Mechanical Behavior Of Soil Research Articles

Two-dimensional finite element modeling of long-term frost heave beneath chilled gas pipelines

Proper estimation of frost heave over the lifetime of a buried chilled gas pipeline is a key design concern. Previously conducted full-scale and centrifuge tests were continued for a limited period of time. Similarly, the numerical analyses with modeling of the coupled thermo-hydro-mechanical process of frost heave were limited to less than half of the design life of typical pipelines. Few studies estimated the long-term frost heave based on decoupled analyses where the heat transfer and frost heave were calculated separately, although both are interrelated processes. This study presents a two-dimensional coupled finite element (FE) modeling of frost heave under chilled gas pipelines buried in frost susceptible soil. The Konrad–Morgenstern segregation potential (SP) model is implemented in commercially available software using user subroutines. Simplified elastic-plastic models that recognize the key influencing factors, including temperature and volumetric ice fraction of frozen soil, are used for modeling the mechanical behaviour of soil. The present numerical approach can properly calculate the temperature gradient in the frozen fringe, which is essential in the SP model to define the volumetric expansion due to water migration to the frozen fringe. The FE calculated heave and frost front penetration are compared with the Calgary full-scale test results. The moisture content profiles obtained from FE simulation show a similar pattern as reported from a full-scale test. The challenges in modeling long-term heave resulting from continued ice accumulation in front of the final ice lens and potential warming of the leading part of the frozen bulb when the pipe moves further up are discussed.

Effect of fiber length on the consolidation parameters of coir fiber-reinforced soft clay

Coir fibers are natural fibers with high tensile strength and pressure resistance, making them an alternative soil reinforcement material. However, the effect of fiber length on improving soil consolidation properties has yet to be largely explored. Therefore, this study investigated the effect of the length and content of coir fibers on soft soil mechanical behavior through a series of one-dimensional consolidation tests. Fibers of >10 mm to 30 mm and >30 mm to 50 mm lengths were mixed randomly into the soil with varying content, ranging from 0.00% to 1.25% of the total weight of the mixture. The relationship between the effective stress and the void ratio was explored, unveiling that the void ratio of soil specimens reinforced with coir fibers decreased more gradually than those unreinforced. An increase in the fiber content reduced the compression index (Cc) value and enhanced the coefficient of consolidation (Cv) value, with longer fibers producing more significant values due to more excellent interactions between fibers. Fibers of >30 mm-50 mm yielded optimum Cc and Cv values at the fiber contents of 0.50% to 0.75%.

Simulation of cyclic laterally-loaded piles in undrained clays accounting for soil small-strain characteristics

The performance of pile foundations subjected to cyclic lateral loading is central to offshore geotechnical engineering. Although non-linearity and path-dependence of soil mechanical behavior at small strains are widely recognized, the influences of these local behavior on global response of pile foundations are less explored. This work presents numerical analyses of cyclically-loaded piles in undrained clays that explicitly account for soil small-strain characteristics. By using intergranular strain (IGS) elasticity method, a soil model proposed by the authors for undrained clays during cyclic loading is extended to include non-linear small-strain behavior. Via comparing against element tests, the constitutive relation is shown capable of representing the observed variation of soil stiffness and damping with strain magnitudes, as well as the dependence of such non-linearity on stress paths. Based on the above soil model, finite element simulations are performed to interpret the response of laterally loaded piles from geotechnical centrifuge tests. The impacts of soil small-strain behavior on pile force–displacement relations, hysteric loops, and the ability of a pile–soil system to dissipate energy are investigated. This work highlights that the sensitivity of these foundation responses to small-strain non-linearity of soils can vary considerably, depending on pile geometry features and head constraint conditions.

Polynomial chaos surrogate and bayesian learning for coupled hydro-mechanical behavior of soil slope

As rainfall infiltrates into soil slopes, the hydraulic and mechanical behaviors of soils are interacted. In this study, an efficient probabilistic parameter estimation method for coupled hydro-mechanical behavior in soil slope is proposed. This method integrates the Polynomial Chaos Expansion (PCE) method, the coupled hydro-mechanical modeling, and the Bayesian learning method. A coupled hydro-mechanical numerical model is established for the simulation of behaviors of unsaturated soil slope under rainfall infiltration, following by training a cheap-to-run PCE surrogate to replace it. Probabilistic estimation of soil parameters is conducted based on the Bayesian learning technique with the Markov Chain Monte Carlo (MCMC) simulation. A numerical example of an unsaturated slope under rainfall infiltration is presented to illustrate the proposed method. The effects of measurement durations and response types on parameter estimation are addressed. The result shows that with the increase of measurement duration, the uncertainties of soil parameters are significantly reduced. The uncertainties of hydraulic properties are reduced significantly using the pore water pressure data, while the uncertainties of soil strength parameters are reduced greatly using the measured displacement data.

Finite element geotechnical analysis incorporating deep learning-based soil model

Owing to the complicated mechanical behaviors of soils, their constitutive models often involve obscureformulations and suffer from poor applicability in engineering practice. In this study, a novel framework for the finite element (FE) analysis of geotechnical engineering problems is proposed, in which a deep learning (DL) model is employed to depict the constitutive behaviors of soils, circumventing the difficulties associated with conventional approaches. The DL model can incorporate different neural network architectures and is trained with stress–strain data, obtained either experimentally or numerically, before being integrated into the FE solver for analyzing various boundary value problems (BVPs). During the FE solution, the DL model receives strains at the Gauss integration points and returns the predicted stresses to advance the computation. The applicability and capacity of the framework were demonstrated by analyzing three BVPs, in which different geometries, meshes, and boundary conditions were considered. It was shown that the framework is capable of reproducing satisfactory solutions without resorting to any constitutive theory. Furthermore, the use of the DL model not only avoids the stress integration of the conventional FE analysis, but also leads to better computational efficiency.

Influence of Abaca Fiber Inclusion on the Unconfined Compressive Strength of Reconstituted Sandy Silts

The present investigation determines the influence of abaca (Musa textilis) fiber inclusion on the simple compressive strength of reconstituted sandy silt specimens. For this purpose, fibers of different lengths (5, 10 and 15 mm) and quantities (0.5, 1.0, 1.5 and 2.0% of soil dry weight) are added to produce the reconstituted specimens. Subsequently, the physical and mechanical behavior of soil–fiber mixtures were evaluated through compaction and unconfined compression tests. The experimental results showed that increases in fiber content or length, or both, led to a 1235.1% increase in maximum compression stress (compared to the fiber-free soil). Compression failure occurred at a greater axial strain when 10 and 15 mm fibers were added at 1% dosage or in percentages equal to or greater than 1.5% regardless of fiber length. A series of linear mixed models identified statistically significant effects of fiber length and percentage on the level of effort and on the unitary deformation.

Failure mode of rainfall-induced landslide of granite residual soil, southeastern Guangxi Province, China

Abstract. Granite residual soil landslides are widely distributed in the southeast of Guangxi, China. They pose threats to local communities, economic development and ecological restoration. To understand the failure mode, the landslide can provide a scientific basis for early warning and prevention. In this study, we conducted artificial flume model tests to investigate the failure mode of granite residual soil landslide. The macroscopic phenomena of landslides were observed and summarized. The response and variations of soil moisture content and pore water pressure were analyzed. And the discrepancies in landslide initiation were explored. The results had three aspects: (1) the response of volume moisture content was not synchronized with that of pore water pressure. Their variations were influenced by initial dry density, slope angle and rainfall intensity. The fluctuation of pore water pressure depended on soil mechanical behavior and its diffusion. (2) The differences in the formation process of granite residual soil landslides included the initiation time and mode. The starting time of landslide was delayed with increasing initial dry density and slope angle but shortened with increasing rainfall intensity. The failure mode could be changed from a sudden type to a progressive type due to the increase in initial dry density. (3) There are five stages in the landslide mobilization as follows: rain infiltration and crack generation, soil slide at the slope toe, occurrence of surface runoff and soil erosion, formation of steep-free surface, and soil slide at the upper slope. This research can provide valuable reference for the prevention and early warning of granite residual soil landslide in southeastern Guangxi.

Real-time prediction of the mechanical behavior of suction caisson during installation process using GA-BP neural network

Due to the short construction period, convenient transportation and strong geological adaptability, the suction caisson has received more and more attention in offshore geotechnical foundation engineering associated with oil and gas production platforms. A good understanding of the mechanical behaviors of soils, such as real-time effective stress and settlement, around the suction caisson during its installation is important for analyzing the stability and loading capacity of the platforms in deep water. The objective of this research is to develop a numerical model for predicting the mechanical behavior of soils around the suction caisson during installation based on the data including real-time settlement and effective stress produced from the centrifuge tests in the literature by using the genetic algorithm-back propagation (GA-BP) neural network method. Furthermore, the nonlinear relationship among the settlement, penetration pressure, effective stress, and suction required during the installation is thoroughly investigated. It is found that, compared with the experimental results, the relative error of the prediction results from the proposed model is −0.3%∼1.4% for settlement, 0.8%∼2.3% for effective lateral stress in a single clay layer, and −2.5%∼4.5% for normalized required suction in multilayered soils at the final stage. It can be concluded that the GA-BP neural network method can be used to predict the real-time hydromechanical behavior of the caisson foundation during the installation process in terms of efficiency and accuracy.

Determination of Some Soil Properties on Penetration Resistance and Consistency Limits

Atterberg limits and penetration resistance are the factors that affect the mechanical behavior of soil. In this study, it was investigated the direct and indirect effect of some soil properties such as particle size distribution, moisture and organic matter content, aggregation rate, aggregate stability, and clay activity index on penetration resistance, liquid limit, plastic limit, and plasticity index and revealing the change of all studied properties along with the soil layers. A pasture was selected as the study area and 20 sample points were determined randomly. Penetration resistance (PR) was measured with a penetrologger at these points and soil samples were taken from three different soil layers (0-25, 25-50, and 50-75 cm). The analyses were carried out to determine the soil properties in the laboratory. One-way variance analysis (ANOVA) was used to determine the variation of the soil properties along with the sample layers, and the path analysis was used to determine the direct-indirect effects of the properties affecting the penetration resistance, liquid limit, plastic limit, and plasticity index. The path analysis results showed that clay content directly affected the penetration resistance with the highest coefficient, and organic matter content affected the aggregation rate. The clay content had the highest direct effect, and the organic matter content had the highest indirect effect on the penetration resistance. The highest direct effect coefficient was obtained from organic matter in the plastic limit and liquid limit, while the aggregation rate was in the plasticity index.

Assessment of probability of failure on rainfall-induced shallow landslides at slope scale using a physical-based model and fuzzy point estimate method

Shallow hillslope failure caused by rainfall is characterized by complex soil hydrology and mechanical behavior. It is important to understand the hydraulic behavior of hillslopes and quantify the effect of the uncertainty of mechanical parameters on hillslope stability for forewarning and hillslope management. Intra-hole deformation and displacement were record for the hillslope of the Babaoliao collapse site in the Chiayi County, as a case study. The fuzzy point estimation method and physical-based model were combined with the local factor of safety (LFS) theory to calculate the internal local factor of safety of the hillslope. A reliability analysis was then performed to determine the failure probability at different depths. Historical rainfall events were used to validate the model and predict the development of the failure probability for different rainfall patterns with the same warning rainfall. The results revealed that the failure probability model could effectively predict the area of hillslope instability and its changes over time and space. Different rainfall patterns affected the infiltration flux, leading to the difference in hillslope failure time. The delayed rainfall pattern had a significant impact on the time of slope instability, and shallow collapse was most likely to occur earlier. This study can be used as a reference for developing future hillslope warnings.

Improving the Mechanical Behavior of Soil Contaminated with Gas–Oil Using Organoclay and Nanoclay

Improving the Mechanical Behavior of Soil Contaminated with Gas–Oil Using Organoclay and Nanoclay

Modeling the Mechanical Behavior of Methane Hydrate-Bearing Sand Using the Equivalent Granular Void Ratio

For the safe extraction of methane from hydrate reservoirs, modeling the mechanical behavior of the methane hydrate-bearing soil properly is crucial in order to enable designers to analysis hydrate-dissociation-induced geotechnical failures. Hydrate morphology is one of major factors affecting the mechanical behavior of soil containing hydrate. This paper presents a new constitutive model for methane hydrate-bearing sand (MHBS) using the equivalent granular void ratio as a state variable, which can quantify the effects of the pore-filling and load-bearing hydrate morphology under a unifying framework. The proposed model is a combination of generalized plasticity and an elastic damage model so as to take into account the observed frictional and bonding aspects of MHBS, respectively. By using the concept of state-dependent dilatancy, the equivalent granular void ratio is formulated and adopted in the generalized plasticity model. In addition, a nonlinear damage function is implemented to elucidate the degradation of hydrate bonds with respect to shearing. Compared with the basic generalized plasticity model for host sand, only three additional parameters are required to capture key mechanical behaviors of MHBS. By comparing the triaxial test results of MHBS synthesized from a range of host sands with a predicted behavior by the proposed model, it is demonstrated that the new model can satisfactorily capture the stress–strain and volumetric behavior of MHBS under different hydrate saturations, confining pressures, and void ratios.

Italian seismic amplification factors for peak ground acceleration and peak ground velocity

ABSTRACT Ground motion modification over large areas is generally evaluated by focusing on source effects disregarding local lithostratigraphic site conditions. Hence, amplification maps of peak ground acceleration and peak ground velocity are proposed to improve the forecast of ground motion on a national scale. Topological information about litho-type successions and soil mechanical behaviour were retrieved from the Italian database of seismic microzonation and more than 30 million of seismic site response analyses were performed to quantify the amplification factors (i.e. the ratio between expected ground motion at the site of interest and that at the outcropping engineering bedrock). The maximum value of the amplified peak ground acceleration on the Italian territory results in about twice as much as the value expected at the outcropping of the engineering bedrock. Finally, damage scenario maps based on the amplified ground motion could be produced as a supporting tool for urban planning and emergency system management.

Alkali-activated system of carbide lime and rice husk for granular soil stabilisation

This study investigated the utilisation of an alkali-activated system to stabilise a granular soil. Rice husk ash (RHA) was used as the precursor and carbide lime (CL) as the activator. An experimental programme was carried out to analyse the strength and stiffness of sand–RHA–CL mixtures. Different binder contents (10 and 20%), densities (15.5, 16.5, 17.5 kN/m3), curing periods (7 and 28 days) and calcium/silicon dioxide (Ca/SiO2) ratios (1, 1.5, 2) were evaluated. Microstructural analyses were conducted on the mixed materials. The increase in binder content, dry density and curing period led to the improvement of strength and stiffness, while the increase in calcium/silicon dioxide ratio hindered the mechanical behaviour. The statistical analysis revealed that all factors studied influenced the mechanical behaviour of soil–binder mixtures. The condition to obtain the highest strength and stiffness was evidenced in the combination of higher dry unit weight, binder content, curing period and lower molar ratio. The alkali-activated system was shown to be a promising binder agent for soil stabilisation for both strength and stiffness. Finally, two calcium aluminosilicate hydrate structures were identified in the soil–binder mixtures, soulunite and jaffeite, indicating ideal structures for the composition of cement hydrates.

Numerical analysis of internal erosion impact on underground structures: Application to tunnel leakage

Water leakage is one of the most critical factors that affect the ground movement and structural behaviour during and after the construction of the shield tunnel. Currently, very limited attention has been paid to the effect of the loss of fine particles induced by the water leakage, namely the internal erosion. In this study, the evolution of soil porosity, gradation, seepage flow and the induced ground movement and lining stress change due to tunnel leakage has been numerically investigated using a novel coupled hydro-mechanical approach formulated within the continuous porous medium framework. The detachment and transport of fines particles within the seepage flow are considered by a four-constituent model of internal erosion. The induced influence on the soil mechanical behaviour is modelled by a critical-state-based constitutive model considering the evolution of the fines content. Using the proposed approach, the time–space evolution of the eroded zone and the hydro-mechanical response in the cases of a single tunnel and two crossing tunnels are identified. The results indicate that the commonly used pore pressure reduction-based method without considering internal erosion will under-estimate the leakage induced lining stress change and ground movement. Moreover, the influence of three-dimensional conditions, hydraulic boundary conditions and tunnel characteristics are highlighted.

Extension of 3-D coupled DDA-SPH method for dynamic analysis of soil-structure interaction problems

Soil-structure interaction problems are an important issue in the research field of geotechnical engineering. Understanding and modeling the soil-structure interaction problems is thus critical. Such interaction problems involve the mechanical behaviors of both soil and structure as well as their complex interaction. Discontinuous deformation method (DDA) is appropriate for modeling mechanical behavior of structure, while smoothed particle hydrodynamics (SPH) offers a feasible technique for describing the mechanical behavior of soil material. A coupled DDA-SPH method can integrate the advantages of both DDA and SPH. For three-dimensional (3-D) dynamic analysis of the soil-structure interaction problems, the original 3-D coupled DDA-SPH method must be extended, which is the primary purpose of this paper. In the extended 3-D coupled DDA-SPH method, an elastic-plastic soil constitutive model associated with the Drucker-Prager yield criterion is implemented. The interaction between soil and structure is realized through a newly proposed coupling scheme based on a penalty method using the Mohr-Coulomb failure criterion. Furthermore, the extended 3-D coupled DDA-SPH method is validated through the investigation of four experiments. The simulation results suggest that the extended 3-D coupled DDA-SPH method can accurately simulate the large deformations and post-failure behavior of soil-structure interaction problems.

Compressive Strength of Acrylic Polymer-Stabilized Kaolinite Clay Modified with Different Additives.

Although numerous studies have shown the successful use of acrylic-based polymers as one of the chemical substances to improve soil mechanical behavior, their basic ingredients in commercial products are not revealed due to the manufacturers’ confidential policy. Among them, additives including pH control agents, thickeners, antifoams, and wetting agents are widely well-known owing to their enhancement effects on different properties of polymers. However, the effect of additives on the soil–polymer mixture is not completely investigated. Therefore, in this study, some of the frequently used additives in acrylic polymers were selected to investigate the effects of each one on the compressive strength of clayey soil. These additives include xanthan gum, Tylose, and carboxymethyl cellulose (CMC) as thickeners, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and Kenon 10 as wetting agents, an ether-based antifoaming agent, and ammonia solution as a pH control agent. A combination of each additive (between 0 and 5% by weight) and polymethyl methacrylate-co-butyl acrylate (with 5% by weight) was added to kaolinite soil to measure the variation of unconfined compressive strength (UCS) and the stress–strain behavior of the soil–polymer–additive mixture. The results indicated that thickeners significantly affected the unconfined compressive strength up to 248% and increased the ductility of the stabilized samples. Acidic pH of the emulsion led to higher unconfined compressive strength of the stabilized soil up to 2.33 times that with alkaline. It is also demonstrated that the use of a higher amount of anionic wetting agent resulted in higher failure strain and lower unconfined compressive strength.

Mechanical Behavior of Low Plasticity Clay Soil Stabilized with Rice Husk Ash

There is much research on how the addition of rice husk ash (RHA) and lime improves the mechanical behavior of the soil, particularly in clayey soils. RHA is a waste material and polluting for the environment; Therefore, its use can be considered as an economic and ecological alternative. The main objective of this analysis is to determine the influence of rice husk ash (RHA) to stabilize this type of soil. This research is based on the development of an alternative method for the improvement of low plasticity clay soils using an agricultural residue such as rice husk ash and lime for use in civil works. Soil mixtures with rice husk ash were made in different percentages to evaluate its geotechnical behavior as a stabilizer. Laboratory tests like OMC, MDD tend to increase when RHA is added. Shear strength increased as ash was added, where it reached a higher value with the addition of 40% RHA, increasing from 197.70 kPa to 323.00 kPa. Finally, the results obtained show an improvement due to the presence of RHA, however, the investigation is still in process to determine if the addition of higher RHA continues to improve or decrease its shear stress.

Effect of Oil Contamination on the Behavior of Collapsible Soil

Loessial soil is moisture-sensitive soil susceptible to settle when fully saturated. In this study, efforts were made to investigate the effect of oil pollutants on mechanical behavior of soil. The loess soil was contaminated by 2,4,6,8 and 10% dry weight of lamp oil and gasoline. Atterberg limits, direct shear, unconfined compressive strength (UCS) and scanning electron microscope (SEM) tests were performed to evaluate the behavior of oil-contaminated collapsible soils. The results of Atterberg tests showed that the plasticity of the soil decreased, due to the reduction in the thickness of the absorbed surface layer and double water layer. According to the direct shear test, with increasing contamination up to 10% of lamp oil and gasoline, the cohesion of the soil was decreased from 14.5 kPa to 7.3 kPa and 7 kPa, respectively, which was due to the reduction in soil plasticity and diffuse double-layer. Because of the lubrication of soil particles, the internal friction angle of soil was reduced from 18.5° to 13.6° and 13.9° for 10% lamp oil and gasoline. UCS of contaminated soil increased in low strains due to the apparent cohesion of hydrocarbons and it decreased 31% for gasoline and 53% for lamp oil at high strains due to the softening behavior of the contaminated soil. SEM test revealed that hydrocarbons covered the soil particles and changed the soil fabrication to dispersed skeleton. Generally, collapsible soil contaminated with different lamp oil and gasoline contents showed a decrease in shear strength and UCS with increasing oil content.

Role of free iron oxides in the physicochemical and mechanical properties of natural clay

While it is widely acknowledged that interparticle bonding due to free iron oxide (FIO) dramatically affects the behavior of natural clay, the exact role of FIO in determining soil physicochemical and mechanical properties and the underlying mechanism remain unknown. In response, this study removes FIO from natural Zhanjiang clay, a structured marine clay with cementation, to investigate how FIO affects the physicochemical and mechanical behaviors of soil. The immersion method and leaching method (with dithionite-citrate-bicarbonate solution) are used for FIO removal. The test results indicate that the removal of FIO significantly changes the soil physical indices and degrades the mechanical properties. The effects of FIO removal are explained from the perspective of microstructural alterations as revealed by scanning electron microscopy (SEM) observations, mercury intrusion porosimetry (MIP) tests, energy-dispersive X-ray spectroscopy (EDS), and zeta potential measurements. FIO is distributed at the contacts between soil particles and exists in the bridging form. Due to the attraction between the positively-charged FIO and the negatively-charged clay mineral surfaces, soil particles are bounden to form larger soil aggregates with enhanced stability. The removal of FIO leads to the breakdown of soil aggregates and the generation of large pores, thereby increasing soil compressibility and decreasing the shear strength. This study provides some new micro-level understandings of how FIO affects the behavior of natural clay.