Effects of cyclic loading on lateral bearing capacity of single pile in silty seabed
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摘要: 在较大的波浪荷载作用下，海洋单桩会出现承载力降低、甚至失稳现象。利用GDS三轴仪对杭州湾重塑海相粉土进行了静三轴、动三轴和循环后静三轴不排水剪试验，研究了循环荷载作用对循环后粉土变形和不排水强度特性的影响，分别建立了动孔压比与循环应力比和循环次数、动孔压比与循环后不排水强度比及割线模量比的经验关系式。在此基础上，根据波浪荷载在海床深度方向的剪应力比分布，得到了桩侧粉土刚度和强度的衰减比深度分布，计算了波浪荷载对单桩横向承载特性的影响。在本算例条件下，波浪荷载对粉土海床的强度和刚度弱化随深度急剧衰减，影响深度约40 m，海床浅部约5 m深度有液化现象，循环荷载后桩身的刚性反应增强、位移和反弯点深度增加，弯矩和侧压力减小，总的横向承载力降低约40%。Abstract: Under larger wave loading, the bearing capacity of marine single pile foundation will be reduced, even instability occurs. A series of undrained shear triaxial tests on the remolded marine silt in Hangzhou Bay are carried out by means of the GDS triaxial apparatus, including monotonic, cyclic and post-cyclic monotonic loading. The effects of cyclic loading on the post -cyclic monotonic deformation and undrained strength of silt are studied, and the relationships among dynamic pore pressure ratio, cyclic stress ratio, cycle number, post-cyclic undrained strength ratio and secant modulus ratio are established, respectively. On this basis, according to the distribution of shear stress ratio induced by wave loading along the seabed depth, the lateral soil stiffness and strength reduction ratio of single pile are calculated, and the influences of wave loading on the lateral deformation and bearing capacity of single pile foundation are calculated. In the presented example, the strength and stiffness reduction of silt seabed caused by wave loading decrease sharply with the depth, and the affected depth is about 40 m. Liquefaction occurs in the shallow part of the seabed about 5 m. After cyclic loading, the rigid response of pile body is enhanced, the displacement of pile body and the depth of the reverse bending point increase, the bending moment and the lateral pressure decreased, and the total lateral bearing capacity was reduced about 40%.
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图 1 累积孔压比-循环次数比关系
Figure 1. Relationship between accumulated pore pressure ratio and cycle number ratio
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图 2 循环后不排水强度比与循环孔压比关系
Figure 2. Relationship between post-cyclic undrained strength ratio and cyclic pore pressure ratio
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图 3 循环后变形模量比与循环孔压比关系
Figure 3. Relationship between post-cyclic deformation modulus ratio and cyclic pore pressure ratio
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图 4 循环应力比、循环后强度比和模量比与深度关系
Figure 4. Relationship between cyclic stress ratio, post-cyclic strength ratio, modulus ratio and depth
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