## 1 Introduction  
Traditionally, bridges are designed and constructed with expansion joints and bearings to accommodate the expansion and contraction of the bridge due to temperature and stress changes. However, expansion joints and bearings need regular maintenance and replacement due to cyclical deck movement, traffic loading, trapped debris, and salt and moisture intrusion [1, 2]. Degradation of expansion joints is a persistent cause of costly maintenance and rectification work [3]. Failure to maintain the bridge joints and bearings could cause overstress and structural distress in the bridge structure, which must be avoided. Rectification work is often disruptive to traffic flow and causes an increase in travel time that also incurs socio-economic costs for road users. Although conventional or jointed bridges still outnumber integral bridges, the overall trend of bridge construction towards integral bridges is increasing to avoid the recurring maintenance issues related to bridge joints and bearings. Integral bridges have been used since 1938 in Ohio, the United States of America (USA) [4]. During the construction boom of the National Interstate Highway System, in the late 1950s and mid-1960s, several USA states began to use integral bridges as a construction choice for bridges. In 1980, the American Federal Highway Association (FHWA) recommended bridges to be constructed as integral bridges for steel bridges with overall lengths up to 90 m, cast-in-place concrete bridges up to 150 m and post-tensioned bridges up to 183 m [5]. According to [PERSON] et al. [6], approximately 70% of the USA State Department of Transportation (DOT) have already included integral bridges in their jurisdictions. In 1996, the British Highway Agency recommended adopting an integral bridge design approach for any bridge with a length of up to 60 m [7]. Integral bridges in other regions and countries, e.g., Europe, Japan, Canada, China and Oceania, also witnessed rapid development in the last few decades. Under cyclic thermal, environmental and mechanical loading, the bridge superstructure expands and contracts. Movements particularly in the bridge deck of integral bridges will cause the bridge abutment to displace directionally into and away from the approach fill with each cycle. The movements of the abutment and substructure mobilise significant soil-structure interaction (SSI) effects [8; 9; 10; 11], such as stress variations, soil densification, stress ratcheting [12; 13; 14], heave, settlement and/or slumping of the backfill soil [15; 16], which in turn affect the overall performance of integral bridges. Stress ratcheting is the phenomenon that increases the lateral earth pressure applied on the abutments due to cyclic movements transferred from the bridge deck [12]. Pile-supported systems will also be affected by the abovementioned issues of integral bridge. The repeated actions of deck movements, much of which is induced by temperature changes, may be transferred to the piles, changing the soil properties around the pile. Many researchers have reported that the overall pile-soil interaction is dependent on various factors including pile type, pile orientation, pile flexibility, soil properties around piles and substructure stiffness [17; 18; 19; 20]. Cyclic displacements and moments transferred to pile foundations are at risk of causing pile fatigue failure [21]. The complexities associated with pile-soil interaction ultimately affect the overall performance of the integral bridge including the bridge approach. Despite this, [PERSON] [22] reported that only two states in the USA consider the pile stress due to thermal movements, while other states neglect this aspect in the integral bridge design. It is quite evident from literature that different countries and jurisdictions are using a variety of design guidelines and practices to deal with the geotechnical issues for abutments and pile foundations.