Experimental study on dynamic characteristics of calcareous sand-gravel mixtures from islands in the South China Sea
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摘要: 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。Abstract: 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.
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图 3 试样外观图（左）和内部截面图（右）
Figure 3. Appearance view (left) and internal cross-sectional view (right) of specimen
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图 4 松散状态下不同含砾量珊瑚砂砾混合料的不排水循环行为
Figure 4. Undrained cyclic behaviors of loose calcareous sand-gravel mixtures with different gravel contents
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图 5 密实状态下不同含砾量珊瑚砂砾混合料的不排水循环行为
Figure 5. Undrained cyclic behaviors of dense calcareous sand-gravel mixtures with different gravel contents
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图 6 不同初始剪应力下珊瑚砂砾混合料(Gc=20%)的不排水循环行为
Figure 6. Undrained cyclic behaviors of calcareous sand-gravel mixtures with different initial shear stresses
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图 7 围压对珊瑚砂砾混合料抗液化强度曲线的影响
Figure 7. Influences of confining pressures on liquefaction resistance.curve of calcareous sand-gravel mixtures
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图 8 相对密度对珊瑚砂砾混合料抗液化强度曲线的影响
Figure 8. Influences of relative densities on liquefaction resistance curve of calcareous sand-gravel mixtures
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图 9 不同初始剪应力对珊瑚砂砾混合料抗液化强度曲线影响
Figure 9. Influences of initial shear stress on liquefaction resistance curve of calcareous sand-gravel mixtures
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图 10 不同含砾量对珊瑚砂砾混合料抗液化强度曲线的影响
Figure 10. Influences of gravel contents on liquefaction resistance curve of calcareous sand-gravel mixtures
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图 11 珊瑚砂砾混合料最大最小孔隙比与含砾量的关系
Figure 11. Relationship between gravel content and maximum to minimum void ratio
表 1 珊瑚砂砾混合料基本参数
Table 1 Basic parameters of calcareous sand and gravel mixtures
材料 Gc/% d50/mm Cu emax emin 珊瑚砂 0 0.83 1.75 1.271 0.912 珊瑚砂砾料 10 0.89 2.07 1.234 0.893 20 0.97 2.14 1.214 0.877 30 1.11 2.54 1.195 0.869 40 1.35 5.59 1.239 0.953 
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表 2 珊瑚砂砾混合料不排水循环三轴试验工况
Table 2 Undrained cyclic triaxial test conditions of calcareous sand-gravel mixtures
序号 编号 Gc/% Dr /% σ′c /kPa Kc e0 CSR 1 T1-0-0.4-100 0 40 100 1 1.123 0.185 0.230 0.280 2 T1-0-0.4-200 0 40 200 1 1.123 0.185 0.230 0.280 3 T1-0-0.4-300 0 40 300 1 1.123 0.195 0.230 0.250 4 T1-0-0.5-100 0 50 100 1 1.086 0.200 0.300 0.400 5 T1-0-0.8-100 0 80 100 1 0.983 0.255 0.325 0.360 6 T1-0.1-0.4-100 10 40 100 1 1.094 0.210 0.250 0.290 7 T1-0.1-0.8-100 10 80 100 1 0.961 0.280 0.320 0.380 8 T1-0.2-0.4-50 20 40 50 1 1.076 0.190 0.240 0.300 9 T1-0.2-0.4-100 20 40 100 1 1.076 0.230 0.300 0.400 10 T1-0.2-0.4-200 20 40 200 1 1.076 0.250 0.300 0.350 11 T1-0.2-0.4-300 20 40 300 1 1.076 0.190 0.240 0.300 12 T1-0.2-0.65-100 20 65 100 1 0.995 0.240 0.300 0.400 13 T1-0.2-0.8-100 20 80 100 1 0.944 0.295 0.350 0.400 14 T1-0.2-0.8-200 20 40 200 1 0.944 0.300 0.350 0.390 15 T1-0.2-0.8-300 20 40 300 1 0.944 0.295 0.340 0.400 16 T1-0.3-0.4-100 30 40 100 1 1.061 0.300 0.240 0.350 17 T1-0.4-0.4-100 40 40 100 1 1.122 0.270 0.300 0.345 18 T1.27-0.2-0.4-100 20 40 91.7 1.27 1.076 0.300 0.350 0.400 19 T2-0.2-0.4-100 20 40 75 2 1.076 0.460 0.590 0.650
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