黏粒含量对粉土液化后特性影响的试验研究

Influence of Clay Content on Post liquefaction Characteristics of Silt

摘要:

利用多功能动三轴仪的先进功能，对3%、6%、8%、9%、12%和15%黏粒含量的粉土进行了动三轴试验。试样在初始液化后继续施加动荷载，达到不同的双幅轴向应变后施加不排水单调荷载模拟液化后大变形。研究结果表明，相同循环周数时不同黏粒含量对动加载阶段的动剪应力影响规律与其对液化后初始阶段大应变规律有内在联系，即黏粒含量为8%时动剪应力最小而液化后低强度段应变最大，而强度恢复段模量也最低。试验验证结果表明，拟合关系式能较好地反映不同黏粒含量粉土液化后大变形。

Abstract:

Silt is one of the most common soils encountered in the field，and it is prone to liquefaction when earthquakes occur.In China，silt is widely located in the zones of the Qiantang River，the Yellow River，the cities of Kunming and Tangshan，and numerous other regions.The topic of silt liquefaction has been one of the hottest issues since the 1976 Tangshan earthquake.This paper presents the post-liquefaction stress-strain characteristics of silt samples with different clay contents induced by strong earthquakes.Large deformations occur during the post-liquefaction stage，which may trigger a large amount of horizontal ground movement or destroy the structure built there.It is of great importance to take precautions when confronting post-liquefaction deformation induced by earthquakes，especially on horizontal ground.Silt samples with clay contents of 3%，6%，8%，9%，12%，and 15% were used in this research.The original silt，sand，and clay samples were mixed in different mass proportions in order to obtain silt samples with different clay contents.The influence of the clay content on the degree of post-liquefaction deformation was studied by a series of monotonic tests.The test was based on liquefied silt samples by using a specially made triaxial apparatus.Large deformations can be recorded using the adequately large displacement sensors in this apparatus.These samples with different clay contents were isotropically consolidated to the specified pressure.Then cyclic loading was performed to trigger the initial liquefaction and was maintained until the specified severity of liquefaction was reached.Finally，monotonic loading was conducted to simulate the post-liquefaction stage based on the liquefied silt samples.Undrained shear tests were performed during the cyclic and monotonic loading stages.The post-liquefaction shear stress and shear strain were recorded automatically for these test results.From the stress-strain relationship of different clay contents，the 3% and 15% clay content samples showed less strain at the same stress level，and the 8% clay content sample showed the largest strain.This phenomenon can be explained as resulting from the clay content in the silt.Clay particles acted as both the lubricant and the adherent in the silt samples.As the clay content increased，the lubrication decreased and the glutinousness increased.There exists a critical clay content level，where the post-liquefaction strain reaches a maximum at a constant stress level.This explanation is consistent with the effect of clay particles in silt on the cyclic shear stress ratio.The silt sample with 8% clay content produced the minimum shear stress ratio during the cyclic loading stage and thus the maximum strain during the monotonic loading stage.The effect of the clay content on post-liquefaction characteristics can be quantifiably evaluated from our test results. As is known，the strain at nearly zero effective stress was the key strain component of post-liquefaction deformation.The relationship between deformation and the cyclic maximum strain was linear for silt samples with different clay contents.The slopes of these lines reflect the effect of clay content on post-liquefaction stress-strain.Therefore，the effect of the clay content on post-liquefaction characteristics was calculated.It was confirmed that the silt post-liquefaction stress-strain formula compared well with data collected from other tests.