VENICE, Treporti zone and Mobile dams zone (JULY 2001-FEBRUARY 2004)

Inside a project of monitoring the settlements of an experimental embankment, one vertical CPTWD, was carried out in June 2001 down to 110m, in mainly sandy soil, (very dense sand from -50 m).

After the CPTWD test, an experimental embankment (50 m diameter, 8 meters height) has been made, and some CPTU, DMT tests and bore-holes up to -60 m has been carried out in order to withdraw samples and to install the monitoring instrumentation (piezometers, assestimeters, inclinometers).

Due to very high resistance of the sand (sometimes Qc greater than 50 Mpa) , some intervals were carried out by using continuous core drilling (also in order to verify and calibrate the static test) and non coring drilling with MWD.

In order to keep a constant rate of penetration, having high density sandy intervals, the Operator sometimes increased the pressure of the mud injection at intervals in order to allow a 2 cm/s rate. Therefore, in order to evaluate the potential effects of such pressure in the penetrometric parameters, another pressure sensor has been added to the current model, just above the friction sleeve ("U3" according to the recent nomenclature).

The diagram shows the penetrometric graphic (Qc, Fs, U, Fr) from 0 to 110 m.

The CPTWD data have been compared with the data of CPTU, DMT, bore-holes up to the depth of -60. The comparison shows that there is no relevant difference between CPTWD and CPTU data in the same range of depth (0 - -60). No comparison has been possible deeper than -60, due to high density of the sand not allowing deeper penetration to "normal" penetrometer.

At the present time, in the same area not far from the Jesolo site, in the same kind of soil, have been done several comparative tests carried out with traditional method (use of the penetrometer inside predrilled holes) in order to compare CPTWD data with other kind of data

All the tests have been carried out by operating jack-up barges.

As a matter of working time : a bore hole up to -100 m by using CPTWD took around 4-5 working days; a bore hole carried out by using alternatively a drill rig (for cased pre-holes) and 300 kN static penetrometer took around 15 working days.