循环三轴试验加载频率和压实度对重塑砂土液化行为的影响

Influence of loading frequency and relative compaction on liquefaction behavior of reconstituted sand in cyclic triaxial tests

通过对各向同性固结不排水试样进行循环三轴试验,研究了饱和重塑砂土的液化行为。试验采用恒幅正弦载荷,通过测量剪切模量、阻尼比、轴向应变和超孔隙水压力比的变化,评估了加载频率(分别为0.1、0.5、1.0 Hz)和压实度(分别为0.95、0.90和0.80)对砂土液化行为的影响。试验结果表明,对于压实度为0.95的砂样,在5000次加载循环中,0.1 Hz的加载频率对液化过程影响甚微;而对于压实度为0.90和0.80的砂样,此频率的影响显著。对于压实度为0.80的砂样,当频率增加到0.5 Hz时几乎一加载就直接发生液化。这表明增加加载频率会加快液化速度,而增加压实度则会减慢液化速度。因此,通过一系列的试验可以模拟现场砂土在不同频率下的动荷载条件。试验结果表明,饱和砂土的液化行为由以下因素决定:(1)试样的压实度越低,液化越容易发生;(2)加载频率越高,液化越容易发生;(3)循环轴向应变越大,发生液化所需的循环次数越少;(4)超孔隙水压力随加载循环次数增加,直至试样完全液化。

The article investigates the liquefaction behavior of saturated reconstituted sand by cyclic triaxial tests on isotropic consolidated undrained specimens in the laboratory.Experiments conduct using a sinusoidal load with a constant amplitude to evaluate the influence of the loading frequency(at three different frequencies of 0.1 Hz,0.5 Hz,and 1.0 Hz)and relative compaction(three different relative compactions of 0.95,0.90,and 0.80)on the liquefaction behavior of the sand,as measured by the shear modulus,damping ratio,axial strain,and excess pore water pressure ratio.Based on the experimental results,it can be observed that for the sand specimen with a relative compaction of 0.95,the loading frequency of 0.1 Hz has a negligible effect on the liquefaction process,as observed over 5000 loading cycles.In contrast,the effect of this frequency is significant for the sand specimens with relative compactions of 0.90 and 0.80.For the specimen with a relative compaction of 0.80,an increase in frequency to 0.5 Hz results in almost direct liquefaction.This suggests that increasing loading frequency leads to faster liquefaction while increasing relative compaction results in slower liquefaction by contrast.Thus,through a series of tests,these can be considered simulations of the conditions of dynamic loads on the sand particles in the field with different frequencies.The experimental results show that the liquefaction behavior of saturated sand is determined by the following factors:(1)The lower the relative compaction,the easier liquefaction occurs;(2)The higher the loading frequency,the easier liquefaction occurs;(3)The greater the cyclic axial strain,the fewer cycles are required to cause liquefaction;(4)The excess pore water pressure increases with the increase of number of loading cycles until the specimen is completely liquefied.