Wenbo Tu

Bio: Wenbo Tu is an academic researcher from East China Jiaotong University. The author has contributed to research in topics: Caisson & Pile. The author has an hindex of 3, co-authored 8 publications receiving 23 citations. Previous affiliations of Wenbo Tu include Tongji University & Southwest Jiaotong University.

Time domain nonlinear lateral response of dynamically loaded composite caisson-piles foundations in layered cohesive soils

Abstract: A nonlinear Winkler model for composite caisson-piles foundation (CCPF) is proposed by joining the two components, the caisson and the pile group, in which the nonlinear four-spring Winkler model is utilized for the caisson and the axial-lateral coupled vibration equations are derived for the pile group. Then the nonlinear lateral dynamic response of CCPFs embedded in layered cohesive soils and loaded at its top center is investigated by a simplified time domain method based on the model. All the impedance functions of the foundations are frequency independent, which make it easy to conduct a standard time domain analysis. The results are compared with 3D finite element simulations and the consistence convincingly verifies the reliability of the simplified method. The nonlinear Winkler model is also extended to consider the gapping and the cyclic degradation, and it is shown to be capable of reproducing various important nonlinear features such as oval-shaped or s-shaped hysteresis loops. Finally, the lateral dynamic responses of CCPFs with three different configurations of pile group are analyzed. The results indicate that the configuration of pile group beneath the caisson plays an important role in the lateral dynamic response of the CCPF. The results also convincingly illustrate the important role of considering the soil nonlinearity, cyclic degradation and gapping in the dynamic analysis of the CCPF.

Time domain nonlinear kinematic seismic response of composite caisson-piles foundation for bridge in deep water

Abstract: As a new type of bridge foundation in deep water, the composite caisson-piles foundation (CCPF) is inevitability suffered from multiple hazards such as earthquake, scouring and erosion, especially for sea-crossing bridges in ocean environment. In this study, a simplified method in time domain is proposed for predicting the nonlinear kinematic seismic response of CCPF and the effect of scouring on the seismic response is investigated. The proposed method is verified by the results of centrifuge shaking-table tests. It is found that compared with frequency domain method, the proposed time domain method can give good estimations of the acceleration and the displacement of the CCPF, especially at high frequencies. Moreover, the kinematic seismic response of CCPF designed for the Qiongzhou Strait Bridge is analyzed. The results indicate that the proposed model can effectively simulate the soil nonlinearity, and the soil nonlinearity significantly affects the kinematic seismic response of CCPF, especially the acceleration and displacement time histories. Finally, the scouring effect is considered by an analytical model and the performance of the CCPF under combined earthquake and scouring is investigated.

Experimental and analytical investigations on nonlinear dynamic response of caisson-pile foundations under horizontal excitation

Abstract: As a deep-water foundation, composite caisson-pile foundation (CCPF) is usually subjected to horizontal dynamic loads and moments due to the complicated marine environment. In this study, model tests were performed on three different types of deep-water foundation, including caisson, caisson with four piles and eight piles to investigate their lateral nonlinear dynamic characteristics under various excitation forces. Meanwhile, the effect of scour depth on the dynamic response of the foundations were also studies. The test results indicate that the excitation force and scour depth significantly affect the vibration amplitude and resonant frequency of the foundations with an obvious nonlinear behavior. Compared with the caisson, adding piles beneath the caisson results in a decrease of the vibration amplitude and an increase of resonant frequency, and the configuration of the pile also has an influence. The experimental results are compared with the results obtained by a simplified dynamic Winkler analysis model proposed here. Despite its simplicity, a reasonable agreement between the experimental and the calculated responses was observed. Moreover, scaling laws have been applied in the CCPF model to discuss the dynamic behavior of the prototype foundation.

Nonlinear dynamic behavior of laterally loaded composite caisson-piles foundation under scour conditions

Abstract: A simplified method for predicting the nonlinear dynamic response of composite caisson-piles foundation (CCPF) under scour conditions is proposed. The Hardin-Drnevich model is employed to represent...

Scour effects on the dynamic lateral response of composite caisson-piles foundations considering stress history of sand

Abstract: Scour effect have a significant impact on the dynamic lateral response of composite caisson-piles foundations (CCPFs) because of the removal of soils around the foundation and the change of stress history of remaining soil. Based on the simplified method with the dynamic Winkler model, a computational method for predicting the dynamic impedance of CCPFs influenced by scour is developed. Subsequently, theoretical results for the response of CCPFs are verified by the 3D finite element method with sponge boundary. Finally, results from a case study show that scour has a great influence on the dynamic stiffness and damping coefficient, and the deeper scour depth increases, the more remarkable influence on the results. Besides the removal of soil around CCPFs resulting from scour effect, it also shows that the change of stress history will further weaken the bearing capacity of composite foundation and enlarge the dynamic response. Thus, ignoring the change of stress history would result in an overestimate of the dynamic impedance. And stress history is also proved to be of great significance to increase the resonant response of composite foundation, while has little influence on the resonant frequency.

Cyclic soil data for design of gravity structures

Abstract: Constitution d'une base de donnees, a partir d'essais triaxiaux non draines et d'essais de cisaillement simple direct sur argile de Drammen, avec combinaison de contraintes de cisaillement statique et dynamiques

Surface-wave attenuation by periodic pile barriers in layered soils

Abstract: The purpose of this study is to investigate surface-wave isolation by periodic piles from the perspective of attenuation zones. There are three major components. The first is the dispersion equation, which is derived based on periodic theory of solid-state physics. The second component is the main new part of this paper. Finite element method is adopted to calculate the dispersion relation and attenuation zones for surface waves in a periodic pile and layered soil system. Moreover, effects of geometric parameters on attenuation zones and the amplitude reduction spectra are thoroughly investigated. As a result, harmonic responses show that the isolation region on amplitude reduction spectra is consistent with the theoretical attenuation zone. The third component is the feasibility of ground vibration isolation by periodic pile barriers, which is verified in the time domain by investigating train-induced ground vibrations. Using the concept of attenuation zone, one can manipulate the propagation and attenuation of surface waves artificially. This work provides a new insight into the design of periodic piles as wave barriers.

Horizontal dynamic response of pile in unsaturated soil considering its construction disturbance effect

Abstract: Considering the effect of construction disturbance, the horizontal dynamic response of pile embedded in unsaturated soil is investigated when the pile is subjected to time-harmonic horizontal loading and vertical loading. In order to consider this problem, this paper subdivides the inhomogeneous region of pile surrounding soil into a series of sub-zones whose displacements and stresses at the fictitious interface are derived by means of continuous conditions and 3D continuum model. Then, the governing equations of pile are established by using linear elastic Timoshenko beam. Utilizing the Laplace transform and transfer matrix method, the analytical solutions of the dynamic impedance of soil and the horizontal dynamic impedance of pile head are derived. To verify the rationality and accuracy of the present solutions, the computed results are compared with those obtained from existing solutions. Through parametric study method, the influence of construction disturbance range and degree on the horizontal dynamic impedance of pile head is investigated within the low-frequency range concerned in dynamic pile foundation design. The main results show that the variations in the shear modulus and width of boundary zone of pile surrounding soil owing to relaxation effect or compaction effect have a significant influence on the horizontal dynamic response of pile head.

Responses of caisson-piles foundations to long-term cyclic lateral load and scouring

Abstract: The caisson-piles composite foundation is considered as a viable alternative to caisson foundations for the Qiongzhou Strait bridge. It can significantly reduce the caisson height by connecting the lower grouped piles to the upper caisson and improve its mechanical behaviour under lateral loading. A series of model tests are conducted at 1 g to investigate the cyclic responses as well as the coupled cyclic and scouring responses of the caisson-piles composite foundation under 10,000 cycles. The cyclic responses of the caisson-4 piles composite foundation are compared with those of a conventional caisson, including various cyclic load characteristics, i.e., one-way, asymmetric two-way and symmetric two-way cyclic loading. Two scour depths and two cyclic load amplitudes for the one-way cyclic loading are applied in the coupled tests. A framework to predict the accumulated deformation of the caisson-piles composite foundation due to cyclic loading and scouring is developed. It is found that the accumulated residual displacements or rotations are dependent on the applied cyclic load characteristic and scour depth, and the most onerous loading condition is between one-way and symmetric two-way loading. The effect of scouring can be rationally assessed using a modified cyclic load level, replacing the static capacity by the post-scour static capacity.