Effects of cement-enhanced soil on the ultimate lateral resistance of composite pile in clayey soil

The composite pile consisting of core-pile and surrounding cement-enhanced soil is a promising pile foundation in recent years.However,how and to what extent the cement-enhanced soil influences the ultimate lateral resistance has not been fully investigated.In this paper,the ultimate lateral resistance of the composite pile was studied by finite element limit analysis(FELA)and theoretical upper-bound analysis.The results of FELA and theoretical analysis revealed three failure modes of laterally loaded composite piles.The effects of the enhanced soil thickness,strength,and pile-enhanced soil interface characteristics on the ultimate lateral resistance were studied.The results show that increasing the enhanced soil thickness leads to a significant improvement on ultimate lateral resistance factor(N P),and there is a critical thickness beyond which the thickness no longer affects the N P.Increasing the enhanced soil strength induced 6.2%-232.6%increase of N P.However,no noticeable impact was detected when the enhanced soil strength was eight times higher than that of the natural soil.The maximum increment of N P is only 30.5%caused by the increase of interface adhesion factor(a).An empirical model was developed to calculate the N P of the composite pile,and the results show excellent agreement with the analytical results.

Longitudinal vibration characteristics of a tapered pipe pile considering the vertical support of surrounding soil and construction disturbance

This research is concentrated on the longitudinal vibration of a tapered pipe pile considering the vertical support of the surrounding soil and construction disturbance.First,the pile-soil system is partitioned into finite segments in the vertical direction and the Voigt model is applied to simulate the vertical support of the surrounding soil acting on the pile segment.The surrounding soil is divided into finite ring-shaped zones in the radial direction to consider the construction disturbance.Then,the shear complex stiffness at the pile-soil interface is derived by solving the dynamic equilibrium equation for the soil from the outermost to innermost zone.The displacement impedance at the top of an arbitrary pile segment is obtained by solving the dynamic equilibrium equation for the pile and is combined with the vertical support of the surrounding soil to derive the displacement impedance at the bottom of the upper adjacent segment.Further,the displacement impedance at the pile head is obtained based on the impedance function transfer technique.Finally,the reliability of the proposed solution is verified,followed by a sensitivity analysis concerning the coupling effect of the pile parameters,construction disturbance and the vertical support of the surrounding soil on the displacement impedance of the pile.

Study on the Wind Erosion Resistance of Desert Soil Induced by Bacillus Megaterium

With the intensification of global climate change and the worsening of land degradation,desertification has emerged as a significant global issue threatening ecosystems and human activities.The technique of Microbial Induced Calcium Carbonate Precipitation(MICP)has been widely applied in soil stabilization and engineering geology in recent years.This study conducts experiments using Bacillus megaterium to solidify desert sand via MICP,aiming to explore its feasibility as a novel ecological method for desert protection.Experimental results indicate that desert sand treated with MICP exhibits a significant enhancement in wind erosion resistance,providing a potential solution for desert management and land restoration.

High-strain dynamic model of large-diameter pipe piles with soil plug for vertical vibration analysis

A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.

Shear resistance characteristics and influencing factors of root-soil composite on an alpine metal mine dump slope with different recovery periods

Artificial vegetation restoration is the main measure for vegetation restoration and soil and water conservation in alpine mine dumps on the Qinghai-Tibet Plateau,China.However,there are few reports on the dynamic changes and the influencing factors of the soil reinforcement effect of plant species after artificial vegetation restoration under different recovery periods.We selected dump areas of the Delni Copper Mine in Qinghai Province,China to study the relationship between the shear strength and the peak displacement of the root-soil composite on the slope during the recovery period,and the influence of the root traits and soil physical properties on the shear resistance characteristics of the root-soil composite via in situ direct shear tests.The results indicate that the shear strength and peak displacement of the rooted soil initially decreased and then increased with the increase of the recovery period.The shear strength of the rooted soil and the recovery period exhibited a quadratic function relationship.There is no significant function relationship between the peak displacement and the recovery period.Significant positive correlations(P<0.05)exists between the shear strength of the root-soil composite and the root biomass density,root volume density,and root area ratio,and they show significant linear correlations(P<0.05).There are no significant correlations(P>0.05)between the shear strength of the root-soil composite and the root length density,and the root volume ratio of the coarse roots to the fine roots.A significant negative linear correlation(P<0.05)exists between the peak displacement of the rooted soil and the coarse-grain content,but no significant correlations(P>0.05)with the root traits,other soil physical property indices(the moisture content and dry density of the soil),and slope gradient.The coarse-grain content is the main factor controlling the peak displacement of the rooted soil.

AHFO-based soil water content sensing technology considering soil-sensor thermal contact resistance

The actively heated fiber-optic(AHFO)technology has become emerged as a research focus due to its advantages of distributed,real-time measurement and good durability.These attributes have led to the gradual application of AHFO technology to the water content measurement of in situ soil.However,all existing in situ applications of AHFO technology fail to consider the effect of soilesensor contact quality on water content measurements,limiting potential for the wider application of AHFO technology.To address this issue,the authors propose a method for determining the soilesensor thermal contact resistance based on the principle of an infinite cylindrical heat source.This is then used to establish an AHFO water content measurement technology that considers the thermal contact resistance.The reliability and validity of the new measurement technology are explored through a laboratory test and a field case study,and the spatial-temporal evolution of the soil water content in the case is revealed.The results demonstrate that method for determining the soilesensor thermal contact resistance is highly effective and applicable to all types of soils.This method requires only the moisture content,dry density,and thermal response of the in situ soil to be obtained.In the field case,the measurement error of soil water content between the AHFO method,which takes into account the thermal contact resistance,and the neutron scattering method is only 0.011.The water content of in situ soil exhibits a seasonal variation,with an increase in spring and autumn and a decrease in summer and winter.Furthermore,the response of shallow soils to precipitation and evaporation is significant.These findings contribute to the enhancement of the accuracy of the AHFO technology in the measurement of the water content of in situ soils,thereby facilitating the dissemination and utilization of this technology.

Thermomechanical Characterization of Three Soils of Abeche in Chad

The study carried out concerns the valorization of agricultural waste for the development of biosourced materials that can be used as insulation in homes. This article is devoted to the influence of gum arabic on the mechanical and thermal properties of clay soils in the town of Abéché. The mechanical tests were carried out using the CBR press equipped with two devices (bending device and compression device). Thermal property such as thermal conductivity was determined by the hot wire method and thermal resistance was derived by calculation. Thus, the tests were carried out on test pieces made from a mixture of clay and gum arabic in solution. The experimental program includes seven formulations (0%, 2%, 4%, 6%, 8%, 10% and 12%). The results obtained showed that the best flexural and compressive strengths are obtained by using gum arabic with a rate of 8% and a maximum stress of 4.3 MPa. In addition, the thermal results also showed that the thermal conductivity decreases when the percentage of gum arabic increases, which makes it possible to increase the thermal resistance, thus confirming the capacity of gum arabic to provide thermal insulation.

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.

A theoretical analysis of vertical dynamic response of large-diameter pipe piles in layered soil

Considering the viscous damping of the soil and soil-pile vertical coupled vibration,a computational model of large-diameter pipe pile in layered soil was established.The analytical solution in frequency domain was derived by Laplace transformation method.The responses in time domain were obtained by inverse Fourier transformation.The results of the analytical solution proposed agree well with the solutions in homogenous soil.The effects of the shear modulus and damping coefficients of the soil at both outer and inner sides of the pipe pile were researched.The results indicate that the shear modulus of the outer soil has more influence on velocity admittance than the inner soil.The smaller the shear modulus,the larger the amplitude of velocity admittance.The velocity admittance weakened by the damping of the outer soil is more obvious than that weakened by the damping of the inner soil.The displacements of the piles with the same damping coefficients of the outer soil have less difference.Moreover,the effects of the distribution of soil layers are analyzed.The results indicate that the effect of the upper soil layer on dynamic response of the pipe pile is more obvious than that of the bottom soil layer.A larger damping coefficient of the upper layer results in a smaller velocity admittance.The dynamic response of the pipe pile in layered soil is close to that of the pipe pile in homogenous soil when the properties of the upper soil layer are the same.

Effects of variations of voltage and pH value on the shear strength of soil and durability of different electrodes and piles during electrokinetic phenomenon

Electrokinetic(EK)treatment is an effective method in accelerating the consolidation and improving the geotechnical properties of fine-grained soils.This method stabilizes the soil and increases the bearing capacity of piles by improving the soil shear strength.Changing the soil p H,due to the occurrence of chemical reactions of electrolysis in the soil,can increase its shear strength.However,the electrodes used in this method corrode due to the change in the soil p H,which in turn reduces the electrical potential.Electrode corrosion and loss of electrical potential can significantly reduce the efficiency of the EK method.In addition,when using the EK method to increase the bearing capacity of piles,changing the p H can cause corrosion and damage to the piles.One of the most important factors influencing the change in the p H of soil is the voltage applied during the EK process.It was reported that increasing the voltage affects the intensity of chemical reactions and electroosmotic flow and thus increases the efficiency of EK.However,very limited research has been conducted on the effect of voltage on the performance of EK method.In the present study,the effects of three voltages on soil p H and corrosion resistance of four types of electrodes including iron(Ir),stainless steel(St),copper(Co),and aluminium(Al)were studied.In addition,the effects of p H variations on the corrosion rate of three types of piles including steel pile(SP),reinforced cement concrete pile(RCCP),and reinforced lime-cement concrete pile(RLCCP)were investigated.It was observed that increasing the voltage from a specific limit had no effect on the intensity of electrolysis reactions and the soil p H adjacent to the electrodes did not change more than a specific limit.Moreover,increasing the voltage to higher than 35 V(i.e.45 V)did not increase the volume of drained water from the soil,but caused more electric current than the allowable current for Ir,St,and Al electrodes,and the corrosion intensity of these electrodes increased significantly.RCCP reduced the soil p H to 2.4 within 7 d of curing due to severe corrosion(13%corrosion rate).The soil p H values adjacent to RCCP and RLCCP within 28 d of curing reduced to 3.7 and 3.8,respectively,but the two piles were not damaged.In general,the results of this research showed that selecting an optimized voltage had a significant effect on the efficiency of EK,and increasing the voltage did not always lead to increase in the efficiency of EK process.

Probabilistic limit state design methodof the axial resistance of post grouting pile

The reliability of post grouting pile axial resistance was studied by proposing a design method for its probabilistic limit state,which is represented by the partial coefficients of load,end,and side resistance.The hyperbolic,modified hyperbolic,and polynomial models were employed to predict the ultimate bearing capacity of test piles that were not loaded to damage in field tests.The results were used for the calculation and calibration of the reliability index.The reliability of the probabilistic limit state design method was verified by an engineering case.The results show that the prediction results obtained from the modified hyperbolic model are closest to those obtained through the static load test.The proposed corresponding values of total,side,and end resistance partial coefficients are 1.84,1.66,and 2.73 when the dead and live load partial coefficients are taken as 1.1 and 1.4,respectively.Meanwhile,the corresponding partial coefficients of total,side,and end resistance are 1.70,1.56,and 2.34 when the dead and live load partial coefficients are taken as 1.2 and 1.4,respectively.

Cyclic Lateral Responses of Monopiles Considering the Influence of Pile−Soil Relative Stiffness in Sand

The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the effect of pile−soil relative stiffness(K_(R)).This paper presents a series of 1-g cyclic tests aimed at improving understanding of the cyclic lateral responses of monopiles under different pile−soil systems.These systems are arranged by two model piles with different stiffness,including four different slenderness ratios(pile embedded length,L,normalized by diameter,D)under medium dense sand.The K_(R)-values are calculated by a previously proposed method considering the real soil stress level.The test results show that the lateral accumulation displacement increases significantly with the increment of the K_(R)-value,while the cyclic secant stiffness performs inversely.The maximum pile bending moment increases with the cycle number for the rigid pile−soil system,but shows a decreasing trend in the flexible system.For an uppermost concern,an empirical model is proposed to predict the accumulated displacement of arbitrary pile−soil systems by combining the results from this study with those from previous experimental investigations.The validity of the proposed model is demonstrated by 1-g and centrifuge tests.

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.

Potassium Supplying Power of Soils in Heilongjiang Province and the Effect of Potassium Application on Resistance of Crops to Adverse Conditions

The total potassium (K) content of soils in Heilongjiang was relatively high in general and the available potassium content in soils was quite different for different soil types. The results of electro - ultra- filtration (EUF) analysis showed that the dark brown forest soils and the black soils in the northern part contained relatively high EUF-K, ranged from 12.5 to 15.7 mg per 100 g soil. In the black soils in the southern part, the EUF-K ranged from 8 to 9 mg per 100 g soil. The albic and aeolian sandy soils contained low EUF-K, ranged from 3.2 to 4.8 mg per 100 g soil. Field experiment in 1982 indicated that potassium fertilizer in soils with medium or low EUF-K, increased soybean yield by 17%-34%, and obviously prevented the epidemic of meadow moth and soybean mosaic virus. Application of potassium fertilizer increased the protein and total sugar content of the plants, promoted transportation of nutrients, speeded up the growth of the plants, improved the resistance of crops to adverse conditions. Application of potassium fertilizer resulted in early maturity of crops (4 - 7 days earlier than control), which had great significance for preventing crops from early frost damage. Hence, in order to keep nutrients balance in the soil and to increase soil fertility, potassium fertilizer or materials containing potassium must be applied to soils with medium and low EUF- K, such as black soils in the south part, ablic soils and aeolian sandy soils in Heilongjiang province.

A Simplified Method for Estimating the Initial Stiffness of Monopile-Soil Interaction Under Lateral Loads in Offshore Wind Turbine Systems

The interface mechanical behavior of a monopile is an important component of the overall offshore wind turbine structure design.Understanding the soil-structure interaction,particularly the initial soil-structure stiffness,has a significant impact on the study of natural frequency and dynamic response of the monopile.In this paper,a simplified method for estimating the interface mechanical behavior of monopiles under initial lateral loads is proposed.Depending on the principle of minimum potential energy and virtual work theory,the functions of soil reaction components at the interface of monopiles are derived;MATLAB programming has been used to simplify the functions of the initial stiffness by fitting a large number of examples;then the functions are validated against the field test data and FDM results.This method can modify the modulus of the subgrade reaction in the p-y curve method for the monopile-supported offshore wind turbine system.

Numerical Study of the Interaction between a Reinforced Concrete Pile and Soil

This paper proposes a numerical simulation of the mechanical behavior of a reinforced concrete pile foundation under an axial load. In fact, the foundation of a structure represents the essential structural part of it, because it ensures its bearing capacity. Among the types of foundation, deep foundation is the one for which from a mechanical point of view, the justification takes into account the isolated or combined effects of base resistance offered by the soil bed and lateral friction at the soil-pile interface;the latter being the consequence of a large contact surface with the surrounding soil;hence the need to study the interaction between the soil and the pile in service, in order to highlight the characteristics of soil which influence the mechanical behavior of pile and therefore the stability of the structure. In this study, the reinforced concrete pile is supposed to be elastic, and characterized by a young’s modulus (E) and a Poisson’s ratio (ν). The soil obeys to a Camclay model characterized by a cohesion (c), an initial voids ratio (e0), shearing resistance angle (φ) and a pre-consolidation pressure (P0). A joint model with a Mohr Coulomb behavior characterizes the soil-pile interface. The loading is carrying out by imposing a vertical monotonic displacement at the head of pile. The results in terms of stress and displacement show that the bearing capacity of the pile is influenced by various soils characteristics, it appears that the vertical stress and the force mobilized at rupture increase when the initial pre_consolidation pressure, the cohesion and the internal friction angle of soil increase;and when the initial soil voids index decreases.

Effects of Soil Acidification on Yield of Late Rice and Differences in Acid Resistance among Varieties

Effect of soil acidification on yield of late rice was studied and acid resistance of late rice varieties were compared with 23 late rice varieties as materials in Changsha County, Hunan Province. The results indicated that the difference in yield among varieties was obvious, yield in common field was among 5 226.6-9 202.1kg/hm^2, and yield in acidified field was among 3 643.2-7 714. 8 kg/hm^2. Compared with common field, yield of Yueyou 6135, Huayou 18, Jinyou 284 and Ⅱyou 46 increased by 3.24%-26.33% in acidified field, while yield of other varieties decreased by 2.04%-56.79% in acidified field. According to acidification sensitivity, Wufengyou T025, Jinchuyou No.148, Yueyou No.6135, Shenyou No.9586, Xiangfengyou No.103,Zhongyou No.288, Nongxiang No.18, Shanyou No.432, Ⅱ you No.6, and Zhong 9A/R10402 were sensitive to soil acidification; Wuyou No.308, Zhunliangyou No.608,Fengyuanyou No.227, Fengyou No.1167, Fengyuanyou No.299, T you No.272, and Zhong 9A/R9963 were moderately sensitive to soil acidification; Yueyou No.9113,Jinyou No.284, Shenyou No.9588, Huayou No.18, Ⅱ you No.46 and Ⅱ you No.3027 were slightly sensitive to soil acidification

Study on Optimization of Design Parameters for Precast Pipe Pile Treatment of Soft Soil Subgrade on the Jianghan Plain

The soft soil in the Jianghan Plain is characterized by a high water content, liquid limit, sensitivity, porosity ratio, and organic matter content and low strength and is commonly known as “five highs and one low” soft soil. Thus, the construction of expressways in this area is likely to cause subgrade settlement. The manuscript investigated the influence of the design parameters of precast pipe piles on the soft ground treatment in the Jianghan Plain based on the case of the soft soil subgrade project of the Xiaogan south section of the Wuhan city ring expressway, China. Midas GTS NX 2019 finite element software was used to analyse the settlement pattern of the subgrade under the variations in pile length, pile spacing and pile diameter. The results show that precast pipe piles are effective in reducing the settlement of soft soil subgrades with a high compressibility and water content;the soft foundation settlement decreases with increasing pile length and pile diameter and decreasing pile spacing. As the pile tip is embedded in the bearing stratum, the settlement of the soft foundation is greatly affected by the variations in pile length and pile spacing while slightly influenced by the variation in pile diameter;in combination with the curve fitting obtained from the real-time monitoring data, the analysis concludes that the soft foundation treatment plan with a pile length of 15 m, pile spacing of 1.2 m to 1.5 m and pile diameter of 0.6 m can better contain the soft soil subgrade settlement in this section.

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.

Aero-Hydro-Elastic-Servo Modeling and Dynamic Response Analysis of A Monopile Offshore Wind Turbine Under Different Operating Scenarios

This paper constructs a coupled aero-hydro-elastic-servo simulation framework for a monopile offshore wind turbine(OWT).In this framework,a detailed multi-body dynamics model of the monopile OWT including the gearbox,blades,tower and other components(nacelle,hub,bedplate,etc.)has been explicitly established.The effects of pile−soil interaction,controller and operational conditions on the turbine dynamic responses are studied systematically in time domain and frequency domain.The results show that(1)a comprehensive drivetrain model has the capability to provide a more precise representation of the complex dynamic characteristics exhibited by drivetrain components,which can be used as the basis for further study on the dynamic characteristics of the drivetrain.(2)The pile−soil interaction can influence the wind turbine dynamic responses,particularly under the parked condition.(3)The effect of the pile−soil interaction on tower responses is more significant than that on blade responses.(4)The use of the controller can substantially affect the rotor characteristics,which in turn influences the turbine dynamic responses.(5)The tower and blade displacements under the operational condition are much larger than those under the parked condition.The model and methodology presented in this study demonstrate potential for examining complex dynamic behaviors of the monopile OWTs.To ensure accuracy and precision,it is imperative to construct a detailed model of the wind turbine system,while also taking into account simulation efficiency.