Numerical modelling of perimeter pile groups in clay

The load distribution among piles in a group varies such that the inner piles often carry a smaller share of the total load compared to the outer piles, which is a result of increased soil–pile interaction. The main objective of this paper is to establish the relative effectiveness of pile groups with no inner piles (perimeter group), when compared to the more common grid configuration. The numerical investigation utilized the finite element programme ABAQUS and considered a range of variables that affect pile group behaviour including number of piles, pile spacing, length/diameter ratio, and soil strength. It was demonstrated that a complete grid group is less efficient than a perimeter group, where efficiency is defined as the load capacity of the whole group expressed as a ratio of the number of piles in the group multiplied by the load capacity of a single isolated pile. Efficiencies close to unity were observed for some perimeter groups. Perimeter groups also showed that a “block” type group failure could occur, where piles were placed at a spacing of less than 2.0 pile diameters,d, centre-to-centre. This often, but not always, led to a reduction in the efficiency of the pile group

Application of flexi-wall in noise barriers renewal

This paper presents an experimental study on structural performance of an innovative noise barrier consisting of poly-block, light polyurethane foam (LPF) and polyurea. This wall system (flexi-wall) is intended to be employed as a vertical extension to existing noise barriers (sound walls) in an accelerated construction method. To aid in the wall design, several mechanical tests were conducted on LPF specimens and two full-scale walls were then fabricated employing the same LPF material. The full-scale walls were subjected to lateral loading in order to establish their lateral resistance. A cyclic fatigue test was also performed on a full-scale flexi-wall in order to evaluate the performance of the wall under a repetitive loading condition. The results of the experiments indicated the suitability of flexi-wall in accelerated construction and confirmed that the structural performance of the wall system under lateral loading is satisfactory for the sound wall application. The experimental results were discussed and a preliminary design procedure for application of flexi-wall in sound wall applications was also developed

Physical and Numerical Modeling of Seismic Soil-Structure Interaction in Layered Soils

The structural response of buildings subjected to seismic loads is affected by local site conditions and the interaction between the structure and the supporting soil media. Seismic centrifuge model tests were conducted on two layered clay soil profiles at 80 g field to investigate soil-structure interaction and dynamic response of foundation. Several earthquake-like shaking events were applied to the models using an electro-hydraulic shaking table to simulate linear and nonlinear soil behavior. Results showed that the foundation input motion was significantly amplified in both models, especially for weak earthquake motions. Seismic soil-structure interaction was found to have an important effect on structure response by increasing the amplification of foundation input motion. A 3D finite difference numerical model was also developed to simulate the response of centrifuge model tests and study the parameters that affect the characteristics of earthquake at the base of the structure. The results indicated that the stiffness and stratification of the soil profiles had a significant effect on modifying the foundation input motion

Measurement of frequency-dependent dynamic properties of soils using the resonant column device

Dynamic properties of soils are commonly evaluated at resonance; thus, their variation with frequency is difficult to measure. A nonresonance (NR) method has been recently used for testing soils at low frequencies and strain levels below the linear threshold shear strain. However, the NR method has not been validated with the standard resonant method for different shear strain levels. In this study, the NR method is used to measure the dynamic properties of soils at low and midstrain levels for a maximum frequency bandwidth between 5 and 100 Hz using the resonant-column device. A new transfer function (NTF) equation is introduced to compare the dynamic properties measured using the NR method and the conventional transfer function approach. Experimental results for two sands and a sand–bentonite–mud mixture are presented for different strain and stress confinement levels. Results from the NR method compare well with the standard resonant column method at the resonant frequency if the strain levels are the same. The NTF approach can be used to measure the dependence of phase velocity of shear waves with frequency. However, the NTF method cannot be used to measure the variation of material damping with frequency. On the other hand, the NR method can be used to measure the degradation curves of wave velocity and material damping ratio as a function of frequency