Research On The Evaluation Method Of Rock Mass Structural Surface Roughness Based On Smartphone Photogrammetr

Rock mass is a comprehensive geological body that has been formed by the cutting of structural surfaces during a long geological history.It is composed of rocks and structural surfaces.structural surfaces are geological interfaces with different characteristics and origins that exist in rock masses.The strength of a rock mass depends on the mechanical properties of the rocks and structural surfaces that make up the rock mass.As an important component of a rock mass,the presence of structural surfaces reduces the integrity of the rock mass.Moreover,the surface morphology characteristics of the structural surfaces deeply affect the strength,deformation,and seepage characteristics of the rock mass.Roughness is the main parameter that describes the surface morphology characteristics of structural surfaces and has always been an important research topic in the field of rock mechanics.Accurately and quickly obtaining and objectively and quantitatively evaluating the roughness characteristics of rock mass structural surfaces is the key to conducting engineering rock mass stability analysis.This issue has received widespread attention from scholars at home and abroad.In recent years,emerging measurement technologies and algorithms have provided new ideas for intelligent recognition and information interpretation of structural surfaces.With the continuous improvement of smartphone camera performance,smartphones have the potential to perform fine data collection in the field of rock mechanics.This paper proposes a rock joint roughness acquisition process and quantitative evaluation method based on smartphone photogrammetry.The main research content and results of this paper are as follows:(1)The 3D reconstruction technology of rock mass structural surfaces based on photogrammetry was summarized and outlined using the Sf M-MVS 3D reconstruction algorithm.A workflow for 3D reconstruction of rock mass structural surfaces was proposed,which includes the following steps:(1)Smartphone selection: choose a smartphone with a large camera sensor size and high camera resolution;(2)Structural surface preparation or selection:suitable structural surfaces with appropriate working platforms should be selected based on the morphology of the structural surface and the surrounding environment.This facilitates the placement of marked points and shooting.;(3)Marked point setting: non-linear markers should be placed around the structural surface,generally ranging from 4-8 points;(4)Shooting plan design: a targeted shooting route plan should be designed based on the spatial position and dip angle of the structural surface.(2)The proposed smartphone photogrammetry method was compared with conventional3 D laser scanning technology,and it was found that the obtained 3D model of the structural surface had smoother roughness and higher consistency of roughness.The average deviation for small-sized(100×100 mm)samples was 8.1%,and for large-sized(1000×1000 mm)samples,it was 4.3%.The roughness accuracy of the reconstructed model for large-sized samples was higher,which verified the feasibility of reconstructing and calculating the surface roughness of the structural surface using this method.(3)The calculation results of the surface roughness of rock joints are sensitive to the number of photographs required to reconstruct the 3D model.When the photographs fully cover the structural surface of the rock mass,the optimal number of photographs for indoor structural surfaces is 20 or more.For field-sized structural surfaces,the number of photographs should be increased.For example,for a 2.0×2.0 m structural surface,35 or more photographs should be taken.(4)The calculation results of the roughness of some rock mass structural surfaces within the Changshanhao Gold Deposit in Inner Mongolia indicate that there are spatial differences in the roughness of the rock mass structural surfaces within the site.The roughness of the structural surfaces within the site increases as the elevation of the rock mass decreases.The differences in the roughness of the structural surfaces may be caused by the different degrees of weathering caused by the different lithology of main rocks in different regions.(5)In the Changshanhao Gold Deposit,the exposed structural surfaces within the mining area exhibit positive size effect,negative size effect and the combined effect of positive size and negative size,until an effective sampling size is reached.The structural surfaces with large exposed areas have an effective sampling size.The roughness of the structural surfaces within the site exhibits anisotropic effects.As the size increases,the anisotropic radar chart’s principal axis rotates and tends to stabilize.