Kuo Feng Lo

Numerical investigation of the scouring effect on the lateral response of piles in sand

Scouring around a bridge foundation is a problem of much concern to civil engineers. The main purpose of this paper is to gain more understanding of the effect of scouring around the pile on the lateral capacity of the piles embedded in sandy soil. Factors such as soil stiffness, pile head fixity, and pile slenderness ratio (L/B) were studied to show their effects on the variation of the percentage decrease of lateral load capacity (PDC) due to scouring near an isolated pile. The results indicate that the PDC value reaches almost 50% when the scour depth reaches 1.3 to 2.4 times the pile diameter, and that piles with a fixed head are more capable of resisting lateral load loss. Furthermore, the PDC values remain almost constant after the pile slenderness ratio is greater than 10. Hence, the decrease in lateral load due to scouring of the soil will be more serious for short piles.

NONDESTRUCTIVE INTEGRITY EVALUATION OF PC PILE USING WIGNER-VILLE DISTRIBUTION METHOD

Nondestructive evaluation (NDE) techniques have been used for years to provide a quality control of the construction for both drilled shafts and driven concrete piles. This trace is typically made up of transient pulses reflected from structural features of the pile or changes in its surrounding environment. It is often analyzed in conjunction with the spectral response, mobility curve, arrival time, etc. The Wigner-Ville Distribution is a new numerical analysis tool for signal process technique in the time-frequency domain and it can offer assistance and enhance signal characteristics for better resolution both easily and quickly. In this study, five single pre-cast concrete piles have been tested and evaluated by both sonic echo method and Wigner-Ville distribution (WVD). Furthermore, two difficult problems in nondestructive evaluation problems are discussed and solved: the first one is with a pile with slight defect, whose necking area percentage is less than 10%, and the other is a pile with multiple defects. The results show that WVD can not only recognize the characteristics easily, but also locate the defects more clearly than the traditional pile integrity testing method.

Time–Frequency Signal Analysis for Nondestructive Evaluation of Pile with Cap

As stress waves decay as they pass through the pile foundation system, it is extremely challenging for all nondestructive testing methods to evaluate the pile integrity of a shaft underneath a structure. In this study, time–frequency signal analysis (TFSA) is used for signal processing and adopted to interpret the pile integrity testing signal. An experimental case with pile lengths of 58m with caps, were tested by the low strain sonic echo method. Traditional time domain analyses can not identify the pile tip response signals 58m lengths. After time-history curves are transformed into a time–frequency domain distribution, the results indicate the pile tip can be located more easily and clearly than the traditional time-domain analyses of pile integrity testing allowed for.