| Silty mudstone is a kind of expansive soft rock widely distributed in the areas of Hubei,Guizhou and other regions in China,which shows the characteristics of shrinkage cracking and expansion softening under the condition of water and water loss respectively,leading to the continuous deterioration of mechanical properties.Under the influence of subtropical monsoon climate,temperature and humidity tend to aggravate the development of fissures in siltstone rock,resulting in slope instability and damage,which eventually threatens the long-term safe operation of the project.In view of this,this paper carried out relevant physical property tests,analyzed the composition and basic physical properties of siltstone,and then studied the deterioration law of siltstone under the influence of different factors;and based on the test results,systematically revealed the damage mechanism of siltstone under the action of humidity,temperature and fissure.The main research contents and conclusions are as follows.(1)The ultrasonic longitudinal wave velocity test was used to group the siltstone,and it was found that the wave velocity was mainly distributed in the range of 2.55～2.85 km/s.The composition analysis test showed that the main minerals were clay minerals such as quartz,montmorillonite,fluoromagnesite,illite and chlorite,and the main chemical composition was SiO2,Al2O3,Fe2O3 and K2O;the particle The density and gross volume dry density are 2.73g/cm3 and 2.30/cm3,respectively;porosity is 15.80%,water content is 11.78%,water absorption and saturation water absorption are 14.34%and 15.10%,respectively;(2)Dry and wet cycle tests and hot and cold cycle tests were conducted,and ultrasonic longitudinal wave velocity tests were performed on the siltstone during and after the tests,and the results showed that the decrease in external morphology and ultrasonic longitudinal wave velocity of siltstone under the action of dry and wet cycles showed a gradual deterioration and enhancement with the increase in the amplitude of dry and wet cycles and the number of dry and wet cycles,and the decrease in external morphology and ultrasonic longitudinal wave velocity of siltstone under the action of hot and cold cycles showed a gradual deterioration and enhancement with the increase in the temperature of hot and cold cycles and the number of hot and cold cycles;(3)Low-perimeter pressure triaxial compression tests were conducted on the chalky mudstone treated with wet and thermal factors,and the mechanical characteristics of the chalky mudstone under different test conditions were studied according to the stress-strain curve,peak stress,peak strain,elastic modulus,cohesion and internal friction angle.The correspondence between the number of dry and wet cycles,the amplitude of dry and wet cycles,and the external envelope pressure and mechanical parameters were obtained under the action of humidity factor,and the correspondence between the number of hot and cold cycles,the temperature of hot and cold cycles,and the external envelope pressure and mechanical parameters were obtained under the action of temperature factor,revealing the deterioration trend of mechanical properties of siltstone;finally,the compression damage pattern of siltstone was analyzed,and the damage mechanism of rock samples under the action of different external factors was summarized;(4)Based on the characteristic of rapid development of fractures in siltstone under the influence of external environmental factors,uniaxial compression tests were conducted on siltstone with different fracture dips,fracture numbers and fracture distribution locations,respectively,and the deterioration law of mechanical properties of siltstone by different fracture characteristics was obtained through stress-strain curves and compression strength characteristics,and finally the damage mode and fracture evolution mechanism of siltstone were studied by relevant analysis,which deeply revealed the damage law of fractures to siltstone. |
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