Values Of Geotechnical Parameters Research Articles

Spatial transferability of the physically based model TRIGRS using parameter ensembles

AbstractThe development of better, more reliable and more efficient susceptibility assessments for shallow landslides is becoming increasingly important. Physically based models are well‐suited for this, due to their high predictive capability. However, their demands for large, high‐resolution and detailed input datasets make them very time‐consuming and costly methods. This study investigates if a spatially transferable model calibration can be created with the use of parameter ensembles and with this alleviate the time‐consuming calibration process of these methods. To investigate this, the study compares the calibration of the model TRIGRS in two different study areas. The first study area was taken from a previous study where the dynamic physically based model TRIGRS was calibrated for the Laternser valley in Vorarlberg, Austria. The calibrated parameter ensemble and its performance from this previous study are compared with a calibrated parameter ensemble of the model TRIGRS for the Passeier valley in South Tyrol, Italy. The comparison showed very similar model performance and large similarities in the calibrated geotechnical parameter values of the best model runs in both study areas. There is a subset of calibrated geotechnical parameter values that can be used successfully in both study areas and potentially other study areas with similar lithological characteristics. For the hydraulic parameters, the study did not find a transferable parameter subset. These parameters seem to be more sensitive to different soil types. Additionally, the results of the study also showed the importance of the inclusion of detailed information on the timing of landslide initiation in the calibration of the model.

CROSS-SECTION CHANNELS OF HYDRAULICALLY AND STATICALLY STABLE SHAPE

The article presents the results of research on the substantiation of giving a stable shape of cross-section to the channels of hydro-reclamation systems of southern Kazakhstan. The calculations on the stability of irrigation channel slopes were made, as well as their design features and practical substantiation of stable profiles were presented. The shapes of stable slope were determined using of actual values of geotechnical parameters of slope soils. The results showed that the slope profile takes a stable shape during the channel operation, close to the parabolic.

Depth-Integrated Two-Phase Modeling of Two Real Cases: A Comparison between r.avaflow and GeoFlow-SPH Codes

Due to the growing populations in areas at high risk of natural disasters, hazard and risk assessments of landslides have attracted significant attention from researchers worldwide. In order to assess potential risks and design possible countermeasures, it is necessary to have a better understanding of this phenomenon and its mechanism. As a result, the prediction of landslide evolution using continuum dynamic modeling implemented in advanced simulation tools is becoming more important. We analyzed a depth-integrated, two-phase model implemented in two different sets of code to stimulate rapid landslides, such as debris flows and rock avalanches. The first set of code, r.avaflow, represents a GIS-based computational framework and employs the NOC-TVD numerical scheme. The second set of code, GeoFlow-SPH, is based on the mesh-free numerical method of smoothed particle hydrodynamics (SPH) with the capability of describing pore pressure’s evolution along the vertical distribution of flowing mass. Two real cases of an Acheron rock avalanche and Sham Tseng San Tsuen debris flow were used with the best fit values of geotechnical parameters obtained in the prior modeling to investigate the capabilities of the sets of code. Comparison of the results evidenced that both sets of code were capable of properly reproducing the run-out distance, deposition thickness, and deposition shape in the benchmark exercises. However, the values of maximum propagation velocities and thickness were considerably different, suggesting that using more than one set of simulation code allows us to predict more accurately the possible scenarios and design more effective countermeasures.

Integrated Geoenvironmental and Geotechnical Risk Assessment of East Port Said Region, Egypt for Regional Development

The present paper discusses the use of integrated topographical, hydrogeological, and geotechnical data as a tool to assess the suitability of the East Port Said Region (EPR) for the establishment of new major projects. The method comprises geo-environmental and geotechnical characterization of the surficial soil layer and subsurface rock layers and identification of soil behavior along the proposed area. We analyze the digital elevation model to identify the topographic patterns across the project area. The geology of EPR comprises a normal to slightly consolidated fluvio-marine deltaic deposits of Pleistocene to Holocene age with more than 1000 m thick. We carry out a statistical analysis of geotechnical parameters to group the risky effective parameters for regional development. The study correlated the depth-averaged values of the design geotechnical parameters over the entire EPR. It also integrates the geotechnical properties with the topographical and hydrogeological parameters in the Geographic Information System (GIS) platform aiming to identify the spatial distribution and classes of the integrated risks across the EPR. For each geotechnical–environmental domain, it links the averaged values of geotechnical parameters to the groundwater levels and the topographic gradient that control groundwater flow. The methodological approach enters the hydrogeological model of EPR to the GIS environment and crossing with the results of the geotechnical analysis to identify zones of higher water saturation and possible geotechnical risk. The developed integrated geoenvironmental and geotechnical model assesses the prevailed hazards among the entire EPR. The integrated model uses to identify and delineate geotechnical hazards zones and to shape the spatial distribution of the geotechnical hazards classes, based on the dominant geotechnical and geo-environmental specifications. The achieved model shows that the risky zone spread widely along with the middle and southwestern sectors, while the marginal zones spread along with the southeastern and northwestern sectors. The study recommends applying the prefabricated vertical drains or deep mixing technique to stabilize the soft soil in the middle and northern risky zones of EPR. It also recommends the use of gravel drains and a well-compacted sub-base gravel layer for shallow foundations to enhance the properties of unstable clay formation at the southern risk and marginal zones of EPR.

Application of numerical back analysis for determination of soil mass specifications during tunnel construction

Geotechnical parameters play key roles in constructing and developing civil engineering projects, especially underground structures. One of the conventional methods to evaluate the tunnels’ behavior and safety is applying a back-analysis method to assess the displacement amount during the construction of different parts of the tunnel. Applying this method and using displacement values obtained by tunnel monitoring, the estimated values of geotechnical parameters may converge to their real values. The present study was conducted to improve the estimation accuracy of geotechnical parameters for the tunnel route of Karaj (located 36 km west of Tehran, Iran) subway using the alternative univariate back analysis in FLAC3D software and modifying tunnel maintenance requirements, accordingly. The results showed that the use of geotechnical parameters extracted using back analysis lead to a more accurate design of the tunnel. Overall, through the applied back analysis, it is possible to reduce the shotcrete thickness of some subway stations up to 43% and obtain an optimum design.

Comparison of Methodologies for Statistical Evaluation of Characteristic Soil Properties for Top Hole Design

Summary Evaluation of characteristic values of geotechnical parameters (used for oil well design) is associated with uncertainties inherent to the geological processes that change soil strata. Statistical analysis of soil data allows one to deal rationally with these uncertainties. This work addresses some normative recommendations and literature models for statistical characterization of undrained shear strength and submerged unit weight in offshore soils, providing more information to conductor casing design. Three methodologies were selected for the analysis. The NORSOK G-001 (2004) standard recommends using mean values computed conservatively. Lacasse et al. (2007b) propose that the characteristic value should be the mean value minus one-half of a standard deviation of the parameter under analysis. DNV-RP-C207 (2012) suggests different methodologies for dependent and independent soil variables, though both methods of calculating the characteristic value involve linear regressions. Using data from geotechnical investigations that characterize eight oil wells located in two Brazilian offshore basins, the selected methodologies were applied to obtain the characteristic values and compared to each other. The analysis is carried out with data from 17 piezocone penetration tests (CPTu) associated with the eight wells mentioned above. It is noted that the NORSOK recommendation leads to the highest characteristic values, which are assumed tending to the mean value of the data set over the well depth. The values obtained using Lacasse et al. (2007a, 2007b) methodology are more conservative than NORSOK methodology and stand as its lower bound. The models suggested by DNV perform differently when applied to the geotechnical parameters. The dependent variables methodology fits both undrained strength and unit weight accurately. Analysis shows that undrained strength is better described using the methodology for standard deviation proportional to the depth, while for the unit weight, accurate results are obtained by using constant standard deviation. The lower bound procedure proposed by DNV provides, in general, higher results in the first meters and more conservative values along the depth when compared with the other methodologies. Regarding all the formulations addressed, differences between them increase for wells whose CPTu data present higher dispersion. This larger dispersion suggests applications of different statistical-based approaches in order to reliably characterize offshore soil data. The data sets analyzed comprise different levels of scattering and soil heterogeneity, and comparing the statistical recommendations brings additive information for the designer to set the characteristic values of soil properties, aiming for the decision-making process on top hole drilling applications (e.g., conductor casing design). To the authors’ knowledge, few papers perform this comparative analysis.

A Bayesian Approach in the Evaluation of Unit Weight of Mineral and Organic Soils Based on Dilatometer Tests (DMT)

Recently, geotechnical problems that are characterized by a high degree of complexity and uncertainty with respect to input data have been solved using Bayesian analysis. One example is the problem of cautious estimation of geotechnical parameters according to Eurocode 7 requirements. The research included various types of soil such as peat, gyttja, organic mud, and clays. These were studied in order to develop an empirical correlation for determining the unit weight of mineral and organic soils. The compiled database of documented field research sites for different types of soil was used to investigate and develop direct relationships between measured results and dilatometer (DMT) readings, i.e., po and p1 together with pore water pressure (uo) and pressure (Pa). The soil unit weights were determined for both mineral and organic soils. The paper addresses the applicability of the Bayesian approach in geotechnics via a simple example related to the determination of characteristic values of geotechnical parameters for design structures. The results show that it is possible to conduct a more reliable forecast with improved statistical measures compared to other available methods for multilayer subsoils.

Minding the geotechnical data gap: appraisal of the variability of key soil parameters for slope stability modelling in Saint Lucia

Identification of failure thresholds and critical uncertainties associated with slope stability often requires the specification of geotechnical parameter values for input into a physically-based model. The variation of these parameters (including mechanical soil properties such as effective friction angle and cohesion) can have a significant impact on the computed factor of safety. These uncertainties arise from natural variations in soils, measurement techniques, and lack of reliable information. Researchers may use statistical analysis coupled with numerical simulation to determine possible ranges of slope factors of safety and the relative influence of geotechnical and other parameters, such as topsoil depth and rainfall. This study investigates the variation of geotechnical parameters observed on the island of Saint Lucia in the Eastern Caribbean. A database of particle size distributions, in-situ moisture contents, Atterberg and direct shear box test results is compiled from 91 samples of tropical soils in Saint Lucia. A study of various probability distributions shows that the Weibull distribution may be favoured for the effective friction angle of the Saint Lucian soils considered based on the Akaike information criterion, employed as an estimator of the relative quality of statistical models dealing with the trade-off between goodness-of-fit and simplicity of the model.

Geotechnical characteristics of unburnt colliery spoils after coal-recovery

The aim of the study was to determine the geotechnical characteristics of the unburnt colliery spoils after coal-recovery from the dumping site of one of the mines of the Upper Silesian Coal Basin in Poland. Due to grain-size distribution of tested spoils their geotechnical properties were determined using medium-sized apparatuses. In order to verify the suitability of the studied spoils for the construction of hydraulic embankments, the seepage and stability calculations were conducted for models of hydraulic embankments including the effect of flood wave passage on stress conditions within the construction and their slope stability. The test results revealed, that the studied colliery spoils are characterized by favourable values of geotechnical parameters and they fulfil the requirements for soil materials used in the analysed type of constructions. The spoils are characterized by good compactibility, relatively low water permeability and average susceptibility to mechanical disintegration, which in the case of using this material for the construction of hydraulic embankments and using proper compaction technology, should reduce their susceptibility to weathering. The results of seepage and slope stability calculations for hydraulic embankments built of the studied spoils confirmed their suitability for that type of constructions, retaining the proper inclination of slopes, whereas the variant of embankment without sealing is safer from the stability viewpoint.

Variability of local stress states resulting from the application of Monte Carlo and finite difference methods to the stability study of a selected slope

In slope stability analysis it is decisive to represent, in the most realistic way, the heterogeneity of the soil characteristics. The Monte Carlo technique is one of the suitable mathematical tools that could be useful for this purpose. The result of this kind of approach is a set of multiple possible realizations of the same system, characterized by different spatial distribution of the numerical values of the geotechnical parameters. The numerical stress states outcomes, obtained through a stability analysis, would depend on the models employed to define the spatial parameters distribution and, further, on the utilized geomechanical models. Accordingly, first of all, we selected a suitable mathematical model, based on the Monte Carlo technique. Then, we integrated it into a commonly used FDM (Finite Difference Method) commercial code (FLAC2D). Finally, we studied the stability of an actual slope, considered as a test case (Lettomanoppello, Chieti, Italy), whose geological and geomechanical characteristics make it suitable for the application of the selected code. In this step, in order to simplify the analyses, we considered only dry conditions. Therefore, we discussed how the stochastic distributions of the local stress states, resulting from hundreds of repeated runs, were correlated to the mechanical parameters distributions obtained by the Monte Carlo application and assigned to each points as inputs. The results of the test application suggest that our approach can be used to identify sectors of the slopes more sensitive to the variability of the input values of the main geotechnical parameters, which would require a more accurate modelling and monitoring.

Interpolating spatially varying soil property values from sparse data for facilitating characteristic value selection

Limit state design, incorporated into many recent geotechnical design codes, introduces the application of partial or resistance factors to selected characteristic values. Partial or resistance factors are usually set by national standard organizations, while characteristic values of geotechnical parameters are selected by engineers, often based on sparse measurement data combined with subjective engineering experience and judgment. Due to this subjective selection and individual judgment, the characteristic value derived by different engineers from the same dataset may vary greatly, especially when the test data contain significant variability. To address this issue, a new method based on Bayesian compressive sampling (BCS) is proposed in this study. BCS is able to reconstruct a high-resolution geotechnical property profile from sparse measurement data and quantify the uncertainty, e.g., confidence interval (CI) associated with the interpreted profile. The quantified uncertainty in the BCS has a clear statistical meaning: the corresponding confidence level for a CI from the BCS is the expected coverage proportion (i.e., fraction) of the complete profile that falls within the CI, if all data points along depth can be measured to provide the complete profile. This statistical meaning can be used to facilitate objective determination of characteristic values for geotechnical properties.

Prediction of Geotechnical Parameters Using Machine Learning Techniques

In the present study, relationships between in-place density using SPT N-value, compression index (Cc) using liquid limit (LL) and void ratio (e), and cohesion (c) and angle of internal friction (ϕ) using SPT N-value have been established using machine learning techniques. Geotechnical data up to a depth of 50 m from 1053 borehole locations covering almost every district in the state of Haryana have been considered to develop models and statistical correlations. A general trend has been recorded in the observed data and accordingly, the outliers have been excluded. Several models have been developed to establish functional correlations. These correlations have been ranked on the basis their coefficient of determination (R2) value and mean absolute error (MAE). Subsequently, the model with the highest R2 value and minimum mean absolute error has been considered for the development of correlations. Analysis has also been carried out for all the developed models to assess their individual performance. For this purpose, all the developed models have been evaluated by fitting a straight line between observed and modelled values, and in all the cases, a good value of R2 has been observed. The R2 values obtained for all the models range from 0.798 to 0.988. On comparison, it has been observed that the values of geotechnical parameters obtained are in close agreement with the existing work.

Determination of the Characteristic Values and Variation Ratio for Sensitive Soils

In 2008, Romania adopted Eurocode 7, part II, regarding the geotechnical investigations – called SR EN1997-2/2008. However a previous standard already existed in Romania, by using the mathematical statistics in determination of the calculation values, the requirements of Eurocode can be taken into consideration. The setting of characteristics and calculations values of the geotechnical parameters was finally issued in Romania at the end of 2010 at standard NP122-2010 – “Norm regarding determination of the characteristic and calculation values of the geotechnical parameters”. This standard allows using of data already known from analysed area and setting the calculation values of geotechnical parameters. However, this possibility exist, it is not performed easy in Romania, considering that there isn’t any centralized system of information coming from the geotechnical studies performed for various objectives of private or national interests. Every company performing geotechnical studies tries to organize its own data base, but unfortunately none of them use existing centralized data. When determining the values of calculation, an important role is played by the variation ratio of the characteristic values of a geotechnical parameter. There are recommendations in the mentioned Norm, that could be taken into account, regarding the limits of the variation ratio, but these values are mentioned for Quaternary age soils only, normally consolidated, with a content of organic material < 5%. All of the difficult soils are excluded from the Norm even if they exist and affect the construction foundations on more than a half of the Romania’s surface. A type of difficult soil, extremely widespread on the Romania’s territory, is the contractile soil (with high swelling and contractions, very sensitive to the seasonal moisture variations). This type of material covers and influences the construction foundations in one over third of Romania’s territory. This work is proposing to be a step in determination of limits of the variation ratios for the contractile soils category, for the most used geotechnical parameters in the Romanian engineering practice, namely: the index of consistency and the cohesion.

STABILIZATION AND SPECIFICATION OF CHARACTERISTIC VALUE OF GEOTECHNICAL PARAMETERS

Soil stabilization, process, by which the soil properties are improved, is getting growing attention during last periods. Paper is focused on application for earth structures. Methods of soil stabilization together with their applicability for different soils are discussed firstly. The sensitivity of the process of the cautious estimation of the characteristic values of geotechnical parameters which are subsequently used for the design, is shown on the base of the logical scheme of the geotechnical design report for earth structures. Finally the need of the laboratory tests for the closer specification of the soil stabilization technology and also for the determination of the geotechnical data are discussed.

Earth Pressure behind a Retaining Wall under Linearly Varying Geotechnical Parameters

Objectives: The present study discuss estimation of active and passive earth pressure behind a smooth vertical retaining wall with horizontal backfill under linearly varying geotechnical properties, i.e., cohesion (c), angle of internal friction (φ) and unit weight (γ) of backfill vary linearly with depth.It is noted that the earth pressure behind the retaining wall is nonlinear and its variation can be established through regression analysis that follows 2nd order polynomial in the form of pa = -az2+bz+c; where z is the depth below the backfill surface, a, b & c are constants. Methods/Statistical Analysis: Regression analysis incorporating least square error approach option is available in Microsoft excel in data analysis tool pack. The total amount of thrust (active or passive ) estimated through non-linear distribution of earth pressure behind retaining wall is compared with the corresponding values computed through most widely used Rankine’s earth pressure theory in which average values of geotechnical parameters are taken. Findings: It is noted that there is 5-7% reduction in the active earth thrust although not much reduction is achieved in the moment. In passive case, the increase in passive thrust is almost 20%. Application/Improvements: Consideration of non-linear earth pressure distribution is useful in situations where base width of the retaining wall is controlled with respect to base shear. It will ultimately lead to reduction in the total cost of construction of the retaining wall and will help in achieving economy when the length of the retaining wall is large.

The elastic undrained modulus Eu50 for stiff consolidated clays related to the concept of stress history and normalized soil properties

Abstract The paper presents the results of a triaxial test conducted on stiff, consolidated clays. The standard TXCIU procedure (isotropic consolidation and undrained shearing) was applied in the laboratory soil tests. The undrained elastic modulus Eu50 was determined from each test. The Eu50 values were determined for soil samples cut out from different depths and tested under different confining pressures. There was a significant scatter of values with depth, and no relationships between Eu50 modules or other geotechnical parameters (e.g., cu) were observed. This work presents the concept of normalization of Eu50 modulus values using modified normalization SHANSEP (Stress History And Normalized Soil Engineering Properties). This method was first proposed for estimating the value of the undrained shear strength cu normalizing the parameter relative to the in situ effective vertical stress σ′vo and loading history (overconsolidation stress σ′p and overconsolidation ratio OCR) of the soil. The study demonstrated that the concept of normalization of soil properties can also be used for testing elastic modulus Eu50 of consolidated natural clays and normalized values of geotechnical parameters taking into account the state of stress and load history can be correlated with the value of the overburden pressure.

Correlations Between Electrical Resistivity and Geotechnical Parameters for Jiangsu Marine Clay Using Spearman’s Coefficient Test

The correlations and relationships between electrical resistivity and geotechnical parameters of soils have become very important for site investigation. However, there is a lack of understanding about the relationships between electrical resistivity and geotechnical parameter values. The resistivity piezocone penetration tests and laboratory tests have been conducted for geotechnical investigations of marine clay in Jiangsu province of China to establish quantitative relationships between electrical and geotechnical data. The geotechnical investigation reveals that electrical resistivity values are very low for marine clay in Jiangsu, ranging from 5 to 10 Ω m. The correlations between electrical resistivity and geotechnical parameters are examined using Spearman’s rank correlation test that is a rank-based test for correlation between two variables without any assumption about the data distribution. It was shown that the electrical resistivity has strong bonds with the moisture content, void ratio, salt content and plasticity index. In terms of quantitative relationships, good fitting relationships between electrical resistivity and selected geotechnical parameters are observed. The statistical analysis indicates that the electrical resistivity is a good indirect predictor of selected geotechnical parameters. The data studied demonstrates the usefulness of the in situ resistivity method in geotechnical investigations, which have an advantage over other geotechnical methods in cost performance.

Site-specific characterization of soil properties using multiple measurements from different test procedures at different locations – A Bayesian sequential updating approach

Determination of site-specific values of geotechnical parameters (e.g., undrained shear strength, Su) is a key step in geotechnical analyses and designs at a particular site. This, however, has been a challenging task in geotechnical practice because of various uncertainties in geotechnical parameters and the fact that the number of test data obtained during geotechnical site investigation at a site is often too sparse to accurately estimate statistics of the geotechnical parameters. These issues can be rationally addressed under a Bayesian framework. This study proposes a Bayesian sequential updating (BSU) approach for probabilistic characterization of geotechnical parameters based on multi-source information, including the information available prior to the project, referred to as prior knowledge in Bayesian framework, and results of different types of tests that might be performed at different locations in a soil layer within a specific site. In this paper, the proposed BSU approach is formulated for probabilistic characterization of Su of clay using over-consolidation ratio (OCR), standard penetration test (SPT) data, and cone penetration test (CPT) data. OCR, SPT, and CPT data are sequentially incorporated into the Bayesian framework to update statistics (e.g., mean, standard deviation, and probability density function) of the Su profile. Equations are derived from the proposed approach and are illustrated using real OCR, SPT and CPT data. The proposed BSU approach is shown to perform satisfactorily and provide insights into evolution of the statistics of geotechnical parameters as more results of different testing procedures are used. Such insights allow geotechnical practitioners to inspect the quality of information from different testing procedures (including test results and transformation models adopted to interpret them) and to identify the most informative test procedure.

Prediction of the collapsing risk of mining slopes based on geostatistical interpretation of geotechnical parameters

Almost all collapses of rock slopes especially in open pit mines are related to discontinuities such as bedding planes, faults and major joints.Geostatistical assessments can be used for understanding the distribution of regionalized variables in any spatial study. In this paper3D spatial dispersion of the fault planes in the Gole Gohar open pit iron mine, located in Kerman province, south east of Iran, is modeled. Then, regionalized variable theory is used to analyze and interpret spatial distribution of the following geotechnical parameters: Geological strength index (GSI), Rock quality designation (RQD), Cohesion (C) and angle of internal friction (f). In order to define regionalized variable distribution, variogram functions were determined for identifying the regional behavior. Structural analysis of variograms showed that the mentioned parameters have spatial structures that make it possible to set up a geostatistical model to predict their values for each non-sampled block on the pit wall. Results showed that there is a relation between the low values of geotechnical parameters and the existence of discontinuities around the pit area. The role of discontinuities in the occurrence of collapses in the area was clearly demonstrated by comparing the estimated parameters models and the model of discontinuities dispersion.

Effective soil strength parameters and load capacity of shallow foundations according to various Polish design codes

Standard PN-EN-1997-1 (Eurocode 7 introduced in 2010) requires the determination of bearing capacity of the subsoil on the basis of the effective values of geotechnical parameters. The total soil parameters can be used only to determine the bearing capacity in the so called undrained conditions, in transitional situation (with a fast the increase of load and slow the outflow of water). The problem with correct qualification of effective parameter values is the obstacle to the widespread use of the new code. This especially concern a smaller structures, for which advanced researches of substrate is uneconomical. The paper presents the change in the approach to the design of shallow foundations and application for that purpose an effective values of the parameters in the Polish codes over time.