天然沉积结构性软土超载预压作用机理研究

Mechanism of surcharge preloading on deformation of soft natural clays affected by soil structure

分析天然沉积结构性土常规一维压缩试验结果,以及不同超载比、不同超载时间和不同卸载时间下的超载预压一维压缩试验结果,探讨超载预压作用下天然沉积结构性软土的压缩变形机理.结果表明:由于天然沉积过程形成的土结构性,使得原状土压缩曲线位于重塑土上方,同一应力水平下两者存在孔隙比差值,造成当外加应力大于天然沉积土结构屈服压力时将产生大孔隙骨架的坍塌,土颗粒的蠕动变形剧烈,因此仅当超载预压的有效超载比能使土体卸载后的应力-应变状态点位于重塑土压缩曲线下方时,才能有效降低土体的蠕变变形速率;若超载预压引起的超静孔压尚未消散结束就进行卸荷,卸荷之后将仍存在较大的变形速率,从而加大建筑物使用期的地基沉降.

This study aims at making clear the role of surcharge preloading on the secondary consolida- tion for natural clays that are affected by soil structure. A series of oedometer consolidation tests were carried out on soft clay with different surcharge pressure ratios, different preloading durations and un- loading durations. Analysis on the testing results indicates that the coefficient of secondary consolida- tion of naturally structured clays decreases only if the void ratio of natural clays undergone surcharge - preloading -unloading locates below the remolded compression curve. Such a phenomenon can be ex- plained by the following mechanism. The compression curve of natural clays lies above those of remold- ed clays, consequently resulting a difference in void ratio under the same stress level between natural and remolded clays. Hence, collapse can be expected for natural clays when the stress level exceeds the consolidation yield stress, consequently causing dramatic deformation of soil particles or aggregates. That is, the deformation caused by secondary consolidation is still relative large when the compression curve of natural clays after unloading still lies above that of remolded clays. On the other hand, when the ex- cess pore water pressure deduced by surcharge preloading is not dissipated, unloading will increase the settlement of the construction during operation period.