Pile Running in Layered Soils

This paper presents a case study on incidents of offshore pile running in layered soils.The study provides a detailed description of the seabed soil data,pile driving records,and field surveillance video observations.Three-dimensional large deformation finite element(LDFE)analyses were conducted to retrospectively analyze the incidents,considering the remoulding of seabed soil and degradation of the pile-soil interface in the LDFE modeling.By comparing the field observations with the LDFE analysis,the mechanism of pile running was discussed,with a focus on investigating the pile penetration resistance in each layer.The study revealed that pile running in layered soils primarily resulted from a significant reduction in pile base resistance when transitioning from a strong layer to an adjacent weak layer.To further investigate the pile running mechanism in layered soils,a parametric study on the strength variation of adjacent soil layers and its influence on pile base resistance was conducted.Lastly,a simplified prediction model of pile base resistance,suitable for assessing the risk of pile running in layered soils,was proposed.

Longitudinal vibration of pile in layered soil based on Rayleigh-Love rod theory and fictitious soil-pile model

The dynamic response of pile in layered soil is theoretically investigated when considering the transverse inertia effect.Firstly, the fictitious soil-pile model is employed to simulate the dynamic interaction between the pile and the soil layers beneath pile toe. The dynamic interactions of adjacent soil layers along the vertical direction are simplified as distributed Voigt models.Meanwhile, the pile and fictitious soil-pile are assumed to be viscoelastic Rayleigh-Love rods, and both the radial and vertical displacement continuity conditions at the soil-pile interface are taken into consideration. On this basis, the analytical solution for dynamic response at the pile head is derived in the frequency domain and the corresponding quasi-analytical solution in the time domain is then obtained by means of the convolution theorem. Following this, the accuracy and parameter value of the hypothetical boundaries for soil-layer interfaces are discussed. Comparisons with published solution and measured data are carried out to verify the rationality of the present solution. Parametric analyses are further conducted by using the present solution to investigate the relationships between the transverse inertia effects and soil-pile parameters.

Deep Penetration of Spudcan Foundation into Double Layered Soils

The spudcan foundation has been widely used in offshore engineering for jack-up rigs. However, “punch through' failure often occurs where a stronger soil layer overlays a softer soil layer. In this study, spudcan penetration into double layered soils is investigated numerically. The soil profile is set up as a stronger soil layer overlaying a softer soil layer, with the soil strength ratio (bottom soil strength / top soil strength) varied from 0.1 to 1.0 (1 means uniform soil). The bearing behaviour is discussed and the bearing capacity factors are given for various cases involving different layer thicknesses and different strength ratios of the two clay layers. The development of the plastic zones and the effect of soil self-weight on the bearing capacity are also discussed. From this study, it is found that, when a spudcan is distant from the soil layer boundary, the spudcan can be analysed with single soil layer data. However, when a spudcan becomes closer to the soil boundary layer, the influence of the lower soft soil layer is significant, and the bearing capacity of the spudcan decreases. The critical distance is an indication of the occurrence of “punch through' failure. The critical distance between the spudcan and the layer boundary is larger for a rough spudcan than the one for a smooth one, and the critical distance decreases with increasing soil strength ratio. The depth of cavity formed during initial spudcan penetration depends on the top layer soil strength, soil strength ratio and unit soil self-weight, and the cavity affects the spudcan bearing behaviour as well.

Mode-based equivalent multi-degree-of-freedom system for one-dimensional viscoelastic response analysis of layered soil deposit

Discrete models such as the lumped parameter model and the finite element model are widely used in the solution of soil amplification of earthquakes. However, neither of the models will accurately estimate the natural frequencies of soil deposit, nor simulate a damping of frequency independence. This research develops a new discrete model for onedimensional viscoelastic response analysis of layered soil deposit based on the mode equivalence method. The new discrete model is a one-dimensional equivalent multi-degree-of-freedom（MDOF） system characterized by a series of concentrated masses, springs and dashpots with a special configuration. The dynamic response of the equivalent MDOF system is analytically derived and the physical parameters are formulated in terms of modal properties. The equivalent MDOF system is verified through a comparison of amplification functions with the available theoretical solutions. The appropriate number of degrees of freedom（DOFs） in the equivalent MDOF system is estimated. A comparative study of the equivalent MDOF system with the existing discrete models is performed. It is shown that the proposed equivalent MDOF system can exactly present the natural frequencies and the hysteretic damping of soil deposits and provide more accurate results with fewer DOFs.

Stochastic seismic response of multi-layered soil with random layer heights

This paper deals with the effect of layer height randomness on the seismic response of a layered soil. These parameters are assumed to be lognormal random variables. The analysis is carried out via Monte Carlo simulations coupled with the stiffness matrix method. A parametric study is conducted to derive the stochastic behavior of the peak ground acceleration and its response spectrum,the transfer function and the amplification factors. The input soil characteristics correspond to a site in Mexico City and the input seismic accelerations correspond to the Loma Prieta earthquake. It is found that the layer height heterogeneity causes a widening of the frequency content and a slight increase in the fundamental frequency of the soil profile,indicating that the resonance phenomenon is a concern for a large number of structures. Variation of the layer height randomness acts as a variation of the incident angle,i.e.,a decrease of the amplitude and a shift of the resonant frequencies.

Axisymmetric Finite Element Method for Analysis of Plate on Layered Soil

To obtain the fundamental solution of soil has become the key problem for the semi-analytical and semi-numerical (SASN) method in analyzing plate on layered soil. By applying axisymmetric finite element method (FEM),an expression relating the surface settlement and the reaction of the layered soil can be obtained. Such a reaction can be treated as load acting on the applied external load. Having the plate modelled by four-node elements,the governing equation of the plate can be formed and solved. In this case, the fundamental solution can be introduced into the global soil stiffness matrix and five-node or nine-node element soil stiffness matrix.The existing commercial FEM software can be used to solve the fundamental solution of soil, which can bypass the complicated formula derivation and boasts high computational efficiency as well.

ONE-DIMENSIONAL CONSOLIDATION OF LAYERED SOILS WITH IMPEDED BOUNDARIES UNDER TIME-DEPENDENT LOADINGS

On the basis of Terzaghi's one-dimensional consolidation theory, the variation of effective stress ratio in layered saturated soils with impeded boundaries under time-dependent loading was studied. By the method of Laplace transform, the solution was presented. Influences of different kinds of cyclic loadings and impeded boundaries conditions were discussed. Through numerical inversion of Laplace transform, useful illustrations were given considering several common time-dependent loadings. Pervious or impervious boundary condition is just the special case of the problem considered here. Compared with average index method,the results from the method illustrated are more accurate.

Theoretical Formula for Calculating Negative Skin Friction of Pile in Layered Soil and Its Application

Based on Zeevaert＇s method, a theoretical formula was developed to calculate the negative skin friction of pile in layered soil. For practical purpose,a cut-and-try method was proposed to determine neutral point. Case studies indicate that the total calculated negative skin friction was in agreement with the measured one, which verifies the feasibility and practicability of theoretical formula. Furthermore, the methods for calculating efficiency factor of drag load and settlement were also given.

Pile foundation in alternate layered liquefiable and non-liquefiable soil deposits subjected to earthquake loading

Pile foundations are still the preferred foundation system for high-rise structures in earthquake-prone regions.Pile foundations have experienced failures in past earthquakes due to liquefaction.Research on pile foundations in liquefiable soils has primarily focused on the pile foundation behavior in two or three-layered soil profiles.However,in natural occurrence,it may occur in alternative layers of liquefiable and non-liquefiable soil.However,the experimental and/or numerical studies on the layered effect on pile foundations have not been widely addressed in the literature.Most of the design codes across the world do not explicitly mention the effect of sandwiched non-liquefiable soil layers on the pile response.In the present study,the behavior of an end-bearing pile in layered liquefiable and non-liquefiable soil deposit is studied numerically.This study found that the kinematic bending moment is higher and governs the design when the effect of the sandwiched non-liquefied layer is considered in the analysis as opposed to when its effect is ignored.Therefore,ignoring the effect of the sandwiched non-liquefied layer in a liquefiable soil deposit might be a nonconservative design approach.

A simplified method for the determination of vertically loaded pile-soil interface parameters in layered soil based on FLAC3D

The numerical analysis of pile-soil interaction commonly requires a lot of trial works to determine the interface parameters and the accuracy cannot be ensured normally. Considering this, this paper first conducts a sensitivity analysis to figure out the influence of interface parameters on the bearing behavior of a single pile in sand. Then, a simplified method for the determination of pile-soil interface parameters in layered soil is proposed based on the parameter studies. Finally, a filed loading test is used for the validation of the simplified method, and the calculated results agree well with the monitoring data. In general, the simplified method proposed in this paper works with higher accuracy and consumes less time compared with the traditional trial works, especially on the determinations ofinterfacial cohesive and interracial friction angle.

A Simplified Method for the Stress Analysis of Underground Transfer Structures Crossing Multiple Subway Tunnels

According to the design specifications,the construction of extended piles involves traversing the tunnel’s upper region and extending to the underlying rock layer.To address this challenge,a subterranean transfer structure spanning multiple subway tunnels was proposed.Deliberating on the function of piles in the transfer structure as springs with axial and bending stiffness,and taking into account the force balance and deformation coordination conditions of beams and plates within the transfer structure,we established a simplified mechanical model that incorporates soil stratification by combining it with the Winkler elastic foundation beam model.The resolved established simplifiedmechanicalmodel employed finite difference technology and the Newton-Simpsonmethod,elucidating the mechanical mechanism of the transfer structure.The research findings suggest that the load carried by the upper structural columns can be transferred to the pile foundation beneath the beams through the transfer structure,subsequently reaching the deep soil layer and ensuring minimal impact on adjacent tunnels.The established simplified analysis method can be used for stress analysis of the transfer structure,concurrently considering soil stratification,pile foundation behavior,and plate action.The pile length,pile section size,and beam section size within the transfer structure should account for the characteristics of the upper load,ensuring an even distribution of the beam bending moment.

Dynamic Installation Behaviors of A New Hybrid Plate Anchor in Layered Marine Clay

Layered soil profiles create challenges for foundation installation and detrimentally affect the foundation performance.This research explored the free-fall penetration behavior of a new dynamically installed plate anchor,the Flying Wing Anchor?,in layered soil profiles.This new concept anchor combines the advantages of low-cost installation of torpedo piles and high efficiency of plate anchors.Anchor is initially installed through free-fall like a torpedo pile,and followed by drag embedment like a plate anchor.The methodology is to perform free-fall penetration tests with a model anchor in a variety of test beds containing marine clays with different profiles of undrained shear strength versus depth.A calibrated prediction model accounting for the effects of strain-rate and stiff layer produces results similar to those from the model test.The design curves were developed based on the calibrated analytical model,and are valuable to estimate the impact velocity thresholds of prototype anchor to penetrate through stiff layers.The free-fall penetration tests indicated that the penetration ability of FWA?increases with the increased impact velocity.This new dynamically embedded plate anchor can penetrate through the stiff layers that would cause problems for the conventional plate anchor,such as the drag embedded anchor,plowing on the top of stiff layer instead of breaking into it.Therefore,the new dynamically embedded plate anchor can provide a possible solution for layered soil profiles in deep water.

Long Term Effects of Farming System on Soil Water Content and Dry Soil Layer in Deep Loess Profile of Loess Tableland in China

Soil water is strongly affected by land use/cover in the Loess Plateau in China. Water stored in thick loessal soils is one of the most important resources regulating vegetation growth. However, soil water in the deep loess proifle, which is critical for maintaining the function of the“soil water pool”is rarely studied because deep proifle soil samples are dififcult to collect. In this study, four experimental plots were established in 2005 to represent different farming systems on the Changwu Tableland：fallow land, fertilized cropland, unfertilized cropland, and continuous alfalfa. The soil water content in the 15-m-deep loess proifles was monitored continuously from 2007 to 2012 with the neutron probe technique. The results showed that temporal variations in soil water proifles differed among the four farming systems. Under fallow land, the soil water content increased gradually over time, ifrst in the surface layers and later in the deep soil layers. In contrast, the soil water content decreased gradually under continuous alfalfa. The distributions of soil water in deep soil layers under both fertilized and unfertilized cropland were relatively stable over time. Thus farming system signiifcantly affected soil water content. Seven years after the start of the experiment, the soil water contents in the 15-m-deep proifles averaged 23.4%under fallow land, 20.3%under fertilized cropland, 21.6%under unfertilized cropland, and 16.0%under continuous alfalfa. Compared to measurements at the start of the experiment, both fallow land and unfertilized cropland increased soil water storage in the 15-m loess proifles. In contrast, continuous alfalfa reduced soil water storage. Fertilized cropland has no signiifcant effect on soil water storage. These results suggest that deep soil water can be replenished under the fallow and unfertilized farming systems. Dry soil layers （i.e., those which have soil water content less than the stable ifeld water capacity） in the subsoil of the Changwu Tableland region can be classiifed as either temporary dry soil layers or persistent dry soil layers. Temporary dry soil layers, which typically form under annual crops, often disappear during wet years. Persistent dry soil layers generally develop under perennial vegetation. Even after removing the vegetation, persistent dry soil layers remain for several decades. This study provides information useful for the conservation and utilization of soil water resources in the Loess Tableland.

Effects of Phosphorus Application in Different Soil Layers on Root Growth, Yield, and Water-Use Efficiency of Winter Wheat Grown Under Semi-Arid Conditions

Deep phosphorus application can be a usefull measure to improve crops＇ performance in semi-arid regions, but more knowledge of both its general effects and effects on specific crops is required to optimize treatments. Thus, the aims of this study were to evaluate the effects of phosphorus（P） application at different soil layers on root growth, grain yield, and water-use efficiency（WUE） of winter wheat grown on the semi-arid Loess Plateau of China and to explore the relationship between root distribution and grain yield. The experiment consisted of four P treatments in a randomized complete block design with three replicates and two cultivars： one drought-sensitive（Xiaoyan 22, XY22） and one drought-tolerant（Changhan 58, CH58）. The four P treatments were no P（control, CK）, surface P（SP）, deep P（DP）, and deep-band P application（DBP）. CH58 produced larger and deeper root systems, and had higher grain yields and WUE, under the deep P treatments（DP and DBP） than under SP, clearly showing that deep P placement had beneficial effects on the drought-tolerant cultivar. In contrast, the grain yield and root growth of XY22 did not differ between DP or DBP and SP treatments. Further, root dry weight（RW） and root length（RL） in deep soil layer（30-100 cm） were closely positively correlated with grain yield and WUE of CH58（but not XY22）, highlighting the connections between a well-developed subsoil root system and both high grain yield and WUE for the drought-tolerant cultivar. WUE correlated strongly with grain yield for both cultivars（r=0.94, P〈0.001）. In conclusion, deep application of P fertilizer is a practical and feasible means of increasing grain yield and WUE of rainfed winter wheat in semi-arid regions, by promoting deep root development of drought-tolerant cultivars.

A new method for solving Biot's consolidation of a finite soil layer in the cylindrical coordinate system

A new method is developed to solve Biot＇s consolidation of a finite soil layer in the cylindrical coordinate system. Based on the governing equations of Biot＇s consolidation and the technique of Laplace transform, Fourier expansions and Hankel transform with respect to time t, coordinate θ and coordinate r, respectively, a relationship of displacements, stresses, excess pore water pressure and flux is established between the ground surface （z = 0） and an arbitrary depth z in the Laplace and Hankel transform domain. By referring to proper boundary conditions of the finite soil layer, the solutions for displacements, stresses, excess pore water pressure and flux of any point in the transform domain can be obtained. The actual solutions in the physical domain can be acquired by inverting the Laplace and the Hankel transforms.

Spatiotemporal variation of soil organic carbon in the cultivated soil layer of dry land in the South-Western Yunnan Plateau, China

The dynamics of soil organic carbon(SOC)in cropland is one of the central issues related to both soil fertility and environmental safety. However, little information is available at county level regarding the spatiotemporal variability of SOC in the southwestern mountainous region of China. Thus, this study aimed to explore spatiotemporal changes of SOC in the cultivated soil layer of dry land in Mojiang County,Yunnan Province, China. Data were obtained from the second national soil survey(SNSS) of 1985 and soil tests for fertilizer application carried out by the Mojiang Agricultural Bureau in 2006. The ANOVA test was applied to determine any significant differences between the datasets, while semivariogram analysis was performed on geostatistics via an ordinary Kriging method in order to map spatial patterns of soil organic carbon density(SOCD). The results revealed that SOCD in the cultivated soil layer significantly decreased from 3.93 kg m^(-2) in 1985 to 2.89 kg m^(-2) in 2006, with a total soil organic carbon stock(SOCS) decrease of 41.54×10~4 t over the same period. SOCS levels fell most markedly in yellow-brown soil at a rate of51.52%, while an increase of 8.70% was found in the analysed latosol. Geostatistical analysis also showed that the recorded changes in SOCD between 1985 and2006 were spatially structured. The decreasing trend might be attributed to the combined action of intense cultivation, major crop residue removal without any protective tillage measures, unreasonable fertilization and natural climatic diversity inducing a large decrease in SOC in the studied cultivated dry land region of Mojiang County. Therefore, management measures such as protective tillage should be undertaken in order to enhance soil C sequestration.

The impact of land use change on quality evolution of soil genetic layers on the coastal plain of south Hangzhou Bay

Land use change plays an important part in the studies of global environmental change and regional sustainable development. The change of soil quality can particularly reflect the impacts of human socio-economic activities on environment. Taking the coastal plain of south Hangzhou Bay as a study case, we analyzed the effects of land use changes on organic matter （OM）, total nitrogen （TN）, total phosphorus （TP）, available phosphorus （AP）, available potassium （AK）, total salinity （TS）, pH value in soil genetic layers, and assessed soil quality change related to different land use types from 1982 to 2003. The results show that： （1） The general change tendency of soil quality in the coastal plain of south Hangzhou Bay declined obviously in A layer and slightly rise in B （or P） layer and C （or W） layer. The contents of TP decreased generally in all soil genetic layers, but the variety difference of other soil quality indices was relatively great. （2） The change of soil quality in the areas where land use changed is far more remarkable than that with land use unchanged. The value of quality variety is A layer 〉B （or P） layer 〉C （or W） layer. （3） The changes of soil tillage, cultivation, fertilization, irrigation and drainage activities related to land use may make some soil-forming processes disappeared and bring in other new processes which will affect the soil quality and soil genetic layers directly.

Plane strain consolidation of soil layer with anisotropic permeability

This paper presents an alternative analytical technique to study a plane strain consolidation of a poroelastic soil by taking into account the anisotropy of permeability. From the governing equations of a saturated poroelastic soil, the relationship of basic variables for a point of a soil layer is established between the ground surface （z=0） and the depth z in the Laplace-Fourier transform domain. Combined with the boundary conditions, an exact solution is derived for plane strain Biot＇s consolidation of a finite soil layer with anisotropic permeability in the transform domain. Numerical inversions of the Laplace transform and the Fourier transform are adopted to obtain the actual solution in the physical domain. Numerical results of plane strain Biot＇s consolidation for a single soil layer show that the anisotropic of permeability has a great influence on the consolidation behavior of the soils.

A new analytical solution to axisymmetric Biot's consolidation of a finite soil layer

A new analytical method is presented to study the axisymmetric Biot＇s consolidation of a finite soil layer. Starting from the governing equations of axisymmetric Blot＇s consolidation, and based on the property of Laplace transform, the relation of basic variables for a point of a finite soil layer is established between the ground surface （z= 0） and the depth z in the Laplace and Hankel transform domains. Combined with the boundary conditions of the finite soil layer, the analytical solution of any point in the transform domain can be obtained. The actual solution in the physical domain can be obtained by inverse Laplace and Hankel transforms. A numerical analysis for the axisymmetric consolidation of a finite soil layer is carried out.