固结应力状态对超深厚覆盖层深埋砂土动强度参数的影响

在室内固结不排水动三轴试验基础上,对较低有效固结应力到较高有效固结应力范围内超深厚覆盖层深埋紧密砂土的动强度特性进行了研究,重点研究了固结应力状态对动强度参数的影响。结果表明:(1)有效固结围压力对抗液化动剪应力比有明显影响,其影响随土类和相对密度的不同而不同,有效固结围压力越增大,抗液化动剪应力比越减小,相对密度越大,这种效果越明显;(2)有效固结应力比的影响规律比较复杂,在有效固结围压力较低时,抗液化动剪应力比随有效固结应力比的增大而越大,相对密度越大,这种效果越明显;在固结应力较高时,随有效固结应力比的增大,抗液化动剪应力比可能增大,也可能减小,主要取决于相对密度和有效固结应力比的大小;当紧密砂土在较高的有效固结应力下呈现剪胀时,抗液化动剪应力比随有效固结应力比的增大而增大;当紧密砂土在较高的有效固结应力下呈现剪缩时,抗液化动剪应力比随有效固结应力比的增大而减小;(3)对于中密和紧密砂土,在由剪胀到剪缩状态转变的过程中,存在一个剪胀与剪缩分界的临界固结应力状态,其对应的临界有效固结围压力随相对密度的增大而增大。

Effects of effective confining stresses on cyclic resistance ratio of deep buried sands in deep alluvial soils

Liquefaction resistance of two dense sands with different relative density is investigated by labora-tory cyclic undrained triaxial tests, and the effects of confining pressure from moderately high to high range on liquefaction resistance are discussed. The results indicate that:(1)effective confining stresses have significant effects on cyclic resistance ratio, which decreases with increasing effective confining stresses, and the larger the relative density is, the greater the cyclic resistance ratio decreases;(2)the effect of ef-fective consolidated ratio(initial static shear stress) is very complicated, the presence of an initial static shear stress increases the cyclic resistance ratio of dense sands for relatively low confining stresses, and the larger the relative density is, the greater the cyclic resistance ratio increases; for high confining stress-es,the effects of the presence of an initial static shear stress on dense sands depend on the relative densi-ty and the effective confining stress. if dense sands become more dilative under certain effective confining stresses, the cyclic resistance ratio increases with increasing confining stresses, and if dense sands become more contractive under certain effective confining stresses,the cyclic resistance ratio decreases with increas-ing confining; and (3)the complication of effects of the presence of effective consolidated stress state on the cyclic resistance ratio of dense sands actually reflects the complication of the dilative or contractive properties of sands influenced by effective consolidated stresses and relative density. For dense sands, in the transition process of shear dilatancy to shrink, there is a critical stress state which distinguishes shear dilatancy state and Shear shrink state, and the value of the critical stress state increases with increasing relative density.