Gangqiang Kong

Field Tests on Bearing Characteristics of X-Section Pile Composite Foundation

AbstractTo investigate the behavior of X-section cast-in-place concrete piles (XCC pile), a series of static load tests for piled foundation are conducted on the basis of a soft soil reinforcement engineering for a sewage treatment plant in the north of Nanjing, China. The testing results are presented in load-settlement curves, pile-soil stress ratios, distributions of skin friction (side friction) and axial force, and load-sharing between side resistance and end-bearing capacity. Comparative analysis between an XCC pile and a circular section concrete pile (circular pile) with the same cross-sectional area indicates that the XCC pile with its increased perimeter can improve the vertical-bearing capacity by 20% because of the larger skin friction. Also, the XCC pile shows increasing pile-soil stress ratio and reduces settlement. The existing design standards for traditional piles can be referenced by the XCC pile composite foundation, because the axial force and skin friction distribution are the same as...

Flat Cavity Expansion: Theoretical Model and Application to the Interpretation of the Flat Dilatometer Test

AbstractThis paper presents a theoretical model for flat cavity expansion in elastic soil. By using the conformal mapping method, the nonaxisymmetric boundary value problem of flat cavity expansion is transformed from the original physical plane into the axisymmetric boundary value problem in the phase plane, which results in a series of closed-form solutions for the stress and displacement induced by the flat cavity expansion. These closed-form solutions are then validated by FEM and provide the basis for the interpretation of the list-off pressure of the flat dilatometer test. Subsequently, a closed-form solution for the list-off pressure in the flat dilatometer test is given. The suitability of the solution for the list-off pressure is validated by comparing the predictions with a series of field test data provided by previous scholars. Good agreement is achieved. The proposed theoretical model improves on the previous empirical method for the interpretation of the list-off pressure in the flat dilatom...

Analysis of piles under oblique pullout load using transparent-soil models

This paper presents an experimental investigation of internal deformation in transparent sand caused by a pile moving under oblique pullout loads using the digital image correlation (DIC) technique. Transparent sand used in this study is manufactured with fused quartz and a pore fluid (mixture of Norpar 12 and white mineral oil) with a matching refractive index. An optical system consisting of a linear laser, a charge-coupled device (CCD) camera, an optical platform, a frame grabber, and a computer is employed. During the test process, the speckle (which is the interaction between the transparent-soil matrix, impurities, entrapped air, and laser) is generated. The laser speckle images before and after soil deformation are used to measure the relative displacement field using the DIC technique. The belled wedge pile, conventional tapered pile, and equal section pile with the same volume, slenderness ratio L/D = 16.9, and oblique pullout loads at angles α = 0°, 45°, 60°, and 90° are conducted in transparent sand. The load-displacement response, oblique ultimate pulling resistances, internal deformation field, surface heaving, and failure mechanisms have been studied. The normalized values in this paper were compared with previously measured values. The results indicate that the optical system and transparent sand are suitable for studying soil deformation caused by pile–soil interaction under oblique pullout loading.

Performances of Large-Diameter Cast-in-Place Concrete Pipe Piles and Pile Groups under Lateral Loads

AbstractLarge-diameter cast-in-place concrete pipe (PCC) pile is widely used for pile foundation and pile-supported embankment over soft clay in China. However, studies on PCC pile-soil reactions (p-y curves) or performance of the pile groups under lateral load are not widely reported. A large-scale model test of a single PCC pile under lateral load is carried out, and its lateral bearing capacity, bending moment, and p-y curves are measured and analyzed. The deflection and bending moment of this PCC pile is calculated by the p-y curves method and modified pile modulus using LPILE software. Three-dimensional numerical analyses are conducted using ABAQUS software. The reliability and accuracy of the numerical simulation model are verified by comparing the results of the large-scale model test with the LPILE calculation. The distribution of deflection and bending moment along the pile and pile group efficiencies of the PCC piles are comparatively analyzed with those of a drilled shaft, which has the same co...

Upper-Bound Solution for Flat Cavity Expansion Model

AbstractIn this paper, an upper-bound solution for the FCEM is proposed to study the effect of the plastic behavior of soil on the interpretation of a flat dilatometer test. Kinematically admissible displacement fields for the FCEM are derived from Zhou’s elastic solutions for an incompressible material. These displacement fields are then used to obtain an upper-bound solution for a FCEM based on energy conservation principles that the sum of the plastic and elastic work of soil is equal to the flat cavity expansion work, with yield being defined using the Tresca yield criterion. The upper-bound solution is validated by comparing the calculated list-off pressure for the flat dilatometer test using both the proposed upper-bound solution to an elastic solution and a series of field test data. The results show that the proposed upper-bound solution is better than the elastic solution in interpreting the flat dilatometer test.

Vertical Dynamic Response of a Concrete Filled Steel Tube due to Transient Impact Load: Analytical Solution

This paper presents an analytical solution of vertical dynamic response of a concrete-filled steel tube (CFST) due to transient impact loading. Both the concrete and steel are modeled by linear elastic material. The impact load is simulated by a semisinusoidal impulse. Three-dimensional (3D) wave equations those considering the vertical displacement are established. By combining the initial and boundary conditions, the frequency-domain analytical solution of displacement is deduced by Laplace transformation and separation of variables methods. The time-domain dynamic response is then obtained by numerical inverse Fourier transformation (IFT). Numerical examples are presented to verify the validity of the analytical solution developed in this study. The results indicate that the analytical solution proposed in this study shows good consistence with the existing solutions.

Mathematical Model and Analysis of Negative Skin Friction of Pile Group in Consolidating Soil

In order to calculate negative skin friction (NSF) of pile group embedded in a consolidating soil, the dragload calculating formulas of single pile were established by considering Davis one-dimensional nonlinear consolidation soils settlement and hyperbolic load-transfer of pile-soil interface. Based on effective influence area theory, a simple semiempirical mathematical model of analysis for predicting the group effect of pile group under dragload was described. The accuracy and reliability of mathematical models built in this paper were verified by practical engineering comparative analysis. Case studies were studied, and the prediction values were found to be in good agreement with those of measured values. Then, the influences factors, such as, soil consolidation degree, the initial volume compressibility coefficient, and the stiffness of bearing soil, were analyzed and discussed. The results show that the mathematical models considering nonlinear soil consolidation and group effect can reflect the practical NSF of pile group effectively and accurately. The results of this paper can provide reference for practical pile group embedded in consolidating soil under NSF design and calculation.

Elastic Analysis of a Pile Rectangular Cross Section Under Lateral Load

In continuation of our studies, this paper presents an analysis of a laterally loaded pile of rectangular cross section pile in elastic soil using the conformal mapping method of complex variable elasticity. Stress components and displacements around a rectangular rigid plate embedded in an infinity elastic soil are determined. Graphic representations of stress isolines and displacement vectors field are presented.

Numerical Analysis of Dynamic Response and Influence Factors on PCC Pile Composite Foundation of High Speed Railway

In this paper, a reasonable train dynamic loading form is determined, and a finite element model of PCC pile composite foundation for high speed railway is established using ABAQUS software. The dynamic response is simulated on subgrade and pile-soil composite foundation under different train speeds. The dynamic stress and acceleration changes of composite foundation are analyzed by changing the modulus of the roadbed surface layer and cushion. The results show that the changes of train speed, stiffness of roadbed and cushion layer react differently according to the laws of distribution and dispersion for dynamic stress, acceleration response of subgrade and pile-soil composite foundation. The dynamic stress and acceleration in roadbed surface increase with the increase of train speed. The changes in stiffness of roadbed have little effect on dynamic stress of the lower pile area, while the cushion is significantly influenced, by as much as 90%. The cushion has the effect on adjusting pile and soil dynamic stress ratio which may result in up to a 50% change in difference. A dynamic stress arch effect appears in the cushion under the dynamic interaction of the pile and cushion layer, which is similar to the static soil pressure arch effect.

Analytical Solution for Stress and Displacement after X-Section Cast-in-Place Pile Installation

X-section cast-in-place (referred to as XCC) pile, which is one of new pile types developed by Hohai University, is widely used for pile foundation and pile-supported embankment over soft ground in China. However, little research has been carried out on this new type pile, especially the surrounding soil disturbance under XCC pile installation. This paper presents an analytical solution for estimating the horizontal stress and displacement of surrounding soil of XCC pile after XCC pile installation. The reliability and accuracy of the present solution are verified by comparing them with the field test results. Then, parametric studies, such as outsourcing diameter , open arc distance , open arc angle , the undrained strength , the limit pile cavity pressure , and the radius of the plastic zone , are discussed for the practice engineering design. The results show that the stress and displacement distributions of surrounding soil calculated by this paper are in agreement with field test results.