Experimental Study On Expansion Properties Of Anhydrite Rocks With Different Hydration Types

This paper takes anhydrite rock as the research object,through theoretical analysis,experimental verification and other methods to study the expansion mechanism of anhydrite rock,hydration type and expansion performance,explains the expansion mechanism of anhydrite rock,and puts forward the rapid identification method of hydration type of anhydrite rock.The variation law of expansive force of anhydrite rock with different hydration types and that of anhydrite rock with the same hydration type after different cycles of wetting and drying are discussed.The main research results are as follows:(1)based on the regional geological data collecting and existing expansion mechanism by hand specimen identification,test means such as thin section identification,X-ray diffraction experiment analyzed the basic properties of anhydrite rocks,and from the anhydrite crystal structural characteristics of rock mass and the hydration reaction thermodynamics analysis to explain the expansion properties of hardened gypsum rocks.(2)Study the loss of free water and crystal water in anhydrite rock at a certain temperature range,and draw the weight loss curve of anhydrite rock with temperature rise.The high temperature dehydration test was designed to identify the hydration type of anhydrite rock,and the results were compared with those of thermogravimetric analysis.It was found that the two results were similar,and the high temperature dehydration test was more simple and fast to identify the hydration type.(3)Based on the expansion characteristics of anhydrite rock when it meets water,the expansion characteristics of anhydrite rock at room temperature are analyzed by free expansion rate test,confined expansion rate test and expansion force test,and the results show that the expansion force and expansion rate of anhydrite rock are smaller than the theoretical expansion.Based on the study of weight loss curve of anhydrite rock at high temperature,and the design of tests to test the change of expansion force of anhydrite rock at high temperature drying,it is found that drying anhydrite rock at 220℃ can measure the maximum expansion force.(4)Based on the theory of elasticity and constant volume method,the triaxial expansive force test instrument was developed to test the triaxial expansive force of anhydrite rock,and the triaxial expansive force which is close to the theoretical expansion amount and suitable for engineering was obtained.(5)The dry-wet cycle test of anhydrite rock was carried out to analyze the influence of dry-wet cycle action on the expansion force of anhydrite rock under different dry-wet cycle times.The results showed that the expansion force of anhydrite rock decreased with the increase of dry-wet cycle times.