兰州九州重塑黄土抗拉特性研究

Study on Tensile Properties of Remolded Loess in Jiuzhou Development District，Lanzhou，China

摘要:

通过室内三轴快剪、无侧限抗压和无侧限贯入抗拉试验，对兰州九州开发区重塑黄土的抗拉特性进行对比性试验研究。结果表明：抗拉强度随含水量呈二次多项式递减关系；抗拉破坏时的贯入深度随含水量的增长呈现先减小后增大趋势，随干密度的增加呈现先增大后减小的趋势；抗拉强度远小于无侧限抗压强度，且无侧限抗压与抗拉强度呈线性递增关系；无侧限抗压和抗拉强度与黏聚力和内摩擦角正切值的乘积均呈指数递增关系。

Abstract:

Loess is a typical water sensitive structural material with relatively low tensile strength. Under most circumstances in engineering practice，the tensile strength of loess and most geomaterials is negligible.However，there are many earth structures（slopes，subgrades，and tunnels）damaged due to tensile stresses.So the tensile properties of loess become very significant for practical engineering.The shear，unconfined compressive，and tensile properties of remolded loess taken from Jiuzhou Development District in Lanzhou，China, are thoroughly investigated in this study using the undrained triaxial shear test，unconfined compressive test，and unconfined penetration tensile test.The relationships among the tensile strength，shear strength，and unconfined compressive strength of the remolded loess are comparatively analyzed.The test phenomena show that the shear test specimen under low confining pressures fails in a brittle pattern，while under high confining pressures，it fails in a plastic pattern，and that the plasticity seems to grow with the increasing of the water content of the loess.The specimen in the unconfined penetration test fails in a brittle pattern，splitting into two or three petals with peak tensile stresses.The axial tensile stress first increases to a maximum value with the increasing of penetration depth and then has a steep decreasing process with the continued increasing of penetration depth.The test results indicate that the tensile strength of remolded loess decreases in a quadratic polynomial pattern with the increasing of water content，and the degree of correlation is satisfactory.By comparison and analysis，it is shown that the tensile strength of remolded loess is much smaller than the unconfined compressive strength，and the unconfined compressive strength tends to increase with the tensile strength in a linear pattern.The ratio of tensile strength to compressive strength first decreases，then increases，and finally decreases again as the water content increases；however，it increases，then decreases，and finally increases with the increasing of dry density.The maximum ratio of tensile strength to compressive strength occurs around the optimum water content and maximum dry density，while the minimum ratio of tensile strength to compressive strength appears to be at the maximum water content and minimum dry density.Cohesion and internal friction angle are the two indicators of the shear strength of soils，and they are affected by the structural and strength characteristics of soils.Regression analysis on the shear strength，unconfined compressive strength，and tensile strength suggests that the cohesion of the remolded loess decreases with little amplitude at first and then increases approximately in a monotonic linear pattern with the unconfined compressive strength and tensile strength.Both the unconfined compressive strength and tensile strength increase exponentially with the product of cohesion and tangent of internal friction angle.Similar to the water content，the degree of saturation of loess also has something to do with the strength characteristics of loess.The test results indicate that both the unconfined compressive and tensile strength decrease with the increasing of the degree of saturation in a polynomial pattern.