The thermal cone penetration test (T-CPT) allows in situ measurement of the thermal properties of soil during a CPT -that is without withdrawing the CPT tool and introducing another tool such as a thermal needle probe. An interpretation method is presented based on one-dimensional axisymmetric analytical solutions. Numerical verification of the method is given and numerical simulations are presented to derive a calibration factor required for the interpretation model. This factor accounts for the temperature sensor location and two-dimensional geometric effects, particularly internal voids and end effects for the cone penetrometer. Finally field data are presented for the T-CPT and compared with results from in situ needle probe tests and laboratory tests on sampled material. The interpretation model is able to provide thermal conductivity values robustly.

Swabbing pressures can affect borehole stability. Temporary and local pressure reductions in the borehole fluid can disrupt the in-situ gas-fluid-soil equilibrium and may trigger a shallow gas blow-out.This paper presents swabbing pressures measured during riser-less drilling and testing activities. Results show pressure reductions of up to about 1.2 MPa below hydrostatic values. Borehole depths were up to about 400 m below seafloor. Some measurements were made in boreholes in which gas blow-outs occurred shortly after acquisition of the data. The magnitude of the measured swabbing pressures cannot be correlated with water depth and depth below seafloor and soil type. The riser-less drilling and testing practice appears to dominate the magnitude of the measured swabbing pressures.A procedure for shallow gas hazard assessment is proposed. This procedure serves as input for risk management for riserless drilling and associated logging, sampling and testing.

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This paper focuses on ground investigation by deepwater cone penetration tests (CPT). All current offshore CPT systems deploy subtraction-type cone penetrometers. Their use now includes record-breaking deepwater applications. This paper presents results of geotechnical field and laboratory measurements that explore the operational limits of deepwater cone penetration tests in very soft soils. The review of field repeatability studies shows the feasibility of excellent performance of the subtraction penetrometer. The results of specific laboratory experiments indicate a relatively small influence of deepwater ambient pressures on its performance. A further consideration for deepwater applications is the zerocorrection to hydrostatic conditions prior to the start of a test. Seabed-based CPT systems allow zero-correction with an uncertainty approaching the resolution of the CPT system. Downhole CPT systems latch into the lower end of a drill pipe. The pressure conditions in the drill pipe may not be in full equilibrium with the surrounding ground water pressure and zero-correction will be subject to increased uncertainty. The main points are: (1) currently available evidence indicates that a high-quality subtraction-type cone penetrometer is adequate for very soft soil characterisation to a water depth of 3000 metres and probably beyond, (2) Class 1 accuracy results (according to ISSMGE) in very soft soil are likely to be feasible for deepwater seabed systems and (3) deepwater downhole systems are less accurate and will probably give Class 2 results.

Breakout of objects from soft, clayey seafloors is a common, potentially hazardous and costly task, but there is little information about it beyond results of small-scale laboratory studies extracting decimetre-scale objects from 'model' soils. In this study, a unique dataset is presented, comprising thirty-five immediate breakout events of a seafloor template from very soft clay in 200 m to 2000 m water. The measured breakout forces were compared to operational variables and soil characteristics at the exact location of breakout, which were known because geotechnical soil investigations were performed at each site. Predictions from three existing theories, namely Muga (1968), Rapoport and Young (1983), and Das (1991) were tested. The three theories appear to predict breakout force well, and with comparable accuracy. Predictions from all these methods could be valuable in lifting/extraction risk assessments.