Anchored Secant Pile WallPresentation by Kyle R. Beaudry

Overview

Project Description

Execution Plan

Challenges

Key Learnings

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Project background information:

• 100-year old open pit mine located downtown of the city• Past regulations did not obligate tunnel tracking resulting in unknown stopes within mine’s radius• One of those stopes collapsed creating a subsidence near main transportation artery and local businesses

Project sensitivities:

• Many stakeholders involved due to location and type of project (ei. mining operation in the downtown of a city)• Client’s highly enforced safety policies and restrictions due to mining operations near a subsidence

Our task: Constructed the anchored secant pile wall alongside highway and neighboring properties to avoid the enlargement of the subsidence jeopardizing the integrity of the stakeholders’ properties

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Site layout:

• Approximate site size = 7m wide x 60m long • Conceptual layout of secant wall with anchor locations (Light dashed lines)• Red dashed line = subsidence limit• Green dashed line = exclusion zone• Bold dashed line = highway

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Secant wall detail:

• 109 overlapping 0.9m diameter concrete caissons ranging from 4 to 20m in depth• Alternating primary and secondary caissons

• Primary = 30 MPa I beam reinforced concrete• Secondary = 10 MPa unreinforced concrete

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Elevation view:

• Caissons along highway must reach inferred bedrock• Limited bedrock information due to sparse borehole locations away from wall location (locations seen in slide 4)• Entire job bid and planned on estimated bedrock location

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Idealized execution plan:

• Build level guide wall for 100 MT, 100’ high drill rig• Drill all secondary caissons to uncover exact bedrock location• Extrapolate to primary caissons to calculate necessary beam length• Order & cut/splice steel in local shop• Restricted site access forced material & equipment storage off-site

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Augering procedure:

• Drilling & concrete production rate • 4.4m / hour in overburden• 1.0m / hour in bedrock

• Hole had to be clear of water before pouring concrete• GoPro camera attached to string & rod to monitor cleanliness • If water, tremie concrete to remove water

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Anchoring system:

• Drilled through secondary caissons 18-66• Corrosion protected thread bars spanning 16 to 30m• Inserted at 45 degrees into overburden then embedded 3m into bedrock

To perform task:

• Excavate nearly 4m on inner side of the wall• Slope the exclusion zone for safety ALWAYS remaining outside the restricted zone

Challenges encountered:• Minimum 2 week turn-around to acquire any larger sized I beam in Northern Ontario• Strict completion date with harsh penalties if deadline exceeded due to the project affecting the city’s main

transportation artery

Due to inferred bedrock:• First secondary caisson drilled brought us 1.45m deeper than anticipated.• By caisson C10, down an additional 4m• By caisson C34, needed an extra 30m of steel – clearing provisional stock to account for the long turn-around time

Solution:• The tracking system in conjunction with available stocked inventory spreadsheet I created led me to quickly determine

exact sizing and beams needed to purchase in order to quickly perform the purchase limiting the project’s down time

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Key learnings from working on the field with a contracting engineer firm:

1. Things NEVER go as anticipated = must have contingency plans for all situations

2. In order to do so, must have great organizational skills to keep job running smoothly and to stay on top of the problems