scholarly journals Ultimate capacity of piles penetrating in weak soil layers

2018 ◽  
Vol 162 ◽  
pp. 01025
Author(s):  
Ahmed Al-Obaidi ◽  
Pinar Mahmood
Keyword(s):  
Soft Soil ◽  
Soil Layer ◽  
Vertical Direction ◽  
Deep Foundations ◽  
Elastic Model ◽  
Ultimate Capacity ◽  
Weak Soil ◽  
Soil Layers ◽  
Dense Sand ◽  
Pass Through

A pile foundation is one of the most popular forms of deep foundations. They are routinely employed to transfer axial structure loads through the soft soil to stronger bearing strata. Piles generally used to increase the load carrying capacity of the foundation and reduce the settlement of the foundation. On the other hand, many cases in practice where piles pass through different layers of soil that contain weak layers located at different depths and extension, also some time cavities with a different shape, size, and depth are found. In this study, a total of 96 cases is considered and simulated in PLAXIS 2D program aiming to understand the influence of weak soil on the ultimate pile capacity. The piles embedded in the dense sand with a layer of weak soil at different extension and location. The cross section of the geometry used in this study was designed as an axisymmetric model with the 15-node element; the boundary condition recommended at least 5D in the horizontal direction, and (L+5D) in the vertical direction where D and L are the diameter and length of pile, respectively. The soil is modeled as Mohr-Coulomb, with five input parameters and the behavior of pile material represented by the linear elastic model. The results of the above cases are compared with the results found in a pile embedded in dense soil without weak layers or cavities. The results indicated that the existence of weak soil layer within the surrounding soil around the pile decreases the ultimate capacity. Furthermore, it has been found that increase in the weak soil width (extension) leads to reduction in the ultimate capacity of the pile. This phenomenon is applicable to all depth of weak soil. The influence of weak layer extension on the ultimate capacity is less when it is presentin the upper soil layers.

scholarly journals Performance Analysis Of “Toga” Foundation With Cap On Thick Soft Soil Based On Laboratory Models And Finite Element Analysis

UKaRsT ◽  
2020 ◽  
Vol 4 (2) ◽  
pp. 222
Author(s):  
Melissa Kurnia ◽  
Paulus Pramono Rahardjo
Keyword(s):  
Soft Soil ◽  
Soil Conditions ◽  
Deep Foundations ◽  
3D Analysis ◽  
Element Analysis ◽  
Soil Layers ◽  
The Right ◽  
Laboratory Models ◽  
Deformation Relationship ◽  
Plaxis 3D

Various alternative foundations are offered depending on soil conditions from the results of soil investigations. In difficult soil types such as thick, soft soil layers, pile foundation is generally used to avoid the excess settlements, but deep foundations for small buildings are not the right solution when viewed from a cost perspective. One of the more economical foundations is to use the” toga” foundation, with a plate on top and a caisson underneath where the caisson can be inserted into the soil with an open end. Through this study, the carrying capacity of the” toga” foundation will be analyzed. Then the foundation will be made on a laboratory scale and tested with axial load. The load and deformation relationship were analyzed using PLAXIS 3D analysis. It can be concluded the performance of the ”toga” foundation on thick, soft soil can be used for two-floored buildings

Case Study of a Failed Slope of a Port in Southern China

2013 ◽  
Vol 353-356 ◽  
pp. 3-6
Author(s):  
Yong Hua Cao ◽  
Chuan Zhi Huang
Keyword(s):  
Southern China ◽  
Soft Soil ◽  
Soil Layer ◽  
Soil Mass ◽  
Safety Factors ◽  
Soil Layers ◽  
Surface Method ◽  
Calculation Results ◽  
Hard Soil

Uniform safety factors are normally assumed in slope stability analysis and this assumption can influence the rationality of the analysis. New analysis methods were obtained based on Fellenius, Bishop and multi sliding surface method to study a failed slope of a port in southern China. The calculation results show that the safety factors of soft soil layers will be overestimated and the safety factors of hard soil layers will be underestimated if soil mass of slope vary widely in the strength. For the failed slope in this paper, the factors obtained with normal methods will be overestimated because of the hard soil layer of this slope.

scholarly journals Theoretical and Numerical Analysis of Soil-Pipe Pile Horizontal Vibration Based on the Fractional Derivative Viscoelastic Model

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Hao Zhang ◽  
Jienan Niu ◽  
Ningning Huang ◽  
Qifang Yan
Keyword(s):  
Fractional Derivative ◽  
Soil Layer ◽  
Viscoelastic Model ◽  
Dynamic Resistance ◽  
Elastic Model ◽  
Soil Layers ◽  
Pipe Pile ◽  
Function Decomposition ◽  
Dynamic Impedance ◽  
Core Soil

To describe the mechanical properties of the system of pipe pile-soil reasonably and accurately, the constitutive relations of the soil around pile and pile core soil are characterized by the fractional derivative viscoelastic model. We assume that the radial and circumferential displacements of the soil around the pile and pile core soil are the functions of r, θ, and z. The horizontal dynamic control equations of soil layers are derived by using the fractional derivative viscoelastic model. Considering the fractional derivative properties, soil layer boundary condition, and contact condition of pile and soil, the potential function decomposition method is used to solve the radial and circumferential displacements of the soil layer. Then, the force of unit thickness soil layer on the pipe pile and the impedance factor of the soil layer are obtained. The horizontal dynamic equations of pipe pile are established considering the effect of soil layers. The horizontal dynamic impedance and horizontal-swaying dynamic resistance at the pile top are obtained by combining the pipe pile-soil boundary conditions and the orthogonal operation of trigonometric function. Numerical solutions are used to analyze the influence of pile and soil parameters on the soil impedance factor and horizontal dynamic impedance at pile top. The results show that the horizontal impedance factors of the soil layer and horizontal dynamic impedance of pipe pile by using the fractional derivative viscoelastic model can be degraded to those of the classical viscoelastic model and the elastic model. For the fractional derivative viscoelastic model of soil layer, the influence of soil around pile on the dynamic impedance is greater than that of pile core soil. The model parameter TOa, the inner radius of pipe pile, and the pile length have obvious effects on the horizontal impedance of the soil layer and pipe pile, while the influence of the pile core soil on the pile impedance is smaller.

Evaluation of floor acceleration demands from the 2017 Mexico City code seismic provisions using a continuous elastic model and records of instrumented buildings

2020 ◽  
Vol 36 (2_suppl) ◽  
pp. 213-237
Author(s):  
Miguel A Jaimes ◽  
Adrián D García-Soto
Keyword(s):  
Mexico City ◽  
Seismic Design ◽  
Soft Soil ◽  
Response Spectra ◽  
Elastic Model ◽  
Ground Acceleration ◽  
Nonstructural Components ◽  
Floor Response Spectra ◽  
Instrumented Buildings ◽  
Floor Acceleration

This study presents an evaluation of floor acceleration demands for the design of rigid and flexible acceleration-sensitive nonstructural components in buildings, calculated using the most recent Mexico City seismic design provisions, released in 2017. This evaluation includes two approaches: (1) a simplified continuous elastic model and (2) using recordings from 10 instrumented buildings located in Mexico City. The study found that peak floor elastic acceleration demands imposed on rigid nonstructural components into buildings situated in Mexico City might reach values of 4.8 and 6.4 times the peak ground acceleration at rock and soft sites, respectively. The peak elastic acceleration demands imposed on flexible nonstructural components in all floors, estimated using floor response spectra, might be four times larger than the maximum acceleration of the floor at the point of support of the component for buildings located in rock and soft soil. Comparison of results from the two approaches with the current seismic design provisions revealed that the peak acceleration demands and floor response spectra computed with the current 2017 Mexico City seismic design provisions are, in general, adequate.

scholarly journals Design of plate and screw anchors in dense sand: failure mechanism, capacity and deformation

2019 ◽  
Vol 92 ◽  
pp. 16010
Author(s):  
Benjamin Cerfontaine ◽  
Jonathan Knappett ◽  
Michael Brown ◽  
Aaron Bradshaw
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Failure Mechanism ◽  
Progressive Failure ◽  
Vertical Direction ◽  
Shear Plane ◽  
Design Methods ◽  
Embedment Depth ◽  
Limiting State ◽  
Dense Sand

Plate and screw anchors provide a significant uplift capacity and have multiple applications in both onshore and offshore geotechnical engineering. Uplift design methods are mostly based on semi-empirical approaches assuming a failure mechanism, a normal and a shear stress distribution at failure and empirical factors back-calculated against experimental data. However, these design methods are shown to under- or overpredict most of the existing larger scale experimental tests. Numerical FE simulations are undertaken to provide new insight into the failure mechanism and stress distribution which should be considered in anchor design in dense sand. Results show that a conical shallow wedge whose inclination to the vertical direction is equal to the dilation angle is a good approximation of the failure mechanism in sand. This shallow mechanism has been observed in each case for relative embedment ratios (depth/diameter) ranging from 1 to 9. However, the stress distribution varies non-linearly with depth, due to the soil deformability and progressive failure. A sharp peak of normal and shear stress can be identified close to the anchor edge, before a gradual decrease with increasing distance along the shear plane. The peak stress magnitude increases almost linearly with embedment depth at larger relative embedment ratios. Although further research is necessary, these results lay the basis for the development of a new generation of design criteria for determining anchor capacity at the ultimate limiting state.

Application of the vertical model of the seasonally thawed layer for the Tulik Lake area (Alaska)

2021 ◽  
pp. 4-15
Author(s):  
Виктор Михайлович Белолипецкий ◽  
Светлана Николаевна Генова
Keyword(s):  
Air Temperature ◽  
Stefan Problem ◽  
Soil Layer ◽  
Vertical Direction ◽  
Soil Surface ◽  
Dirichlet Condition ◽  
Transfer Model ◽  
Problem Solution ◽  
Computational Domain ◽  
Lake Area

Практический интерес в районах вечной мерзлоты представляет глубина сезонного оттаивания. Построена одномерная (в вертикальном направлении) упрощенная полуэмпирическая модель динамики вечной мерзлоты в “приближении медленных движений границ фазового перехода”, основанная на задаче Стефана и эмпирических соотношениях. Калибровочные параметры модели выбираются для исследуемого района с использованием натурных измерений глубины оттаивания и температуры воздуха. Проверка работоспособности численной модели проведена для района оз. Тулик (Аляска). Получено согласие рассчитанных значений глубины талого слоя и температуры поверхности почвы с результатами измерений Due to the change in global air temperature, the assessment of permafrost reactions to climate change is of interest. As the climate warms, both the thickness of the thawed soil layer and the period for existence of the talik are increased. The present paper proposes a small-size numerical model of vertical temperature distributions in the thawed and frozen layers when a frozen layer on the soil surface is absent. In the vertical direction, thawed and frozen soils are separated. The theoretical description of the temperature field in soils when they freeze or melt is carried out using the solution of the Stefan problem. The mathematical model is based on thermal conductivity equations for the frozen and melted zones. At the interfacial boundary, the Dirichlet condition for temperature and the Stefan condition are set. The numerical methods for solving of Stefan problems are divided into two classes, namely, methods with explicit division of fronts and methods of end-to-end counting. In the present work, the method with the selection of fronts is implemented. In the one-dimensional Stefan problem, when transformed to new variables, the computational domain in the spatial variable is mapped onto the interval [0 , 1]. In the presented equations, the convective terms characterize the rate of temperature transfer (model 1). A simplified version of the Stefan problem solution is considered without taking into account this rate (“approximation of slow movements of the boundaries of the phase transition”, model 2). The model is tuned to a specific object of research. Model parameter values can vary significantly in different geographic regions. This paper simulates the dynamics of permafrost in the area of Lake Tulik (Alaska) in summer. Test calculations based on the proposed simplified model show its adequacy and consistency with field measurements. The developed model can be used for qualitative studies of the long-term dynamics of permafrost using data of the air temperature, relative air humidity and precipitation

3. On Diamagnetic Rotation

1878 ◽  
Vol 9 ◽  
pp. 85-92 ◽  
Author(s):  
George Forbes ◽  
J. Clerk Maxwell
Keyword(s):  
Small Angle ◽  
Vertical Direction ◽  
Positive Current ◽  
End To End ◽  
Pass Through ◽  
Lines Of Force

Faraday's discovery of the magnetic rotatory polarisation of light may be expressed in the following manner:—Let two electromagnets, in the form of iron tubes, surrounded by helices of wire, be placed end to end, so that in the space between them the lines of force are very intense. Let a rod of dense glass be placed in this space, so that a ray of light may pass through the two tubes and the rod of glass. Let such a ray on entrance be plane-polarised, so that the direction of vibration is in a vertical direction. If the electro-magnet be now magnetised, the emergent ray will be polarised, so that its vibrations are inclined to the vertical at a small angle. The direction in which the line of vibration has been rotated is the same as the direction of the positive current in the helices.

scholarly journals Depth-Dependent C-N-P Stocks and Stoichiometry in Ultisols Resulting from Conversion of Secondary Forests to Plantations and Driving Forces

Forests ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1300
Author(s):  
Xiaogang Ding ◽  
Xiaochuan Li ◽  
Ye Qi ◽  
Zhengyong Zhao ◽  
Dongxiao Sun ◽  
...  
Keyword(s):  
Soil Depth ◽  
Soil Layer ◽  
Pinus Elliottii ◽  
Slash Pine ◽  
Pine Plantations ◽  
Secondary Forests ◽  
Masson Pine ◽  
Soil Layers ◽  
Soil C ◽  
Significant Difference

Stocks and stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) in ultisols are not well documented for converted forests. In this study, Ultisols were sampled in 175 plots from one type of secondary forest and four plantations of Masson pine (Pinus massoniana Lamb.), Slash pine (Pinus elliottii Engelm.), Eucalypt (Eucalyptus obliqua L’Hér.), and Litchi (Litchi chinensis Sonn., 1782) in Yunfu, Guangdong province, South China. Five layers of soil were sampled with a distance of 20 cm between two adjacent layers up to a depth of 100 cm. We did not find interactive effects between forest type and soil layer depth on soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) concentrations and storages. Storage of SOC was not different between secondary forests and Eucalypt plantations, but SOC of these two forest types were lower than that in Litchi, Masson pine, and Slash pine plantations. Soil C:P was higher in Slash pine plantations than in secondary forests. Soil CNP showed a decreasing trend with the increase of soil depth. Soil TP did not show any significant difference among soil layers. Soil bulk density had a negative contribution to soil C and P stocks, and longitude and elevation were positive drivers for soil C, N, and P stocks. Overall, Litchi plantations are the only type of plantation that obtained enhanced C storage in 0–100 cm soils and diverse N concentrations among soil layers during the conversion from secondary forests to plantations over ultisols.

scholarly journals CONCERNING THE EXTRACTION OF A SLACK SOIL LAYER FROM COMPRESSIBLE THICKNESS OF FOUNDATION STRATUM OF FINITE WIDTH FOUNDATIONS

2019 ◽  
Vol 7 (4) ◽  
pp. 49-56
Author(s):  
Zaven Ter-Martirosyan ◽  
Armen Ter-martirosyan ◽  
Valery DEMYANENKO
Keyword(s):  
Analytical Solutions ◽  
Soft Soil ◽  
Soil Layer ◽  
Horizontal Displacement ◽  
Creep Model ◽  
Shear Stresses ◽  
Finite Width ◽  
Relative Depth ◽  
Weak Layer ◽  
Horizontal Displacements

The paper provides a quantitative assessment of the deflected mode of foundation stratum of finite width foundation, in the compressible thickness of which there is a slack clay soil layer. A number of criteria for assessing the possibility or impossibility of extruding a slack layer depending on its strength and rheological properties, as well as the relative thickness of the layer to its length (h/l) and the relative depth of the layer (h/d) have been given. Closed analytical solutions are given to determine the rate of Foundation precipitation depending on the rate of extrusion of the weak layer, including taking into account the damped and undamped creep. The analytical solutions in the article are supported by the graphical part made with the help of the Mathcad program. Plots of changes in shear stresses in the layer along the x axis at different distances from the axis and at different values 0, contours of horizontal displacement velocities in the weak layer at different distances from the x axis, plots of horizontal displacement velocities in the middle of the weak layer and plots of horizontal displacement velocities in the weak layer at different distances from the x axis are given. As a calculation model for describing the creep of a slack layer, rheological ones of the soil using power and hyperbolic functions and their modifications have been considered. In addition, most modern rheological models that take into account soil hardening during creep have been considered. Based on these models, the problem is solved by means analytical and numerical methods using the Mathcad PC and the PLAXIS PC according to the Soft Soil Creep model. The graphical part shows the isofields of horizontal displacements for 300 days and 600 days and the corresponding contours of horizontal displacements.

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