Analysis of Large-Scale In Situ Shear Tests of Sandy Gravel with Cobbles

Shear strength of sandy gravel with cobbles is difficult to determine for usually an in situ test needs to be performed. Six group of in situ tests were conducted to investigate the shear strength of sandy gravel with cobbles. However, the inner friction angle was highly underestimated compared with those from the other methods. This failure result could be explained comprehensively. The strength parameters were also investigated using a DCP test, an experimental method and a theoretical method. Moreover, a numerical simulation method was also used to determine the failure mode of the in situ test. Through comprehensive comparison of these results, the soil failure mechanism in the tests did not follow the direct shear failure but did follow the bearing-capacity failure model. The bottom boundary could not provide enough capacity during the test; hence, the shear strength was underestimated. Moreover, the in situ test results could be explained through the Meyerhof bearing-capacity theory on shallow foundations subjected to inclined loads. With increasing normal load, the horizontal force decreased, resulting in a small inner-friction angle. The theoretical result of the inner-friction angle of sandy gravel with cobbles was 42 ~ 47.5° in these test, which coincided with the numerical simulation and empirical methods.