Sand Stratum Research Articles

Fault rupture propagation through stratified sand–clay deposits and engineered earth structures: a meshfree and critical-state modeling approach

Fault rupture propagation through stratified sand–clay deposits and engineered earth structures: a meshfree and critical-state modeling approach

Discrete element simulation of ground collapse induced by buried sewage pipeline breakage and soil leakage

The rupture of buried sewage pipelines constitutes a primary triggering factor of ground collapse. To investigate the phenomenon of ground collapse resulting from buried sewage pipeline breakage and soil particle leakage, numerical simulations employing the discrete element method (DEM) are utilized. The study focuses on examining the ground collapse mechanisms in both dry and water-rich sand stratum scenarios. A positive correlation is identified between the particle loss rate (PLR) and the magnitude of ground collapse, and a microscopic analysis of the mechanism of particle loss is carried out to visualize the soil arching process. The entire collapse process shows that the formation and destruction of soil arching are clearly accompanied by the particle loss phenomena. Additionally, the computational fluid dynamics (CFD) module is incorporated into the DEM to investigate the collapse of water-rich sand stratum. Parametric studies involving the burial depth of the pipeline, water pressure, the defect radius of the pipeline breakage, and the defect shapes are comprehensively conducted. It is found that the water pressure is the primary factor influencing the PLR, which progressively increases with higher water pressure, larger radius of pipe defect, and shallower burial depth.

Characteristics and Mechanism of Hematite Dissolution and Release on Arsenic Migration in Heterogeneous Materials

The migration of arsenic in groundwater is influenced by the heterogeneity of the medium, and the presence of iron minerals adds complexity and uncertainty to this effect. In this study, a stratified heterogeneous sand column with an embedded hematite lens at the coarse-to-medium sand interface was designed. We introduced an arsenic-laden solution and controlled groundwater flow to investigate the spatiotemporal characteristics of arsenic migration and the impact of hematite dissolution. The results showed that the medium structure significantly influenced the arsenic migration and distribution within the lens-containing sand column. The clay layers directed the lateral migration of arsenic, and the arsenic concentrations in deeper layers were up to seven times greater than those on the surface. The extraction experiments of solid-phase arsenic revealed that the main adsorption modes on quartz sand surfaces were the specific adsorption (F2) and adsorption on weakly crystalline iron–aluminum oxides (F3), correlating to the specific and colloidal adsorption modes, respectively. Monitoring the total iron ions (Fe(aq)) revealed rapid increases within the first 14 days, reaching a maximum on day 15, and then gradually declining; these results indicate that hematite did not continuously dissolve. This study can aid in the prevention and control of arsenic contamination in groundwater.

A Multi-Objective Prediction XGBoost Model for Predicting Ground Settlement, Station Settlement, and Pit Deformation Induced by Ultra-Deep Foundation Construction

Building a deep foundation pit in urban centers frequently confronts issues such as closeness to structures, high excavation depths, and extended exposure durations, making monitoring and prediction of the settlement and deformation of neighboring buildings critical. Machine learning and deep learning models are more popular than physical models because they can handle dynamic process data. However, these models frequently fail to establish an appropriate balance between accuracy and generalization capacity when dealing with multi-objective prediction. This work proposes a multi-objective prediction model based on the XGBoost algorithm and introduces the Random Forest Bayesian Optimization method for hyperparameter self-optimization and self-adaptation in the prediction process. This model was trained with monitoring data from a deep foundation pit at Luomashi Station of Chengdu Metro Line 18, which are characterized by a sand and pebble stratum, cut-and-cover construction, and a depth of 45.5 m. Input data of the model included excavation rate, excavation depth, construction time, shutdown time, and dewatering; output data included settlement, ground settlement, and pit deformation at an operating metro station only 5.7 m adjacent to the ongoing pits. The training effectiveness of the model was validated through its high R2 scores in both training and test sets, and its generalization ability and transferability were evaluated through the R2 calculated by deploying it on adjacent monitoring data (new data). The multi-objective prediction model proposed in this paper will be promising for monitoring the data processing and prediction of settlement of surrounding buildings for ultra-deep foundation pit engineering.

Investigating the dynamics of water–sand mixing inrush in viscous sand layers: insights from laboratory experiments

The geological hazard of water–sand inrush is a matter of concern for infrastructure construction and resource exploration activities in China, due to the complex interplay between groundwater dynamics and the stability properties of sand particles. This phenomenon is characterized by its intensity, hazardous nature, and unpredictable behavior. Following comprehensive analysis, this study identifies the critical factors influencing water–sand inrush processes as fissure width, water stress (waterhead height), in-situ sand ground stress within the sand stratum, and clay content. To investigate these factors experimentally, a custom-designed hydraulically coupled water–sand inrush test apparatus was used. The apparatus was equipped with a cylinder to apply ground stress, a pneumatic diaphragm pump to regulate water stress, and a bottom opening in the sand layer. Tests were conducted to investigate the dynamic response of water–sand inrush events under various combinations of factor levels. The findings revealed that the critical value for inrush is only present in the fissure width, which was observed to be 3 mm for the tested sand material. Unlike fissure width, the other factors do not have definitive critical values but instead modulate the intensity of the inrush process without determining its occurrence. The ‘inrush rate’ serves as a measure of the severity of water–sand inrush disasters and shows a linear increase with both increasing groundwater stress and fissure width, a negative exponential function relationship between the inrush rate and the clay content. Notably, ground stress does not exert a significant influence on the intensity of the inrush process itself. Under constant conditions, the inrush rate remains relatively constant across different levels of sand ground stress, for instance, in the experiments, the inrush rate was measured at 1.606 kg/s when the water stress was 0.1 MPa and the fissure width was 5 mm. Grey relation analysis was used to examine the sensitivity of each factor’s influence on the inrush rate. The results showed that water stress has the greatest impact on the intensity of water–sand inrush, followed by ground or soil stress, clay content, and the width of the fissures in the sand layer.

Disturbance characteristics test about double-line shield tunnel excavation in grouting-reinforced water-rich sand stratum

To study the disturbance characteristics of double-line shield tunnel excavation on sand bodies in grouting-reinforced water-rich sand stratum, a similar model test was carried out. Firstly, the physical parameters and strength indexes of the overlying soil strata of the tunnel in the water-rich sand stratum were determined by laboratory tests. The similar soil and tunnel support structures of each stratum were prepared. Then, considering the different seepage modes of upper and lower soil strata under the influence range of tunnel excavation, the model test of double-line shield tunnel excavation in a grouting-reinforced water-rich sand stratum is conducted. The variation rules of sand deformation, surface settlement, and sand body stress during the excavation of a double-line shield tunnel are analyzed utilizing monitoring and analyzing systems such as a flowmeter, micro earth pressure sensors, and dial indicators. It is found that during the excavation of the double-line tunnel, the self-stabilization ability of the grouting reinforced sand bodies is strong under the action of stable seepage. Under the influence of grouting reinforcement, the seepage path around the tunnel structure will change, the fluid-solid coupling effect will decrease, and the sand stratum will be uplifted to varying degrees. The sand body will change its mechanical properties due to the influence of seepage. The fluid-solid interaction effect will be enhanced. The fluid-solid coupling effect of soil particles and water will be further enhanced when the excavation of the subsequent tunnel is carried out. The effect of unsaturated seepage in the overlying soil stratum leads to greater stress at the arch waist of the arch tunnel. In the actual construction process, the grouting amount and grouting time should be strictly controlled. The tunnel basement is supported by anchor spray support to prevent the tunnel structure and surface uplift.

Model test and numerical analysis of shield tunnel face instability in sandy soil with strain-softening properties

During excavation of a shield tunnel in a sandy stratum, variations in the state of the sand affect the stratum stability of the shield tunnel face. When dense sand is loaded, its strength decreases gradually owing to dilatancy and it exhibits strain-softening behavior. Model tests and finite element numerical simulations were performed to clarify the failure characteristics of the tunnel face induced by strain-softening. In the model tests, a dense sand stratum was constructed; the movement of the supporting plate of the excavation face was controlled to simulate the progressive failure of the shield tunnel face. Based on a material state-dependent plasticity model, a numerical analysis model of the tunnel face was established to capture the strain-softening behavior of dense sand by including a nonlocal regularization technique. Comparing the model test and numerical simulation results, the evolution of the material state of the sand with progressive failure of the tunnel face was analyzed, and the failure characteristics caused by the strain-softening of sand were revealed.

Development and application of novel microfine cement-based grout

A novel type of effective microfine cement-based grout (EMCG) is designed for the complicated water-rich sand stratum. Superplasticizer (SP), compound excitation modulator (CEM), enhanced stabilizer (ES) and active activator (AA) were selected as optimizers. Through laboratory tests, main properties of EMCG i.e. fluidity performance, viscosity, bleeding rate, setting time, strength and volume stability were studied. Based on XRD mineral and SEM microstructure tests, hydration mechanism and microstructure of EMCG were studied. The results showed that the optimal parameters were 40% microfine fly ash (MFA), 14–18% microfine steel slag (MSS), 20–25% microfine slag (MS), 2–2.5% naphthalene-based SP (N), and 1–1.5% AA, 0.4–2.0% CEM and 6% ES. The 28d compressive strength of EMCG can reach 12.9–32.8 MPa. The 7 d strength can exceed 70% of 28 d strength. Through grouting injectability and reinforcement simulation tests, injectability of EMCG was acquired under different main influence factors i.e. sand particle size distribution, sand compactness, grout type, water-solid ratio (W/S), grouting pressure, etc. Quantitative relationships among enhancement strength or permeability coefficient and main influence factors were established. The microscopic slurry-rock interface reinforcement mechanism was obtained. Finally, based on field tests, the sealing and reinforcement effects of EMCG on water-rich sand stratum were acquired and discussed. Due to high overall performance and excellent engineering applicability of EMCG, it is an efficient and excellent cementitious grout especially for seepage prevention and reinforcement of water-rich sand stratum in geotechnical and underground engineering.

Study on the Characteristics of Slurry Support Efficiency on Excavation Face Induced by Shield Cutterhead Cutting in Sand Stratum

Study on the Characteristics of Slurry Support Efficiency on Excavation Face Induced by Shield Cutterhead Cutting in Sand Stratum

Slurry flow and its infiltration behavior in sand stratum based on slurry fluid properties

Slurry flow and its infiltration behavior in sand stratum based on slurry fluid properties

A unified empirical method for predicting both vertical and horizontal ground displacements induced by tunnel excavation

An empirical model for describing the soil movements induced by tunneling is proposed, then the mathematical relationship between horizontal displacement and vertical displacement is obtained. By analyzing 25 sets of data from field engineering and 35 sets of data from model tests, the formula for the maximum settlement Sv, max( z) is optimized to adapt to different ground conditions. The Modified Gaussian function is developed by introducing the existing width coefficient of the settlement trough i( z) and the optimized Sv, max( z) to describe the surface and subsurface vertical displacement. Subsequently, the formula for the horizontal displacement is derived based on the Modified Gaussian function. H( z) representing the position of the oriented point of the soil movement is a variable in the formula for horizontal displacement. Based on measured results, a logarithmic function and a quadratic polynomial function are proposed to describe the variation of H( z) with depth in the clay stratum and sand stratum, respectively. Then, the rationality of the proposed method is validated by 4 sets of in-situ data and 4 sets of test data. Finally, the implementation process of the proposed method is illustrated, and the inversion results of the ground displacement field in Beijing Metro Line 12 are presented.

Quasi-Static Model Test of Pile-Supported Wharf under Cyclic Lateral Loading

The pile-supported wharf (PSW) is one of the most common structures in harbor engineering. To investigate the dynamic response characteristics of the PSW, a quasi-static model test of a PSW–ground system under cyclic lateral loading is conducted. The deformation and damage processes of piles and the sand stratum are observed and obtained. The hysteresis characteristics of the PSW–ground system and the response characteristics of piles are systematically explored. The strain energy of the pile group on the sloping ground is calculated and analyzed. The results show that there are two peak bending moments on the pile, and the maximum one occurs at the pile top. The pile embedded depth and the loading direction strongly affect the strain energy distribution of the pile group. Under downslope direction loading, the center piles have the largest strain energy percentage. The strain energy extends from the center piles to the outside piles with the increase in loading displacement amplitude. The test results indicate that the landside pile and center pile should be strengthened during seismic design.

Groundwater Recharge Potentiality Mapping in Wadi Qena, Eastern Desert Basins of Egypt for Sustainable Agriculture Base Using Geomatics Approaches

In arid and hyper-arid areas, groundwater is a precious and rare resource. The need for water supply has grown over the past few decades as a result of population growth, urbanization, and agricultural endeavors. This research aims to locate groundwater recharge potential zones (GWPZs) using multi-criteria evaluation (MCE) in the Wadi Qena Basin, Eastern Desert of Egypt, which represents one of the most promising valleys on which the government depends for land reclamations and developments. These approaches have been used to integrate and delineate the locations of high groundwater recharge and the potential of the Quaternary aquifer in the Wadi Qena basin. After allocating weight factors to identify features in each case based on infiltration, land use/land cover, slope, geology, topology, soil, drainage density, lineament density, rainfall, flow accumulation, and flow direction, these thematic maps were combined. The results of the GIS modeling led to the division of the area’s groundwater recharge potential into five groups, ranging from very high (in the western part) to very low (in the eastern part of the basin). The zones with the best prospects for groundwater exploration turned out to be the alluvial and flood plains, with their thick strata of sand and gravel. The groundwater recharge potential map was validated using data from the field and earlier investigations. The promising recharging areas show high suitability for soil cultivation. The results overall reveal that RS and GIS methodologies offer insightful instruments for more precise assessment, planning, and monitoring of water resources in arid regions and anywhere with similar setups for groundwater prospecting and management.

Seismic response of retaining walls: Theoretical parametric insights after centrifuge validation

To gain insight into the dynamics of retaining systems, the seismic response of a “non-displacing” U-shaped and a “displacing” cantilever retaining wall in dry sand stratum is studied by numerical analyses using a refined constitutive model, with the wall–soil interface allowing separation and sliding. The results were motivated from, and are successfully compared with, a series of comprehensive centrifuge experiments by Sitar and co-workers. Tests and analyses use as base excitation three accelerograms from Kobe, Kocaeli and Loma Prieta. Results are presented in terms of acceleration time-histories, response spectra, plastic strain contours, and lateral soil pressures. Emphasis is given to numerically–obtained soil lateral pressures, and the parametric study shows that while such pressures are difficult to accurately predict, they may nevertheless be in (barely satisfactory) agreement in shape and even often in magnitude with either: (i) Mononobe–Okabe–type, or (ii) the Veletsos and Younan (1994) [39] analytical solutions, depending on the displacement constraints of the wall, the rotational flexibility at the base, and the severity of the excitation.

Experimental Study on Interaction between Slurry and Soil on Excavation Face of Shield in Sand Stratum

In sandy soil, the timely and effective formation of a filter cake is crucial for maintaining the stability of the excavated face during slurry shield tunnelling. Obtaining real-time information on slurry infiltration and particle migration is challenging, which greatly impacts the formation of the filter cake. Real-time monitoring of slurry infiltration and particle deposition is achieved through the use of electrical resistivity and pore water pressure measurements of the soil. It has been discovered that the primary pathway for slurry infiltration is inevitable in sandy soil, and it is crucial to take note of the persistent slurry leakage resulting from this situation in the shield excavation face. The distribution of slurry particle deposition is highly non-uniform in the penetration direction, with the maximum particle deposition occurring at the slurry-soil interface. However, this deposition is susceptible to disturbance from shield cutting tools, which can compromise the safety of the excavation face. Even if the particle size of the slurry is smaller than the pore size of the sand stratum, the slurry with higher viscosity can still form an internal filter cake. Furthermore, the research indicates that slurry infiltration can induce regular changes in soil electrical resistivity.

Numerical modelling of shield tunnel face failure through a critical state sand plasticity model with nonlocal regularization

During shield tunneling in sand strata, variations in the state of sand can lead to localized instability and strength loss, which brings about numerical difficulties. This paper numerically investigates how nucleation and propagation of plastic deformation zones, including those leading to localized banding, possibly promote failure of shield tunnel faces excavated in sand. To this end, a material state-dependent model is used to capture the mechanical responses of sand. Nonlocal enhancement is introduced, through the volumetric strain increment that drives the change of void ratio and related material hardening/softening behavior, to regularize ill-posed boundary value problems caused by the activation of strain localization. Simulations of tunnel face failure indicate that lower initial void ratios result in more concentrated plastic deformation in the vicinity region near the face and a strain-softening trend in global deformation responses. Conversely, initial looser states drive the deformation zone to propagate spatially to the ground surface, and the resultant global deformation responses exhibit strain-hardening. The second-order work is used to explain the link between material instability around the tunnel faces and initial density. It was found that material instability usually occupies a fraction of plastic deformation regions, and shrinks as sand initial density increases.

Settlement Analysis of Mud-Water Shield Passing Full-Face Water-Rich Sand and Cobble Stratum Under Luo River

Settlement Analysis of Mud-Water Shield Passing Full-Face Water-Rich Sand and Cobble Stratum Under Luo River

Bearing Capacity of a Strip Model Footing on Loose Sand Reinforced With Pomegranate Sticks Mat

A series of laboratory model tests has been carried out to investigate the using of pomegranate sticks mat as reinforcement to increase the bearing capacity of footing on loose sand. The influence of depth and length of pomegranate sticks layer was examined. In the present research single layer of pomegranate sticks reinforcement was used to strengthen the loose sand stratum beneath the strip footing. The dimensions of the used foundation were 4*20 cm. The reinforcement layer has been embedded at depth 2, 4 and 8 cm under surcharge stresses . Reinforcing layer with length of 8 and 16 cm were used. The final model test results indicated that the inclusion of pomegranate sticks reinforcement is very effective in improvement the loading capacity of loose sand. The optimal benefit in bearing capacity value was realized as the (D/B) ratio (embedded depth to footing width) equal to 0.5.The bearing capacity of a reinforced soil with single layer of pomegranate sticks at (D/B) ratio of o.5 increased by about 4 times (corresponding to S/B =10%) than that for the unreinforced case and continuous in increasing beyond that with no failure. The improvement in bearing capacity decreased with increasing depth of embedment of reinforcement layer until reach to a specified point in which the bearing capacity of a reinforced soil approximately identical with the case of no reinforcement. Also it was found that increase the length of pomegranate sticks layer has no beneficial effect on the improved the bearing capacity of loose sand.

Liquefaction proneness of stratified sand-silt layers based on cyclic triaxial tests

Most studies on liquefaction have addressed homogeneous soil strata using sand or sand with fine content without considering soil stratification. In this study, cyclic triaxial tests were conducted on the stratified sand specimens embedded with the silt layers to investigate the liquefaction failures and void-redistribution at confining stress of 100 kPa under stress-controlled mode. The loosening of underlying sand mass and hindrance to pore-water flow caused localized bulging at the sand-silt interface. It is observed that at a silt thickness of 0.2 H ( H is the height of the specimen), nearly 187 load cycles were required to attain liquefaction, which was the highest among all the silt thicknesses with a single silt layer. Therefore, 0.2 H is assumed as the optimum silt thickness ( t opt ). The silt was placed at the top, middle and bottom of the specimen to understand the effect of silt layer location. Due to the increase in depth of the silt layer from the top position (capped soil state) to the bottom, the cycles to reach liquefaction ( N cyc,L ) increased 2.18 times. Also, when the number of silt layers increased from single to triple, there was an increase of about 880% in N cyc,L . The micro-characterization analysis of the soil specimens indicated silty materials transported in upper sections of the specimen due to the dissipated pore pressure. The main parameters, including thickness ( t ), location ( z ), cyclic stress ratio (CSR), number of silt layers ( n ) and modified relative density ( D r,m ), performed significantly in governing the liquefaction resistance. For this, a multilinear regression model is developed based on critical parameters for prediction of N cyc,L . Furthermore, the developed constitutive model has been validated using the data from the present study and earlier findings. ©2022 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Experimental study on new grouting material of acidic sodium silicate and its properties of grouted-sand

Slurry selection and ratio optimization are the key points and difficulties in the construction of subway tunnels in poorly graded medium sand strata. In this paper, a kind of acidic grouting material was prepared by using sodium silicate and phosphoric acid. The properties of the acidic grouting material including gel time and viscosity were studied. Orthogonal test was carried out to optimize the ratio of sodium silicate to phosphoric acid for poorly graded sand stratum. At the same time, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the sand consolidation process of the slurry. The results show that the gel time and funnel viscosity of the phosphoric acid-sodium silicate slurry are related to the Baume degree of sodium silicate and the volume ratio of sodium silicate to phosphoric acid. The compressive strength of the grouted sand is related to four factors, i.e., water content of the sand, and Baume degree, pH value and curing time of the slurry, the influence degree of which is in the following order: D (curing time) > A (water content) > B (Baume degree of sodium silicate) > C (pH value of the slurry). The final slurry selected for grouting reinforcement of the weakly alkaline medium sand strata was prepared by 30 °Bé sodium silicate with 14 % phosphoric acid at a volume ratio of 0.5. It has a gel time of 51.48 min, a funnel viscosity of 16.43 s and a pH value of 3.47. The increased amount of silica gel in the sample is the main reason for the increased strength of the grouted sand. The amount of silica gel generated increases with the increase of the curing time of the sample.