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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
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
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)
Trenchless Methods
• Horizontal Directional Drilling (HDD)• Microtunneling• Pipe Jacking• Auger Boring• Auger Boring• Pipe Ramming
Horizontal Directional Drilling (HDD)• Pilot hole• Reaming pass(es)• Spoils removed by recirculation of drilling mud•• Pipe insertion
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
Microtunneling
• Jacking shaft• Spoil Removal via slurry lines• Slurry pressure provides •excavation face support• Hydraulic jacks advance pipe string and MTBM
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
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
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
Auger-boring• Jacking Shaft• Spoil Removal via auger flight though jacking pipe• Hydraulic jacks advance pipe string and auger flight
Auger-boring• Strengths−Good in cohesive soils−Minor line and grade control
• Weaknesses− Difficult to control groundwater−Max. drive length of around 300’
Pipe Ramming
• Excavated pit• Pneumatic tool advances pipe• Minimal Spoil Removal• Face support provided by soil plug• Face support provided by soil plug
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’)
Martha LakeProject Overview• Alderwood Water & Wastewater District • Lynnwood, WA
Site
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%
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
Martha Lake Trenchless Crossing
TILL
• 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
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
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
WSDOT
PUD
WSDOT
Boulders!!
Boulders!!
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
Trenchless Tips
• Use in combination with other methods• Pay a premium for short crossings• Talk with machine manufacturers and local contractors!contractors!
Questions?