Study On Damage Evolution Law Of Cement Stabilized Soil Based On Mereury Intrusion Porosimetry

The main characteristics of soft soil which is short for soft cohesive soil are thatit has the high water content in nature, high compressibility, low bearing capacity,soft plastic to flow plastic’s physical state, and the soft soil is wildly distributed inChina. With the need of our rapid development of China’s economic construction,cement-stabilized soil is more and more widely used in the engineering construction,especially in soft soil areas such as Shanghai, Dalian, Shenzhen and so on. With theincreasing of super high-rise buildings and land reclamation and other largeengineering, the effect of ground reinforcement plays important role in the entirequality of the project. The present study for cement-stabilized soil mainly focus onlooking for external macroeconomic factors’ effects of on mechanical properties,such as cement mixing ratio, age, strength grade of cement and soil composition andother factors, but ignores that the microstructure of cement soil is the key mechanicalproperty.Through the study, we can find that compared with the soil, stress-strain curve ofcement-stabilized soil has obvious linear elastic stage and compared with the concrete,as cement-stabilized soil will have a large plastic deformation under the load, and itsmechanical property is in constant change in the loading process,so it is difficult todescribe the deformation characteristics of soil cement by usual constitutive model.But the damage mechanics is a good solution to this problem and can better reflectthe stress-strain relationship of the solidified soil. In order to study the interpretationand study macroscopic damage mechanism from the microscopic point of view, withthe help of porosity, set up the damage constitutive model and obtain the relationshipof porosity, strain and stress. So we can use the porosity to judge stress state offoundation and predict the probable deformation and settlement deformation in engineering project. This study has a certain significance for the further study onmechanical properties of solidified soil, and can better guide the practice inengineering to reduce the blindness and randomness.Based on the National Natural Science Fund Project of research on improvementscheme to soft soil of cement reinforcement with high content of organic matter, thepaper will take stabilized soil which is made of the soft soil from Lianyungang Areasolidified with cement and take for curing with28days as the research object.According to stress strain curves of the unconfined compression test, the wholeprocess can be divided into four stages which are the phase of closure in cracks andholes, the phase of linear elastic response, steady expansion stage in micro defect andunsteady expansion stage of crack coalescence. Then, the paper takes specimens inthe unconfined compression test for mechanical analysis by using FLAC3D software.Then we can obtain the failure process of specimen, analysis its failure mechanism,simulate and explain the damage phenomena in the experiment. On the basis of abovestudy, combined with the previous results and fractal theory, the paper analyzes themicrostructure data obtained from mercury injection test and divides specifically thesamples’ void interval, then obtaining the variation rules of cement solidified soil inexternal loads. The rules can be summarized as below. First of all, in the crack andhole closure stage, medium holes are compressed, while the content of small andmicro pore increases. Secondly, with the increasing of pressure, the micro porecontent decreases gradually. Because the fine pores forms after the destruction of thesample, the micro pore content increases significantly. Thirdly, while the variation ofsuper large and large pores in sample did not change significantly in low level stress,the content increase significantly, when the specimen deformation reaches its limit.The injury is micro structural changes which can cause degradation propertiesof solid materials in the load and environment. In the study of microscopic structure,we can find that the change in size and shape of the micro morphology and structureis the essence of injury, and at the same time, the porosity change can reflect well thestress state and internal damage of the soil. In order to study macroscopic damagemechanism from the microscopic point of view, the paper defines damage variableswith the help of porosity, plots the relationship curves between the damage variable and strain based on the experimental data. Then based on what we have studied, thepaper optimizes the definition of the previous damage variables. After comparingthree kinds of relation curves of damage variable and strain and the damage evolutionequation, the paper finds that the overall trend of image is the same for the samedamage field. Comparing the damage evolution equation by fitting, finally the paperdetermines the damage variables and the damage evolution equation, which lays thefoundation for the further research of constitutive model of damage.