南海岛礁珊瑚砂砾混合料动力特性试验研究

Experimental study on dynamic characteristics of calcareous sand-gravel mixtures from islands in the South China Sea

在南海岛礁实际建造工程中,上部吹填地基材料以大小砂砾共存、混杂无序的状态分布。地层中砂砾混合分布状态使地基在地震等动荷载下呈现出复杂的力学响应。通过开展一系列不同含砾量、密实度、围压和初始剪应力条件下的不排水循环三轴剪切试验,研究珊瑚砂砾混合料在不同工况下的动力特性。试验结果表明,无论是在松散还是密实状态,含有珊瑚砾的混合料试样在循环荷载下表现出更缓的轴向应变增长和孔隙水压上升的变化趋势。与单一珊瑚砂所构成的试样相比,珊瑚砂砾料试样具有更高的抗液化能力。珊瑚砂砾混合料抗液化强度随着含砾量、密实度和初始剪应力的增大而显著提高。密实珊瑚砂砾料的抗液化强度随围压的增大而减小,而针对松散试样没有发现明显规律,这可能是围压和密实度耦合影响引起的。试验结果表明含砾量对试样抗液化强度的影响主要受混合料骨架结构所控制,混合料骨架大致可分为粗颗粒(珊瑚砾)和细颗粒(珊瑚砂)结构主导两种状态。二元介质属性是开展砂砾混合料力学特性研究所必须考虑的影响因素。

In the construction process of reef islands in the South China Sea,the upper reclamation foundation materials exist in the form of a combination of large calcareous gravels and small calcareous sand mixed in random proportions.Such composition state makes the foundation exhibit complex mechanical properties under dynamic loads such as earthquakes.A series of undrained cyclic triaxial tests under different conditions of gravel content,relative density,confining pressure and initial shear stress are carried out to study the dynamic response of calcareous sand-gravel mixtures.The test results show that the mixtures display a lower axial strain growth and pore pressure rise rate than the pure calcareous sand under cyclic loading,regardless of loose and dense states.It indicates that the calcareous sand-gravel mixtures exhibit higher liquefaction resistance than the calcareous sands.The liquefaction resistance of the calcareous sand-gravel mixtures increases significantly with the gravel content,relative density and initial shear stress.In dense state,the liquefaction resistance of mixtures decreases with increasing confining pressure,but not for the loose samples,which probably relates to the coupled effects of the confining pressure and density.The effects of the gravel content on the liquefaction resistance of the calcareous sand-gravel mixtures are controlled by the grain skeleton structure.The grain-scale structure is dominated by coarse particles(calcareous gravel)or small particles(calcareous sand).The binary media characterization is an important factor for the study on mechanical properties for the calcareous sand-gravel mixtures.