Saturated Sand Research Articles

Soil Dynamic Constitutive Considering Post-Liquefaction Deformation and Reversible Pore-Water Pressure

In the seismic response analysis of liquefiable sites, the existing soil dynamic constitutive model is challenging to simulate saturated sand’s post-liquefaction deformation, and the current pore-water pressure buildup model cannot reflect the decrease in the actual pore-water pressure under unloading stress. We aim at these problems to propose a feasible and straightforward time-domain post-liquefaction deformation constitutive model through experimental analysis and theoretical research, consisting of reversible pore-water pressure. According to the dynamic triaxial test data, the regularities of large deformation stress and strain behavior of the saturated sand after liquefaction are obtained, and the corresponding loading and unloading criteria are summarized. Combined with the effective stress constitutive model proposed by the author, a soil dynamic constitutive that can describe saturated sand’s post-liquefaction deformation path is obtained. According to the test results, the model can simulate the deformation of saturated sand during the whole liquefaction process. The self-developed program Soilresp1D realized the dynamic response analysis of the liquefiable site, and the results were compared with the experimental results. It shows that the model based on the effective stress-modified logarithmic dynamic skeleton and post-liquefaction deformation constitutive can be directly applied to the dynamic response analysis of the liquefiable site.

New insight into enhanced transport of multi-component porous covalent-organic polymers with alkyl chains as injection agents for levofloxacin removal in saturated sand columns

Levofloxacin (LEV) is prone to be retained in aquifers due to its strong adsorption affinity onto sand, thus posing a threat to groundwater quality. In-situ injection technology for remediating LEV-contaminated soil and groundwater is still challenging owing to the lack of appropriate remedial agents. Herein, two novel multi-component porous covalent-organic polymers (namely, SLEL-1 and SLEL-2) with alkyl chains were constructed through Schiff-base reactions to adsorb LEV from an aqueous solution, in which the kinetics, isotherms, influenced factors were investigated. Plausible adsorption mechanisms were proposed through characterization and experimental analysis, including pore filling effect, π-π electron-donor-acceptor (EDA) interaction, hydrogen bonding force, hydrophobic-hydrophobic interaction as well as electrostatic force. In addition, response surface methodology (RSM) revealed the treatment optimization and reciprocal relationship within multi-variables. Furthermore, taking advantage of favorable dispersion and outstanding competitive behavior, SLEL-1 was established as an in-situ adsorptive agent in dynamic saturated columns on a laboratory scale to investigate the removal of LEV from water-bearing stratum. Overall, the findings of this work provided an insight into the fabrication of SLELs as long-term mobile and reusable adsorptive agents for practical in-situ applications in the future.

Effect of embedding depth on the monotonic lateral response of monopiles in sand: centrifuge and numerical modelling

An experimental campaign is conducted on a 100g centrifuged monopile model, impact driven, into saturated dense sand, down to three embedding depths, corresponding to three slenderness ratios of 5, 4 and 3. These models are instrumented with optical fibres to measure the bending moment profile along the monopile. A new method is developed to determine the experimental soil reaction curves by considering the distributed moment part from the measured bending moment. This distributed moment is assessed by the one-dimensional finite-element (1D FE) model of the PISA (pile soil analysis) method. The key features of this study are: (a) the monopile behaves from pure rotation to combined rotation–flexure as the slenderness ratio is enhanced from 3 to 5, inducing a less pronounced linear rotation–deflection response at ground level; (b) although the distributed moment assessed in the PISA project is very low, the developed method is useful to explore the experimental local behaviour of laterally loaded monopiles; (c) the 1D FE PISA model captures reasonably well the overall behaviour of laterally loaded centrifuged driven monopiles, even if it is less accurate for the local behaviour.

Purification of heavy metal chromium in saturated sand by artificial freezing: Mechanism and method optimization

Heavy metal pollution of soil has become one of the most common hazards in human development. The artificial freezing method, especially the progressive freezing method, can reduce heavy metal pollutants in the soil and promises to be an effective in-situ treatment of contaminated sites. This study analyzes the freezing purification mechanism of heavy metal contaminants in saturated sand and identifies three main factors that impact the effects of purification: freezing rate, initial concentration, and diffusion coefficient. Moreover, one-dimensional freezing tests are carried out by different freezing modes. The experimental results show that the heavy metal chromium could only be removed effectively with a slow freezing rate. By optimizing the freezing mode and freezing rate, a long section of soil was frozen and purified, with the maximum purification rate reaching 65.8%. This study shows that it is feasible to treat contaminated saturated sand by a gradual-cooling freezing method.

Cyclic shear stress-strain prediction of saturated sand based on the unrolled seq2seq model and scheduled sampling

The simulation of stress-strain response of saturated sand under numerous cyclic loadings is of significant interest to the development of constitutive model, and the simulation results form basic data for soil dynamic characteristic estimation, such as pore water pressure build-up, liquefaction strength, dissipated energy, and damping ratio. Traditional constitutive models are usually constructed based on complicated theories and assumptions, and numerous model parameters complicate the calibration process, which limits their application in the rapid evaluation of soil dynamic properties. Although the data-driven model can effectively avoid these problems, it's difficult for a conventional data-driven model to simulate under numerous cyclic loadings due to the simpleness of the model and training strategy. In this study, a novel data-driven constitutive model is proposed to well simulate the stress-strain behaviour of saturated sand and rapidly estimate soil properties only based on a small amount of experimental data. The unrolled sequence-to-sequence recurrent neural network (RNN) is first introduced in soil data-driven constitutive model to modify conventional one-step ahead prediction to multistep one, and a novel RNN training strategy named scheduled sampling, is introduced to reduce the discrepancy of the model behaviour in the training phase and that in testing due to the unknown stress-strain information at next step. The performance of the proposed model is verified through a dataset collected from a triaxial test along with the comparison with feedback neural network, one-step RNN, and non-data-driven constitutive model. Based on the simulation of stress-strain, the dynamic properties of saturated sand are estimated. Both the simulation and estimation results show that the proposed method performs reasonably well.

Experimental Study on the Mechanical Properties of Saturated Tailing Sand with Different Particle Sizes

The particle size distribution of tailing sand will affect its strength, deformation and mechanical properties, thus affecting the overall safety and stability of the tailing dam. The main purpose of this study is to obtain the gradation of sand samples with the best shear strength and seepage effect by studying the influence of particle size on the mechanical properties of saturated iron tailing sand. The tailings were sampled from Yangjiawan tailing reservoir of Chengchao Iron Mine, and the moisture content test, particle size distribution analysis and scanning electron microscope test (SEM) were carried out on the samples. It is measured that the average moisture content of the tailings is 12%, and the gradation is generally poor. SEM was used to observe the microstructure of the three kinds of particles, and it was found that these structures were more likely to be damaged under load, which was not conducive to the improvement of the strength of tailings. Through the consolidation undrained test of five particle size groups, it is concluded that the larger the particle size is, the greater the shear strength will be. The Cu indicates the width of the distribution range of the grading curve, the Cc indicates the distribution pattern of the grading curve, and they are both used to indicate the particle grading of sand. Then, by changing the sample gradation, the coefficient of uniformity (Cu) and the coefficient of curvature (Cc) of the gradation parameters are controlled to remain unchanged, respectively. By changing another parameter, it is found that there is a close relationship between the coefficient of uniformity and the coefficient of curvature and the shear strength through the triaxial shear action, three kinds of tailing sand gradation with better strengths are obtained. Based on the study of strength characteristics, the permeability coefficients of three kinds of tailing sands are calculated by using the seepage failure test. The test results show that when the coefficient of uniformity is 5.5 and the coefficient of curvature is 1, the permeability coefficient is 1.699 × 10−3 cm/s, and the shear strength and permeability of the sample are the best.

The influence of sedimentary architecture on the formation of earthquake-induced liquefaction features: A case study in the New Madrid seismic zone

This study is aimed at understanding how the arrangement of fluvial sedimentary deposits and their physical properties influences the formation and location of liquefaction features resulting from earthquake strong ground motions. The study site is located in the Mississippi River floodplain in the New Madrid seismic zone of the central United States, an area that hosts abundant liquefaction deposits resulting from both historic and prehistoric earthquake sequences. We combine satellite imagery, electrical resistivity tomography, soil textural analyses and ditch exposures of liquefaction features to develop a model of how the spatial distribution of sedimentary deposits, such as point bars, overbank, levee, backswamp and channel-fill, contribute to pore pressure build-up and subsequent development of liquefaction features, such as sand dikes and sand blows, as water and entrained sediment forcefully flow toward the surface. The model helps to explain (1) the abundance of earthquake-induced liquefaction features present in the Mississippi River valley, where fine- to medium-grained saturated sands are interbedded with or overlain by fine-grained portions of channel-fill, levee, overbank or backswamp deposits, and (2) the concentration of liquefaction features along the margins of abandoned-channel fill, point bar and overbank deposits, as seen in other locations worldwide. This understanding can contribute to identifying areas where liquefaction may be a threat to engineered structures and limiting the extent of areas in which detailed engineering geology measurements (e.g., in situ testing) may be necessary.

Seismic Response of Utility Tunnels with Different Burial Depths at the Non-Homogeneous Liquefiable Site

Damage to underground structures induced by soil liquefaction under cyclic loads such as earthquakes has long been an important issue in underground engineering practice. In this paper, five models are developed using Flac3D software to analyze the effect of burial depth on the force, deformation characteristics, and uplift behavior of utility tunnels in the non-homogeneous site containing a liquefied layer. The cyclic shear property of saturated sand and the increase in pore water pressure during the earthquake are modeled using a cyclic load-volume strain increment model, using Shell-Type structural elements to model underground utility tunnels, and by using plastic hinges to represent the bending moment capacity of member’s joints. Numerical results show that for shallow-buried utility tunnels, increasing the burial depth increases the bending moment, shear force, and deformation of the structure while significantly reducing its uplift. Therefore, for high-strength shallow-buried utility tunnels, appropriate increase in burial depth can improve its seismic safety.

On the cyclic stability diagram of offshore wind turbine supported on multiple foundations in saturated dense sand

This study explored the issue of cyclic loading on a tripod suction bucket foundation system in silty sand through three-dimensional (3D) finite element (FE) models by developing a cyclic stability diagram, in which the response is presented in terms of the average load ratio (ALR) and the cyclic load ratio (CLR), and three regions are identified: (1) no cyclic load effects, (2) cyclic load effects, and (3) severe load effects after approximately 1000 one-way load cycles. The simulations, based on dynamic FE analysis, enabled the identification of the ‘’self-healing’’ phenomenon due to enhanced stiffness degradation of a foundation in tension by incorporating the correct estimate of the soil-foundation interface and geometric nonlinearities. In addition, an approximating expression for the calculation of the accumulated rotation of offshore wind turbine (OWT) supported on multiple foundations is provided as a function of ALR and CLR utilizing modified least-squares method (MLSM). The proposed expression leads to notable improvements in the prediction of induced rotation of OWTs such that the coefficient of determination, R2, was obtained ranging from minimum value of 0.89 to a maximum value of 0.99. This study suggests that the salient features of multiple foundations must be considered in the design process of offshore wind turbines.

Study on the liquefaction characteristics of saturated sands by millisecond delay blasting

The liquefaction in saturated sands under blast loading is an important research topic in geotechnical engineering. The effect of blast loading on the liquefaction characteristics of saturated sands was studied through a large-scale millisecond delay blasting (MDB) liquefaction field test. Based on the field test, a numerical model was established by the LS-DYNA finite element program to study the propagation of blast waves and the effects of explosive mass, scaled distance, and blast delay on the liquefaction characteristics of saturated sands. The results show that there was a significant sand boiling phenomenon in saturated sands under blast loading, and high values of the excess pore water pressure ratio were observed at monitoring points during the field test. The numerical simulation results show that the scaled distance and the blast delay significantly affected the excess pore water pressure. While the blast delay increased from 110 ms to 330 ms, the excess pore water pressure of the central area can increase by more than 18%. Based on the field and numerical tests, an empirical equation is established that can take into account both the scaled distance and blast delay, which provides a theoretical basis for future large-scale liquefaction sites by MDB.

The Attenuation Ability of Saturated Joints Filled with Granular Materials under High-Amplitude Stress Wave Loading

Existing experimental evidence shows that the propagation of explosive waves in the free fields of soils is remarkably affected by the degree of saturation. In the surrounding rocks of underground protective structures, the underground water is normally unavoidable, which is supposed to reduce the isolation efficiency of a passive antiblast barrier. To investigate the effect of water saturation on the stress wave attenuation ability of infilled joints, impact tests were carried out on artificial joints filled with dry and saturated granular materials using a split Hopkinson pressure bar (SHPB). The test results revealed that under the same conditions, the stress and energy transmission coefficients of the waves crossing saturated sand-filled joints were about 3.16–4.13 times and 9.75–11.4 times those of joints filled with dry sand, respectively. The dynamic stress-strain relationship of the filling layer during the impact process and the crushing index of the infill were analyzed. The results showed that the compressibility and the granular crushing index of the dry sand were much greater than that of the saturated sand, and the dynamic stress-strain relationship of the dry sand exhibited three-stage nonlinear characteristics. The experimental results quantitatively uncovered the serious adverse effect of water on the wave absorption properties and markedly diminished the potential of the filled joints as a wave elimination barrier, which should be a matter of great concern in the design of underground protective structures.

Influence of grading and fabric arising from the initial compaction on the geomechanical characterisation of compacted copper tailings

Tailings dams constructed using the upstream method are generally less stable, because of its operational and constructive approach; this presents increased risks, which is the reason why such structures are being closed in Brazil. A feasible option to ensure the safety of closing operations in such dams consists of extracting tailings from behind the dam (reservoir), reducing moisture content through dewatering and compacting it into stable stacks. This demands knowledge of the compacted material's response. Thus, the present research assesses the mechanical response of compacted copper ore tailings extracted from two different sampling locations within the dam reservoir (i.e. about to be de-characterised) from northern Brazil. For this, drained and undrained triaxial compression tests were carried out on compacted dewatered dense, medium and loose specimens, which were assembled using the tailings retrieved from upper and lower beaches to evaluate the influence of grading, as well as the influence of the fabric arising from the initial compaction on the critical state lines (CSLs) of these saturated non-plastic silty sand tailings. The results indicated that the critical state parameters, in the υ–ln p′ space, are dependent on the fabric arising from the initial compaction. Distinct CSLs, which are all curvilinear and parallel to each other, were found in the research.

Energy-based assessment of cyclic liquefaction behavior of clean and silty sand under sustained initial stress conditions

In practical engineering, sand deposits containing some finer particles usually sustain an initial static shear stress. This study investigates the sustained initial stress effect on liquefaction response of saturated sand through conducting cyclic undrained triaxial tests. The obtained response of sand samples containing a small amount of silty fines is compared to that of clean sand under similar relative densities. The results exhibit that various stress conditions result in two response patterns named as cyclic mobility and residual deformation accumulation. It is shown that the addition of silty fines can either enhance or reduce the cyclic liquefaction resistance of sand, depending on the fines content, while the sustained initial stress plays a beneficial role in resisting cyclic failure for samples with or without the addition of fines under otherwise identical testing conditions. It is also found that the dissipated energy accumulated in both the silty and clean sand follows a power-law relationship to the generated residual pore pressure during cyclic loading. A unified relationship is further established between the liquefaction resistance and dissipated energy, which may be useful for developing an energy-based assessment of in-situ soils using strength data from laboratory experiments.

Seismic Response of a Liquefiable Site-Underground Structure System

To study the dynamic response of a saturated sand-underground structure system subjected to earthquakes, a series of shaking table tests with a geometric scale ratio of 1/30 were conducted. Based on the experimental acceleration records of testing soil deposits, the relationship between dynamic shear stress and horizontal soil displacement was analyzed by the 1D shear beam inverse calculation method. Meanwhile, the development law of the equivalent dynamic horizontal subgrade reaction coefficient and the dynamic strain of the sidewall in the underground structure has also been discussed. The testing results indicate that the dynamic shear stress of the soil deposit under the bottom plate of the underground structure is larger than that of the soils surrounding the sidewall and above the roof plate; in addition, the soil displacement tends to decrease with the buried depth. The dynamic shear stress–displacement hysteretic loop of the soil deposits tends to be plump as the input amplitude increases. The spectral characteristics of ground motions obviously influence both the dynamic shear stress–displacement hysteretic curve and the excess pore water pressure ratio of saturated sand soil, especially under medium and strong excitations. The equivalent dynamic horizontal subgrade reaction coefficient decreases with the increase of soil depth, and the difference between the coefficient above and underneath the underground structure model can reach 7.589 MN/m3. On the contrary, the equivalent dynamic horizontal subgrade reaction coefficient decreases with the increase of the input amplitude of ground motions, and the maximum reduction ratios of the coefficient are 74.4%, 66.7%, and 47.3%, corresponding to the El-Centro, Kobe, and Wolong ground motions, respectively. The soil liquefaction has a certain effect on the equivalent dynamic horizontal subgrade reaction coefficient. In general, the dynamic strain at the top of the sidewall in the underground structure is higher than that at the bottom of the sidewall, which illustrates that the deformation of underground structures is in good agreement with the seismic deformation mode of soil deposits.

Multi-objective optimisation of tunnel parameters in a liquefied sand lens under seismic loads

If underground structures built close to the surface lie within a liquefied sand lens, they will be significantly damaged in the case of a seismic event. To achieve an optimal design in terms of depth, diameter and tunnel lining thickness, it is important to consider factors such as ground subsidence, bending moment and axial forces exerted on the tunnel lining. This study intended to perform multi-objective optimisation of relevant tunnel parameters within a liquefied sand lens location under seismic loads. The Flac3D software was used to model the saturated sand lens and determine changes in pore water pressure and effective tension after lens liquefaction. An artificial neural network was used to find optimal values in the genetic algorithm. All optimal design points were obtained per the target function with a revised non-dominated sorting genetic algorithm II algorithm. The results pertaining to depth, diameter and tunnel lining thickness were in opposition to one another, as reducing ground subsidence resulted in increased bending moment and axial force exerted on the tunnel lining. According to the results, it is possible for the designer of the tunnel to use Pareto charts in order to determine the optimal values regarding tunnel depth, diameter and lining thickness within the liquefied sand lens.

Effects of sand and slurry characteristics on pressure infiltration of bentonite slurry into sand

Two series of experiments were carried out to examine pressurised bentonite slurry infiltration into saturated sand columns. Three types of sand were examined, and water–bentonite and water–bentonite–sand slurries were used in series 1 and 2, respectively. Series 1 investigated the effect of sand particle size and series 2 examined the effect of the fine-sand particle content in the slurry. Scanning electron microscopy (SEM) imaging was used to observe the morphological features of the dry slurry-infiltrated sand samples. A solution for the infiltration distance during mud spurt for water–bentonite–sand slurry infiltration was verified using the data from series 2. The infiltration test results showed that the hydraulic conductivity of the slurry-infiltrated coarse sand for slurry in series 2 was lower than that in series 1. Visual observations and the SEM images showed that sand particles were bound to a bentonite film, indicating that, during infiltration, the channels for fluid flow among the sand particles are blocked by the bentonite particles adhered to the sand particles. The solution for the infiltration distance during mud spurt for water–bentonite–sand slurry infiltration showed good agreement with the experimental results.

Effects of physical properties and undrained cyclic shear conditions on the pore water pressure responses of saturated sands and clays

For clarifying the effects of relative density (Dr) and Atterberg’s limits on the cyclic shear-induced pore water pressure properties of soils, sandy soils with similar index properties and clayey soils with different Atteberg’s limits were collected from Vietnam and Japan and used for this study. Specimens at Dr = 50% of Nam O sand and Dr = 70% of Toyoura sand, and those of Hue clay and Japanese Kaolin clay were consolidated under the vertical stress of σvo = 49 kPa. They were then subjected to undrained cyclic shear for various cyclic shear directions and wide ranges of the number of cycles and shear strain amplitudes. Under the same cyclic shearing conditions, specimens of sand at higher Dr (Toyoura sand) and clay with higher Atterberg’s limits (Kaolin) show a lower pore water pressure ratio. The number of cycles and the cumulative shear strain at the starting point of pore water pressure generation were observed for different soils and testing conditions. In addition, using the cumulative shear strain, a new strain path parameter, the effects of shear strain amplitude and cyclic shear direction can be captured, resulting in a unique uacc/σ’vo - G* relation on each soil. Based on this, fitting lines can be drawn and referred to promote a prediction of the cyclic shear-induced pore water pressure accumulation for the used soils under different cyclic shear conditions.

Experimental investigation on dynamic properties of muddy sand from Pearl River Delta of China

Muddy sand, which comes from a sea-land cross sedimentary layer containing a large number of skeletal residues from marine organisms, has different internal structures compared with other types of sand. The dynamic characteristics of the muddy sand needs to be studied owing to a great risk of earthquakes, which are prone to liquefaction and large ground deformation. In this study, a series of undrained cyclic loading tests were carried out on both undisturbed and remolded saturated muddy sand, which was excavated from Pearl River Delta of the South China Sea. A concept of pore entropy (PE) was taken based on microscopic tests, to analyze the liquefaction characteristics of saturated muddy sand from the perspective of the microstructure. The results show that the inflection point appears in axial strains for both undisturbed and remolded saturated muddy sand, but the stress and strain path of the undisturbed specimens shows better plasticity and ductility due to the structure of undisturbed soil. In the stage of initial liquefaction, the strain is 0.5–2% and the damping ratio (λ) is 0.35–0.55. When the relative density (Dr) exceeds 0.7 and the cyclic stress ratio (CSR) is <0.1, no liquefaction occurs in muddy sand. Due to the existence of mud, the particles in the soil appear stationary. CSR and loading frequency (f) are sensitive to the change of particles in soil. This study provides a theoretical and experimental results to reveal the relationship between the microstructural evolution and liquefaction properties of muddy sand. It can provide a useful reference for the safety of submarine engineering design and construction.

Transport behaviors of biochar particles in saturated porous media under DC electric field

The mobility of biochar in saturated quartz sand under a direct current (DC) electric field was investigated by column transport test. The effects of biochar preparation temperature (350 and 550 °C), solution chemistry (pH of 4, 7, and 10, and ion strength of 1, 10, 100 mM) and voltage gradient (0, 0.5 and 1.0 V cm−1) on the mobility of biochar were explored. It was found that DC electric field could significantly promote the migration of biochar, and the recovery rate of particles could be improved by 0.5–6.1 folds under 0.5 V cm−1. Higher voltage potential, solution pH and ionic strength were more favorable for biochar migration. The transport of biochar could be well interpreted by deterministic nonequilibrium convection-dispersion equation model. The enhanced mobility caused by DC electric field was attributed to the following reasons: enhanced electromigration following electrostatic attraction from the anode; increasing surface negative charges and functional groups on biochar surface as a result of electrochemical oxidization; reducing size blocking of biochar particles by decreasing particle size. Moreover, the interaction between biochar particles and electrode could alter solution chemistry, in particular, increasing solution pH, which in turn facilitated the transport of biochar. This study provided a perspective to modulate the transport behavior of biochar particle in the soil for the remediation of polluted sites.

Seismic evaluation of frictional FRP piles in saturated sands using shaking table tests

This manuscript presents results of two shaking table tests that were used to characterize seismic performance of Fibre-Reinforced Polymers (FRP) pile groups in saturated sand. A laminar shear box with a dimension of 1.0 m × 1.0 m and a depth of 1.0 m was employed to contain the soil medium and allow the soil to respond in the same fashion as the free field. Two types of composite group piles (2 × 2) made of Carbon FRP (CFRP) and Glass FRP (GFRP) along with a series of Aluminum model piles were manufactured and embedded as frictional piles within the soil. The pile-soil models were subjected to acceleration time histories adopted from the 2010 Val-des-Bois Earthquake in Canada and the 1995 Kobe Earthquake. The foundation motions recorded along the model piles showed significantly higher levels of excitation compared to the accelerations recorded within the soil at the same level. This was attributed to strong interaction between the soil and the foundation, and higher flexural stiffness of the model piles. Pile material was also found to influence the seismic response of pile caps and its superstructure through kinematic soil-pile interaction and possible rocking motion. The aluminum pile cap experienced significantly higher acceleration response compared to the FRP piles. Among the FRP piles, GFRP piles were shown to provide slightly better performance and could be an appropriate alternative piling material for frictional traditional piles especially in liquefiable soils.