Saturated Loose Sand Research Articles

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.

Static liquefaction as a form of material instability in element test simulations of granular soil

Static liquefaction is a form of unstable behaviour of granular soil. It is most common in saturated loose sands under monotonically loaded undrained conditions. Predicting static liquefaction using an elastic-plastic model that incorporates the non-associated plastic flow rule and strain hardening is possible. The article briefly describes the unstable behaviour of saturated sand in undrained conditions under a monotonic load. A simple elastic-plastic model with deviatoric hardening and a Drucker–Prager load surface is presented. The constitutive relationships were programmed in a Python script. Simulations of triaxial tests under mixed stress-strain control demonstrated the model’s ability to predict various undrained sand responses, including fully stable responses (no liquefaction) and partial and complete liquefaction under triaxial compression and tension. Predicting static liquefaction is possible by properly selecting the proportions of the parameters involved in plastic potential and loading functions and the parameter A used in the deviatoric hardening rule of hyperbolic type.

Effects of pre-shearing and pre-consolidation histories on liquefaction behaviour of saturated loose sand: DEM investigation

PurposeThe study aims to investigate the effects of pre-loading histories (pre-shearing and pre-consolidation) on the liquefaction behaviour of saturated loose sand via discrete element method (DEM) simulations.Design/methodology/approachThe pre-shearing history is mimicked under drained conditions (triaxial compression) with different pre-shearing strain levels ranging from 0% to 2%. The pre-consolidation history is mimicked by increasing the isotropic compression to different levels ranging from 100 kPa to 300 kPa. The macroscopic and microscopic behaviours are analysed and compared.FindingsTemporary liquefaction, or quasi-steady state (QSS), is observed in most samples. A higher pre-shearing or pre-consolidation level can provide higher liquefaction resistance. The ultimate state line is found to be unique and independent of the pre-loading histories in stress space. The Lade instability line prematurely predicts the onset of liquefaction for all samples, both with and without pre-loading histories. The redundancy index is an effective microscopic indicator to monitor liquefaction, and the onset of the liquefaction corresponds to the phase transition state where the value of redundancy index is one, which is true for all cases irrespective of the proportions of sliding contacts.Originality/valueThe liquefaction behaviour of granular materials still remains elusive, especially concerning the effects of pre-loading histories on soils. Furthermore, the investigation of the effects of pre-consolidation histories on undrained behaviour and its comparison to pre-sheared samples is rarely reported in the DEM literature.

Laboratory Study of Grouting Method to Improve Loose Sand Against Liquefaction

Liquefaction is a phenomenon when soil behaves like liquid during earthquake, and only occurs in saturated loose fine sand with grain size ranging from 0.2 to 0.02 mm. Liquefaction can be devastating, causing failure and deformation to buildings, roads, and bridges. Thus, research study on the application of grouting method for improving liquefiable fine sand in the laboratory is carried out. Grouting is a soil improvement method that injects cementing agent into a soil mass. After the grout has solidified, the soil density and consistency of the soil will improve. This research proves, mathematically and experimentally, that grouting can improve the density and consistency of liquefiable sand, thus reducing the liquefaction potential. Grouting liquefiable saturated sand basically compacts the soil, leading to consolidation as soil pore-water is dissipated during the grouting process. It is found that the volume of grout per unit volume of soil mass treated is directly proportional with the reduction of void ratio and increase in soil density.

Improvement of liquefaction potential in saturated sandy soil by CKD and bentonite

AbstractDue to the increase in earthquake activity in Iraq and Middle East during the last two decades, the study and understanding of probable destructive action and the best method to mitigate this effect became more important. So, many improvements and mitigation methods can be used. In this study, the use of permeation grout technique was adopted to prevent the existing soil condition in urban area by using cement kiln dust and bentonite clay. The tests were executed by using 1 g shaking table apparatus to simulate a sinusoidal motion (vibration) at specified different frequencies. The liquefaction phenomena were observed for loose saturated sand at 60 s, 25 s, and 10 s for 0.5 Hz, 0.75 Hz, and 1 Hz, respectively. After mitigation process, the soil liquefaction did not occur until 100 s, 60 s, and 30 s, for the same mentioned frequencies. Besides, the use of cement kiln dust decreases the liquefaction potential and increase the factor of safety.

Thermal Behavior of Saturated Sand at Different Relative Densities

Abstract With the proposal of a dual carbon goal in China, shallow geothermal energy as a kind of clean energy has been gradually promoted and applied. At the same time, more and more geotechnical workers have gradually paid attention to the influence of temperature on the mechanical characteristics of rock and soil mass. Existing experimental research has shown that the thermodynamic behavior for cohesive soil such as clay and silt is relatively mature but is relatively less mature for noncohesive soil, especially for sand. Based on the hollow cylinder triaxial specimen, a series of temperature-controlled triaxial tests have been carried out on saturated Fujian sand under different initial relative density and temperature conditions to capture the change of axial and volumetric strains for saturated sand specimen with increasing temperature. In addition, a bulk volumetric coefficient of thermal expansion of the sand specimen has been put forward, and the relationship between this coefficient and initial relative density also has been established. Then, the thermal deformation mechanism of saturated sand specimen has been revealed. After that, based on the test data during undrained shearing, the stress–strain relationship, deviatoric stress, and pore water pressure at peak state for loose and medium-dense saturated sand specimens have been explored, which can be used to provide some theoretical guidance for shallow geothermal energy and other temperature-related engineering applications.

Shaking Table Test on Mitigation of Liquefaction-Induced Tunnel Uplift by Helical Pile

The tunnels located in the shallow depths of loose saturated sand are significantly prone to liquefaction-induced uplift. Research works are, therefore, in progress to propose efficient techniques for mitigating uplift. In this study, 1 g physical modeling was used to assess the performance of helical piles for decreasing liquefaction-induced uplift. The effects of pile length, number of pile helixes, and the pile spacing in plan view were investigated. The uplift mechanism of the tunnel and helical pile system was also analyzed. The results demonstrate that the penetration of the helical piles into the dense layer underlying the superficial liquefiable sand has decreased tunnel uplift significantly. However, excessive close pile spacing along the tunnel resulted in shear surface interference, and the efficiency of the excessive number of helical piles decreased significantly. The detailed view of the uplift mechanism showed that utilization of the piles extended the transition phase of uplift during shaking. Helical piles can efficiently restrict the possibility of rapid uplift of the tunnel and shorten the duration of the primary uplift phase.

Numerical Modeling of the Effect of Desaturation on Liquefaction Hazard Mitigation

Earthquake-induced liquefaction is always a concern when the soil near the surface of a site is composed of relatively loose saturated sand. One of liquefaction mitigation methods is to induce gas bubbles into the deposit to reduce the degree of saturation. A coupled pore-scale model is presented herein to investigate liquefaction resistance of desaturated granular materials. The multiphase fluid, which mimics the behavior of air and water, is modeled using the multiphase single component lattice Boltzmann method. The solid phase is modeled using the discrete element method. The coupled framework was utilized to study the behavior of a soil deposit with the different degrees of saturation of 100%, 92%, and 82% during an earthquake loading. Based on the results of the simulations performed, liquefaction occurred in the fully saturated granular deposit and was not observed anywhere at depth in the desaturated deposits. It has also been found that reducing the saturation level from 100% to 92% significantly affects behavior. In desaturated deposits, higher average coordination number, lower pore pressure buildup, and slower effective stress decay were observed compared to fully saturated deposits. However, it turned out that a further reduction in the degree of saturation from 92% to 82% does not have a significant impact on the calculated parameters.

Investigation of Dynamic Compaction and Vibro-compaction to Mitigate Liquefaction: A Case Study

Liquefaction is one of the phenomena that can be triggered by an earthquake. Earthquake causes an increase in pore-water pressure in soil, reducing soil’s effective stress to zero or near-zero. In this state, the soil loses its strength and behaves like a liquid. This is known as liquefaction. When soil loses its strength, so it also loses its bearing capacity, causing damage or failure to structures. The soil type that is most prone to liquefaction is loose saturated fine sand. Such soil can be found in many of coastal areas in Indonesia. Indonesia is also one of the most earthquake prone countries in the world, hence liquefaction is one of the natural hazards that Indonesia has to face. Earthquake cannot be prevented, and its occurrence cannot be accurately predicted. Fortunately, liquefaction can be prevented by doing soil improvement to increase the sand density. The two most commonly used ground improvement techniques to increase sand density is dynamic-compaction and vibro-compaction. A case study from Aceh province, where both ground improvement techniques were used, is presented in this paper to compare the performance of dynamic compaction and vibro-compaction.

Mitigating liquefaction-induced displacements of shallow foundation using helical piles

During previous earthquakes, displacements of shallow foundations on liquefiable sites caused significant damage to overlying super-structures leading to casualties and catastrophic economic loss. Various countermeasures have been developed to lessen liquefaction-related damages while minimising cost and environmental impacts. This study aims to evaluate the use of helical piles as a possible technique to mitigate the settlement, tilting, and sliding of shallow foundations during seismic liquefaction. For this purpose, 12 1g shaking table tests were conducted on loose saturated sand under harmonic base input for (a) free-field condition, (b) a model foundation on the soil surface and (c) a model foundation underpinned by helical piles. The effects of input amplitudes and the number of helical piles were investigated in terms of acceleration response, excess pore-water pressure and foundation displacements. The results confirmed the satisfactory performance of helical piles in reducing shallow foundation displacements. In particular, the mean permanent settlements were reduced by 45 and 75% when using four and eight helical piles, respectively. Similar trends were observed for the shallow foundation permanent tilting and sliding: permanent tilting was reduced by 30 and 59% when using four and eight helical piles, respectively, while these results were 45 and 68% for the sliding.

Study to explore the use of Quality Factor of Body Waves (S waves) as a tool to investigate the soil liquefaction potential

Liquefaction events occur in deposits of saturated loose sand. Due to the incompressible nature of water, the pore water pressure rises dramatically. Built-up pressure pushes sand particles so that the effective stress between particles becomes zero. Or in other words, these sand particles do not touch each other in the water. So these sand particles are now ^swimming^ in water. These sand deposits behave like water, can flow, and do not have shear strength like normal soil. Not having shear strength means that this soil does not have the carrying capacity of the regular soil against loads above the ground such as buildings etc. This research investigates the possibility of using the Q (quality) factor of seismic waves to estimate the potential liquefaction of soil deposits. We employ Ottawa sand in the laboratory and apply various vibrations using small shaking tables. The results promise of possibilities of using the Q (quality) factor to estimate potential liquefaction.

Experimental study on the mechanism of sand boils and associated settlements due to soil liquefaction in loose sand

Sand boils are a recognized phenomenon associated with soil liquefaction. However, the exact conditions required to produce sand boils remain unclear, and sand boil-induced settlement is difficult to quantify. The mechanism of sand boils and associated settlements due to soil liquefaction is investigated in this study using model testing. Loose saturated sand deposit is made in a transparent acrylic cylinder applied with torsional shaking to reproduce liquefaction and sand boils. An acrylic circular plate, whose diameter is slightly smaller than the cylinder's inner diameter, is placed on the model ground surface to mimic a non-liquefiable layer. The gap allows the liquefied sand to be ejected, leading to sand boils. The mechanism of sand boils and induced settlements is investigated by the transient variations of the measured water pressure at the sidewall, the recorded plate settlement, and the monitored video image. The influence of different thicknesses of the non-liquefiable layer, the gap sizes, and the overburden pressures on the sand boil-induced settlement is assessed quantitatively. It is found that the thicker the non-liquefied layer or the smaller ejecta gap size, the lower the amount of ejecta and associated subsidence is observed. The overburden pressure had relatively minor effect on the amount of ejecta, but it affected the amount of consolidation settlement significantly. Based on the observation of test results, a theoretical ejection head is proposed to determine the condition leading to sand boils.

Assessment of Liquefaction-Induced Differential Ground Settlement and Lateral Displacement Using Standard Penetration Tests with Consideration of Soil Spatial Variability

One of the major risks to civil structures during an earthquake is the occurrence of liquefaction in loose saturated sand deposits. The main consequences of liquefaction include lateral spreading deformations and postliqufaction reconsolidation settlement. In situ tests, such as standard penetration tests (SPTs), commonly are used in one-dimensional models for estimating liquefaction-induced deformation, which provide ground deformation only at limited locations at which SPTs are performed. However, magnitudes of liquefaction-induced ground deformation within a specific site may exhibit significant spatial variation when subsurface soils are not homogeneous or when they vary spatially within a site. Therefore, using the ground deformations estimated from limited SPT locations to represent a whole site might provide misleading results and cannot properly predict the differential ground settlement or displacement, posing a significant risk to civil structures. To deal with this challenge, a novel approach was developed in this study for characterizing spatial variation of the soil lateral spreading displacement and reconsolidation settlement in a cross section of a specific site from limited SPTs with consideration of soil spatial variability along both depth and the horizontal direction. The proposed method was illustrated using both simulated data and real data.

New Method for Internal Pore-Water Pressure Measurements

Abstract The triaxial test is the most common procedure performed in a geotechnical laboratory to investigate the mechanical behavior of soils. However, often only global pore-water pressure (pwp) is measured at the bottom of specimen during conventional triaxial tests, which cannot detect the variation in internal pwp values to represent the true effective stress path adjacent to the failure surface. Here, a modified triaxial testing apparatus capable of measuring internal pwp within the soil using a filterless rigid piezometer (FRP) is outlined. To validate the effectiveness and capability of this novel test method, a series of consolidated undrained tests were conducted on saturated loose and dense sand. The FRP measurements provide a reliable pwp response, especially at pressures above 400 kPa where the FRPs have a faster response than the base transducer. Moreover, the internal pwp measured by FRPs during the initiation of shearing in loose sand can capture the rapid development of excess pwp before liquefaction or failure. The results also show that there are increases of 25 % in average peak strength of the loose specimen and 8 % in average residual strength of the dense specimen with internal pwp measurement, respectively, compared with only global pwp measurement because of the FRP installation. However, FRP installation appears to have no apparent effect on average peak strength of the dense specimen and average residual strength of the loose specimen. The new triaxial testing method can be applied to study the response and distribution of pwp at specific zones within the soil.

Influence of Excess Pore-pressure on the Seismic Response of Single and Closely Adjacent Structures on Saturated Sand

ABSTRACT This study was initiated following recognition that most structures exist, not in isolation, but in a setting where there is sharing of the common supporting foundation soil. Generally, structures exist in clusters, particularly in CBDs, with varying degrees of interaction. In truth, engineers deal with “systems”, where no structure exists in isolation. However, experimental evidence of the seismic response of multiple structures, particularly on saturated sand, is scarce since most studies are numerical and focus on stand-alone structures. The present study helps bridge this paucity of experimental work by developing an understanding of the seismic response of closely adjacent structures on saturated loose sand. A variety of configurations of single degree-of-freedom structures, with different fixed-base fundamental frequencies, were studied using a large laminar sand-filled box on a shake table. Recorded ground motions from the Canterbury earthquake sequence were used. The free-field and the stand-alone case for dry and saturated sand were studied as references. Differences between the response of stand-alone structures on saturated and dry sand are discussed. The response of a structure of focus, standing adjacent to neighbouring structures, on saturated sand is compared to that of the stand-alone case. In general, structures in a cluster experienced an attenuated response.

Shear strength behaviour of liquefiable sand of petobo on treated by agarose under direct shear test

Liquefaction process is associated with the loss of the shear strength of the saturated loose sands caused by strong earthquakes. Due to mitigitation of liquefaction hazard, an appropriate mitigation of liquefaction using environmentally friendly methods is critical and becoming increasingly important and unavoidable. The laboratory investigation was carried out to study the shear strength behaviour of liquefiable sand of Petobo treated by agarose on different concentration 1%,3% 5%. A series of direct shear test were conducted under three level of vertical stress 10 kPa, 20 kPa, and 30 kPa on the specimen. It was found that the optimum content of agarose which can be considered is at 1%-3%, using stress ratio (τ/σv) analysis shows that stress ratio decreases with increasing the vertical stress on the same agar content. The implication this result that the application of this method must consider variation of material source and characteristic, and the suitable level of vertical stresses.

Mitigating the impact of the static and cyclic loading on loose coastal saturated sands utilizing a waterproof and super-fast curing polymer

According to the dramatic increase in construction near loose coastal saturated soils, stabilizing these soils due to saturation conditions has always faced challenges. The main purpose of this investigation is to assess the static and dynamic performance of saturated sand stabilized with polyvinyl acetate powder - as a newly introduced source of polymers which besides helping vegetation grow, owing to its numerous features such as anti-acid, and most importantly waterproof properties and super-fast curing, is superior to its rival, traditional liquid polyvinyl acetate. This paper Analyzes the dynamic properties of soil stabilized based on the results of tensile test crack pattern, microscopic observations of matrix texture, and elasticity modulus of hysteresis loops. Lack of significant change in the strength of samples in saturated and dry conditions indicated waterproofness of polyvinyl acetate powder and revealed a significant rise in the compressive and tensile strength of saturated specimens up to 6% of the polymer. Also, an exponential correlation of unconfined compressive strength (UCS) with direct tensile strength (DTS) was found by data fitting. Also, evaporation tests showed a 7% reduction in evaporation rate with 6% polymer, which can confirm this polymer as a suitable option for improving vegetation. Shear modulus and damping ratio also increased and decreased up to 2% of the polymer, respectively, and by increasing the polymer beyond the 2%, dynamic properties were changed due to the zigzag crack pattern and consequently more ductility of the soil matrix, reduction of elasticity modulus, and increasing the thickness of polymer membranes between soil particles. Ultimately, the research results confirmed polyvinyl acetate powder's efficiency, especially with these tiny amounts, as a potential method for controlling saturated grounds.

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.

Flow liquefaction potential of loose sand: stress path envelope and energy-based evaluation

Flow liquefaction, which is characterized by sudden collapse following the unstable behavior of saturated loose sand, may lead to the most catastrophic consequence of all liquefaction-related phenomena. This note presents a systematic experimental investigation into the flow liquefaction potential of sand under various initial and cyclic shear conditions. The cyclic flow liquefaction responses are compared with the monotonic shear results under an identical initial testing condition. It is found that the effective stress path of a monotonic test appears to envelop that of its corresponding cyclic test. The energy-based liquefaction potential evaluation indicates that the accumulative dissipated energy is uniquely correlated not only with the pore pressure and axial strain induced in sand, but also with the degraded stiffness during cyclic loading. Furthermore, the energy capacity for triggering the flow liquefaction appears to be intimately related to the cyclic resistance of sand; this signifies the potential applicability of energy-based liquefaction potential evaluation using strength data available in conventional analysis.

Seismic response of a novel hybrid foundation for offshore wind turbine by geotechnical centrifuge modeling

Offshore wind farms are built in coastal areas prone to have earthquakes. When offshore wind turbines (OWTs) erected on cohesionless sediments are subjected to earthquakes, liquefaction might occur in the shallow deposits that might lead to severe overturning and settlement of the foundation structure. A novel hybrid foundation structure is proposed in this paper consisting of three major components: monopile, friction wheel, and suction bucket. This paper focuses on the performance of the hybrid foundation under earthquake loads. Hybrid foundation models with different dimensions were installed on both dry and saturated loose sand deposits and subjected to dynamic geotechnical centrifuge tests. Pore-water transducers were embedded in the soil to monitor its susceptibility to liquefaction. The dynamic responses of the superstructure were also monitored by linear variable differential transducers (LVDTs) and accelerometers. The experimental results indicated that the new hybrid foundation improved the ground liquefaction resistance. The extent of improvements was more significant in saturated sand than in dry sand. In saturated sand, it was observed that the hybrid foundation with larger bucket depth densified the surrounding soil and helped to mitigate the liquefaction. Consequently, the hybrid system showed responses of a stiffer foundation where the lateral displacement and settlement were reduced significantly.