球应力和偏应力对粗粒土变形影响的真三轴试验研究

为了研究p,q,θσ单独变化对粗粒土变形的影响,使用河海大学TSW-40型真三轴仪,对粗粒土进行了等q等b(b=(σ2-σ3)/(σ1-σ3))试验,等p等b试验和等p等q试验,试验结果表明:q,b保持不变,p单独减小时,初期几乎不产生偏应变,但会产生膨胀的体积应变,随着p的减小,体积膨胀增大,偏应变也逐渐增大,但偏应变数值上比体积应变小,到后期体积应变和偏应变都加速发展,直至破坏;p的减小直接引起体积膨胀,体积膨胀后颗粒结构松动,进而导致偏应变的产生;p,b保持不变,q单独增大时,初期几乎不产生体积膨胀,但会产生偏应变,随着q的增大,偏应变增大,体积膨胀也逐渐增大,但体积应变数值上比偏应变小,到后期体积应变和偏应变都加速发展,直至破坏;q的增大直接产生偏应变,偏应变使得颗粒之间产生错动,进而导致体积膨胀的产生;p,q保持不变,应力罗德角θσ单独变化会产生不可恢复的体积应变和偏应变,但数值上很小。引入参数sp(sp=(p/q-p0/q0)/(1/Mf-p0/q0))和sq(sp=(q/p-q0/p0)/(Mf-q0/p0)),p0,q0分别为初始球应力和偏应力,Mf为破坏应力比,发现q,b保持不变,p单独减小时,dεv/dp与1/(1-sp)1/2-1成正比例关系,dεs/dp与-sp1/(1-sp)1/2-1]成正比例关系,应力–剪胀方程为dεv/dεs=-1/sp;p,b保持不变,q单独增大时,dεs/dq与1/(1-sq)1/2-1成正比例关系,dεv/dq与-sq1/(1-sq)1/2-1]成正比例关系,应力–剪胀方程为dεv/dεs=-sq。最后根据本文试验结果对粗粒土柔度矩阵元素的特性进行了分析。

True triaxial tests on influence of spherical and deviatoric stresses on deformation of coarse-grained soil

In order to study the influence of p, q and θ_σ on the deformation of coarse-grained soil, several tests in which only one of the three variables changes while the other two keep constant are performed on coarse-grained soil by using the TSW-40 type true triaxial apparatus in Hohai University. The results show that if p decreases with constant q and b, few deviatoric strain but some volumetric dilation will be generated at the preliminary stage. With the decrease of p, the volumetic dilation increases, which causes the increase of deviatoric strain that is smaller than the volumetric strain in absolute value. Later both the volumetric strain and the deviatoric strain will be accelerated until failure. It indicates that the decrease of p induces the volumetric dilation immediately, which loosens the particle structure, and then the deviatoric strain will be generated. If q increases with constant p and b, little volumetric dilation but some deviatoric strain will be produced at the preliminary stage. With the increase of q, the deviatoric strain increases, which causes the increase of the volumetric dilation that is smaller than the deviatoric strain in absolute value. Later both the deviatoric strain and the volumetric strain will be accelerated until failure. It demonstrates that the increase of q induces the deviatoric strain directly which causes particle dislocation, and then the volumetric dilation will be produced. If θ_σ changes with constant p and q, some but very small unrecoverable volumetric and deviatoric strains will be generated. Two parameters s_p (s_p =(p/q-p₀/q₀)/(1/M_f-p₀/q₀)) and s_q (s_p=(q/p-q₀/p₀)/(M_f-q₀/p₀)) are introduced, in which p₀ and q₀ are the initial spheric stress and the deviatoric stress respectively, M_f is the stress ratio at failure. The test results show that when p decreases with constant q and b, dε_v/dp and 1/(1-s_p)^1/2-1 are in direct proportion; dε_s/dp and -s_p1/(1-s_p)^1/2-1] are in direct proportion; stress-dilatancy equation is dε_v/dε_s= -1/s_p. When q increases with constant p and b, dε_s/dq and 1/(1-s_q)^1/2-1 are in direct proportion; dε_v/dq and -s_q1/(1-s_q)^1/2-1] are in direct proportion; stress-dilatancy equation is dε_v/dε_s= -s_q. Finally the characteristics of the flexibility matrix of coarse-grained soil are analyzed according to the test results.