Interface Of Soil Layers Research Articles

Effect of Median Soil–Particle Size Ratio on Water Storage Capacity of Capillary Barrier

Capillary barriers are widely used as a cover system to enhance the upper-soil-layer water storage capacity and reduce water infiltrate into the lower soil layer. In this paper, the effects of the median soil–particle size ratio on the water storage capacity of capillary barriers were studied using a series of indoor one-dimensional soil column infiltration tests. The results show that the water storage capacity rises with an increase in the median soil–particle size ratio until it exceeds 10. The variation in the total water storage capacity is related to not only the median soil–particle size ratio but also the particle size of coarse-grained soil or fine-grained soil. When the fine-grained soil-layer particle size is constant, the total water storage first increases, then decreases, and finally remains constant after increasing the median soil–particle size ratio. In contrast, when the coarse-grained soil layer particle size is constant, the relationship between the capillary barrier’s total water storage and median soil–particle size ratio can be defined as a power function. Using the capillary barrier can increase coarse-grained sand by 90% in water storage capacity and can only increase fine-grained sand by 7% in water storage capacity. The breakthrough time increases with the increase in the median soil–particle size ratio. The presence of the coarse and fine-grained soil layer interface in the capillary barrier can affect the fine-grained soil layer infiltration rate.

Seismic response of offshore tetrapod piled jacket foundations subjected to environmental loads in soft-over-stiff clay deposit

Under the combined action of environmental and seismic loadings, offshore wind turbines supported by tetrapod piled jacket (TPJ) foundations may experience tilting and rotational failures, and even the shutdown. However, there is still a notable gap in the research on the dynamic response of the TPJ system in this condition, especially in the multilayered clay deposits. This study conducts advanced three-dimensional finite element simulation to investigate the seismic response of TPJ systems in soft-over-stiff clay deposit under the combined influence of wind and wave loadings. The results indicate that with a minor strength ratio between two layers, especially for strength ratios < 0.28, the peak values of the pile bending moment envelopes increases obviously, which is located near the soil layer interface. Near the soil layer interface, a sudden expansion in the soil plastic strain can be observed at this location. When the top layer thickness is substantial, surpassing 0.75 times the pile length, the restraining effect of the bottom stiff layer on the pile results in the peak value of the acceleration response envelopes and a significant reduction in bending moment near the pile end.

Numerical Simulation of Double-row Piles in Deep Foundation Pit Excavation

This paper aims to investigate the stress and deformation characteristics of double-row piles in deep foundation pit excavation by selecting representative strata in the Changchun area. The changes in bending moment, displacement, and earth pressure of double-row piles during the excavation are established using the FALC 3D software. The findings indicate that the deformation of the front pile is larger than that of the back pile, and the earth pressure distribution of the fornt pile deviates from the conventional Rankine earth pressure theory. Moreover, there are noticeable variations in earth pressure at the soil layer interface of the rear pile.

Study on Spatiotemporal Transport Characteristics of Soil Moisture in Layered Heterogeneous Vadose Zone Based on HYDRAS-3D

The heterogeneity of layered soils affects the transport processes of water in the vadose zone. However, the mechanism of soil moisture transport in the vadose zone under heterogeneous media conditions, especially the three-dimensional transport mechanism, is a frontier problem to be studied. In order to reveal the law of soil water transport in the vadose zone under heterogeneous media, this paper constructs a three-dimensional model of water transport using HYDRAS-3D (V 2.x) software through in situ tests of water transport in 3 × 3 × 4 m sample and verifies and analyzes the model. The vertical distribution and variability of soil water content and the temporal and spatial rules of soil water transversal transport at the soil–layer interface were analyzed. The results indicate that after adjusting the parameters in the HYDRAS-3D model using measured values, the simulation results are reasonable, and the model has high reliability. To represent the water content variability characteristics of the test tube profile, water movement in the vadose zone was classified as follows: (I) steady period (April–September, less affected by rainfall), (II) slow change period (January–March), and (III) rainfall rapid change period (June, when the impact of rainfall on the test cylinder was greater). The two largest values of the soil water potential variation gradient, 19.9 and 17.8 cm/d, were observed in the silty clay layer of the test cylinder, and the influence of evaporation and infiltration in the silty clay layer was most notable at the interface. The lateral transport of soil water at the interface was influenced to a certain degree by the layered heterogeneity, wherein the fine sand layer exhibited the most pronounced impact. This was followed by silt and silty clay layers, with the silt layer showing the lowest degree of influence. The research results can provide scientific reference for the rational planning of water resources in the Yinchuan Plain.

Measured Rainfall Infiltration and the Infiltration Interface Effect on Double-Layer Loess Slope

It is of great theoretical and engineering significance to carry out field rainfall tests and research on double-layer soil slopes in loess areas. Based on the developed rainfall simulation system with slow-moving injection, field rainfall tests were carried out on a natural double-layer loess slope. The characteristics of volumetric water content were monitored, and the rainfall infiltration characteristics and infiltration effect at the interface of the soil layer were analyzed by numerical simulation. The results showed the fastest infiltration at the top platform of the slope, followed by that at the upper surface of the slope, and the slowest infiltration at the lower surface of the slope during rainfall. Under various rainfall intensities, the erosion of the upper silty loess slope was greater than that of the lower clay loess slope, and the erosion patterns were quite different at the end of rainfall. During the infiltration process in the double-layer loess slope, a stagnant transition area was formed near the interface of the soil layer. The equipotential line of water content in the stagnant transition area of the upper region was roughly parallel to the slope surface, and the equipotential line in the lower region was roughly parallel to the interface of the soil layer. With an increase in rainfall intensity, the upper transition area at the interface of the soil layer continued to extend from the slope surface inward, showing the interface infiltration effect that became increasingly significant with the intensification of rainfall. The infiltration effect at the soil layer interface could provide an evaluation basis for rainfall infiltration analyses of multi-layer soil slopes.

Similarity Model Test on Stress and Deformation of Freezing Pipe in Composite Strata during Active Freezing

In order to prevent the problem of freezing pipe fracture in the process of artificial freezing construction, taking the main shaft freezing project of Shandong Yuncheng Mine as the background and based on the similarity theory, the similarity model test of freezing pipe in the composite stratum of the active freezing section is carried out. The test results show that the distribution of freezing temperature field in sand layer and clay layer is “W”-shape, and the temperature at the interface of outer ring pipe is slightly higher than that of the inner ring pipe. The change rate of freezing temperature can be divided into three stages: rapid decreasing section, slow decreasing section, and stable section. Compared with the clay layer, the sand layer has the shorter freezing closure time and the lower freezing average temperature. The frozen pipe is always in the state of vertical compression in the clay layer, while in the state of vertical compression first and then vertical tension in the sand layer. The maximum compressive strain in the clay layer is −305 με, which is equal to the vertical compressive stress of 64.1 MPa. The maximum tensile strain in the sand layer is 406 με, which is equivalent to the tensile stress of 85.2 MPa. The bending direction of different freezing pipes is different in the different soil layers. The maximum bending strain of the frozen pipe in the clay layer is 779 με, which is 2.6 times the vertical strain at the same location, corresponding to the bending stress of 163.4 MPa and reaching 0.69 times of the yield limit of frozen pipe, while the bending strain in the sand layer is very small. The vertical strain and bending strain of freezing pipes at the interface of soil layers are very small, but the bending strain is still dominant.

Image based probabilistic slope stability analysis of soil layer interface fluctuations with Brownian bridges

Accurate interpretation of stratigraphic profiles, the phreatic surface and the spatial variability of geomaterials are essential to produce representative behaviour of geomechanical systems through numerical simulations. When considering slope stability, variations in soil layer boundaries and the phreatic surface may result in misleading metrics such as the Factor of Safety (FoS) and the Probability of Failure (PoF). This paper presents an image-based technique for generating continuous stratigraphic profiles, including random fluctuations based on Brownian motion. Brownian bridges are used to produce random walks between known points on both soil layer boundaries and the phreatic level that overlap with the slope profile image. Quadtree decomposition is used to discretise the stratigraphy and the phreatic level through an automatic process using generated digital images for mesh generation while also integrating material properties. The Scaled Boundary Finite Element (SBFEM) is used to analyse the slope stability problem. Images based on random walks along an unknown stratigraphic material boundary and the phreatic surface are randomly generated and have many random possibilities, which are used to undertake probabilistic analysis to obtain PoF. This process is complex when using numerical methods, such as the Finite Element Method, as it requires mesh generation from different slope profiles with alternating material interfaces at each probabilistic instance. When the Scaled Boundary Finite Element Method is applied, probabilistic numerical analyses can be fully automated for randomly generated material interfaces. The feasibility of the proposed method is illustrated through several cases of a slope with multiple material layers, in addition to a slope incorporating a Brownian bridge phreatic surface formulation.

Dynamic installation of torpedo anchors in slightly overconsolidated clay-overlaying-sand deposit

Torpedo anchor installation involves uncertain design and construction parameters, especially in layered soil deposits. Large deformation finite element and coupled Eulerian–Lagrangian (LDFE/CEL) analyses are performed in this study to elucidate the dynamic installation of torpedo anchors in an over consolidated clay-overlaying-sand deposit. The parametric analysis is conducted after model verification to explore the effect of upper clay layer thickness, anchor impact velocity, anchor submerged weight, soil properties and anchor geometric dimensions. The soil failure patterns and dynamic installation behaviour in the clay-overlaying-sand soil deposit are found to differ substantially from those in single-layer clay and sand deposits, which exhibit a squeezing flow pattern at the clay-sand soil layer interface. As the demarcation of the two velocity phases during the anchor penetration process (acceleration and deceleration phases) falls below the interface of two soil layers, the contribution of the internal friction angle of sand to the anchor final penetration depth exceeds that of the clay undrained shear strength. Based on intensive modelling data, an empirical method for predicting the anchor penetration depth in single and layered soil deposits is derived for engineering applications.

Soil flow mechanisms around cone penetrometer in layered clays

The cone penetrometer test is widely used for in situ site investigations and for establishing direct penetrometer-to-foundation or -anchor design correlations. This paper focuses on soil flow mechanisms during the continuous penetration of a cone penetrometer in layered clays. A series of centrifuge tests was conducted with the cone penetrating through soft–stiff, stiff–soft, soft–stiff–soft and stiff–soft–stiff clay profiles. Particle image velocimetry allowed accurate resolution of the soil flow mechanism around the cone where a half-cone model was penetrated into layered clays against a transparent window. The observed soil movement was compared both with previous observations for piles/cones and with movement from the shallow strain path method (SSPM). A comparison with SSPM results showed that the SSPM can provide reasonable evaluations on maximum lateral and vertical displacements even though the upheave movement can be overestimated. The effect of soil layering on the failure mechanisms was studied extensively by exploring soil flow mechanisms and soil displacement paths at various distances from the advancing cone centreline and soil layer interface. The reported characteristics of cone penetration in layered soils provided in-depth understanding of cone penetration responses that will lead to the development of mechanism-based theoretical models for cone penetration in layered fine-grained soils.

Inner soil heave of stiffened caisson during installation in soft-over-stiff clay

The identification of soil heaves inside a caisson during installation is important for the caisson’s design length, since the inner soil heave during the caisson installation affects the final effective caisson penetration depth, hence caisson capacity. This paper reports an extensive parametric study of stiffened caissons penetrating in double-layer of soft-over-stiff clay using large deformation finite element (LDFE) analyses. The LDFE analysis was first validated against the existing results from centrifuge tests and numerical analyses. Then the parametric study was carried out to explore the inner soil movements during stiffened caisson installations with various influencing factors, such as caisson diameter, caisson stiffener width, top-layer soil strength, double-layer soil strength ratio, and roughness of soil-caisson interface. It is found that the caisson diameter, stiffener width, and top-layer soil strength have significant influences on the inner soil behaviors. Besides, the movements of both soil surface and soil layer interface were also investigated. Based on the LDFE results, design formulas are proposed to estimate the inner soil heaves for soft-over-stiff clay. A design formula to estimate the movement of the soil layer interface for soft-over-stiff clays is also reported.

Study on the penetration process of torpedo anchor into layer soils

Wing torpedo anchor is a new type of gravity anchor which is installed by self weight and anchored by gravity and seabed resistance. Based on the T98 torpedo anchor, the penetration process of torpedo anchor in layer soils is numerically simulated, and the change laws of penetration resistance, acceleration, velocity and penetration energy with depth is analyzed. The results showed that the end resistance and the friction resistance broke at the interface of soil layers, and the friction resistance increased with increasing of depth, while the end resistance first increased and then decreased. With the increasing of depth, the acceleration increased and the velocity decreased. In the early stage of penetration, the work is mainly done by the end resistance, whereas the work is mainly done by the side friction resistance in the later stage, suggesting that the side friction resistance consumed more anchor energy than the end resistance.

Influence of phase difference between kinematic and inertial loads on seismic behaviour of pile foundations in layered soils

A series of dynamic centrifuge experiments was conducted on model pile foundations embedded in a two-layered soil profile consisting of soft-clay layer underlain by dense sand. These experiments were specifically designed to investigate the individual effect of kinematic and inertial loads on a single pile and a 3 × 1 row pile group during model earthquakes. It was observed that the ratio of free-field soil natural frequency to the natural frequency of structure might not govern the phase relationship between the kinematic and inertial loads for pile foundations as reported in some previous research. The phase relationship obtained in this study agrees well with the conventional phase variation between the force and displacement of a viscously damped simple oscillator subjected to a harmonic force. Further, as expected, the pile accelerations and bending moments can be smaller when the kinematic and inertial loads act against each other compared to the case when they act together on the pile foundations. This study also revealed that the peak kinematic pile bending moment will be at the interface of soil layers for both single pile and pile group. However, in the presence of both kinematic and inertial loads, the peak pile bending moment can occur either at the shallower depths or at the interface of soil layers depending on the pile cap rotational constraint.

Dynamic Response Characteristic of Layer Interface of Soft Soil Subgrade with Dry Crust Covering and Its Engineering Application

AbstractConsidering the obvious wave impedance difference between dry crust and soft, the phenomenon of dynamical stress mutation at the hard-soft soil interface, which is a specific performance of shell effect of dry crust in dynamic scope, is revealed by the transmission coefficient based on stress-wave theory. The attenuation law of vertical dynamic stress peak in subgrade soil under vehicle load is obtained by numerical simulation. Based on the negative exponential function characteristic of an attenuation curve, a transfer coefficient at soil layer interface is derived. This coefficient can synthetically represent the law of dynamical stress mutation. The corresponding calculation method and application range of the transfer coefficient are offered. This calculation method has simpler processing and higher precision than existing methods based on monitoring data verification. By practice validation of expressway engineering, the mechanical state of subgrade soil can be correctly evaluated, and its re...

Simplified Boundary Element Method for Kinematic Response of Single Piles in Two-Layer Soil

A simple approach is formulated to predict the elastic, kinematic pile bending during harmonic or transient excitation for a circular pile (rather than a simplified thin strip). The kinematic response of a pile embedded in two-layer soil is resolved in the frequency domain caused by the upward propagation of shear waves from the underlying bedrock. The simplified approach is generally valid to nonhomogeneous soil profiles, in light of the good comparison with the dynamic FE method and BDWF solution. It employs the soil-displacement-influence coefficientsIsto consider the pile-soil interaction (resembling the spring constantkxin the BDWF) and provides conservative estimations of maximum kinematic bending moments at the soil-layer interface (with a sharper stiffness contrast). The accuracy of the approach may be improved by incorporating the interaction of soil into the soil-displacement-influence coefficientsIsfor such cases withVb/Va&lt;3.

Enhanced Biogeochemical Cycling and Subsequent Reduction of Hydraulic Conductivity Associated with Soil‐Layer Interfaces in the Vadose Zone

Biogeochemical dynamics in the vadose zone are poorly understood due to the transient nature of chemical and hydrologic conditions but are nonetheless critical to understanding chemical fate and transport. This study explored the effects of a soil layer on linked geochemical, hydrological, and microbiological processes. Three laboratory soil columns were constructed: a homogenized medium-grained sand, a homogenized organic-rich loam, and a sand-over-loam layered column. Upward and downward infiltration of water was evaluated during experiments to simulate rising water table and rainfall events, respectively. In situ collocated probes measured soil water content, matric potential, and Eh. Water samples collected from the same locations were analyzed for Br, Cl, NO, SO, NH, Fe, and total sulfide. Compared with homogeneous columns, the presence of a soil layer altered the biogeochemistry and water flow of the system considerably. Enhanced biogeochemical cycling was observed in the layered column over the texturally homogeneous soil columns. Enumerations of iron- and sulfate-reducing bacteria showed 1 to 2 orders of magnitude greater community numbers in the layered column. Mineral and soil aggregate composites were most abundant near the soil-layer interface, the presence of which likely contributed to an observed order-of-magnitude decrease in hydraulic conductivity. These findings show that quantifying coupled hydrologic-biogeochemical processes occurring at small-scale soil interfaces is critical to accurately describing and predicting chemical changes at the larger system scale. These findings also provide justification for considering soil layering in contaminant fate and transport models because of its potential to increase biodegradation or to slow the rate of transport of contaminants.

DETERMINATION OF INTERFACES IN SOIL LAYERS BY SOUND WAVE ANALYSIS WITH CONE PENETRATION TESTS

This experimental study precisely identifies the soil layer interface using sound signals collected during cone penetration tests (CPTs). Using the high sensitivity of the sound sensor at the cone tip, this study effectively increases the accuracy in identifying the soil interface location. Shiluo sand and Jhongda Lateritic soil were used to construct large-scale soil layers. An acoustic CPT was applied to determine sound pressure and its root mean square (RMS). The Fourier spectrum and Hilbert-Huang transform (HHT) method were utilized and compared in their ability to analyze sound signals. The HHT method with a local energy-instantaneous frequencytime distribution performed well. According to analytical results, both the RMS and HHT methods are more effective than cone resistance in locating the soil interface. The major contribution of this study is that it uses the RMS of sound wave as a more accurate, effective and easy method for exploration of soil distribution and detection of soil interfaces.

Three-Dimensional Large Deformation FE Analysis of Square Footings in Two-Layered Clays

In strong over soft two-layered clays, there is a potential for the footing to experience a punch-through failure, where the footing penetrates a large distance at a short time after the initial peak resistance is reached. Three-dimensional (3D) large deformation finite-element analyses using 3D RITSS method were conducted to simulate the penetration responses of square footings in strong over soft clays. The effects of surface soil heave and soil layer interface deformation during footing penetration were studied in weightless soils. Fitted equations were proposed to express the footing capacity response against the penetration depth. Based on the fitted equations, formulas to calculate footing peak bearing factor and the corresponding penetration depth were developed. The peak footing capacity factor and the corresponding penetration depth increases with the increasing of soil layer strength ratio, relative top soil layer thickness and soil weight factor, thus the potential of punch-through failure was reduced accordingly. It was also found that the soil weight effect can be a simple surcharge based on the formula developed in the weightless soil. Design charts for the peak footing capacity factor and the corresponding penetration depth were developed.

Kinematic response analysis of piled foundations under seismic excitation

This paper presents the results of an extensive parametric study on single piles and pile groups embedded in a two-layer subsoil profile, and is aimed to evaluate kinematic bending moments developing during earthquakes. A quasi three-dimensional finite element program has been used to perform dynamic analyses in the time domain. Piles have been considered as elastic beams, while the soil has been modelled using a linear elastic constitutive model. The aims of the paper are: (i) to evaluate kinematic bending moments in single piles and pile groups with dynamic analyses in the time domain, in different subsoil conditions; (ii) to review some existing design methods; (iii) to propose a simplified analysis procedure to evaluate maximum kinematic bending moments between two subsequent soil layers. The results of the dynamic analyses have shown that some of the simplified approaches provided in published literature tend to be conservative and can predict bending moments at the soil-layer interface with adequate accuracy only within certain depths of the soil layer interface. On the basis of the obtained results, a modified criterion to evaluate the transient peak bending moments at interfaces between layers is proposed.

KINEMATIC SEISMIC RESPONSE OF PILES IN LAYERED SOIL PROFILE

This paper is aimed at highlighting the importance of Kinematic Seismic Response of Piles, a phenomenon often ignored in dynamic analysis. A case study is presented where the end bearing pile is embedded in two layer soil system of highly contrasting stiffness; a typical case where kinematic loading plays important role. The pile soil system is modeled as continuous system and as discrete parameter system. both are based on BDWF (Beam on Dynamic Winkler Foundation) formulation. For discrete parameter system, a finite element software SA P2000 is used and the modeling technique of kinematic interaction in finite element software is discussed. For pile soil system modeled as continuous system, a general MATLAB code is developed capable of performing elastic sate response analysis in two layer soil system, solving differential equation governing kinematic interaction, and giving as output the maximum ground displacement, maximum pile displacement, rotation, moment and shear distribution along pile length. The paper concludes that kinematic seismic actions must be evaluated particularly at the interface of soil layers of significantly differing soil stiffnesses.

Thin-layer effects on the CPT qc measurement

A numerical analysis is presented to model the cone penetration test (CPT) tip resistance in layered soil. Analyses are performed for two-layer soils composed of either sands with different relative densities or different materials (sand and clay). Parametric numerical modeling is used to determine the distance that a cone senses a new upcoming soil layer interface or a layer interface behind. Analyses are also carried out for a thin sand layer embedded in soft clay. It is seen that the full tip resistance may not be reached in thin stiff layers. This is especially true for penetration in thin dense sand layers interbedded in softer clay. A correction factor is suggested to correct the cone tip resistance in thin sand layers. The higher the stiffness and the thinner the layer, the larger the correction factor. The numerical results obtained in this paper are in good agreement with experimental observations. Some limitations of a previously proposed correction factor are discussed.Key words: cone tip resistance, modeling, sand, clay, interface influence distance, layering.