Finite element analysis of steep excavation slope failure by CFS theory

The distribution of Coulomb failure stress （CFS） change in the steep excavation slope is calculated by finite element method in this paper, and the failure mechanics under different conditions have been investigated. Comparing the CFSs before and after the slope excavation （stress loading and unloading processes）, the dangerous internal zone and the most likely failure external area are attained. Given the shear cracks on the top surface while tensile stress or cracks along the toe of the slope, we analyze the high cutting-angle steep slope in Kaixian county of the Three Gorges Reservoir region. We bring forward that the peak value of CFS after excavation can reach to the order of 0.1 MPa, which is greatly higher than that of before. Our preliminary results are useful for optimizing the reinforcement structure during the steep slope stabilization engineering.

Analysis and Comparison of Slope-cutting Widening Schemes in Highway Reconstruction and Expansion Project Based on MIDAS Software

In this paper,the geological condition of the right-side slope of the K114+694–K115+162 section of Yong-tai-wen Expressway is investigated and analyzed with the results showing that the strength of rock mass is the main contributor to the stability of the slope.Then,two widening schemes are proposed,which are the steep slope with strong support and the gentle slope with general support schemes.The static/slope module of MIDAS GTS finite element analysis software and the strength reduction method were used to compare the two schemes.The results show that the steep slope with a strong support scheme has obvious advantages in land requisition,environmental protection,and safety and is more suitable for reconstructing and expanding the highway slope.

Slope deformation partitioning and monitoring points optimization based on cluster analysis

The scientific and fair positioning of monitoring locations for surface displacement on slopes is a prerequisite for early warning and forecasting.However,there is no specific provision on how to effectively determine the number and location of monitoring points according to the actual deformation characteristics of the slope.There are still some defects in the layout of monitoring points.To this end,based on displacement data series and spatial location information of surface displacement monitoring points,by combining displacement series correlation and spatial distance influence factors,a spatial deformation correlation calculation model of slope based on clustering analysis was proposed to calculate the correlation between different monitoring points,based on which the deformation area of the slope was divided.The redundant monitoring points in each partition were eliminated based on the partition's outcome,and the overall optimal arrangement of slope monitoring points was then achieved.This method scientifically addresses the issues of slope deformation zoning and data gathering overlap.It not only eliminates human subjectivity from slope deformation zoning but also increases the efficiency and accuracy of slope monitoring.In order to verify the effectiveness of the method,a sand-mudstone interbedded CounterTilt excavation slope in the Chongqing city of China was used as the research object.Twenty-four monitoring points deployed on this slope were monitored for surface displacement for 13 months.The spatial location of the monitoring points was discussed.The results show that the proposed method of slope deformation zoning and the optimized placement of monitoring points are feasible.

Influence of excavation schemes on slope stability: A DEM study

Slope failure due to improper excavation is one of common engineering disasters in China.To explore the failure mechanism of soil slope induced by toe excavation,especially to investigate the influence of excavation unloading path and rate on slope stability,a numerical slope model was built via particle flow code PFC2 D.The development of crack and strain during excavation were obtained and used to evaluate the deformation characteristics.Furthermore,excavation types representing different unloading paths and rates were compared in terms of crack number and strain level.Results indicate that crack number and strain level induced by horizontal column excavation are much greater than those of vertical column excavation and oblique excavation.The crack number and strain level increase with excavation unloading rate.Besides,the feasibility of taking the average strain of slope surface and the average value of maximum strain along monitoring lines to represent the global deformation characteristics were discussed.This study can provide a theoretical guidance for slope monitoring and preliminary optimal selection of excavation scheme in the design and construction of slope engineering.

Slope excavation quality assessment and excavated volume calculation in hydraulic projects based on laser scanning technology

Slope excavation is one of the most crucial steps in the construction of a hydraulic project. Excavation project quality assessment and excavated volume calculation are critical in construction management. The positioning of excavation projects using traditional instruments is inefficient and may cause error. To improve the efficiency and precision of calculation and assessment, three-dimensional laser scanning technology was used for slope excavation quality assessment. An efficient data acquisition, processing, and management workflow was presented in this study. Based on the quality control indices, including the average gradient, slope toe elevation, and overbreak and underbreak,cross-sectional quality assessment and holistic quality assessment methods were proposed to assess the slope excavation quality with laserscanned data. An algorithm was also presented to calculate the excavated volume with laser-scanned data. A field application and a laboratory experiment were carried out to verify the feasibility of these methods for excavation quality assessment and excavated volume calculation. The results show that the quality assessment indices can be obtained rapidly and accurately with design parameters and scanned data, and the results of holistic quality assessment are consistent with those of cross-sectional quality assessment. In addition, the time consumption in excavation quality assessment with the laser scanning technology can be reduced by 70%e90%, as compared with the traditional method. The excavated volume calculated with the scanned data only slightly differs from measured data, demonstrating the applicability of the excavated volume calculation method presented in this study.

Comprehensive Analysis Method of Slope Stability Based on the Limit Equilibrium and Finite Element Methods and Its Application

To study the safety and stability of large slopes, taking the right side slope of the Yuxi’an tunnel of the Yuchu Expressway Bridge in Yunnan Province as an example, limit equilibrium and finite element analysis were applied to engineering examples to calculate the stability coefficient of the slope before and after excavation in the natural state. After comparative analysis, it was concluded that the former had a clear mechanical model and concept, which could quickly provide stability results;the latter could accurately determine the sliding surface of the slope and simulate the stress state changes of the rock and soil mass. The stability coefficients calculated by the two methods were within the stable range, but their values were different. On this basis, combined with the calculation principles, advantages and disadvantages of the two methods, a comprehensive analysis method of slope stability based on the limit equilibrium and finite element methods was proposed, and the rationality of the stability coefficient calculated by this method was judged for a slope case.

High Slope Stability of Diversion Power System Intake of Jinchuan Hydropower Station

The excavated height of the left bank slope of the diversion power system intake in Jinchuan hydropower station is about 16o m. The stability and safety of the slope during construction and its operation/utilization become one of the most important geological engineering problems. At the same time, it is also crucial to select a safe and economic excavation gradient for the construction. We studied the problem of how to select a safe and economic slope ratio by analyzing the geological condition of the high slope, including the lithology, slope structure, structural surface and their combinations, rock weathering and unloading, hydrology, and the natural gradient. The study results showed that the use of an excavation gradient larger than the gradient observed during site investigation and the gradient recommended in standards and field practice manuals is feasible. Then, we used the finite element method and rigid limit equilibrium method to evaluate the stability of the excavation slope under natural, rainstorm and earthquake conditions. The calculated results showed that the excavated slope only has limited failure, but its stability is greatly satisfactory. The research findings can be useful in excavation and slope stabilization projects.

New risk assessment methodology for coal mine excavated slopes

This paper presents a new risk assessment methodology for coal mine excavated slopes. This new empirical-statistical slope.stability assessment m. ethodology （SSAM! is intended for use by geotechnical engineers at both the design review and operational stages of a mine＇s life to categonse the risk of an excavated coal mine slope. A likelihood of failure is determined using a new slope stability classification system for excavated coal mine slopes developed using a database of 119 intact and failed case studies sourced from open cut coal mines in Australia. Consequence of failure is based on slope height and stand-off distance at the toe of the excavated slope. Results are presented in a new risk matrix, with slope risk being divided into low, medium and high categories. The SSAM is put forward as a new risk assess- ment methodology to assess the potential for, and consequence of, excavated coal mine slope failure. Unlike existing classification systems, assumptions about the likely failure mode or mechanism are not required. Instead, the SSAM applies an approach which compares the conditions present within the exca- vated slope face, with the known past performance of slopes with similar geotechnical and geometrical conditions, to estimate the slope＇s propensity for failure. The SSAM is novel in that it considers the depo- sitional history of strata in an excavated slope and how this sequence affects slope stability. It is further novel in that it does not require explicit measurements of intact rock, rock mass and/or defect strength to rapidly calculate a slope＇s likelihood of failure and overall risk. Ratings can be determined entirely from visual observations of the excavated slope face. The new SSAM is designed to be used in conjunction with existing slope stability assessment tools.

Crucial problems on security assessment of a building site adjacent to an excavated high slope

The subject of this work is the assessment on the stability of an excavated high slope in order to insure the security of the building site adjacent to the slope, which is frequently encountered in town construction in mountainous areas due to terrain limit. On the base of some typical engineering cases in Chongqing, several crucial problems on security assessment of building site adjacent to an excavated high slope, including the natural geological conditions and man-destroyed degree, engineering environment, potential failure pattern of the high slope, calculation parameters and analysis methods, are roundly discussed. It is demonstrated that the conclusion of security assessment can be determined according to the aspects above-mentioned, and the security assessment is one of the fundamental data to insure the safety of the related construction, site and buildings.

黄土生态护坡优化措施研究及水土流失治理效果预测

The large-scale management of ditches and implementation of land projects in loess areas have increased the arable land area but have caused considerable engineering issues, resulting in severe soil erosion. In this study, field tests were performed at different time scales, a control group was established, organic material–plant joint restoration technology was proposed as an optimized management measure, and the erosion control mechanism and restoration mode of organic material–plant joint restoration technology were analyzed. Based on the obtained experimental data, a Water Erosion Prediction Project(WEPP)-based hydraulic erosion model was constructed, sensitivity parameters were calibrated, and the soil erosion intensity and corresponding spatial distribution in the watershed of the study area were simulated via the geo-spatial interface for WEPP(GeoWEPP) after organic material–plant joint restoration technology was adopted to predict the effect of optimized management measures. The results showed that among the slopes with different restoration measures, organic material–plant joint restoration technology effectively controlled loess slope erosion, and the average erosion modulus of the organic material–grass and shrub transplantation slope reached only 23.37 t/km^(2), which is a decrease of 97.68% relative to the traditional grass–shrub protection slope. Moreover, the sand content of the joint restoration slope was reduced by 392.41 g/L relative to the bare slope, reaching only 0.29 g/L, and the runoff yield was reduced by 8.88 L/min. The GeoWEPP modeling results revealed that the total runoff yield and average annual erosion modulus of the watershed were lower after joint restoration than during the prerestoration period. Similarly, the total runoff yield of the watershed was 4.6%, the simulated 10-year average annual total sand production reached 2048.3 t,and the average annual erosion modulus was 582.75 t/km^(2), which is 52.15% lower than that under untreated conditions. This study provides a new strategy for solving soil erosion problems and restoring the ecology of slopes after managing ditches and implementing land projects.