Rheological Characteristic Test And Mechanism Study Of Natural Soils Under Hydrochemical Environment

Land mineral resources are gradually exhausted.In order to strengthen the exploitation of marine oil and gas resources and ensure the strategic energy security and sustainable development of energy in China,the exploitation and utilization of marine mineral resources is imminent.Whether the mining system can operate safely on the deep-sea thin soft subsoil is extremely critical.Because the deep-sea sediments are generally located 1000 meters below the sea level,the sedimentary environment and material composition are extremely special,high water content,low intensity and remarkable rheological characteristics will lead to unstable internal structure of the deep-sea sediments and easy to collapse and settlement.In addition to engineering activities,the local ocean currents and magma existing in the deep sea will cause significant changes in the hydrochemical environment and temperature of the seabed sediment.There are some differences between the chemical environment of deep seawater and terrestrial and shallow sea,so it is necessary to carry out systematic research on the evolution process and internal mechanism of the rheological characteristics of deep-sea sediments under the chemical conditions of deep seawater.The main factors affecting the deep-sea soil rheology is the basic physical properties of soil,volume fraction,temperature and the concentration of salt solution,due to the difficulty of deep-sea soil sampling,and its main composition is clay minerals,so choose Longsheng,Binhai and Sanmenxia three different natural clay,natural soil under the influence of the test study,the influence of different physical parameters of deep-sea soil,provide theoretical basis and technical support for the physical and mechanical characteristics of deep-sea sediment and indoor in situ preparation.The main conclusions are as follows:1.The shear stress of natural soil increases with the volume fraction,and the yield stress of soil will also increase with the volume fraction,which can be fitted by exponential relationship;the apparent viscosity decreases with the shear rate,showing a trend of shear thinning,and the viscosity value will increase with the volume fraction,which is consistent with the change of viscosity coefficient in the model.The modulus obtained by using the shock mode increases with the volume fraction,and the larger the volume fraction,the soil sample mobility weakens.2.The increase of temperature makes the soil more stable,and the shear stress tends to increase,while when the yield is reached,the thermal softening decreases with the increase of temperature.The yield stress increases slightly with the increase of temperature.According to DLVO theory,the increase of temperature increases the repulsion force,making the distribution of soil particles of mud samples more dispersed,thus increasing the influence of temperature increase on the apparent viscosity and modulus value is consistent with the shear stress.3.Salt concentration can change the structure and then change the rheological characteristics of the soil,and this trend is closely related to the composition and water content of the clay.The yield stress of Longsheng soil increases only with the maximum volume fraction,and the other volume fraction;the shear stress of the three volume fractions.The concept of contact state and suspension state is introduced to explain the above test results.When the mud is in contact,the salt solution will cause the flocculation structure of the sample,resulting in the increase of yield stress and dynamic modulus with the salt concentration;In the suspension state,mainly the intergranular repulsion works,the greater the concentration,the repulsion decreases and the yield stress decreases.