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The Seismic Dilatometer test (SDMT) in geotechnical inshore and offshore investigation Studio Prof Marchetti www.marchetti-dmt.it
Some examples of maritime construction Mooring Trench for pipe Wind generators Sheet piles Oil and gas platform
Common tests in offshore investigation Close water (harbours and bays) - inshore tests Open water (sea) - offshore tests Shallow water < 30 m Deep water > 30 m • Short test (5 m) • cables • - pipes Short test (5 m) Deep test (30 m) - foundations Deep test (30 m)
La Spezia (Italy)Shipyard Beconcini Pier Guidepipe Seabed Harbour: DMT test from pier Steps • Make a hole in the deck; • Set up the guidepipe; • Fix the penetrometer and do the test;
Beam braching Harbour: DMT test from provisional pier Salerno harbour (Italy) Trapezio Deck
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 test with Torpedo - layout Rig Jackup SEA LEVEL SEABED
Vado Ligure, ItalyNew embankement area Venice lagoon, Italy (MO.SE.) DMT test from Jack-up
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)
10 days rental ≈ 10.000 € Jackup vs Floating Barge: cost comparison 10 days rental ≈ 300.000 € 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 Expensive heave compensated ship for offshore test DMT test for seabed < 100 m of depth; Test depth: 30-40 m;
Seafloor DMT for shallow water Pontoon Test depth: 5-7 m
Seafloor DMT in deep water Ok usingany vessel with at least 2 ton crane Test depth: 5-7 m Limitation: Max seabed depth: 100m (due to DMT cable)
What about DMT tests at depth > 100 m ? No pneumatic cable between vessel and DMT MEDUSA PROJECT
Medusa Project Elettronic 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