## 3 Geotechnical Guidelines and Practices for the Design of Integral Bridges
### Finnish Practices
#### 3.9.2 Proposed Strategies to Minimise the Effects of SSI  
The adverse effects of SSI may be mitigated using the principle of isolation [4; 84; 85; 86]. Three degrees of isolation are generally used between the bridge structure and the backfill/foundation soil to deal with soil-structure interactions, namely:  
* No isolation;
* Partial isolation;
* Full isolation. The interactions may include superstructure and/or substructure interactions with backfill/foundation soils or both. The soil-structure interactions are complex and depend on (a) traffic and environmental loadings; and (b) the design of the integral and semi-integral abutment, abutment foundation and backfill/foundation soils. While the vicissitudes of traffic and environmental loadings are difficult, if not impossible, to control, engineers have some control over the design of the integral bridge. The question is in choosing the appropriate ways to mitigate or manage the adverse effects of soil-structure interactions in integral bridges with or without soil-structure isolation. This can only be answered by rigorous investigation and developing critical insights and understanding of the soil-structure interactions. Partial and full isolation techniques such as (a) placing compressible inclusions (CIs), made of low stiffness, highly compressible, and elastic materials, between the abutment and the backfill [15; 34; 41; 42] (Figure 4a,b) MSE stabilised embankment with compressible inclusion [10; 15; 86] (Figure 4b) have been proposed to minimize or eliminate inherent geotechnical problems in integral bridges. Figure 4: (a) partial isolation technique; (b) full isolation technique. [PERSON] [15] suggested that a compressible inclusion (Figure 4a) would accommodate deck expansion. It helps to decrease the lateral pressure on the abutments. However, compressible inclusions seem ineffective at controlling subsidence behind the integral abutment [8,87]. In winter, as the superstructure contracts and pulls the abutment away from the backfill, compressible inclusion is unable to restrain the soil from slumping downward and towards the abutment [8,88,89]. A complete separation between the abutment and self-stable retained soil could be another solution to avoid the effects of SSI in integral abutments (e.g., using self-stable MSE approach embankment) (Figure 4b). The space between the abutment and self-stable soil can be left as a void or filled with a compressible inclusion. However, leaving a void is considered unacceptable due to the difficulty of maintenance [22]. Alberta province has avoided the use of foam inclusion materials behind the integral abutments to minimize the earth pressure behind the abutment [56]. This is because the foam material can be compressed due to backfill compaction during the construction and due to the cyclic movements, and this could lead to unequal movements at the bridge abutments. A similar recommendation is also advised by the Manitoba province, Canada. The practice in Canada contrast with most of the design recommendations to use inclusion materials behind the abutment to minimize the earth pressure due to the abutment movements. There is little or no information regarding the solutions to minimise the pile-soil interaction in the IABs. Some design practices have recommended the single row of piles and weak axis orientation with the centerline of the integral and semi-integral abutment. A study conducted by [PERSON] et al. [6] showed that 21 out of 37 states in the USA prefer to orient the pile to bend along the weak axis (due to longitudinal thermal movement), whereas 5 out of 37 prefer to orient the pile to bend along the strong axis, and five states do not have any preference. Pile orientation (see Figure 5) in integral bridges can affect the amount of restraint to the thermal movements, force in the pile and overall pile performance in the integral bridges.