The Seismic Dilatometer test (SDMT) in geotechnical inshore and offshore investigation
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Transcript of The Seismic Dilatometer test (SDMT) in geotechnical inshore and offshore investigation
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