Mechanical Behavior Of Soil Research Articles

Prediction of tunnelling-induced effects on a historic building in Rome

Tunnelling in urban environments often poses serious concerns regarding potential detrimental effects induced on the surrounding structures and infrastructures, as in the case of the soon-to-be-built new Flaminio railway station. The station’s project involves the conventional excavation of three adjacent shallow tunnels, whose roofs are located very close to the foundation of a historic building. To minimize the risk of damaging the building, the excavation is preceded by ground improvement works and the installation of a very stiff pre-support system made of concrete-filled steel pipes just above the tunnels’ roofs. This paper presents a Class A prediction of tunnelling-induced effects, obtained developing a three-dimensional numerical model that accounts for the complexities of the problem’s geometry and construction phases. The soil mechanical behaviour is described by an advanced constitutive model (the Hardening Soil model with small strain stiffness). The results provide useful insights about the soil-tunnel-building system’s behaviour. The expected settlements are very little and the potential damages to the building practically negligible. In addition to drastically reducing the risk of local instabilities, the heavy ground improvement works and the installation of the pre-support – whose effects are quantified through comparative analysis – further reduce settlements and distortions induced on the building. Finally, the results are compared with the predictions obtained adopting a simple linear elastic perfectly plastic constitutive model (Mohr-Coulomb model) both using the parameters employed at the design stage, calibrated assuming precautionary medium–high strain levels, and attempting to capture a more realistic level of induced strains. A comprehensive monitoring system will record a significant amount of data concerning the soil-structure interaction, enabling to better understand the behaviour of the system and to test the accuracy of the numerical predictions.

The Duncan-Chang statistical damage correction model of unsaturated soil considering matric suction

In order to reflect the whole deformation process of unsaturated foundation soil, the consolidated drained triaxial compression test is carried out on the unsaturated soil of a foundation project. It is found that the partial stress-strain curve of unsaturated soil is similar to hyperbola, and the matrix suction has an obvious influence on the mechanical behavior of soil. The greater the matrix suction, the higher the partial stress of soil. According to the deformation characteristics and engineering characteristics of unsaturated soil, the Duncan-Chang hyperbolic model is selected as the basic model, and the statistical damage theory is introduced. Assuming that the micro element strength of unsaturated soil obeys the Weibull probability density distribution, the Duncan-Chang statistical damage model is established. By establishing the relationship between the initial tangent modulus and matrix suction, a new Duncan-Chang statistical damage model of the unsaturated soil considering matrix suction is established. The parameter analysis method is given, and the empirical expression of the Weibull distribution parameters is obtained, which is used to modify the model. The damage accumulation law of unsaturated soil under different matrix suction conditions is analyzed, and the partial stress-strain test curve of unsaturated soil is compared with the traditional Duncan-Chang model, which proves the feasibility and rationality of the model. The research results provide a certain reference for the study of mechanical properties and identification simulation of unsaturated soil.

Experimental Investigations on Black Cotton Soil Stabilized with Sand and Cement

Abstract: Has our Lands getting increasing of population and the reduction of available land, more and more construction of building sand other civil engineering structures has to be carried out on weak or soft soil. Owing to such soil of poor shear strength and high swelling & shrinkage, a great diversity of ground improvement techniques such as soil stabilization and reinforcement are employed to improve mechanical behavior ofsoil, thereby enhancing the reliability of construction. Black cotton soil is one of the major soil with this we are going to improve the soil by using sand and cement in deposits of India. The disappointments of asphalt in from of hurl dejection splitting and unevenness are brought about by the occasional dampness variety in subgrade soil. So, in this we using the various type of tests like plastic limit, liquid limit, California bearing ratio test, freewell index and specific gravity.Instead of cutting out and replacing the unstable soil,soil adjustment isthe only alternative asitsaveslot of time and ofmoneytoo.Theexhibithigh swelling and shrinking when exposed to changes in moisture content and hence have been found to be most troublesome from engineering considerations. Keyword: Black cotton soil, stabilization, CBR, sand and cement, sub- grade, Montmorinolite kaolinite, hydrated cations, Liquid Limit, Plastic Limit, Free swell index, Specific gravity.

Characterisation of natural and remoulded Onsøy clay with focus on the influence of mica

Loss of strength caused by the destructuration of sensitive soils has been identified as the trigger of numerous landslides, some of them of devastating proportions. Norwegian sensitive clay deposits are typically found with a mineralogical composition of inert rock flour, including clay-sized chlorite and dioctahedral mica. The present paper presents a cross-scale study conducted on a sensitive clay from Norway with special focus on the role of mica on the material characteristics. Block samples of Onsøy clay obtained from different depths (4–10 m) were characterised and studied in terms of their mechanical properties, fabric and mineralogy. Oedometer compression tests were carried out in a high-pressure oedometer, applying stress up to 25 MPa on samples in an undisturbed and remoulded state. Microstructural investigations were carried out on undisturbed and remoulded samples using cryo-broadionbeam scanning electron microscopy (cryo-BIB-SEM). Mineral composition was analysed using X-ray diffraction on the bulk samples and the fraction ≤2 μm confirming absence of expandable clay minerals (smectites) and kaolinite. Coarse silt sized and irregular shaped particles were dominated by Na-rich and Ca-rich feldspar, quartz, and framboidal pyrite aggregates. A comparison with data sets from several Norwegian sensitive clay deposits showed that the plasticity index of these clays showed a tendency to decrease with an increasing amount of mica when the salinity is lower than 10 g/l. In contrast, for deposits with a salt concentration of more than 10 g/l, a significant increase in the plasticity index was observed with increasing amount of mica. The formation of aggregates was discussed with relation to its impact on the soil mechanical behaviour-

Theoretical analysis of long-term setup of driven piles considering soil anisotropy, destructuration and creep effects

The soil adjacent to the pile suffers a severe destructuration during pile installation and then regains its strength during the setup stage. This paper presents a theoretical approach to evaluate the long-term setup of driven piles in soft sensitive clays. An advanced elastic-viscoplastic model that accounts for fabric anisotropy, particle bonding and viscosity, is used in both stages of pile installation and setup. A semi-analytical solution for the undrained cylindrical and spherical cavity expansion in soft sensitive clays is developed to capture the pile installation effects. The changes in the stress state and fabric anisotropy of the soil adjacent to the pile caused by pore pressure dissipation and sustained service loads are analyzed. The evolution of soil mechanical behavior is incorporated into the load-transfer models of shaft friction and base resistance. Comparisons between measured and predicted results of field tests at three different sites demonstrate the applicability of the proposed approach. The calculated results illustrate that the ultimate bearing capacity increases steadily with time during the long-term setup stage. An extensive study is carried out to evaluate the effects of soil's initial anisotropy and bonding on the load-settlement behavior of driven piles.

Laboratory Test of EPB Shield Tunneling in Mixed-Face Conditions

Field measurements and laboratory tests were carried out to study the mechanical behaviors of soil in response to earth pressure balance (EPB) shield tunneling in mixed-face conditions, i.e., layers of granite and sand. Specifically, an experimental investigation was carried out using a laboratory-scale model to replicate the EPB tunneling operations in such ground conditions. The effects of the ratio of rock/sand at the tunnel face (Tr/Ts) and the cover-to-diameter ratio (C/D) on the soil pressure in the chamber, ground displacement, and volume loss were examined. The results show that the soil's response to the mixed-face conditions differs significantly from that in the homogenous ground and highly depends on the ratio of rock/sand, especially for relatively shallow tunnels. As the ratio of rock/sand at the tunnel face increased, the pressure gradient in the chamber became more inconsistent. The translated cumulative curve does not always provide a good fit in the mixed-face conditions, particularly in cases when the rock/sand ratios are high. A smaller width of settlement trough has been observed for cases with a large rock/sand ratio compared to that in clay and cohesionless soil.

Fracturing behaviors of soil subjected to monotonic and fatigue pneumatic loading

The mechanical behaviors of soil exposed to monotonic and cyclic pneumatic loading are investigated through laboratory testing. The fracture morphology, air pressure, and earth pressure (EP) were monitored and analyzed. In monotonic pneumatic fracturing, pressure of air is the crucial factor that determines the length and number of fractures. In cyclic pneumatic fracturing, the number and propagation of fractures is greater than that under the monotonic loading, as well as the disturbance zone of the pressurized air to the soil. It is found that high-frequency injection maintains higher air pressure inside the soil, coupled with the cyclic loading, the fatigue fracturing effect is much better than that under monotonic loading. The patterns of fractures subjected to monotonic and cyclic loading are presented. It is concluded that the higher the injection frequency and air pressure, the larger the number and propagation range of fractures.

Modelling the mechanical behaviour of soils using machine learning algorithms with explicit formulations

Modelling the mechanical behaviour of soils using machine learning algorithms with explicit formulations

A Procedure to Prepare Sand–Clay Mixture Samples for Soil–Structure Interface Direct Shear Tests

A large number of experimental studies on sand–clay mixtures are well documented in the literature; however, the preparation protocol is rarely clearly detailed or varies a lot according to the authors. Variations in the preparation technique obviously increases the challenge of comparing different test results. As a consequence, sample preparation for sand–clay mixtures should be kept as constant as possible to ensure homogeneity and uniformity of samples and limit result variability. This paper develops a detailed procedure on how to prepare sand–clay samples for interface direct shear tests. Sand–clay mixtures are prepared with Fontainebleau sand, kaolinite clay and distilled water by the S1 (sand–water–clay) protocol. The uniformity of the reconstituted specimens is assessed by measuring the water content and density on three slices from the top to the bottom across the specimens. The repeatability of the samples is checked with oedometer and interface direct shear tests. This sample preparation procedure can be used for preparing sand–clay mixture for interface direct shear tests to investigate the influence of clay content or other effects (e.g., temperature) on the mechanical behavior of soil–structure interface. It has demonstrated great performance in preparing samples with good homogeneity and shape, compared to other traditional reconstitution techniques. With the sample preparation procedure, we can obtain repeatable test results as well.

Bio-cementation improvement via CaCO3 cementation pattern and crystal polymorph: A review

Due to environmental and sustainable concerns, the green bio-cementation technique has received growing attentions from both the academic world and engineering field. One of its essential applications is ground improvement, since the precipitated CaCO3 crystals in bio-cementation process could act as the solid bridges to cement separated particles together and enhance the mechanical behaviors of soils. Although researchers have realized the significance of the precipitated CaCO3 bondings and microstructures of bio-cemented materials, only few studies focus on improving the bio-cementation efficiency from a microscopic perspective. Consequently, in this paper, an integrative review is adopted to collect, review, and analyze the published studies and literature, indicating that the CaCO3 cementation pattern and crystal polymorph are the two principal aspects that reflect the bio-cementation efficiency to a certain extent. Subsequently, the major factors affecting the CaCO3 cementation pattern and crystal polymorph are comprehensively discussed. In a nutshell, the conducted discussions in this paper attempt to provide noteworthy insights into bio-cementation improvement, which may potentially inspire future studies.

A modified subloading Cam-clay model for granular soils subjected to suffusion

ABSTRACT Suffusion, one of the modes of internal erosion, occurs when fine particles are detached under hydraulic force. More fine particles are washed out with the void growth, which subsequently causes the failure of earthworks. At present, constitutive models considering suffusion are mostly established through DEM simulations and constitutive models that can capture the main features of eroded soils are quite limited. This study aims to establish constitutive equations to model the mechanical behaviour of soils subjected to suffusion by using drained triaxial experimental data. The modified subloading Cam-clay model incorporated with the normal yield surface for the eroded soil is proposed, which can express the variation of the normal yield surface with the loss of fine particles. The determination method of the erosion-related model parameters is also proposed. The erosion-related model parameters are estimated through empirical equations with curve-fitted parameters. Finally, the capability of this modified model is demonstrated through the comparisons with experimental results.

A permanent deformation predictive model for fine tropical soils considering the effects of the compaction moisture content on material selection

The evaluation of the mechanical behavior of soils should be considered as an important step for material selection and pavement design. The analyses of the elastic and plastic behaviors of the pavement unbound materials have generally been based on resilient modulus (RM) and permanent deformation (PD) tests, respectively. Such mechanical characteristics are significantly affected by factors including gradation, traffic speed, loading history, and moisture content. However, special attention should be given to the moisture content, given that the use of inadequate water content during compaction can lead to premature failure of the pavement system. This paper investigates the effects of the compaction moisture content on the plastic behavior of fine soils by means of PD. Based on the analysis of two existing models that take this key factor into account, a predictive model tailored for fine tropical soils is proposed. Four soils of different classifications were tested with three distinct compaction moisture contents (below the optimum, at the optimum moisture, and above the optimum moisture contents) to analyze interaction effects for a PD predictive model. Two additional fine soils are used to validate the model. A statistical analysis considering the six fine soils indicates that the proposed PD model can efficiently predict the effects of the compaction moisture content on the long-term resistance to PD of the fine soils and that the suggested procedure can be potentially used as a tool for material selection.

Land-use change and its impact on physical and mechanical properties of Archaeological Black Earth in the Amazon rainforest

The intense pressure of anthropic actions to change the use and management can promote the degradation of anthropogenic soils with high natural fertility and high content of organic matter such as the Archaeological Black Earths of the Brazilian Amazon. Therefore, this study aimed to quantify the impact of land use and occupation in the Amazon biome on the physical and mechanical properties of Archaeological Black Earth. The research was carried out in the municipality of Novo Aripuanã, in the south of Amazonas State (Brazil), in a Chromic, Pretic, Acrisol with native forest, pasture, and pigeon pea. The soil properties of bulk density, mean weighted diameter, soil resistance to penetration, macroporosity, microporosity, particle size distribution (sand, silt, and clay), water-dispersible clay, flocculation index, total organic carbon, and preconsolidation pressure were assessed in the 0.0–0.1 and 0.1–0.2 m soil layers. Archaeological black earth under native forest showed better soil structural properties such as greater macroporosity and lower bulk density and resistance to penetration. The conversion to other uses promotes soil compaction and increases the resistance to compression. However, the greatest negative impacts on soil properties occurred when the land-use change was for pasture than for pigeon pea. The pigeon pea crop promoted the increase of soil total organic carbon in the 0.0–0.1 m layer. The soil mechanical behavior showed a greater load-bearing capacity in the native forest area for the surface layer than the subsurface layer. The preconsolidation pressure allowed to determine that the pasture land-use has a greater occurrence of compaction and might suffer additional compaction if the applied pressures on the soil during grazing are larger than the higher limit of the confidence interval of load-bearing capacity models when compared to the pigeon pea land-use.

Effects of salinity and sodicity of water on friability of two texturally-different soils at different matric potentials

Soil salinisation and sodification are two principal processes in arid and semi-arid regions which have been irrigated with poor-quality waters. A laboratory experiment was carried out to study the effect of soil texture, salinity (EC) and sodicity (SAR) of irrigation water and matric potential on soil friability. Intact soil aggregates/clods with different size ranges of 4–8, 8–15, 15–20, and 20–40 mm were collected from two texturally-different soils of sandy loam (SL) and clay loam (CL). Undisturbed soil samples were also taken for determination of soil water contents at matric potentials (h) of –30, –100, –200, and −400 kPa. All of the soil samples were subjected to five wetting/drying cycles using twelve different water quality treatments, combinations of four levels of EC (0.2, 1, 6, and 10 dS m−1) and three levels of SAR [1, 5 and 12 (meq L−1)1/2]. The tensile strength of aggregates/clods was determined by the indirect Brazilian test. Then, the soil friability was calculated by employing three methods of coefficient of variation (F1), ranking order (F2), and volume-dependence (F3). The results showed that the F values varied considerably depending on the friability calculation method and matric potential. Soil friability was not affected by the treatments at the wet range because of the dominant effect of high water content on soil mechanical behavior; whereas soil aggregates/clods of 4–8, 8–15 and 15–20 mm at h of −400 kPa showed the highest friability. Soil friability decreased with an increase in SAR and increased with an increment in EC at low matric potentials (i.e., –200 and −400 kPa) due to the negative and positive effects of sodium and soluble ions on soil microstructure, respectively. The effects of SAR on soil stability, dispersion clay and tensile strength and as a consequence on soil friability was more pronounced at low EC values. Results showed more influence of water quality (EC and SAR) in clay loam than sandy loam soil due to its higher clay content. Comparison of the F values with well-known classification revealed that F1 and F2 were about 2–4 orders of magnitude higher than F3, especially for aggregates size ranges of 4–8 and 8–15 mm at h of –200 and −400 kPa and air-dry condition; and the coefficient of variation and ranking order methods were more acceptable and reliable than the volume-dependence method for characterizing the soil friability.

Numerical investigation into the dynamic behavior of sands

The aim of this paper is to provide further understanding of the mechanical behavior of soils when subjected to high-pressure and high-rate loadings. To this end, finite-element (FE) analyses of dynamic compaction and penetration events were conducted using the advanced elastic/plastic soil model of Lade (1977) which was extrapolated to large pressures and implemented into the FE framework. To ensure improved accuracy of the results for conditions involving loading/unloading and stress path changes, an implicit integration scheme was adopted. The simulation results for dynamic densification show that the initial precompaction of the material has a strong influence on both the wave speed and the shape of the wave front. As concerns the initiation of penetration, the simulation results indicate that for the same material, the inception and nature of the localization bands are also strongly dependent on the level of precompaction of the target material. Namely, for a low precompaction level, upon impact multiple bands develop whereas for a larger initial precompaction level, a primary localization band develops.

Biochar Amendment Effects on Microstructure Resistance of a Sandy Loam Soil Under Oscillatory Stress

Current research on the impacts of biochar (BC), an organic compound used as soil amendment, focuses on soil physical and chemical properties, such as nutrient or water retention, while little attention is paid to the effects on soil mechanical behavior, especially on the microscale. Our objective was to investigate how BC amendment impacts the microscale mechanical behavior of a weathered soil under oscillatory stresses. Substrates were prepared by mixing soil with two BC types obtained from rice and soybean straw (application rate: 10 t ha−1) and incubating the mixture. Disturbed soil samples were collected 15, 30, 45, and 60 days after mixing to conduct rheological tests to characterize the soil microstructural stability and shear behavior. Along the incubation (except for at 45 days), the BC amendment decreased the soil shear strength in the order of treatments: rice BC-amended soil = soybean BC-amended soil > unamended soil (control). A possible cause, the lubricating impact of increased water retention and low aggregation potential of BC, is discussed. The soil viscoelasticity was not affected by biochar application. Already shear stresses of moderate intensity caused structural breakdown of the BC-amended soil, making it more susceptible to deformation and erosion processes.

Validation of a thermo-hydro-mechanical model of freezing of water-saturated soil based on laboratory tests results

Frost heave of freezing water-saturated soils is an important worldwide problem from an engineering point of view. In cold regions, this phenomenon significantly affects foundations of buildings and road pavements. Application of artificial ground freezing to underground construction due to frost heave can cause an undesirable uplift of the ground surface and an increase in pressure acting on a lining and frozen wall. In the present paper, a mathematical model of soil freezing enabling one to predict soil deformation due to phase transformation of pore water into ice is proposed. The model is based on a set of nonlinear equations of water transfer, heat transfer, and equilibrium which are solved relative to porosity, temperature, and displacement variables. Constitutive relations of the poromechanics theory along with Bishop-type effective stress are used to simulate the mechanical behavior of soil during the process of pore water freezing and to evaluate pore pressure depending on a changein porosity and volumetric strain. Moreover, equations of the associated flow rule of plasticity are incorporated into the model to describe an inelastic volumetric expansion of the freezing soil induced by pore ice pressure. The ability of the model to capture essential features of the freezing process of water-saturated soils is demonstrated by numerical simulation of two laboratory tests. For the first test, a comparison between results of the numerical simulation and experimental measurements of variations of temperature and uplift of the top surface of silty clay specimens with time has been conducted. It has been shown that the numerical results are highly consistent with the measurements when the soil specimen is frozen with the growth of a massive cryogenic structure. In the numerical simulation of the second test, the calculated radial deformation of freezing soil is in good agreement with the experimental measurements, obtained by a fiber-optical sensor during the radial freezing of the quartz sand sample in a closed system.

Numerical investigation on the mechanical behaviour of karst sinkholes

The mechanical behaviour of soils overlying weathered bedrock is often a concern when it comes to the risk of sinkhole occurrence. Cavities often form near the interface between cover soil and fissured bedrock and propagate upwards with internal soil erosion, ultimately resulting in surface collapse known as sinkhole. This paper presents and discusses the mechanical behaviour of sinkholes by investigating the stability associated with the size and depth of the cavity. The two failure modes considered in this study correspond to tensile failure and excessive yielding around a subsurface cavity. Numerical modelling with the finite-difference software Flac was employed to determine the stress distributions and deformations around the cavity. The results of numerical analyses were used to quantify the effects of factors affecting sinkholes such as bedrock depth, cavity size, overburden thickness and soil strength. The results also illustrate the yielding behaviour, which is related to a cover-subsidence sinkhole with a gradual depression over time but no structural collapse. The analysis result shows that the critical overburden thickness of around 25 m turns the yielding condition from unstable to stable.

Investigating the effect of inoculation of chickpea with rhizobium and mycorrhizal fungi (Funneliformis mosseae) on soil mechanical and physical behavior

Symbiosis with plants by mycorrhiza and rhizobium (bio-fertilizers) is effective in improving soil structure and increasing the stability of aggregates against compression. In addition to soil deformation, soil structural properties should be included for the assessment of compaction. The purpose of this study was to investigate the effect of application of rhizobium and mycorrhizae on plant yield, some soil physical properties, and the confined compression curve and its characteristics, which have not been reported in any research so far. Experiments were conducted in a completely randomized design with three replications in the field and glasshouse. Mycorrhizal fungi (Funneliformis mosseae), rhizobium (Mesorhizobium), mycorrhiza - rhizobium and control (no inoculation) were the treatments of the field experiment. Sterilized mycorrhiza background material and non-plant-non-inoculation were the two additional treatments of the glasshouse experiment. The plant cultivated in this experiment was chickpea. Mycorrhizal and rhizobium treatments increased the stability of aggregates compared to non-plant-non-inoculation treatment. Mycorrhiza and rhizobium increased the macroporosity and near-saturation water content. The smallest total yield was found in the sterilized mycorrhiza background material and control treatments. Mycorrhiza and rhizobium increased the void ratio at different compression stresses by 9–16% and 19–25%, respectively, compared to non-inoculation treatments under the glasshouse experiment. Pre-compression stress was increased by 84.3% in the control treatment with plant compared to the mycorrhiza treatment in the glasshouse experiment, but did not change significantly in the field experiment. Symbiosis of mycorrhiza and rhizobium as a sustainable biological method improved the physical and mechanical properties of the soil by affecting plant yield and root exudates.

DeltaSand: A state dependent double hardening elasto-plastic model for sand: Formulation and validation

Numerical simulations of pile installation in sands require advanced constitutive models which are able to predict the mechanical behaviour of soils in a wide range of soil stresses under different loading conditions such as cyclic and monotonic loadings. In this paper, an elasto-plastic constitutive model within a double hardening framework is described which is capable of reproducing the mechanical behaviour of sands in different soil states (stress and relative density) under deviatoric and volumetric loadings. First, the formulation of the model is described and then the capability of the model is shown by simulating laboratory tests data of Karlsruhe sand for various relative densities, stress states and loading conditions.