Martha Lake Gateway Sewer. An Introduction to Trenchless Methods and Evaluation for the Installation of New Pipelines

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Vernon Gregory
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1 Trenchless Crossing Evaluation on the Martha Lake Gateway Sewer An Introduction to Trenchless Methods and Evaluation for the Installation of New Pipelines

2 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

3 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)

4 Trenchless Methods Horizontal Directional Drilling (HDD) Microtunneling Pipe Jacking Auger Boring Pipe Ramming

5 Horizontal Directional Drilling (HDD) Pilot hole Reaming pass(es) Spoils removed by recirculation of drilling mud Pipe insertion

$Elevated risk of frac-out or settlement Smaller diameters (< 36 ) Difficult to control line$

6 Horizontal Directional Drilling (HDD) Strengths Performs well in groundwater Drilling mud mix can be altered for 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

7 Microtunneling Jacking shaft Spoil Removal via slurry lines Slurry pressure provides excavation face support Hydraulic jacks advance pipe string and MTBM

difficulties excavating obstructions larger than 1/3 the diameter Most do not allow face access to

8 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 Weaknesses Has difficulties excavating obstructions 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

9 Pipe Jacking Jacking Shaft Open face allows manned access Spoil Removal via mechanical or manned methods Hydraulic jacks provide advance pipe string and pipe jacking machine

Control Weaknesses Difficult to control groundwater

10 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

11 Auger-boring Jacking Shaft Spoil Removal via auger flight though jacking pipe Hydraulic jacks advance pipe string and auger flight

12 Auger-boring Strengths Good in cohesive soils Minor line and grade control Weaknesses Difficult to control groundwater Max. drive length of around 300

13 Pipe Ramming Excavated pit Pneumatic tool advances pipe Minimal Spoil Removal Face support provided by soil plug

Performs well above or below groundwater Weaknesses

14 Pipe Ramming Strengths Minimal risk of ground settlement Excavation continuously supported Performs well above or below groundwater Weaknesses Difficult to control line and grade Short drive lengths (< 300 )

15 Martha Lake Project Overview Alderwood Water & Wastewater District Lynnwood, WA Site

16 Martha Lake Project Overview I-5 and 164 th St. SW 3,400 LF of 12 to 15 gravity sewer Residential Septic Commercial Pump Stations 1700 LF of 24 water main added Currently at 60%

17 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

18 Martha Lake Trenchless Crossing TILL

19 Martha Lake Trenchless Crossing Drive Length 535 Pipe Diameter(s) 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

20 Martha Lake Trenchless Evaluation Trenchless Methods Soil Types (G Glacial Till) Gr round Water (Gr ravel Pockets) Ro ock / Boulders Set ttlement Risk Drive Length (535') Lin ne and Grade Control TOTAL HDD Microtunnel Pipe Jack Auger-bore Pipe Ramming

21 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 HOBAS Reinforced Concrete Steel (PermaLok) GO BIG!!! = 60 Casing

22 WSDOT PUD

23 ulders!! Bou WSDOT

24 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 machine Require obstruction removal plan for pipe jacking GBR Must apply to both pipe jacking and microtunneling operations

25 Trenchless Tips Use in combination with other methods Pay a premium for short crossings Talk with machine manufacturers and local contractors!

26 Questions?

Pipe Jacking/Microtunnelling. Dr. Mark Knight. Centre for Advancement of Trenchless Technologies (CATT) University of Waterloo.

Pipe Jacking/Microtunnelling. Dr. Mark Knight. Centre for Advancement of Trenchless Technologies (CATT) University of Waterloo. Pipe Jacking/Microtunnelling Dr. Mark Knight Centre for Advancement of Trenchless Technologies (CATT) University of Waterloo 1 New Installations New Installations Non-Steering Methods Steering Methods