Advances in Instrumentation and Monitoring in Geotechnical Engineering

[Extract] Geotechnical instrumentation to monitor the performances of earth and earth-supported structures is increasingly becoming popular. Verification of long-term performances, validation of new theories, construction control, warning against any impending failures, quality assurance, and legal protection are some of the many reasons for geotechnical instrumentation. They are not only used in field situations, but in laboratories too. With the recent advances in materials and technology, and the need for more stringent performance control, there had been significant developments in the recent past in instrumentation and monitoring techniques

New spectrophotometric techniques for the estimation of Perphenazine in bulk drug form

Perphenazine is an atypical antipsychotic drug.  The simple and accurate and precise absorption ratio method has been developed for the simultaneous estimation of Perphenazine in the pure drug form. The absorption maxima were found to be 310nm in Method A (0.1N HCl Buffer) and show linearity over the concentration range of 0.002-0.02 µg/mL with regression equation y=0.5372x-0.0099(r2 = 0.9990). In Method B (Sodium acetate buffer, pH 4.5) the drug obeys Beer Lambert’s law (λmax 310nm) in the concentration range of 0.002-0.02 µg/mL with regression equation y=0.4257x - 0.0084(r2= 0.9992). In Method C (Phosphate buffer, pH 6.8) the drug obeys Beer Lambert’s law (λmax 310nm) in the concentration range of 0.002-0.02 µg/mL with regression equation y=0.482x - 0.0074(r2= 0.9991). In Method D (phosphate buffer, pH 7.2) the drug obeys Beer Lambert’s law (λmax 310nm) in the concentration range of 0.002-0.02 µg/mL with regression equation y=0.3686x - 0.0055(r2= 0.9992). In Method E (0.1N NaOH Buffer) and shows linearity over the concentration range of 0.002-0.02 µg/mL with regression equation y=0.4864x-0.0081(r2 = 0.999). In Method F (Methanol) the drug obeys Beer Lambert’s law (λmax 300nm) in the concentration range of 0.002-0.02 µg/mL with regression equation y=0.6323x - 0.003(r2= 0.999). In Method G (Ethanol ) the drug obeys Beer Lambert’s law (λmax 300nm) in the concentration range of 0.002-0.02 µg/mL with regression equation y=0.3686x - 0.0055(r2= 0.9991).   First derivative spectrophotometric methods (A1, B1, C1, D1, E1, F1 and G1) were developed in 0.1NHCl and Sodium acetate pH 4.5 and phosphate buffer, in pH 6.8 and phosphate buffer, pH 7.2, 0.1N NaOH Buffer, which Perphenazine obeys Beer Lambert’s law(λmax310nm) in the concentration range of 0.002-0.02 µg/mL and  0.002-0.02 µg/mL and    0.002-0.02 µg/mL  and 0.002-0.02 µg/mL and0.002-0.02 µg/mL  with regression equations y=0.0357x - 0.0006 and y=0.0201x+0.0004 and y=0.0196x-0.0002 and y=0.0162x+0.0002  and y=0.0239x - 0.0002  and Perphenazine obeys Beer Lambert’s law(λmax300nm) for methanol and ethanol in the concentration range of 0.002-0.02 µg/mL and  0.002-0.02 µg/mL  with regression equations y=0.0423x-0.0003 and y=0.0371x+0.0003 respectively.&nbsp

Model for predicting the variation of shear stress in unsaturated soils during strain-softening

Several of the geotechnical structures constructed with unsaturated soils undergo a large deformation prior to reaching failure conditions (e.g. progressive failure of a soil slope). During this process, the shear stress in soils typically increases initially and then reduces with an increase in the shear strain. The prediction of the stress-strain relationship is critical for reasonable interpretation of the mechanical behavior of those geo-structures that undergo large deformation. This paper introduces a model based on the disturbed state concept (DSC) to predict the variation of shear stress in unsaturated soils during strain-softening process under consolidated drained triaxial compression condition. In this model, the apparent stress-strain relationship is formulated as a weighted average of a hyperbolic hardening response extending the pre-peak state stress-strain curve and a linear response extending the critical state stress-strain curve with an assumed disturbance function as the weight. The prediction procedure is described in detail and the proposed model is validated using several sets of published data on unsaturated soils varying from coarse- to fine-grained soils. Finally, a comprehensive error analysis is undertaken based on an index of agreement approach.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Stability analysis of unsaturated soil slope considering softening and non-softening approach

In conventional geotechnical engineering practice, peak shear strength parameters are widely used in the design of geo-structures constructed with or within unsaturated soils. However, a reduction inshear strength from the peak to the residual value is typically observed during the shear deformation in typical fine-grained unsaturated soils. Several geo-structures in unsaturated soils undergo a large shear deformation prior to reaching the failure condition. Thus, the factor of safety of such geo-structures will gradually but significantly decrease with the development of the shear deformation. For this reason, the strain-softening behaviour of unsaturated soils should be considered for reliable design of the geo-structuresin unsaturated soils. In this study, an unsaturated clay slope under 10 years rainfall infiltration were modelled using softening and non-softening approach using commercial finite element software SIGMA/W. The responses of the studied slope to the long-term rainfall infiltration were analysed. The results of the softening and non-softening analysis were compared. This study provides valuable information with respect to the significance of the strain-softening that are useful in the rational design of slopes in unsaturated soils

Stability analysis of unsaturated soil slope considering softening and non-softening approach

In conventional geotechnical engineering practice, peak shear strength parameters are widely used in the design of geo-structures constructed with or within unsaturated soils. However, a reduction inshear strength from the peak to the residual value is typically observed during the shear deformation in typical fine-grained unsaturated soils. Several geo-structures in unsaturated soils undergo a large shear deformation prior to reaching the failure condition. Thus, the factor of safety of such geo-structures will gradually but significantly decrease with the development of the shear deformation. For this reason, the strain-softening behaviour of unsaturated soils should be considered for reliable design of the geo-structuresin unsaturated soils. In this study, an unsaturated clay slope under 10 years rainfall infiltration were modelled using softening and non-softening approach using commercial finite element software SIGMA/W. The responses of the studied slope to the long-term rainfall infiltration were analysed. The results of the softening and non-softening analysis were compared. This study provides valuable information with respect to the significance of the strain-softening that are useful in the rational design of slopes in unsaturated soils

Prediction of Soil-Water Characteristic Curves using two Artificial Intelligent (AI) Models and AI Aid Design Method for Sands

In this paper, two artificial intelligent models (i.e., artificial neural networks (ANN) and multivariate adaptive regression splines (MARS)) were developed using cumulative percentiles from grain-size distribution (GSD) curve as input information to predict the soil-water characteristic curve (SWCC). The importance of each input variable was testified using two different sensitivity analyses. The results show a strong correlation between the SWCC and GSD curves based on large volume of datasets. The ANN provides higher accuracy due to its unique structure; however, MARS model facilitates in developing a regression equation that contributes to stable performance. The SWCC can be reliably predicted with MARS regression equation using one data point from the GSD curve and bulk density information. Sensitivity analysis suggests that the prediction of the SWCC is also possible with a reasonable degree of accuracy by using single data point information from the GSD curve as an input variable. Finally, a novel AI aid design method is proposed by combining MARS regression equation along with physico-empirical model and fitting equation that provides a rapid and reliable technique for predicting the SWCC of sands.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Undrained Shear Strength of Unsaturated Soils under Zero or Low Confining Pressures in the Vadose Zone

In geotechnical engineering practice, many projects such as stability analysis of slopes or trenches and pavement design involve soils in vadose zones at shallow depths, where soils are under unsaturated conditions. For these types of projects, undrained shear strength test results obtained under zero or low confining pressure can be effectively used to analyze the behaviors of unsaturated soils. Experimental procedures to determine the undrained shear strength for different soil suction values, however, is time consuming even under low confining pressure. For this reason, we attempted to develop a semi-empirical model to predict the undrained shear strength of unsaturated soils at a shallow depth assuming zero confining pressure as a function of soil suction. In addition, existing empirical or semi-empirical models are also presented along with the characteristic behaviors of unsaturated soils under axial forces at low or zero confining pressures. Finally, the advantages and disadvantages of each model are discussed based on the comparison between the measured undrained shear strengths under zero or low confining pressures with those predicted using the existing and proposed models

Performance estimation of a shallow foundation on an unsaturated expansive soil slope subjected to rainfall infiltration

In the last two decades, there has been a significant increase in infrastructure development on slopes of hilly regions of the world, due to population growth. There are many infrastructures on unsaturated expansive slopes, especially in semi-arid and arid regions. Rainfall infiltration is one of the major factors that contributes to the slope and infrastructure foundations failures on hilly slopes with unsaturated expansive soils. In the current study, a rational approach is proposed considering the combined influence of the foundation-slope behavior based on the principles of unsaturated soil mechanics. This is achieved by a novel numerical modelling approach using the commercial software Geo-studio to investigate the performance of strip foundation located on the top of the unsaturated expansive soil slope subjected to various rainfall infiltration conditions. Hydro-mechanical coupling analysis is conducted to evaluate the rainfall water infiltration influence combined with slope stability analysis using limit equilibrium method. Comparisons are made between both the foundation bearing capacity, slope stability before and after rainfall water infiltration. Different failure mechanisms of the foundation and slope system are presented with and without foundation loading for various rainfall scenarios. Results summarized in this paper are helpful for the geotechnical engineers for understanding the performance of shallow foundations on unsaturated expansive soil slopes considering the influence of rainfall infiltration conditions

A numerical technique for modeling the behavior of single piles in unsaturated soils

Pile foundations are widely used in both saturated and unsaturated soils. In certain scenarios, these foundations are subjected to combined vertical and lateral loads. Conventionally, saturated soil mechanics principles are routinely used for the design of pile foundations in unsaturated soils. Such approaches contribute to unreliable estimates of the behavior of piles due to ignoring the influence of matric suction. In this paper, a comprehensive numerical technique is proposed for simulating the behavior of single piles subjected to combined vertical and lateral loads in unsaturated soils by taking account of the nonlinear behavior of shear strength and the elastic modulus of unsaturated soils. This is achieved through a subroutine that was developed for use in the ABAQUS software. The proposed numerical method provided reliable prediction of the vertical load-displacement behavior of a published model pile tested in saturated and unsaturated sands. In addition, 3D finite element analysis was extended to simulate the influence of variations in ground water table (GWT) on the vertical bearing capacity and the influence of vertical loads on lateral response of piles. The proposed numerical technique is a promising tool for implementing the state-of-the-art understanding of the mechanics of unsaturated soils into conventional engineering practice

Prediction of the variation of swelling pressure and 1-D heave of expansive soils with respect to suction using the soil water retention curve as a tool

ABSTRACT: The one-dimensional (1-D) potential heave (or swell strain) of expansive soil is conventionally estimated using the swelling pressure and swelling index values which are determined from different types of oedometer test results. The swelling pressure of expansive soils is typically measured at saturated condition from oedometer tests. The experimental procedures of oedometer tests are cumbersome as well as time-consuming for use in conventional geotechnical engineering practice and are not capable for estimating heave under different stages of unsaturated conditions. To alleviate these limitations, semi-empirical models are proposed to predict the variation of swelling pressure of both compacted and natural expansive soils with respect to soil suction using the soil water retention curve (SWRC) as a tool. An empirical relationship is also suggested for estimating the swelling index from plasticity index values, alleviating the need for conducting oedometer tests. The predicted swelling pressure and estimated swelling index are then used to estimate the variation of 1-D heave with respect to suction for expansive soils by modifying Fredlund (1983) equation. The proposed approach is validated on eight field sites from six countries; namely, Saudi Arabia, Australia, Canada, China, US, and the UK, and on six different compacted expansive soils from US. Le soulèvement potentiel unidimensionnel (ou déformation de gonflement) des sols gonflants est estimée conventionnellement en utilisant la pression de gonflement et l'indice de gonflement, qui sont déterminées à partir de différents types de résultats d'essais oedométriques. La pression de gonflement des sols gonflants est généralement mesurée à l'état saturé à partir de tests oedométriques. Les procédures expérimentales des essais oedométriques sont généralement trop lourdes et demandent trop de temps pour leur utilisation de façon routinière dans la pratique de l'ingénierie géotechnique conventionnelle, et elles ne permettent pas d'estimer le soulèvement à différents degrés de saturations. Pour pallier ces limitations, un modèle semi-empirique est proposé pour prévoir la variation de la pression de gonflement du sol expansif par rapport à la succion du sol en utilisant la courbe de rétention d'eau (CRE) comme outil d'estimation. Une relation empirique est également suggéré pour estimer l'indice de gonflement à partir de l'indice de plasticité, réduisant le besoin d'essais oedométriques. La pression de gonflement l'indice de gonflement calculés sont ensuite utilisées pour l'estimation de la variation unidimensionnelle du soulèvement en fonction de la succion pour des sols gonflants en modifiant l'équation de Fredlund (1983). L'approche proposée est validée en utilisant huit sites différents situés dans six pays différents; à savoir l'Arabie saoudite, l'Australie, le Canada, la Chine, les Etats-Unis et le Royaume-Uni; ainsi que sur six types de sols gonflants compactés provenant des Etats-Unis.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author