中风化泥质粉砂岩石灰改良回填料试验研究

Experimental research on lime-improved backfill ofmiddle-weathered argillaceous siltstone

中风化泥质粉砂岩遇水易软化崩解造成工程性质不稳定,为合理利用中风化泥质粉砂岩,克服常规碎石基料来源困难并解决成本高的问题,依托浙中某地铁项目,对开挖区典型中风化泥质粉砂岩的物理力学特性进行了分析。然后采用生石灰对中风化泥质粉砂岩进行改良配合比设计,开展了不同石灰掺量及含水率下的石灰改良回填料的无侧限抗压强度和最优含水率试验研究。结果显示,中风化泥质粉砂岩干强度最高,天然强度次之,饱和强度最低,干强度和饱和强度差与天然强度比值达46%;石灰掺量4%~20%范围内石灰改良回填料的应力应变关系曲线呈现峰前硬化及峰后软化的特征,无侧限抗压强度随石灰掺量增加而升高;含水率10%~20%范围内石灰改良回填料干密度随含水率增加呈现出先升高后降低的特征,最优含水率随石灰掺量增加而增加。石灰改良回填料的强度及含水率试验结论可以为后续工程应用提供重要指导。

Middle-weathered argillaceous siltstone exposed to air results in unstable engineering properties because of susceptibility to being softened and disintegrated by water.In order to reasonably utilize the middle-weathered argillaceous siltstone and avoid the scanty supply and high cost of conventional crushed stone base,the physical properties of typical middle-weathered argillaceous siltstone were analyzed in the excavation area of a certain metro project in Zhejiang.Lime was used to improve middle-weathered argillaceous siltstone for the design of mix proportion scheme.Experimental study was conducted on the unconfined compressive strength and the optimum moisture content of the lime-improved backfill under different lime contents and moisture contents.Results show that middle-weathered argillaceous siltstone has the highest strength in the dry state,the moderate strength in the natural state and the lowest strength in the saturated state.Ratio of the difference between dry strength and saturated strength to natural strength reaches 46%;the stress-strain curve of lime improved backfill in the range of 4%—20%lime content shows pre-peak hardening and post-peak softening characteristics,and the unconfined compressive strength of lime-improved backfill increases with the lime content;the dry density of lime-improved backfill in the range of 10%—20%moisture content increases initially and then decreases.Optimal moisture content of lime-improved backfill increases with the lime content.Lime-improved backfill strength and water content test conclusions can provide important guidance for subsequent engineering applications.