Cone Penetration Testing IV

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT: Screw piles have been suggested as an alternative foundation solution to straight-shafted piles for jacket supported offshore wind turbines in deep water. The significant environmental loads in the marine environment will require substantially larger screw piles than those currently employed in onshore applications. This raises questions over the suitability of current design methods for capacity and installation torque. This paper aims to address this issue by presenting a screw pile installation torque prediction method based on cone resistance values from Cone Penetration Test (CPT) data. The proposed method, developed using centrifuge modelling techniques in dry sand, provides accurate predictions of installation torque for both centrifuge and field scale screw piles. Furthermore, unlike existing CPT-torque correlations, the proposed method is shown to be applicable to multi-helix screw piles.

Using discrete element method (DEM) to create a cone penetration test (CPT)-based method to estimate the installation requirements of rotary-installed piles in sand

“…Prediction methods based upon in-situ cone penetration tests (CPT) have been shown to be potentially more reliable, due to the availability of continuous data logging along the path of installation and the full displacement nature of the CPT test. Existing CPT design methods are typically used to predict the installation torque of screw piles (Gavin et al, 2013;Spagnoli, 2017;Davidson et al, 2018), with a single method proposed for associated installation force by Al-Baghdadi (2017). A common assumption in all of these methods is that the screw piles are installed at P i that matches the geometric pitch (P g ) of the helix, so that for each rotation the screw pile displaces one P g vertically.…”

“…The simulations took place in soils at three different relative densities in sand. Using the results of the simulations, an improvement to the existing CPT based design method for predicting installation torque and force proposed by Davidson et al (2018) and Al-Baghdadi (2017) respectively are made to include the effects of varying installation pitch and pile base geometry.…”

“…Consideration of the results is undertaken with a view to improving the shaft and base component terms in the existing CPT based installation prediction techniques for rotary pile installation (Al-Baghdadi, 2017;Davidson et al, 2018) where these methods are broken down into force and torque predictions based upon CPT cone resistance (q c ). To assess whether the percentage reduction in vertical force due to varying P i is consistent across different relative densities, the base resistance (q b ) and the vertical component of shaft resistance (τ sv ) (Figure 4) were normalised by the CPT cone resistance (q c ) from a 10mm model scale (0.5m prototype scale) virtual CPT conducted in each of the 50g DEM chambers.…”

“…Both rotary press-in piles and the screw piles are installed in a similar way, through the application of rotational and vertical displacement with the only difference being the addition of helices to the screw pile. The necessary increase in pile size limits the ability to predict the installation requirements, of both techniques, in terms of torque and vertical force ("crowd force"), which may not be adequately captured by current analytical and empirical based approaches (Davidson et al, 2018). In addition to this, the effects of geometry and installation properties such as installation pitch (P i ) (the ratio between vertical and rotational or angular velocity) (Equation 1) on the required installation ( ) ( ) torque and force have seen little previous attention.…”

Effect of soil deformability on the failure mechanism of shallow plate or screw anchors in sand

“…However, they have attracted greater attention recently as a possible foundation solution for offshore structures (Byrne andHoulsby 2015, Gaudin et al 2017). Their behaviour under coupled lateral and compression loading was previously studied by Al-Baghdadi et al (2015 and there is ongoing work to improve prediction of installation requirements (Al-Baghdadi et al 2017b, Davidson et al 2018. The use of screw piles as anchors has the potential to combine the uplift capacity of a plate anchor with the lateral resistance of a pile, coupled with the advantage of low-vibration/low-environmental impact during installation when compared to driven piles.…”