Ground source heat pump (GSHP) systems exchange heat with the ground, often through a vertical, U-tube, borehole heat exchanger (BHE). The performance of this U-tube BHE depends on the thermal properties of the ground formation, as well as grout or backfill in the borehole, The design and economic probability of GSHP systems need the thermal conductivity of geological structure and thermal resistance of BHE. Thermal response test (TRT) method allows the in-situ determination of the thermal conductivity (lambda) of the ground formation in the vicinity of a BHE, as well as the effective thermal resistance (R-b) of this latter. Thermal properties measured in laboratory experiments do not comply with data of in-situ conditions. The main goal has been to determine same in-situ ground type of BHE, including the effect of borehole's depths (60 m: VB2; 90 m: VB3). As shown in these results, X and Rb Of the VB2/VB3 boreholes are determined as 1.70/1.70 W m(-1) K-1 and 0.05/0.03 KW-1 m, respectively. (C) 2008 Elsevier B.V. All rights reserved.