Original Stress Release And Engineering Properties Of Mudstone

With rapid development of urban construction, a large of towering structures has been widespread used in many cities. Foundation work of the tower building have also become much complex. In recent years, with increasing of foundation depth, the mudstone of Tertiary often are chose as the foundation supporting layer and supporting layer of Pile top of the important and high-rises construction. Therefore, it is inevitable to involve the problems about determining the geotechnical parameters of mudstone and pit slope stability. The parameters of before mudstone experiment showed much characteristic of discrete and variation. They appears uncertainty and fuzzy in engineering practice.Through discussing the geological history of Nanning Basin in the former two chapters and summing up engineering characters of mudstone and influencing factors, the thesis shows there is important relationship between engineering characters variation of mudstone and virtual stress release. Firstly, there is high lever bearing capacity of mudstone; Secondly, saturated mudstone and mudstone with high water content will not swell and collapse. Water-rock interaction has little influence on mudstone with low water content. The negative mechanical effect between mudstone and water only act in unloading disturbance and exposure environment. So, mudstone micromechanics effect of water-rock interaction is the micromechanics property variety which caused by mudstone structure variety.Based on above theories, the thesis analyzes initial stress state of mudstone. It also selects the initial stress state which consolidated by K0of the tradition. From exploration sampling, excavation pit and pile foundation, the thesis studies initial stress releases in the three typical engineering. Aiming at mudstone experimental scheme of specialty design, it makes sample preparation of free swelling ratio with100%. Adjusting and controlling density and moisture content of each sample, the thesis has made four different typical experiments by these samples, they are as follows:Simulation experiments of mudstone in different stress states, simulation experiments in different initial stress states and stress releases and simulation experiments of stress release in drilling water-rock interaction. It has drawled the follow four conclusions.1Eigen material composition and structural property of mudstone are cannot be changed. Variable factors influenced on mudstone include mechanical disturbance, water-rock interaction and stress release.2Study on saturated samples shows that strength parameters of soils in different stress states are different. The strength parameters of mudstone samples in different stress states which formed by different stress history have huge difference. The parameters of samples which have stress history of KO consolidation are all higher than samples which have initial and isotropic consolidation stress states. Stress path of KO consolidation is beneficial for soil alignment and soil structure. All strength parameters enhanced.3Experimental study on unsaturated samples shows that mechanical properties of mudstone in different stress states will be obviously changed after stress released.Without stress release, strength and soil structure of mudstone samples in KO consolidation are all higher than isotropic consolidation, especially on internal friction angles.Stress release has a certain influence on soil structure. Strength decrease of mudstone in isotropic consolidation appears on cohesive force. Cohesive force and internal friction angle of mudstone in K0consolidation all decreased, but the total strength is higher than isotropic consolidation.4Experiments on different drilling depth temples shows that drilling depth has influence on sample strength. It appears cohesive force decreased, tangent modulus decreased and internal friction angle increased. When drilling hole is before failure surface, internal friction angle increase can remedy cohesive force decrease. When drilling hole surpass failure surface, internal friction angle increase cannot remedy cohesive force decrease and the total strength will decrease. Mudstone softening when touching water the softening degree depends on water volume. The key factor which acting on mudstone swelling pressure when touching water is mudstone material composition structure. Tip resistance of the pier foundation which used mudstone for bearing stratum has a little change after soaking water, and it is only3%of the strength without soaking.