Trenchless Crossing Evaluation on the Martha Lake Gateway Sewer PNCWA... · 2016. 7. 14. ·...
Transcript of Trenchless Crossing Evaluation on the Martha Lake Gateway Sewer PNCWA... · 2016. 7. 14. ·...
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Trenchless Crossing Evaluation on the Trenchless Crossing Evaluation on the Martha Lake Gateway Sewer
An Introduction to Trenchless Methods and Evaluation for the Installation of New Pipelines
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Introduction
• Purpose− Provide engineers and owners with one example of a trenchless crossing evaluation.
• Outline−
•− Trenchless Considerations− Trenchless Methods
HDD, microtunneling, pipe jacking, auger-boring, pipe ramming.
−Martha Lake Sewer Project Overview−Martha Lake Trenchless Evaluation− Conclusion of Evaluation− Next Steps
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Trenchless Considerations
• Ground Conditions− Soil Type−Groundwater− Rock / Boulders−−Mixed Face Conditions−Wood−Man-made Debris (concrete, steel, VW Bugs, etc.)
• Crossing Length• Pipe / Casing Diameter• Alignment (Horizontal and Vertical) • Depth (cover over excavation)
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Trenchless Methods
• Horizontal Directional Drilling (HDD)• Microtunneling• Pipe Jacking• Auger Boring• Auger Boring• Pipe Ramming
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Horizontal Directional Drilling (HDD)• Pilot hole• Reaming pass(es)• Spoils removed by recirculation of drilling mud•• Pipe insertion
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Horizontal Directional Drilling (HDD)• Strengths− Performs well in groundwater− Drilling mud mix can be alteredfor ground conditions
− Very long crossings−−− Curved alignments
• Weaknesses− Elevated risk of frac-out or settlement− Smaller diameters (< 36”)− Difficult to control line and grade− Requires a 2% minimum slope for gravity applications
− Large area for pullback layout
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Microtunneling
• Jacking shaft• Spoil Removal via slurry lines• Slurry pressure provides •excavation face support• Hydraulic jacks advance pipe string and MTBM
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Microtunneling• Strengths− Performs well above or below groundwater− Slurry pressure can be varied based on support needed at excavation face
− Longer Drive Lengths−Good line and grade control−Good line and grade control
• Weaknesses− Has difficulties excavatingobstructions larger than 1/3 the diameter
−Most do not allow face access to remove obstructions− Rescue pit required if stopped by an obstruction− Can be deflected by mixed-face conditions
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Pipe Jacking
• Jacking Shaft• Open face allows manned access• Spoil Removal via mechanical or manned methods• Hydraulic jacks provide advance pipe string and • Hydraulic jacks provide advance pipe string and pipe jacking machine
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Pipe Jacking• Strengths− Face access allows removal of obstructions− Longer Drive Lengths−Good line and Grade Control
• Weaknesses− Difficult to control groundwater− Difficult to control flowing soils− Can be deflected by mixed-face conditions
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Auger-boring• Jacking Shaft• Spoil Removal via auger flight though jacking pipe• Hydraulic jacks advance pipe string and auger flight
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Auger-boring• Strengths−Good in cohesive soils−Minor line and grade control
• Weaknesses− Difficult to control groundwater−Max. drive length of around 300’
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Pipe Ramming
• Excavated pit• Pneumatic tool advances pipe• Minimal Spoil Removal• Face support provided by soil plug• Face support provided by soil plug
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Pipe Ramming• Strengths−Minimal risk of ground settlement
− Excavation continuously supported
−− Performs well above orbelow groundwater
• Weaknesses− Difficult to control line and grade
− Short drive lengths (< 300’)
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Martha LakeProject Overview• Alderwood Water & Wastewater District • Lynnwood, WA
Site
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Martha Lake Project Overview
• I-5 and 164th St. SW• 3,400 LF of 12” to 15” gravity sewer• Residential Septic• Residential Septic• Commercial Pump Stations• 1700 LF of 24”water main added• Currently at 60%
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Martha Lake Trenchless Crossing• Ground Conditions− Soil
§ Dense Glacial Till overridden by fill−Groundwater
§§ Perched groundwater on top of Till§ Pockets within Till
− Rock / Boulders§ Boulders: 1.5’ to 7’
−Mixed Face Conditions – None Known−Wood – None Known−Man-made Debris – None Known
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Martha Lake Trenchless Crossing
TILL
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• Drive Length− 535’
• Pipe Diameter(s)− 54” - 60” Casing
Martha Lake Trenchless Crossing
− 54” - 60” Casing− 12” Ductile Iron Sewer− 24” Ductile Iron Water− Six 4” Conduits
• Alignment− Vertical profile lies completely within Glacial Till
• Depth− 14’ minimum, 25’ maximum
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Martha Lake Trenchless Evaluation
Trenchless Trenchless Trenchless Trenchless MethodsMethodsMethodsMethods
Soil Types
(Glacial Till)
Ground Water
(Gravel Pockets)
Rock / Boulders
Settlem
ent Risk
Drive Length
(535')
Line and Grade
Control
TOTA
LTOTA
LTOTA
LTOTA
L
(Glacial Till)
Ground Water
(Gravel Pockets)
Rock / Boulders
Settlem
ent Risk
Drive Length
Line and Grade
HDD 6 8 5 6 9 4 38
Microtunnel 7 8 6 8 8 8 45
Pipe Jack 8 5 8 6 8 8 43
Auger-bore 5 4 5 6 1 4 25
Pipe Ramming 4 8 2 8 1 3 26
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Conclusion
• Microtunneling or Pipe Jacking− Two options increases number of eligible contractors− Contractor can chose machine he believes will work best for ground conditions
− Three jacking pipe options give more flexibility− Three jacking pipe options give more flexibility§ HOBAS§ Reinforced Concrete§ Steel (PermaLok)
• GO BIG!!! = 60” Casing
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WSDOT
PUD
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WSDOT
Boulders!!
Boulders!!
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Next Steps
• Specifications− Specify MTBM best suited for ground conditions− Specify options for rescue shaft to free MTBM− Require mitigation plan for encountering groundwater with a pipe jacking machinewith a pipe jacking machine
− Require obstruction removal plan for pipe jacking• GBR−Must apply to both pipe jacking and microtunneling operations
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Trenchless Tips
• Use in combination with other methods• Pay a premium for short crossings• Talk with machine manufacturers and local contractors!contractors!
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Questions?