Xiao-nan Gong

A Model Test on the Behavior of a Static Drill Rooted Nodular Pile Under Compression

A static drill rooted nodular pile is a new type of composite pile foundation with high bearing capacity, and mud emissions can be largely reduced using the static drill rooted method. This report presents a model test on the behavior of this composite pile in a test box. The load-displacement response, axial force, skin friction, and mobilized base load are discussed in the report; in particular, the force in the cemented soil was investigated based on the measured data. Moreover, the finite element software ABAQUS was used to help investigate this behavior more thoroughly. It was determined that the function of the cemented soil around the pile shaft was different from that at the enlarged pile base; the stress in the cemented soil around the shaft increased suddenly when nearing the pile base; the ultimate skin friction obtained in the model test was larger than that estimated in the field test; and the relative displacement between the precast nodular pile and the cemented soil could be ignored during the loading process, which corresponded to the result of the field test and demonstrated that the nodular pile and cemented soil act as one entity during the loading process.

Influence of Intermediate Principal Stress on Undrained Behavior of Intact Clay under Pure Principal Stress Rotation

This study presents the accumulations of the excess pore water pressure and the deformation as well as the noncoaxial behavior of intact soft clay subjected to pure principal stress rotation. Series of tests were carried out by using a dynamic hollow cylinder apparatus to highlight the influence of intermediate principal stress parameter b. It was found that the rate of PWP evolution was greatly influenced by b, but the influence was not monotonous. Specimens under the condition b = 0.75 had the highest accumulation of pore water pressure while under the condition b = 0 had the strongest resistance to the pore pressure generation. PWP accumulated mainly in the first cycle. The failure of specimens under principal stress rotation was controlled by the strain other than the pore pressure. The shear stiffness decreased more quickly with higher b value. The direction of the principal strain increment was strongly dependent on the principal stress increment orientation and less influenced by the b value and the number of cycles.

Field Tests on Behavior of Pre-bored Grouted Planted Pile in Soft Soil Area with Existing Pile Foundation

This paper presents a practical renewal project in soft soil area, and the site foundation should be improved owing to the increasing load from superstructure. The installation of “new” pile foundation was a great challenge due to the existing square piles in the foundation. A group of field tests were conducted to investigate the compressive bearing capacity of the PGP pile and bored pile, and the applicability of these two piles in soft soil area with existing pile foundation was also studied. The results show that the ultimate unit skin friction of the PGP pile is about 1.22 times the ultimate unit skin friction of the bored pile. The PGP pile was chosen as the foundation of this renewal project, and the existing square piles around were scarcely disturbed during the PGP pile installation process.

Analytical Solutions for Seepage Field of Underwater Tunnel

Based on the patterns of the hydraulic head outside the lining layer obtained from numerical simulation, a new boundary condition for the tunnel is proposed that the hydraulic head appears sinusoidal distribution on the lining’s external circumference. The analytical solutions about the hydraulic head and water ingress are derived rigorously, which could consider the effect of the lining property such as the lining thickness and permeability. The new solution is compared with another three classic analytical solutions in the existent literature. It is found that the traditional assumption that the lining layer is an equipotential surface could overestimate the water ingress especially when the tunnel is buried shallowly.

Semi-analytical Solutions on Seepage Field of Twin Tunnels

Based on the governing equation of steady-state seepage, the semi-analytical solutions of seepage field of twin tunnels considering the effect of lining is derived rigorously using the technique of conformal mapping. These solutions can provide the values of total hydraulic head at an arbitrary point in the seepage field and the tunnel water ingress. Discussion is given about the effects of the tunnel distance on the distribution of the total hydraulic head outside the twin tunnels and the tunnel water ingress. It is found that simplifying the twin tunnels as a single tunnel in analysis could overestimate the hydraulic head around tunnels and the tunnel water ingress.

Hammer's Impact Force on Pile and Pile's Penetration

Methods of energy and momentum conservation, vibration theories, and model tests are employed to research the impact force of a hammer on a pile and the piles penetration. An analytical formula of impact force of the hammer on pile is obtained. A comparison of results from the three methods finds that the analytical formula proposed by this article conforms well to practical situations. Research results show that if the hammers impact energy remains unchanged, penetration increases with the increase of hammer weight and cushion stiffness. In addition, the impact force received by the pile head degrades with the increase of hammer weight, but increases with the increase of cushion stiffness. Impact time decreases with the increase of cushion stiffness, but increases with the increase of hammer weight. The model test shows that, when compared with a cotton cloth cushion, an elastic cushions advantages lie in that the relatively small pile head impact force can achieve significant pile penetration. The cotton cloth is gradually compacted with the increase of blow counts; hence, the impact force the pile head receives tends to increase gradually.