Numerical analysis of vertical drains accelerated consolidation considering combined soil disturbance and visco-plastic behaviour

Azari, Babak,Fatahi, Behzad,Khabbaz, Hadi Techno-Press 2015 Geomechanics & engineering Vol.8 No.2

Soil disturbance induced by installation of mandrel driven vertical drains decreases the in situ horizontal hydraulic conductivity of the soil in the vicinity of the drains, decelerating the consolidation rate. According to available literature, several different profiles for the hydraulic conductivity variation with the radial distance from the vertical drain, influencing the excess pore water pressure dissipation rate, have been identified. In addition, it is well known that the visco-plastic properties of the soil also influence the excess pore water pressure dissipation rate and consequently the settlement rate. In this study, a numerical solution adopting an elastic visco-plastic model with nonlinear creep function incorporated in the consolidation equations has been developed to investigate the effects of disturbed zone properties on the time dependent behaviour of soft soil deposits improved with vertical drains and preloading. The employed elastic visco-plastic model is based on the framework of the modified Cam-Clay model capturing soil creep during excess pore water pressure dissipation. Besides, nonlinear variations of creep coefficient with stress and time and permeability variations during the consolidation process are considered. The predicted results have been compared with V$\ddot{a}$sby test fill measurements. According to the results, different variations of the hydraulic conductivity profile in the disturbed zone result in varying excess pore water pressure dissipation rate and consequently varying the effective vertical stresses in the soil profile. Thus, the creep coefficient and the creep strain limit are notably influenced resulting in significant changes in the predicted settlement rate.

Analyzing consolidation data to predict smear zone characteristics induced by vertical drain installation for soft soil improvement

Parsa-Pajouh, Ali,Fatahi, Behzad,Vincent, Philippe,Khabbaz, Hadi Techno-Press 2014 Geomechanics & engineering Vol.7 No.1

In this paper, the effects of variability of smear zone characteristics induced by installation of prefabricated vertical drains on the preloading design are investigated employing analytical and numerical approaches. Conventional radial consolidation theory has been adopted to conduct analytical parametric studies considering variations of smear zone permeability and extent. FLAC 2D finite difference software has been employed to conduct the numerical simulations. The finite difference analyses have been verified using three case studies including two embankments and a large-scale laboratory consolidometer with a central geosynthetic vertical drain. A comprehensive numerical parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Furthermore, the construction of the trial embankment is recommended as a reliable solution to estimate accurate smear zone properties and minimise the post construction settlement. A back-calculation procedure is employed to determine the minimum required waiting time after construction of the trial embankment to predict the smear zone characteristics precisely. Results of this study indicate that the accurate smear zone permeability and extent can be back-calculated when 30% degree of consolidation is obtained after construction of the trial embankment.

Analyzing consolidation data to obtain elastic viscoplastic parameters of clay

Le, Thu M.,Fatahi, Behzad,Disfani, Mahdi,Khabbaz, Hadi Techno-Press 2015 Geomechanics & engineering Vol.8 No.4

A nonlinear creep function incorporated into the elastic visco-plastic model may describe the long-term soil deformation more accurately. However, by applying the conventional procedure, there are challenges to determine the model parameters due to limitation of suitable data points. This paper presents a numerical solution to obtain several parameters simultaneously for a nonlinear elastic visco-plastic (EVP) model using the available consolidation data. The finite difference scheme using the Crank-Nicolson procedure is applied to solve a set of coupled partial differential equations of the time dependent strain and pore water pressure dissipation. The model parameters are determined by applying the algorithm of trust-region reflective optimisation in conjunction with the finite difference solution. The proposed method utilises all available consolidation data during dissipation of the excess pore water pressure to determine the required model parameters. Moreover, the reference time in the elastic visco-plastic model can readily be adopted as a unit of time; denoting creep is included in the numerical predictions explicitly from the very first time steps. In this paper, the settlement predictions of thick soft clay layers are presented and discussed to evaluate and compare the accuracy and reliability of the proposed method against the graphical procedure to obtain the model parameters. In addition, comparison of the available experimental results to the numerical predictions confirms the accuracy of the numerical procedure.

Performance of laterally loaded piles considering soil and interface parameters

Fatahi, Behzad,Basack, Sudip,Ryan, Patrick,Zhou, Wan-Huan,Khabbaz, Hadi Techno-Press 2014 Geomechanics & engineering Vol.7 No.5

To investigate the soil-pile interactive performance under lateral loads, a set of laboratory model tests was conducted on remoulded test bed of soft clay and medium dense sand. Then, a simplified boundary element analysis had been carried out assuming floating pile. In case of soft clay, it has been observed that lateral loads on piles can initiate the formation of a gap, soil heave and the tension crack in the vicinity of the soil surface and the interface, whereas in medium dense sand, a semi-elliptical depression zone can develop. Comparison of test and boundary element results indicates the accuracy of the solution developed. However, in the boundary element analysis, the possible shear stresses likely to be developed at the interface are ignored in order to simplify the existing complex equations. Moreover, it is unable to capture the influence of base restraint in case of a socketed pile. To bridge up this gap and to study the influence of the initial stress state and interface parameters, a field based case-study of laterally-loaded pile in layered soil with socketed tip is explored and modelled using the finite element method. The results of the model have been verified against known field measurements from a case-study. Parametric studies have been conducted to investigate the influence of the coefficient of lateral earth pressure and the interface strength reduction factor on the results of the model.

Comparison of five international indices of adherence to the Mediterranean diet among healthy adults: similarities and differences

Aoun, Carla,Papazian, Tatiana,Helou, Khalil,El Osta, Nada,Khabbaz, Lydia Rabbaa The Korean Nutrition Society 2019 Nutrition Research and Practice Vol.13 No.4

BACKGROUND/OBJECTIVES: To compare five indices of adherence to the Mediterranean Diet (MD) among adults living in the Mediterranean region. SUBJECTS/METHODS: A total of 100 healthy Lebanese adults aged between 18 and 65 years. Face-to-face interviews to collect sociodemographic and medical information, to take anthropometric measurements, and to fill a validated, culturally adapted, food frequency questionnaire (FFQ). The score for each item was calculated following the recommendations for each corresponding index. The five MD indices were Mediterranean Diet Scale (MDScale), Mediterranean Food Pattern (MFP), MD Score (MDS), Short Mediterranean Diet Questionnaire (SMDQ), and the MedDiet score. RESULTS: Significant correlations were detected between items with P-values < 0.001. Minimal agreement was seen between MDScale and MedDiet score and maximal agreement between MDS and MedDiet score. Univariate and multivariate analyses showed that MDS and MedDiet scores had significant correlations with fiber and olive oil intake, main components of the MD. MDScale showed a significant correlation with waist-to-hip ratio and with total energy intake but none of the five indices was correlated to body mass index (BMI). CONCLUSIONS: The indices that showed the highest correlation with variables related to the MD are the MDScale and the MedDiet score; therefore, they can be used to assess our future study populations. Based on the current results, more than half of the study population was non-adherent to the MD and adherence to this diet did not appear to protect against being overweight ($BMI{\geq}30$).

Comparison of five international indices of adherence to the Mediterranean diet among healthy adults: similarities and differences

Carla Aoun,Tatiana Papazian,Khalil Helou,Nada El Osta,Lydia Rabbaa Khabbaz 한국영양학회 2019 Nutrition Research and Practice Vol.13 No.4

BACKGROUND/OBJECTIVES: To compare five indices of adherence to the Mediterranean Diet (MD) among adults living in the Mediterranean region. SUBJECTS/METHODS: A total of 100 healthy Lebanese adults aged between 18 and 65 years. Face-to-face interviews to collect sociodemographic and medical information, to take anthropometric measurements, and to fill a validated, culturally adapted, food frequency questionnaire (FFQ). The score for each item was calculated following the recommendations for each corresponding index. The five MD indices were Mediterranean Diet Scale (MDScale), Mediterranean Food Pattern (MFP), MD Score (MDS), Short Mediterranean Diet Questionnaire (SMDQ), and the MedDiet score. RESULTS: Significant correlations were detected between items with P-values < 0.001. Minimal agreement was seen between MDScale and MedDiet score and maximal agreement between MDS and MedDiet score. Univariate and multivariate analyses showed that MDS and MedDiet scores had significant correlations with fiber and olive oil intake, main components of the MD. MDScale showed a significant correlation with waist-to-hip ratio and with total energy intake but none of the five indices was correlated to body mass index (BMI). CONCLUSIONS: The indices that showed the highest correlation with variables related to the MD are the MDScale and the MedDiet score; therefore, they can be used to assess our future study populations. Based on the current results, more than half of the study population was non-adherent to the MD and adherence to this diet did not appear to protect against being overweight (BMI ≥ 30).