Discontinuous rock slope stability analysis by limit equilibrium approaches - a review

Slope stability is one of the most important topics of engineering geology with a background of more than 300 years. So far, various stability assessment techniques have been developed which include a range of simple evaluations, planar failure, limit state criteria, limit equilibrium analysis, numerical methods, hybrid and high-order approaches which are implemented in two-dimensional (2D) and three-dimensional (3D) space. In the meantime, limit equilibrium methods due to their simplicity, short analysis time, coupled with probabilistic and statistics functions to estimate the safety factor (F.S), probable slip surface, application on different failure mechanisms, and varied geological conditions has been received special attention from researchers. The presented paper provides a review to limit equilibrium methods used for discontinuous rock slope stability analyses with different failure mechanisms of natural and cut slopes. The article attempted to provide a systematic review for rock slope stability analysis outlook based on limit equilibrium approaches

Membrane Effects in Clay-Lined Inward Gradient Landfills

Inward gradient landfills are attractive because the inward flow of groundwater is believed to inhibit outward movement of contaminants. However, clay liners may act as semipermeable membranes and exhibit coupled solute and water flow behavior. Our initial evaluation of the membrane behavior of clays used as liners for inward gradient landfill cells suggests that the situation is not as simple as previously thought. The total volume flux (water plus dissolved solutes) through a clay liner may not always be directed inward during the lifetime of an inward gradient landfill even though an inward-directed hydrostatic head difference is maintained. Thus we recommend that synthetic liners be used at least on the basal portion of inward gradient landfill cells to limit outward coupled flux of the dissolved components of leachate and water and that groundwater monitoring may be more important than previously thought for inward gradient landfills. We also suggest that the membrane behavior of clay liners used at inward gradient landfills be incorporated in the design of the cell

Site Characterization Considerations for LNAPL Spills on the Buried Valley Train Surfaces of the Lower Mississippi River Valley

A large number of potential light nonaqueous-phase liquid (LNAPL) traps exist in poorly sorted sands underlying the buried valley train surfaces in the lower Mississippi River Valley (LMRV). These traps should be considered during site characterization and remediation activities related to spilled nonaqueous-phase liquids and leaking underground storage tanks on the valley train surfaces of the LMRV. These traps have apparent average dimensions of 0.84 by 0.21 km (0.52 by 0.13 mi), with an average closure height of 2.7 m (8.85 ft). The maximum apparent lateral dimensions are 4.19 by 0.69 km (2.6 by 0.42 mi) and the minimum observed lateral dimensions are 0.06 by 0.02 km (0.03 by 0.01 mi). Apparent closure heights range from less than 1 m (3 ft) to an apparent maximum of 7.6 m (24.93 ft). A depth of about 4.3m(14.1 ft)is assumed to be a maximum likely excavation depth for underground storage tank installations in the LMRV. The top stratum thickness in 47 of the 100 borings used to construct cross sections in this study was less than 4.3 m (14.1 ft). Thus, it is likely that underground storage tank installations, for example, have or will breach the top stratum at many sites on the valley train surfaces. In order for spilled LNAPLs from underground storage tank sites to migrate into one of these traps, it is probably necessary that the original excavation breach the low-permeability top stratum and that the water table seasonally fluctuates from below the base of the top stratum to above the base of the top stratum

Earthquake hazard assessment in Assalouyeh area based on NGA seismicity model

Earthquakes are presented as the most dangerous geological phenomenon which is causing many damages to cities, infrastructures, buildings, etc. Researchers have been extremely dynamic in assessing and predicting the earthquake events and have made noteworthy advances, but still, face many uncertainties. Along these lines, the best approach in this field studies the logical patterns and parameters involved and the interaction between earthquakes and urban construction or seismic retrofitting. In order to implement a seismic resistant structure, the first step is to have sufficient knowledge on seismicity and earthquake hazard analysis of the area in which for estimating and analyzing the sites seismic parameters, many empirical and computer-based approaches have been presented. In this regard, the computer-based methods (simulations) due to their high accuracy and computational power nowadays are getting more attention and application. One of the newest approaches for identification of different regions seismicity is using the next-generation ground motion analysis (NGA) models. This model by defining attenuation relations for the study area can estimate the seismicity parametrical coefficients with high accuracy. This advantage can help to describe the geological and seismotectonic structures of different regions to observe the impact of seismic parameters. In this study, the NGA model for the Assalouyeh area based on geological and tectonically conditions are prepared and engineering parameters for seismic design are estimated locally and the seismic zoning map of the region is provided. According to the NGA model results for Assalouyeh region within 100 km radius, the PGA, PGD, PGD and PSA parameters for the 100-year return period are estimated as 0.29g, 18.2cm/sec, 24.2 cm and 0.19g respectively. Based on the results of this research, the study area is divided into four zones in terms of risk potential degree and Assaluyeh is located in high earthquake risk potential one

Drastic model optimization in vulnerability assessing of Meymeh aquifer to Nitrate Contamination

Locating and identifying vulnerable areas of the aquifer and managing water supplies use and land use is a good approach to preventing underground water pollution. Nitrate has always been considered as a water pollution index. The aim of this study was assessing the vulnerability of Meymeh aquifer to nitrate through GIS, statistical methods, and Drastic Model. Drastic Model identified the vulnerability of Meymeh Aquifer as low and medium (75-128). After calculating the drastic new index using Raster Calculation in ArcGIS, the correlation between nitrate concentrations in groundwater samples and the new drastic index was calculated. The correlation coefficient of -0/162 (before optimization) to0/842 (after optimization) has increased. These correlations were significant at the 95% probability level (P-value <0/05). To gain nitrate concentration maps, samples were taken through standard sampling principles from 10 wells and analyzed through spectrophotometry approach. Next, nitrate concentration maps were drawn using interpolation models. Combining vulnerability map and nitrate concentration map indicates that most of the area under study was safe and low-risk and only one area of Meymeh was a high-risk area with nitrate concentration above 50 milligrams per liter in underground water. According to the nitrate concentration zonation map, The highest concentrations were observed in groundwater in the southern region of the Meymeh aquifer is due to the interaction of pollution caused by farming activities, Return water irrigation, Lithology, Higher nutrition rates, Hydraulic Conductivity and The permeability of the soil

Landslide susceptibility assessment of South Pars Special Zone, southwest Iran

This study assesses the landslide susceptibility of the South Pars Special Zone (SPSZ) region that is located in southwest Iran. For this purpose, a combinatorial method containing multi-criteria decision-making, likelihood ratio and fuzzy logic was applied in two levels (regional and local) at three critical zones (northwest, middle and southeast of the project area). The analysis parameters were categorised in seven main triggering factors such as climatology, geomorphology, geology, geo-structure, seismic activity, landslide prone areas and man-made activities which have different classes with multi-agent partnership correlations. Landslide susceptibility maps were prepared for these levels and zones after purified and enriched fuzzy trending runs were performed. According to the results of the risk-ability assessment of the landslide occurrences for SPSZ, the north part of the study area which includes the south edge of the Assalouyeh anticline and the southern part of the Kangan anticline were estimated as high-risk potential areas that were used in landslide hazard mitigation assessment and in land-use planning

Application of fuzzy expert decision-making system for rock slope block-toppling modeling and assessment: a case study

The strategy applied in this study is fuzzy logic based decision-making system to achieve a rapid way to assess block-toppling failure instability in discontinuous rock slopes as justified by kinematic analysis that are applied to real cases. Referring to fuzzy logic based decision-making; the best option was selected from multiple fuzzy variables through performing a comparison and by obtaining the fastest solution for approximation. The expert system offers a capable fuzzy application for engineering judgment to be utilised in geotechnical decision making for engineering design. Kinematic analysis is currently used for the stability assessment of all types of toppling failures which provides the 'occurrence possibility' and is not capable of describing the stability conditions (degree of occurrences) in discontinuous rock slopes. Application of fuzzy logic complements kinematic analyses through giving a more accurate stability assessment. This study offers a complementary method for block-toppling failure instability assessment in discontinuous rock slopes based on artificial intelligence and a fuzzy expert decision-making system