgabs1# are calculated to draw the cutting force F t About Thrust F n The relationship curve is obtained, the curve intercept b is obtained, and the constant m in the Hoek-Brown criterion is calculated. i ; Substitute θ and #imgabs2# intercept b into the equation of rock cohesion c to calculate cohesion c, and then calculate the rock uniaxial compressive strength UCS; Substitute the calculated constant m i The uniaxial compressive strength UCS is substituted into the H-B criterion to calculate the triaxial compressive strength TCS of the rock. i The accuracy, scientificity and simplicity of the method cannot be guaranteed.

The invention discloses a shear test device and method for a soil body in a drill hole, relates to the technical field of soil body shear strength tests, and aims to solve the problems of sampling disturbance, narrow application range, low test efficiency and the like in a traditional soil body shear strength test. The test device comprises a connecting rod, three groups of round rollers, a shearing assembly, a pressurizing assembly and a data acquisition assembly. The shearing assembly drives a shearing plate to be inserted into a soil body through a hydraulic jack for shearing, the pressurizing assembly applies horizontal radial pressure through an air bag to simulate different stress conditions, and the data collecting assembly records bending moment, rotating angle and pressure changes in real time. The test method comprises the following steps: drilling to a test depth, then installing the test device, pressing the shear plate, applying pressure, carrying out a shear test, and obtaining the friction angle and cohesive force in the soil body through data analysis. The in-situ test is directly carried out in the drill hole, sampling disturbance is avoided, the device is suitable for stratums difficult to sample such as sandy soil and fully-strongly weathered bedrock, and the device can go deep into different depths to research the mechanical properties of deep soil bodies.

The present application provides a dangerous rock mass risk source area identification method and device, comprising: obtaining a dangerous rock mass image, generating dangerous rock mass point cloud data, determining the occurrence information, trace length data and structure surface spacing of the dangerous rock mass structure surface; dividing the dangerous rock mass into multiple sub-regions, and determining the control type structure surface of each sub-region; determining the shear strength of each control type structure surface based on each topographic parameter, wall surface strength, roughness coefficient, normal stress and basic friction angle; determining the uniaxial compressive strength of the rock in each sub-region; determining the radius and normal density of the dominant structure surface group in each sub-region, and determining the integrity coefficient of each sub-region; determining the dangerous rock sensitivity index of each sub-region based on the maximum trace length, the minimum structure surface spacing, the shear strength, the uniaxial compressive strength and the integrity coefficient in each sub-region, and determining the risk source area of the dangerous rock mass based on the dangerous rock sensitivity index of each sub-region. The present application improves the accuracy of the identification result of the dangerous rock mass risk source area.

The invention discloses a composite foundation design method based on the influence of soil around a pile on the strength of a gravel pile and application, and the design method comprises the steps that each soil layer is subdivided, and the relation between the undrained shear strength value and the depth of each subdivided soil layer is recorded; performing statistics on the data by adopting a mean square error method according to the dynamic sounding hammering number data of the gravel pile, so as to obtain the dynamic sounding hammering number N of each subdivided soil layer; counting the statistical relationship between the undrained shear strength value of each soil layer and the dynamic sounding hammering number N of the gravel pile, and evaluating the compactness of the soil layer; crushing gravel with different compactness through a large direct shear test or a large triaxial test, and establishing a relationship between the different compactness of the gravel and an internal friction angle; establishing an empirical relationship between the strength of the soil around the pile and the value of the internal friction angle of the gravel; and composite foundation parameters are selected according to the subdivided soil layer parameters. The internal friction angle parameter of the gravel pile can be obtained in a layered mode according to the distribution of the soil layer, and the actual mechanical property can be better reflected.

The invention discloses a small-clear-distance tunnel backward shield excavation face support pressure determining method which comprises the steps that soil parameters are collected, data comprise soil cohesion and internal friction angle data, geometric parameters of tunnel diameter, burial depth and clear distance are recorded, numerical model construction is conducted through the collected parameters, numerical models of a tunnel and surrounding soil are constructed, and the tunnel backward shield excavation face support pressure is determined. Meanwhile, analyzing the stress state, stratum type and address characteristic data of the soil body by utilizing a numerical model, simulating an excavation process after data analysis is completed, simulating a propelling process of a shield tunneling machine, gradually removing the soil body, applying corresponding support pressure, and recording the support pressure, soil body deformation and displacement data at different time points; the method is based on numerical simulation and machine learning methods, the multi-factor coupling influence is systematically considered, blindness of an experience method is avoided, the established relational expression covers a wide parameter change range, and the method can be suitable for small-clear-distance projects with different geological conditions and tunnel design parameters.

The application discloses a rock stratum horizontal stress measuring method based on a digital drilling technology, and steps of the method comprise the following steps: step 1, a rock digital drilling test is carried out by using a digital drilling device, a relationship between a cutting stress and a feed force is obtained, and then a contact friction angle θ between a cutting surface of a diamond blade and a compression crushing zone is calculated; step 2, the contact friction angle θ obtained in step 1 is used to solve an internal friction angle φ of the rock; and step 3, α, θ, φ', φ obtained in steps 1 and 2 and a rock cohesion c measured are used to solve a confining pressure P of surrounding rock f The method has the advantages of low cost, simple calculation and high precision.

The application discloses a method for calculating the inner friction coefficient of a three-dimensional natural fracture wall surface in space, which comprises the following steps: determining the strike of the natural fracture and the included angle between the natural fracture and the horizontal plane; determining the horizontal maximum principal stress direction; determining the in-situ three-directional principal stress; determining the poroelastic constant and the formation fluid pressure; determining the natural fracture approaching angle; determining the unit normal vector of the three-dimensional natural fracture surface; determining the normal stress and the shear stress of the three-dimensional natural fracture surface; determining the effective stress; and determining the inner friction coefficient of the spatial natural fracture. The application considers that the natural fracture in the underground reservoir is spatially distributed, and is kept in static mechanical balance under the joint action of the in-situ stress field and the formation fluid. The application obtains the calculation method of the inner friction angle of the three-dimensional natural fracture in space in the rock mass containing the natural fracture medium by using a mathematical method, fills the blank of the method for obtaining the inner friction coefficient of the three-dimensional natural fracture in space, and can show the influence of the strike and the dip angle of the natural fracture on the inner friction coefficient of the fracture surface.

This invention relates to the field of slope stability analysis technology, and in particular to a method, device, and storage medium for measuring the stability of unsaturated soil slopes. The unsaturated soil slope stability measurement method of this invention is based on the soil-water characteristic curve of unsaturated soil and uses the finite element method to solve the Richards equation to obtain the transient seepage field distribution of the unsaturated soil slope. This method is more consistent with reality than the seepage field assumed by empirical formulas in the past. While the SMP criterion proposed by Songgang-Zhongjing considers the influence of intermediate principal stress, the SMP criterion is only suitable for cohesive soil failure criteria. Therefore, this invention modifies the SMP criterion by considering the influence of cohesion, friction angle, and matrix suction, making it applicable to unsaturated cohesive soil slopes. Based on the calculation of the slope's self-weight stress, and using a modified SMP material model, we conduct stability analysis of unsaturated soil slopes using the strength reduction method, considering the influence of the intermediate principal stress of the soil, resulting in more reasonable results.

The present application belongs to the technical field of oil and gas field exploration and development, and discloses a method, device and method for establishing a strike-slip fault activity prediction model. The method for establishing the prediction model comprises: extracting the horizontal maximum principal stress, the minimum horizontal principal stress and the vertical stress in a present-day stress model based on a fracture-vug three-dimensional carving model; calculating a normal stress model and a shear stress model from the horizontal maximum principal stress, the minimum horizontal principal stress and the vertical stress; calculating a criterion internal friction angle model from the normal stress model, the shear stress model and a roughness model; and subtracting the data in the criterion internal friction angle model from the data in the shear stress model to obtain the strike-slip fault activity prediction model. The present application can more accurately establish a complex strike-slip fault activity prediction model that meets the needs of exploration and development production.

The application discloses a kind of based on deformation monitoring data's slope instability evaluation method, it is related to slope engineering monitoring data analysis field, method is: obtaining the related data such as topography, stratum, foundation monitoring point in the range around slope;According to the distribution of deformation foundation monitoring point and deformation fitting potential sliding surface;Establish three-dimensional finite element model of slope, and determine the cohesion and internal friction angle of potential sliding surface by inversion;The inversion cohesion and internal friction angle of sliding surface are calculated by strength reduction method, and the safety factor of slope is determined;According to the horizontal displacement direction of foundation monitoring point and potential unstable slope body, the sliding direction of slope is determined;Finally, the slope, potential unstable slope body and its sliding direction are displayed through visual platform, and the volume of potential unstable slope body and the safety factor of slope are displayed by text.The application determines the three-dimensional sliding surface of slope by surface fitting, and then calculates the safety factor of slope by parameter inversion and strength reduction method, realizes the early warning description of slope instability form including instability volume, direction and other characteristics.

The invention provides a tunnel surrounding rock brittleness-ductility transformation critical confining pressure prediction method and device under a complex crustal stress field, and relates to the technical field of rock mechanics analysis. The method comprises the following steps: by introducing parameters representing rock strength anisotropy, correcting a Mohr-Coulomb strength criterion, and constructing a strength prediction model; dividing stress areas according to the ground stress level, and establishing a corresponding joint surface friction strength model for each divided stress area in combination with joint surface stress state analysis; converting the rock strength from anisotropy to isotropy as a critical condition of brittle-ductile conversion, and combining the strength prediction model with the joint surface friction strength model of the corresponding stress area to obtain a critical confining pressure theoretical model; in the critical confining pressure theoretical model, the static internal friction angle is replaced with a rock instantaneous internal friction angle changing along with the confining pressure, and a critical confining pressure prediction model is obtained; and inputting the mechanical parameters of the surrounding rock of the target tunnel into the critical confining pressure prediction model, and calculating to obtain a critical confining pressure value.

The application discloses a method and device for determining an anti-overturning coefficient of a pit-in-pit double-row-pile supporting structure, and relates to the technical field of foundation pit engineering. The method comprises the following steps: determining a trapezoidal cross-section earth covering rupture angle and an earth covering rupture surface of a trapezoidal cross-section earth covering between a pit-in-pit structure and a double-row-pile supporting structure according to an internal friction angle of soil; determining an anti-sliding force of soil above the earth covering rupture surface according to the size of the trapezoidal cross-section earth covering between the pit-in-pit structure and the double-row-pile supporting structure, the trapezoidal cross-section earth covering rupture angle and the shear strength of the soil layer; and determining the anti-overturning coefficient according to the anti-sliding force of the soil above the earth covering rupture surface, the earth pressure outside and inside the foundation pit, the distance between the anti-sliding force action point and the bottom of the double-row-pile supporting structure and the self-weight of the double-row-pile and the soil between the piles. The method solves the problem that the embedded depth of the supporting structure is generally designed according to experience and is too conservative in the prior art, and the embedded depth of the supporting structure is too deep, which greatly increases the construction cost.

The invention belongs to the field of tunnel engineering and rock-soil mechanics, and discloses a fault fracture zone excavation face limit support force calculation method based on local instability, through a fault fracture zone tunnel excavation simulation test, an excavation face local instability form is obtained, an improved cone instability model is provided, and a fault fracture zone excavation face limit support force calculation method is provided. The problem that the lateral soil pressure coefficient is difficult to accurately estimate is solved, and calculation is simplified; carrying out mechanical analysis based on symmetry of the rotating body, and establishing a calculation method for the ultimate supporting force of the tunnel excavation face in the fault area; and the accuracy is verified by comparing with the existing test result, and the influence of key factors such as cohesive force, internal friction angle and soil weight is analyzed.