Dense Sand Layer Research Articles

Bearing capacity of ring footings placed on dense sand underlain by a loose sand layer

The ultimate bearing capacity of a ring footing on loose sand deposit, with an inclusion of a dense sand layer on its top, has been determined numerically in a bound form by following the finite element limit analysis (FELA). The friction angles ϕ1 and ϕ2 were varied from 40° to 46° and 30° to 36° for the top dense sand and the bottom loose sand respectively. The Mohr-Coulomb’s yield criterion has been assumed to be applicable. The bearing capacity has been found to increase quite extensively with an increase in the thickness of the dense sand layer thickness up to a certain optimal thickness before attaining a constant value. The magnitude of has been found to lie generally between 1.5 and 4.7, and the corresponding maximum value of the bearing capacity with an inclusion of the dense sand layer varies in a wide range of 2.32–82.45 times the corresponding value for an unimproved loose sand deposit; the parameters and refer to the inner and outer radii of the ring, respectively. Similar to a ring footing on homogeneous sand deposit, the bearing capacity for different chosen combinations of internal friction angles of the two sand layers, tends to become maximum generally for a value of closer to 0.25. For the validation, the results for a ring footing on two-layered sand deposit were also determined by using the displacements based elastoplastic finite element (EP-FE) method. The results from the FELA were found to compare well with (i) the obtained solutions based on the EP-FE method, and (ii) the published results by using experiments and the method of stress characteristics.

Numerical study of ultimate bearing capacity of rectangular footing on layered sand

Purpose: The purpose of this study is to investigate the ultimate bearing capacity of the rectangular footing resting over layered sand using finite element method. Design/methodology/approach: Finite element analysis was used to investigate the dimensionless ultimate bearing capacity of the rectangular footing resting on a limited thickness of upper dense sand layer overlying limitless thickness of lower loose sand layer. The friction angle of the upper dense sand layer was varied from 41° to 46° whereas for the lower loose sand layer it was varied from 31° to 36°. Findings: The results reveal that the dimensionless ultimate bearing capacity was found to increase up to an H/W ratio of about 1.75 beyond which the increase was marginal. The results further reveal that the dimensionless ultimate bearing capacity was the maximum for the upper dense and lower loose sand friction angles of 46° and 36°, while it was the lowest for the upper dense and lower loose sands corresponding to the friction angle of 41° and 31°. For H/W = 0.5 and 2, the dimensionless bearing capacity decreases with the increase in the L/W ratio from 0.5 to 6 beyond which the dimensionless ultimate bearing capacity remains constant for all combinations of parameters. The results were presented in nondimensional manner and compared with the previous studies available in literature. Research limitations/implications: The analysis is performed using a ABAQUS 2017 software. The limitation of this study is that only finite element analysis is performed without conducting any experiments in the laboratory. Further the study is conducted only for the vertical loading. Practical implications: This proposed numerical study can be used to predict the ultimate bearing capacity of the rectangular footing resting on layered sand. Originality/value: The present study gives idea about the ultimate bearing capacity of rectangular footing when placed on layered sand (dense sand over loose sand) as well as the effect of thickness of top dense sand layer on the ultimate bearing capacity. The findings could be used to calculate the ultimate bearing capacity of the rectangular footing on layered sand.

Centrifuge modeling of batter pile foundations in laterally spreading soil

Batter piles are widely used in geotechnical engineering construction. Observations regarding the performance of batter piles in seismic hazards are controversial, and few studies have evaluated batter piles in liquefiable and laterally spreading ground. Three centrifuge experiments were performed to gain a better understanding of the performance of batter piles in liquefiable ground and to reveal the influence of the overlying nonliquefiable layer on the batter pile foundation design. The results reveal that for symmetrically placed batter piles, the bending moment of the front pile is greater than that of the rear pile, as a result of the liquefaction-induced lateral deformation in all three cases, and the bending moment reaches its maximum value at the middle of the pile. The presence of the overlying nonliquefiable dense sand layer reduces the potential for liquefaction and lateral spreading of the underlying ground, the settlement and bending moments of the batter piles.

Modeling of Large Diameter Piles in Soil Formations Including Soft Clay

In Egypt, large diameter piles are used in some sites with diameters exceeding 2 m. In some cases, these piles carry foundations of heavy structures and/or large vertical and lateral loads. The analysis and design methodologies of large diameter piles are mainly controlled by the relatively smaller diameter piles, usually ranging between 60 and 120 cm. However, there is a special need for the analysis and design of larger diameter piles (i.e., larger than 120 cm) to assess their actual load carrying capacities. This paper presents numerical modeling of end bearing piles constructed in thick layer of soft to very soft clay underlain by a dense sand layer, typical to large zones in Northern and North Eastern zones in Egypt. The finite element analysis software ADINA (2018) [2] is used to simulate the behavior of the large diameter bored piles. Results showed that increasing the pile diameter cause a corresponding increase in pile capacity. It is also noticed that increasing pile embedded length in the end bearing sand layer has an enormous effect on pile capacity especially for larger diameter piles.

Foundation Design and Construction Challenges with Marsh Deposits in a High Seismic Risk Zone

Driven piles are ideal for supporting structures over very soft ground, especially in high seismic risk zones. Challenges include achieving sufficient vertical and lateral load capacities within the constraints of pile spacing and geologic conditions. Through a unique case study, the authors will describe the process of site exploration, foundation selection, pile design, and installation of over 3,000 concrete piles in a small 4.5-acre (1.8 hectare) site (average of one pile per 65 square feet). A state-of-the-art, $180 million plant for biosolids processing, biogas management and energy recovery was sited in marshland next to an existing sewage treatment plant. The new construction included a 70-foot (21 m) tall building and three closely spaced, 90-foot (27 m) high, 65-foot (20 m) diameter, egg-shaped steel digester tanks. The site, classified as class “F”, was underlain by up to 45 feet (14 m) of highly compressible peat and organic clays, below which was a dense sand and gravel layer. The groundwater was very shallow and site-specific seismic hazard analyses were required. Particularly challenging was achieving the needed lateral resistance to seismic loads in the very weak clay and peat deposits. The project was instructive of the importance of adequate characterization of geologic conditions even in small sites; the necessary iterative collaboration process between geotechnical and structural engineers; and the value of a well-designed indicator pile program. The test pile program allowed for refining (shortening) the design pile lengths for considerable cost savings and reduced installation time. Of interest to the reader will be the surprising depth to refusal for some areas of the site, despite the test pile program.

Evaluating liquefaction induced settlement of shallow foundation on layered soil deposit

The occurrence of liquefaction in saturated layered soil deposit underlying the shallow foundation can cause a wide range of problems from settlement to tilting of structures and foundations. It this study in order to evaluate the liquefaction induced settlement of shallow foundation on the ground surface of layered soil deposit, numerical studies have accomplished. The soil deposit involves a continuous saturated fine sand that is sandwiched between two dense continuous sand layers and the whole system had been subjected to a base shaking. The settlement of shallow foundation has been evaluated by considering the influence of relative density (Dr) of middle sand layer. The variation of relative density of middle continuous soil layer was examined by using the finite element method in OpenSEES software. It was observed that the liquefaction has occurred up to the depth of 6 m. In addition, by examining the slope of the settlement–relative density curve, it was found that in continuous fine sand layer for relative densities higher than 60% the effect of this layer on settlement of shallow foundation can be neglected, but for relative densities less than 60% the slope of curve is sharper and as a result, the shallow foundation is experienced higher settlement with 17 cm for Dr = 40% in compare with settlement 10 cm for a uniform soil deposit with Dr = 75%.

Local Scale Displacement Fields in Grains\u2013Structure Interactions Under Cyclic Loading: Experiments and Simulations

Soils encounter cyclic loading conditions in situ, for example during the earthquakes and in the construction sequences of pavements. Investigations on the local scale displacements of the soil grain and their failure patterns under the cyclic loading conditions are relatively scarce in the literature. In this study, the local displacement fields of a dense sand layer interacting with a rigid footing under the plane-strain condition are examined using both experiments and simulations. Three commonly used types of cyclic loading conditions were applied on the footing. Digital particle image velocimetry (DPIV) is used to measure the local scale displacement fields in the soil, and to understand the evolution of the failure envelopes in the sand media under the cyclic loading conditions. The experimental results are compared with corresponding finite element analysis (FEA), in which experimentally-characterised constitutive relations are fed as an input into the FEM simulations. For comparison purposes, the case of footing subjected to the quasi-static loading condition was also studied. In general, the results show a good level of agreement between the results of the experiments and simulations conducted here. Overall, relatively shallower but wider displacement fields are observed under the cyclic loading, when compared with that of the quasi-static load test. The vorticity regions are highly localized at the shear bands in the sand media under the ultimate load. The research contributes to new understanding on the local scale displacement fields and their link to the bearing capacity of the footing under the cyclic loading environments.

Bearing capacity of ring footing on weak sand layer overlying a dense sand deposit

ABSTRACT The present paper deals with the numerical investigation on the ultimate bearing capacity of ring footing resting on loose sand overlying a dense sand deposit. The study followed the use of lower and upper bound finite element limit analysis in conjunction with second-order conic programming. The analysis was carried out by varying the thickness as well as the angle of internal friction of the top and the bottom sand layers for the ring footing with the variation in the radius (ratio of internal radius to external radius) ratio. The results were expressed in terms bearing capacity ratio, which was found to decrease with an increase in the thickness and the friction angle of the dense sand layer. Further, the results obtained from this study compared well with the data available from the literature.

Bearing capacity of strip footings on layered sands

In this paper we investigate the bearing capacity of strip footings resting on the top of a relatively thin layer of dense sand, which overlays a weaker sand layer. We use the Finite Element Limit Analysis method to calculate the collapse load and identify the geometry of the failure mechanism, as well as how this geometry changes with varying problem parameters. Results are benchmarked against published experimental data and methods used in practice for the design of working platforms for tracked plant, based on the punching shear model. The observed discrepancies are attributed to the development of a transitional mechanism when the bottom layer is rather dense, and the increase in the shear strength at the interface of the two layers is not abrupt. To cover this gap, we propose a new factor to calculate the bearing capacity in cases where a transitional mechanism will govern failure of the footing.

Experimental studies of seismic soil pressures on vertical flexible, underground structures and analytical comparisons

Seismic soil pressures are critical analysis components to understand and design for soil-structure interaction of sub-surface structures. A large scale experimental research program conducted at E-Defense's Shake table in Miki, Japan, included unprecedented seismic soil pressure measurements on a vertical, flexible, hollow shaft with model scale dimensions of 0.8 m square and 7.0 m in height. The densely instrumented vertical shaft was part of a larger system of underground structures, placed in an 8.0 m diameter laminar soil box. The two-layer soil stratigraphy consisted of an upper layer of medium dense sand and a lower layer of simulated bedrock. The hollow vertical shaft was constructed of aluminum and scaled to 1/20th of its prototype dimension. Two-directional, scaled ground motions of the 1995 Kobe earthquake were applied via shake table loading and seismic pressures were recorded using contact pressure sensors. Experimental results, including a dynamic system characterization, site response analyses, pressure time histories, and seismic pressure distribution profiles provide a critical benchmark for imminent numerical studies and the advancement of seismic soil pressure models for flexible structures. Following a thorough review of soil pressure analysis methodologies in literature, a detailed description of the large scale test and experimental results is presented. A comparison with limit state and elastic-based analytical approaches for retaining walls found in literature showed that, despite the unique shaft geometry, analytical methods accounting for the structural flexibility were able to closely predict the experimental soil pressures, while methodologies derived for rigid subsurface elements can only serve as rough preliminary estimate and should not be employed in performance based geotechnical analyses.

Full-scale in-situ tests on energy piles: Head and base-restraining effects on the structural behaviour of three energy piles

Energy piles, due to their dual roles, are exposed to temperature change throughout their life time, which may cause axial displacements, additional axial stresses and changes in the shaft resistance along their lengths. The extent of these effects highly depends on the level of restrictions along the energy piles, from the surrounding soil, as well as from the superstructure. A full-scale in-situ test has been performed on three energy piles, with the purpose of investigating their thermo-mechanical behaviour with respect to the corresponding end-restraining conditions. Thermal loads with maximum temperature of 45 °C and minimum of 8 °C were applied to the test piles for a 6-week period along with conventional mechanical load tests. Two of the test piles were designed to have base resistance from the very dense sand layer while the shorter pile was tipped into a stiff clay layer with the purpose of representing different end-restraining conditions. Moreover, the thermal loads were applied to the longer piles with and without the presence of mechanical load at the head. In this paper, the full-scale in-situ test setup is presented, along with the test results of the three test piles giving emphasis to the restraining effects of the mechanical load at the head and the base resistance from underlying soil layers. It is concluded from the results that the distribution of thermally induced axial stresses and the mobilization of shaft resistance during heating and cooling episodes are highly dependent on the location of the dominant restriction. Moreover, the end-restraining effects fade away at depths farther from the dominant restriction, leading to the degree of freedom of test piles with diverse end-restraining conditions to converge.

Technical performance of basalt fiber reinforced polymer BFRP confined RC driven piles new construction methodology

Pile foundations are often necessary to support large structures when the surface soil conditions are not strong enough to support the structure with shallow foundations. Pile foundation can be founded in dense sand layers at deeper, and also provide additional frictional support along their length to resist vertical loads. Load carrying capacity of Basalt FRP confined and unconfined piles were found out using the dynamic formulae and pile load test. Safe load carrying capacity of piles determined from piles load test was slightly higher than the dynamic formulae. The experimental result also shows that surface roughness of specimen is significantly changes the interface friction angle. The shear strength at the interface increases with the increase in surface roughness of the specimens.

Numerical analyses of pile performance in laterally spreading frozen ground crust overlying liquefiable soils

Lateral spread of frozen ground crust over liquefied soil has caused extensive bridge foundation damage in the past winter earthquakes. A shake table experiment was conducted to investigate the performance of a model pile in this scenario and revealed unique pile failure mechanisms. The modelling results provided valuable data for validating numerical models. This paper presents analyses and results of this experiment using two numerical modeling approaches: solid-fluid coupled finite element (FE) modeling and the beam-on-nonlinear-Winkler-foundation (BNWF) method. A FE model was constructed based on the experiment configuration and subjected to earthquake loading. Soil and pile response results were presented and compared with experimental results to validate this model. The BNWF method was used to predict the pile response and failure mechanism. A p-y curve was presented for modelling the frozen ground crust with the free-field displacement from the experiment as loading. Pile responses were presented and compared with those of the experiment and FE model. It was concluded that the coupled FE model was effective in predicting formation of three plastic hinges at ground surface, ground crust-liquefiable soil interface and within the medium dense sand layer, while the BNWF method was only able to predict the latter two.

Interaction of a rigid beam resting on a strong granular layer overlying weak granular soil: Multi-methodological investigations

In the geotechnical and terramechanical engineering applications, precise understandings are yet to be established on the off-road structures interacting with complex soil profiles. Several theoretical and experimental approaches have been used to measure the ultimate bearing capacity of the layered soil, but with a significant level of differences depending on the failure mechanisms assumed. Furthermore, local displacement fields in layered soils are not yet studied well. Here, the bearing capacity of a dense sand layer overlying loose sand beneath a rigid beam is studied under the plain-strain condition. The study employs using digital particle image velocimetry (DPIV) and finite element method (FEM) simulations. In the FEM, an experimentally characterised constitutive relation of the sand grains is fed as an input. The results of the displacement fields of the layered soil based DPIV and FEM simulations agreed well. From the DPIV experiments, a correlation between the slip surface angle and the thickness of the dense sand layer has been determined. Using this, a new and simple approach is proposed to predict theoretically the ultimate bearing capacity of the layered sand. The approach presented here could be extended more easily for analysing other complex soil profiles in the ground-structure interactions in future.

Geosynthetic Protection for Buried Pipes Subjected to Surface Surcharge Loads

Geosynthetics have been extensively used as reinforcement in several geotechnical engineering applications. Regarding pressurised buried pipes, geosynthetics can protect the pipe against mechanical damages and reduce the consequences of explosions and leakages. This paper presents and discusses the use of geosynthetic reinforcement for the protection of buried pipes against the influence of localized surcharges on the ground surface. Model tests were carried out under plane-strain conditions where increasing surcharge pressures were applied on the surface of a dense sand layer containing a buried pipe. Three polymeric geogrids were used as reinforcements. Reinforcement arrangements consisting of a geogrid horizontal layer, an inverted U arrangement and an arrangement where the geogrid completely enveloped the pipe were tested. The results obtained showed that the presence of the reinforcement was effective in reducing the vertical stresses transferred to the pipe as well as in reducing pipe strains. The arrangement with the geogrid enveloping the pipe was the most efficient and the geogrid that combined satisfactory tensile stiffness and aperture to soil particle diameter ratio was the one which performed best. The testing programme showed the potentials for the use of geosynthetic reinforcement in reducing the effects of surface surcharges on buried pipes.

Peak punch-through capacity of spudcan in sand with interbedded clay: numerical and analytical modelling

The presence of a thin soft clay layer inside a bed of sand may significantly reduce the bearing capacity of the sand layer, imposing a risk of punch-through failure. In this paper, finite element (FE) simulations are reported using a hardening soil (HS) model for sand. The FE model has been verified against centrifuge tests involving loose and dense sand layers overlying clay soil. The effects of sand stiffness, foundation roughness, sand friction angle, undrained clay strength, clay strength nonhomogeneity, and sand and clay layer geometries on the foundation peak capacities have been studied. Punch-through failure is initiated with an inclined sand plug being sheared and pushed into the underlying soft clay. During punch-through, the clay layer fails due to significant radial squeezing. Existing analytical models do not capture the combined failure mechanism of sand shearing and clay radial squeezing. A new analytical model is developed to estimate the peak punch-through capacity of a spudcan in sand with an interbedded clay layer, showing improved performance over the current industry guidelines.

Bearing Capacity of Foundations with Inclusion of Dense Sand Layer over Loose Sand Strata

The lower- and upper-bound finite-element limit analysis in conjunction with second-order conic programming (SOCP) was used to estimate the ultimate bearing capacity of strip and circular footings with an inclusion of a layer of dense sand over existing loose sand strata. The analysis followed the Mohr-Coulomb yield criterion and an associated flow rule. The results are expressed in terms of an efficiency factor that increases quite significantly with increases in the (1) thickness and (2) friction angle of the upper densified layer. While keeping the same thickness of the upper dense sand layer, the circular footing exhibits greater efficiency-factor values as compared to strip footing. The numerical results compare well with data available from the literature. (C) 2017 American Society of Civil Engineers.

Behavior of Piled Raft Foundation Model Embedded within a Gypseous Soil Before and after Soaking

The paper explain an experimental study to show piled raft system behavior when embedded within gypseous soil in three different stats (dry, socking for 1 day and placing a bearing layer of dense sand below the gypseous soil when socking for 1 day). A small-scale “prototype” model of steel box with dimension of (60cm length x 60cm width x 75cm heights) was used for carried out the model tests. Two different lengths of reinforced concrete pile models (40cm and 45cm) of 2.0cm dia. were used to keep the same imbedded length ratio during testing piled raft and piles only. Three different configurations of pile groups (single, three and six piles) were tested in the laboratory in two ways, first; the raft does not contact with the soil and the second; the raft is in contact with the soil. In dry state, the gypseous soil showed a very high carrying capacity with reduction in settlement. Piled raft foundations show an efficient in dry state, where the load carrying capacity increased and the settlement decreased. The improvement ratios in the load carrying capacity were about 16% for single piled raft and 39% for group of three-piled raft, while settlement reduction ratios were about 18% for single piled raft and 45% for group of six-piled raft. When the gypseous soil socked with water for 1 day, the ultimate bearing capacity of foundations is generally reduced by about (69%-83%) compared with dry state for all model configurations. The improvement ratios in ultimate bearing capacity due to using piled raft in soaking state was about (11% -50%) whilst the reduction settlement ratios was about (16% -44%).

Behaviour of circular footing resting on layered foundation: sand overlying clay of varying strengths

A series of laboratory model tests was performed on rigid circular footing, 150 mm in diameter (D), resting on surfaces of different layered foundations. The experimental programme considered different foundation configurations by varying the thicknesses (H) of dense sand layers, in the range of 0.63–2.19D, overlying clay subgrades of different strengths, ranging from very soft (c u = 7 kPa) to stiff (c u = 60 kPa). The responses of homogeneous foundations (configured with the sand and clays) were also obtained in order to compare the performances. The pressure–settlement responses of homogeneous and layered foundations depicted non-linear variations within the range of footing settlement tested (s = 0–24% of D). The layered foundations indicated significant improvements in bearing capacities for the softer clay subgrades (c u ≤ 30 kPa) as compared to corresponding homogeneous clay beds; while, reduced bearing pressures were noted for stiff clay subgrade having c u = 60 kPa. In general, foundation responses depicted higher bearing pressures for stiffer subgrades (c u ), thicker sand-layers (H/D) and at greater footing settlement levels (s/D); however, in terms of bearing pressure ratios (BPR), a decreasing trend was observed with increase in stiffness of the clay subgrades (c u ). In the testing programme maximum of about 5.34-fold improvement in bearing pressure was obtained for layered foundations having c u = 7 kPa; while, it was about 0.9 for the stiff clay subgrade (c u = 60 kPa) as compared to the corresponding homogeneous clay beds. Responses of the model tests were in significantly good agreement with that of the theoretical analyses reported earlier.

Analysis of Laterally Loaded Pile Groups in Improved Soft Clay

AbstractThe use of p-multipliers in the analysis of the lateral loading behavior of pile groups is based on the concept of modifying the single-pile p-y curve to obtain the p-y curve for a pile in a group. The p-multipliers account for the reduced soil resistance mobilized at a given deflection as a result of overlapping of shear zones. Different factors can influence the p-multipliers; however, because of the lack of experimental data, most researchers and design guidelines consider only the normalized pile spacing in the direction of loading in their recommendations. In this study, the effects of pile spacing and clay stiffness on the p-multipliers were investigated using the results of two series of centrifuge tests. The soil profile consisted of four lightly overconsolidated clay layers overlying a dense sand layer. The pile groups had a symmetrical layout consisting of 2 × 2 piles spaced at center-to-center distances of 3.0 and 7.0 pile diameter (D) and were driven into improved (stiff clay) and unim...