Influence of Neutral Principal Stress on the Elastic-Plastic Solution of Expansion of Cylinder Cavities

In the elastic-plastic solution of expansion of cylinder cavities based on Tresca strength criterion and Mohr-Coulomb strength criterion, the influence of neutral principal stress is not considered. In this paper the influence of neutral principal stress on elastic-plastic solution of expansion of cylinder cavities is considered. The calculation shows that the radius and displacement of plastic zone will reduce when the neutral principal stress is considered. The conclusions are of practical significance for geotechnical engineering.     

Testing and modeling studies on creep characters of supports for tunnel using nonlinear constitutive model

Creep characters of tunnel supports structure is analyzed according to triaxial creep test of concrete specimen of deep tunnel supports structure adopting MTS815 hydraulic servo system. The creep parameters of nonlinear creep model are presented based oncreep curve. The finite element numerical model has been established considering tunnel construction process, creep characters of surrounding rock and support structure. The displacement characteristics, the effective stress and the maximum shear stress in different position in primary support and second lining are obtained through creep characters analysis of surrounding rock and supports structure. The features of displacement and stress dependent time of tunnel supports has visible difference comparing with discard creep effect and calculation displacement and practical monitoring results is basic concordance. The creep characters of surrounding rock and tunnel supports should be considered for deep tunnel.     

Finite Element Analysis on Interaction of Neighboring Highway Tunnels under Construction

Recently, the construction of neighboring highway tunnels with small interval gets more and more in China. The construction of such tunnels proceeds usually by excavating one after another. The second tunnel is constructed with the surrounding rock disturbed by the first one. And the construction of second tunnel also has effect on the first excavated one. For revealing the interaction laws of such tunnel construction in combination with the engineering practice of Lanfeng tunnel at Jinshan Road in Chongqing, The FE numerical simulation analysis was used to study the characters of surrounding rock deformation, stress field, and plastic zone of the tunnel. From this analysis, it clearly shows that the excavation of second tunnel has significant influence on the first one. This study provides a scientific basis for design and excavation of neighboring highway tunnels.     

Slip Line Field of Plane Strain Problem Obeying the GeneralizedHoek Brown Failure Criterion

According to the characteristics of plane strain problem of elastic and plastic mechanics, the bi parametric expressions were derived for stress components satisfying the generalized Hoek Brown failure criterion. Being substituted into the static equilibrium partial differential equations, a group of first order hyperbolic pseudo linear differential equation partial differential equations was obtained. Utilizing the determinant method and proper variable transformation, the characteristic direction and the differential relation equation for the stress partial differential equations were acquired. The characteristic direction indicted that in plastic zone obliquely intersecting conjugate shear slip surfaces formed two families of non orthogonal slip lines, in which conjugate angle varied with the limit stress state and the material physical properties of Hoek Brown rock mass. Since the principal direction of the maximum principal stress was circumferential in perfectly elasto plastic surrounding rock of the plastic zone around a circular opening suffering the symmetric initial stress field, the angle between the tangential direction of slip line with the principal direction of the maximum principal stress was the function of the minimum principal stress(i.e. the radial stress). Combined with the analytical solution, the polar coordinate differential equation was derived and furthermore, the polar coordinate curve equation for the slip line was obtained.     

Analysis of Seismic Dynamic Responses of Tunnel throughFault Zone in High Earthquake Intensity Area

Based on dynamic time history analysis, dynamic response behavior of an un supported tunnel through fault zone which was simulated by interface and solid elements was studied under uniform input earthquake wave excitation. The analyses of response behaviors, including displacement difference, acceleration magnification, and plastic zones and so on, were carried out when earthquake wave excitation was input along transverse, longitudinal and vertical of tunnel respectively. The results show that simulation method for fault zone is effective; the earthquake causes obvious displacement difference at fault zone and surrounding rock contacting part. The maximal displacement difference reaches to 51.8mm under transverse uniform input earthquake wave excitation. And the displacement difference under vertical and longitudinal is only 44.3% and 23.1% of the transverse value, respectively; the acceleration magnification in fault zone is significantly greater than that in surrounding rock. Shear failure zone appears at the fault zone and surrounding rock contacting part, and it is especially prominent under input longitudinal earthquake wave excitation. It is proposed that fault zone has significantly influence on the dynamic performance of tunnel. The fault zone and the transitional zones are the control zones of seismic design when tunnel passes through fault zone, thus, the study on the anti seismic measures should be further strengthened.     

Simulation Analysis of Spatial Distribution of Roadway′s Surrounding Rock Stress

To get the spatial distribution characteristic of roadway's surrounding rock stress, circular section roadway was taken as a case study. The solution of stress was got by using complex function method, and roadway's surrounding rock stress field was analysed after the solution of mapping space was transformed into the solution of roadway space. As a result, the visual diagram of stress field distribution of roadway's surrounding rock was obtained, which could describe intuitively stress distribution of roadway's surrounding rock at any position. Considering the influence of different radius and side pressure coefficients on surrounding rock stress field, the following conclusions have been obtainded: the peak value and direction of circular roadway's surrounding rock stress has nothing to do with the radius; when side pressure coefficient is less than 1/3,the roof can produce tensile stress; when side pressure coefficient is more than 3, the surrounding rock in two sides can produce tensile stress. And the change rule of hoop stress, radial stress, shear stress and the maximum and minimum of stress have also been generated.     

Study on the Terzaghi Ultimate Bearing Capacity of Foundation Based on the Unified Strength Theory

The ultimate bearing capacity of foundation based on Mohr-Coulomb strength criterion did not analyze effect of intermediate principal stress on yield and failure of soil so that the disparity between results obtained using Mohr-Coulomb strength criterion and those from experimental data are produced .In the paper , The ultimate bearing capacity of foundation based on unified strength theory is established and a unified solutions are obtained. The corresponding solutions of different materials can be got from it .The unified solution can not only be used to fit the properties of the materials with different tension-pressure strength but also those with equal tension-pressure strength, Results show that ones make full use of the properties of the materials so as to reduce supports,which is of important significance for engineering.     

Study of Tunnel Supporting Effect

Based on the elastic theory, an analysis can be made on stress and plastic deformation under tunnel excavation and shotcrete support.FLAC 3D can be used to simulate the mechanical behavior of excavation and support, getting the deformation of surrounding rock stress and plastic without support and shotcrete. The results show that, the prestress applied on the anchor equals to the supporting force when the tunnel plastic zone disappears. This support improves the self bearing capacity of surrounding rock, effectively suppresses the expansion of the plastic zone after the tunnel excavation, and prevents further damage to the tunnel surrounding rock.     

Elasto-plastic analysis on surrounding rock of roadways based on seepage, strain softening and dilatancy

According to seepage body force, strain softening and rupture expansion of rock mass, elastic-plastic mechanics theory, distribution laws of stress and displacement of surrounding rock in seepage field are derived, and relationships between different zonation range of the surrounding rocks, pore water pressure, strain softening and rupture expansion are established. The results show that the pore water pressure and rupture expansion rock mass have a more obvious impact on the surrounding rock rupture area than the plastic zone. Both the plastic zone and the rupture area are larger when the seepage field is considered. The impact of strain softening on both the plastic zone and the rupture zone of surrounding rock is very significant, and both seepage and strain softening rupture expansion affect deformation of surrounding rock of roadways obviously. It provides certain reference values for the roadway support engineering in seepage field.     

Earthquake Response Properties of the Support Structure of Large Cross Section Tunnel

The response properties of displacement and stress of tunnel support structure are discussed in detail under the action of horizontal earthquake acceleration(Ya),longitudinal earthquake acceleration(Za) and horizontal-longitudinal earthquake acceleration(YZa).This discussion is based on an analysis of the surrounding rock-support structure-earthquake interaction,adoption of an ADINA nonlinear finite element and construction mechanics,and transient dynamic time domain analysis of a large cross section tunnel.Results of analysis show that:(1) Horizontal earthquake acceleration has important influence on horizontal displacement,maximum principal stress,acceleration and velocity.(2) Longitudinal earthquake acceleration has important influence on longitudinal displacement,effective stress,maximum and minimum principal stress,maximum shear stress,acceleration and velocity.(3) When Ya=0.191g and 0.440g or Za=0.141g and their combined action,the initial support of tunnel would be damaged and the local lining would have partial damage.(4) When Ya=0.440g or Za=0.326g and their combined action,the lining of tunnel would be damaged.(5) When Ya=0.880g or l Za=0.652g,the support structure of tunnel would have severe damage.     

The Method on Surrounding Rock Classification for Highway Tunnel Construction Period in The Karst Areas of South China

Through the statistical analysis of analyzed the particularity of karst surrounding rock classification, finally obtained the rock classification index system of south karst highway tunnel construction based on rock strength, rock complete coefficient ,groundwater state, structural plane state the structural plane strike to tunnel influence, karst development to tunnel influence. And the model is applied to tianshengqiao tunnel and guanshang 2 tunnel with the example verification, and compared with the classification results and experts judgment to get the accuracy is 93.3%.     

Elastic-Plastic Analysis of Surrounding Rocks Considering Material Dilatancy and Softening

Based on stress dropping model, an elastoplastic-brittle model was established by using a softening threshold value to model the features of the geotechnical materials. According to the Mohr-Coulomb criterion, the radius of the rupture and plastic zone, the displacement and stress expressions of surrounding rock were obtained with the consideration of the strain-softening and dilatancy of geotechnical materials. Furthermore, the model was verified by case study and the influence of strain-softening, dilatancy and elastic modulus deterioration on calculation result were presented.     

Elasto- plastic Analysis of Pressure Circular Tunnel with Liner

According to the strain nonlinear softening constitutive model having inflexion point after peak stress of practical rock and considering intermediate principal stress, the plastic zone of circular cavern with liner under the condition of uniform pressure is analyzed. The elasto - plastic boundaries both for the lining and surrounding rock are discussed. The stress distribution law is different due to the different position of elastic - plastic boundary. Based on this, different stress formulas are gained. The critical pressure caused by excavation of cavern leading to the yield zone and that caused by inner pressure leading to the yield of the liner and surrounding rock is introduced.     

Analysis on Interfacial Stress Between Surrounding Rock and Shotcrete Lining

According to the characteristics of interfacial stress between surrounding rock and shotcrete support, mechanical model of composite curved beame for support system of tunnel surrounding rock and shotcrete lining was established, considering the interfacial deformation coordination and the effects of bearing arch of surrounding rock. Then from static equilibrium of two differential elements, the differential equations for the radial displacement of composite curved beam were obtained. All analytic formulas of both interfacial stress and internal forces between surrounding rock and shotcrete lining by arbitrary distribution load were derived. And thus the mechanical condition of interface zone and the stress concentration position were obtained, which is convenient to assess the stability of surrounding rock and predict the safety. Finally, the analysis of tunnel project excavated by bench method showed that shotcrete lining made the formation of compressive stress zone in surrounding rock by transferring stress from the interface between surrounding rock and shotcrete, which is beneficial to improve the stability of surrounding rock.     

Analysis of the Lateral Deformation of Structural Soft Dredger Fill with True Triaxial Test

In order to study the mechanical properties and structural properties of soft dredger fill under lateral deformation. Based on true triaxial and WF stress path apparatus, lateral unloading undrained tests were carried out. The results derived from true triaxial test, WF stress path test and routine triaxial shear test were analyzed. The contrastive conclusions are as follows: The stress-strain curve of true triaxial unloading test shows a softening behavior, which is different from the hardening behavior for that of conventional triaxial shear test. With the increase of initial confined pressure, the dilatancy of soil transfers from shrinkage to expansion. The structural yield stress of the unloading soil with true triaxial test method is dramatically larger than that with the latter two tests due to the effect of intermediate principal, which exhibits a nonlinear growth as the coefficient of intermediate principal bd stress jumps. The shear strength indexes of unloading soil with true triaxial test is larger than that with WF stress path test. Compared with the results of routine triaxial test, the internal friction angle of true triaxial test is bigger while the cohesion is smaller.     

Neural Network Model for Predicting the Transformation Tendency of the Stress on the Surrounding Rocks of Tunnel

The stress on the surrounding rocks affects severely the stability of tunnel. To estimate the stability of tunnel needs the transformation tendency of the stress on the surrounding rocks. After the transformation tendency of the stress on the surrounding rocks and the factors affected it are analyzed, the neural network model for predicting the stress on the surrounding rocks is created. The model is applied successfully to predict the change of the stress of the Guanyingyan tunnel in the Qiwan expressway, which proves that it is feasible to predict the stress on the surrounding rocks with the neural network model. The method is convenient and correct.     

Study on strain localization and progressive failureof surrounding rock under high pressure environment

This paper uses the Mohr-Coulomb criterion with tension cut-off strain-softening model and the large-strain calculation method to study the localized deformation and progressive failure.It investigates the process of stain localization appearing,growing and sample failure,and uses the physical and numerical simulation to explore the relationship between strain localization and progressive failure of surrounding rock.The results show that the soften character of rock sample is caused by stain localization.The breach point of progressive failure is founded based on the distribution law of plastic zones and soften strips.The key causes of the tunnel convergence deformation after opening are the plastic extrusion and the elastic deformation of rock yield units caused by stress release.     

直墙拱形巷道围岩应力场分析

为得出直墙拱形巷道围岩应力分布规律,应用复变函数弹性理论推导了直墙拱形巷道围岩应力分布的解析表达式。对直墙拱形巷道边界的围岩应力和巷道水平线方向的围岩应力分布规律进行分析,并考虑直墙拱形巷道断面高宽比和侧压系数对其影响规律。研究表明：在不同巷道断面高宽比、侧压系数下,直墙拱形巷道围岩应力集中区域主要集中在直墙底部底角处、拱形顶板中点附近和底板中部3个位置。不同巷道断面高宽比下,直墙拱形巷道沿水平线的应力分布规律基本相同。侧压系数大于1时,采用巷道断面高宽比小于1较有利于巷道稳定;侧压系数小于等于1时,采用巷道断面高宽比大于1较有利于巷道稳定。     

Dynamic Prediction Analysis of Surrounding Rocks Stability for Non-symmetric Double-Arch Highway Tunnel

During the construction of non-symmetric double-arch rock highway tunnel, the complicated geological condition may affect the safety of the constructor and the engineering quality. In this paper, two treatment methods are put forward. At first, the site monitoring of surrounding rock displacement must be carried out, then, BP neural network is applied in predicting the displacement of surrounding rock based on the learning sample of measured value, so the stability of surrounding rocks may be analyzed and forecasted. During the analysis of BP neural network, the effects of joint and fracture of surrounding rock on displacement can be comprehensively considered, comparing the predicted values of displacement with those by FEM. The results show that not only the predicted error of BP neural network is relative small, but the predicted values of surrounding rock displacement are close to measured ones. So, the predicted values of BP neural network are reliable and may guide the engineering construction in site.     

Elastic-plastic Solution of Expansion of Spherical Cavities under 3D Loading

In elastic-plastic solution of expansion of spherical cavities, based on Mohr-Coulomb strength criterion, the effect of intermediate principal stress on yield and failure of soil is not analyzed. Therefore, there is disparity between results obtained by Mohr-Coulomb strength criterion and those obtained from experimental data. In this paper, the elastic-plastic solution of expansion of spherical cavities, based on unified strength theory is established and unified solutions are obtained. The corresponding solutions of different materials can be obtained. The unified solution cannot only be used to fit the properties of the materials with different tension-pressure strength, but also those with equal tension-pressure strength. The results show that by this solution, full use of the properties of the materials can be attained to reduce supports, which is of important significance for engineering