Machine Learning-Based Estimation of Soil’s True Air-Entry Value from GSD Curves

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 high-level 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

Investigation and Treatment Analysis of Barikan Landslide

In last several years periodic reports indicating damages toward resident;s homes due to ground movements in Barikan region, 120km far from tehran, have been issued. The earth movements are demonstrated by tension cracks and scraps on ground surfaces and walls of in site homes and gardens. Since the slow and continuous earth movements were observed in the site, a course of site investigation consisted of the monitoring of surface and deep earth movements has been considered to study the affecting factors and the extent of of landslide. In addition to ground movement measurements, by using the geotechnical properties of different soil layers, stability analysis of the soil mass was performed. Results showed that the village would be stable at static conditions in all relative groundwater levels. However, in case of earthquake with value of horizontal acceleration equal to 0.14g, analyses indicated total instability of the site. It seems that the movements, which apparently widen the cracks and damage the houses and walls of the gardens, are due to the mild in site earthquakes or accelerations of the farther occurred earthquakes of the area, which by reducing the F.S. of the slope, increase the severity of movements rate in the village. In this paper the results of conducted researches, as well as possible remedial solutions for ground movements, with regard to known effective factors of landslide, are presented

A viscoplastic SANICLAY model for natural soft soils

This paper focuses on constitutive and numerical modeling of strain-rate dependency in natural clays while also accounting for anisotropy and destructuration. For this purpose the SANICLAY model that accounts for the fabric anisotropy with the additional destructuration feature that accounts for sensitivity of natural clays, is considered as the reference model. An associated flow rule is adopted for simplicity. The model formulation is refined to also account for the important feature of strain-rate dependency using the Perzyna’s overstress theory. The model is then implicitly integrated in finite element program PLAXIS. Performance of the developed and implemented model is explored by comparing the simulation results of several element tests and a boundary value problem to the available experimental data. The element tests include the constant strain-rate under one-dimensional and triaxial conditions on different clays. The boundary value problem includes a test embankment, namely embankment D constructed at Saint Alban, Quebec. For comparison, the test embankment is also analyzed using the Modified Cam-Clay (MCC) model, the SANICLAY model, and the viscoplastic model but without destructuration. Results demonstrate the success of the developed and implemented viscoplastic SANICLAY in reproducing the strain-rate dependent behavior of natural soft soils.Support to conduct this study is provided by the University of Nottingham’s Dean of Engineering award, and the Natural Sciences and Engineering Research Council of Canada (NSERC)

Rate-dependency and Stress-Relaxation of Unsaturated Clays

This paper presents the experimental program conducted for evaluation of the rate-dependent and stress-relaxation behavior of unsaturated reconstituted London clay. A series of drained constant rate of strain (CRS) compression-relaxation tests with single-staged (SS-CRS) and multistaged (MS-CRS) loading modes was performed in an innovative CRS oedometer cell where soil suction evolutions were monitored using two high-capacity tensiometers (HCTs). Specimens were tested at two strain rates of 4.8×10−7 and 2.4×10−6  s−1 and over a suction range of 0–1,905 kPa. The coupled and independent effects of strain rate and soil suction on one-dimensional stress–strain and stress-relaxation responses, including the effects of prerelaxation strain, stress, and strain rate under both saturated and unsaturated conditions, were evaluated. An increase in suction and strain rate resulted in an increase of the yield vertical net stress (σp). Furthermore, it was observed that the rate and magnitude of the relaxed stresses increased with increases in prerelaxation strain, stress, and strain rate, and decreased with an increase in soil suction. At constant suction, an increase in the prerelaxation strain rate by a factor of five resulted in an increase of the relaxed stresses by a factor of 2.2–3.6. Moreover, the coefficient of relaxation (Rα) was found to be suction dependent, falling within a range of 0.011–0.019 and 0.017–0.029, respectively, for slow and fast strain rates during MS-CRS tests. Comparing these results with the Cα/Cc ratio obtained from conventional multistage loading (MSL) oedometer test results revealed the validity of Rα=Cα/Cc correlation for unsaturated reconstituted specimens

Transport in porous media with nonlinear flow condition

We investigate local aspects and heterogeneities of porous medium morphology and relate them to the relevant mechanisms of momentum transfer. In the inertial flow range, there are very few experimental data that allow to recognize the effects of porous structure on the flow and transport through porous media. An experimental analysis was performed in order to understand above processes at different Reynolds numbers in randomly structured porous media. The objective of the analysis is to explore the effects of porous media particle size on inertial and viscous forces and determine range of the Reynolds numbers in which the inertial flow predominantly contributes in dispersive processes. Transport characteristics of the randomly structured porous media and the influence of inertial force on longitudinal and transverse dispersion coefficients were studied

Creep and consolidation of a stiff clay under saturated and unsaturated conditions

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- 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 curve (Cc) and the creep index (Cαe) values, and an increase in yield vertical net stress (σp). Moreover, the Cαe/Cc ratio for London Clay was found to be stress- and suction-dependent, unlike the previously suggested hypotheses

BS-CLAY1 : anisotropic bounding surface constitutive model for natural clays

In this paper, a multi-surface anisotropic constitutive model is proposed for clayey soils, based on bounding surface theory and a classical anisotropic critical state-based model. In the proposed model, in addition to volumetric hardening law, rotational hardening rule is also incorporated into the bounding surface formulation with a non-associated flow rule. The model uses the bounding surface plasticity theory to produce a more realistic representation of the nonlinear behavior of clays with high overconsolidation ratios. The detailed model formulation is presented including an innovative approach for finding image stress points on the bounding surface which offers an original conception of changing the projection center even at the absence of plastic loading. Moreover, a modification procedure is discussed to improve the performance of the proposed model for simulating the highly overconsolidated clays. The proposed modifications besides the novel mapping rule form a novel framework that improves the simulation capabilities of the models with elliptical yield/bounding surfaces, particularly in the case of highly overconsolidated clays, and is applicable to all constitutive models with elliptical yield/bounding surfaces. Furthermore, the efficiency of the framework is demonstrated by comparing the simulation results against element test data from a number of different clays at lightly to highly overconsolidated conditions. The new model shows promising capability in capturing important aspects of natural clays response during straining, in particular the combined effects of small strain nonlinearity with fabric orientation

Creep analysis of an earth embankment on soft soil deposit with and without PVD improvement

In this paper, an anisotropic creep constitutive model, namely Creep-SCLAY1S is employed 10 to study the installation effects of prefabricated vertical drains (PVDs) on the behavior of a full 11 scale test embankment, namely Haarajoki embankment in Finland. The embankment was 12 constructed on a natural soft soil with PVD installed to improve the drainage under one half of 13 it. The Creep constitutive model used in this study, incorporates the effects of fabric 14 anisotropy, structure and time within a critical state based framework. For comparison, the 15 isotropic modified Cam clay (MCC) model and the rate-independent anisotropic S-CLAY1S 16 model are also used for the analyses. The numerical predictions are compared with field 17 measurements and the results indicate that the creep model provides an improved 18 approximation of field settlements, and excess pore pressure build-up and dissipations. In 19 addition, the application of two commonly used permeability matching techniques for two 20 dimensional (2D) plane-strain analysis of the PVD problem is studied and the results are 21 discussed highlighting their limitations and advantages

Double image stress point bounding surface model for monotonic and cyclic loading on anisotropic clays

In this paper, an anisotropic non-associative constitutive model, based on the well-established critical state soil mechanics framework, is developed for the natural and reconstituted clays subjected to monotonic and cyclic loadings. A robust non-elliptical yield surface is implemented in the model which enables it to capture a wide variety of yield stress points. In addition to a realistic soil stiffness simulation, the employed flexible plastic potential surface equips the proposed model to predict a more accurate coefficient of earth pressure at rest. The model uses a combination of conventional volumetric and comprehensive rotational hardening rules to control the evolution of the yield surface caused by plastic strain increments. The adopted rotational hardening rule uses the concept of governing plastic strain increment which not only ensures the existence of the equilibrium state of anisotropy but also takes the effect of plastic strains at different constant stress ratios into account more sensibly. The proposed model is enhanced with a novel double-image stress point bounding surface plasticity type theory to capture nonlinear behaviour inside the yield surface, and also to simulate the cyclic responses. The detailed model formulation is discussed in both triaxial stress space and th

Adaptive anisotropic constitutive modeling of natural clays

In this paper, an adaptive anisotropic constitutive model, namely AA1‐CLAY, is developed for clays based on the critical state framework. The model has a non‐associated flow rule, and it can also reduce to basic critical state constitutive models. A versatile yield surface (YS) is implemented in the model which can generate a broad range of shapes to improve the possibility of capturing experimental yield points of different clay types with high accuracy. In addition to the isotropic hardening rule, an innovative rotational hardening (RH) rule is also incorporated into the model to control the YS rotation rate. The proposed RH rule uses a transitional function to govern the effect of plastic strains at different constant stress ratios more realistically. Furthermore, the equilibrium state of anisotropy, which the YS tends to reach during plastic straining, is defined uniquely based on the experimental findings. The detailed model formulation is presented, and important features of the model are elaborately discussed. The capabilities of the model are also demonstrated by comparing the simulation results of several element tests on a number of different clays against the available experimental data