Effects of surrounding soil stiffness and shaft length in the impact-echo test of drilled shaft

Estimating the flaw size in drilled shafts using an impulse response method

“…An alternative formula, without the need for the P/Q information, was also developed, and it can be used to evaluate the minimum possible flaw size existing in a shaft. In addition, the shaft slenderness ratio that is detectable by using the surface reflection method has been found to be 30 (Higgs, 1979;Kim and Kim, 2003;Liao and Roesset, 1997) without considering the variation in soil stiffness around the shaft, although soil stiffness is important for successful use of such methods (Fukuhara et al, 1992;Lin et al, 1991). Therefore, an additional formula is developed to assess the detectable shaft slenderness ratio, which is correlated with the stiffness ratio, and it varies from 10 to 30.…”

“…Although research has shown that soil stiffness limits the application of the surface reflection method (Fukuhara et al, 1992;Lin et al, 1991), the maximum detectable slenderness ratio of shafts by such methods has been found to be 30, based on assuming the soil stiffness around the shafts is a constant parameter and neglecting the effect of the soil stiffness on the maximum detectable L/D ratio (Higgs, 1979;Kim and Kim, 2003;Liao and Roesset, 1997). Finno and Gassman (1998) also indicated that the identification of the shaft bottom is dependent on the soil and concrete properties in addition to the L/D ratio, according to the ideal resolution chart they provided.…”

Integrity Evaluation of PCC Piles Using the Surface Reflection Method

“…Inclusion of soil in the numerical model would further suppress the magnitude of reflections from the locations of the impedance change. However, the soil around the piles was not included in the numerical models, producing an effect similar to an infinitely compliant surrounding soil, 20 to obtain higher resolution signals 21 …”

“…The PCC piles were modeled by eight-node three-dimensional solid elements in the numerical simulation. The mass density, Young's modulus, However, the soil around the piles was not included in the numerical models, producing an effect similar to an infinitely compliant surrounding soil, 20 to obtain higher resolution signals. 21 Figure 5(a) shows the constructed model of the defective PCC pile.…”