循环荷载作用下钙质砂动力特性三轴试验研究

Experimental Study on Triaxial Test for Dynamic Behavior of Calcareous Sand under Cyclic Loading

为了保障南海岛礁交通基础设施的运营安全,有必要深入探究循环荷载作用下吹填钙质砂的动力特性。针对南海岛礁吹填钙质砂,采用GDS循环三轴仪开展了一系列排水循环三轴试验,定性和定量分析了钙质砂的残余应变、颗粒破碎、特征循环次数、临界循环应力比和失稳动剪应力等变量的变化规律,并提出了一个残余应变预测的经验模型。结果表明:钙质砂的临界循环应力比随围压增加而减小,二者关系可用幂函数表达,钙质砂的归一化失稳动剪应力随失稳循环次数增加而减小,二者满足对数函数关系。当循环应力比小于临界循环应力比时,钙质砂的残余应变随循环次数增加而增加;当循环应力比等于临界循环应力比时,钙质砂达到临界稳态,其临界稳态残余应变随临界稳态循环次数和围压增加而增加,但随临界循环应力比增加而减小;当循环应力比大于临界循环应力比时,钙质砂发生渐进失稳,其失稳残余应变随钙质砂的归一化失稳动剪应力增加而快速增加。钙质砂的稳态循环次数随围压和循环应力比增加而增加,而临界稳态和失稳循环次数分别随临界循环应力比和归一化失稳动剪应力增加而减小。对比分析钙质砂循环三轴试验结果与残余应变模型预测结果可知,推荐的经验模型能够描述多重因素作用下钙质砂的残余应变变化趋势和演化规律。

In order to ensure the operation safety for traffic infrastructures in the coral reefs of South China Sea,it is necessary to deeply explore the dynamic behavior of calcareous sand with the hydraulic fill under cyclic loading.A series of drained and cyclic triaxial tests are carried out on the calcareous sand with the GDS cyclic triaxial apparatus,the evolution rules of residual strain,particle breakage,characteristic cyclic number,critical cyclic stress ratio and dynamic strength of calcareous sand are qualitatively and quantitatively analyzed,and an empirical model is put forward to predict the residual strain.The result shows that(1)The critical cyclic stress ratio decreases with the increase of confining pressure,which is expressed by a power function,and the normalized instability shear stress also decays with the increase of cyclic number in the failure state,which can be characterized by a logarithmic function.(2)When the cyclic stress ratio is less than the critical cyclic stress ratio,the residual strain of calcareous sand increases with the increase of cycles;when the cyclic stress ratio is equal to the critical cyclic stress ratio,calcareous sands reach the critical steady state,and the critical steady state residual strain increases with the increase of the critical steady state cycle times and confining pressure,but decreases with the increase of the critical cyclic stress ratio;when the cyclic stress ratio is greater than the critical cyclic stress ratio,calcareous sand gradually destabilizes,and its instability residual strain increases rapidly with the increase of instability shear stress.(3)The steady cycle times of calcareous sand increase with the increase of confining pressure and cyclic stress ratio,while the critical steady cycle times decrease with the increase of critical cyclic stress ratio and instability shear stress respectively.(4)The comparison between test data and model predictions indicates that the proposed empirical model can represent the trend and the evolution of residual strain of calcareous sand subject to the multiple factors.