Highly Stressed Driven Piles in Soil

Michael Wysockey, PhD, P.E. – Thatcher Foundations

Brett Gitskin, P.E. – ECS Midwest, LLC

Project – Union West/Haymarket

• Project going up in the thriving West Loop area of Chicago

• Former Meat Packing area, prior to recent resurgence most notable project in last 50+ years was Harpo Studios (Oprah Winfrey)

• Starting about 12 years ago, the hip, happening area for Chicago business/retail/residential

• Home to:• Google Midwest Headquarters

• McDonalds new Corporate Headquarters

• Ace Hotel

• Award Winning Restaurants!

Project – Union West/Haymarket

Project – Union West/Haymarket

Project – Union West/Haymarket

Halloween 20 years ago

• Project involved twin 15 story buildings, along with some single story retail and associated structures

• Mixed use high rise, retail first floor, parking garage levels, residential on the upper floors

• Challenges• Variable soil conditions, including variable, and/or missing “Hard Pan” soils

typically used to support high rise structures on belled drilled shafts (caissons)

• Nearby projects had used mixture of drilled shafts and driven piles

• Site was not conducive to drilled shafts, at least on half of the site due to deep granular soils which pose construction problems for drilled shafts

Project – Union West/Haymarket

• Typically high rise structures are supported on belled drilled shafts (caissons) bearing on very dense clayey till soils, referred to as “Hard Pan” resulting from the retreat of the Wisconsin Age Glaciers

• West Loop is known as an area of variable soil conditions, even across individual project sites

• Project soils offered 2 obstacles to caissons:• Poor quality soils (relatively low bearing pressures of 9,000 to 12,000 psf)

• The very dense to extremely dense materials were essentially granular, and therefore not conducive to belled drilled shaft construction

Project – Union West/Haymarket

• Two driven H pile solutions were considered• Driven H Piles to rock (utilizing the full structural capacity of the pile)

• Driven H Piles extended about 10 feet into the extremely dense granular soils

• It was our belief that the soils were so dense that effective “refusal” would be encountered before the piles reached rock.

• We recommended the piles be driven to effective “refusal” in the extremely dense soils, however, we would still count on the ultimate capacity of the piles, in accordance with the Chicago Building Code

Project – Union West/Haymarket

• Other factors affecting design:• Brand new Chicago “Code Memorandum” issued shortly after original

geotechnical report allowed for up to 42% of the pile’s yield stress to be utilized, provided a load test was performed (50% if sacrificial pile).

• We recommended the piles be driven to “effective refusal” in the extremely dense soils, however, we would still count on the ultimate capacity of the piles, in accordance with the Chicago Building Code and new memorandum, even though not bearing on rock

• Design loads of 320 (21 ksi) and 386 kips (25 ksi)

Project – Union West/Haymarket

• Now comes the fun part:• Called up Thatcher Foundations to discuss feasibility of driving the piles to

effective refusal at least 10 feet in the extremely dense granular soils

• Can you do this (felt confident they could drive, but could they do so without damaging/overstressing the pile)?

• Thatcher said “We are definitely intrigued, we think we can. Let us get back to you”.

• Thatcher got back to us “We know we can. We are a little concerned, and we will need a bit of luck, but yes, we can do it.”

Plan View

Pressed Sheet Piles

Press

Core Piles

Pile Layout

939909

922

Clear Obstructions

Union West

909 W. Washington

• HP 12x53 piles

• 260 kips design load (17 ksi)

• 2 static load tests: • 620 kips (40 ksi) geotechnical failure

• 720+ kips (46.5 ksi +) did not fail

922 W. Washington

• HP 12x63 piles

• 320 kips design load (17.4 ksi)

• Tests up to 793 kips w/o failure

922 W. Washington Dynamic Testing Results

TP-1

TP-3

Uplift Test

Tension Tests

Static Load Test - Compression

Test Pile 1 showing 640 kips

TP3 Taken to Structural Yield 772 kips

Local Buckling

Buckeled Pile

Summary of Static Load Test Results

Highly Stressed Driven Piles in Soil

Michael Wysockey, PhD, P.E. – Thatcher Foundations

Brett Gitskin, P.E. – ECS Midwest, LLC

THANK YOU