连云港海相软土不排水强度特征

连云港地区软土为碱性环境下沉积的非均质海积软土，软土抗剪强度具有固有各向异性。采用三轴不固结不排水剪切（UU）试验、无侧限抗压强度（UTC）试验、快剪试验和原位十字板剪切（FVT）试验4种方法，对连云港地区软土的不固结不排水抗剪强度特征进行了研究。结果表明：土体水平剪切面强度最低，竖直面抗剪强度最高；土体制样采用垂直方向的切取试样方式时，土体强度最高。根据三轴UU试验得出的黏聚强度和内摩擦角基于土体单元极限平衡理论恢复了土体剪切破坏时的应力状态，计算出土体实际抗剪强度。三轴UU试验得出的抗剪强度平均值约为13.13 kPa，试样破裂面与水平面的夹角在45.1°~45.7°区间最为集中。UTC试验测得的土体平均抗剪强度近似等于三轴UU试验测得的平均抗剪强度。FVT试验测得软土抗剪强度平均值为19.72 kPa，与三轴UU试验和UTC试验得出的抗剪强度平均值相比高了约6.60 kPa，这种现象与室内试验试样的机械扰动、土体应力状态改变和剪切面特征有关。

Shear Strength and Failure Characteristics of Marine Soft Soil in Lianyungang

The soft soil in Lianyungang is a heterogeneous marine soft soil deposited in an alkaline environment, its shear strength is inherently anisotropic. We studied the unconsolidated undrained shear strength of soft soil by tri-axial UU test, UTC test, Fast shear test, and FVT test. The results indicate that the horizontal plane shear strength is the lowest; while the vertical plane shear strength is the highest. Using the cohesion and friction angle obtained by the three axis UU test, we restored the stress of soil shear failure state based on the soil unit limit equilibrium theory, and calculated the actual shear strength of soil. The average shear soil strength of the tri-axial UU test is 13.13 kPa. The angle between the sample fracture surface and the horizontal plane is most concentrated in the range of 45.1°-45.7°. The average strength of the UTC test approximately equates that of the three axis UU test. The average soft soil strength by the conventional FVT test is 19.72 kPa, nearly 6.60 kPa higher than that by the other two tests. This phenomenon is related to the mechanical disturbance of the lab test samples, the change of the stress state of the soil, and the characteristics of shear plane.