Experimental Study On Strength Softening Of Soft Rock In Deep Mine Under Temperature Humidity Environment

This thesis are supported by science and technology research project ofHeilongjiang department of education—“The mechanism study of hydrology,physicochemical, and strength softening characteristics of deep soft rock”(12511480),innovation research project for postgraduate students of Heilongjiang university ofscience and technology—“The experimental study of strength softening of deep softrock under temperature humidity environment”(YJSCX2013-004HKJ), and specialfunds funded project of central universities’ R&D funds for China University ofMining (Beijing)—“The study of hydraulic characteristics of clay type of soft rock indeep mining”(2010QL07).After the deep mining of coal mine, surrounding rock of roadway is in hightemperature and high moisture environment for a long time. The study of thehydraulic characteristics and the strength softening law of soft rock in deep miningundertemperature humidity environment are in urgent need.The following researchwas carried out aiming at reveal the hydraulic characteristics and the strengthsoftening law of soft rock in deep mining undertemperature humidity environment.1. The study of the hydraulic characteristicsof soft rock in deep miningundertemperature humidity environment.Sandstone in Heilongjiang Hegang, Qitaihe sandstone, Yunnan Fuyuan finesandstone, Shandong Laiwu red sandstone were achieved on the spot. After drilling,incising and grinding, rock samples for experiment of the four typs rock which wasmaintained above were achieved. Short samples of Hegang sandstone, Qitaihesandstone, Yunnan fine sandstone were divided into two sets follow which have theinitial moisture content and which are dry. Aiming at study the water absorptioncharacteristics of soft rock in deep mining which have initial moisture content or notunder temperature humidity environment, water absorption tests were carried out for allthe rock samplesunder30℃,50℃,70℃high humid environment (RH＞95%).Aiming at study thehydraulic characteristics ofsoft rock in deep miningundertemperature humidity environment for a long time, water absorption tests as longas90days were carried out for Yunnan fine sandstone and Shandong red sandstoneunder30℃,50℃,70℃high humid environment (RH＞95%).Aiming at studythefactors which affect water absorption of soft rock in deep mining under temperaturehumidity environment,SEM (scanning electron microscope), XRD (X-ray diffraction),mercury injection test and other testing means were employed to determine the microstructure characteristics, mineral composition and relative content, poremicrostructure characteristics.2. The study of the strength softening lawof soft rock in deep miningundertemperature humidity environment.Uniaxial compression strength tests for Yunnan fine sandstone and Shandong redsandstonewere carried out under30℃,50℃,70℃high humid environment (RH＞95%), When the time for water absorption were set as30d,60d,90d separately.Uniaxial compression strength tests for rock samples of dry and saturated state werealso carried out.Splitting tensile strength tests for Yunnan fine sandstone sampleswhich have achieved the gas-liquid equilibrium state under30℃,50℃,70℃highhumid environment (RH＞95%) after water absorption. Splitting tensile strength testsfor Yunnan fine sandstone samples of dry and saturated state were also carried out. Atthe meantime, splitting tensile strength tests were carried outfor Yunnan finesandstone dry sample, the angle between splitting direction and bedding plane was setas0°,30°,90°separately. Shear strength tests were carried out forShandong redsandstone which have achieved the gas-liquid equilibrium state under30℃,50℃,70℃high humid environment (RH＞95%) after water absorption. Variable angle(55°,45°,65°) shear strength tests were also carried out for samples of dry andsaturated state.The innovation point of this thesis is reveal the hydraulic characteristics and thestrength softening law of soft rock in deep mining undertemperature humidityenvironment.Through the above research content, following results have been obtained.1. Regardless of whether there have initial water content or not, water absorptionof all kinds of soft rock in deep mining can reach gas liquid equilibrium state after acertain time. The higher of water absorption temperature, the faster of waterabsorption rate of soft rock, the greater of the final water quantity, and the shorter ofthe time needed for reach gas liquid equilibrium. The function of water absorptionprocess for soft rock samples which with initial water content is Qt=Q0+a(1-e-bt),and most of the water absorption characteristic curves are linear. The function ofwater absorption process for dry soft rock samples is Qt=a(1-e-bt), andhe waterabsorption characteristic curves aremostly convex type. In combination with theanalyzeresults of SEM, XRD and mercury injection tests,the main factors which affectsoft rock water absorption is water absorption temperature, the content of the clay minerals content in soft rock, species of clay minerals and occurrence features, andmicroscopic pore structure characteristicsof soft rock.2. The attenuation function of uniaxial compression strength changes of soft rocksamples with the growth of time under temperature humidity environment ist=as+(c-as)×e-bt. The attenuation function of uniaxial compression strengthchanges of soft rock samples with the growth of water content under temperaturehumidity environment is w=as+(c-as)×e-bw.3. When water content of soft rockincrease with the increase of temperature ofwater absorption, splitting tensile strength of soft rock attenuate follow a form ofnegative exponent and tend to full water splitting tensile strength, the attenuationfunction isRtw=Rtas+(Rtc－Rtas)×e-bw. Splitting tensile strength of soft rockreached themaximum value when the splitting direction perpendicular to bedding plane, andreached the minimum value when the splitting direction parallel to bedding plane.4. With the increase of samples water absorption, sandstone cohesion attenuatefollow a form of negative exponent attenuation trend to the cohesion when samplesfull of water. The influence of moisture content to sandstone cohesion is much largerthan to internal friction angle. Variable angle shear strength experiment was carriedout under temperature humidity environment, the shear strength attenuation functionfor Shandong red sandstone was obtained--(c a e b1w) tan(a e b2w).