## 3 Geotechnical Guidelines and Practices for the Design of Integral Bridges
### USA Practices
#### 3.1.2 Practices in USA States  
The consideration of the design loads that emerged from the lateral earth pressure acting on the abutment of integral bridges in the USA varies from state to state. In fact, there is no single approach in the USA to address this point, notwithstanding the availability of the AASHTO [23] guidelines. The DOTs rely primarily on previous experience and, in a few cases, on data from in-service bridges to develop their design methodologies. Most of the USA states have defined and discussed the integral and semi-integral abutment as the two types of abutment in integral bridges. Here, integral abutment refers to an abutment of an IAB, while semi-integral abutment refers to an abutment of an SIAB. Alaska has discussed only the SIAB [31], while Idaho [32] and North Dakota [33] have discussed only the IAB in their design manuals. Virginia [34] and Maine [35] have used the term \"full integral abutment\" instead of \"integral abutment\". The recommended limiting design criteria for the design of integral bridges in the different states, such as length of the bridge, the bridge's skew angle, and the preferred type of abutment foundation, vary from state to state. Most of the states have recommended IABs as the first design choice of the bridge and SIABs as a second choice only if the design requirements exceed the limiting design criteria of IABs. Some states, such as Ohio, also emphasized the choice and design of integral bridge based on the foundation requirements [36]. Ohio prohibited the integral abutment from being placed on mechanically reinforced earth (MSE), and spread footing is recommended for the semi-integral abutment [36]. The magnitude of the thermal movements of the integral bridge directly relates to the temperature changes in that region. Therefore, the maximum allowable length of the integral bridge should depend on the weather conditions in the state. As such, the maximum allowable length of the integral bridges is not uniformly standardized in the design guidelines of the states. Very few states, in fact, have provided the design criteria for the design of integral bridges based on maximum allowable abutment displacement, such as provided by Utah [37] and Oregon [38]. New Jersey [39] has provided the expansion length of the bridge as limit criteria to limit the construction of integral bridge, whereas Ohio [36] has provided both expansion length and total bridge length as limit criteria. Not all the states (e.g., Alaska [31]) have recommended considering the thermal effects on lateral earth pressure in the design of integral bridges. Some states (e.g., Ohio [36], Utah [37] and Massachusetts [40]) have provided the equations to calculate the design earth pressure distribution behind the abutum of IABs and SIABs based on abutment displacement. However, most states are still using the traditional earth pressure theories (e.g., Rankine or Coulomb earth pressure theory), which were developed specifically for the retaining structures under monotonic loadings. The necessity of the SSI analysis for the design of integral bridges has been recommended in only a few states. Even in states that have recommended SSI analysis (e.g., Virginia [34] and Massachusetts [40]), the guidelines on SSI are not comprehensive. Few states provided advice on mitigation measures to lessen the effects of the SSI in integral bridges (IABs and SIABs). A thick sheet of compressible inclusions (e.g., polystyrene, expanded polystyrene (EPS) and expanded polyethylene pad) has been recommended to be used behind the integral and semi-integral abutments in some states [34,41,42]. The use of approach slab is the most common method adopted by these states to minimise the settlement and cracking issue near the bridge abutments. The integral connection between the approach slab and bridge abutment helps to shift the soil settlement away from the abutment, to where soil settlement is less problematic, and maintenance is more accessible and less expensive.