Subsoil stiffness effects on the bridge-abutment dynamic behaviour

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4. Subsoil stiffness effects on the bridge-abutment dynamic behaviour

Integral abutment bridges (IABs) are robust structures that avoid the use of bearings and expansion joints and are relatively
maintenance-free compared to conventional bridges. The seismic design code of IABs is not fully developed, and the
complex soil-abutment interaction is not well understood. Therefore, research was carried out at the Schofield centre, the
University of Cambridge, to understand the backfill-abutment interaction under earthquake loading, aimed at developing
design guidelines for the industry. Understanding the mechanics by which the foundation soil stiffness and strength govern
the abutment deformation and, thus, the earth pressures generated behind the abutment is essential. Two centrifuge tests
have been conducted simulating an abutment with the conventional abutment-deck connection (or semi-integral abutment
bridge), where moment restraint is released. In this paper, the dynamic response of the abutment founded on dry and
liquefiable sandy soil is compared. Different deformation modes have been observed depending on the relative abutmentsoil
stiffness. The abutment experienced minimal base displacement in dry sands. Conversely, the abutment witnessed
cyclic rotational ratcheting about the deck level in liquefiable soil. The dry soil test helped identify the zones where soil
stiffness and strength loss can be critical. In the case of the saturated test, the water table level was up to one-third of the
abutment height, fully saturating the foundation soil while the backfill height was dry. The comparative results highlight
the vulnerability of semi-integral abutment walls to liquefaction-induced failure, as witnessed in the 2011 Christchurch
earthquakes.

8th International Symposium on Deformation Characteristics of Geomaterials (ISDCG2023)

II.2) Physical and numerical modelling