| Expansive soil is a kind of high plastic clay with hydrophilic minerals in high proportions.It is sensitive to dry and wet climate change and has characteristics of significant volumetric deformation and even shrinkage cracking due to the absorption or loss of water,which brings great harm to engineering construction activities.Thus,how to effectively improve over-wetted clays to meet the requirements of engineering construction is a engineering technical problem needed to be solved.This paper is supported by Anhui Province Natural Science Foundation“Experimental Study on Engineering Properties and Micro-Mechanism of Expansive Soils treated with Iron tailing sands”?1608085 MD81?,combined with the research results of the research group.In this study,expansive soil,excavated from a foundation pit in Hefei city,Anhui province,is research target,and indoor experiments combined with theoretical analysis is the method.Through extensive laboratory experiments on effects and mechanism of expansive soil treated with iron tailing sands and calcium carbide,following conclusions are obtained:?1?These indexes,free swelling ratio,expansion force,liquid limit and plasticity index,have very high connection with clay content,which all increase with the increase of clay content.While the correlation between plastic limit,loaded swelling rate and clay content are low.?2?During drying-wetting cycles,the swelling capacity,free swelling ratio,expansive force,the liquid limit and the plastic index of the specimen increases initially and then followed by a decreasing trend,and reached the threshold when the number of cycles was 7 times.While a reverse trend can be observed for the evolution of loaded swelling rate and plastic limit.?3?For specimens with curing time of 14d,the unconfined compressive strength initially increases with the increase of the drying-wetting cycle.After the achievement of the peak value,the unconfined compressive strength starts to decrease and the decreasing rate reduces with the increase of drying-wetting cycle.After 10 cycles of drying-wetting,the unconfined compressive strength tends to be stable.For specimen with curing time of 28d,only the latter two stages could be observed in the strength and compressibility coefficient evolution with the drying-wetting process,and the evolution is also verified from the perspective of microstructure.?4?An exponential relationship can be adopted to describe the evolution of the unconfined compressive strength and the compression coefficient with the drying-wetting cycles for expansive soils treated with iron tailing sands and calcium carbide slag.These functions are both related to the initial conditions of the sample and the number of cycles,which simulate the effects of seasonal changes on the improved soil and provide a reference for engineering construction.?5?Investigations on the expansion characteristics,unconfined compressive strength,the compression coefficient and the Atterberg limits show that,the critical?CCSCS of 10%could be determined as the optimal value for improvement of the expansive soils,which implies the minimum effect of drying-wetting cycles on the properties of the specimen.?6?Investigations on the microstructure of specimen show that,the changes of pore and aggregate in the microstructure are consistent with the changes in macro-mechanical properties. |
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