Some applications of a backpropagation neural network in geo-engineering

A MATLAB based backpropagation neural network (BPNN) model has been developed. Two major geo-engineering applications, namely, earth slope movement and ground movement around tunnels, are identified. Data obtained from case studies are used to train and test the developed model and the ground movement is predicted with the help of input variables that have direct physical significance. A new approach is adopted by introducing an infiltration coefficient in the network architecture apart from antecedent rainfall, slope profile, groundwater level and strength parameters to predict the slope movement. The input variables for settlement around underground excavations are taken from literature. The neural network models demonstrate a promising result predicting fairly successfully the ground behavior in both cases. If input variables influencing output goals are clearly identified and if a decent number of quality data are available, backpropagation neural network can be successfully applied as mapping and prediction tools in geotechnical investigations.     

Morphology and geotechnique of active-layer detachment failures in discontinuous and continuous permafrost, northern Canada

Fifty active-layer detachment failures triggered after forest fire in the discontinuous permafrost zone (central Mackenzie Valley, 65° N.) are compared to several hundred others caused by summer meteorological triggers in continuous permafrost (Fosheim Peninsula, Ellesmere Island, 80°N). Most failures fall into compact or elongated morphological categories. The compact type occur next to stream channels and have little internal disturbance of the displaced block, whereas the elongated types can develop on any part of the slope and exhibit greater internal deformation. Frequency distributions of length-to-width and length-to-depth ratios are similar at all sites. Positive pore pressures, expected theoretically, were measured in the field at the base of the thawing layer. Effective stress analysis could predict the instability of slopes in both areas, providing cohesion across the thaw plane was set to zero and/or residual strength parameters were employed. The location of the shear planes or zones in relation to the permafrost table and the degree of post-failure secondary movements (including headwall recession and thermokarst development within the failure track) differed between the localities, reflecting dissimilarity in the environmental triggers and in the degree of ground thermal disturbance.     

A giant deep-seated slope deformation in the Italian Alps studied by paleoseismological and morphometric techniques

This work proves the existence of a large deep-seated gravitational slope deformation (DGSD) in a hilly region of the southwestern Alps, whereas DGSD are usually linked with high relief energy in mountain environments. Moreover, we describe the usefulness of applying paleoseismological techniques by means of trench excavation to date and understand the deformation history and genesis of recent morphostructures, and we found evidence of causative relationships between DGSD and surface landslides. The studied DGSD of Mt. Croce della Tola–Mt. Scincina, Italy, is the largest of the western Alps: it is 7-km long and involves a minimum area of 16 km² with a volume ≥3.5 km³ probably extending further NE beneath Lake Maggiore surface. Several parallel scarps, representing the surface expression of slip-planes, affect the upper part of the slope, whereas the lower part presents a convex profile. DGSD at Mt. Croce della Tola started in the last interglacial period (120–40 ka BP) and the following glacial phase was not able to significantly modify the general slope geometry. Post-glacial deformation also occurred, especially at Mt. Scincina, after 25 ka BP. Post-glacial and active surface landslides developed on the convex lower part of the slope, suggesting that they resulted from instability due to the new profile assumed by the slopes during the deep-seated deformation. The occurrence of Mt. Scincina DGSD with a very low topographic gradient is interpreted as an effect induced by on other large DGSD.     

Modeling historical climate variability and slope stability

This study presents scenario models for historical variations of climate and slope stability. A model for historical annual patterns of temperature and rainfall was established on the basis of seasonal proxies. A process-based, spatio-temporal model for groundwater variations and slope stability was developed using the GIS environment of the software PCRaster. We applied the slope stability model to study the effects of the different climate scenarios on slope stability for three different hillslopes in the area around Bonn (Germany). The findings indicate three climatic phases with different annual temperature and precipitation patterns over the historic period. The modeling results show that a climatic scenario representing unstable conditions of a transition from the more humid Little Ice Age to dryer recent climate produces the highest slope instabilities. The intensity of this impact, however, varies with the sensitivity of the geomorphic system, i.e. local landforms and lithology, and cannot be generally related to the stability of a specific hillslope. More unstable areas are not necessarily more sensitive to climatic changes: the location of permeable layers (prone to groundwater rise) in relation to sensitive layers (lower strength) and higher gradients (higher stress) influences the sensitivity of a site with respect to climate changes. The presented method is capable of modeling landscape sensitivity to climate change with respect to groundwater-controlled landslides.     

Three-dimensional stability analysis of the Kettleman Hills landfill slope failure based on observed sliding-block mechanism

Previous studies of the Kettleman landfill slope failure of 1988 had concluded that the failure, which slid along the underlying liner interfaces with low shearing resistance, occurred as a result of attaining the critical waste fill height. These studies showed, however, some discrepancies in regard to the adopted material strength data as well as the computed factors of safety. Based on the observed sliding-block mechanism, a 3D analysis model was established herein which allowed for variations in material strength mobilization within the sliding mass and at the slip surface. With a careful consideration on the interface strength data, results of forward analysis for the pre-slide slope generally showed better agreement with the field observations. Results of backward analysis for the post-slide slope indicated a consistency in the estimated material strength with the laboratory test data. The current study also showed slightly higher computed 3D factors of safety than the associated 2D values, in both pre-slide and post-slide cases.     

Determination of the rate and volume of leakage using the slopes of time-drawdown data

Quantification of leakage is very important in the selection and design of the remediation systems of leaky aquifers that receive contaminated leakage. This is an approach for the calculation of leakage using only two slopes of time-drawdown data. These slopes represent before and after the start of leakage, and are applied to four examples. Results generally agree with those determined by the Hantush approach. Comparison of the two approaches, however, shows that the Hantush approach quantifies leakage using three aquifer parameters (transmissivity, storativity, and leakage factor), the value of which depend on the pumping test method used; it assumes constant hydraulic head in the aquifer supplying leakage, which may not be valid under field conditions; and it ignores differences between the viscosities of the leakage water and the aquifer water, which influence the leakage rate. The proposed approach is free from all three limitations.     

Reinforcing a Dangerous Rock Mass Using the Flexible Network Method

Because the main failure type of a dangerous rock mass is collapse, the treatment of such a mass should focus on controlling collapse failure. When treating dangerous rock masses, disturbing the mass （e. g. by blasting） needs to be avoided, as this new damage could cause collapse. So the self-bearing capacity of the mountain mass must be used to treat the dangerous rock mass. This article is based on a practical example of the control of a dangerous rock mass at Banyan Mountain, Huangshi, Hubei Province. On the basis of an analysis of damage mechanism and the stability of the dangerous rock mass, a flexible network reinforcement method was designed to prevent the collapse of the rock mass. The deformations of section Ⅱ w of the dangerous rock mass before and after the flexible network reinforcement were calculated using the two-dimensional finite element method. The results show that the maximum deformation reduced by 55 % after the application of the flexible network reinforcement, from 45.99 to 20.75 ram, which demonstrates that the flexible network method is effective, and can provide some scientific basis for the treatment of dangerous rock masses.     

SLIP4EX – A Program for Routine Slope Stability Analysis to Include the Effects of Vegetation, Reinforcement and Hydrological Changes

SLIP4EX is a straightforward computer program developed in connection with the EU funded ECOSLOPES project for routine stability analysis and the assessment of the contribution of vegetation to slope stability. The slope section is drawn up and dimensions and parameters are fed in to the Microsoft Excel based program for stability calculations and comparisons of Factors of Safety using different methods of analysis (Bishop, Janbu, Fellenius, Simple, Greenwood). The background and assumptions involved in the derivation of each of the methods is briefly described. The simplicity of the program enables the user to understand the nature of the analysis, explore the parameter assumptions made and compare the different methods of analysis. Soil reinforcement by geosynthetic layers or anchors, and vegetation effects of enhanced cohesion, changed water pressures, mass of vegetation, wind forces and root reinforcement forces are readily included in the analysis. The program is freely available on request from the Author.     

龙滩水电工程左岸B区边坡压脚工程效果分析

龙滩水电工程左岸蠕变体B区边坡的变形和稳定是工程安全的关键。根据边坡地质与稳定性分析,边坡的整体稳定性主要取决于坡脚岩体的稳定性,因此,B区边坡治理采取了压脚的工程措施。本文采用数值模拟方法(三维离散单元法)分析了压脚前后B区边坡的整体稳定性,结果表明B区边坡压脚工程可有效控制边坡岩体的变形。同时,数值分析结果也与边坡地表和深部位移动态监测结果一致,证明了压脚工程的显著效果。     

沈阳市方形广场地下通道工程施工技术

通过地下通道施工实例,介绍了小导管超前注浆预加固的施工及注浆材料、注浆参数的确定方法。