- For determination of the in-situ deformation modulus of rock mass at Bakhtiari Dam site, located in southwest of Iran, plate jacking tests (PJT) and dilatometer tests (DLT) carried out during the geotechnical investigations. In this study, the results of PJTs and DLTs were compared. This comparison involves 89 vertical and horizontal PJTs and 83 DLTs carried out in 6 rock units of Sarvak formation. Although, both PJTs and DLTs in the Bakhtiari Dam site were performed in same geological and geotechnical conditions, but there are not sufficient side by side data to make a paired two samples correlation. Therefore, the mean of in-situ data was compared at each rock unit. Besides Mann–Whitney U tests were performed to compare in-situ test results. The comparison shows that the deformation modulus measured by both methods has no significant differences. However, in low quality rock masses the moduli measured by the use of DLTs were greater than the modulus measured by PJTs. Conversely, in high quality rock masses the results of PJTs were greater than DLT’s.

Keywords