The Seismic Dilatometer test (SDMT) in geotechnical

inshore and offshore investigation

www.marchetti-dmt.it

Studio Prof Marchetti

Some examples of maritime construction

Trench for pipe

Sheet piles Oil and gas platform

Wind generators

Mooring

Common tests in offshore investigationClose water (harbours and bays)- inshore tests

Open water (sea)- offshore tests

Short test (5 m)- cables- pipes

Deep test (30 m)- foundations

Shallow water < 30 m

Short test (5 m)

Deep test (30 m)

Deep water > 30 m

Harbour: DMT test from pier

Steps

Make a hole in the deck; Set up the guidepipe; Fix the penetrometer and do

the test;

La Spezia (Italy)Shipyard Beconcini

Guidepipe

Pier

Seabed

Harbour: DMT test from provisional pierSalerno harbour

(Italy)Trapezio

Deck

Beam braching

DMT test with Floating Wheels Module

Two ton static penetrometer mounted on a floating raft, with screws for anchoring.

Only for very shallow water: 1-2 m;Short test: 5 m

DMT with SPT hammer for shallow water: Costa Rica

RigJackup

DMT test with Torpedo - layout

SEABED

SEA LEVEL

DMT test from Jack-upVenice lagoon, Italy

(MO.SE.)Vado Ligure, Italy

New embankement area

SDMT tests from a floating barge

SDMT test from a floating barge: layout

Test execution

Barge is free to float.

The upper end of the telescopic pipe is fixed on the pontoon, the lower end is on the seabed. It is a guide for the dilatometer rods.

The operator pushes the rods carefully during floatation.

When the prefixed depth is reached, the operator stops the pushing system, disconnects rods and starts to take the DMT readings.

All the reading are taken when the DMT is fixed, not during penetration.

SDMT from a floating barge: Genova (Italy)

New Terminal Container – Calata Bettolo (Genova Horbour)

DMT from a pontoon: pushing phase

DMT from a pontoon: reading phase

Jackup vs Floating Barge: cost comparison

10 days rental ≈ 300.000 €

10 days rental ≈ 10.000 €

In 10 days you save 290.000 €

DMT from floatinf barge and jackup: Barcelona (ES)

Enlargment Barcelona harbour – collapse of the pier

DMT test with torpedo in deep water: layout

DMT test for seabed < 100 m of depth;Test depth: 30-40 m;

Expensive heave compensated ship for offshore test

Seafloor DMT for shallow water

Test depth: 5-7 m

Pontoon

Seafloor DMT in deep water

Ok using any vessel with at least 2 ton crane

Limitation:Max seabed depth: 100m(due to DMT cable)

Test depth: 5-7 m

What about DMT tests at depth > 100 m ?

No pneumatic cable between vessel and DMT

MEDUSA PROJECT

Medusa ProjectElettronic Board

Pressure Transducer

Pressure Generator

Designed for seabed up to 2000m

Summary and Conclusions- Same blade for offshore and onshore sites- No calibration necessary for the (high) pore pressure- DMT test is independent from the method and speed of penetration (same high quality data using many different penetration methods)- Test is rapid and economical if performed with a penetrometer on a floating barge- Today SDMT tests are possible up to 100m (using expensive vessels)

In the near future..• The seafloor DMT will allow to perform shallow tests (5-7 m depth) with a seabed up to 100 m. The test will be very economical because it may be performed using a common vessel with a little crane (2 ton)• The Medusa DMT will allow to perform DMT tests up to the depth of 2000 m