Study On Influence Factors Of Unconfined Compressive Strength Of Cement-soil

With the deep great development of Northwest China, there are lots of road engineering and hydraulic engineering in the northwest of China. Loess is one of the main building materials in Northwest China, however, because the Loess has the characteristics of collapsibility, unsaturated, seismic subsidence, the strength of it often can not meet the actual needs of building engineering, such as the settlement of foundation and subgrade bearing capacity. In order to meet the requirements of engineering, we always mix cement or lime to improve the strength of loess. Cement-soil is a mixture which is after three steps of mixing, vibrating and maintenance,with soil as the main aggregate, with Portland cement as the cementing material, with water as the medium of the composition, and admixture is added to improve the engineering properties. It has a number of advantages of high compressive strength, frost resistance,impermeability, corrosion resistance, erosion resistance and durability, and it is widely used in pavement, slope reinforcement, foundation stability, anti-seepage lining, and wall materials of rammed earth building. In this paper, according to the previous results, we mainly used earth material for dam construction of Shaanxi Yanan Ansai Yuquan Temple reservoir as the reinforce object and unconfined compressive strength test as test method, studied on the influences of cement content, dry density, water content, curing age and curing method on the unconfined compressive strength and the relationship between stress and strain of cement-soil, and drawed the following conclusions in the end.(1) With the increase of the quantity of cement, the maximum dry density and optimum water content of cement-soil had a little increase, and the unconfined compressive strength increased linearly. Under the same cement content conditions, the unconfined compressive strength of cement-soil increased linearly with the increase of dry density; the unconfined compressive strength of cement-soil decreased and had a quadratic functional relationship with the increase of water content; the unconfined compressive strength of cement-soil increased and had a power functional relationship with the increase of curing age.(2) There were pressure dense stage, elastic stage, plastic hardening stage and stress decay stage four stages in cement-soil stress-strain curve; The increase of cement dosage and curing age can decrease the elastic-plastic deformation of cement-soil; But the increase of dry density and water content can increase the elastic-plastic deformation of cement-soil.(3)Through soaking the cement-soil with different combinations of salt solution(Na2SiO3, NaOH and Na2SO4), and changing the combination way of three solutes, we foud the best solution combination which can enhance the unconfined compressive strength of cement soil mostly. Through the analysis of range and variance analysis of orthogonal test results, we determined the optimum combination of salt solution is(Na2SiO3)3(NaOH)1(Na2SO4)2,that is, Na2SiO3 is 0.4mol/L, NaOH is 0.1mol/L, Na2SO4 is 0.02 mol/L, also known as the 312 solution.(4) No matter what the curing age is, the order from high to low of the unconfined compressive strength of cement-soil were: 312 solution maintenanceâ†'saturated limewater curingâ†'standard curing. The cement-soil samples of 312 solution maintenance and saturated limewater cured, along with the age increasing, their maintenance increase would tend to be gentle.(5) In the standard curing condition, with the increase of curing period, the elastic-plastic deformation of cement-soil reduced and brittleness was more and more obvious; 312 solution maintenance can increase the cement-soil elastic-plastic deformation and improve its plasticity, but along with the age increasing, its maintenance increase would tend to be gentle; Saturated limewater curing can not increase the cement-soil elastic-plastic deformation, but can maintain the cement-soil plasticity remain unchanged.