Study On Wetting-drying Cycle Effect Of Erosion Environment On Cement Modified Expansive Soil

Expansive soil is a kind of special cohesive soil that is sensitive to environmental factors,especially the changes of temperature and moisture can easily cause the dry and wet cycle effect of expansive soil,which leads to its expansion and contraction deformation,which causes the water swelling and softening of soil.Dehydration shrinkage cracking phenomenon,will cause the degradation of the soil compressive performance,and then make the building on it crack,tilt and other damage.In view of the above-mentioned problems in expansive soils,physical,chemical or biological measures are often used to improve the performance of expansive soils..Cement modification is a kind of expansive soil modification method with strong applicability and significant effect.For the modification measures of expansive soil,the existing research mainly considers the impact of the modified material itself,and less considers the influence of environmental factors.However,the modified expansive soil is often in the environment of erosion,wet-dry alternation,and so on.Therefore,it is very important to study the coupling effect of environmental factors and alternating wet and dry changes on the effect of expansive soil modification..The expansive soil in Binhu New Area,Hefei City,Anhui Province was selected as the research object.An indoor modification test was designed.Firstly,the effect of different cement content?0,5%,10%,and 15%?on the modification performance of expansive soil was compared.And through 3 times of dry and wet cycle test?the change rate of moisture content is between 10%and 20.35%?and the corresponding unconfined compression test,the volume change rate of corresponding soil caused by the change of cement content was studied comparatively.The variation of the peak load-displacement curve of the soil and the fluctuation of the corresponding soil,and thus the effect of the change of the cement content on the expansion and contraction characteristics and compressive performance of the expansive soil.Then,the corrosion effects of pure water,different concentrations?1.5%,9%,18%?and different types?MgCl₂,NaCl,Na₂SO₄?of chemical solutions on cement-modified expansive soils under wet and dry cycles were studied.According to the macro crack development and volume change of the sample,the corresponding load-displacement curve and the peak strength,the change law of mechanical properties of cement-modified expansive soil under different erosive environments with the number of dry-wet cycles is obtained,and the corresponding effects are obtained.The mechanism is elaborated in depth.The results show that with the increase of cement content,the swelling and shrinkage deformation of expansive soil is effectively suppressed,its compressive performance is effectively improved,and the stability under the action of dry and wet cycle is improved.The dry and wet cycles of the erosion environment have a significant effect on the mechanical properties of cement-modified expansive soils,and become more pronounced as the concentration of the etching solution and the number of wet-dry cycles increase.The effect of low concentration of erosion solution on the compressive strength of soil under high-frequency wet-dry cycles is consistent with the effect of high concentration of erosion solution on the compressive performance of soil under low-frequency wet-dry cycles.However,only the high-concentration sodium sulphate solution's wet-dry cycle has obvious differences in the expansion and contraction of the soil relative to the pure water,and the effects of the wet-dry cycles of other solutions with different concentrations on the expansion and contraction of the soil are affected.The water is closer.The research results can provide scientific basis for the study of the stability and durability of the cement modified expansive soil under the complex environments such as erosion and dry-wet alternating,and it has certain guiding significance for the engineering design and foundation treatment of the expansive soil area.