Study On The Prediction Of Shaft Deformation With Huge Unconsolidated Soil Layer Based On FBG Monitoring

In East Area of China, approximately 100 shaft linings in huge unconsolidated soil layer fractured in various degrees, it is mainly caused by the vertical additional force acted on shaft lining by surrounding soils during dewatering of unconsolidated aquifers. Predicting the settlement deformation of aquifers with effective monitoring method and the recognition of the characteristics of the deformation from micro to macro is essential for avoiding above-mentioned disaster, which has very important significance.The basic characteristics and principle as well as the engineering geological conditions of the shaft deformation with huge unconsolidated soil layer in East Area of China are studied. The process and the occurrence mechanism of shaft deformation are analyzed. Based on the Terzaghi consolidation theory of the acquifer, the dewatering settlement deformation principle of bottom acquifer is studied, and the shear stress of the surface of the shaft is analyzed. The computational model of the vertical additional stress of the shaft is built, and the checking method of shaft deformation is proposed.The deformation and load transferring principle of unconsolidated soil layer is studied. The stability analysis and strength checking method and process of the shaft are proposed, and a real example of shaft strength checking is given. Based on the economic and technical comparison of all kinds of prediction methods of shaft deformation, an integrated shaft safety evaluation and prediction system of "take FBG monitoring as main method, and assisted by other monitoring methods, integrated with several monitoring methods" is proposed.A borehole embedded fiber Bragg grating sensing method is proposed to monitor the rock strata settlement deformation. A mechanical model of the borehole embedded fiber Bragg grating sensing method is built. With the analysis of the strain transferring theory, the changing principle of the strain transferring rate with the elastic modulus of cement mortar, Poisson's ratio and diameter of the borehole is obtained. A special fiber Bragg grating sensor used for the monitoring of rock strata deformation is designed and the strain transferring rate of this sensor under prepared borehole-diameter is calculated, and the relationship of the strain of the bottom acquifer and the shaft vertical additional stress is analyzed.The borehole embedded fiber Bragg grating sensing method is applied to the monitoring of the settlement deformation of the unconsolidated soil layer around air shaft of No. 3 Jining Coal Mine, which realized the real-time monitoring of the rock strata deformation. A fiber Bragg grating rock strata deformation monitoring software is developed. The rock strata deformation monitoring data are gained and managed by TeeChart control and Access database. This software has friendly windows and can be operated easily, which can meet the requirement of practical engineering applications. The monitoring results can reflect the settlement deformation process of the unconsolidated soil layer, and can predict the real stress distribution of the shaft, which can provide evidence for the deformation of the shaft and its maintenance.