The Effects of Base-Only-Restrained and Both-Ends-Restrained Conditions on the Ultimate Bearing Capacity of Energy Piles using Physical Modeling

Abstract

Today, one of the best and most efficient ways to reduce energy consumption is using geothermal heat pumps. In the conducted studies, the high efficiency and low consumption of this system have been proven by researchers, and the main problem with the system is the high cost of its installation due to the high cost of drilling. Using energy piles eliminates the cost of drilling and makes this system affordable. In order to spread the use of energy piles, it is necessary to complete studies in this field. Load transfer mechanics in energy piles significantly changes under various thermomechanical loading due to thermal and mechanical interactions. This study modeled an energy pile installed in dry Firoozkooh sand using fully controlled 1-g physical tests. The ultimate bearing capacity of an energy pile was compared in the two general base-only-restrained and both-ends-restrained conditions. For each of these two conditions, the relative densities of 48% and 85% and the temperature changes of ΔT = 17°C and ΔT = 30°C were regarded as variables. The soil and pile temperatures, the pile head, the pile tip displacements, and the thermomechanical strains in a pile were recorded during the test. These parameters are used for calculating the temperature profile, the thermal stresses of the pile, the side shear stresses, and the ultimate bearing capacity of the pile. The results showed that the increase in relative density and temperature led to an increase in thermal stress and ultimate bearing capacity. In addition, higher thermal stresses were observed when both ends of the energy pile were restrained compared to the base-only-restrained condition. The minimum ultimate bearing capacity increase was obtained for the base-only-restrained condition with a relative density of 48% and ΔT = 17°C which was about 10%, while the maximum increase of 21% was obtained for the both-ends-restrained condition with a relative density of 85% and ΔT = 30°C.