利用落锥试验确定深水软黏土的不排水抗剪强度

Determination of Undrained Shear Strength of Deepwater Soft Clays Through Fall Cone Test

不排水抗剪强度是黏性土的重要力学指标,在边坡稳定性分析、地基和桩基承载力的计算中都有广泛的应用。在国内海洋勘察工程中,通常软黏土不排水抗剪强度的确定方法有不固结不排水三轴压缩试验、手动十字板试验、电动十字板试验和无侧限压缩试验等。中国南海北部陆陂深水海域,海底浅层沉积物多为饱和软土,这种软土土质比较均一,具有高含水量、高液限和塑性指数、容重小、抗剪强度低等特点,从而使这种沉积物与常规意义上的饱和软土特性相比可能存在差异,利用落锥试验方法确定其黏性土不排水抗剪强度,具有很强的适用性。本文介绍了落锥试验的试验方法和试验关键技术点,通过该深水海域两个孔位的部分土质资料对比,说明落锥试验确定的黏性土不排水抗剪强度与海上工程设计、分析中使用的不排水抗剪强度具有很好的相关关系。

Undrained shear strength is an important mechanical property of clayey soils and is widely applied for analyzing the slope stability and calculating the bearing capacities of the foundation and the pile foundation.In the domestic marine engineering investigation,the methods for determining the undrained shear strength of soft clays are usually the unconsolidated-undrained triaxial compression test,the torvan test,the miniature vane test and the unconfined compression test.In the deepwater area of the northern South China Sea,the shallow sediment is mostly saturated soft clay,which is relatively homogeneous,high in water content and liquid limit and plasticity index,small in volume weight and low in shear strength.This type of sediment may differ in its property from the commonly saturated soft clays.It may be,therefore,suitable to use the fall cone test for determining the undrained shear strength of such clay.The methods and key techniques for the fall cone test are introduced.By comparing with the data of soil material from two boreholes drilled in the study area,the undrained shear strength of the clay determined through the fall cone test is well correlated to those designed for the marine engineering and used for the analysis.