RESULTS OBTAINED WITH THE CPTWD

Parma zone (July 2000)

The CPTWD system has been employed near Parma (Italy) in the geotechnical surveys for the project of some TAV (high speed train project) works on sites characterized by an alternance of fine soils (clay, silt, sand) and gravel layers often interlayed by clay intervals of little thickness (about a decimetre).

The execution of "traditional" static penetrometric tests would have been impossible due to the frequent presence of gravel intervals of different depth.

The geotechnical conditions in this site were well known due to the wide amount of tests which have been carried out; therefore it has been possible to compare the CPTWD results and assess its reliability.

The CPTWD test has been carried out as follows:

The drilling starts with the use of the CPTU cone and MWD down to the top of the gravel; the core barrel with the CPTU cone was recovered at regular intervals (of about 1-2 m) in order to check the reliability of the data as well as the condition of the cone.

-As soon as the gravel was encountered, that is, as the Qc was reaching 50 MPa, the "safety device" was trigged and the piezocone was retracted in to the core barrel. At the same time, the Operator had a way to realize not only the retraction of the cone, but also the variations of the drilling parameters, constantly monitored in real time, (every 2 cm), indicating a very dense layer.

-Once the cone was retracted, the core barrel with the piezocone was recovered and the data related to the last interval before getting to the gravel was down loaded and stored. After recovering the data, the CPTU cone was again installed in the core barrel and the cylinder of the "safety device" was again pressurized so that the CPTU cone could again be placed in position.

-After this, a non coring-tool (tricone) that made the non coring drilling possible, was installed and with simultaneous detection of the drilling parameters every 2 centimetres, drilling was carried out until another "penetrable" layer (clay, silt, sand) was found and then the CPTU+MWD started again.

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