Soil nailing is one of the slope stabilisation techniques useful for the strengthening of existing slopes. It helps to reinforce the soil with passive inclusions that increase the overall shear ...strength of the soil slope and also restrains its displacements. The limit equilibrium method is usually employed to estimate factor of safety (FOS) of nailed slopes through either finite element or finite difference methods. Alternatively, soft computing methods such as multi-gene genetic programming (MGGP), support vector regression (SVR) and artificial neural network (ANN) can also be used to predict the FOS for different soil properties. Among these methods, MGGP possesses the ability to evolve the model structure and its coefficients automatically. Although widely used, the MGGP method has the limitation of producing models that perform poorly on testing data. Therefore, in this study, an integrated structural risk minimisation-multi-gene genetic programming (SRM-MGGP) method is proposed to formulate the mathematical relationship between FOS and the six input variables of cohesion, frictional angle, nail inclination angle, nail length, slope height and slope angle of 3-D nailed slope. The results indicate that the SRM-MGGP model outperforms the other three models (MGGP, SVR and ANN) and is able to generalise the FOS satisfactorily for any given input variables conditions. This would be useful for engineers in their design calculations of slopes with different soil, slope and nail conditions based on certain limitations such as ignorance of effect of pore water pressure or overburden pressure.
•An integrated SRM-MGGP method for FOS prediction of nailed slope is proposed.•Proposed SRM-MGGP is compared to those of MGGP, SVR and ANN.•Out of four methods, SRM-MGGP evolves a model with better generalisation ability.•SRM-MGGP method also represents explicit formulation of FOS of nailed slope.
With growing importance of green infrastructure, sustainable natural fibers such as coir and jute are extensively used for shallow depth embankment reinforcement. The motivation of the study is to ...investigate the reinforcing potential of an invasive weed species (water hyacinth) for subgrade reinforcement and juxtapose its reinforcing efficacy with that of the conventionally used coir and jute fibers. For such a comparison, a series of unconfined compression strength (UCS) tests was conducted on clayey silt reinforced with randomly distributed fibers extracted from the selected species. The results were used to study the influence of different fiber percentages, soil-fiber composite density and moisture content on the strength improvement factor (SIF) of the soil-fiber composite. Further, the test results were used to study the soil-fiber composite ductility using all three fibers. To explain the soil-fiber composite ductility, two new physical parameters has been identified. Among the three fibers tested, jute showcased the highest strength in majority of the tested conditions. However, coir and WH fibers are equally competent for increasing SIF at least by 50%. Among the tested soil-fiber composite, coir reinforced soil showcased highest ductility at the tested conditions, which is attributed to its high elongation at break. The post peak ductility of soil-fiber composite is dependent mainly on the fiber percentage and the compaction state. This is mainly governed by the development of fiber bridges in the shear band and also due to “lubrication” effect.
The concept of sponge city has become very popular with major thrust on design of waste containment systems such as biofilter and green roofs. Factors that may influence pollutant ions retention in ...these systems will be soil type and also their interactions. The study investigated single and competitive interaction of copper in two soils and its influence on the fate prediction. Freundlich and Langmuir nonlinear isotherms were selected to quantify the retention results. Series of numerical simulations were conducted to model 1 D advection-dispersion transport for the two soils and analyse the role of isotherms. The results indicated that contaminant fate prediction of copper-soil interaction based on the two non-linear isotherms was different for both single and that in competition. Retardation factor obtained from Freundlich (RF) isotherm predicts more than Langmuir (RLa). This observation is more explicit at the higher range of equilibrium concentration. Fate prediction based on retardation value obtained from retention isotherms exhibited some anomalous trends contradicting the experimental findings due to inherent assumptions in governing equations. The necessity to have an approximate assessment of contaminant concentration in the field to effectively use contaminant retention results for accurate fate prediction is highlighted here. The study is important for modellers in design or analysis of biolfilter system (sponge city), where multiple ions tend to exist in waste water.
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•Single and competitive interaction of copper in two soils•Contaminant fate prediction of copper-soil interaction varies with competition.•Retardation factors different for Freundlich (RF) isotherm and Langmuir (RLa)•Fate prediction theorms do not consider multiple contaminant interaction
The knowledge of unsaturated soil is indispensable for several hydrological and geoenvironmental problems such as permeation of water through vadoze zone, ground water recharge, and deciding ...irrigation requirements for crops. The accuracy of these studies depends on the precise characterization of unsaturated soil, which includes the development of the soil suction–water content relationship (SWR) or soil–water characteristic curve (SWCC). It is believed that each soil has a unique SWCC. However, past studies clearly indicate that there are different parameters that would influence the uniqueness of the SWCC. Therefore, the present study purports to critically review the findings reported in the literature to reveal the influence of different parameters on the SWCC. The review is divided into two sections. The first section deals with those parameters that need a critical assessment, and the second section deals with apparent factors that influence the SWCC. The critical evaluation brings out the anomalies associated with the influence of some of the parameters, such as compaction state, measurement procedures, stress history, and range of suction measurement on the SWCC. Compaction water content has a more significant influence on the SWCC than density. The SWCC is found to be unique at a high range of soil suction for which adsorptive forces are predominant. It was found that the extent of influence of parameters on the SWCC is soil specific. However, further experimental investigations are required to quantify soil-specific parametric influence on the SWCC.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Purpose The purpose of this paper is to numerically investigate the combined effects of canopy (leaf area index LAI) and root properties (root distribution function Rdf and root area index RAI) on a ...suction induced in soil-root composite under three different scenarios. Design/methodology/approach Richards equation coupled with sink term was solved using a commercial finite element package “HYDRUS” to investigate suction induced in soil-root composite. Findings Scenario 1 unveiled that soil-root composite induces 1 to 20 per cent higher suction than bare soil under the absence of transpiration. From Scenario 2, value of suction at depth of maximum RAI in case of linearly decreasing Rdf was found to be higher than that of other Rdfs. However, depth of suction influence zone (SIZ) for uniform Rdf and non-linear Rdf was found to be 10 and 11 per cent higher than that of linearly decreasing Rdf. Depth of evaporation dominant zone (EDZ) for uniformly decreasing Rdf and non-linear Rdf was found to be 1.08 to 3 times higher than that of linearly decreasing Rdf. From Scenario 3, influence of LAI on depth of SIZ is minimal. Depth of EDZ was found to decrease with the increase in LAI. Based on simple calculation on infinite slope stability, influence of variation in root and shoot properties was found to be significant on its factor of safety. Research limitations/implications Numerical constitutive model has limitations that it does not consider aging of plant. This model is only applicable for a particular set of soil conditions. A long-term study is required in this field to further quantify parameters for improving calibration and modeling performance. Practical implications Following are the practical implication: consideration of vegetation properties into engineered design of green infrastructure (slopes in this case) and selection of vegetation with appropriate characteristics in design for enhancement of stability of green infrastructure. Originality/value Contents of this paper are original, and they have not been submitted to any other journal.
This study investigates and compares mechanical factor (a dimensionless parameter and defined as the ratio of the compressive strength of fiber reinforced soil to that of unreinforced soil) for soils ...reinforced with four different fibers (three natural fibers and one synthetic fiber). An integrated methodology was utilized, including 351 laboratory experiments for obtaining data and Extreme Learning Machine (ELM) technique for developing functional relationships between mechanical factor and soil and fiber parameters. Soils reinforced with synthetic fiber (Polypropylene) and with natural fibers exhibited different characteristics when subjected to the same variation in soil parameters. This phenomenon can be attributed to the differences in surface morphology and water absorption capability of Polypropylene comparative to other natural fibers. Polypropylene-soil composite shows the maximum sensitivity to the soil moisture. It also shows the least sensitivity toward soil density and fiber content among all tested fiber-soil composites.
•Explores the utility of a harmful weed, water hyacinth (WH) for soil reinforcement.•Effect of density is significant in case of lower moisture content soil–fiber composite.•WH fiber modified the ...brittle behavior of soil to ductile behavior of soil–fiber composite.•WH fiber content of 0.5–0.75% is found to mobilize maximum compressive strength.
Growing awareness of sustainability in construction has increased attention toward increase in use of natural fibers for soil reinforcement applications. Researchers have explored the utility of natural limited life fibers such as jute, reed and sisal for soil reinforcement. In this study, an attempt was made to demonstrate the use of local weed named water hyacinth (Eicchornia crassipes) as soil reinforcement. A series of unconfined compression strength (UCS) tests was conducted on silty sand reinforced with randomly distributed fiber. These series of tests aim to study influence of different fiber content, soil density and moisture content. The stress–strain response of fiber reinforced soil shows the increase in post peak strength and ductility. This was mainly attributed due to presence of cellulose content. The effect of soil density on increased strength due to inclusion of fiber is significant in case of lower moisture content.
Natural or lignocellulose fibres have been widely used for reinforcing soils in geotechnical infrastructures by using their mechanical reinforcement. However, less attention has been taken to the ...hydraulic properties of soil-lignocellulose fibre composites, namely Soil Water Retention Curve (SWRC) and soil water permeability. These hydraulic properties are the key parameters when conducting transient seepage analysis in reinforced slope stability calculation. Till now, there is no model yet that can capture SWRC and water permeability of soil-lignocellulose fibre composite. This technical note aims to develop a new and simple model for predicting the SWRC and water permeability of soils mixed with lignocellulose fibres. The model considers the void ratio change by incorporating the air void from fibres. The void ratio function is then fed into a void-ratio-dependent SWRC model. SWRCs and water permeability of soils mixed with two lignocellulose fibres (jute and coir) were measured systematically to provide high quality data to validate the proposed model. There were three replicates for each case. It shows that the presence of pore structures in natural fibres reduced air entry value of soils from 8 kPa to 2–3 kPa, while it had no effects on desorption rates. Moreover, those pores in lignocellulose fibres increased the water flow path, resulting in increased water permeability. As demonstrated by dye tracer experiments, the increased water flow was along the cellulose, hemicellulose fibrils inside the fibre and soil-fibre interface. The comparisons between experimental measurements and model predictions indicate that the proposed simple model can capture the effects of natural fibres on soil hydraulic properties quite well, with the maximum discrepancy less than 15% and 28% for SWRC and water permeability, respectively.
The application of biochar in agricultural practices and vegetative slopes has been rigorously recommended in previous literature. However, its potential application in other industries is scarcely ...explored. Biochar is a chemically stable material with a low thermal conductivity, which makes it a perfect fit for blending with soil to use as thermal backfills. A thermal backfill is an essential component for maintaining the ambient temperature around the underground pipelines and storage tanks of crude oil industries. This study investigates the potential application of eighteen soil-biochar blends as thermal backfill. Highly plastic silt and clayey sand (SC) soil were amended with three different biochar types viz. hardwood biochar, water hyacinth biochar, and sugarcane bagasse biochar (SBBC), at three biochar contents of 2.5%, 5%, 7.5% (w/w). Thereafter, their compaction characteristics, thermal and physicochemical properties were investigated. The thermal conductivity (
K
) and volumetric heat capacity (
C
) of MH soil were reduced by 22%, 29%, 33%, and 16%, 24%, 26% with 7.5% amendment of hardwood, water hyacinth, and SBBC. Similarly,
K
and
C
values of SC soil decreased by 22%, 34%, 37%, and l2%, 18%, and 20%. The micrographic analysis of soil-biochar blend reveals that the entrapped air in biochar particles governs the heat transfer in biochar-amended soil. An inverse correlation of thermal conductivity with pH and electrical conductivity was also observed for the soil-biochar mixes. This study extends the domain of biochar application highlighting the engineering properties of different blends, which would be helpful for its field-scale application.
Graphical Abstract
•Evolutionary GP (MGGP) method is proposed for factor of safety prediction.•The performance of MGGP is compared to those of SVR and ANN.•Out of three methods, MGGP evolves a model with better ...generalization ability.•MGGP is able to predict FOS at different root depth, root ratio and slope angle.
Use of roots as one of slope stabilization technique via mechanical reinforcement has received considerable attention in the past few decades. Several mathematical models have been developed to estimate the additional cohesion due to roots, which is useful for the calculation of factor of safety (FOS) of the rooted slopes using finite element method (FEM) or finite difference method. It is well understood from the literature that the root properties such as root area ratio (RAR) and root depth affects the mobilized tensile stress per unit area of soil consequently affecting the FOS of the rooted slope. In addition, a fracture phenomenon also influences the FOS of the rooted slope and should also be considered. In the present work, a new evolutionary approach, namely, multi-gene genetic programming (MGGP) is presented, and, applied to formulate the mathematical relationship between FOS and input variables such as slope angles, root depth and RAR of the rooted slope. The performance of MGGP is compared to those of artificial neural network and support vector regression. Based on the evaluation of the performance of the models, the proposed MGGP model outperformed the two other models and is proved able to capture the characteristics of the FEM model by unveiling important parameters and hidden non-linear relationships.
