Study On The Characteristics Of Swelling-Creep And Damage Of Soft Rock Under Hydration

Soft rock is a general term for soft,loose,broken,expansive,rheological,strongly weathered alteration and high ground stress rock mass.The soft rock is a worldwide problem that was originally raised in the 1960 s,especially for the soft rock in coal mine,which has been one of the important problems with the production and construction.Red mudstone is widely distributed and swelling soft rock due to its relatively new sedimentary geological age and weak structure connection,and clay minerals such as kaolinite,illite and montmorillonite,which tend to soften and swell with exposure to water and shrink with loss of water.In this paper,the red mudstone was taken as the research object,and a large number of experimental studies were carried out on the expansion and rheological characteristics of the red mudstone under the combined action of load and hydration.By using damage mechanics and rheological theory,the model of swelling and rheological damage of the red mudstone under hydration was constructed.This paper mainly studies the following aspects :(1)experimental study on the expansion characteristics of red mudstone;(2)study on the expansion mechanism and model of red mudstone;(3)experimental study on the basic mechanical properties of red mudstone under hydration;(4)experimental study on rheological characteristics of red mudstone;(5)study on damage constitutive model of expansion and creep of red mudstone.Based on the above research,the main conclusions and innovations are drawn as follows:The swelling-creep test under the lateral unconfined condition was completed with a simple self-designed saturated equipment on the platform of microcomputer controlled rock shear rheological tester RYL-600.The swelling-creep coupling curve was presented under the effects of both hydration and load of red mudstone.By comparing the swelling test results under the confined lateral and unconfined lateral condition,it is found that for the red mudstone,the axial swelling deformation is greatly restricted under the constraint of the lateral confined condition.The red mudstone specimens under different water contents were applied for uniaxial compression test at differently low loading rates,the mechanical characteristics of red mudstone were studied under the impacts of both loading rate and water content,and the influence of the loading rate and water on the compressive strength,elastic modulus and peak strain of the red layer was analyzed.The strength of water toward the red mudstone is obviously weakened,and the peak compressive strength of the red mudstone and the elastic modulus are negatively correlated with the water content.The peak compressive strength and the elastic modulus of the red mudstone linearly decrease with the increase of the water content of the rock.The saturated red mudstone samples are the least sensitive to the loading rate,and the differences in peak strength are very insignificant under the effect of several loading rates.The peak strength of the dry and crude red mudstone shows a positivecorrelation with the loading rate,and the peak strength ascends obviously with the increase of loading rate.Under different loading rates,the strength of the uniaxial test of hydration and load coupling is slightly higher than that of the saturated rock sample,and its peak strength is significantly affected by the loading rate.The peak strength gets smaller as the loading rate is smaller.Meanwhile,the peak strength of hydrated sample is obviously less than that of other three different rock samples of water content,and the failure degree of rock samples is much higher than that of other three samples.The effects of stress and hydration swelling on deformation,long-term strength and failure mode of rock samples were studied under different loads from dry state to saturated state through the coupling test of swelling and creep of red mudstone under hydration.The stress level of accelerated creep of red mudstone is reduced,and the time of accelerated creep of red mudstone is shortened due to the effect of water softening and swelling stress.The creep deformation trend and the creep deformation of general water content for the sample rocks are obvious different under the joint interaction of hydration and load.The axial deformation decreases gradually because of the influence of hydration swelling deformation,and it begins to increase gradually when reduced to a certain degree.Correspondingly,the deformation rate steadily increases,and finally it builds dramatically and produces damage.The west of the original changed parameters creep model was established to describe the conventional rheological characteristics of red mudstone.The damage variables were employed into the west of the original model,the creep damage constitutive model of west changed parameters and swelling model were jointed,set up under the hydration of the swelling creep damage model of red mudstone was established under hydration in order to better present the hydration swelling and degradation characteristics of rock damage.