Behaviour of piles driven in chalk

Abstract

Driving resistance is difficult to predict in chalk strata, with both pile free-fall self-weight 'runs' and refusals being reported. Axial capacity is also highly uncertain after driving. This paper reviews recent research that has explored these topics. Programmes of onshore tests and novel, high-value offshore, experiments involving static, dynamic and cyclic loading are described. The key findings form the basis of the Chalk ICP-18 approach for estimating the driving resistance and axial capacity of piles driven in low-to medium-density chalk. The new approach is presented and the highly significant impact of setup after driving is emphasised. It is shown that Chalk ICP-18 overcomes the main limitations of the industry's current design guidelines by addressing the underlying physical mechanisms. While further tests are required to enlarge the available test database, the new approach is able to provide better predictions for tests available from suitably characterised sites. A new Joint Industry Project is outlined that extends the research to cover further axial, lateral, static and cyclic loading cases.

Laboratory investigation of interface shearing in chalk

“…[2] demonstrated that, as with sands and clays, pile shaft failure in chalk is controlled by the Coulomb failure criterion. The preliminary design rules for piles driven in chalk outlined by [17] call for representative δ′ measurements. The limited sets published data for interface shear tests on chalk indicate ultimate δ′ values of ≈30.5° falling below the chalks' typical φ′ values and possibly being affected by the shear displacements and normal stress levels imposed during testing [18,19].…”

Pile driveability in low- to medium-density chalk

“…The performance may be improved by further calibration of the rate dependent viscosity parameters in chalk and/or reducing the lower limit on h/R*. The method may also be combined with the preliminary Chalk ICP-18 method (Jardine et al, 2018) which aims to predict static long term axial capacity for piles installed in low to medium density chalk. (Lehane et al, 2005) WK Wikinger offshore wind turbine location Zv Velocity times impedance and Simons (1986) and Deeks and Randolph (1991) (Bristow et al, 1972) are not encountered at the test site Figure 6 Traditional soil resistance models adapted from Smith (1962) Figure Rational soil resistance models adopted at the shaft and at the base; adapted from Randolph and Simons (1986) and Deeks and Randolph (1991)…”

“…A range of important oil, gas, offshore wind, port and transport structures are founded on piles driven in chalk over the large outcrops found in NW Europe (see Jardine et al (2018)). However, there is no method currently available to predict the conditions applying to such piles during driving in chalk.…”

Finite deformation hyperplasticity theory for crushable, cemented granular materials

“…These studies have been motivated by the need of obtaining a better understanding of the mechanical response of such materials as observed in a number of practical applications, such as the evaluation of pile bearing capacity of offshore platforms [McLelland, 1988, King and Lodge, 1988, Jardine et al, 2018, the subsidence phenomena associated to hydrocarbon extraction [Potts et al, 1988], the evaluation of the stability conditions of underground excavations and sub-vertical cuts in open pit quarries [Evangelista et al, 2000, Bianchi Fasani et al, 2011.…”