Experimental Research On The Influence Of Porosity On Soft Similar Material Damage

Nowadays, large area geotechnical excavation were carried out in all the major projects.With the increase of excavation depth,soft rock which is involved in the project is also gradually increasing.Supporting problem of surrounding rock and soft rock rheological phenomenon is more prominent.All of these bring the great potential safety hazard to the construction personnel and construction equipment.Porosity is a important indicator about water-physical,thermal property and mechanical property of rock,it has great research value.Increase of excavation depth, lead to more complex geological environment, at the time, it also increase the sampling cost.It is apparently impractical, if still completely using real rock as the research object.Geomechanics model test is a study way of complex engineering problem,it is based on similar principle to produce similar model, through model test study can offer the further research of geotechnical engineering.This article is based on the national natural science fund project " study of the energy law and several coupling of deep soft rock solid flow transformation theory "(51374134).Through various physical and mechanical test of a large number of soft rock similar material specimen to study the effect of porosity on soft rock similar material damage. In this paper, the main work has been done would be as follows:Based on geomechanics model test similarity principle, choose a certain geometric similarity scale, can simulate the shale in the sedimentary rocks.In this article, author prepared a batch of five different porosity soft rock similar material specimens, obtained a series of the range of parameters that model test shall meet.Through uniaxial compression test, the Brazilian splitting test, triaxial compression test, it can obtained that various parameters of five different porosity soft rock similar materials are prepared in this article conform to the principle of similar parameters.By the above three trials come to theconclusion:Uniaxial compressive strength, elastic modulus, tensile strength, cohesive force and internal friction Angle of soft rock similar material decreases with the increase of porosity; however, poisson’s ratio of soft rock similar material increase with the increase of porosity.Through repeatedly loading and unloading experiments performed on specimens, come to a conclusion: With the increase of porosity, the plastic hysteresis grow larger gradually.In the process of loading and unloading, specimens’ wasted energy increase which is wasted as the following form: internal crack closure, material yield,damage, fracture and sliding friction of fracture surface.Through the uniaxial and triaxial creep test of three of five different porosity soft rock similar material, come to a conclusion: the creep curve of three different porosity soft rock similar material is very similar to creep curve of real rock, they all have three phases: the initial creep stage, the stable creep stage and the accelerated creep stage.With the decrease of porosity, breaking load and axial strain all has increase.On the basis of triaxial creep experiment, using the ANSYS software to analyze the creep in soft rock tunnel excavation, can come to a conclusion:With the increase of porosity, the final creep value decreases, creep trends to be stable.Through simulation and find: The strain of roof and floor is obvious, it prove that roof fall and bass drum phenomenon would happen. This can fit engineering practice well.