Design and Reliability analysis of energy pile using soft computing technique and a comparative study between the developed soft compu-ting models
Authors: Kumar Ashutosh , Bag Ramakrishna , Samui Pijush 
Published: November 2023

Geothermal or energy piles, are environmentally friendly piles that extract heat energy from shallow depths of the earth surface to heat or cool the structures constructed over them, such as multi-storey residential buildings, industrial complexes, and shopping malls [1]. Through the energy piles, the heat is injected into the ground or extracted from the ground by the fluid circulating mechanism inside the heat exchanger pipes (HEP). The fluid is passed through the (HEP), which are attached to the reinforcement cage of the pile foundation element [2]. The use of energy piles to meet the thermal needs of the built structures has proven to be both environmentally and economically viable, as well as having significant social benefits [3]. A lot of uncertainties are associated with geotechnical engineering applications, which are unavoidable as they deal with natural materials. The reliability analysis of geotechnical structures has gained much attention in the last few decades [4]. Therefore, this paper aim is to study the reliability analysis of the ultimate group capacity) of energy piles along with the comparative study of the models developed using soft computing techniques. In the current study, cone penetration test (CPT) was carried out at Manali, Chennai (India), which falls in earthquake zone 3. Furthermore, () of piles was determined using CPT data by considering various parameters (such as pile length (), pile diameter (), cone resistance, average cone penetration resistance, an average of minimum cone penetration resistance ), Young’s modulus (), temperature change (), and coefficient of thermal expansion ()) and then the reliability analysis was performed. IS 2911 (Part 1): 2010 was followed to find out the  . The total load (mechanical load and thermal load) coming on a single pile was computed by assuming mechanical load as 100 kN and thermal load as stated in [5]. The average annual temperature variation of the ground surface was considered as 21 and the average yearly ground temperature as 13 to determine the thermal load applied to piles through the heat-circulating fluid (HCF). A cast-in-situ concrete energy pile of M35 grade was considered in this work. Based on the total applied load and  of the pile, the various parameters of the bored cast-in-situ concrete energy piles (9.0 m × 0.7 m) were determined.  Two U shape copper pipes having a diameter of 40 mm, and a thickness of 3mm, were embedded and placed  250 mm apart in the energy pile to carry fluid, i.e., water [5] as shown in Figure 1. A laminar flow having a heat-carrying flow inlet velocity of 0.183 m/s and a flow rate of 0.326 m3/h was considered for this work[6]. The thermal conductivity and heat capacity of the steel and concrete materials used in this work are {44.4 (W/m K) and 475 (J/kg K) } and {1.8 (W/m K) and 880 (J/kg K)}, and Young’s modulus of steel and concrete are 200× (MPa) and 32× (MPa), respectively [7]. The reliability index (β) was calculated using equation 1 for reliability analysis.    

β =                            ( 1 )

where and  are the standard deviation of capacity (C) and demand (D). After designing and selecting various parameters of the energy pile, 100 sets of data were generated randomly for,,