The effects of dam-reservoir interaction on the nonlinear seismic response of earth dams

The objective of this study is to investigate the effects of dam–reservoir interaction (DRI) on the nonlinear seismic response of earth dams. Although DRI effects have for long been considered as insignificant for earth dams, that conclusion was mainly based on linear elastic investigations which focused only on the acceleration response of the crest without examining the seismic shear stresses and strains within the dam body. The present study explores further the impact of DRI focusing on the nonlinear behavior of earth dams. The effects of reservoir hydrodynamic pressures are investigated in terms of both seismic dam accelerations and nonlinear dynamic soil behavior (seismic shear stresses and strains). It is shown that although dam crest accelerations are indeed insensitive to DRI, the stress and strain development within the dam body can be significantly underestimated if DRI is ignored.</p

Steady-state and transient dynamic visco-elastic response of concrete and earth dams due to dam-reservoir interaction

The aim of this study is to investigate the effects of dam–reservoir interaction on the dynamic response of dams. Both thin rectangular concrete cantilever and large trapezoidal earth dams are considered with empty and full reservoir. It has recently been shown by Pelecanos et al. [32] that the amplification of accelerations at the crest of the dam depends on the combinations of the frequency of the harmonic acceleration load and the fundamental frequencies of the dam and the reservoir. This study considers transient dynamic loading and selected scenarios of different combinations of the above-mentioned frequencies are examined under random seismic acceleration load. It is shown that for certain cases the amplification of accelerations of the dam can be affected by the presence of the upstream reservoir. In general, thin rectangular concrete cantilever dams are found to be considerably more sensitive to dam–reservoir interaction than large trapezoidal earth dams. Therefore, this investigation examines the significance of dam–reservoir interaction and when this interaction should be taken into consideration or it could be neglected

Pile driveability in low-to-medium density chalk

Pile driving in low to medium density chalk is subject to significant uncertainty. Predictions of Chalk Resistance to Driving (CRD) often vary considerably from field driving behaviour, with both pile refusals and free falls under zero load being reported. However, recent field studies have led to better understanding of the processes which control the wide range of behaviour seen in the field. This paper describes the primary outcomes of the analysis of dynamic tests at an onshore and an offshore site and uses the results to propose a new method to predict CRD. The method is based on phenomena identified experimentally: the relationship between cone penetration resistance and CRD, the attenuation of local stresses as driving advances and the operational effective stress interface shear failure characteristics. The proposed method is evaluated through back analyses of driving records from independent pile installation cases that were not included in developing the method, but involved known ground conditions, hammer characteristics and applied energies. The proposed method is shown to lead to more reliable predictions of CRD than the approaches currently applied by industry

Effective stress regime around a jacked steel pile during installation ageing and load testing in chalk

This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method