## 4 Conclusions  
This review paper discussed the geotechnical design guidelines and practices for integral bridges in the USA, Australia, New Zealand, Canada, Japan, UK, and a number of European countries. The SSI effects on integral bridges and how they have been incorporated in the design are reviewed. Although the popularity of integral bridges is increasing, the knowledge gaps on the SSI effects and current design guidelines of integral bridges present many challenges for geotechnical engineers in mitigating stress ratcheting, settlement, and pile flexural stiffness and fatigue issues. Therefore, augmenting design guidelines to enhance the applicability of integral bridges and to mitigate the geotechnical problems will help to strengthen the current design practice. The main conclusions drawn from the past studies and current design practices of integral bridges are summarized below:  
1. The nomenclatures on integral bridges in the design guidelines are not standardised across different jurisdictions. For example, AASHTO [5] defines an integral bridge as an IAB and does not further sub classify the integral bridges. In European countries, integral bridges are commonly defined as either fully integral bridges or semi-integral bridges based on the structural connection between the bridge deck and abutment, though these are analogous to the definitions of IABs and SIABs, respectively. A portal frame bridge (PFB) in Japan and end screen bridge in Sweden are other prominent examples of disparate terminologies of the integral bridges in different countries. There are also disagreements on the definitions and types of abutments in different states of the USA. In this review, we have attempted to unify some of the nomenclatures. An integral bridge is defined in this paper as a bridge structure where the bridge deck is without any joints for expansion or contraction of the deck and may be further sub-categorised as an integral abutment bridge (IAB) or a semi-integral abutment bridge (SIAB) depending on the connection between deck and abutment. 2. The design method and the design lateral earth pressure distribution behind the abutment (whether SSI is needed or not) are defined with respect to the type of abutments, length, and skew angle limit of integral bridges. In addition, the design practices of integral bridges, including threshold limits on the bridge length and skew angle, and types of abutments, vary across the literature. Knowledge gaps still exist  
Figure 6: Sleeves around the piles. in understanding the effects of different type and geometry of abutment, length and skewness of bridge, type of backfill and SSI. Filling the knowledge gaps is necessary to extend the application and improve the performance of integral bridges. 3. The factors considered and the equations used to calculate the earth pressure distribution behind the integral and semi-integral abutment (see Table A1 in Appendix A) in the USA vary from state to state. Some states are still using the traditional Rankine and Coulomb active and passive earth pressure theories derived for retaining structures under monotonic loading cases. In addition, the designed abutment displacement is considered as the displacement at the top, irrespective of the mode of displacement and flexibility of the abutment. Moreover, the displacement of the abutment is cyclic in nature, and the abutment displacement also depends on the nonlinear response of the backfill. 4. Most of the design practices lack comprehensive design guidelines on pile foundation for the integral bridges. The types of abutment foundation, restriction on the abutment foundation, and design of the abutment foundation (such as the orientation of the pile, type of pile and embedded length of the pile) have resulted in conflicting practices in some cases. In addition, the transferred effects from the abutment and abutment-soil interaction could have different effects on the pile foundation.