Loose 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.

Sub‐arctic river bank dynamics and driving processes during the open‐channel flow period

AbstractThere is growing concern that rapidly changing climate in high latitudes may generate significant geomorphological changes that could mobilise floodplain sediments and carbon; however detailed investigations into the bank erosion process regimes of high latitude rivers remain lacking. Here we employ a combination of thermal and RGB colour time‐lapse photos in concert with water level, flow characteristics, bank sediment moisture and temperature, and topographical data to analyse river bank dynamics during the open‐channel flow period (the period from the rise of the spring snowmelt flood until the autumn low flow period) for a subarctic river in northern Finland (Pulmanki River). We show how variations of bank sediment temperature and moisture affect bank erosion rates and locations, how bank collapses relate to fluvial processes, and elucidate the seasonal variations and interlinkages between the different driving processes.We find that areas with high levels of groundwater content and loose sand layers were the most prone areas for bank erosion. Groundwater seeping caused continuous erosion throughout the study period, whereas erosion by flowing river water occurred during the peak of snowmelt flood. However, erosion also occurred during the falling phase of the spring flood, mainly due to mass failures. The rising phase of the spring flood therefore did not affect the river bank as much as its peak or receding phases. This is explained because the bank is resistant to erosion due to the prevalence of still frozen and drier sediments at the beginning of the spring flood. Overall, most bank erosion and deposition occurrences were observed during the low flow period after the spring flood. This highlights that spring melt, while often delivering the highest discharges, may not be the main driver of bank erosion in sub‐arctic meandering rivers. © 2019 John Wiley & Sons, Ltd.

Influence of Motion Energy and Soil Characteristics on Seismic Ground Response of Layered Soil

The present study focuses on assessing local site effects (especially large-scale soil heterogeneity) and motion characteristics on seismic ground response using nonlinear one-dimensional numerical analysis. All nonlinear and curve-fitting parameters used for soil models were verified using the Class C1 prediction of centrifuge test results available in the literature. The comparison demonstrates that the available MKZ (pressure dependent Modified Kondner Zelesko) formulation with non-Masing hysteresis loading and unloading rule can reliably compute the 1-D ground response of cohesionless soil. Horizontal soil layers with different relative densities were considered next in various hypothetical models to assess the effect of subsurface properties on responses. One novel aspect of this study is that 51 different ground motions with a wide range of variation in their spectral accelerations, frequency contents, and duration characteristics were used to evaluate the effect of ground motion characteristics on the soil response. The results reveal that layering conditions play a significant role in modifying the seismic ground response of heterogeneous soil, especially when the loose liquefiable sand layer is sandwiched between two non-liquefiable soil layers. Relations were obtained to quantify the effect of different seismic inputs and varying site conditions on seismic ground response. The best correlation was obtained between the maximum excess pore water pressure (EPWP) development and the damage potential (Arias intensity) of an input ground motion. These relations can be used for estimating seismic ground response of an identical soil profile to that used in the present study for known design motion characteristics.

Treatment and reinforcement of the loose sands of the city of Kenitra

The Kenitra city belongs to the Rharb-Mamora domain, which is affected by a continuous subsidence from the Middle Vindobonien to the present day. The sedimentary cycle of the tertiary era ends at the Pliocene, characterized by regressive character deposits identified in outcrop at the margins of the basin: They are conglomerates in the North, yellow sands in the East, sands and sandstone in the South-East. These sandy deposits vary from more or less clayey sand to greying sand, with the appearance of a very loose sand layer, at varying depths. It is with this directive that the objective of this article is to define the risks, which may affect the works built on this soil, and also determine the actions to be taken to control these risks. As a first step, an experimental approach was carried out, including in situ and laboratory tests in order to identify these formations and define their mechanical behavior. Then, the results of geotechnical survey were analyzed and exploited in calculations of bearing capacity, settlement, liquefaction,… eventually resulting in the necessity of treatment and reinforcement of this soil. These approaches have shown that there are several soil reinforcement techniques, the choice of which depends on the granulometry of soil and the cost of project.

State-of-the-Art of Colloidal Silica-Based Soil Liquefaction Mitigation: An Emerging Technique for Ground Improvement

In the booming field of nanotechnology, colloidal silica (CS) has been introduced for ground improvement and liquefaction mitigation. It possesses a great ability to restrain pore pressure generation during seismic events by using an innovative stabilization technique, with the advantages of being a cost-effective, low disturbance, and environmentally friendly method. This paper firstly introduces molecular structures and some physical properties of CS, which are of great importance in the practical application of CS. Then, evidence that can justify the feasibility of CS transport in loose sand layers is demonstrated, summarizing the crucial factors that determine the rate of CS delivery. Thereafter, four chemical and physical methods that can examine the grouting quality are summed and appraised. Silica content and chloride ion concentration are two effective indicators recommended in this paper to judge CS converge. Finally, the evidence from the elemental tests, model tests, and field tests is reviewed in order to demonstrate CS’s ability to inhibit pore water pressure and lower liquefaction risk. Based on the conclusions drawn in previous literature, this paper refines the concept of CS concentration and curing time being the two dominant factors that determine the strengthening effect. The objective of this work is to review CS treatment methodologies and emphasize the critical factors that influence both CS delivery and the ground improving effect. Besides, it also aims to provide references for optimizing the approaches of CS transport and promoting its responsible use in mitigating liquefaction.

Experimental testing of a full-scale of group efficiency in multiple soil layers

Results of in-situ tests showed that the performance of single isolated piles and individual piles within a group is largely different. When piles are arranged in a group, the interaction between piles and the foundation depends on the pile arrangement and the pile group effect. To date, studies on the pile group effect in Vietnam have been limited to reduced-scale laboratory testing or static load testing where piles are installed into homogeneous sandy or clayey foundation. This paper presents in situ tests which were performed on both single piles and pile groups, loaded to failure, with the aim of studying the pile group effect of piles embedded in multi-layered foundation. Strain gauges were installed along the shaft of 10 m long steel pipe piles, with a diameter of 143 mm. The influence of loose sand layers on the group effect in case of friction piles was evaluated. The experimental results indicated that the influence of sand layers was evident, and the group factor was calculated to be 1.237.
 Keywords:
 group efficiency; pile groups; axial capacity; load transfer.

Lateral Extent and Environmental Effects of Dynamic Compaction in a Coastal Area of Southern Iran

ABSTRACT The lateral extent, depth of densification, and environmental effects of dynamic compaction (DC) were investigated for a very loose to loose silty sand layer with thickness varying from 6 to 12 m in a coastal area in southern Iran. Cone penetration testing (CPT) was done at different distances from the center of the point of impact before and after DC. The increase in cone resistance at different distances is plotted versus dimensionless distance X/D (X = distance from center point of impact and D = diameter of tamper), and equations are proposed to describe them. The amount of soil densification decreased progressively until the distance from the center of the tamper increased to about 3.3 times the diameter of the tamper, beyond which there was no densification. The peak partial velocity (PPV) measured at different distances from the center point of impact was used to determine the environmental effect caused by the impact of the tamper. Equations describing the relationship between the weight of the tamper, tamper drop height, distance from the center point of impact, and PPV for this site are proposed.

Centrifuge modelling of submarine landslides due to static liquefaction

Sand erosion and scouring caused by waves and marine currents result in gradual increase of local seabed inclination and formation of slopes around hydraulic structures and offshore foundations. During this process, shear stresses in the soil body increase monotonically which may lead to static liquefaction and damage of the adjacent offshore infrastructure. This paper presents the details of a newly developed static liquefaction triggering actuator to be used at an enhanced gravity condition in a geotechnical centrifuge. This actuator simulates the steeping process of submarine sand layers due to scouring and enables the investigation of failure mechanisms in submerged slopes. The details of the centrifuge test set-up designed and constructed to simulate the process of triggering static liquefaction in loose sand layers are presented. Furthermore, the performance of the novel integrated model preparation facility using sand fluidization is explained. The set-up was used to conduct several centrifuge tests at four different slope steepening rates to investigate the slope steepening rate effects. Moreover, the effect of viscosity of the submerging pore fluid on the behaviour of the slopes at the onset of failure is investigated. The Coriolis effect on loose saturated sand samples during increase of g-level is examined as well. Results show that the built-up of pore pressure due to local shear deformations can be detected and considered as one of the triggering mechanisms of this kind of submarine slope instabilities.

Coupled sedimentological and geotechnical data analysis of surficial sediment layer characteristics in a tidal estuary

In situ geotechnical testing of surficial sediment layers in areas of active sediment dynamics can provide essential information about physical and geotechnical variations of sediment properties, which have the potential to contribute to engineering activities in subaqueous environments. Portable free fall penetrometers have been used for the rapid geotechnical investigation of subaqueous sediment layers. However, data analysis methods and interpretation are still hampered by a lack of understanding of surficial sediment layer mechanics. Field measurements were conducted at four different locations along the York River Estuary in Virginia, USA. A portable free fall penetrometer was deployed 45 times, and complementary sediment samples were collected. The collected samples were tested and analyzed to obtain vertical profiles of bulk densities and grain size distribution through the upper seabed, X-ray images of sediment texture, and the erodibility of the sediment surfaces. The data were investigated regarding the impact of sedimentological characteristics on the in situ geotechnical behavior of surface sediments. With regard to processes and forces governing the resistance against the penetrating object at the surface of the seabed, the role of soil drag and soil buoyancy was explored. The results indicated that soil buoyancy has a limited influence on the sediment resistance, but soil drag seemed to have a significant impact, especially in the case of loose sand or soft mud top layers. The erodibility of surficial sediments appeared inversely proportional to the geotechnical sediment strength, providing empirical insight into a possible correlation of sediment strength and erodibility. In conclusion, a coupled analysis of geotechnical and sedimentological properties of surficial layers allowed insights into a potential transition from fluid-like to soil behavior of the uppermost seabed surface layers, and potential relations between sedimentological characteristics and in situ geotechnical properties.

Experimental Investigation on Crack Development Characteristics in Shallow Coal Seam Mining in China

The development of cracks in mining is the scientific basis for the safety and environmental exploitation of shallow multiple-seam. According to the “thickness of coal seam, interactive distance, and buried depth,” four mining coal mines are selected in Shen Fu-Dong Sheng coalfield (SFDSC). To research the mining conditions of shallow coal seam under different base-load ratio mining conditions and different working faces by the physics simulation and in-sit measurement, the key roof caves are sketched by different colors. This study shows that the typical shallow coal seams in the thin overlying bedrock and thick loose sand layer (LSL) as well as the development of the setup entry cracks (SEC) is dominated by LSL arch damage. The surface cracks are almost directly above the setup entry. The flat seam mining and the SEC development is dominated by parabolic type. The surface cracks are located inside the setup entry. With the mining height increased typically in a shallow coal seam, the rate of crack development and the extent of damaged area increased significantly. The SEC and boundary cracks are fixed. The dynamic periodic cracks (DPC) show the ability of the strata to self-repair. During the multiple-seam mining, the above three kinds of cracks have the phenomenon of activation and development. Through the reasonable coal pillar distance arrangement, the development of boundary cracks can be effectively controlled and the relatively uniform surface settlement and crack closure can be achieved. The purpose of reducing damage mining can also be achieved. Furthermore, it provides scientific support for the green mining in the shallow coal seam.

Behavior of Pyramidal Shell Foundations on Reinforced Sandy Soil

Shell foundation has been considered as the best shallow foundation for transferring heavy load to weak soils because of the high bearing capacity values, where a conventional shallow foundation submit to excessive settlement. An experimental work has been conducted to investigate the behavior of pyramidal shell foundations as compared with flat counterpart on loose sandy soils. Four types of aluminum rigid foundation were casted for this purpose; flat footing and shell footing of dimension (20 × 20 cm) and different angles (20°, 30°, and 45°). Twenty eight loading tests were carried out on these types of footings which were settled on the surface of loose sand layer with and without geogrid reinforcement. The geogrid sheet was inserted within the sand layer (single and double layers) under the footing base. The shell foundation on reinforced and unreinforced sand showed higher ultimate load capacity than those on unreinforced sand for flat foundation and the load- settlement curves were clearly modified. The shell foundations over reinforced soil can be considered as a good method to increase the effective depth of the foundation and decrease the resulting settlement. The bearing capacity ratio (BCR) reaches to 88.5% and settlement reduction factor (SRF) reaches to 37.3%, where the BCR is the ratio of bearing capacity for a foundation resting on reinforced (qR) to that resting on unreinforced soil (q) while the SRF is the ratio of settlement for a foundation resting on reinforced soil (SR) to that resting on unreinforced soil. The experimental work were also verified and analyzed numerically using ABAQUS software taking into a consideration the effect of different relative densities (15%, 20%, 30%) on settlement and bearing capacity of soil. The improvement range was greater at relative density (15%), compared with the others which reflects the improvement in loose condition due to shell effect. This confirms the premise that shells are reputably better performers in weaker soils that necessitate a large load transferred to them.

Study of soil deformation pattern in earth slope stabilised with pile

This paper studies the slip surface shape of piled and no-piled slopes. Physical and numerical modelling of the foundations was performed adjacent to layered and homogenous slopes. This paper also studies the effects of pile position, surcharge distance from the slope crest, and the effects of loose layer thickness of piled and no-piled slopes on soil deformation patterns, the bearing capacity improvement ratio factor (BCR), and slope stability improvement ratio (Nps). According to the no-piled slope results, for a 0 to 2.0B dense layer distance from the ground surface, the slip surface lies on the dense layer. The soil layer angles significantly affect slope stability and footing bearing capacity. Increasing the soft bound layer angle, decreased not only the thickness of the loose sand layer, but also the soil bearing capacity and slope stability. Furthermore, increases in the surcharge load distance from 2B causes general failure of the slope, whereas lower distances allow the failure shape to be surficial. According to the tests and numerical results, the use of pile elements was provided considerable lateral movement resistance. All tests are analysed numerically and a good agreement is observed between the experimental and numerical results.

Application of Nor Sand Constitutive Model in a Highway Fill Embankment Slope Stability Failure Study

This paper presents a case study of a static load induced liquefaction in a simple roadway widening project constructed in north eastern part of Ohio in 2008. The widening required an embankment fill, which moved nearly 4 feet vertically and 1 foot laterally after two days of installation. The main objective of the work is to demonstrate how a simple Constitutive model, in this case Nor Sand model, can represent the static liquefaction in loose sand layers under specific conditions. A set of parameters is assumed based on the soil properties and an Excel Spreadsheet is used for simulations of triaxial compression of sand. It was considered that the situation which led to the failure, and the situation after the solution adopted. Moreover, slope stability analysis is provided for validation of the original results using a commercial software. It was found that the model can represent through stress strain curves and stress paths the behavior of the soil layer which led to the embankment fill movement. As the original work considered only slope stability analysis to explain this phenomenon, the present study shows a different approach for the case study, and this is the main contribution of this research.

INTERACTION BETWEEN BEDDING SAND THICKNESS AND SHELL GROOVE-UNDERSIDE SHAPED CONCRETE BLOCK PAVEMENT

Underside Shaped Concrete Block (USCB) has groove shaped at the underside block surface to produce resistance in horizontal plane and to grip onto the bedding sand layer. However, the horizontal movement of block units is the major problem in pavement due to vehicle braking and accelerated action. This paper presents the laboratory evaluation on vertical and horizontal displacement of shell groove-USCB pavement laid onto different bedding sand layer thickness. A pavement laboratory test was conducted to investigate the interaction between USCB type of the Shell-Rectangular 15 mm (Shell-R15) and bedding sand on three different loose bedding sand layer thicknesses of 50 mm, 70 mm and 90 mm respectively. Then, push-in loading test and horizontal loading test were performed. The results showed that interaction between USCB Shell-R15 and bedding sand layer thickness had significant influence to the vertical and horizontal displacement compared to control of 50 mm loose bedding sand layer thickness. The loose bedding sand layer thickness of 70 mm performed better compared to others.

Remediation of liquefaction effects for an embankment using soil-cement walls: Centrifuge and numerical modeling

Numerical simulations of a centrifuge model test of an embankment on a liquefiable foundation layer treated with soil-cement walls are presented. The centrifuge model was tested on a 9-m radius centrifuge and corresponded to a 28 m tall embankment underlain by a 9 m thick saturated loose sand layer. Soil-cement walls were constructed through the loose sand layer over a 30 m long section near the toe of the embankment and covered with a 7.5 m tall berm. The model was shaken with a scaled earthquake motion having peak horizontal base accelerations of 0.05 g, 0.26 g, and 0.54 g in the first, second, and third events, respectively. The latter two shaking events caused liquefaction in the loose sand layer. Crack detectors embedded in the soil-cement walls showed that they developed only minor cracks in the second shaking event, but sheared through their full length in the last shaking event. The results of the centrifuge model test and two-dimensional nonlinear dynamic simulations are compared for the two stronger shaking events using procedures common in engineering practice. The effects of various input parameters and approximations on simulation results are examined. Capabilities and limitations in the two-dimensional simulations of soil-cement wall reinforcement systems, with both liquefaction and soil-cement cracking effects, are discussed. Implications for practice are discussed.

Rammed aggregate pier installation effect on soil properties

This paper describes the changes in in situ index properties following installation of rammed aggregate piers in a loose sand deposit in New Madrid, Missouri, with a particular focus on the time-dependent strength gain, commonly called sand ageing, as indicated by increased cone penetration test (CPT) tip resistance and dilatometer test (DMT) indices. The method of disturbing the soil and the magnitude of disturbance significantly influence the magnitude of sand-ageing effects. This paper provides the first data on sand ageing following the installation of displacement rammed aggregate piers. In this study, CPT and DMT were performed both immediately before and after the installation of piers. Additionally, CPTs were performed 1 month following the installation of piers. The DMT horizontal stress index increased roughly 100% and the dilatometer modulus increased ∼200% in a loose clean sand layer immediately following the installation of the piers. The CPT tip resistance increased roughly 100% in this layer immediately following the pier installation and a further 33% in the month following the installation.

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.

Preliminary study of soil liquefaction hazard at Terengganu shoreline, Peninsular Malaysia

Terengganu is a shoreline state located in Peninsular Malaysia which is a growing hub for port industries and tourism centre. The northern part offers pristine settings of a relax beach areas whereas the southern part are observed to be a growing centre for development. The serious erosion on soil deposit along the beach line presents vulnerable soil condition to soil liquefaction consists of sandy with low plasticity and shallow ground water. Moreover, local earthquake from nearby fault have present significant tremors over the past few years which need to be considered in the land usage or future development in catering the seismic loading. Liquefaction analysis based on field standard penetration of soil is applied on 546 boreholes scattered along the shoreline areas ranging 244 km of shoreline stretch. Based on simplified approach, it is found that more than 70% of the studied areas pose high liquefaction potential since there are saturated loose sand and silt deposits layer ranges at depth 3 m and up to 20 m. The presence of clay deposits and hard stratum at the remaining 30% of the studied areas shows good resistance to soil liquefaction hence making the area less significant to liquefaction hazard. Result indicates that liquefaction improving technique is advisable in future development of shoreline areas of Terengganu state.

Load sharing ratio of pile-raft system in loose sand: an experimental investigation

This technical note presents the results of a series of tests carried out on instrumented model pile-raft foundation to investigate the load sharing ratios between the foundation’s components where a loose sand layer is encountered near the ground surface. Four different pile-raft models with two different pile numbers and lengths were considered. In each model, the settlement of the raft and the load of each pile were monitored during the load application process. The experiments showed the effectiveness of pile length on reducing the overall settlement of the pile-raft system. The results showed also that the proportion of load transferred to any pile in a closely spaced pile group increases with its distance from the centre of the group. Unlike some previous studies that classified soil profiles containing loose sands near the surface as unfavourable situations for piled rafts, the experimental results herein represent an evidence of the efficiency of piled rafts even in soil profiles with loose sands immediately beneath the raft. Indeed, ignoring the contribution of the raft would lead to unnecessary over-conservatism in the design of piled rafts.