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.     

Load Calculation Method of Shallow Tunnel under Unsymmetrical Loadings in Broken Surrounding Rock

Tunnel portal section mostly faces unfavorable geologic and topographical conditions, such as broken surrounding rock, shallow and unsymmetrical loadings. The current Chinese code for design of road tunnel provides the load calculation method of tunnel under unsymmetrical. However, according to the mechanic and deformation characteristics of the tunnel lining on site, the assumption is not suitable for the shallow tunnel under unsymmetrical loadings in broken surrounding rock. Therefore, through engineering case analysis and results of three-dimensional numerical analysis, the failure mechanism of shallow tunnel under unsymmetrical loadings in broken surrounding rock is presented firstly, that is, deep buried side broken surrounding rocks slump down after excavation and squeeze the lining, which makes the lining deform outward and bear passive earth pressure. Through the failure mechanism, the surrounding rock mainly includes slumping area and passive area. Then the corresponding formulas are deduced based on limit equilibrium theory. Finally, a case study is adopted to verify the feasibility of the new method. It is show that the new method is more reasonable than the method of current code.     

Field test and deformation controlling for single tunneling lining stability

The construction process of anchor,fiber concrete and its mechanical principle of interaction with surrounding rocks is studied by field tests from the view of researching stability of single layer tunneling lining. The mechanical properties of single layer lining in the practical application of tunnel engineering are measured. On the basis of this study,the mechanism of single layer tunnel lining is discussed,which is finally applied to the engineering practice,formatting a set of theoretical support for the design method of single layer lining. Studies found that close effect between fiber reinforced concrete and rock is well,which shows that the single layer lining design method to ensure quality and safety proposed in this paper is feasible,and construction characteristic of retaining structure is reliable. The method can be widely applied in engineering practice,and has remarkable economic benefit and social benefit.     

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.     

A POWER FLOW IN INFINITE VISCOELASTIC CYLINDRICAL SHELLS

In this paper, a solution of propagation wave in an. unconstrained damping viscoelastic cylindrical shells of infinte length under forced vibration is derived by Fourier integral transform techniques. The power flow transmitted along it is analysed. The power flow in an elastic cylindrical shell and that in a viscoelastic shell are compared. The effects of vibration reduction in two viscoelastic shells with different thickness are compared. The results provide a reference for designer in structural vibration reduction.     

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。     

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.     

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.     

Calculation of Crack Space and Crack Width of Tunnel Lining Based on Elastic Foundation Curved Beam Model

Based on the elastic foundation beam,the control differential equation of tunnel lining is worked out,according to the theory of Saint-Venant,the predominance equation about the center angle to the crack space is established, then the crack space of tunnel lining under the loads can be worked out and according to the crack space,the crack width can be calculated.     

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.     

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.     

A THEORETICAL BASIS OF EQUATION OF CORRELATION BETWEEN STRENGTH AND ELASTIC MODULUS OF CONCRETE

The equation of correlation between compressive strength and elastic modulus of concrete is derived on the basis of modified Burger's model. The result shows that the derived equation is similar to the empirical equation of correlation between compressive strength and elastic moulus of concrete. So this empirical equation is confirmed by rheology theory of concrete.     

Rock classification method for tunnel boring machine

In order to study the geological factors which impact penetrating rate of tunnel boring machine (TBM), this paper uses three-dimensional discrete element model 3DEC to build simulated models on rock fragment by TBM cutter. It analyzes the influence of different geological conditions on TBM penetrating rate and classified the surrounding rock in west route of south-to-north transfer project according to the drill ability of TBM in surrounding rock. The results show that the penetrating rate of TBM is closely related to the mechanical properties of rock and joint conditions in rock mass. In certain extent, TBM penetrating rate will be increased with the decrease of rock strength or closely distributed joints. TBM penetrating rate will be decreased with the increase of rock strength or rarely distributed joint. Another result is that the surrounding rock by TBM penetrating can be divided into three classes based on the drill ability of TBM in surrounding rock, which can guide the TBM penetrating.     

Damage Constitutive Equation and Experiment of Layered Rock

The microcosmical study on many speciments of sedimentary rock by SEM and petrography theory show that rock is formed of microcrystalline and micropore with all kinds of forms.Therefrom the microstructure model of rock is established.Further the three dimensional nonlinear damage constitutive equation and damage evolution equation of layered rock including respective process of damage evolution,mechanical parameter,effective stresses,and unequal biaxial stress in different rocks are derived.The results of the experiment indicate that the theoretical curve is fairly close to the experimental curve.     

Analysis on the influence from rectangle cavity behind the lining to the primary support of tunnel

In process of the tunnel construction throw New Austrian Tunnelling Method, the result of smoothwall blasting to rock tunnel is not good, there are more and more cavities produced behind the lining. On the basis of engineering project, this paper makes the three-dimensional elastic-plastic analysis throw numerical simulation, discusses the stress-strain behavior of primary support when there is a different size of rectangle cavity behind the lining. In addition the safety factor of tunnel is calculated with cavity based on the strength reduction finit element method. This factor is compared with the factor of health tunnel. The stability of tunnel structure system is estimated through the linear regression analysis between stress of lining and safety factor.     

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.     

THE THEORETICAL ANALYSIS OF RADIAL DISPLACEMENT AND COMPATIBLE CONDITIONS OF BOTTOM PLATE OF PISTON FRAME IN LARGE CONTAINER

Taking aecount of shear action between the piston truss the bottom plate, this paper assumes the bottom plate to be a part-ring and supposes that the shear distribution follows the power series law, making the problem to be a problem of mixed boundary condition of part plate. In the paper, the solution of this elastic plane problem is derived. The general expressions of radial displacement of bottom plate are given. The compatible conditions both at the nodes of the lower chord of the truss and at the central cylindrical shell are analyzed.     

Coupled Vibration of Saturated Fractional Derivative Type Viscoelastic Soil of a Circular Tunnel with Partially Sealed Shell Lining

Considering the compression of medium and fluid, coupled vibration of saturated fractional derivative type viscoelastic soil and a circular tunnel with partially sealed shell lining in the frequency domain is investigated according to theories of Biot and elastic shell. The stress and displacement constitutive behavior of the soil skeleton is described by fractional derivative model which reflects the rheological properties of the medium while regarding soil as a liquid-solid saturated porous medium. The expressions of displacement, stress and pore water pressure are obtained while the inner boundary of circular tunnel is subjected to axially symmetric radial traction and axially symmetric fluid pressure respectively by introducing a partially permeable boundary condition. With the parameter analysis, it is revealed that the order of fractional derivative model on the responses for the system subjected to the symmetric radial traction is much greater than that of the system under the axially symmetric fluid pressure. And resonance phenomenon occurs obviously. Nevertheless the system responses do not have remarkable resonance phenomenon under axially symmetric fluid pressure.     

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.