Loose Sand Layer Research Articles

Effect of loose sand layers within dense sand on the lateral capacity of extra-extra-large monopiles

A series of 3D finite element analyses were performed to examine the influence of loose sand layers on the monotonic lateral capacity of an extra-extra-large semirigid monopile in dense sand. The SANISAND-04 advanced constitutive model, which was meticulously calibrated, validated and verified using triaxial compression tests, centrifuge tests and a numerical study based on field tests, was adopted for this study. The impact of loose sand layers on monopile response is discussed in terms of its mode of deformation, critical lateral capacity, bending moment, shear force and soil resistance. Results show that the magnitude of the reduction in the monopile lateral capacity is dependent on the thickness and depth of the loose sand layer. Presence of loose sand at the tip of the monopile is also shown to have a significant effect on its lateral capacity.

Study on Reinforcement of Tunnel Loose Sand Layer by Grouting

Study on Reinforcement of Tunnel Loose Sand Layer by Grouting

Study on seismic response of liquefiable soil-pile group considering pile cap and soil contact

In this paper, based on the centrifuge test of liquefied soil-pile foundation system, a numerical model of liquefied soil-pile foundation-structure system is modelled by using OpenSees platform. In the simulation model, the friction effect between liquefied ground and low pile cap is considered, and the method of establishing virtual nodes is used to deal with the non-linear contact between liquefiable soil and low pile cap. The rationality and effectiveness of the numerical simulation method adopted in this paper has been verified and evaluated by comparing with the results of centrifuge experiments. A typical liquefaction soil-pile integrated finite element model is modelled using validated numerical simulation methods. The law of seismic response of the pile foundation system with different embedding depths of pile cap, different contact modes between the pile cap and saturated sand, and the thickness of the overlying saturated loose sand layer are discussed. The results show that the pile cap and pile foundation in the high pile cap system show higher seismic response characteristics than the other three low pile cap system conditions; Under the condition of different contact modes between the pile cap and the surrounding saturated sand, the peak bending moment and residual displacement of the pile foundation calculated by the bond contact are larger than calculated by the friction contact, and the deformation of pile is more significant. By comparing the working conditions of different thicknesses of overlying saturated loose sand layer, it is found that the degree of liquefaction in shallow soils is less affected by thickness of the saturated loose sand. As the thickness of saturated loose sand layer increases, the peak bending moment and residual displacement at the top of the pile also gradually increase. The change of peak bending moment at the soil interface is more obvious.

Solid waste slurry grouting transformation mechanism of loose sand layer based on slurry-water replacement effect

During coal mining, when loose water-bearing sand layers are exposed and connected, it is extremely easy to cause water and sand inrush accidents, threatening the lives and properties in mines. Because of the intricate and tortuous internal structure of the sand layer, the diffusion pattern of grouting slurry within the loose sand layer has not been accurately characterized. Improving the efficiency of grouting and reducing the cost of grouting are common difficulties faced by industrial and mining enterprises in the grouting renovation of loose water-bearing sand layers. This paper innovatively proposes the mechanism of slurry-water displacement effect based on the diffusion characteristics of grouting slurry within the water-bearing sand layer. It studies the power-law fluid seepage and diffusion mechanism of porous media tortuosity effect and slurry-water displacement effect and derives the spherical diffusion equation of power-law fluid seepage grouting considering the coupling of porous media tortuosity effect and slurry-water displacement effect. At the same time, an indoor experimental device considering the slurry-water displacement effect is designed to verify the rationality of the spherical seepage grouting diffusion equation considering the superimposed effects of the two. Furthermore, relying on the COMSOL Multiphysics platform, a three-dimensional numerical calculation model of the power-law fluid spherical seepage grouting mechanism considering the porous media tortuosity effect and slurry-water displacement effect is constructed. It analyzes the seepage and diffusion characteristics of power-law grouting slurry in water-bearing sand layers, and studies the influence of different porosity of loose water-bearing sand layers, spacing between slurry and water holes, grouting pressure, and slurry viscosity on the volume of loose water-bearing sand layers. The key factors affecting the volume of loose water-bearing sand layers are grouting pressure > spacing between slurry and water holes > porosity of sand layer > slurry viscosity. Compared with previous grouting technologies and processes, the slurry-water displacement grouting technology can solve the problems of small grouting diffusion range and poor grouting effect in high-pressure underwater water-bearing sand layers to a certain extent.

LEAP centrifuge tests on retaining walls at Cambridge University

Retaining walls and other waterfront structures were seen to suffer severe damage due to soil liquefaction in previous earthquakes. As part of the LEAP project, cantilever retaining walls with loose, saturated backfill were tested at various centrifuge centres participating in this endeavour. The toe of the retaining wall penetrated about 0.5 m into the dense sand layer underlying the loose sand layer. Retaining walls with different ratios of the retained height h over the penetration depth d were tested. As part of the LEAP project, additional testing was carried out at Cambridge to consider the effect of the wall size on its deformation following liquefaction. It will be shown that a larger wall will suffer more rotation and wall top displacement than a smaller wall with the same h/d ratio. This can have implications for numerical modelling in terms of how well the constitutive models capture the suppressed soil dilatancy at higher confining pressures.

Bearing Capacity of Skirted Ring Footing on Dense Sand Overlying Loose Sand

Introduction: The ultimate bearing capacity of an unskirted/skirted ring foundation on dense sand overlying loose sand is estimated using finite element analysis in this study. Methods: The range of thickness ratio (thickness of top dense sand layer divided by external diameter of ring) was kept between 0.25 and 1.5. The friction angle of the upper dense and bottom loose sand layers was maintained between 40° and 44° and 30° and 34°, respectively. In the case of skirted ring footing, the skirts are attached at the inner edge, outer edge, and both the edges, respectively. Results: According to the results, the bearing capacity increases with an increase in either the friction angle of upper dense and lower loose sand layers or the thickness ratio. A double-skirted ring footing was observed to provide the greatest bearing capacity, followed by footing with skirts attached at the outer and inner edges, respectively. Conclusion: To sum up, the bearing capacity of the ring footing was higher than the circular footing for the given friction angle of the top and bottom layer and thickness ratio.

Study on different reinforcement methods of inclined liquefiable site

The existing earthquake damage investigations indicate that the lateral spreading of site is more likely to occur in inclined liquefiable site under earthquake, therefore the way of foundation reinforcement is often adopted to reduce the lateral spreading phenomenon of inclined liquefiable site. In order to study the reinforcement principle of inclined liquefiable site by the two reinforcement methods of concrete pile and gravel pile, based on the verified numerical model of free field model, the model of concrete pile reinforcement and crushed rock pile reinforcement was established, the dynamic response and reinforcement effect of two different reinforcement methods in inclined liquefiable site were analyzed, and the effects of buried depth and pile diameter on the earthquake dynamic response and the effects of different reinforcement models are discussed. It is found that the concrete pile has a better reinforcement effect on inclined liquefiable site than gravel pile under the same buried depth and pile diameter. When the concrete pile is adopted to reinforce the inclined liquefiable site, the reinforcement effect is better when the concrete pile are embedded in dense sand layer at a certain depth; When adopting the gravel pile to reinforce inclined liquefiable sites, the effect is better when only clay and loose sand layer are reinforced, moreover, increasing the diameter of gravel piles greatly improves the reinforcement effect of inclined liquefiable sites. The pile group reinforcement model can greatly reduce the lateral displacement of site soil compared with the single pile reinforcement model.

Sumatra-fault Earthquake Source Variation for Analysis of Liquefaction in Aceh, Northern Indonesia

Introduction: Areas that are situated on active faults experience a severe risk of earthquakes. During earthquake shocks, pore water pressure increases and soil shear strength decreases, resulting in water saturation of the loose sand layer and the possibility of liquefaction. Banda Aceh is a city on Sumatra Island, northern Indonesia, located on active faults that run along Sumatra Island. Aims: To ascertain the liquefaction potential in Banda Aceh City, it is important to conduct a research analysis on the soil profile below Banda Aceh City. This research focused on earthquake acceleration to determine the strength capacity of soil to withstand loads and wave propagation to minimize infrastructure failure. Methods: The liquefaction potential of Banda Aceh was determined by analyzing N-SPT records from three sites using three different approaches. This liquefaction study considered the cyclic loading and seismic acceleration associated with the Sumatra-fault earthquake source, which has a design magnitude of Mw 9.3. Results: The results of cyclic loading showed that Banda Aceh City has liquefaction potential. Using the 3D surface approach, soil profiling gives a cross-vault-shaped soil profile that shows liquefaction potential starting at 2.5 m and the hard soil layer found at 6.0 to 10 m. Conclusion: This study examined the liquefaction potential of Banda Aceh City. The research was carried out using a simplified approach to determine the liquefaction potential index (LPI) at three-dimensional cross faults of discontinuous sand generated by the Sumatra-fault acceleration of earthquake.

Three-dimensional finite element analysis of the effect of soil liquefaction on the seismic response of a single pile

Soil liquefaction is considered as one of the most significant issues that leads to failure of shallow and deep foundations. However, the effect of liquefaction on the seismic response of piles still poorly understood. Therefore, this research examines the seismic response of a pile embedded in soil stratum of saturated fine-grained soils. Midas GTS/NX is used to carry out the number assessment. In addition, the modified UBCSAND soil constitutive model is used to depict the nonlinear features of saturated sand during earthquake waves. The developed three-dimensional model is first validated using the results of a shaking table test of a pile embedded in coarse-grained soil, where good agreement is obtained between the finite element model and the experimental results for the displacement, acceleration, and liquefaction ratio demonstrated good agreement. Furthermore, the orientations of the vectors produced by the numerical study, that matched a global circular flow characteristic, reflected the movement of the liquefied soil all around pile. The findings showed a considerable decrease in the pile frictional resistance during the seismic events as a consequence of increasing the pore water pressure and subsequent liquefaction. Regarding this, before the soil was entirely softened, resistance due to friction was observed near the ground, in correspondence with the loose sand layer. In addition, the pile showed excessive settling, which is due to the decrease of the soil stiffness caused by the increase of the pore water pressure. The results of this research provide an insight into the mechanism of the behavior of pile in saturated coarse-grained soils and thus, it helps to improve future research on the topic and also achieve better design of piles embedded in saturated coarse-grained soils.

A Soil-Pile Response under Coupled Static-Dynamic Loadings in Terms of Kinematic Interaction

Abstract Although the axial aptitude and pile load transfer under static loading have been extensively documented, the dynamic axial reaction, on the other hand, requires further investigation. During a seismic event, the pile load applied may increase, while the soil load carrying capacity may decrease due to the shaking, resulting in additional settlement. The researchers concentrated their efforts on determining the cause of extensive damage to the piles after the seismic event. Such failures were linked to discontinuities in the subsoil due to abrupt differences in soil stiffness, and so actions were called kinematic impact of the earthquake on piles depending on the outcomes of laboratory tests and other numerical analyses. In this research, numerical modeling is used to explore the kinematic forces created in a single pile erected in two sand layers under two different conditions (dry and saturated states). Based on the obtained results from the physical model, the maximum bending moment was observed at a depth around 200 mm below the ground surface in the loose sand layer, then these values gradually reduced until it becomes negative in the dense sand layer. It has been demonstrated that this modeling may be used to predict how a pile foundation would respond to “kinematic” loading generated by ground movements during a seismic event. Consequently, the current findings could be used in the design and construction of bored aluminum or steel piles in Al-Karbala soil.

Nonlinear Solid–Fluid Coupled Seismic Response Analysis of Layered Liquefiable Deposit

A seismic response analysis of layered, liquefiable sites plays an important role in the seismic design of both aboveground and underground structures. This study presents a detailed dynamic site response analysis procedure with advanced nonlinear soil constitutive models for non-liquefiable and liquefiable soils in the OpenSees computational platform. The stress ratio controlled, bounding surface plasticity constitutive model, PM4Sand, is used to simulate the nonlinear response of the liquefiable soil layers subjected to two seismic ground motions with different characteristics. The nonlinear hysteretic behavior of the non-liquefiable soil under earthquake excitations is captured by the Pressure Independent Multi Yield kinematic plasticity model with a von Mises multi-yield surface. The soil elements are modelled utilizing the solid–fluid fully coupled plane-strain u-p elements. The seismic response of the layered liquefiable site in terms of the development of excess pore water pressure, acceleration, ground surface settlement, and stress–strain and effective stress path time histories under two representative earthquake excitations are investigated in this study. The numerical results indicate that both the characteristics of ground motions and the site profile have a significant influence on the dynamic response of the layered liquefiable site. Under the same intensity of ground motion, the loose sand layer with a 35% relative density is more prone to liquefaction and contractive deformation, which causes irreversible residual deformation and vertical settlement. The saturated soil layer can effectively filter the high-frequency components and amplify the low-frequency components of ground motions. Moreover, the liquified site produces a 40% post-earthquake consolidation settlement after the excess pore pressure dissipation.

Near-surface resistivity imaging using resistivity Tomography in some most impacted areas due to the 2018 Earthquake in North Lombok Island

The Lombok earthquake in July 2018 caused considerable damage to public facilities and residential areas. Most of the houses in the north of the island of Lombok were damaged by the 6.9 magnitude earthquake. We want to know what parameters cause houses and buildings in North Lombok not to experience a severe liquefaction process. We used near-surface tomographic resistivity imaging to characterize the subsurface of North Lombok to map the subsurface of the most affected areas in North Lombok. The geological condition of northern Lombok is the most vulnerable area to liquefaction due to volcanic loose sand layers, shallow groundwater, and thick deposits. However, almost all subsurface images from resistivity tomography from North Lombok show limestone layers at shallow depths, which may play an important role as a protective layer from liquefaction phenomena in this area.

The slenderness ratio effect on the response of closed-end pipe piles in liquefied and non-liquefied soil layers under coupled static-seismic loading

AbstractThis study presents the findings of a 3D finite element modeling on the performance of a single pile under various slenderness ratios (25, 50, 75, 100). These percentages were assigned to cover the most commonly configuration used in such kind of piles. The effect of the soil condition (dry and saturated) on the pile response was also investigated. The pile was modeled as a linear elastic, the surrounded dry soil layers were simulated by adopting a modified Mohr-Coulomb model, and the saturated soil layers were simulated by the modified UBCSAND model. The soil-pile interaction was represented by interface elements with a reduction factor (R) of 0.6 in the loose sand layer and 0.7 in the dense sand layer. The study was compared with the findings of 1g shaking table tests which were performed with a slenderness ratio of 25. In the validation case, there was a clear correlation between the laboratory findings and the numerical analyses. It was observed that the failure mechanism is influenced by the soil condition and the slenderness ratio to some extent. Under the dry soil condition, no base pile deformation was observed; However, tip pile movement was observed under the saturated soil condition with pile slenderness ratios of 25 and 50. The findings of this study are also aimed to include an approximation of the long-term deformations at the ground surface which has experienced shaking.

Seismic behaviour of piles in non-liquefiable and liquefiable soil

This paper investigates the nonlinear soil–pile–structure interaction employing three-dimensional nonlinear finite element models verified with the results of large-scale shaking table tests of model pile groups-superstructure systems. The responses of piles in both liquefiable and non-liquefiable soil sites to ground motion with varying intensities were evaluated considering both kinematic and inertial interaction. The calculated piles and soil responses agreed well with the responses measured during the shaking events. The numerical models correctly predicted the different pile deformation modes that were exhibited in the experiments. The finite element analysis was then employed to perform a parametric study to evaluate the kinematic and inertial effects on the piles' response, considering different ground motion Intensity and piles characteristics. It was found that the bending moment of piles in the liquefiable site increases significantly, compared to the non-liquefiable site, due to the loss of lateral support of the liquified soil, and the maximum bending moment occurs at the interface between the loose and dense sand layers. The inertial interaction contributes the most to the bending moments at the pile top and the interface between the top clay and liquefied loose sand layers. For piles with a larger diameter, the bending moment due to kinematic interaction increases significantly, and the bending moment distribution corresponds to short (rigid) pile behaviour. In addition, the piles at the saturated site displace laterally as a rigid body during strong ground motions because the pile base loses the lateral support due to the soil liquefaction. Finally, the kinematic interaction effect becomes more significant for piles with higher elastic modulus.

Pressure Settlement Behaviour and Bearing Capacity of Asymmetric Embedded Plus Shaped Footing on Layered Sand

The aim of the present numerical study was to analyse the pressure settlement behaviour and bearing capacity of asymmetric plus shaped footing resting on loose sand overlying dense sand at varying embedment depth. The numerical investigation was carried out using ABAQUS software. The effect of depth of embedment, friction angle of upper loose and lower dense sand layer and thickness of upper loose sand on the bearing capacity of the asymmetric plus shaped footing was studied in this investigation. Further, the comparison of the results of the bearing capacity was made between the asymmetric and symmetric plus shaped footing. The results reveal that with increase in depth of embedment, the dimensionless bearing capacity of the footings increased. The highest increase in the dimensionless bearing capacity was observed at embedment ratio of 1.5. The increase in the bearing capacity was 12.62 and 11.40 times with respect to the surface footings F1 and F2 corresponding to a thickness ratio of 1.5. The lowest increase in the dimensionless bearing capacity was observed at embedment ratio of 0.1 and the corresponding increase in the bearing capacity was 1.05 and 1.02 times with respect to the surface footing for footings F1 and F2 at a thickness ratio of 1.5.

Passive Resistance of Retaining Walls Supporting Layered Cohesionless Backfill: A Plasticity Approach

A theoretical model was developed to determine the seismic passive earth pressure on vertical cantilever retaining walls supporting a two-layered cohesionless backfill with a loose sand layer overlying a dense sand stratum. Seismic inertial forces were considered in the analysis by employing the classical pseudostatic approach. The theoretical formulation was developed based on the method of stress characteristics, which does not require any predefined failure mechanism to initiate the analysis. The charts are presented in terms of passive earth pressure coefficient, which includes the contribution of both the layers. In addition to the generation of the actual failure mechanism, rapid mobilization of stresses at the layer interface and at the wall backface is presented in the form of normalized stress contours. The failure surface and the passive earth pressure distribution behind the wall were found to be nonlinear, with different input parameters. The passive resistance of backfill soil decreased in the presence of the loose sand layer resting on the denser soil stratum.

Seismic axial behaviour of pile groups in non-liquefiable and liquefiable soils

This paper investigates the axial load transfer during seismic events for pile groups installed in loose and dense sand layers. The analysis was conducted employing three-dimensional (3D) nonlinear finite element models (FEM) that were validated using the results from shaking table tests of a model superstructure supported by a pile group installed in saturated (liquefiable) and dry (non-liquefiable) soil profiles. The FEM was employed to explore the axial load transfer at the liquefiable and non-liquefiable tests. The results of the liquefiable test demonstrated that the excess pore water pressure and associated liquefaction during the shaking caused dramatic decrease in the shaft friction resistance. Nonetheless, positive shaft friction was observed through the loose sand layer until the soil becomes fully liquefied. In addition, the end bearing forces decreased dramatically, and the pile exhibited excessive settlement, which mobilized additional end bearing resistance. At the non-liquefiable test, the pile experienced compression and tension loading cycles, but the loads were less than its static capacity. The effects of ground motion intensity, pile diameter, and thickness of the loose sand layer on the load transfer mechanism were also evaluated. It was found that as the pile diameter increased, higher excess pore water pressure developed in the dense sand, which reduced the bearing pressure. Also, as expected, the reduction in shaft resistance was higher as the thickness of the loose (liquefiable) sand layer increased, especially for piles with a small diameter. For the non-liquefiable soil, the strain in the soil increased for larger pile diameters, and consequently, the bearing forces decreased but later increased as the pile settlement mobilized higher resistance.

Impacts of Fixed-End and Flexible Boundary Conditions on Seismic Response of Shallow Foundations on Saturated Sand in 1-g Shaking Table Tests

Abstract A key consideration in physical modeling of seismic problems in geotechnical engineering is the impact of the model container boundaries on the soil layer response. The container boundaries may alter the stress-strain behavior from free-field conditions through the possible reflection of incident shear waves and generation of P-waves within the soil layers. In this study, 1-g shaking table experiments were performed to evaluate the impacts of container boundary conditions on the response of saturated loose sand layers subjected to harmonic base motions (1) in a free-field condition, (2) with a shallow foundation, and (3) with a shallow foundation supporting a single degree of freedom superstructure. The sand layers were formed in a newly fabricated laminar shear container that can be converted to a rigid box by adding elements to the end walls. Acceleration, excess pore water pressure, and settlement measurements demonstrate that the rigidity of the container boundaries can have a major impact on seismic behavior of the models. In particular, the observed permanent settlement of the foundations increased by 58–115 % in the soil models with fixed-end (or rigid) boundaries compared with those in soil models with flexible conditions. This was attributed to nonuniformity of strains near the fixed-end container boundaries and a higher level of energy trapped inside the model. Furthermore, higher spectral accelerations were captured in tests with fixed-end boundary conditions compared with those with flexible boundary conditions. Scaling issues associated with 1-g shaking table testing were also discussed.

Applications of deep mixing technology for mitigating earth-quake disaster in Urban Area

Many earthquakes take place every year in Japan, in which the 1995 Hyogoken-Nambu earthquake and the 2011 Tōhoku earthquake induced both a humanitarian crisis and massive economic impacts. As liquefaction, which occurs in a loose and saturated sand layer, induces quite large damages of infrastructures, the importance of liquefaction mitigation has been emphasized to minimize earthquake disasters for many years. Many kinds of ground improvement techniques based on various improvement principles have been developed for earthquake disaster mitigation. Among them, the deep mixing technology has been often applied to liquefaction mitigation. In the techniques, in-situ soil is mixed with binder by several types of methods: mechanical mixing, high pressure injection mixing and combined mixing. The high applicability of the method was confirmed in several earthquakes, including the 1995 Hyogoken-Nambu earthquake and the 2011 Tōhoku earthquake. In this paper, the outline of the deep mixing method and some applications of the deep mixing method to earthquake disaster mitigation are briefly introduced.

Seismic performance of earth dams founded on liquefiable soil layer subjected to near-fault pulse-like ground motions

Liquefaction-induced flow slide is one of the main reasons to cause severe damage of embankment dams. In this paper, the effect of near-fault pulse-like ground motions on the seismic performance of earth dams susceptible to liquefaction-induced damage is quantitatively investigated. A generic earth dam founded on a liquefiable soil layer is modeled in OpenSees based on a finite-element approach. Two suites of near-fault ground motions, namely one pulse-like and one ordinary suite, respectively, are selected from the NGA-West2 database. Both selected ground-motion suites have statistically comparable earthquake magnitudes, rupture distances, and shaking intensities. Dynamic analyses are then conducted for the earth dam subjected to both ground-motion suites. Comparative results indicate that the pulse-containing ground motions have a greater potential to trigger liquefaction in the loose-sand layer as compared to the ordinary near-fault motions. As to post-liquefaction performance, using the pulse-containing ground-motion suite leads to an enlarged distribution of both maximum lateral displacements and crest settlements of the earth dam, in comparison with those caused by the ordinary ones. Therefore, when subjected to pulse-like ground motions, an earth dam at sites susceptible to liquefaction hazard would possibly suffer an exacerbated post-liquefaction deformation and damage. Besides, it is found that the resultant lateral displacements and crest settlements for the pulse-like suite are strongly correlated to the duration and cumulative-energy parameters of ground motions.