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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 altemance of fme 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 freąuent presence of gravel intervals of different depth.

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the gravel was encountered, that is, as the Q_c was reaching 50 MPa, the "safety device" was trigged and the piezocone was retracted in to the core barrel.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-Once the cone was retracted, the core barrel with the piezocone was recovered and the data related to the last interval before getting to the gravel was down loaded and stored.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 madę 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.

Results are shown in the following graph:

Picture 10.

Picture 10

From left to right are Q_c, U, F_r, ROP (ratę of penetration), Torque, Mud pressure.

The CPT graph is interrupted where there are layers of gravel. These are where the CPTU has been interrupted and MWD non coring drilling has been carried out.

3.2 PIACENZA ZONĘ (FEBRUARY-MARCH 2001)

The system has been used for the execution of two deep tests, carried out using a rig on a smali jack-up barge, in order to investigate mainly sandy soils with gravel intervals. The drillings have been located on the two projected supports of the new tali bridge TAV (high speed train project) on the river Po. Different from the work previously described, morę advantage has been taken of the potentials offered by the wire-line recovery system.

In these soils, the CPTWD method has not been used continuously, but instead intermittent with c.c. drilling, non coring drilling and the withdrawal of undisturbed samples, always using the same basie system and without changing the casing.

Picture 11 is an example of a penetrometric graphic (Qc, Fs, U, Fr) from 60 to 120 m and one of the c.c. drilling operations in the same hole.