Vegetation Removal on 3D Point Cloud Reconstruction of Cut-Slopes Using U-Net

The 3D point cloud reconstruction from photos taken by an unmanned aerial vehicle (UAV) is a promising tool for monitoring and managing risks of cut-slopes. However, surface changes on cut-slopes are likely to be hidden by seasonal vegetation variations on the cut-slopes. This paper proposes a vegetation removal method for 3D reconstructed point clouds using (1) a 2D image segmentation deep learning model and (2) projection matrices available from photogrammetry. For a given point cloud, each 3D point of it is reprojected into the image coordinates by the projection matrices to determine if it belongs to vegetation or not using the 2D image segmentation model. The 3D points belonging to vegetation in the 2D images are deleted from the point cloud. The effort to build a 2D image segmentation model was significantly reduced by using U-Net with the dataset prepared by the colour index method complemented by manual trimming. The proposed method was applied to a cut-slope in Doam Dam in South Korea, and showed that vegetation from the two point clouds of the cut-slope at winter and summer was removed successfully. The M3C2 distance between the two vegetation-removed point clouds showed a feasibility of the proposed method as a tool to reveal actual change of cut-slopes without the effect of vegetation.

Influence of Freeze-Thaw on the Stability of Road Cut Slopes near Atal Tunnel in Indian Himalayan Region

The rock slopes in the Indian Himalayan region are exposed to recurrent freeze-thaw. Freeze-thaw plays a dominant role in the instability of rock slopes in cold regions. Extensive field investigations have been carried on the two rock slopes of the Solang valley roadway in Himachal Pradesh. Freeze-thaw testing has been carried out in the laboratory on the rock samples collected from the studied slopes. The test has been repeated for 30 freeze-thaw cycles. The laboratory tests have been conducted to determine the mechanical properties of rock with and without freeze-thaw conditioning. The micro-photographs from scanning electron microscope have been obtained to identify the microscopic damages due to freeze-thaw activity. The macroscopic damages have been recognized in tensile, compressive and triaxial compressive strength of rock. Further, a three-dimensional numerical analysis has been performed to evaluate the stability and corroborate the results with the field observations. FT conditioning results reveal a reduction of about 27–39 % in rock strength and subsequently a decrease in the factor of safety by 10–39 % for rock slopes.

Examining the Effects of Suction and Nonlinear Strength Envelopes on the Stability of a High Plasticity Clay Slope

Slope failures in high plasticity clay deposits are common occurrences in many parts of the world. In western and central Alabama, expansive Prairie clays are commonly found, and shallow slope failures have occurred in both fill and cut slopes containing these high plasticity clays. The objective of this study was to examine the effects of suction and the use of nonlinear strength envelopes on the embankment stability of a section of highway AL-5. The testing program consisted of fifteen ring shear tests performed using a Bromhead Ring Shear Device. The results of the tests were used to develop both linear and nonlinear fully softened and residual strength envelopes. The saturated strength envelopes are then used in a limit equilibrium slope stability analysis with and without the effects of suction. The results show stability (factor of safety >1) for all cases except the residual friction angle without suction. Given these results, large slope failures are unlikely to occur in this area, but surficial failures and deformations due to creep may be possible. These results demonstrate the importance of considering the effects of suction and nonlinear strength envelopes when examining the potential for shallow slope failures in high plasticity clays.