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Day 4 Dredging Engineering 2019 (2.4 Maintenance Dredging (Pre dredging…
Day 4 Dredging Engineering 2019
2.1 Geo technical issues in dredging and dredge material management : Example Lumsden General Wharf Development
Footprint dries at low tide
Tidal range 0.3m <>7.5m
Greenfield project
Access Channel
Swing Basin
2 berths
1 land backed wharf area
Data should be interpreted by the dredging contractors themselves
Onshore geotechnical observation
Objective: determine whether geotechnical unsuitable soft / silty marine sediments had to removed prior to reclamation
Data dervied from:
Sieve Analysis
Bore Logs
Share Vane Tests
DCP tests
Offshore geotechnical investigation. A dramatic change in design to an offshore option which results in:
Reduction in dredging of conglomerate layer
Cost saving up to 160 million against onshore option
Dredging quantities
No impact on other developments within the port
Significant reduction in pre-reclamation removal of marine sediments
2.2 Dredging equipment selection
When selecting equipment, these considerations
should include
Dredging materials, obstructions
Dredged materials disposal. Spoil ground needs to be considered safe under UKC (Under Keel Clearance)
Type of dredging materials
Dredged Materials Reclamation
Dredged materials transport
Dredged tolerances and acccuracy
Environmental parameters, restrictions or limitations
Design versus equipment geometry
During high and low tides?
Require relatively clean/clear service water to be able to operate
End of cuts location
Equipment characteristics or peculiarities. i.e. a TSHD with a single trailing arm?
Equipment adaptability: Ability for a CSD's ladder to pivot point to achieve better efficiecny when dredging shallowly is a special feature and not common to all CSDs
Auxiliary and spare equipment's needed
External environmental factors to consider
when selecting equipment:
Depth of water in the reclamation area
Reclamation methodology
Depth of water in the dredging area
Environmental limitations
Soil conditions
2.4 Maintenance Dredging
Compliance management
Shipping delays: interface management
There is a local marine notice
Pre dredging requirements
Operations and communication plan
Disposal site
Dumping permit
Discharge permit
Approvals
Pre dredge survey
Estimated dredging quality
Dredging locations
An example Hydrographic survey analysis. Consequence of this is dredgign method, establishment of quantities, dredge selection.
Spoil ground selection
Mobilisation
Dredging activity
Obstructions
Sand Bar
Sweeping Operations =The sweep dredge is able to work in shal- low water and to remove very thin layers of polluted fine-grained sediments at high concentrations.
Iron ore obstructions
Obstructions and culture
2.5 Dredging Tender Process and Contracts
Principals representative administered
Tenders: General conditions of tendering
Content
Drawings
General conditions of contract
Deliverables can incliude
Proposed personnel
Gantt chart
Insurance requirements
Financial statements
Proposed work/execution method
Schedule of rates
Equipment specifications
Scope of work
2.3 Dredging Projects
FIRST EVER STEP IS
Preparations. This includes
STEP 1: Magnetometer Survey = required depending on history of dredging area. Needs to be conducted in areas where unexploded ordnance and obstructions are suspected to avoid injury or damage to the dredging equipment = Magnetometer surveying is used to detect and map small changes in the earth's magnetic field caused by concentrations of ferrous-based minerals within the soil and subsoil, and by materials buried beneath the surface.
STEP 2: Hydrographic survey: Hydrographic survey is the science of measurement and description of features which affect maritime navigation, marine construction, dredging, offshore oil exploration/offshore oil drilling and related activities.
STEP 3: Establish reference sites
STEP 4: Identify the different stakeholders with shared facilities
STEP 5: Design
STEP 6: Environmental
approvals and management
Understand limitations set by approvals
Clearly define environmental responsibilities between contractor and client
Be prepared for those occasions when it will go wrong
Ensure enough background data has been gathered
NEXT IS EXECUTION. Few things to note:
Setting ACHIEVABLE safety standards
Safety
take 5
SAZ or 3D
Legislation
Dealing with interfaces
Dredging and reclamation with CSD
Dealing with SILT
Design considerations
Existing infrastructure
Weir box
Construction materials
ESA
Capacity
Seepage prevention
Drainage channel
Utah road
Bund construction
Dealing with hyper saline water
Issues
Logger data used in wp report to phpa
Position of logger
Distance at 60m v 100m
In vertical plane/water column
In relation to creek bottom
Reliability of logger data (calibration
Navigation and design process control
Strict dredging navigation control is critical for dredgign operations and record keeping
Data should be interpreted by an experienced dredging consultant
Overdredging execution
Expressed as vertical and
horizontal tolerance
Defined by: any project requirement for accuracy
Soil conditions
Type of dredging equipment
Always be applied beyond the official design limits
Reclamation
To find out where best to position pipeline discharge points. This is critical to avoid trapping silt in between them and creating a soft area within the reclaimed area.
THE FURTHER THE DISCHARGE POINTS ARE PLACED APART, THE GREATER THE RISK.
Idea/concept: Expanding the iron ore export facility at anderson point, port hedland