Values Of Geotechnical Parameters Research Articles

Geotechnical Susceptibility Constraints on Seismicity of Karewa Group and Its Implication in Quaternary Earthquakes Around Kashmir Valley, India

The seismically sensitive soft sediment deformations of Karewa Group have been geotechnically analysed to explore the status and frequency of past Quaternary earthquakes in Kashmir valley, India. The detailed studies were performed to establish the sequences of sedimentary structures in general and deformed structures in particular in view of geotechnical parameters. For the purpose the collected sediments from different deformed zones were analysed as per American Standard of Testing Materials for determination of size gradations, liquid limit, plastic limit and flow indices. The studied sequences of deformations were established in space and time by using empirically relationship. The structural architectures of sedimentary features (cross-beddings, massive beddings/loads) reveal the fluvial environments of fluctuating energy conditions for formation of sediment successions. In addition, the sandwiched-zonations of some peculiar structures preserved in the litho-succession may be formed through mechanism different from sedimentations. The size distribution of sediments from sandwiched-zone exhibits medium to fine sands and silt with sorting coefficients ranging from 1.21 to 2.54, coefficient of uniformity ranging from 1.26 to 3.6 with some exceptional values like 5.0, 16.6 and coefficient of curvature ranging from 0.67 to 1.80. The sediments of the same zone show the values of liquidity index ranging from 0.16 to 0.88 and plasticity index ranging from 3.69 to 18.57 with low blows values. These above size sensitive geotechnical parameter values show the higher flow indices and least resistance to flow. The sediments of the peculiar structural zone with characteristically higher flow indices and low resistance support the formation of the soft-sediment structures under seismic stress condition. The demarcated sandwiched zones with such conditions at the time frame of 1,06,566.6 years, 93,245.8 years and 54,502.8 years ago from recent appears to supports three prominent earthquake events (I, II and III) in the geological history of Quaternary deposits around Kashmir Valley, India.

A strategy for GIS-based 3-D slope stability modelling over large areas

Abstract. GIS-based deterministic models may be used for landslide susceptibility mapping over large areas. However, such efforts require specific strategies to (i) keep computing time at an acceptable level, and (ii) parameterize the geotechnical data. We test and optimize the performance of the GIS-based, 3-D slope stability model r.slope.stability in terms of computing time and model results. The model was developed as a C- and Python-based raster module of the open source software GRASS GIS and considers the 3-D geometry of the sliding surface. It calculates the factor of safety (FoS) and the probability of slope failure (Pf) for a number of randomly selected potential slip surfaces, ellipsoidal or truncated in shape. Model input consists of a digital elevation model (DEM), ranges of geotechnical parameter values derived from laboratory tests, and a range of possible soil depths estimated in the field. Probability density functions are exploited to assign Pf to each ellipsoid. The model calculates for each pixel multiple values of FoS and Pf corresponding to different sliding surfaces. The minimum value of FoS and the maximum value of Pf for each pixel give an estimate of the landslide susceptibility in the study area. Optionally, r.slope.stability is able to split the study area into a defined number of tiles, allowing parallel processing of the model on the given area. Focusing on shallow landslides, we show how multi-core processing makes it possible to reduce computing times by a factor larger than 20 in the study area. We further demonstrate how the number of random slip surfaces and the sampling of parameters influence the average value of Pf and the capacity of r.slope.stability to predict the observed patterns of shallow landslides in the 89.5 km2 Collazzone area in Umbria, central Italy.

Trenching effects on structural safety assessment of integrated riser/semisubmersible in cohesive soil

This paper models an integrated riser/semisubmersible system and subjected to irregular waves. The riser’s pipe is suspended from a semisubmersible and smoothly extending down to the cohesive seabed soils at the touchdown point in a catenary shape. Pipe–soil interaction is modelled using a hysteretic non-linear model in the vertical seabed direction and Coulomb friction model in the lateral direction together with an improved model that includes the breakout soil resistance. Initially, this study discusses the significance of pipe–seabed interaction on the riser response for deepwater applications when subjected to random waves on cohesive clay. In the next step, this study investigates the sensitivity of fatigue performance to geotechnical parameters through a parametric study. The influence of the uncertainty in the geotechnical parameters and the development of the trench in the seabed on the dynamic response are determined. The structural behaviour and the uncertainty of fatigue performance in the touchdown zone are presented. It is noted that the confidence in seabed interaction modelling and geotechnical parameter values is needed in order to have structural safety assurance in the final numerical analysis results.

Test fill on soft plastic marine clay at Onsøy, Norway

The test fill at Onsøy, close to the town of Fredrikstad in Norway, was built on a very soft marine clay with in situ vane strength as low as 11 kPa and a plasticity index varying from 34 to 50. The dimensions at the bottom of the long fill were 20 m × 60 m and the height 2.3 m. The fill, as placed, had a computed factor of safety against foundation failure of 1.35 based on in situ vane strength. The fill was allowed to sit for about 3 years (from 1972 to 1975) before it, in a second stage, was brought to failure by raising the height. The main purpose of the first stage was to study the stress–strain–time relationships for the soft clay and compare the values of geotechnical parameters determined by careful laboratory tests with those back-calculated from the observed field behaviour. The test fill foundation was heavily instrumented to measure clay deformations and pore pressures with time. Field observations showed that the Onsøy test fill turned out to be more of a drained loading case than an undrained case in spite of the fairly rapid construction of the fill. Actually, subsequent undrained triaxial and direct simple shear tests strongly indicate that the fill might have failed if less drainage had taken place, i.e., if the drainage paths had been longer and (or) if the coefficient of consolidation had been lower.

BAYANAL code in geotechnical design based on Eurocode 7

Abstract BAYANAL code in geotechnical design based on Eurocode 7. Geotechnical problems that are characterized by a high degree of complexity and uncertainty with respect to the input data are solved recently, using the Bayesian analysis (for instance the problem of a cautious estimation of the geotechnical characteristic parameters according to the Eurocode 7 requirements). The applicability of the Bayesian approach to geotechnics via a simple examples related to determination of characteristic values of geotechnical parameters for design structures is in the paper addressed. In order to select the characteristic parameters for the geotechnical design a new numerical code called BAYANAL was developed. Example of applying the BAYANAL code to analyse the DMT tests demonstrates that it is a powerful and promising tool in evaluation of ground properties and geotechnical parameters.

Geotechnical Characteristics of Marine Sediments in Selected Sectors off West Coast of India vis-a-vis Provenances

Geotechnical parameters of three selected sectors in the nearshore waters off West Coast of India, viz. (1) Kandla, Gujarat, (2) Devgarh, Maharashtra and (3) Tadri, Karnataka, having three different provenances, are discussed in this paper. As the geotechnical parameters are also likely to change in accordance with composition and texture of the sediments, silty clay and clayey silt samples only were selected so as to maintain homogeneity. Studies confirm that the nature and composition of marine clayey sediment from shelf area to a large extent are dependent on the lithology of hinterland. It is observed that in the Kandla area, where hinterland is mainly composed of sedimentaries, the values of geotechnical parameters like water content, wet unit weight, void ratio, porosity, liquid limit, plastic limit, plasticity index, and liquidity index are low, whereas in the Tadri area, where hinterland is mainly crystallines and metasedimentaries, the values are relatively higher. In Devgarh area, where the provenance is mainly Deccan basalts, the values are the highest.

General and local estimation of local average and their application in geotechnical parameter estimations

Two kinds of estimation variance functions for estimating a local average (LA) of a stationary (homogeneous) random field (RF) are derived. One is local estimation (LE) and the other is general estimation (GE) of LA. The former is for estimating LA at the observation location, and the latter is for obtaining LA at any arbitrary location within the RF. The geotechnical implications of these two estimations are that LE is for estimating LA of geotechnical parameters at the spot where the investigations are made, whereas GE is for estimating LA at any arbitrary location within the same layer. The behavior of the two estimation variance functions differs greatly, controlled by the number of observations (i.e. sample size) and the normalized layer thickness (layer thickness divided by autocorrelation distance of RF). Based on the derived estimation variance functions, methods for determining reliable characteristic values of geotechnical parameters and necessary sample size are proposed. The methods are based on the same framework as that of the traditional statistical theory, i.e. confidence interval of estimated parameters. However, the assumption of independently and identically distributed (i.i.d.) samples in the traditional statistical theory is replaced by the assumption of correlated samples from a stationary RF. The results obtained from the proposed methods for LE and GE differ from each other as well as from the traditional results, which has significant implications for geotechnical parameter estimation in geotechnical engineering practice.

Computer program for stability analysis of steep, cohesive riverbanks

The ability to predict the stability of eroding riverbanks is a prerequisite for modelling alluvial channel width adjustment and a requirement for predicting bank erosion rates and sediment yield associated with bank erosion. Mass-wasting of bank materials under gravity occurs through a variety of specific mechanisms, with a separate analysis required for each type of failure. This paper presents a computer program for the analysis of the stability of steep, cohesive riverbanks with respect to planar-type failures. Planar-type failures are common along stream channels destabilized by severe bed degradation. Existing stability analyses for planar-type failures have a number of limitations that affect their physical basis and predictive ability. The computer program presented here is based on an analysis developed by Darby and Thorne. The software takes account of the geotechnical characteristics of the bank materials, the shape of the bank profile, and the relative elevations of the groundwater and surface water to estimate stability with respect to mass failure along a planar-type failure surface. Results can be displayed either in terms of a factor of safety (ratio of resisting to driving forces), or probability of failure. The computer analysis is able to determine the relative amounts of bed degradation and bank-toe erosion required to destabilize an initially stable bank. Data for the analysis are supplied in the form of either HEC-2 hydrographic survey data files or user-supplied bank profile data, in conjunction with user-supplied geotechnical parameter values. Some examples, using data from the Upper Missouri River in Montana, are used to demonstrate potential applications of the software. Copyright © 2000 John Wiley & Sons, Ltd.

Computer program for stability analysis of steep, cohesive riverbanks

The ability to predict the stability of eroding riverbanks is a prerequisite for modelling alluvial channel width adjustment and a requirement for predicting bank erosion rates and sediment yield associated with bank erosion. Mass-wasting of bank materials under gravity occurs through a variety of specific mechanisms, with a separate analysis required for each type of failure. This paper presents a computer program for the analysis of the stability of steep, cohesive riverbanks with respect to planar-type failures. Planar-type failures are common along stream channels destabilized by severe bed degradation. Existing stability analyses for planar-type failures have a number of limitations that affect their physical basis and predictive ability. The computer program presented here is based on an analysis developed by Darby and Thorne. The software takes account of the geotechnical characteristics of the bank materials, the shape of the bank profile, and the relative elevations of the groundwater and surface water to estimate stability with respect to mass failure along a planar-type failure surface. Results can be displayed either in terms of a factor of safety (ratio of resisting to driving forces), or probability of failure. The computer analysis is able to determine the relative amounts of bed degradation and bank-toe erosion required to destabilize an initially stable bank. Data for the analysis are supplied in the form of either HEC-2 hydrographic survey data files or user-supplied bank profile data, in conjunction with user-supplied geotechnical parameter values. Some examples, using data from the Upper Missouri River in Montana, are used to demonstrate potential applications of the software. Copyright © 2000 John Wiley & Sons, Ltd.