Variability Of Geotechnical Properties Research Articles

Probabilistic slope stability analysis in Kahrizak landfill: effect of spatial variation of MSW’s geotechnical properties

The geotechnical properties of municipal solid waste (MSW) in landfills vary considerably depending on the composition, time, and the rate of waste density. This variability in geotechnical properties leads to many uncertainties in the analysis of landfill slope stability. This study, using probabilistic methods investigates the slope stability and the probability of failure of a Kahrizak landfill under the conditions of spatial variability of physical and geotechnical properties of MSW. To achieve this goal, the random field theory has been used with a finite difference numerical method in the framework of the Monte Carlo simulation. MSW’s shear strength parameters such as cohesion and friction angle as well as the unit weight of layers are considered as random variables. An extensive literature review was conducted to address the probable variation of above-mentioned parameters in Kahrizak landfill. The results of several different laboratory researches on MSW samples collected from Kahrizak landfill were also employed in the modelings. Output results are presented in the form of probability distributions of the factor of safety as well as the probability of failure corresponding to these distributions. Moreover, the effect of various parameters such as coefficient of variation and correlation distance of input parameters on these output results has been investigated. The results show that considering the spatial variability in probabilistic methods would help to determine the various mechanisms affecting the performance and the probability of failure of the landfill slope. In addition, the output of such probabilistic analyses can be used as guidance for engineers to design safe and reliable landfill.

Impact of spatial variability of geotechnical properties on uncertain settlement of frozen soil foundation around an oil pipeline

The spatial variability of geotechnical properties can lead to the uncertainty of settlement for frozen soil foundation around the oil pipeline, and it can affect the stability of permafrost foundation. In this paper, the elastic modulus, cohesion, angle of internal friction and poisson ratio are taken as four independent random fields. A stochastic analysis model for the uncertain settlement characteristic of frozen soil foundation around an oil pipeline is presented. The accuracy of the stochastic analysis model is verified by measured data. Considering the different combinations for the coefficient of variation and scale of fluctuation, the influences of spatial variability of geotechnical properties on uncertain settlement are estimated. The results show that the stochastic effects between elastic modulus, cohesion, angle of internal friction and poisson ratio are obviously different. The deformation parameters have a greater influence on stochastic settlement than the strength parameters. The overall variability of settlement reduces with the increase of horizontal scale of fluctuation and vertical scale of fluctuation. These results can improve our understanding of the influences of spatial variability of geotechnical properties on uncertain settlement and provide a theoretical basis for the reliability analysis of pipeline engineering in permafrost regions.

Maintaining geological reality in application of GSI for design of engineering structures in rock

In rock engineering design, significant advances have occurred in recent years in numerical modelling capability with increasing trends to ever greater use of synthetic rock mass models and discrete fracture network (DFN) modelling, but all too often with little comparative improvement in geologic base data. As a consequence, there is even more need that reliable estimates be available of strength and deformation characteristics of the rock masses on which or within which engineering structures are to be created, be it a tunnel, a foundation or a slope. Geological Strength Index (GSI) characterization, linked with Hoek-Brown strength determination as a basis for modelling has been widely adopted by engineers and geologists involved in design and construction of engineering structures. The need for geological definition of rock mass properties required as inputs into numerical analysis, constitutes one of the greatest reasons for application of the GSI chart, allowing characterization of even difficult-to-describe rock masses, including tackling even the most problematic of weak and complex rock masses. Back-analyses of tunnels, slopes and foundation behaviour using GSI and its reliable application in rock engineering designs attest to its reliability. With continuing use worldwide, the GSI system has continued to evolve, but greater understanding is needed in the definition of input constants, for establishing both GSI and intact rock properties. This need for improved evaluation, particularly from a geological perspective, is addressed in this paper. Geological processes of tectonism, weathering and alteration all affect GSI. Evaluation of these factors, which are each critical to proper GSI definition, are analyzed based on real rock mass cases. Suggested ranges in variability of intact rock parameters uniaxial compressive strength σci and material constant mi for common rock masses are presented in the context of a composite new GSI chart. This chart allows selection of appropriate GSI ranges for any specific rock suite. Specific key engineering geological characteristics that differentiate igneous, metamorphic and sedimentary one from each other are highlighted through discussion of various example rock units (including gneisses, granites, ophiolites, limestones, schists, siltstones/mudstones/shales, and molassic and flysch formations). Illustrations are given of how geological differentiation dictates variability in geotechnical properties of most common rock masses.

Geotechnical Characterization of Road Cut Hill Slope Forming Unconsolidated Geo-materials: A Case Study

Geotechnical characterization of the unconsolidated geo-materials (which are mainly soils) is one of the major concerns for geotechnical engineers, administration and city planners. Recently, large scale highway projects in hilly regions leads to increase the road cut hill slope (RCHS) frequency. The slope failure along these RCHS is an uninterrupted source of suffering for human habitants and keeping human life in danger. The stability of these cut slopes mainly depends upon the geotechnical characterization of slope forming geo-materials. The present study was carried out to evaluate the geotechnical properties of unconsolidated geo-materials (i.e. basaltic soils) of Malshej Ghat, located in Maharashtra, India. Malshej Ghat is one of the most vulnerable hilly region, composed of basaltic rock and soils of Deccan plateau and suffers frequent RCHS failures, which block the National Highway-222 very frequently. A number of tests such as natural moisture content (NMC), specific gravity, grain size analysis, Atterberg limits, compaction, unconfined compressive strength and triaxial compression test were conducted to evaluate the geotechnical properties of unconsolidated geo-materials. The result of these tests indicates that the soils collected from five representative locations show high variability in geotechnical properties. Thus, the parameters from one location are not sufficient for the characterization and analyses of complete section of RCHS. For the quantification and numerical modeling of the RCHS, the geotechnical parameters of each location needs to be analyzed scientifically.

Site Effects from the Building Scale to the Seismic Microzonation Scale: Examples from the Experience of L’Aquila

This paper illustrates the site characterization for evaluating local ground motion amplifications at two sites in the urban area of L’Aquila, performed for the reconstruction of buildings damaged by the April 6, 2009 earthquake. The paper is focused on the comparison between results obtained from site investigations carried out at the building scale and from information contained in the seismic microzonation study. Local amplifications inferred from microzonation may be considerably different from those provided by ground response analyses based on punctual soil data, due to the complex geological setting and the marked variability in geotechnical properties of the foundation soils. The practice of using seismic microzonation data for deriving the seismic action on buildings, not infrequent in structural engineering design, should be avoided or considered with caution.

Modeling spatial variability in offshore geotechnical properties for reliability-based foundation design

Design of foundations for offshore energy production typically requires soil characterization over large areas. Often, in uniform geological settings, it is neither practical nor economical to acquire geotechnical data at every foundation location. Additionally, the zone of interest for the foundation may extend deeper than the available geotechnical data. This paper describes a model of spatial variability in geotechnical properties for foundation design in deep water Gulf of Mexico. The geology consists of normally to slightly over-consolidated marine clays. Data are available for about 100 locations with soil borings, jumbo piston cores and cone penetration tests. A random field model that describes spatial variations in the design undrained shear strength is formulated and calibrated. This model is incorporated into a reliability-based framework to account for uncertainty due to spatial variability in foundation design. In this setting, depth-averaged values of design undrained shear strength are correlated over longer distances than point values due to stratigraphic features. There is less variation and greater spatial correlation in the design undrained shear strength for deeper versus shallower deposits and along the continental shelf versus off from the shelf. The increased conservatism required in foundation design due to spatial variability when site-specific strength data are not available is generally small.

A Procedure to Quantify the Variability of Geotechnical Properties

The geotechnical properties of soil should be considered for several civil engineering purposes. Geotechnical informa- tion is used for urban planning, environmental management, slope stability analysis, and foundation design, among others. Given the importance that geotechnical information assumes in several engineering applications, geotechnical mapping is deemed rele- vant. Methods for integrating field tests and quantifying estimate uncertainty in the construction of these geotechnical maps is preferably used in the decision-making process. A methodology to build this kind of maps is proposed based on geostatistical sto- chastic simulation. Maps covering an area of 4 km2 were built, based on the information derived from 141 boreholes, where stan- dard penetration tests (SPT) were carried out. Sequential Gaussian simulation was used for building these maps, since it reproduces data statistics and spatial continuity. The soil resistance to penetration of panels of 100 x 100 m2 was estimated and the estimation error was calculated. The results demonstrate the appropriateness and usefulness of the methodology for mapping geotechnical attributes.

The geology and geotechnical properties of till and related deposits in the Edmonton, Alberta, area

Deposits of the Quaternary Period in the Edmonton area consist of a lower and an upper till, in places separated stratigraphically by a sand, with lacustrine clays, silts, and sands overlying this sequence. Detailed field investigations suggest the possible existence of complexities that have not been fully integrated into an understanding of the Quaternary history of the Edmonton area.The lower till is a moderately stony sandy silt till. In places the upper portion has been reworked or sheared by the ice that deposited the upper till producing a thin zone of slightly lower strength. The upper till is a moderately stony sand till. Regionally it appears to be quite variable lithologically and contains inclusions of sand and gravel; therefore it is more reasonable to think in terms of an upper till unit composed of till and genetically related material. In some localities this upper unit is one single bed of till; in other places, however, it is a layered sequence of paratills, sands, and silts resulting probably from deposition in standing water. The lenses of sand and gravel associated with this unit have caused problems in tunnelling operations and other construction as they contain water, which can cause flooding when encountered during excavation. The paratills known from the examination of outcrops consist of sequences of interbedded till-like material and sands. These sequences are probably the result of turbidite deposition in an ice-marginal lake. These materials would resemble till when encountered in drilling operations.Problems associated with the Quaternary deposits of the Edmonton area include borehole interpretation to develop site stratigraphy, and the determination of geotechnical properties of the deposits and an assessment of their local variation over a specific site. Also of concern are the joints and fractures in the deposits, which affect slope stability and permeability of the soil mass.An understanding of the Quaternary history and the intrinsic variability of the deposits formed predominantly under the influence of ice is necessary for an understanding of potential sources of variability in geotechnical properties. Interaction between the geologist and the geotechnical engineer can only enhance their mutual comprehension of potential problems and their solutions.