Research On The Stress Status And Evolvement Rule Of Vertical Shaft-Lining In Deep Alluvium

The stress states and evolvement law of vertical shaft-lining in deep alluvium were systematically and comprehensively studied by means of theoretical analysis, numerical simulation, laboratory test and engineering measurement.Based on the twin shear unified strength theory, the plastic limit load formular under the condition of shaft-lining stress in deep alluvium was derived and the plastic limit load envelope line was obtained. The dissertation analyzed the relationships between plastic limit load of shaft-lining and the various factors, such as material properties, geometric features of well case and intermediate principle shear stress.The new field measurement method of shaft-lining stress by partially double porosity stress relief method was first brought out. The reliability, stability and maneuverability were confirmed by physical simulation and numerical simulation. It is shown that the stress attenuation rate of shaft-lining was 57% after the partially double porosity stress relief. The field measurement gained a large amount of stress data of Kongzhuang auxiliary shaft vs. the depth of well case in Datun mining area.Through the non-destructive test by rebound tester, the strength variation law of shaft-lining with the depth of well case was studied. The decrease rate of concrete strength of shaft-lining vs. the depth of well case was 0.0895MPa/m. It is shown that because of the long-term high horizontal pressure and vertical additional stress, there probably is some micro-fracture and micro-damage, which will weaken the material strength.By means of numerical simulation and field measurement, the stress response of shaft-lining to the formation grouting was studied and the variation law of vertical, hoop and radical stress vs. the grouting pressure was gained. According to large amounts of measurement data of the additional strain of shaft-lining during the grouting period, we analyzed the stress response of shaft-lining to grouting and evaluated the security of shaft-lining during the grouting period via the plastic limit load relationship.The long-term evolvement law of the shaft-lining additional stress was studied by the R/S analysis method. According to analyzed results of the additional stress evolvement trend during the period of dewater, it is shown that the R/S analysis method can well predict the evolvement trend of additional stress. At the same time, the additional stress evolvement trend before and after the rupture of shaft-lining was analyzed. The time course of Hurst index shows that the H value appears the abnormal change when the well case will rupture in the coming 2-5 months. So, the Hurst index is very meaningful for the intermediate and short-term prediction of shaft-lining rupture. Its abnormal variation reveals the time process from the disorder to order when the well case begins to rupture.