Stress And Seepage Properties Of Loess Joint

Joints are widely developed in the loess region. The existence of joint destroys thecontinuity and integrity of loess. The joint surface forms a weak shear strength surface.It will accelerate water migration. It constitutes a safety hazard for cavity and thestability of the slope in the loess area. At present, research mainly focus on thegeological properties of joint. The engineering properties are short. The characteristicsof joint’s shear strength and seepage are lack of research. This article launches somestudy on the shear and seepage properties of loess joint.The shear strength parameter is obtained based on the joint’s direct shear test underdifferent water content, dry density and surface morphology. It shows that: Therelationship between internal friction angle and loess moisture content is a parabolawith. There is a “limit water content”, so that when the moisture content of loess reachthe threshold value, the internal friction angle get the maximum. At low moisturecontent, surface morphology affect the cohesion greatly. The cohesion of rough jointsurface is significantly greater than the smooth one. With the moisture contentincreasing, the impact of surface morphology on cohesion decreases gradually.The seepage properties of loess joint is studied though three kinds of experiment,including joint variable water head test, model test of joint’s surface saturatedinfiltration in laboratory and field joint irrigational test as well. The main conclusionsare as follows: the joint variable water head test shows that when there are joints inloess, the flow can still be described by Darcy’s Law. But with the increase of waterhead, results of test gradually deviate from the Darcy’s law; model test of saturatedinfiltration simulates joint’s saturated surface infiltration. Tests show that joint has apromoting effect on water infiltration. The flow quantity increases with the increase of joint aperture; field joint irrigational test shows that the vertical joint of loess has highpermeability in the early infiltration time. The infiltration velocity of loess along thedirection of joint is greater than the rate along the horizontal direction.The seepage problem of loess joint is theotically studied. The problem of jointedloess flow is a two-dimensional one including both along the joint and perpendicular tothe joint’s direction. Considering the vertical flow to the loess and the loess flow speeditself, it creates a two-dimensional model of loess joint. By using this model, it deductsa seepage differential equation of flow velocity under the help of Eulerian variationalmethod. Further deduction works out the two-dimensional steady flow equation of loessjoint, which is based on the flow characteristics and the boundary conditions of loessjoint. This equation can be treated as an extension of The Cubic Law in the rock jointresearch field. What’s more, working with The Darcy Law, this paper also gives apermeability coefficient of loess joint. When the2-D water motion of loess joint isconsidered, water’s generalized resistance increases.The numerical analysis method of loess joint is established. Firstly, the2-dimensional permeability matrix of loess joint is worked out. And then, it establishesnumerical model for calculating moisture field, considering the existence of the joint inloess. Further, the finite element method of unsaturated transient seepage algorithm isestablished by using the inferior quadrilateral element. This method considers thecondition that major coefficient of permeability is not overlap with axis. At last, byusing this seepage model and calculate method, it calculates some2-D water infiltrationproblem of loess joint under various head boundary conditions. It verifies theapplicability of the model. The movement law of wetting front under the infiltrationprocess is given.