Research On The Extraction Method Of Tunnel Surrounding Rock Information Based On 3D Laser Scanning

During the construction process of underground tunnels,the complexity of the tunnel construction environment may result in unstable tunnel structures and the risk of collapse.The stability of the rock mass inside the tunnel is mainly affected by factors such as rock type,bedding inclination and dip angle,rock mass structure,and groundwater,among which rock mass structure is a prominent one.However,in China’s engineering practice,the survey of tunnel rock mass is often conducted using manual geological investigation methods,and technical personnel need to conduct on-site sampling investigations in person.This method is difficult to accurately and quickly determine the geological conditions of the tunnel,and it also comes with certain safety risks.Therefore,how to safely,accurately,efficiently,and comprehensively obtain the structural surface information of the rock mass inside the tunnel is of great significance for predicting the stability of the tunnel and reducing the risk of tunnel construction.Three-dimensional laser scanning technology,as an emerging non-contact measurement method,has gradually attracted widespread attention.It can scan the tunnel invert rock mass from a long distance,with high precision and efficiency.By using a laser scanner to shine a laser beam on the rock surface,the time and spatial information of the light reflected from the rock surface can be measured to obtain three-dimensional coordinate data of the object’s surface,which can then be used for three-dimensional modeling and digital reconstruction of the object,and thus extract and identify the structural surface information of the tunnel invert rock mass.In this study,based on the point cloud data obtained from 3D laser scanning,the following achievements were mainly obtained:(1)A comprehensive exposition was given on the development process and research status of 3D laser scanning technology,which introduced the principles,system classification,and technical characteristics of this technology in a relatively comprehensive manner.Meanwhile,the widely used methods for extracting and identifying rock mass structural information were summarized and concluded.The advantages of using 3D laser scanning technology for extracting and identifying the structural surface of tunnel invert rock mass were analyzed in comparison to traditional measurement methods.(2)The data acquisition,operation process,precautions and data processing process based on 3D laser scanning technology are elaborated,mainly including: selection of scanner position,scanning pitch,coordinate conversion,etc.(3)Based on the 3D point cloud data,this study used an improved spherical projection method to establish the correspondence between the point cloud data.Next,the Delaunay algorithm was applied to generate triangles,and a 3D triangular mesh model was constructed based on the corresponding relationships.This method can preserve the original topological structure between the 3D point clouds as much as possible,thus restoring the surface features of the tunnel.(4)In this study,the clustering method of density is used to separate the points and data of the palm face,which provides a strong technical support for the subsequent 3D modeling of the tunnel palm face.(5)The surface of the tunnel palm face was modeled in 3D,and the yield feature values(Inclination,Dip)and distance feature values were calculated for each triangle in the 3D model;the identified structural faces were further optimized based on the dynamic clustering algorithm.At the same time,the characteristic parameters of the structural surfaces are extracted.Using the minimum cost path human-computer interaction method,the trajectory line and related parameters are successfully extracted.(6)In this study,the feasibility of the proposed method was verified by applying it to a tunnel engineering project in Chongqing.The comprehensive analysis results show that the method proposed in this study can accurately separate the point cloud data of tunnel invert and reconstruct its three-dimensional model,and thus identify the structural surface information and trajectory lines of the tunnel invert.At the same time,the characteristic values related to the rock structure surface can also be successfully calculated and extracted.The identified results are basically consistent with the results of manual investigation.Based on the parameters obtained from the above research,the tunnel rock mass is classified using the RMR method.