Study On Preparation And Mechanical Properties Of Two Types Of Modified Cemented Soil

In recent years, with the rapid development of economy construction, the scale of infrastructural construction is getting larger and larger in our country. Many projects are constructed on soft soil foundation. Because of the poor physical and mechanical properties of soft soil, the foundation should be reinforced. Cemented soil has obtained excellent effect in treatment of soft ground, and been widely applied in many engineering fields, such as civil engineering, water conservancy and communications since economic, environmental and convenient to construct. The shortcomings of cement-soil, such as low early strength, serious deformation in the late stage and poor toughness, however, restrict its further application. This thesis in line with the development of "green" building materials the purpose and refers to the modification measures of cemented soil and other cementitious materials, and uses secondary fiber and microorganisms to improve the mechanical properties of cemented soil.Firstly, according to the unconfined compression tests on two types of modified cement-soil, this thesis has studied the stress-strain relationships, strength, modulus and toughness and analyzed the influence of secondary fiber or microorganisms and curing time on mechanics behaviors of cemented soil.Secondly, this thesis has analyzed the mechanism of fiber ratio or microorganisms to improve the mechanics properties of cemented soil by using microstructural test, such as scanning electronic microscope(SEM) test and mercury intrusion porosimetry(MIP) test.Thirdly, shock compression test of two types of modified cemented soil have been done by separate Hopkins pressure bar(SHPB) test device, and comparative analyzed their static and dynamic mechanical properties.Then, suitable damage variable has been selected for two types of modified cement-soil based on the damage mechanics theory, and reveals the damage evolution law of two types modified cemented soil by cyclic loading-unloading experiments.Finally, the bearing capacity characteristic value of composite foundation and settlement of reinforced field in composite foundation has been calculated based on the laboratory test results of microbial cemented soil.Laboratory test results showed that secondary fiber could increase the toughness of cemented soil effectively. Strength, elastic modulus and toughness of cemented soil has increased with the increase of bacterial concentrations. Compared with the results of unconfined compressive strength test, the strength and elastic modulus of two types of cemented soil have increased and the toughness has decreased under the impact load. The application of microbial cemented soil in composite foundation showed that the bearing capacity characteristic value has increased and the settlement of reinforced field has decreased with the increase of bacterial concentration.