Development Model of Excess Pore Pressure for Geogrid Reinforced Coral Sand Based on Strain Characteristics
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摘要:
地震荷载下珊瑚砂中超静孔压增长，直至液化，是导致结构破坏的关键因素.开展了一系列不排水动三轴试验，研究土工格栅层数、相对密实度Dr和循环应力比CSR对加筋珊瑚砂超静孔压和轴向应变发展特性的影响.试验结果表明：土工格栅加筋及增加格栅层数可减小珊瑚砂中超静孔压和轴向应变发展速率，提高珊瑚砂抗液化强度.在相同循环振次比下，加筋珊瑚砂中超静孔压发展远高于硅质砂；随着CSR的增加，加筋珊瑚砂超静孔压发展曲线逐渐由S型过渡到双曲线型，而经典的Seed孔压应力模型难以描述该种孔压发展趋势变化的特性.提出了基于应变特性的加筋珊瑚砂超静孔压发展模型，该模型可较好地预测不同Dr和CSR下加筋珊瑚砂超静孔压发展趋势，可为我国南海珊瑚砂岛礁区基础设施抗震设计和基于有效应力的稳定性分析提供理论依据.
Abstract:The accumulation of excess pore pressure in coral sand under seismic loading until liquefaction is a key factor leading to structural damage. A series of undrained cyclic triaxial tests were conducted in this study to investigate the effects of geogrid reinforcement layer, relative density (Dr) and cyclic stress ratio (CSR) on the development of excess pore pressure and axial strain in reinforced coral sand. The results indicate that geogrid reinforcement as well as an increase in the number of geogrid layers reduce the development rate of excess pore pressure and axial strain, thereby improving the liquefaction resistance of coral sand. The pore pressure of coral sand is much higher than that of siliceous sand under the same cyclic vibration ratio, and the pore pressure development curve of reinforced coral sand gradually transitions from an S-type to a hyperbolic type with the increase of cyclic stress ratio, thus the classic Seed pore pressure stress model is difficult to describe its pore pressure development trend. Based on the above findings, a strain-based excess pore pressure development model for geogrid-reinforced coral sand is proposed. This model accurately predicts the development trend of excess pore pressure in reinforced coral sand under different Dr and CSR, which provides a theoretical basis for the seismic design of infrastructure and stability analysis using effective stress in coral sand island reef area of the South China Sea.
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Key words:
- coral sand /
- geogrid reinforcement /
- liquefaction /
- excess pore pressure /
- axial strain /
- engineering geology
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图 1 珊瑚砂级配曲线及电镜扫描图
Fig. 1. Grain size distribution curve and scanning electron micrograph image of coral sand
图 2 土工格栅布置示意图(H=试样高度)
Fig. 2. Schematic diagram of geogrid arrangement (H=sample height)
图 3 超静孔压、轴向应变与循环振次关系曲线
Fig. 3. Relationship curves of excess pore pressure and axial strain-number of cycles
图 4 加筋珊瑚砂超静孔压比-循环振次比关系曲线
Fig. 4. Relationship curves of excess pore pressure ratio-number of cycle ratio of reinforced coral sand
图 6 偏应力和超孔压比-循环振次关系曲线
Fig. 6. Relationship curves of deviator stress and excess pore pressure ratio-number of cycles
图 7 加筋珊瑚砂超静孔压比-双幅轴向应变关系曲线
Fig. 7. Relationship curves of excess pore pressure ratio-double-amplitude axial strain of reinforced coral sand
图 8 不同循环应力比和相对密实度下加筋珊瑚砂超静孔压比-双幅轴向应变关系曲线
Fig. 8. Relationship curves of excess pore pressure ratio-double-amplitude axial strain for reinforced coral sand under various CSRs and relative densities
图 9 Dr=85%时加筋珊瑚砂超静孔压比实测发展模式和不同模型拟合结果对比
Fig. 9. Comparison of the measured development pattern of excess pore pressure ratio and the fitting results of different models for reinforced coral sand at Dr=85%
图 11 参数A×Dr和B-循环应力比关系曲线
Fig. 11. Relationship curves of parameter A×Dr and B-cyclic stress ratio
图 12 超静孔压比-双幅轴向应变关系试验数据和预测趋势对比
Fig. 12. Comparison of test data and predicted trend of excess pore pressure ratio-double-amplitude axial strain relationship
表 1 固结不排水动三轴试验工况
Table 1. Consolidated undrained dynamic triaxial test conditions
编号 格栅层数 相对密实度Dr (%) 循环应力比CSR #1 0 70 0.24 #2 1 70 0.24 #3 2 70 0.24 #4 3 70 0.21、0.24、0.27、0.30 #5 3 50 0.15、0.18、0.21、0.24 #6 3 85 0.24、0.27、0.30、0.33 
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