澳门近海软土孔压静力触探CPTu推算不排水强度S_u方法

Method for calculating undrained strength S_u by CPTu for soft soil in Macao offshore

通过澳门近海区域软土层孔压静力触探试验(CPTu)结果推求软土的不排水强度S_u,与同场地的十字板剪切试验(VST)不排水强度Cu实测值对比,分析计算结果的准确性,并确定参数锥体经验系数(Nkt和NΔu)的取值范围。对比结果表明:利用修正锥尖阻力qt按照基于承载力理论计算不排水强度S_u,锥体经验系数Nkt=15.5,不排水强度S_u计算值和十字板剪切强度实测值Cu对比,0~4 m深度内误差较大,而4 m以下误差较小;而利用孔隙水压力u2计算不排水强度S_u,经验系数NΔu=10.6,不排水强度S_u计算值和十字板剪切强度实测值Cu在0~4 m深度内误差优于利用修正锥尖阻力qt的计算结果,4 m以下误差稍大。因此,建议在澳门地区近海软土层中,浅部0~4 m利用CPTu孔隙水压力u2快速计算不排水强度S_u,4 m以下可利用修正锥尖阻力qt推求不排水强度S_u。

The undrained strength Su of soft soil is calculated by piezocone penetration test（CPTu） in Macao offshore,compared with the measured vale of undrained strength Cuof vane shear test（VST） in the same site, we analyzed the accuracy of the calculation results, and determined the value range of the cone empirical parameter（Nktand NΔu）. The comparison results show that undrained strength Su calculated by using corrected cone resistance qtbased on the method of bearing capacity theory with cone empirical coefficient Nkt= 15.5, compared with the calculated value of Su and the measured value of Cu, the error in the depth of 0 to 4 m is larger, while the error below 4 m is smaller. The undrained strength Su calculated by using pore pressure u2 with NΔu=10.6, the calculated value of Su and the measured value of Cuin the depth of 0 to 4 m, which is superior to the use of corrected cone resistance qt, and the error is slightly larger below the 4 m. Therefore, it is suggested to calculate undrained strength Su using the CPTu pore pressure u2 within shallow 0 to 4 m and using corrected cone resistance qtto calculate Su deeper than 4 m in the offshore soft soil layer of Macao.