基于原位测试指标的砂土时间效应定量表征初步研究

Characterization of ageing effect of sands based on field testing indices

时间效应对土体抗液化强度有显著影响,其定量表征是砂土地震液化判别的研究难点之一。基于土体小应变剪切模量Gmax和静力触探锥尖阻力qc的经验表达式,对土体密实度和有效应力作归一化处理,提出了砂土时间效应的表征指标AI。该表征指标在数学上表达为小应变剪切模量与大应变静力触探锥尖阻力的结构性参数的比值函数。通过分析已有室内试验数据发现重塑砂土具有稳定的AI值,而对现场数据的分析则揭示了砂土沉积年代越久、AI值越大的整体趋势。该表征指标能揭示土体力学特性随时间的演变规律却不含时间变量,因此是一个"表观时间"参数,为进一步研究时间效应对砂土抗液化强度的影响规律提供了基础。

Ageing has significant effect on soil liquefaction resistance, and the quantitative characterization of ageing effect is one of the key research themes in assessment of soil liquefaction. An ageing index（AI） characterizing soil ageing effect is proposed based on small strain shear modulus（Gmax） and cone penetration resistance of CPT testing（qc）, with further normalization of soil density and stress state. This index is expressed by a function of the ratio between the fabric parameter of small strain shear modulus and that of large strain penetration resistance. The analysis of laboratory test data shows that the reconstituted sand has a stable reference AI value, while the field data reveal that AI increases with the increase of geologic age of the soil deposit. AI is an apparent parameter as it can characterize the extent of soil ageing without the variable of time, which provides a sound basis for further researches on the effect of soil ageing on liquefaction resistance.