development of guidelines for construction and development ... · development of guidelines for...
TRANSCRIPT
Development of Guidelines for Development of Guidelines for Construction and Development on Construction and Development on Dispersive Soils.Dispersive Soils.
Presented By Marcus Hardie• TIAR, UTAS, DPIW, CSIRO.
Background to Dispersive Soils• What is a dispersive soil• Why are dispersive soil important• Potentially dispersive soils in Tasmania• Case Studies of problems associated with
dispersive soils.• Management Approach• Purpose of Workshop.
Problems withProblems with SodicSodic / Dispersive soils./ Dispersive soils.
Erosion• Gully erosion• Tunnel erosion• Dam collapse
Water Quality• Extreme turbidity (never settles) • Sediment deposits
Construction / Development• Collapse of Fill• Pipe & Cable Collapse• Breaching Septic Trenches• Dam Failure
What is a What is a Dispersive SoilDispersive Soil
Dispersive Soils• Disperse into basic particles sand, silt and
clay in fresh water.• Appear to ‘dissolve’ in water.• Results in cloudy ring in fresh water• Responsible for tunnel erosion.• Dispersive soils are usually sodic.• Structurally unstable, require special
consideration for development.
SodicSodic Soils & Dispersion.Soils & Dispersion.Sodic soils are prone to dispersion, collapse of clay structure in the soil.
Dispersion: Process where individual clay platelets separate from clay structures.
Normal: Clay Platelets are bunched together.
Dried Aggregates in Rainwater
What is aWhat is a SodicSodic SoilSoil
• ESP Greater than 6
Exchangeable Sodium (ESP) = Exchangeable Na x 100 Percentage Cation Exchange Capacity
Definition of sodic soilsNon-sodic - ESP <6SSodicodic -- ESP ESP 66--1414Strongly sodic - ESP ≥15
National Snapshot.National Snapshot.
• 200 million ha affected by sodicity• 5 times more sodic affected land, than saline land.• Affected area 90 million ha.• Estimated yield loss for wheat alone $ 6.75 Billion(National Audit soil sodicity)
Sodosols
Approx. 30% of
Australia is sodic
Dispersive Soils in TasmaniaDispersive Soils in Tasmania
• Never been specifically Mapped !!!• Occur on a range of Rock Types.• Occur in a range of soil types.
Geology Includes• Tertiary Clays• Triassic Sandstones• Permian Mudstones
Vertosol
Difficult to Infer from Existing Soil and Geological Maps
Kurosol
Sodosols
Potentially Potentially Dispersive Dispersive Soils in Soils in TasmaniaTasmania
(Soil Classification Approach)
DRAFT
Potentially Potentially Dispersive Dispersive Soils in Soils in TasmaniaTasmania
(Soil Classification Approach)
Tunnel erosion is found in all council areas in southern Tasmania.
Potentially Potentially Dispersive Dispersive Soils in Soils in TasmaniaTasmania
(Land Systems Approach)
Activities that increase likelihood of Activities that increase likelihood of tunnel erosion / soil dispersion.tunnel erosion / soil dispersion.
• Overgrazing• Removing topsoil• Excavation of dispersive soil• Poor compaction of sodic clay• Concentration of runoff• Septic trenches• Drains and Culverts
Prevention Strategies• Awareness & education• Avoid ponding water• Topsoil• Burial• Compaction• Gypsum• Pasture / land management
Poor Compaction & Dam FailurePoor Compaction & Dam Failure
Tunbridge: Blackman Crk. Dam
Penna: Permian Mudstone.
Installation of Installation of Cables / PipesCables / Pipes
Chain of Lagoons: Granite
Dunalley : Dolerite / T. Sandstone
Excavation, Cut & FillExcavation, Cut & Fill Woodbridge.
Clarence: House construction on existing tunnel system.
Tasman Hwy: Near Copping
Repair of Tunnel ErosionRepair of Tunnel Erosion
Dunalley• 380 meters long• Excavation• Repacking• Gypsum• Sand blocks• Fencing /sowing• 6 people 5 weeks• $75,000
Repair of Tunnel ErosionRepair of Tunnel Erosion
Before
Penna.• 10m (75m) Long• Excavation• Refilling• Gypsum• Sandblocks• (Poor compaction)• $ ?? 75 Meter Long excavation
TakeTake--Home Messages.Home Messages.• Current mapping is unreliable.
• Tunnel erosion occurs in all municipalities in southern Tasmania.
• Hazard is potentially severe but isolated.
• Be alert not alarmed.
• Focus on Awareness and education.
• Applied research is limited.
Way ForwardWay Forward
• Awareness and Prevention based
approach.
• Engagement Councils & Service
Industries.
• Development of ‘Guidelines for
Construction and Development of
Dispersive Soils’.
• Publication, engagement and extension
Questions for the Discussion Groups.Questions for the Discussion Groups.
1) How would you rate understanding of dispersive soils in
your organisation?
2) How well has your understanding of dispersive soils
developed?
3) What are the risks to your council from dispersive soils?
4) How well is your organisation positioned to address the
risks of dispersive soils?
5) What do you need from a set of guidelines?
Questions for the Discussion Groups.Questions for the Discussion Groups.
6) What approach should the guidelines take: technical,
non technical, both, how big etc, what would you
expect?
7) Who in your organisation should use the guidelines?
8) How would you use the guidelines in your role in your
organisation?
9) Which non-local government industries would you
expect to use the guidelines?