Saturated Sandy Soil Research Articles

Response of saturated cohesionless soil subjected to irregular seismic excitations

Irregular stress waves generated during an earthquake induce irregular shear stresses in the soil, which affect the dynamic behaviour of soil significantly. Laboratory investigations on the response of soils during real earthquake scenario are very limited. This paper reports about the response of saturated sandy soils subjected to irregular cyclic stress histories using stress-controlled cyclic triaxial tests. Tests were conducted at different relative densities (30–90%) and confining stresses (50–150 kPa) representing varying compactness of soil obtained from different confining depths. Cyclic loading was applied as per the three different earthquake motions considered having different peak ground accelerations (PGAs). The responses are presented in terms of stress–strain variations, excess pore-water pressure ratio and shear strain accumulation in the soil specimen. The results indicated that the accumulated shear strains and excess pore-water pressures get significantly affected by the increase in confining stress and simultaneous changes in the relative density. Further, the study emphasized that the strong motions scaled to the same PGA levels produce substantially differing soil responses due to the variation in the associated strong-motion parameters.

Effect of saturation on response of a single pile embedded in saturated sandy soil to vertical vibration

The dynamic response of a single pile embedded in dry and saturated sandy soil excited by two opposite rotary machines was considered experimentally. A small-scale physical model was manufactured. It consists of: two small motors supplied with eccentric mass (.012 kg) and eccentric distance (20 mm) representing two opposite rotary machines, aluminium shaft with 20 mm in diameter as pile, and a steel plate with dimensions of (160 × 160 × 20 mm) as a pile cap. The experimental work was achieved taking the following parameters into considerations: pile embedment depth ratio (L/d) and operating frequency of the rotary machines. Twenty-four tests were conducted in medium dense sandy soil with 60% relative density. Half of these tests were performed in dry soil and the other was conducted in saturated soil. In all these tests, the strain along pile’s length and the amplitude of vertical vibration for the pile cap were measured. It was found that the axial strain along the pile becomes frequency-dependent, which means that it increases with increasing the operating frequency, as well as its oscillation increases too. The amplitude of vibration at pile head also be frequency-dependent, it increases with increasing the operating frequency.

A practical method for construction of p-y curves for liquefiable soils

In practice, the analysis of laterally loaded piles is often carried out using a “Beam on Non-linear Winkler Foundation method” whereby the lateral pile-soil interaction is modelled as a set of non-linear springs (also known as p-y curves). During seismic liquefaction, the saturated sandy soil changes its state from a solid to a viscous fluid like material, which in turn alters the shape of the p-y curve. Typically, p-y curves for non-liquefied soil looks like a convex curve with an initial stiff slope that reduces with increasing pile-soil relative displacement (y) i.e., elasto-plastic softening response. However, recent research conclusively showed that p-y curve for liquefied soil has a different shape, i.e., upward concave with practically-zero initial stiffness (due to the loss of particle to particle contact) up to a certain displacement, beyond which the stiffness increases due to reengaging of the sand particles. This paper presents a practical method for construction of the newly proposed p-y curves along with an example.

Evaluation of liquefaction-resistance of soils using standard penetration test, cone penetration test, and shear-wave velocity data for Dhaka, Chittagong, and Sylhet cities in Bangladesh

The evaluation of liquefaction-resistance for saturated loose sandy and silty soils up to a depth of 20 m is an important component of geotechnical site characterization in an earthquake-prone region. In the present study, the standard penetration-test blow count (SPT-N), cone penetration test (CPT) tip resistance (qc), and shear-wave velocity (Vs) data of near-surface soils from Dhaka, Chittagong, and Sylhet cities were used to evaluate the liquefaction-resistance by a simplified procedure. At each site in the cities, the liquefaction-resistance is evaluated using a peak horizontal ground acceleration of 0.15, 0.20, and 0.25 g for a scenario earthquake of magnitude 7.5 (Mw). Then, the liquefaction potential index (LPI) is calculated for each site using the safety factors of liquefaction-resistance and thickness of liquefiable soil layers to predict the severity of liquefaction. The results indicate that sand boils (LPI > 5) and lateral spreading (LPI > 12) will be generated due to liquefaction in the Holocene saturated sandy and silty soils in Dhaka, Chittagong, and Sylhet cities. The evaluation of liquefaction-resistance using the SPT-N, qc, and Vs data shows considerable variation in the prediction of safety factor and LPI. Therefore, it is necessary to use two or more in situ test data to properly evaluate the liquefaction-resistance of soils for an area; and the simplified procedure needs to be used carefully. The results of the liquefaction-resistance of soils can be used to improve the ground condition in Dhaka, Chittagong and Sylhet cities for the construction of earthquake-resilient structures and future urban development.

Experimental and Numerical Analysis of Piled Raft Foundation Embedded within Partially Saturated Soil

This paper presents an experimental and numerical study to investigate the load carrying capacity of piled raft foundation embedded within partially saturated sandy soil. The effect of matric suction on the bearing capacity of the foundation system was investigated. The experimental work consists of two models of foundation, circular raft foundation and circular piled raft foundation. The circular raft foundation has dimensions of 10cm in diameter, and 2.5cm thickness, while the piled raft foundation has the same dimensions of the circular raft model but with a single pile of 2.0cm in diameter and 40.0cm in length fixed at the center of the raft. Both models are loaded and tested under both fully saturated condition and unsaturated conditions, which are achieved by, predetermined lowering of water table. The lowering of water table below the soil surface was achieved in to two different depths to get different values of matric suction and the relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil water characteristic curve (SWCC) estimated by applying fitting methods through the software (SoilVision). A validation process then was carried out for the case of circular piled raft foundation with lowering the water table 45cm bellow soil surface in the aid of a sufficient finite element computer program ABAQUS 6.12. An eight-node axisymmetric quadrilateral element CAX8RP and CAX8R were used to simulate the soil continuum and piled raft respectively. The interaction method used to simulate the intersect surfaces of the system (pile-raft-soil) is a surface-to-surface discretization method under the concept of master and slave theory. The behavior of piled raft material is simulated by using a linear elastic model while the behavior of soil is simulated by an elasto-plastic model by the use of the Mohr-Coulomb failure criterion. The results of the experimental work demonstrate that the matric suction has a significant role on the bearing capacity of all tested models. It shows that the ultimate bearing capacity of circular raft foundation under a partially saturated condition is increases by about (7.0-8.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. While the ultimate bearing of circular piled raft foundation under partially saturated condition increases by about (8.0-9.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. The results of the ultimate bearing capacity of piled raft foundation that obtained from the experimental model and from the numerical modelling for the same soil condition and same matric suction indicate that a successful validation is achieved for the simulation process.

Remediation of groundwater contaminated with the lead–phenol binary system by granular dead anaerobic sludge-permeable reactive barrier

ABSTRACTComputer solutions (COMSOL) Multiphysics 3.5a software was used for simulating the one-dimensional equilibrium transport of the lead–phenol binary system including the sorption process through saturated sandy soil as the aquifer and granular dead anaerobic sludge (GDAS) as the permeable reactive barrier. Fourier-transform infrared spectroscopy analysis proved that the carboxylic and alcohol groups are responsible for the bio-sorption of lead onto GDAS, while phosphines, aromatic and alkane are the functional groups responsible for the bio-sorption of phenol. Batch tests have been performed to characterize the equilibrium sorption properties of the GDAS and sandy soil in lead and/or phenol containing aqueous solutions. Numerical and experimental results proved that the barrier plays a potential role in the restriction of the contaminant plume migration and there is a linear relationship between longevity and thickness of the barrier. A good agreement between these results was recognized with root mean squared error not exceeding 0.04.

Dynamic Properties of Saturated Sands Mixed with Tyre Powders and Tyre Shreds

This study examined the effect of adding tyre powders and tyre shreds on the liquefaction potential of loose saturated sandy soil. Also, the dynamic properties of reinforced soil such as the damping ratio and shear modulus were investigated. To this end, a series of 1-g shaking table model tests were carried out at different percentages of sand–tyre powders and sand–tyre shreds mixtures. The results showed that the use of tyre powders and tyre shreds decreases pore-water pressure due to liquefaction. Maximum shear modulus of reinforced soil increased with the increase in tyre powder content in the mixture. However, an increased percentage of tyre shreds had no noticeable effect on maximum shear modulus. Furthermore, the mean damping ratio increases with the increase in tyre powder content in the specimens. Therefore, as the percentage of tyre shreds is increased up to 10%, the mean damping ratio experiences an increasing trend. Nevertheless, at values above 10%, the mean damping ratio reduces. In general, reinforcing soil with tyre powders and tyre shreds reduces the deformations caused by liquefaction.

ФОРМИРОВАНИЕ КАЧЕСТВЕННОЙ ГОРОДСКОЙ СРЕДЫ С УЧЕТОМУСЛОВИЙДЕФОРМАЦИЙ ГРУНТОВ ОСНОВАНИЯ

In the article questions of deformation reasons elements constituting the City Wednesday, inter alia, vibration and vibropolzuchesti saturated sandy soils. An analysis of the methods of fixing soils, increase the sustainability of buildings and structures. This is especially true now, when the construction of buildings and structures increases the load on vibration caused by heavy traffic while increasing mass of buildings and, accordingly, the loads on the base.

Using sewage sludge as a permeable reactive barrier for remediation of groundwater contaminated with lead and phenol

ABSTRACTWe investigated the efficiency of granular dead anaerobic sludge (GDAS) biosorbent as a permeable reactive barrier for remediation of groundwater contaminated with lead–phenol (Pb-Ph) present simultaneously. Batch tests were performed to characterize the equilibrium sorption properties of the GDAS and sandy soil in the Pb-Ph containing aqueous solutions. Computer solutions (COMSOL) Multiphysics 3.5a software was used for simulating the two-dimensional equilibrium transport of lead–phenol including the sorption process through the saturated sandy soil in the presence of GDAS. A good agreement between the predicted and experimental results was recognized with the root-mean-squared error not exceeding 0.049.

Dynamic behaviour of saturated sandy soil reinforced with non-woven polypropylene fibre

This research presents results of shaking table tests which were carried out on the soil reinforcement with randomly distributed synthetic fibres. The main scope of the study is to investigate the reliability and performance of polypropylene fibres in improving liquefaction resistance of loose sand prone to liquefaction. Dynamic properties of reinforced sand such as shear modulus and damping ratio were obtained, analysed and compared to those of unreinforced sand. The results indicated that shear modulus and damping ratio are increased by adding fibrous materials as a reinforcement to the host sandy soil. However, no meaningful improvement was achieved by reducing pore water generated during shaking. Outcomes also demonstrated that liquefaction-induced settlement is slightly higher in reinforced soil when compared to unreinforced soil.

Development of Excess Pore Water Pressure around Piles Excited by Pure Vertical Vibration

In this study, an assessment to excess pore water pressure generated around a single pile and pile group excited by two opposite rotary machines embedded in saturated sandy soil was considered experimentally. A small-scale physical model was manufactured to accomplish the experimental work in the laboratory. The physical model consists of: two small motors supplied with eccentric mass of 0.012 kg and eccentric distance (20 mm) representing the two opposite rotary machines, an aluminum shaft 20 mm in diameter as the pile, and a steel plate with dimensions of (160 × 160 × 20 mm) as a pile cap. The experimental work was achieved taking the following parameters into considerations: pile embedment depth ratio (L/d), spacing between piles (S) and operating frequency of the rotary machines. Twelve tests were conducted in medium dense fine sandy soil with 60 % relative density. In all these tests, the change in excess pore water pressure was measured around the pile at two spots: at the middle of the pile and at its tip. The results revealed that the generation of excess pore water pressure was affected by the following parameters: slenderness ratio of the pile, operating frequency of the machines, and the soil permeability. However, for all cases, it was found that the pore water pressure generated during operation was not greater than 20 % of the initial hydrostatic pressure. Using pile foundation reduced the amplitude of vertical vibration by about (300 %) for all operating frequencies, lengths of piles, pile spacings and number of piles. In addition, the presence of piles reduced the disturbance (fluctuation) in this amplitude by about (400 %). For single pile, and under the same operating frequency, a small decrease in the amplitude of vertical vibration resulted from increasing the length of the pile.

Effect of Freezing Saturated Sandy Soil under Undrained Condition on a Buried Steel Pipe

Buried water pipe is exposed to excessive ground stress resulting from ground freezing and thawing in low temperature of winter which might lead to the rupture or deformation of water pipe. This paper is intended to identify, through a full scale model test, the ground temperature variation around the buried pipe depending on variation of ambient temperature as well as the displacement of the buried pipe and the stress behavior, and consequently, stress concentration and frost heaving were observed around buried pipe when ground was frozen. And despite of using sandy soil which is considered non-frost susceptible material for the test, frost heaving was occurred depending on water content and drainage condition. Viewing such result, even in case of displacing bedding and backfill material with non-frost heaving material, the countermeasure to protect from frost heaving is necessary depending on surrounding drainage condition, groundwater level and water contents.

Use of agar biopolymer to improve the shear strength behavior of sabarmati sand

Loose saturated sandy soils are low shear strength soils, which are also prone to liquefaction under earthquake conditions. Many soil treatment techniques using admixers are available such as cement, chemical grouts, epoxy, acrylamide, phenoplast, polyurethane, etc. However, these admixtures have negative impact on environment or ecosystem. In the current research, the agar biopolymer has been chosen to strengthen the loose saturated Sabarmati soil (cohesionless soil) due to its gel forming capability and environment friendly nature. Sabarmati soil has been treated using different concentration of agar biopolymer (0.5, 1, 2, and 3%) at different curing time (4hrs, 8hrs, 1, 3, and 7 days). A series of shear strength tests has been performed on Sabarmati soil before and after its treatment to evaluate its shear stress behavior at different agar content and curing time. The settlement behavior of treated soil has been evaluated by obtaining vertical displacement during its shear deformation, which showed significant decrease in settlement of soil after its treatment. The agar treatment technique has also been evaluated for its applicability in moisture exposed region by performing shear strength tests on treated soil after water soaking, which exhibited small reduction in the shear strength of treated soil after moisture absorption.

Shear Strength Response of a Geotextile-Reinforced Chlef Sand: A Laboratory Study

During the last earthquake that occurred in Chlef (El Asnam 1980, Algeria), a significant decrease in the shear strength has caused major damages to several civil and hydraulic structures (earth dams, embankments, bridges, slopes and buildings), especially for the saturated sandy soil of the areas near Chlef valley. This paper presents a laboratory study of drained compression triaxial tests conducted on sandy soil reinforced with horizontal layers of geotextile, in order to study the influence of geotextile layer characteristics both on shear stress–strain and on volumetric change–strain. Tests were carried out on medium and dense sand. The experimental programme includes some drained compression tests performed on reinforced sand samples, for different values of the geotextile layers number (N g), of confining pressure (\( \sigma_{\text{c}}^{\prime } \)) and relative density (D r). The test results have shown that the contribution of the geotextile at low values of the axial strain (e 1) is negligible, for higher values of (e 1); geotextile induces a quasi-linear increase in the deviator stress (q) and leads to an increase in the volume contractiveness within the reinforced samples. A negligible influence of geotextile layers number (N g) on the stress–strain behaviour and the volumetric change has been shown, when normalized with N g. The results indicate that the contribution of geotextile to the stress–strain mobilization increases with increasing confining pressure, while its contribution to the volume contraction decreases with the increase in the confining pressure.

Influence of initial stress distribution on liquefaction-induced settlement of shallow foundations

During earthquakes, saturated sandy soils may generate significant excess pore pressures and approach a state of liquefaction. Structures founded on shallow foundations above such soils may consequently undergo large settlements. Recent case history analysis has shown that the stress imposed by the foundation is a key factor in the estimation of such settlements. However, the case history data showed that although increasing bearing pressure caused an increase in settlements as expected, this was only true up to a point, and that very heavy structures appeared to settle less than some lighter structures. This work aims to investigate these counter-intuitive results by means of controlled experimental testing using a geotechnical centrifuge. Results of the centrifuge tests show that the trend derived from case histories is correct and that liquefaction-induced settlements peak for a given bearing stress (90 kPa for the models tested) and reduce for greater applied stresses. Further, by analysis of excess pore pressure distributions beneath the foundations it is shown that the main factor inhibiting pore pressure generation beneath the footings is not so much the confining pressure as the in-situ static shear stress around the edge of the foundation. This is supported by element test data from the literature. When this initial static shear stress is so high that the applied cyclic shear stress cannot exceed it (i.e. the direction of shear stress does not reverse) then pore pressure generation is greatly reduced, thus causing the observed reduction in expected settlements.

Estimation of liquefaction potential from dry and saturated sandy soils under drained constant volume cyclic simple shear loading

Understanding the liquefaction mechanism of sandy soils still remains as one of the challenges in geotechnical earthquake engineering, since clean sands, silty sands and clayey sands do not necessarily show identical reactions under seismic loading. This study investigates the cyclic simple shear responses of three sandy soils: clean sand (Sile Sand 20/55), silty sand (Sile Sand 20/55 with 10% IZ silt) and clayey sand (Sile Sand 20/55 with 10% kaolin) based on many dry and saturated specimens. Drained constant volume cyclic simple shear tests on clean and silty sand specimens have shown that liquefaction potential of those soils could also be determined via dry samples. This is an important observation, since dry specimens are much easier to prepare and less time consuming compared to their saturated counterparts, as the demanding saturation process is eliminated. However, cyclic responses of dry and saturated clayey sand specimens were shown to be quite different, and therefore saturation of these specimens is still a must for liquefaction assessment. For both silt and kaolin, adding 10% fines to the base sand increased the liquefaction potential of resulting sandy soils considerably compared to the clean sand at the same void ratio. But this difference relatively decreased as the specimens became looser.

Influence of Particle Size Distribution and Wettability on the Displacement of LNAPL in Saturated Sandy Soils

AbstractImmiscible displacement processes are of key importance in remediation actions of light nonaqueous phase liquid (LNAPL) contaminated soil and groundwater. LNAPLs remain trapped in soil pores after a spill or flushing process due to the interplay of viscous, gravity, and capillary forces. In this research immiscible displacement tests were conducted in homogenous and heterogeneous sand samples. Also, the influence of fine content, mineralogy, and wettability was evaluated by testing mixtures of coarse sand with silt, zeolite, bentonite, and hydrophobic sand. Obtained results highlight the importance of pore-scale heterogeneities on the resulting displacement pattern in macroscopically homogeneous samples, and show the preferential accumulation of LNAPLs at the interfaces between different materials in heterogeneous samples. Fine particle content shows no important consequences on residual saturation but significantly changes relative permeability. In addition, the presence of hydrophobic particles ...

Numerical Analysis of Machine Foundation Resting Saturated Sandy Soil

Numerical Analysis of Machine Foundation Resting Saturated Sandy Soil

Modeling of Trichloroethylene Migration in Three-Dimensional Saturated Sandy Soil

This study characterized the temporal and spatial distribution of trichloroethylene (TCE) dissolved plume from continuous source in 3D bench-scale sand aquifer. COMSOL Multiphysics 3.5a (2008) software based on the finite element numerical scheme taking into account the sorption process was used to interpreted the experimental results. A conservative tracer is employed for the determination of the longitudinal dispersivity. The sorption characteristics of TCE onto the aquifer sand are independently determined from batch equilibrium data. TCE concentrations at specific downstream locations within the aquifer for different periods of time are measured under flow rates values equal to 20, 40 and 100 ml/min. The predicted TCE concentrations were found to be reasonably agreed with the bench-scale experimental results with mean error <5%.

Insight into the Effects of Gradation on the Pore Pressure Generation of Sand–Silt Mixtures

Liquefaction of saturated sandy soils has been considered as the main cause of most geotechnical hazards during earthquakes. Generation of excess pore water pressures in saturated silty sands when subjected to monotonic, cyclic, and earthquake loading has been shown to cause the liquefaction, which can be defined as the transformation of stable soil structure into unstable liquid form. The proposed research investigated the effect of grading characteristics on the generated excess pore water pressure of sand–silt mixture samples in loose, medium dense, and dense states. The laboratory investigation aimed at understanding the extent or degree at which excess pore pressure of sand–silt mixture soil is affected by its gradation under static loading conditions. For the purpose of clarifying and evaluating the generated pore pressure characteristics of sandy soils, a series of undrained monotonic triaxial tests were carried out on different reconstituted samples of sand–silt mixtures with various gradations. The soil samples were tested under a constant confining pressure (σ3′ = 100 kPa) and at three relative densities (Dr = 20 %, 53 %, and 91 %). The results from this laboratory investigation were used to develop insight into the pore water pressure response of sand and sand–silt mixtures under monotonic loading conditions. The analysis of the obtained data revealed that the grading characteristics [D10, D50, Cu, effective size ratio (ESR), and mean grain size ratio (MGSR)] have significant influence on the generation of the excess pore water pressure. It was found that maximum positive excess pore water pressure (Δumax) can be correlated to the grading characteristics for the sand–silt mixture. The ESR and MGSR appear as pertinent parameters to predict the excess pore water pressure response of the sand–silt mixtures for soil gradation under study.