Study On Mechanical Property Of Cemented Soil Under Environmental Contamination

Cemented soil is a type of compact mixture of Portland cement,soil, aggregate and water.It has beeh widely used for foundation treatment, foundation pit protection and many other projects.However,s eawater,th e groundwater in most areas often contain some erosive ions such as SO₄^2-,Cl^-, Mg²⁺af fected by envir onmental factors as agriculture,industry,sewage of daily life.So it is of great importance to study on various mechanical properties of cement-mixed soil,especially under the condition of environmental erosion.H₂SO₄,MgSO₄,CaSO₄,NaSO₄ and MgCl₂ solutions were made up in laboratory to simulate erosion environments.The blocks of cement-mixed soil were cured in the solutions until to schedule time,and then apparent photos of cemented soil blocks in erosion environments were taken by using a high-precision digital camera.And tests of unconfined compressive strength of cemented soil in various erosion environments and different curing time were carried out by the use of electronic controls universal testing machine.The fracturing process of cemented soil was observed in real time.Therefore, corresponding load-displacement curves,ultimate strength and other testing results are obtained.And the meantime corresponding macroscopic processing photos are obtained.Secondly,the cracking feature of cemented soil under environmental erosion was analyzed.It proved that main damaging style of cemented soil including 12%cement under uniaxial compression is brittle crack.And in all kinds of environment,the damaging features and modes are the same.The test results show that the SO₄^2-,Cl^-,Na⁺ and Mg²⁺environmental erosions make the unconfined compressive strengths of cemented soil block reduced,and the Strength degrees are related closely with the type of chemical solution and its concentration.The most remarkable and sensitive effects on mechanical properties of cemented soil is the transformation of erosive environments. Moreover,the erosive mechanism of cement-mixed soil under environmental erosion is a series of physical and chemical reaction between mineral components in cemented soil and chemical components in environmental erosion.It causeS the change of microscopic structure of cemented soil and so does the mechanical properties.In environmental erosion,acid solutions have degraded effect on cemented soil.If the contains of sulfate is used appropriately and the crystal particles of sulfate are well-distributed in the whole cemented soil,it will enhance the strength of cemented soil,whereas it will be reduced.And also magnesium salts can reduce the strength of cemented soil.The result will be the same if there are large amount of chloride in groundwater.Therefore,the erosive environmental influence on cemented soil should be taken into consideration and suitable measure should be used to ensure the safety of the structure in a practical project.At last,the design formula of upright bearing capacity of cement-mixed soil pile under environmental erosion is modified based on experimental data. And a coefficient named of environmental effect factor is proposed with its range of value qualitative analyzed.The study provides basis for the design and application of cement-mixed soil in complex environment.Further more, erosion-resistant measures to cemented soil under polluted environment are proposed.