循环荷载下饱和南沙珊瑚砂的液化特性试验研究

Experimental study on liquefaction characteristics of saturated coral sand in Nansha Islands under cyclic loading

针对饱和南沙岛礁珊瑚砂,开展了一系列不排水循环加载试验,研究了相对密度D_r和初始围压■对饱和珊瑚砂的超孔隙水压力、应变发展、有效应力路径及动强度特性的影响,并比较了珊瑚砂与福建砂的液化特性差异。试验表明,珊瑚砂的超静孔压Δu的发展模式与石英砂的有较大区别,可用修正后的Seed模型进行表征。珊瑚砂液化时的累积能量耗散远比福建砂的大。珊瑚砂的轴向应变ε_(DA)随着循环振次增加而逐渐变大,不会发生急剧增大的现象。在有效应力路径接触相转换线后,珊瑚砂会发生剪胀和剪缩交替出现的现象,仍然会存在有效应力。较之福建砂Δu的波动特征,珊瑚砂Δu的波动更大,且当Δu接近■时波动明显增大,产生"瞬时液化"现象。珊瑚砂的动强度随着D_r以及■的增大而增大。珊瑚砂的动强度大于石英砂的动强度。

Undrained cyclic traxial tests are carried out on the saturated coral sand in Nansha Islands,South China Sea.The experiment aims at investigating the characteristics of pore water pressure,axial strain,effective stress path and cyclic resistance of coral sand under different Dr and■.The differences between coral sand and Fujian sand about liquefaction characteristic are also discussed.The test results indicate that the development of pore water pressure(Δu)of coral sand is different from that of siliceous sand,which can be fitted by a modified Seed model.The accumulative energy dissipation of liquefied coral sand is greater than that of liquefied Fujian sand.The axial strain(εDA)of coral sand has no sudden enlargement phenomenon during cyclic loading,and the amplitude ofεDA increases continuingly with the loading time.When touching the phase transformation line,the coral sand shows the alternation of dilatancy and contraction as the effective stress still exists.Compared with the Fujian sand,the coral sand has a greater fluctuation in especially when approaching■,and a phenomenon of transient liquefaction can be observed in the tests.The cyclic resistance of coral sand increases with the increase of Dr and■.The cyclic resistance of coral sand is basically higher than that of siliceous sand.