采用双曲线模型描述可液化土层动力本构关系的关键是给出循环荷载作用下饱和砂土循环最大剪切模量和循环极限剪应力。针对不同相对密度的几种砂土,通过新型高精度动三轴仪均等固结不同等幅循环应力作用下的液化试验,研究孔隙水压力对饱和砂土循环最大剪切模量和循环极限剪应力的影响模式和规律,提出了考虑孔压增长下的砂土循环最大剪切模量和极限剪应力的具有不同精度的计算公式。主要结果为:孔压增长对饱和砂土循环最大剪切模量和极限剪应力影响明显,循环最大剪切模量比和极限剪应力随孔压比的上升不断降低;孔压增长下饱和砂土循环最大剪切模量和孔压比的关系可表达成与砂土类型及相对密度无关的统一线性关系式,孔压比等于循环最大剪切模量的相对减小量;孔压增长下饱和砂土循环极限剪应力和孔压比的关系,精确要求下可表达成与砂土类型及相对密度相关二次曲线关系;简化考虑下可以表达为与砂土类型及相对密度无关的统一的线性关系式,孔压比等于循环极限剪应力的相对减小量;孔压增长下饱和砂土循环最大剪切模量并不服从Hardin初始最大剪切模量计算公式,若以此计算将导致液化过程中循环最大剪切模量估计过高,特别是在孔压比为0.6-0.8的敏感区间内,循环最大剪切模量会被高估约80%-140%。
Abstract
The key for using a hyperbolic model to describe stress-strain relationship of liquefiable soil is to determine its cyclic maximum shear modulus and its cyclic ultimate shear stress under cyclic loading. Aiming at several kinds of sand soil with different relative densities, liquefaction tests under the action of cyclic stresses of different equal-amplitudes were uniformly consolidated using a new high-precision dynamic tri-axial apparatus to study effects’ mode and law of pore-water pressure on maximum shear modulus and ultimate shear stress of saturated sand soil. Formulas to calculate cyclic maximum shear modulus and ultimate shear stress of sand soil with different precisions were proposed considering increase in pore-water pressure. The results showed that effects of increase in pore-water pressure on cyclic maximum shear modulus and ultimate shear stress of sand soil are obvious, sand soil’s cyclic maximum shear modulus and ultimate shear stress decrease with increase in pore-water pressure; the relation between saturated sans soil’s maximum shear modulus and pore water pressure ratio can be expressed as a unified linear relation expression to be independent upon sand soil types and their relative densities, pore water pressure ratio is equal to the relative reduction of cyclic maximum shear modulus; the relation between cyclic ultimate shear stress of saturated sand soil and pore water pressure ratio can accurately be expressed as a quadratic curve relation to be dependent on sand soil types and their relative densities, it also can be expressed as a unified linear relation expression to be independent upon sand soil types and their relative densities considering simplification, pore water pressure ratio is equal to the relative reduction of cyclic ultimate shear stress; Hardin initial maximum shear modulus calculation formula is not suitable for calculation of cyclic maximum shear modulus considering increase in pore water pressure, Hardin formula generally overestimates sand soil’s cyclic maximum shear modulus in liquefaction process; especially, the cyclic maximum shear modulus can be overestimated almost 80%-140% within the sensitive interval of pore water pressure ratio of 0.6 ~0.8.
关键词
砂土液化 /
双曲线模型 /
循环最大剪切模量 /
循环极限剪应力 /
孔隙水压力
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Key words
sand soil liquefaction /
hyperbolic model /
cyclic maximum shear modulus /
cyclic ultimate shear stress /
pore water pressure
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参考文献
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脚注
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