Relative Density Of Sand Research Articles

Monotonic, cyclic and post-cyclic shearing behavior of sand-EPS geofoam interface

Sand-EPS geofoam is commonly used as a seismic buffer in a variety of geotechnical applications to alleviate damages imposed by seismic vibrations. Evaluation of the properties of the sand-EPS geofoam interface is an essential part of the design and installation of EPS geofoam in direct contact with the parent sand. In this study, a series of laboratory tests are carried out using a large-scale direct shear apparatus to evaluate the monotonic, cyclic and post-cyclic behavior of the sand-EPS geofoam interface. Adopting the relative density of the parent sand, the density of EPS geofoam, the applied normal stress, the cyclic shear strain semi-amplitude and the number of cycles as the variable parameters, their influence on the response of the sand-EPS geofoam interface is investigated. According to the experimental results, with the increase in the number of cycles, sand relative density, EPS geofoam density and the applied normal stress, the equivalent or secant stiffness of the sand-EPS geofoam interface increases while its damping ratio declines. The results of the monotonic (MDS) and post-cyclic monotonic (CMDS) shearing experiments also show that with an increase in the EPS density and normal stress, which offers greater resistance against sliding, the mobilized shear stresses generally increase.

Behaviour of Square Footing Due to the Effect of Adjacent Excavation in Sand

In today scenario, urbanization and related infrastructure development in the form of an excavation adjacent to the existing structure are inevitable. In this case, the stability of an existing structure closer to the excavation is a serious concern. The main issue here is that, what is the safe distance at which new construction can take place from the existing structure? There are many research articles that states on the failure of an existing structure due to new construction adjacent to it in the form of excavations. Given the above, the paper presents the numerical results based on the finite element analyses that were performed for various parameters to examine the behaviour of existing square footing due to the effect of adjacent excavations in loose sand using PLAXIS3D software. In the finite element analysis, the behaviour of the footing and sheet pile walls were modelled using a linear elastic material and the elastoplastic behaviour of soil was modelled using a Mohr-Coulomb model under drained conditions. The literature available on this topic reveals that the excavation dimensions, shape of the footing, depth of the footing, location of the footing from the excavation, relative stiffness factor and relative density of sand are influencing the response of existing footing. Two different shapes of excavations such as a long length with narrow excavation under plane strain condition and short length of excavation under three-dimensional conditions were considered in this study. Numerical results indicate that the response of the square footing due to the effect of adjacent excavations are very much significant and mainly depends on the size of the excavation. The vertical and horizontal displacement, bending moment of the footing is increasing with an increase in depth of excavation. The footing located very closer to the excavation is significantly influenced as compared to the footing located far away from the excavation. The safe location of the square footing based on the settlement criteria is found to be 1.3 m from the excavation for shorter length excavation under three-dimensional conditions and 10 m for longer length of excavation under three-dimensional conditions.

A cone penetration test (CPT) approach to cable plough performance prediction based upon centrifuge model testing

Cable ploughing is an important technique for burying and protecting offshore cables. The ability to predict the required tow force and plough performance is essential to allow vessel selection and project programming. Existing tow force models require calibration against full-scale field testing to determine empirical parameters, a requirement that may hinder their use. In this study the factors controlling the plough resistance were investigated using a series of dry and saturated 1/50th scale model cable plough tests in sand in a geotechnical centrifuge at 50g at a range of target trench depths, sand relative densities, and plough velocities. An improved model for predicting cable plough tow force that separates out the key components of resistance and allows tow force prediction without the use of field-derived empirical coefficients is presented. It is demonstrated that the key parameters in this model can be easily determined from in situ cone penetration tests (CPTs), allowing it to be used offshore where site investigation techniques may be more limited compared to onshore locations. The model is validated against the centrifuge cable plough tests, demonstrating it can correctly predict both the static (dry) and rate effect (saturated) tow forces.

Modeling the Response of a Piled-Raft Footing: Ultimate Bearing Capacity

The design of pile–raft foundation is a complex problem due to pile-to-pile, pile-to-soil, pile-to-raft and raft-to-soil interaction effect; hence, a simplified and standard procedure could not be evolved so far; in spite of the fact that this type of footing finds versatile applications in the field and its use as a foundation system helps to transfer a heavy load satisfactorily and that comes with a reduced settlement, and thus, it offers an economical design without compromising the safety of the structure. The present paper presents an analytical model to predict the ultimate bearing capacity of piled-raft footings. The study has been derived using an extensive set of experimental data obtained from the studies carried out in the laboratory. Finally, the response of a full-sized raft footing, designed using the proposed model, was simulated on PLAXIS-3D for the validation purpose. The results from the model are in good agreement with the values obtained during the simulation study carried out on the PLAXIS-3D. Sensitivity analysis carried out with a soil stratum of loose and dense sand indicates that there is a significant effect of the soil properties on the load-carrying capacity of the piled-raft footing. Accordingly, a relationship is proposed to take into account the effect of the sand relative density during the analysis.

Bearing Capacity of Square Footing Resting on Layered Soil

The bearing capacity of layered soil studies was carried out with various approaches such as experimental, theoretical, numerical, and combination of them. This work is focused on the settlement and bearing capacity of shallow foundations subjected to the vertical load placed on the surface of layered soils. The experimental part was performed by manufacturing soil cubic container (570 mm x 570 mm x 570 mm). A model square footing of width 60 mm was placed at the surface of the soil bed. The relative density of sand was constant at 60%, and the clay was prepared with a density of 19.2 (kN/m3) and water content of 14.6%. PLAXIS 3D FEM was used to simulate the experimental tests and performing a parametric study. The results showed that there was a good agreement between experimental work and corresponding numerical results. The value of the bearing capacity was obtained from load-settlement curve. The bearing capacity of layered soil showed higher value for footing resting on clay over sand soil. It was found that an increase in the ultimate bearing capacity regarding the clay over sand with increasing in first layer thickness ratio; while, a decrease has been indicated for the sand over clay. The critical depth was found at H = (2-3m), and the failure pattern was not unique for layered soil.

Evaluation of variable permeability model in simulation of seismic behavior of uniform level and gently sloping sand layers

In this study, a fully coupled dynamic finite element model was employed for numerical simulation of the response of level to gently sloping saturated sand layers subjected to cyclic loading. This model utilized a critical state two-surface-plasticity constitutive model to simulate the cyclic behavior of sandy soil. Moreover, a recently proposed variable permeability function was implemented in the numerical model to reflect the effects of soil permeability variations during the liquefaction phenomenon. The numerical model was validated by simulating a number of well-documented geotechnical centrifuge tests with different relative density of sand, base acceleration time history, and surface slope of the sand layer. The obtained results confirmed that the developed model was capable of simulating the behavior of saturated sand under cyclic loading for both level and gently sloping conditions.

Behaviour of circular footings confined by rigid base and geocell reinforcement

Soil in nature may exist in a stratified state. A possible condition is the case of a rigid layer underlying a weak sand stratum. In this instance, the bearing capacity of a shallow footing is affected by the lower rigid boundary. The treatment of thin soil layer by geocell reinforcement to raise the load carrying capacity of single shallow footing has been limited in the literature. Accordingly, rigid base and geocell reinforcement are investigated separately and in combination to study their influence on the behaviour and BC of shallow circular footings in dry sand bed. To capture that effect, different size rigid circular footings were tested on a bed in fully instrumented small- and large-scale laboratory installations. The ratio of sand layer thickness to footing diameter was changed considering optimum dimension and embedment depth for geocell mattress. The extensive laboratory part involved monitoring subgrade deformations, soil-geocell stresses and strains revealing the appropriate models for failure mechanisms in the presence of such confinements. Large increase in bearing capacity up to 225% and significant settlement reduction up to 66% are measured for the combined case. Base confinement less than three times the footing diameter in combination with the geocell mattress resulted in favourable higher design performance factors. New equations are proposed to estimate these factors for design and to extend classical formulations for footings strengthened by combined geocell-base confinement. A design performance factor is dependent on footing diameter, sand relative density and the ratio of layer thickness to footing diameter. As this ratio increases, this design factor decreases reaching a constant value at the critical depth.

Uplift behaviour of axial granular pile anchor encased with geogrid in cohesionless soil

Purpose The purpose of this paper is to provide a cost-effective foundation technique for the design of foundations of transmission towers, heavily loaded structures, etc. Design/methodology/approach Experimental model tests are conducted in a model test tank to find out the effect of length and diameter of geogrid encased granular pile anchors, the relative density of sand and the angle of inclination of the pile from the vertical on uplift behavior of granular pile anchors. Findings The uplift capacity of the geogrid encased granular pile anchor increased with increasing length and diameter of granular pile anchor. Further, increasing the relative density of surrounding soil increased uplift capacity of geogrid encased granular pile anchor system. Moreover, increasing the angle of inclination of loading also increased uplift capacity of whole system. Thus, the proposed system can be effectively used in field for further applications. Originality/value The paper is helpful for the engineers looking for cost-effective foundation techniques for heavily loaded structures.

Thermal Upheaval Buckling of Buried Pipelines: Experimental Behavior and Numerical Modeling

Pipelines transporting oil and natural gas may experience upheaval buckling due to substantial compressive forces induced by high temperature and pressure of the fluid content. Such upheaval buckling may pose a major threat to the structural integrity, safety, and operability of pipelines. This study presents results from a series of scaled physical model tests conducted to investigate the uplift behavior and upheaval buckling of buried pipelines. The first set of experiments investigated the resistance force during vertical pullout for different pipe geometries, embedment depths, and relative densities of sand. The second set of experiments investigated the development of global upheaval buckling due to high axial compression of a buried pipe. The study examined the effect of embedment depth on the buckling characteristics and the postbuckling behavior of the pipe. Numerical analyses simulated the experiments and validated the numerical models. A parametric investigation based on rigorous numerical simulations examined the effect of trench-base initial imperfection, internal pressure, and soil strength on the upheaval buckling resistance. The results showed that as the geometric imperfection amplitude increased and its distribution length decreased, the upheaval buckling resistance substantially decreased. Similarly, an increase of the internal pressure of the pipeline may significantly decrease upheaval buckling resistance.

Experimental study of surface failure induced by tunnel construction in sand

An experimental study was conducted to determine the effects of tunnel construction on ground movements in sand. In this regard, a small-scale three-dimensional model test was developed, and several laboratory model tests were carried out under single gravity in a sand sample with three different relative densities of 30, 50, and 75% and a cover-to-diameter ratio of 3. To simulate the volume loss induced by the tunnel boring machine, the casing method was utilized. In the model tests, an elastic aluminium liner was used as a tunnel supporting system and a pipe casing was utilized to model a tunnel shield. By pulling out the tunnel shield progressively and replacing it with tunnel liner, the soil was allowed to move toward the tunnel and the surface settlements were measured by using linear variable differential transformers. The results show that increasing the value of the relative density of sand reduces the ground movements induced by tunneling. The settlement trough width increased almost linearly with increment of the overburden. Also, the results reveal that in dense sand the ground settlement trough is slightly less than the volume loss. For loose sand, the volume of settlement trough is nearly twice the volume loss. In shallow tunneling and loose sand produces remarkable movement on the ground surface.

Dynamic Response of a Single Pile Embedded in Sand Including the Effect of Resonance

In this paper, responses of a single pile embedded in sand soil (loose and dense) under dynamic loading (sinusoidal dynamic vibrations of 0.1 g to 0.5 g) have been investigated by two-dimensional analysis using the finite element method (FEM). Viscous (dashpot) boundaries have been used for taking the boundary effects of far-field into account. The applicability and accuracy of site responses of two-dimensional analysis due to the FEM modelling have been well verified with one-dimensional site responses. The results indicate that the relative density of sand (loose, dense) becomes prominent for the displacements of the pile, specifically under the frequency effects of resonance. While the pile in loose sand causes the displacements of 0.1 m to 0.5 m, the pile in dense sand leads to the displacements of 0.05 m to 0.25 m, proportionally with the dynamic loads from 0.1 g to 0.5 g. Moreover, the displacements reach their peak value at the frequency ratio of the resonance case. Viscous boundaries are found sufficient for modelling excessive displacements due to dynamic loading. However, the displacements reveal that high vibrations (> 0.1 g for loose sand, > 0.2 g for dense sand) influencing the pile deformations are critical for the issues of settlements. This is more significant for the resonance case in order for ensuring sufficient design. Consequently, the findings from the study are promising good contributions for pile design under the dynamic effect.

Effect of density on skin friction response of piles embedded in sand by simple shear interface tests

This study focuses on a particular phenomenon related to the reduction in sand–pile skin friction with initial relative density increment from medium to dense. Frictional behaviour of a sand–pile interface is simulated using a simple shear-type device capable of inducing a constant normal stiffness condition. Sand–pile interface sliding and soil deformation components are distinguished quantitatively. The effects of initial relative density of sand, initial normal load, and constant normal stiffness on the magnitude of the pile skin friction and shear displacement at failure are examined. Results indicate that the magnitude of the mobilized shear stress at failure relies significantly on the shear stress state with respect to the inflexion point on the volume change graph, which is equivalent to the position of the peak stress ratio. Good correlations exist between results of this study and field data of several heavily instrumented piles embedded in dense to very dense sands. The presented procedure is a useful framework for establishing more accurate skin friction calculation methodologies and “t-z” curve developments of axially loaded piles.

Seismic settlement of a strip foundation resting on a dry sand

Seismic settlement of shallow foundations constructed in seismic active areas should be considered for a reasonable estimation of the total settlement. However, the trend of the seismic settlement of shallow foundation constructed on a sandy soil is not clearly understood and it is estimated by designer using simple analytical methods. These methods do not consider the effect of the soil–structure interaction. This research, therefore, reports the results of 105 robust finite element models developed to investigate the seismic settlement of a shallow foundation constructed on a dry sand. The influence of the load applied on the foundation, relative density of sand, foundation embedment, peak ground acceleration of the earthquake shake, thickness of the sandy soil, and the dominant frequency of the earthquake shake have been examined to provide a comprehensive understanding of the parameters influencing the seismic settlement. The results of the analyses showed that increasing the load applied on the foundation or the peak ground acceleration remarkably increases the seismic settlement, while increasing the embedment depth remarkably reduces the seismic settlement. In addition, the relationship between the thickness of the sandy layer and the seismic settlement is found to be very complex and noticeably influenced by the relative density of the sand. More importantly, it was found that the seismic settlement dramatically increases when the dominant frequency of the earthquake approaches the natural frequency of the system. Thus, all these parameters are important and should be considered by designers for a reasonable estimation of the seismic settlement. The conclusions drawn from this paper will aid the development of a good analytical method in future, and the results reported in this paper also provide useful and novel database to designers and practitioners.

Model study of single pile with wings under uplift loads

Several structures as in the case of offshore structures like jetty, flood wall and wind turbines are mostly subjected to uplift loads. Thereby, the safe design for such cases is using piles. In this research a novel recent technique is adopted to improve the uplift capacity of the pile. In this paper, the uplift capacities of single regular piles (without wings) and anchor winged vertical piles installed in dry sand with different densities are investigated. A total number of sixty experimental model single regular and anchor winged piles tests were performed. Model test series were performed at a fixed embedment depth, and pile diameter. The effect of wings which were designed at the tip of the pile at different values of length and diameter was studied. The test results demonstrated that the uplift capacity of anchor winged piles increases with the increase of sand relative densities. At the ratio of wing length to pile length (Lw/Lp) = 0.50 and at the ratio of the maximum diameter between the outer edges of the wing to pile diameter (Dw/Dp) = 3.0 the efficiency of improvement in the uplift capacity reached to 2.0, 2.38 and 2.77 times of regular piles without wings at sand relative densities of 30 %, 50 % and 80 % respectively. The presence of such wings at the tip of the mono-pile provided an ideal anchorage system because of the significant locking-up influence of the wings within the soils, ensuing improved uplift capacity and reduced the pile movement. The existence of such wings can significantly increase the earth pressure and skin friction around the pile shaft in the form of (K) and (Fs) respectively.

PERFORMANCE OF SKIRTED CIRCULAR SHALLOW FOOTINGS RESTING ON SANDY SOIL UNDER INCLINED LOADS

Experimental tests were conducted to study the behavior of skirted foundations rested on dry medium sandy soil subjected to vertical and inclined loads. To achieve this goal, a small-scale physical model was designed and performed which contained an aluminum circular footing (100 mm) in diameter and (10 mm) in thickness and skirts with different heights, local medium poorly graded dry sand is placed in a steel soil container (2 mm) thick with internal dimensions (1000 mm x 1000 mm in cross section and 800 mm in height). The main objective of this study was to evaluate the response of skirt attached to the foundation at different skirt (L/D) ratios (0.0, 0.5, 1.0 and 1.5) and is subjected to point load at different angles of inclination (θ) (90 °, 80 °, 70 ° to 60 °) varying with the horizontal. In all tests, the relative density of sand was kept constant and equal to (60%). Four tests were conducted on a foundation without a skirt, for comparison reasons, and twelve tests were conducted on a skirt attached to foundation. The results showed that with decreasing the angle of inclination of load with the horizontal the load carrying capacity decreased due to increase the horizontal component of applied load which leads to increase the shear stresses under the foundation, however that effect decreases with increase the skirt height.

Experimental Investigation of Square Footing Resting on Sand over Gypseous Soils

This study included (40) tests of loading a square footing (100*100 mm) resting on two layered soils (sand over gypseous soils) using a steel box with the dimensions of (900*900*500 mm). Gypseous soil was brought from Tikrit-University with gypsum content 61%. The tests were divided into two groups. The first groups included (4) tests for gypseous soil only by using the field and maximum densities (14.5, 18.75 kN/m3) respectively, without soaking and with soaking where gypseous soil lost a great value of its resistance. The second group included (36) tests of loading two layers of soil by replacing a layer of gypseous soil by sandy soil with relative density (30%, 60%, and 80%) and depths (B/2, B and 3/2 B). The results showed that the replacement process gave an improvement in the bearing capacity when the gypseous soil was compacted to field density and soaked with a relative density of sand (80%) while the other cases did not have any improvement. The results of loading the two layers of soil also show that the soaking of gypseous soil under the sandy layer affects on the resistance of sand through reducing it especially when the depth of sand was (B/2) this effect decreased gradually with increase in the depth of the sandy layer.

Ultimate Shear Strength of Sand to Concrete Interface

One several studies have been performed by many researchers regarding laboratory interface testing. Interface tests were performed to determine the soil to structure shearing resistance angle (δ). This angle is used for the design of geotechnical structures such as friction piles, retaining walls, culverts, etc. Also, test results are useful for determination of parameters for constitutive modeling of interface response. Correlations between sand relative density, and corresponding friction angle (Ø), and interface shearing resistance angles (δ) are obtained. In addition, (δ) is represented as a function in (Ø). These relations are based on degree of interface roughness and particle shape of sand. Two types of sand, and in addition one mix (50%-50%) of the two sand types, are investigated. The first type of sand is siliceous sand and has rounded to sub-rounded particles. The second type of sand is fragments of weathered igneous rock of granite and basalt. This type of sand has angular shaped particles. To form a surface representing the retaining structure, ordinary Portland concrete mix was made from locally available material (sand, ordinary Portland cement and potable water). The mix was then poured into a steel mold having 4 sides 59 mm long, and 19 mm high to fit into the shear box bottom half. In order to simulate a smooth surface of concrete, the mold was placed on to smooth plastic sheet, and then the paste is poured into the mold. Interface tests have been performed on many types of soil-to-structure, soilto-rock, and rock-to-rock interfaces. In this section, previous studies of soil-to-concrete and soil-to-steel interfaces are emphasized. The results of tests performed on both types of interfaces provide valuable insights into fundamental aspects of interface behavior.

Model studies of plus and double box shaped skirted footings resting on sand

The paper presents the investigation on the model unskirted/skirted footings (plus and the double box) on sand. Skirt depth, sand relative density, footing interface condition and skirted footing type were varied parameters. Skirt depth (Ds) varied in this investigation was from 0.25 B to 1.5 B (B, footing width). The results show that the footing geometry and the skirt increased the bearing capacity and improved the overall behaviour. The results further revealed that the lowest percentage improvement for the square shaped footing with Ds/B = 0.25 was 26.08% at a relative density of 60%, whereas the highest improvement for the double box shaped footing with Ds/B = 1.50 was 364.12% at a relative density of 30%. The settlement reduction factors with the use of skirt from this investigation ranged from 0.16 to 1.0 and depended on the pressure applied and the depth ratio of the skirt. Finally, for the settlement reduction factor, an empirical equation was developed. This expression can be used to calculate the settlement of the plus and double box shaped skirted footings on sand.

Global and local sand–geosynthetic interface behaviour

The influence of overall particle shape, mean particle size, initial relative density and effective normal stress on the global and local soil–geosynthetic interaction is investigated here through an extensive series of direct shear interface tests between six sands in contact with one multifilament woven geotextile, one non-woven geotextile and one geomembrane. Analysis of the soil–geosynthetic data highlights mobilisation of higher peak friction angles with increases in initial relative density and angularity of sand particles and decrease in the effective normal stress. The average frictional efficiencies of the sand–geosynthetic interfaces are 0·95 and 0·79, respectively, for the sand–geotextile and sand–geomembrane interfaces. It is shown that the interface slip increases with the initial relative density of sand and regularity of particles, and decreases with increasing the mean particle size and effective normal stress. Analysis of the local particle movements by means of digital particle image velocimetry revealed that the average thickness of the shear zone for the sand–geosynthetic interfaces tested ranges from 3·8 to 11·9 (with an average of 7·0) times the mean particle size of the contact sand. The experimental data indicate that thicknesses of the shear and dilation zones are almost equal for the sand–geosynthetics interfaces tested.

Nonlinear Dynamic Analysis Adopting Effective Stress Approach of an Embankment Involving Liquefaction Potential

Stability of an embankment under earthquake loads is challenging in the process of analysis and design. Some embankment design consist of saturated granular material that is potential to liquefaction. Earthquake loads to the embankment under this conditions is one of major cause of embankment failure. Seismic performance involving stress-deformations and excess-pore-water pressure was evaluated in this paper. The evaluation adopts effective stress approach with non-linear elasto-plastic constitutive model. Numerical simulations through parametric studies were performed to estimate minimum density and embankment height efficiently to tolerate lateral displacements due to liquefaction. A number of parametric analyses were performed to investigate the relationships among relative densities of sand, ground accelerations, embankment height to excess-pore-pressure and lateral displacement of the embankment. The liquefaction analysis is conducted numerically using a finite difference method FLAC Dynamic 2D software adopting Finn-Byrne constitutive model.