A. Blake

In Situ Measurement of the Dynamic Penetration of Free-Fall Projectiles in Soft Soils Using a Low-Cost Inertial Measurement Unit

Six degree-of-freedom motion data from projectiles free-falling through water and embedding in soft soil are measured using a low-cost inertial measurement unit, consisting of a tri-axis accelerometer and a three-component gyroscope. A comprehensive framework for interpreting the measured data is described and the merit of this framework is demonstrated by considering sample test data for free-falling projectiles that gain velocity as they fall through water and self-embed in the underlying soft clay. The paper shows the importance of considering such motion data from an appropriate reference frame by showing good agreement in embedment depth data derived from the motion data with independent direct measurements. Motion data derived from the inertial measurement unit are used to calibrate a predictive model for calculating the final embedment depth of a dynamically installed anchor.

The Dynamically Embedded Plate Anchor: Results From an Experimental and Numerical Study

Dynamically embedded plate anchors are rocket shaped anchors that penetrate to a target depth in the seabed by the kinetic energy obtained through free-fall. After embedment the central shaft is retrieved leaving the anchor flukes vertically embedded in the seabed. The flukes constitute the load bearing element as a plate anchor. This paper provides an overview of an experimental and numerical study undertaken to provide the first performance data for this anchor concept. The experimental work includes geotechnical centrifuge modelling and field tests using three different reduced anchor scales, whereas the numerical work focused on investigating anchor capacity for a rage of geometries, embedment depths and seabed conditions. The experimental work indicates that expected tip embedments are in the range 2 to 3.3 times the anchor length and depend on the impact velocity, anchor mass and shear strength of the soil. As with other plate anchors, the anchor needs to key before maximum capacity can be mobilised. Both the centrifuge and field experiments show that this keying and pullout behaviour is typical of other vertically installed plate anchors, where the main issue is the loss in embedment during keying. Both the experimental and numerical studies showed that the capacity of the DEPLA is much higher than that of other dynamically installed anchors with capacities up to 40 times the dry weight of the plate and plate bearing capacity factors of about 15.

A modified CPT based installation torque prediction for large screw piles in sand.

The intermediate soil (e.g. silt, sandy silt, clayey silt) response at the standard cone penetration (CPT) velocity of 20 mm/s is generally partially drained, falling between that of sand and clay. As a result, a proper interpretation of CPT (or CPTU) in such mixed soils is not always straightforward. In order to properly analyse the in situ soil response and avoid incorrect estimates of soil parameters, the preliminary assessment of drainage conditions is essential. In this paper, changes in normalized CPTU measurements caused by changes in cone velocity are analysed. Penetration rate effects are assessed by means of No. 8 piezocone tests, with penetration rates ranging from about 0.9 to 61.7 mm/s. Tests were performed at a site located at the southern margin of the Po river valley (Northern Italy), where the subsoil mainly consists in a clayey silt deposit. Limitations on the applicability of some widely used empirical correlations, proposed for sands, are investigated and some preliminary results are shown. tests carried out at variable rates are nowadays recognized as an effective way to identify the transition point from undrained to partially drained and drained responses. A dimensionless velocity V (Finnie & Randolph 1994), given by: