|
Neben den kommerziellen Spitzen (Geomil) werden selbstentwickelte Piezometer eingesetzt, die auf Mantelreibung verzichten, alle anderen Parameter aber präziser und verlässlicher messen. Das Instrument hat zwei Porendruck-Messpunkte, die am Konus (Position u1) und 80 cm oberhalb des Konus (Position u3, gemäss der CPT Nomenklatur) angebracht sind.
|
|
The 380-580 cm long deep-water (DW) free-fall CPT instrument is equipped with a standard 15 cm2 CPT piezocone with strain gauges inside the probe to measure cone resistance qc (25 MPa range) and sleeve friction fs (0.25 MPa range). In addition to the commercial cones (Geomil) we use a self-developed probe without friction sleeve that offers a more precise and reliable measurement of the remaining parameters. The instrument has two pore pressure ports, which are located at the cone (u1) and 80 cm above the cone (u3, following the CPT nomenclature); both ports are connected to high-resolution (10 Pa) differential pressure transducers (Validyne DP215, ±120 kPa range) via stainless steel tubing to a sea bottom water reference port. An absolute pore pressure sensor measures hydrostatic pressure (i.e. water depth) down to 3 km water depth. To prevent the entrapment of gas inside the tubing, especially during the initial phase of deployment when the instrument is lowered through the water column, valves are used to bleed the gas from the tubing. The pressure sensors are protected by valves in case high excess pore pressures are encountered. Temperature sensors and 2 bi-axial acceleration sensors are also connected to the Avisaro microcontroller (1 kHz operating frequency).
|