Embedded Length Research Articles

Bond behavior between bundled steel-FRP composite bars and grouted corrugated duct

The utilization of steel-fiber reinforced polymer (FRP) composite bars (SFCBs) reinforcement in precast concrete structures offers numerous benefits, including controllable post-yield stiffness and reduced residual displacement. Employing bundled reinforcement can improve construction efficiency. This study presents direct pull-out tests conducted on SFCBs embedded in grouted corrugated ducts. The results show that bond strength decreases with both the number of bars in a bundle (nb) and the actual embedded length (la). The bond strength of single bar SF-1b-3d with 3d embedded length is 24.21 MPa, while that of 2-bar bundled SF-2b-3d and 3-bar bundled SF-3b-3d is 17.41 MPa and 12.61 MPa, respectively. Additionally, the error in predicting the bond strength between bundled SFCBs and grouted corrugated duct using the equivalent diameter method is found to be less than 8.4%. Utilizing the mBPE constitutive model, an analytical hardening-slip model with a linear slip field assumption accurately predicts the full-range behavior, bond stress distribution, and SFCB's axial stress distribution. Furthermore, the effects of different parameters on yield slip sy, ultimate slip su, and critical anchorage length Ltr are investigated by considering different local bond-slip constitutive models (varying peak bond strength τm and its corresponding slip sm and ascending section coefficient (α) as variables. The yield slip sy varies from 0.1 mm to 1.3 mm, while the ultimate slip su can reach a maximum of 35.0 mm. Furthermore, the validity of existing models for evaluating the anchorage length of single SFCB and bundled SFCBs grouted in corrugated duct connections is discussed, and a formula to estimate the critical anchorage length of bundled SFCBs and grout considering the number of bars within one bundle (nb) is proposed.

Multi-factor analysis and optimization on seismic behavior of precast pier-footing socket connection considering different connection parameters

Accelerated bridge construction technology, with its various connection methods, has experienced extensive global usage. Common methods include post-tensioned, cast-in-place joint, sleeve, and socket connections. Each method has its advantages and limitations, such as the energy dissipation issue in post-tensioned connections and the on-site challenges of cast-in-place joints. Precast pier-footing socket connections have emerged as a promising solution due to their rapid construction and durability. However, previous research has predominantly focused on the minimum embedded length, overlooking critical factors such as grouting material strength, shear key configuration, and axial compression ratio during service. Furthermore, existing studies often isolated individual factors, neglecting their interconnected effects. This study addressed these gaps by testing two specimens and analyzing thirty-eight models through experimental and numerical methods. The results indicated that an embedment depth of at least 1.0 times the diameter (bc) of the precast pier was recommended. Furthermore, to ensure optimal seismic performance, it was essential to enhance the stiffness of the footing sidewalls beyond this depth. Additionally, while shear keys improve bending resistance, their effectiveness decreases with greater embedment depth (>1.5 times the diameter). This study highlights the importance of considering the interplay of multiple factors to ensure project safety and cost-effectiveness.

Seismic behavior of drift-hardening precast concrete walls reinforced with SBPDN rebars

Six precast concrete walls reinforced with weakly bonded ultra-high strength (WBUHS) rebars were fabricated and tested under reserved cyclic lateral loading and constant axial compression to investigate the seismic behavior of the precast drift-hardening concrete walls. The emphasis was placed on clarifying the proper embedded length for WBUHS rebars and verifying the influence of the shear span ratio. The experimental variables were the embedded length of the WBUHS rebar, the shear span ratio of the walls, and the axial load ratio. Test results indicated that if the embedded length of the WBUHS rebar, whose ends were anchored by nuts and a washer, was 20d (d is the nominal diameter of rebar) and/or longer, the precast walls could exhibit identical seismic performance to the cast-in-site walls and had sufficient drift-hardening capability up to at least 2.0 % drift ratio. Test results also showed that the larger the shear span ratio, the less the residual drift. The residual drifts after unloading from the 2.0 % transient drift were less than 0.4 % regardless of the axial load level and the shear span ratio. Furthermore, an analytical method was presented to evaluate the seismic behavior of the precast walls reinforced by WBUHS rebars. The analytical method can consider the effect of bond slippage of WBUHS rebars and the confinement effect by transverse steels placed in the boundary elements on the cyclic response of the walls. Comparison between the measured cyclic loops and the predicted ones has indicated that the proposed analytical method can predict the cyclic behavior of the precast walls very well in important aspects such as overall performance, the ultimate lateral resistance, and the deformation capacity.

Reinforcement bond performance in 3D concrete printing: Explainable ensemble learning augmented by deep generative adversarial networks

Integrating various reinforcements into 3D concrete printing (3DCP) is an efficient method to satisfy critical requirements for structural applications. This paper explores an explainable ensemble machine learning (EML) method to predict the bond failure mode and strength of various reinforcements in 3DCP. To overcome the problem of insufficient experimental data for the 3DCP technology, a deep generative adversarial network (DGAN) is integrated for data augmentation. The trained EML models augmented by the DGAN accurately and reliably evaluated the bond performance. The relative embedded length, concrete cover, and compressive strength of 3D printed concrete were identified as the three most important features based on the explanatory analysis. The effect of the amount of training data and integration of the proposed method in the additive manufacturing process were also investigated. The proposed method combining EML, data augmentation, and model interpretation can be extended for other aspects of digital fabrication with concrete.

Performance of high strength steel bar splice with novel grouted deformed sleeve under tensile load

High-strength steel (HSS) bars can solve bar congestion problem in beam-column joints of monolithic precast concrete frame structure. Unfortunately, its application in precast concrete structures is greatly hindered by few researches on HSS bar grout splice. In this paper, utilizing large-diameter HRB600 reinforcements with specified yield strength of 600 MPa, 34 splice specimens were prepared considering the parameters of embedded length, grout strength and inner cavity structure of sleeve. Through uniaxial tension test, it is shown that the embedment length has the greatest effect on the structural performance of grouted splice. For the d28 bar grout splice, 8db is the minimum embedded length to ensure bar fracture failure, which is longer than the normal-strength steel bar grout splice. For the splices with embedded length not smaller than 5db and concentric ribs not less than five, excessive ribs set on the sleeve cannot significantly increase the tensile strength of the grouted splice, but further adding one rib still can effectively reduce the elastic residual deformation. Similar test results have been observed for the effect of grout strength. As the compressive strength increases from 95.3 MPa to 118.2 MPa, the tensile strength improves only by about 2.52%, but the residual deformation decreases significantly by 11.68% on average. For a high-strength large-diameter bar grout splice, it is recommended to set six concentric ribs at each side of the sleeve, and select 8db as the minimum embedded length to achieve reliable performance.

Experimental study and modeling on bond-slippage behavior of steel bar in polyvinyl alcohol-steel hybrid fiber engineered cementitious composite

In order to understand and estimate the composite action of steel bar and fiber reinforced low drying shrinkage engineered cementitious composite (LSECC), bond strength-slip relation of steel bar embedded in LSECC was studied in this paper. Series pullout tests, smooth steel bar and deformed steel rebar, with four LSECC mixtures and two embedded lengths were performed. Failure on bond between steel bar and LSECC under pullout load can be divided into debonding and pullout stages. In debonding stage, constant bond strength that principally controlled by chemical and physical bond of steel bar and cement matrix can be used to describe the pullout behavior. In pullout stage, bond strength first increases with slippage (slip-hardening stage of bond). After the peak, bond strength decreases with slippage (slip-softening stage of bond). In the slip-hardening stage, much higher bond strength is observed in slip-hardening stage of rebar than that of the smooth bar, while much smaller slippage corresponding to the peak bond strength is observed of rebar than that of the smooth bar. An analytical three stage bond strength-slippage model was proposed based on pullout test results with small embedded length (30 mm). Meanwhile, pullout model of steel reinforcement from ECC with arbitrary embedded length was developed based on debonding and pullout theory, which can well simulate initial ascending, slip-hardening and slip-softening stages under pullout load. Good agreement between model and test results in terms of load-slippage relationship of longer reinforcement embedded in ECC was observed.

Combined corrosion and inclination effects on pullout behavior of various steel fibers under wet-dry cycle deterioration

The interfacial bond behavior of corroded fibers in cracked steel fiber reinforced concrete (SFRC) is critical for understanding its structural deterioration performance, while available research focused on aligned straight or hooked-end fibers. This study investigated the combined effects of corrosion and inclination on the pullout performance of various steel fibers bridging artificial cracks exposed to wet-dry cycles of chlorides. Three deformed steel fibers, i.e., hooked-end (H), crimped (C), and milled-cut (M) fibers, with three angles of 0°, 30°, and 45° were examined under both uncorroded and corroded conditions. After corrosion, the average bond strength of H fibers was enhanced due to increased roughness and compact rust layer if the high inclination-induced fracture was avoided, while that of C and M fibers was decreased at various angles because of loose and porous rusts. The highest bond strengths of corroded H, C, and M fibers were discovered at 30°, 30°, and 0°, as a result of the combined mechanisms of snubbing effect, matrix spalling, or corrosion-induced fracture. The ultimate displacement of all fibers increased with angles due to increased matrix spalling area and fiber plastic deformation. The inclination effect of corroded fibers was more significant on energy absorption capacity than average bond strength, regardless of fiber type. A degradation model that describes the snubbing and matrix spalling effects, as well as the corrosion-induced deterioration and fracture was developed, based on which the critical inclination angle was found to decrease with increasing embedded length and decreasing tensile strength.

Comparative bond-slip response of ribbed CFRP bar to UHPC after exposure to high temperature

Ribbed carbon fiber reinforced polymer (CFRP) bar and ultra-high-performance concrete (UHPC) have high potential in terms of utilization of load-carrying capacity and maintenance of the concrete structure. Bonding behavior of ribbed CFRP bars to UHPC after exposure to elevated temperature is of importance due to its susceptibility of thermal effects. This study investigated the residual bond strength of the ribbed CFRP bar embedded in UHPC at ambient temperature and after exposure to elevated temperature. The bond strength of ribbed CFRP bars with different embedded length and cover thickness were also considered and the bond strength was compared with the sand coated CFRP bars. Both at ambient temperature and after exposure to elevated temperature, the bond strength of the ribbed CFRP bar increased with an increased embedment length and cover layer due to the mechanical resistance of the ribs. However, the difference reduced as the elevated temperature increased. Compared with the sand coated CFRP bars, the decreasing rate of bond strength is slightly lower in ribbed CFRP bars and the residual bond strength after exposure to elevated temperature at 400 ℃ was more than 10 MPa, which satisfies bond strength of FRP bar suggested by ACI 440.5 M. The critical temperature of the ribbed and sand coated CFRP bars was suggested as 300 ℃ with consideration of decreasing rate in this study. The modified bond equations were presented to reflect the reduction of bond strength due to the elevated temperature, and the bonding behavior of the ascending branch was compared using the modified BPE and CMR models and presented the coefficient of each parameter.

Research on the natural frequencies of an integrated offshore wind turbine model considering blades

The offshore wind turbine (OWT) is a high-rise structure that is extremely sensitive to dynamic loads such as wind, waves, and earthquakes. Therefore, in order to avoid resonance, it is extremely important to accurately calculate the natural frequencies of the OWT at the design stage. The integrated finite element model of DTU (Technical University of Denmark) 10 MW OWT is established based on OpenSees finite element software. The correctness of the superstructure simplification method is confirmed by comparing it to the frequencies calculated by the wind turbine dynamic analysis software HAWC2 for the single-blade model and the fixed constraint model at the bottom of the tower. The frequencies and mode shapes calculated by the overall model are compared with those calculated by the fixed model at the mudline and the concentrated mass model at the top of the tower. Then, the parameters of the soil shear modulus G0, void ratio e, pile embedded length L, pile diameter D, water depth, and blade stiffness are analyzed using the lumped mass model and the blade model at the top of the tower, and some regular conclusions about the variation of natural frequency with the parameters are obtained. Finally, based on the blade model, the influence of short-term cyclic loading on the natural frequency for OWT monopiles in dense sand is studied. The results indicate that the pile-soil interaction has a significant impact on the natural frequencies, the blade has a higher influence on the second bending frequency of the OWT, and the front-after direction is more significantly impacted than the side-side direction. The short-term cyclic loading are unlikely to significantly affect natural frequency for OWT monopiles in dense sand.

Bond behavior between high-strength steel wire meshes and ECC: Experimental study and analytical modelling

In this study, a novel methodology was proposed to investigate interfacial bonding performance between high-strength steel wire mesh (HSSWM) and engineering cementitious composites (ECC), and the inhomogeneous distribution of bond stresses was taken into account. A simple bond-slip model was constructed and compared with the existing average bond-slip model to estimate the bond behavior of the HSSWM-ECC matrix joints. The results showed that the proposed model was more appropriate to estimate the interfacial bond property between HSSWM and ECC. With the bond-slip model, the local bonding performance of HSSWM-ECC interface was analyzed using the numerical simulation method. An analytical model was proposed for predicting the critical embedded length between HSSWM and ECC, while the effects of the matrix properties, high-strength steel wire (HSSW) diameter, transverse HSSW spacing, and HSSW mechanical properties were comprehensively studied. Finally, a simple analytical model was proposed to calculate the interfacial bearing property between HSSWM and ECC and verified by the experiment results.

Seismic Response of Embedded Retaining Wall for Excavation Support

A comparative analysis of the solutions for the seismic impact on a flexible retaining wall designed to strengthen the construction excavation for a multi-storey building in Sofia has been performed. For this purpose, the following FEM calculation models of the interaction of the wall with the surrounding soil body were compiled: (1) a 1D beam-column-spring model of the wall, including spring support in its embedded length and pseudostatic seismic loading of the wall with active earth pressure, determined by the Mononobe-Okabe method; (2) a 2D model of the wall and soil body, with pseudostatic seismic loading in the form of inertial forces applied at the finite element nodes; (3) a time history FE analysis conducted with the accelerograms of two landmark earthquakes from the Balkan Peninsula - the 1976 Vrancea (Romania) earthquake and the 1986 Kalamata (Greece) earthquake. The pseudostatic seismic loading in analyzes (1) and (2) was determined on the basis of the reference pseudostatic acceleration of 2.3 m/s2, determined for the city of Sofia according to the seismic hazard map for Bulgaria. The accelerograms in analysis (3) were scaled to a maximum value of acceleration of PGA = 2.3 m/s2. The physical modelling of the soil body uses the HSM and HSsmall advanced constitutive laws, implemented in the Plaxis software.

Numerical analysis of a slope stabilized with piles and anchor cable frame beams

A landslide located in northern Sichuan Province, China was investigated. A series of numerical models of the landslide stabilized with piles and anchor cable frame beams were developed using a three-dimensional finite-element method. The Strength Reduction Method was employed to investigate the stability of slopes, the internal forces of piles, and the axial forces of anchor cables. A parametric study consisting of pile position, pile length, and pile spacing was carried out. The results show that compared to anchor cable frame beams, the combination of piles and anchor cable frame beams is a more effective retaining structure to improve slope stability. During slope destabilization, the proportion of thrust shared by piles gradually increases, while the proportion of thrust shared by anchor cables gradually decreases. Piles installed on the leading edge of a trail-mode landslide can make the slope mostly stable. As the piles move from the leading, middle, and trailing edges of the slope, the proportion of thrust shared by the anchor cables gradually increases, while local instability may occur in front of the pile. Increasing the pile length can improve the stability of the slope. However, excessive embedded length of piles has little effect on further improving the slope stability. The critical embedment length of piles found in this study is 1/3 of the total length of the pile. The critical pile spacing found in this study is 2.5 times the width of the pile section. Beyond this spacing, the effective soil arch between the piles is difficult to develop and the anchor cables may share more proportion of the landslide thrust. This study provides a reference for reinforcement system design of engineering projects considering piles and anchor cable frame beams.

The efficiency of granular pile anchor foundation system in reducing heave of Irbid expansive clayey soil: An experimental investigation

This study is devoted to investigate the efficiency of granular pile anchor (GPA) in controlling heave of shallow foundations constructing over expansive soils. In this study heave measurements were made on laboratory model footings reinforced with GPAs having different diameter (3 cm, 4 cm and 5 cm) and embedded length (20 cm, 30 cm and 40 cm). The GPAs foundation system was constructed on expansive clay compacted in a steel box 60 cm in diameter and 70 cm in height. The measured percent reduction in heave was found to increase with increasing embedded length and diameter of GPA. The experiments conducted in this study showed that the percent reduction in heave when using GPAs may reach as high as 93 %. A theoretical formulation for the prediction of the percent reduction in heave was developed in this study. A comparison of the predicted percent reduction in heave using the developed formulation with the measured values in this study indicated good agreement and suggested that the proposed formulation in this study can be used to estimate the percent reduction in heave of shallow foundations constructing over expansive soils reinforced with GPAs.

Balance interlaminar improvement and in-plane adverse impact of hexagonal semi-embedded fine Z-pin reinforced polymer composite

This article aims to minimize the adverse impact of Z-pins on the in-plane properties of unidirectional carbon fiber reinforced polymer (CFRP) composites while enhancing their interlaminar fracture toughness by using CF Z-pins. A novel method was developed for implanting fine Z-pins of 0.1 mm diameter with semi-embedded length in the thickness center of laminate in an ultra-low distribution density of hexagonal array pattern. Mechanical properties and failure mechanisms of different Z-pinned composites were analyzed. Taking traditional CFRP as a reference, the semi-embedded Z-pinned CFRP has considerably increased (by 123%) propagation GIC and negligibly reduced in-plane mechanical properties. Correspondingly, the Z-pinned CFRP with full-thickness embedded length shows a rise of 244% in the propagation GIC and a reduction of less than 9% in the in-plane properties. The failure modes indicate that pull-outs of Z-pins and their fractures both contribute to the enhancement of the fracture toughness of Z-pinned laminates, which are influenced by the distribution density and the embedded length of pins. It manifests that shortening the embedded length of pins can narrow the scope of waviness in planar fibers and relieve the induced stress concentration, which is conducive to improving the retention ratio of in-plane mechanical properties of Z-pinned composites. Finally, with 0.10% areal density, a better balance between interlaminar and in-plane properties of Z-pinned composites is successfully achieved for those with semi-embedded pins. Moreover, the Z-pin enhancement effect on interlaminar toughness is limited by its lower areal distribution density.

Experimental study on local bond-slip constitutive model between steel and steel fiber reinforced concrete structure of circular cross-section

The interface slip between shape steel and concrete is one of the biggest problems in numerical simulation of composite structures, this paper aims to investigate interfacial bond-slip behavior between steel and steel fiber reinforced concrete. For this purpose, a series of push-out tests on 15 circular section specimens which were designed and fabricated with different steel fiber ratio, interface embedded length and concrete cover thickness have been done. Experimental results show that average bond strength versus free end slip curves of each specimen is similar, and then a basic average bond strength-free end slip constitutive model was proposed in this paper. Meanwhile, considering the distribution regularities of steel strains, local bond strength and relative slip along the interface embedded length at different load levels were obtained through the mechanical derivation, the results show that the maximum local bond strength was located near the free end, and the local bond strength away from free end tended to be steady. Based on the basic average bond strength-free end slip constitutive model, two position functions were proposed to describe the local bond-slip constitutive model considering the variation of positions. Two position functions are of great significance for further research on SSFRC non-linear properties by FEM.

Effect of slope on lateral bearing capacity of nearshore large-diameter monopiles in cohesive soil

This study investigates the effect of slope on the lateral bearing capacity of nearshore large-diameter monopiles in cohesive soil by the finite element limit analysis (FELA) method. The reduction coefficient is introduced to quantify the capacity reduction due to the slope effect, and the critical distance making the slope-induced capacity reduction negligible is normalized for generalization. After the validations by cases of different soils, an alternative way to quickly and straightforwardly assess the pile bearing capacity in sloping stratum for the most frequently-encountered cases in engineering practice is provided by multiplying the reduction coefficients in several design tables with the capacity in level stratum. The subsequent parametric studies indicate that the reduction coefficient and critical dimensionless distance are mainly governed by the internal friction angle, slope angle, and pile embedded length-diameter ratio but are almost insensitive to dimensionless cohesion and slope height-pile embedded length ratio. In addition, the failure mode of the pile-slope system would develop from local failure to transitional failure and global failure with a significant drop in pile bearing capacity while the pile-slope parameters cannot guarantee slope stability.

Method for calculating local bearing capacity of concrete under bond stress from reinforcement in straight anchor section

A pull-out test is performed on 30 concrete specimens to determine the effect of bond stress on the local bearing capacity. The parameters include the dimensions of the headed bars, strength grade of the concrete, embedded length of the reinforcement, and diameter of the reinforcement. The dimensions of the headed bars are 50 mm × 50 mm × 20 mm and 60 mm × 60 mm × 20 mm, and the strength grades of concrete are C30, C40, and C50. The diameters of the reinforcement are 25 mm and 32 mm and its embedded length is divided into five types in the test. The local bearing capacities of 30 concrete specimens are obtained, and three failure modes are observed in specimens. The different modes of failure primarily depend on the combined action of the shell structure and wedge of the concrete. The pull-out test results indicate that the local bearing capacity of concrete under headed bars increases with an increase in the embedded length of reinforcement and the strength grade of concrete, with an almost linear relationship. In addition, the local bearing capacity decreases with an increase in the relative protective-layer thickness of the concrete specimens. Finally, a calculation method is proposed for the local bearing capacity of concrete under the action of bond stress from the reinforcement in a straight anchor section. The calculations considered the relative embedded length and the relative protective layer thickness of concrete as independent variables and the ratio of the local bearing capacity of concrete to the bearing capacity of concrete under the headed bars as a dependent variable. This calculation method provides a theoretical basis for standard revision and engineering applications.

Bond behavior of an ultra-high performance concrete-filled anchorage for carbon fiber-reinforced polymer tendons under static and impact loads

To investigate the bond behavior of an ultra-high performance concrete (UHPC)-filled bond-type anchorage for carbon fiber-reinforced polymer (CFRP) tendons, both static tensile tests and impact tests were performed on 20 groups of specimens. The anchorages with embedded lengths of 50, 100, 150 and 200 mm were subjected to the static tension and longitudinal impact loads with drop heights of 150, 300, 600 and 900 mm. During the tests, the longitudinal tension and slip of the anchorage were obtained, and the effect of anchorage length and loading rate on the bond behavior was discussed. The results show that in the static tests, slip failure occurred for the anchorages with lengths from 50 to 150 mm, and CFRP bar ruptured as the length raised to 200 mm. When subjected to impact loads, slip failure was observed for all specimens. The damages on the CFRP bar to UHPC interface under impact loads were slighter than those under static tension, and correspondingly the dynamic bond strength was approximately half of the static one owing to the weakened mechanical interlocking. With increasing the embedded length, the bond strength and slip increased due to the radial constraining effect of outside steel tube. Based on the experimental results, a strain rate-dependent function was proposed to quantify the retention of bond strength under impact loads, and prediction formulas were established for determining the dynamic bond strength and critical embedded length of the bond-type anchorage.

A fracture mechanics approach to the design of hybrid-reinforced concrete beams

The Updated Bridged Crack Model (UBCM) is proposed as a fracture mechanics tool to thoroughly predict the structural behaviour of hybrid-reinforced concrete (HRC) beams. The cementitious matrix is assumed to be linear-elastic perfectly-brittle, whereas nonlinear constitutive laws are used to describe the toughening action of the reinforcing phases, which is due to the yielding of steel-bars and to the pull-out of the short fibres.Under these assumptions, the model predicts different HRC post-cracking structural behaviours that can be synthetically described by three scaling dimensionless numbers: the bar-reinforcement brittleness number, NP, which is directly related to the steel-bar reinforcement percentage, ρ; the fibre-reinforcement brittleness number, NP,f, which depends on the fibre volume fraction, Vf; and the pull-out brittleness number, Nw, which is a function of the critical embedded length of the fibre-reinforcement, wc. An effective relationship between the two reinforcement brittleness numbers is proved to define the minimum reinforcement conditions for HRC beams. All the other parameters being the same, it can be translated into a relationship between the steel-bar and the short-fibre reinforcement ratios, thus providing an effective and straightforward tool for the minimum reinforcement design of HRC structures.

Numerical investigation of geothermal pavements: Design optimisation & boundary conditions

Geothermal pavements comprise a newfound type of thermal geo-structures, an innovation in pavement construction contributing to ground source heat pump (GSHP) systems, resulting in a better cost-efficiency compared to conventional GSHP systems. Ground heat exchangers are formed by embedding pipe into the pavement structure (e.g., base, sub-base or subgrades). Developing accurate models with appropriate boundary conditions is crucial to obtaining a deep understanding of the performance and function of geothermal pavement systems. This paper introduces an experimentally validated 3D finite element model (FEM) and compares the effect of surface boundary condition choices on the results of the simulation. The model uses two different approaches for boundary conditions: i) using ambient temperature and ii) implementing energy balance equations on the surface, as surface boundary conditions. The model is further utilised to perform a parametric study and the results are employed by a statistical tool (Minitab) to determine the optimum heat exchanger design for a geothermal pavement project in Adelaide, an Australian city subjected to temperate climate conditions and good solar irradiation throughout the year. Results show that the choice of both boundary conditions leads to similar fluid temperature trends, but with differences in values, particularly during the heating season, resulting in a reduced embedded pipe length of up to 30 % and up to a 10 % better annual average coefficient of performance (COP(when using the energy balance equations on the surface. The parametric study shows that the system annual COP increases with the length of the pipe and spacing between the pipes, whilst the pipe depth placement is inversely proportional to the annual average COP given the advantages obtained during the heating season over the cooling season. Finally, considering the interaction effect between various parameters, a pipe heat exchanger with 400 m length, 0.76 m pipe spacing and 0.45 burial depth is evaluated as the best design to maximise COP for the case study at hand.