Soil Modulus Research Articles

Evaluation of the Curing Time Effect on the Swelling, Unconfined Strength and Resilient Modulus of an Expansive Soil Improved with Hydrated Lime

Soils with high plasticity and high swell potential undergo great volume changes in the presence of unstable water content changes. The resulting expansion leads to damage to pavements and/or lightweight structures with such a subsoil. Expansive soils can be improved by adding chemical stabilizers such as lime, fly ash and micro cement. To construct a highway on an expansive subgrade soil, the subgrade should be stabilized to satisfy the minimum requirements of the highway standards. In this research, expansive clay samples were collected from clay deposits in the Akyurt district of Ankara (Turkey), near Esenboğa Airport. The swelling, strength and resilient modulus properties of the soil samples were determined via laboratory tests. First, reference tests were carried out on natural soil samples. Then, the clay samples were mixed with lime agent at different percentages (1%, 3%, 5%, 7% and 9%) according to the dry weight of the soil. The index, swelling, strength and resilient modulus (Mr) properties of these samples were determined. The soil samples were tested at 7, 28, 56 and 90-day curing times for each percentage of lime agent considered. The changes in the abovementioned properties, especially with regard to the effect of curing time on improvement, were interpreted in this research. Designing for a 7% lime content and a 28-day curing time can be a sound solution for addressing the expansive clay studied in this research, since the criteria of the Turkish Highway Standards are satisfied under these conditions.

Effect of Pile Driving on Ground Vibration in Clay Soil: Numerical and Experimental Study

In this study, peak particle velocity (PPV) values for driving three piles with diameters of 40 cm, 50 cm, and 70 cm in a clayey soil through the impact piling method are investigated by an experimental study and a numerical simulation. An experimental study is carried out on a scale of 1:20 of the operation. Numerical simulation is performed by using an axisymmetric model in PLAXIS 2D finite element software. Properties of the soil and the piles used in the experimental study are obtained from geotechnical tests and employed in the numerical simulation. The model has been verified by comparing the acquired PPV values with those measured in the experimental study. The results show a good agreement between the computed values and the experimental data. Moreover, measured peak particle velocities in the experimental study indicate that an increase in the diameter of the pile can increase the level of ground vibration. Some sensitivity analyses have been performed by numerical modeling to determine the effect of soil and pile properties on the changes of PPV. Also, increase in friction angle of the soil and pile diameter and reduction in elastic modulus of soil will increase the level of ground vibration. The results indicate that the amount of PPV at a distance of 100 cm is about 10.33% of the amount of PPV at a distance of 25 cm from the impact site to the pile with a diameter of 3.5 cm. In addition, this amount of reduction for pile with a diameter of 2.5 and 2 cm is equal to 8.31% and 12.77%, respectively.

Global sensitivity analysis of the deformation behavior of sluice chamber structure

The engineering of sluice has many functions, such as flood control, irrigation, navigation, and power generation. The safety of sluice structure is the premise of its functions and benefits. Moreover, the deformation behavior of the sluice chamber is closely related to the safe operation of the sluice. Firstly, existing literature on sluice research using FEM is investigated and analyzed to determine the calculation model and influencing factors. Secondly, the global sensitivity analysis method of the sluice chamber is constructed based on the Sobol sequence random sampling method and the global sensitivity analysis method based on variance. Finally, according to the distribution rule of the first-order and total-order sensitivity coefficients in the sluice chamber, the typical locations are determined, and the linear and nonlinear relations between the main influencing factors and the deformation indexes of each location are analyzed. An example shows that the deformation of the sluice chamber is mainly settlement, and the major factor is the deformation modulus of foundation soil. Each index model of sluice deformation can be considered as additive. The research results have significant reference value for clarifying the influence mechanism of the sluice chamber deformation behavior and improving the design, operation management, and safety evaluation of sluice structure.

Investigation of Dynamic Factor, Rail Stress and Track Foundation Modulus of Ballasted Railway Track for Different Bed Conditions Using Numerical Methods

The track stiffness is the primary function of roadbeds thickness and subgrade characteristics. For this purpose, numerical scale track finite element technique representing the ballasted track with multi layered substructure founded on subgrade was simulated. The track deflection, stress was abstracted in static and dynamic conditions. The track significant design parameters: Foundation modulus, rail fatigue strength, rail bending stress and stress on subgrade levels were evaluated by using improved current track design numerical methods and compared against field test results which were carried out on part of MG Double track high speed main line (1600 km). Mathematical equations were developed to correlate the variables; ballast thickness, settlement, track stiffness, rail bending stress and rail fatigue strength on varying subgrade soil modulus. Incorporation of this parametric study will improve and optimise the conventional track design and maintenance standard. A simple improved track design was introduced by using single track stiffness parameter from conventional plate bearing test (PBT) on Force Displacement (FD) conventional curve method. The improved method with deriving equivalent track stiffness from rail pad and track substructure tested C value are accurate and simple. The current test method to determine the track stiffness in live track condition is expensive and unsafe with operational requirements. This PBT is simple, cost saving on labour, safe and without applying live train load.

Analytical modeling for the calculation of underground train-induced vibrations in inhomogeneous soils with uncertainty

In this paper, an analytical wave function method was used to calculate the underground train-induced vibrations with the inhomogeneous soils taken into account. The wave function method is suitable for solving dynamic problems of multi-layered soils; therefore, inhomogeneous soils with uncertainty could be achieved by assigning different soil parameters to each soil layer. Based on the method, a half-space dynamic model with a viscoelastic cylinder tunnel was established. The dynamic shear modulus of the soil was the main uncertain variable in this study, and models with different load frequencies are compared to analyze the effect caused by the uncertainty. According to the numerical results, the relationship between the uncertainty of the soil modulus and the dynamic response of the model was given. When the dynamic shear modulus changes randomly with the range of 20%, the vertical displacement of the surface can be from 1.02 to 1.12 times to that in the model where the soil is homogeneous, while the displacement of the tunnel vault is 1.03–1.1 times.

Resilient Response of Cement-Treated Coarse Post-Glacial Soil to Cyclic Load.

Stabilisation with cement is an effective way to increase the stiffness of base and subbase layers and to improve the rutting of subgrade. The aim of the study is to investigate the effect of different percentages of cement additives (1.5%, 3.0%, 4.5% and 6.0%) on the resilient modulus of coarse-grained soil used on road foundations. The influence of the compaction method, the standard Proctor and the modified Proctor, as well as the sample curing time is analysed. The cement addition significantly increases the resilient modulus and reduces the resilient axial strain. Extending the curing time from 7 to 28 days also improves the resilient modulus. The change in the compaction energy from standard to modified does not increase the resilient modulus of the stabilised gravelly sand due to its compaction characteristics. The test results of the resilient modulus of the gravelly sand stabilised with cement indicate the possibility of using it as a material for the road base and subbase due to meeting the AASHTO requirements. However, the non-stabilised gravelly sand does not meet the above requirements. It has been sheared during cyclic tests at the first load sequence, regardless of the compaction method.

Characterization of Properties of Soil–Rock Mixture Prepared by the Laboratory Vibration Compaction Method

This paper presents a study of the properties of soil–rock mixtures (SRM) prepared by the vibration compaction method. First, the results of laboratory experiments and field tests are compared to determine the reasonable parameters of the vibration compaction method (VCM) for soil–rock mixtures. The compaction characteristics, CBR, and resilient modulus of the laboratory-prepared soil–rock mixtures by the static pressure compaction method (SPCM) and vibration compaction method are compared. The effects of the soil to rock ratio and the maximum particle size and gradation on the compaction characteristic, resilient modulus and CBR of soil–rock mixtures prepared by the vibration compaction method are investigated. Finally, field measurements are subsequently conducted to validate the laboratory investigations. The results show that the reasonable vibration frequency, exciting force, and static surface pressure of the vibration compactor for soil–rock mixtures are recommended as 25 Hz, 5.3 kN, and 154.0~163.2 kPa, respectively. Soil–rock mixtures prepared by vibration compaction method has smaller optimum water content and gradation variation and larger density than specimens prepared by the static pressure compaction method, and the CBR and resilient modulus are 1.46 ± 0.02 and 1.16 ± 0.03 times those of specimens prepared by the static pressure compaction method, respectively. The ratio of soil to rock, followed by the maximum particle size, lead obvious influences on the properties of soil–rock mixtures. Moreover, the results show that the CBR and resilient modulus of soil–rock mixtures prepared by vibration compaction method have a correlation of 86.9% and 89.1% with the field tests, respectively, which is higher than the static pressure compaction method.

Artificial neural network prediction model for in situ resilient modulus of subgrade soils for pavement design applications

Artificial neural network prediction model for in situ resilient modulus of subgrade soils for pavement design applications

A Machine-Learning Approach for Extracting Modulus of Compacted Unbound Aggregate Base and Subgrade Materials Using Intelligent Compaction Technology

This study presents a rigorous approach for the extraction of the modulus of soil and unbound aggregate base materials for quality management using intelligent compaction (IC) technology. The proposed approach makes use of machine-learning methods in tandem with IC technology and modulus-based spot testing as a local calibration process to estimate the mechanical properties of compacted geomaterials. A calibrated three-dimensional finite element (FE) model that simulates the proof-mapping process of compacted geomaterials was used to develop a comprehensive database of responses of a wide range of single and two-layered geosystems. The database was then used to develop different inverse solvers using artificial neural networks for the estimation of the modulus from the characteristics of the roller and information about the geomaterials. Several instrumented test sites were used for the evaluation and validation of the inverse solvers. The proposed approach was found promising for the extraction of the modulus of compacted geomaterials using IC. The accuracy of the inverse solvers is enhanced if a local calibration process is incorporated as part of a quality management program that includes the use of in situ measurements using modulus-based test devices and laboratory resilient modulus testing. Moreover, compaction uniformity plays a key role in the retrieval of the modulus of geomaterials with certainty. The proposed approach fuses artificial intelligence with mechanistic solutions to position IC as a technology that is well suited for the quality management of compacted materials.

Influence of Foundation Rigidity on the Structural Response of Mat Foundation

A mat is a type of shallow foundation that is appropriate for structures supported on soil having relatively low bearing capacity or excessive settlement. Structural analysis of a mat foundation can be accomplished by either assuming the mat to be perfectly rigid or by considering the soil-structure interaction. This study researches the relationship between the mat-soil rigidity and structural response in terms of the soil bearing pressure, bending moment, and shear within the mat. To accomplish the objective of the study, 70 different mats are analyzed using a linearly elastic finite element approach. The variables that are considered in the analysis are the number of bays in each direction, center-to-center column spacing, mat thickness, panel aspect ratio, column cross section dimensions, soil modulus of subgrade reaction, and modulus of elasticity of concrete. A dimensionless mat rigidity measure was developed that determines whether a given mat can be reasonably analyzed by assuming it to be infinitely rigid. The developed rigidity factor takes into consideration all parameters that significantly affect the mat structural response. Results of the analysis indicate that there is strong correlation between the developed rigidity factor and critical soil bearing pressure and maximum internal bending moment within the mat. No correlation was observed between the mat rigidity and critical shear force. Relationships between the rigidity factor and the critical soil bearing pressures and bending moments, relative to the response of the infinitely rigid mat, are proposed. A parametric study is included to demonstrate the impact of the variables that affect the rigidity index on the response of the mat.

Slope stability analysis and protection of deep accumulation excavation foundation pit in the Sichuan Bank of the Kahalo Jinsha River Bridge

The Kahalo Jinsha River Super Large Bridge of the Sichuan Riverside Expressway spans the deep canyon of the Jinsha River and is situated in a high-intensity, complex, and dangerous mountainous area. Long-term deformation and stability of the gravity anchor slope are the main controlling factors affecting bridge safety. The maximum slope height formed by the excavation of the gravity anchor foundation pit on the Sichuan Bank of the Kahalo Jinsha River Bridge is 110m, and the anchorage area is located on the Q3h thick accumulation with a thickness of more than 170 m. First, the important soil mechanical parameters, such as shear strength, deformation modulus and bearing capacity eigenvalues of rock and soil were obtained by conducting field shear tests, deformation tests, and load tests. On this basis, the pseudo-static method was used to simulate the seismic conditions, and a three-dimensional numerical analysis and calculations of the potential instability range of the high slope of the gravity anchor foundation pit excavation were conducted. The results reveal that the slope of the super-deep foundation pit with a huge thick mixed accumulation layer will deform and become unstable under the influence of an earthquake, with a maximum deformation of about 20 m in the slope body. A two-level earthquake prevention and disaster-reduction target for the bridge foundation pit and slope engineering protection is proposed based on the two-level seismic fortification requirements of super-long-span suspension bridges. An active reinforcement scheme of excavation pre-reinforcement, step-by-step excavation, and zoning protection is designed and proposed based on this target and the deformation and stability analysis results of the field test and three-dimensional numerical calculation.

Effect of Spatial Variability of the Elastic Modulus in Composite Ground on the Structural Performance of Large-diameter Tunnels

The spatial variability of soil properties is often neglected in design and construction, resulting in underestimating or overestimating the tunnel structural performance. Furthermore, the risks of ignoring the spatial variability of ground properties increase significantly as the tunnel diameter increases. This study investigates the effects of ground spatial variability on the convergence of shield tunnels in the composite ground, based on a real case of a cross-sea tunnel typically embedded in a ground mixture of soft clay and hard rock in Shenzhen, China. The influence of scale of fluctuation (SOF) for the soil and rock elastic modulus on tunnel convergence is investigated. It is found that the mean value of the tunnel convergence is less affected. In contrast, the tunnel convergence coefficient of variation is strongly affected by changing the elastic modulus SOF of the soil or rock layer. Moreover, the results indicate that as the elastic modulus follows the lognormal distribution, the vertical and horizontal convergence of the tunnel agrees well with the lognormal distribution.

Influence of cap beam restraint condition on the lateral deformation behavior of large-scale bored piles

The restrained force at the pile cap plays an important role in assessing the stability of bored piles. The constraining force of the cap beam is difficult to calculate due to spatial variability in soil properties, nonlinear soil behavior, and measurement errors. Based on theoretical analysis and field measurements this study proposes an analytical model combining Bayesian theorem and Markov Chain Monte Carlo Simulations (MCMCS) to quantify the restrained force of a pile cap beam. A simplified mechanical model of the constrained effect of the cap beam is established and verified by the results of field measurements. Based on a field excavated slope project, a Bayesian updating modeling approach is established by combing prior information, empirical knowledge, field instrumentation results, and site investigations to calculate the constrained effects of the cap beam. To verify its effectiveness, the model is combined with a finite element model, taking into account the uncertainties of soil moduli and measurement errors. The modeling takes into account the spatial variability and strain dependence of Young’s modulus. By comparisons, it can be found that the predicted displacements of the support pile are in good agreement with the field measurements. The results show that a Bayesian back updating approach can reduce the impact of uncertainty that can guide geotechnical engineering design and construction of similar projects.

Normalized Shear Modulus and Damping Ratio of Soil–Rock Mixtures With Different Volumetric Block Proportions

The volume fraction of rock blocks plays a particularly significant role in static/dynamic shear behaviors of soil–rock mixtures (SRM). Large-scale cyclic triaxial tests for SRM with different volumetric block proportions (VBPs) were performed at different confining pressures to investigate the reduction of dynamic shear modulus (G) and the increase of damping ratio (λ). Results indicate that VBP has a significant effect on the dynamic behaviors of SRM. The higher VBP is more likely to result in a gentler reduction of G and a faster increase of λ. The variations of dynamic shear modulus ratio (G/G0) and normalized damping ratio (λnor) fall within relatively narrow bands but are very different with gravelly soils and sands due to VBP with particle size larger than 2 mm. The G/G0 and λnor can be characterized by empirical functions about normalized shear strain amplitude (γnor).

Dynamic Triaxial Test and Microscopic Study of Solidified Muddy Soil With Different Mixing Ratios and Curing Ages

Aiming to explore the optimal mixture ratio and curing age of solidified muddy soil under dynamic load, the paper intends to investigate whether the solidified muddy soil can be used as filling of high-speed railway subgrade. Based on the dynamic triaxial test, the investigation measured the dynamic strain and dynamic elastic modulus of solidified muddy soil under different mix ratios and curing ages, and also observed the microscopic morphology of solidified muddy soil samples by using scanning electron microscope. The results show that the addition of cement and curing agent significantly increases the dynamic strength and elastic modulus of muddy soil, which effectively improve the dynamic characteristics of muddy soil. The curing effect of the curing agent is more obvious with the increase of the dosage of cement and curing agent under different mix ratio. The content of curing agent plays a leading role in the hydration reaction between cement, curing agent and soil particles. Additionally, in case of the same test conditions, when the ratio of cement mass to dry silt mass is 1:20, the ratio of diluent volume to dry silt mass is 1:20, with 28 days of curing age, its curing effect will reach the best.

Characterization of elastic and shear moduli of adapazari soils by dynamic triaxial tests and soil-structure interaction with site properties

Determination of shear modulus along with damping ratio values in the field when shear strains exceeds those maximum strains obtained from laboratory tests has a crucial importance in the seismic design of structures whose interaction with soil is more pronounced. In this study, shear modulus of undisturbed samples, obtained from Adapazarı city center during drilling works conducted within the scope of the geotechnical investigation following the 1999 Kocaeli earthquake, were determined. Elasticity of undisturbed Adapazarı samples was measured using a cyclic triaxial test rig. The aim is to obtain relationships between the elasticity moduli from the stress–strain relations of specimens in dynamic and static loading setups, and the axial strains following termination of dynamic tests. Minimum and maximum shear moduli were determined for non-plastic soils and for soils with the plasticity index of PI = 40%. The elasticity modulus ratio (EN=20/EN=1) for samples with plasticity index of PI = 40% is higher than those with PI = 20% at the same level of deformation. As the plasticity increases at the same deformation level, both of the Eds/EN=1 and Eds/EN=1 ratios increase. Moreover, seismic performance of a reinforced concrete frame is evaluated for both fixed and soil-structure system. Seismic demand in soil-structure model with the frame and soil profile considered in this study is observed to be higher as compared to fixed-base frames.

Resilient modulus of coarse-grained subgrade soil for heavy-haul railway: An experimental study

Large-scale dynamic triaxial tests under train-induced repeated load were conducted to study the variation of resilient modulus of the coarse-grained soil under different moisture contents, dynamic stress amplitudes, number of loading cycles and confining pressures. The results show that the state of specimens under the dynamic load can be divided into three categories: stable, critical and failure in accordance with the development trends of the accumulated plastic strain. For the saturated stable specimen, the resilient modulus tends to be stable at about 1000 cycles, while for the unsaturated stable specimen, the resilient modulus shows an increase trend with the increasing number of loading cycles. Resilient modulus increases with the increase of dynamic stress amplitude and confining pressure, but decreases with the increase of moisture content. The larger the amplitude of confining pressure and dynamic stress is, the more the resilient modulus decreases with the increase of moisture content.

Prediction of resilient modulus with consistency index for fine-grained soils

It is crucial to accurately predict the resilient modulus of subgrade soils. The modulus is influenced by a soil’s properties, as characterised by the soil’s moisture index values. Thus, it may be feasible to predict resilient modulus based on the soil index. Consistency index, as one of the common soil indices, incorporates plasticity index and moisture content. Therefore, this study aims to establish its relationship with resilient modulus. By collecting and analysing the previous testing results, it is found that resilient modulus was well correlated and increased with consistency index. Two prediction models, a consistency index model and a modified consistency index model, were also proposed to evaluate the resilient modulus of 15 soils with plasticity indices ranging from 6 to 52 at various moisture contents. Model parameters of the consistency index model were estimated from the plasticity index and exhibited excellent correlation. The modified consistency index model incorporated stress states to predict resilient modulus. The models were validated using selected testing results. Despite some limitations, it proves reasonable as a simple alternative means to determine the resilient modulus of fine-grained soils for foundation design, in place of complex resilient modulus testing.

Application of phosphogypsum to solidification of silty soil: Mechanical properties and microstructure

As a type of common industrial waste, phosphogypsum (PG) has raised concerns about environmental pollution and its comprehensive usage. However, scholars need to deepen the research on the application of PG in the solidification of silty soils. The impacts of PG on the microstructure and mechanical properties of solidified soil remain unknown under complex environmental conditions. Firstly, combined with several consolidation tests, this study analyses the impact of different PG contents on the compression modulus of silty soil with a cement-lime curing agent. Secondly, a scanning electron microscopy (SEM) test was used to take microscopic photos, and Image-Pro Plus 6.0 (IPP 6.0) software was used to process microscopic photos. Then, three microstructure parameters (Dp, Db and e) of solidified silty soil were calculated. Finally, the connection between the compression modulus and the microstructure parameters was assessed quantitatively. Results revealed that PG can stimulate the formation of calcium silicate hydrate (C–S–H) gels and react with calcium aluminate to produce ettringite. As a result, the compression modulus of solidified silty soil increased from approximately 7.39% to 51.3%. Given the excessive volume expansion produced by ettringite, the compression modulus with 4% of PG declined from 4.76% to 6.8% after reaching its maximum 24.98 MPa at 14 days of curing. A linear relationship was observed between the compression modulus and the three microstructure parameters at the declining stage of the compression modulus. The correlation coefficient R 2 of fitting lines were all greater than 0.9, thus representing the connection between the macroscopic mechanical properties and the microstructure of the solidified silty soil. This study seeks to provide theoretical basis and practical experiences for the efficient utilization of PG in the field of soil solidification.

Impact of bedding plane direction and type of plastic microparticles on stiffness of inherently anisotropic gap-graded soils: Index, wave propagation and micromechanical-based interpretations

Sand-clay mixtures are often encountered in natural deposits and compacted soils in earth structures in the form of gap-graded soils. They commonly display anisotropic fabric which markedly influences their wave propagation and mechanical properties. In this study, a comprehensive experimental program is carried out to thoroughly examine the influence of the inclined bedding plane and clay type on the small strain shear modulus (Gmax) of granular soils mixed with various portions of low and high plasticity fines, controlling in this way the double diffuse layer of the microparticles. To this end, cylindrical samples containing different fines contents are prepared with their corresponding optimum water contents and maximum dry densities in a standard proctor mold. Undisturbed specimens are then extracted by the continuous coring method and wave propagation tests with bender elements are applied at different angles with respect to the bedding plane (α-direction), evaluating in this way shear wave velocity and Gmax. The test results suggested that α-direction has a significant influence on Gmax of sand-clay mixtures and this influence is amplified at lower fines contents and higher confining pressures. Mixtures of sand with high plasticity clay are observed to have lower degree of anisotropy compared to those containing low plasticity clay, specifically at lower confining pressures. The contribution of fines in the load carrying structure of the solid skeleton decreases for high plasticity clays; the phenomenon which is primarily attributed to the thick diffuse double layer of the microparticles. This trend becomes more pronounced at higher contents of fines inclusion where the sand-in-fine structure dominates. A previously proposed expression for sands is rectified and extended so as to develop a Gmax model of sand-cohesive clay mixtures taking into account the bedding plane direction. Micromechanical-based interpretations are further elaborated considering the intervention of the microparticles on the contact response of sand grains altering their normal and tangential contact behavior, so as to supplement the findings, from the wave propagation tests, with multi-scale insights.