Construction Of 3D Geological Body Model And Long-term Stability Analysis Of Jianchuandong No.3 Dangerous Rock Mass

In 2019,the currency volume of the Yangtze River Waterway reached 144 million tons and showed an increasing trend year by year,making the Yangtze River Waterway a veritable"golden River".However,a large number of dangerous rock masses with high,steep and large volume have been found through the investigation of the slopes on both banks.At the same time,the periodic fluctuation of water level in the Three Gorges Reservoir area forms a fluctuation zone of up to 30m.Through investigation,it is found that a large number of dangerous rock bases are located in the subsidence zone and are affected by periodic fluctuation of water level for a long time.These factors have a very bad effect on the stability of dangerous rock mass.Once the dangerous rock mass is unstable,it will bring great loss to passing ships,nearby scenic spots and residents’life and property safety.After investigating the dangerous rock mass in the Three Gorges Reservoir area,Jianchuandong No.3 dangerous rock mass with fissure development in foundation and karst cave system is selected.Through field investigation and indoor data analysis,different three-dimensional data acquisition methods were used to acquire three-dimensional point cloud data of dangerous rock mass,and the three-dimensional geological body model was constructed with the data,and the model construction process was formed.Based on the application analysis,the geological body model is used for numerical calculation and stability calculation.The long-term stability of dangerous rock mass is analyzed under different calculation modes and working conditions.By analyzing the deformation mechanism and instability mode of the dangerous rock mass,the paper provides security for the safe operation of the Yangtze River waterway and people’s life and property.The paper draws the following conclusions:(1)Through the indoor data collection and field investigation of engineering geological conditions of Jianchuandong No.3 dangerous rock mass,the 3D data of dangerous rock mass is acquired by UAV.It is obtained that the volume of the dangerous rock mass is 12.3×104m~3,the karst cave system exists in the base rock mass,and the fracture development on the surface of the base rock mass.(2)The UAV tilt photography technology and 3D laser scanning technology are used to collect 3D data of dangerous rock mass.The data collected by UAV was reconstructed by using different modeling software.After comparative analysis,the model post-processing software of DJI Intelligent map was selected.The reconstructed UAV point cloud data and 3D laser scanning data were used for point cloud compression,point cloud denoising and point cloud triangulation,and a triangular mesh model was constructed.The triangulated mesh model is used to obtain the data of karst caverns in dangerous rock mass,so as to fully understand the development of karst caverns in rock mass.(3)The UAV tilt photography technology and 3D laser scanning technology are used to collect 3D data of dangerous rock mass.The data collected by UAV was reconstructed by using different modeling software.After comparative analysis,the model post-processing software of DJI Intelligent map was selected.The reconstructed three-dimensional point cloud data were compressed,denoised and triangulated,and a triangular mesh model was constructed.Based on this model,the data of karst caves in dangerous rock mass were acquired.The data of different models were fused according to the same feature points,the redundant grid surfaces were deleted,and the overlapping grid surfaces were reconstructed.The grid plane model is segmented by two vertical planes,and the segmented grid model is combined with the meshed plane to construct the solid model.At the same time,the geological elements of the 3D data model were constructed according to the point,line and surface construction methods,and the3D geological body model construction process was established by using the above methods.(4)The stability coefficient of the dangerous rock mass against sliding failure is 3.6 and the stability coefficient against toppling failure is 6.8.Numerical software is used to calculate the stability coefficient of anti-sliding failure and crushing failure of dangerous rock mass.The numerical calculation under two groups of working conditions of two instability modes shows that,with the deterioration of rock mass,cracks at the base of dangerous rock mass gradually expand,the plastic zone on the surface of the cave mouth extends outward,and there is a phenomenon of stress concentration inside.After the element yields,the plastic zone passes through to the bottom of the base,and the coefficient of anti-sliding stability and crushing stability of dangerous rock mass both show a downward trend.The rock mass of Jiandaodong No.3 will be degraded,crushed and collapsed under long-term changes.(5)A comparative analysis of stability based on random cracks was carried out.Under the same water level period,the stability coefficient of the foundation with random cracks is obviously smaller than that of the foundation without cracks.The distribution of plastic element after sliding failure,plastic element model profile 1 and shear stress profile were selected for comparative analysis.From the distribution of the plastic zone and the yield of the internal elements,it can be seen that the expansion of random cracks reduces the strength of the base rock mass,and the internal rock mass has obvious stress concentration along the random cracks.It can be concluded that the construction of random cracks has an important effect on the stability of dangerous rock mass.