Application Of Loess Anisotropy And Tensile Constitutive Relation In Tunnel Engineering

Measure the loess of Wangjiagou tunnel on the horizontal direction and vertical direction of shear strength anisotropy from Yuzhong county,Lanzhou city,through indoor strain controlled triaxial apparatus.Using the method of UP to measure the tensile strength of anisotropy on the horizontal and vertical direction.Measure the shear and tensile strength of reshape loess in under the different dry density and water content Lanzhou Jiuzhou. Measure the shear and tensile strength of remolded loess in Wangjiagou tunnel and Beiershilipu tunnel. Detailed comparison and analysis the anisotropy of shear and tensile strength.Study water content, dry density, cohesive force, internal friction angle,void ratio and saturation effect on the tensile strength of loess.Discuss water content and dry density,cohesive force and angle of internal friction, void ratio and saturation under the action of the dual factors such as joint effect on the tensile strength of loess,through TableCuver3 D three-dimensional data processing software.Discuss the applicability of the traditional method for calculating the UP method to measure tensile strength of loess,based on the method of UP to measure the tensile strength of soil and analysis the sample failure mode for mechanics mechanism.In view of the characteristics of the loess collapsibility,analyzing the reasons of the easy collapse accidents in loess tunnels during excavation process,and explore the loess tensile strength’s application in the tunnel collapse accidents.The results showed that unconfined compressive strength,tensile strength and shear strength on the vertical direction were higher than horizontal direction,and the loess anisotropy model was simplify as elliptical.The loess’ s maximum deviation stress ratio of vertical and horizontal direction was bigger under low confining pressure,reaching to 1.35,and smaller under the high confining pressure,only 1.03,indicating loess anisotropy had greater influence and the deviation stress and strain relations of the loess showed the strain softening at low confining pressure,and It was strain hardening rule at high confining pressure and the horizontal plastic was stronger than the vertical.the loess samples shear failure process would be divided into the linear elastic stage,elastic-plastic stress peak stage and plastic stage,if we modify the traditional E-P model,to get a model suitable for a peak strain softening.The loess could be divided into a strong hardening, weak hardening,weak softening,softening,strong softening six classes in accordance with the rules of hardening by the test results.The tensile strength of remolded loess decreased exponentially with the increasing of water content,While the tensile failure strain tended to firstly decrease but then increase with the increasing of water content, and to firstly increase then decrease with the increasing of density.The unconfined compressive strength tended to increase with the tensile strength in linear pattern.Maximum value of tensile and compressive strength ratio appeared near the optimal water content and maximum dry density,while minimum value appeared in the smallest of dry density and the maximize water content.Both the unconfined compressive strength and tensile strength increased exponentially with the product of cohesion and tangent of internal friction angle.,tensile and unconfined compressive strength decreases with the increase of void ratio,degree of saturation,Saturation and porosity ratio respectively tensile and unconfined compressive strength of a quadratic polynomial.The tensile geometric model simplified into three categories:the political density low moisture content,water content and dry density center,low dry density and high water content.The comprehensive factors influence tensile strength the results showed that tensile strength with water content and dry density was indicated in a three-dimensional spiral surface,and similar with saturation, void ratio. The main factors affecting the tensile strength are water content and saturation, the secondary factor are dry density and void ratio. Tensile strength with cohesion and internal friction angle showed tangent concave slightly curled upward trend, Cohesion had a decisive influence on the tensile strength but the internal friction angle had little effect.It could be concluded that the tensile strength,cohesive force and the unconfined compressive strength had a linear relation,through the analysis of the mechanical properties of UP test.The test results proved that the ratio of unconfined compressive strength and tensile strength close to 13.2,and the ratio of the tensile strength and cohesive force of close to 0.23.Tunnel collapse could be divided into shallow buried overall collapse and deep buried partial collapse.The former applied to Moore-Coulomb’s theory or general Moore-coulomb theory,that was to say that the landslide was caused by the insufficient shear strength.the latter applied to the largest elongation tensile strain theory,that was to say landslides was caused by lack of tensile strength.