Study On The Mechanism Of Mechanical And Damage Behavior Of Sandstone With Different Water Content Based On 3D Reconstruction Technique

The mechanical and damage behavior of engineering rocks has been a hot topic of research in practical projects such as tunnels,slopes,and oil and gas extraction,where water plays an important role among the many influencing factors.The presence of water in the micropores has great influence on the mechanical properties and damage fracture behavior of rocks.It is necessary to fully understand the mechanism of this influence,which is present throughout all stages of rock compression and damage.Few previous studies have investigated the effects of water in micropores on the mechanical and damage behavior of rocks at different stages of compression.Also,in terms of the scale of the study,the morphology,spatial distribution and its evolutionary characteristics of rock damage in different water content have rarely been studied from the microstructure of the rock interior such as particles,pores and microcracks,so as to correctly predict the macroscopic mechanical behavior of the rock.Based on this,this paper investigates in detail the mechanisms of changes in mechanical properties(strength,energy,strain,etc.)of sandstone at different compression stages with different water content and realistically reproduces the three-dimensional cracking behavior using three-dimensional reconstruction techniques,and quantitatively determines the influence of micro-pore moisture on the failure mode and cracking process of sandstone through digital analysis of X-ray CT images,and through a digital model with realistic microstructure geometry and topology numerical studies were conducted to effectively verify the strength behavior.The main findings are as follows.1 Under uniaxial compression conditions,both compressive strength and modulus of elasticity of sandstone specimens decreased with increasing water content,but the decrease pattern was different.Compared with the compressive strength,the decreasing trend of the elastic modulus is more linear.After the specimens were damaged by compression,their cracking forms were complex,and the main damage forms were all shear damage.Statistical analysis was carried out by parallel experiments.It was found that the crack types of the specimens were more complicated at the water content ?=1% and water content ?=2.5%,i.e.,lower water content conditions;when the water content increased to ?=3.5% and ?=4.5%,the crack types were relatively simple.The effect of different loading methods on the crack types was not significant.2 The effect of water content on the total energy was found to be consistent at different compression stages through cyclic loading and unloading experiments,i.e.,it increased with the increase of water content.In terms of the variation of dissipation energy at each stage,the dissipation energy decreases slightly with increasing water content when unloading at low stress levels;the dissipation energy of the specimen increases significantly with increasing water content when unloading at high stress levels.3 When unloading immediately after compression to different stages,the residual strain tends to decrease with increasing water content when the unloading stress is at 5MPa and 10 MPa(low unloading stress level);when the unloading stress exceeds 20 MPa,the residual strain increases significantly with increasing water content.4 X-ray CT imaging and 3D reconstruction techniques are favorable tools for accurately identifying the details of cracks and observing the real rupture behavior inside the specimen in real time.The damage form of the specimen in uniaxial and unloading experiments is complex and contains multiple crack types.5 The characteristics of the microscopic pore network were quantified by defining digital microstructural variables,i.e.,as the water phase in the specimen micropores increases,the digital pore size first decreases,then increases,and finally in decreases.This variation trend is consistent with the variation of the digital water phase size.In addition,it was found in the statistics of the spatial distribution of the microscopic phases that the proportion of the distribution of the solid phase decreases when the water phase in the micropores rises due to the dissolution effect of water on the cemented material.6 The mechanism of the effect of water in micropores on mechanical properties is well investigated by numerical simulations of real microstructure models.Porosity and volumetric water content play a decreasing role on the uniaxial compressive strength of sandstone,while pore water saturation plays a facilitating role on the compressive strength.7 Based on the segmented digital CT images,the digital damage rate is defined to define the degree of damage and quantify the three-dimensional cracking behavior of sandstone at different water contents.Based on the damage rate curves,the compression process of the rock is divided into five stages.The results of this experiment are instructive for predicting the fracture behavior of rock structures in wet environments such as tunnels,slopes,nuclear waste disposal,geothermal,oil and gas extraction,and even ancient stone ruins.