Papers by Meghdad Bagheri
Gondwana Research
The application of machine learning (ML) methods has proven to be promising in dealing with a wid... more The application of machine learning (ML) methods has proven to be promising in dealing with a wide range of geotechnical engineering problems in recent years. ML methods have already been used for the prediction of soil water retention curves (SWRC) and estimation of air-entry values (AEV). However, the reported works in the literature are generally based on limited data and conventional, less accurate approaches for AEV estimation. In this paper, a large database, known as UNsaturated SOil hydraulic DAtabase (UNSODA), is studied and the conventional and true AEVs of 790 soil samples are estimated based on determination methods reported in the literature. A ML approach is then employed for the development of a predictive model for the estimation of true AEV from water content-based SWRCs of a wide range of soil types taking into account the impact of bulk density and grain size distribution parameters. The obtained results reveal an enhanced accuracy in AEV determination, featuring R2 values of 0.964, 0.901 and 0.851 for training, validation, and testing data, respectively, which confirm the marked performance of the developed ML model. Based on the results of a sensitivity analysis, the particle sizes of 50 and 250 μm are found to have the highest impact on the AEV estimation.
International Journal of Geomechanics, 2019
Please refer to published version for the most recent bibliographic citation information. If a pu... more Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.
Geotechnical Research, 2018
High-capacity tensiometers (HCTs) are sensors made to measure negative pore water pressure (sucti... more High-capacity tensiometers (HCTs) are sensors made to measure negative pore water pressure (suction) directly. In this paper, a new approach is proposed to expand the range and duration of suction measurements for a newly designed HCT. A new technique is employed to reduce significantly the roughness of the diaphragm’s surface on the water reservoir side in order to minimise the possibility of gas nuclei development and the subsequent early cavitation at the water–diaphragm interface. The procedures employed for the design, fabrication, saturation and calibration of the new tensiometers are explained in detail. Furthermore, the performance of the developed HCTs is examined based on a series of experiments carried out on a number of unsaturated clay specimens. An improvement in maximum sustainable suction in the range of 120–150% of their nominal capacity was obtained from different surface treatment methods. Moreover, the results show an improvement of up to 177% for the long-term s...
Geotechnical Testing Journal, 2019
Please refer to published version for the most recent bibliographic citation information. If a pu... more Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.
Canadian Geotechnical Journal, 2019
In this paper, the one-dimensional (1D) time-dependent behaviour of natural and reconstituted Lon... more In this paper, the one-dimensional (1D) time-dependent behaviour of natural and reconstituted London Clay samples under saturated and unsaturated conditions is studied. For this purpose, a set of 1D consolidation tests including multi-staged loading (MSL) oedometer tests and single-staged loading (SSL) long-term oedometer creep tests were carried out on saturated and unsaturated specimens. Conventional oedometer cells were used for tests on saturated specimens, whereas a newly designed unsaturated oedometer cell, equipped with two high-capacity tensiometers (HCTs) for suction measurements, was used for unsaturated tests. The tests results revealed stress dependency and suction dependency of primary and secondary consolidation responses of the soil samples. Furthermore, counter to formerly acknowledged suggestions of independency of the slope of normal consolidation line to suction changes, it was observed that an increase in suction results in a decrease of the slope of compression ...
IOP Conference Series: Earth and Environmental Science, 2015
Clayey soils tend to undergo continuous compression with time, even after excess pore pressures h... more Clayey soils tend to undergo continuous compression with time, even after excess pore pressures have substantially dissipated. The effect of time on deformation and mechanical response of these soft soils has been the subject of numerous studies. Based on these studies, the observed time-dependent behaviour of clays is mainly related to the evolution of soil volume and strength characteristics with time, which are classified as creep and/or relaxation properties of the soil. Apart from many empirical relationships that have been proposed in the literature to capture the rheological behaviour of clays, a number of viscid constitutive relationships have also been developed which have more attractive theoretical attributes. A particular feature of these viscid models is that their creep parameters often have clear physical meaning (e.g. coefficient of secondary compression,). Sometimes with these models, a parameter referred to as initial/reference volumetric strain rate, ̇ has also been alluded as a model parameter. However, unlike , the determination of ̇ and its variations with stress level is not properly documented in the literature. In an attempt to better understand ̇ , this paper presents an experimental investigation of the reference volumetric strain rate in reconstituted clay specimens. A long-term triaxial creep test, at different shear stress levels and different strain rates, was performed on clay specimen whereby the volumetric strain rate was measured. The obtained results indicated the stress-level dependency and non-linear variation of ̇ with time.
Geotextiles and Geomembranes, 2017
The version presented here may differ from the published version or, version of record, if you wi... more The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP URL' above for details on accessing the published version and note that access may require a subscription.
E3S Web of Conferences, 2016
The paper presents an experimental investigation of very small strain stiffness of unsaturated sa... more The paper presents an experimental investigation of very small strain stiffness of unsaturated sand. A triaxial test apparatus was equipped with bender elements and compression discs in order to assess the stiffness at very small strains by measuring the velocity of propagation of shear and compression waves through an unsaturated sample. The negative water column method was adopted to apply suction at the base of the sample. The experiments were designed to investigate the independent effect of suction and degree of saturation on the wave propagation velocities. This was achieved by testing the sand sample on both the drying and wetting path.
International Conference on Soil Mechanics and Geotechnical Engineering , 2022
The very small strain shear modulus (stiffness) of soils, Gmax, is one of the most important para... more The very small strain shear modulus (stiffness) of soils, Gmax, is one of the most important parameters for predicting ground movements and dynamic responses of geo-structures. In this study, the combined effect of clay fraction and moisture content on shear stiffness of an unsaturated sand-clay mixture at very small strains was investigated using bender elements. Compacted soil specimens were prepared at three different clay contents of 10, 20, and 30%, and at four different initial moisture contents of 3, 6, 9 and 12%. Bender element tests were carried out under isotropic and constant moisture content conditions and inside a modified triaxial testing system equipped with a pair of piezoelectric bender-extender elements. Gmax was calculated based on the velocity measurement of shear waves propagated through the specimen. The tests results showed that Gmax decreases approximately linearly with an increase in moisture content, and non-linearly with an increase in clay content. A basic empirical equation was derived from an examination of trends in evolution of Gmax with clay and moisture content. Additional empirical correlations were also derived for estimation of moisture content and degree of saturation based on the compression wave velocity measurements. RÉSUMÉ : Le module de cisaillement (rigidité) à très petite déformation, Gmax, est l'un des paramètres les plus importants pour prédire les mouvements du sol et les réponses dynamiques des géo-structures. Dans cette étude, l'effet combiné de la fraction d'argile et de la teneur en eau sur la rigidité au cisaillement d'un mélange de sable-argile insaturé à de très petites déformations a été étudié en utilisant un système de mesure d'ondes type «Bender Elements». Des échantillons de sol compactés ont été préparés à trois teneurs différentes en argile de 10, 20 et 30%, et à quatre teneurs en eau initiales différentes de 3, 6, 9 et 12%. Les essais «Bender Elements» ont été effectués dans des conditions isotropes et constantes de teneur en eau à l'intérieur d'un système triaxial modifié équipé d'une paire de «Bender Elements» piézoélectriques. Gmax a été calculé sur la base de la mesure de la vitesse des ondes de cisaillement propagées à travers l'échantillon. Les résultats des tests ont montré que Gmax diminue approximativement linéairement avec une augmentation de la teneur en eau, et de manière non linéaire avec une augmentation de la teneur en argile. Une équation empirique de base a été déduite d'une étude des tendances de l'évolution de Gmax avec l'argile et la teneur en eau. Des corrélations empiriques supplémentaires ont également été calculées pour l'estimation de la teneur en eau et du degré de saturation sur la base des mesures de la vitesse de l'onde de compression.
Gondwana Research, 2022
The application of machine learning (ML) methods has proven to be promising in dealing with a wid... more The application of machine learning (ML) methods has proven to be promising in dealing with a wide range of geotechnical engineering problems in recent years. ML methods have already been used for the prediction of soil water retention curves (SWRC) and estimation of air-entry values (AEV). However, the reported works in the literature are generally based on limited data and conventional, less accurate approaches for AEV estimation. In this paper, a large database, known
as UNsaturated SOil hydraulic DAtabase (UNSODA), is studied and the conventional and true AEVs of 790 soil samples are estimated based on determination methods reported in the literature. A ML approach is then employed for the development of a predictive model for the estimation of true AEV from water content-based SWRCs of a wide range of soil types taking into account the impact of bulk density and grain size distribution parameters. The obtained results reveal an enhanced accuracy in AEV determination, featuring R2 values of 0.964, 0.901 and 0.851 for training, validation, and testing data, respectively, which confirm the marked performance of the developed ML model. Based on the results of a sensitivity analysis, the particle sizes of 50 and 250 μm are found to have the highest impact on the AEV estimation.
International Journal of Geomechanics, 2022
This paper investigates the effect of soil moisture evaporation rate on the soil water retention ... more This paper investigates the effect of soil moisture evaporation rate on the soil water retention curve (SWRC) of clays obtained using high-capacity tensiometer (HCT) technique and following the continuous drying (dynamic) method. SWRC measurements, with and without soil moisture evaporation rate control, were carried out on reconstituted London clay specimens using 12 performance-improved HCTs recently developed at the University of Warwick. Furthermore, the HCTs’ performance in terms of the maximum attainable suction (smax) and maximum measurement duration (tmax) was evaluated. Moreover, the suitability of a curve fitting-based model, available in the literature, for attaining the entire retention curve (beyond the capacity of HCTs) was evaluated. The SWRCs for tests with controlled evaporation rate were found to be generally exhibiting higher suctions at a given water content, hence inducing air-entry values that were on average 16% higher than those obtained from tests without evaporation rate control. It was also found that for suctions beyond 2 MPa, the curve fitting-based model predictions of data obtained from tests with controlled evaporation rate exhibit significantly lower suctions at a given water content than those without evaporation rate control, suggesting that such curve fitting correlations should be used with caution.
The paper presents an experimental investigation of very small strain stiffness of unsaturated sa... more The paper presents an experimental investigation of very small strain stiffness of unsaturated sand. A triaxial test apparatus was equipped with bender elements and compression discs in order to assess the stiffness at very small strains by measuring the velocity of propagation of shear and compression waves through an unsaturated sample. The negative water column method was adopted to apply suction at the base of the sample. The experiments were designed to investigate the independent effect of suction and degree of saturation on the wave propagation velocities. This was achieved by testing the sand sample on both the drying and wetting path.
The paper describes a series of experimental testing on natural stiff London clay samples retriev... more The paper describes a series of experimental testing on natural stiff London clay samples retrieved from the New Hook Farm in the Isle of Sheppey, UK. The experimental program includes determination of macroscopic and microscopic properties, chemical compositions, Atterberg limits, permeability, and compressibility parameters in both intact and reconstituted states. The paper integrates the earlier studies, the new findings, and the commercial investigation results with the aim to extend the current knowledge of the geological and geotechnical characteristics of this stiff clay from the east of the London basin. Some comparisons are also made with shallow depth London clay from Heathrow Terminal 5 site.
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Papers by Meghdad Bagheri
as UNsaturated SOil hydraulic DAtabase (UNSODA), is studied and the conventional and true AEVs of 790 soil samples are estimated based on determination methods reported in the literature. A ML approach is then employed for the development of a predictive model for the estimation of true AEV from water content-based SWRCs of a wide range of soil types taking into account the impact of bulk density and grain size distribution parameters. The obtained results reveal an enhanced accuracy in AEV determination, featuring R2 values of 0.964, 0.901 and 0.851 for training, validation, and testing data, respectively, which confirm the marked performance of the developed ML model. Based on the results of a sensitivity analysis, the particle sizes of 50 and 250 μm are found to have the highest impact on the AEV estimation.
as UNsaturated SOil hydraulic DAtabase (UNSODA), is studied and the conventional and true AEVs of 790 soil samples are estimated based on determination methods reported in the literature. A ML approach is then employed for the development of a predictive model for the estimation of true AEV from water content-based SWRCs of a wide range of soil types taking into account the impact of bulk density and grain size distribution parameters. The obtained results reveal an enhanced accuracy in AEV determination, featuring R2 values of 0.964, 0.901 and 0.851 for training, validation, and testing data, respectively, which confirm the marked performance of the developed ML model. Based on the results of a sensitivity analysis, the particle sizes of 50 and 250 μm are found to have the highest impact on the AEV estimation.