天然土层初始状态与土体压缩性的相关性刍议

DISCUSSIONS ON INTERRELATION BETWEEN INITIAL STATE OF NATURAL SOIL STRATA AND THE COMPRESSIBILITY

通过分析自钻式旁压仪等原位测试手段获取静止侧压力系数偏高现象,揭示了传统理论估算天然土层垂向应力偏小的事实。经历勘探开采的卸荷膨胀,室内实验取得的原状样本重力密度不再等同于地层埋藏条件的初始状态。初始状态不会背离土体压缩性本质,因此以均匀性假设条件认知上覆压力作用下天然土层土体的物理性质并不恰当。本文采取固结压力附加100kPa等技术措施变革压缩实验分析模式,探索构建与压缩和回弹性质及应力历史条件相关的天然土层初始状态数学模型。结合应用实例,提出室内实验观察的回弹指数不足以体现样本的膨胀状况,最小干密度和液限状态的物理意义或是土体原始压缩的最大孔隙特征,以及压缩指数不能圆满诠释土体压缩性原理等见解。

The analysis of some in-situ test means,such as self-boring pressure meter has revealed a phenomenon that the coefficient of lateral earth pressure at rest in natural soil strata is commonly on the high side.One of the reasons of the phenomenon is that the vertical stress estimated with the traditional theory is on the low side.For undisturbed sample had gone through the process of unloading and expanding,the gravity density of the soil tested in lab is no longer equal to that at the initial state in buried conditions before exploration and excavation.Influenced by the overburden pressure in initial state,the physical properties of soil should not be deviated from the compressible nature.So it is improper that the natural soil is identified in the idea of homogenization assumption.This paper takes technical measures,for example,adding 100kPa to the consolidation pressure in order to reform the analyzing model for compression test.It tries to build the mathematical model of the initial state of the soil with the conditions associated with the virgin compression,recompression and stress history of the soil body.Combined with case analysis,the recompression index proposed in experimental observation is not enough to reflect the expansion of samples.The physical meanings of minimum dry density and limit of liquidity may be the virgin compression of soil’s characteristics of void ratio in loosest state.The compression index cannot give expression to the compressibility principle satisfactorily.