Geotechnical Design Challenges in the high-seismic, softground environment
Geotechnical Design Challenges in the high-seismic, softground environment of the Port Access Road project. Michael Ulmer, P.E. Principal Engineer/V.P. 1 Project Information Who.is building it? Fluor-Lane SC, JMT, KCI, D&F, S&ME Whatare you building?
11 Major structures (14,000 Ft.) and some roadway, pavement Where.is it being built? I-26 Exits 217 & 218 near Cosgrove Ave When..will it be done? Done when its doneBy 2020 How.much does it cost? $221 Million..so far
2 Project Information WHAT New fully directional interchange on I-26 Bainbridge Connector Road Extension of Stromboli Avenue and associated roadway improvements to surface streets to serve the Hugh Leatherman, Sr. Terminal 3 Project Information WHERE I-26 Exits 217 and 218 in
Neck Area of Charleston 4 Project Information WHEN Not soon enough: Completion by Q1 2020. 5 Project Information HOW MUCH Flour-Lane South Carolina
$220,700,745 Traylor-United Joint Venture $235,757,435 Skanska-PCL Joint venture $297,812,467 Projected Construction Cost of $234 Million in 2010 6 Division of Work
Mainline Area (KCI) Elevated structure Pipe pile foundations Drilled shafts in Shipyard Creek Interchange Area (JMT) Roadway design Six Ramp structures Drilled shaft interior/Pile at end bents Local Road Area (D&F) Right-of-Way acquisition, utility, and railroad coordination Flat-slab bridge structures on piles. Drainage for the entire project The lowly Geotechnical Engineer had to serve all these masters
simultaneously. 7 Geotechnical Exploration 260 Test Locations (to date) 58 borings from the Base Line Report >200 borings during design-build phase Roughly half are CPT/DMT soundings Roughly half are soil test borings A boring at every bent, two at each abutment, and more along the roadways, walls, signs, etc. In situ testing included vane shear, shear wave velocity (MASW and SCPT), and DMT Lots or coordination with Contractor for site access Permission to access private property Salt marsh areas, un-level areas Wooded areas needed clearing Traffic control (lots of traffic control) Significant lab testing program Field Exploration has been completed on time and on budget
8 Geotechnical Exploration 9 HAZMAT Investigation Project is in the historic industrial Neck Area of Charleston Numerous parcels are contaminated (Three NPL sites close by) SCDOT spent significant resources to study the project corridor and identify the parcels of concern and how those concerns would affect design and construction. Lots of scientists, engineers, and lawyers involved The Big ones: Solvay, Navy Base, and Macalloy Five other parcels with Voluntary Cleanup Contracts Numerous other parcels with concerns, some to be found
All drilled shaft and shallow excavations located on contaminated parcels require HAZMAT sampling and testing Data collected is used to characterize the spoils for disposal Significant parallel effort completed on time and on budget. Drums on Macalloy 10 Charleston is East Coasts Highest Seismic Hazard 11 The 7.3 magnitude Earthquake August 31st, 1886 The most damaging earthquake to occur in the Southeast United States and one of the largest historic shocks in Eastern North America According to U.S.
Geological Survey Structural damage was noted as far away as: -Alabama -Ohio -Kentucky -Virginia -West Virginia 12 The 7.3 magnitude Earthquake August 31st, 1886 -Damaged or destroyed many buildings and killed somewhere between 60 and 124 people (depending on
sources) -Property damage was estimated at $5-$6 million (1886 dollars), and damage impacted thousands of buildings 13 Earthquakes. So what, right? -1989 Loma Prieta - 1994 North Ridge 14 Wrong. Seismic case controls most of the design. - 1995 Kobe
15 Tuesday, June 12, 2007 -Old sand geyser shows quakes part of life here. Researcher's digs indicate regular pattern. -To create Liquefaction resulting in a Sand Blow, magnitude must be at least 5.5 -Magnitude 5.5 occurs roughly every 500 yrs Pradeep Talwani Professor of Geophysics, USC Director, South Carolina Seismic Network 16 Findings Terrible Worse
Bad 17 Findings Fill All this liquefies or loses strength during an earthquake SWMU Toothpaste 18 Geotechnical Solutions
Bridge Foundations Drilled Shafts. Driven Piles (HP, OEP (30 to 36), and PSC). All shafts have permanent casing to the marl. Embankments, RSSs, and MSE Walls Fill heights over 20 ft in many areas. Tight ROW in some spots. EQ drains, fabrics, and surcharging in many areas. Surcharge for stability and settlement. Column supported embankments in the terrible areas. Soils are just to soft. Accelerated project schedule does not allow time for conventional staged surcharge program. Seismic design case controls everything. 19 Geotechnical Design Drilled Shafts Skin Friction All shafts on environmental parcels are permanently cased to the marl (which is all of them).
RFP and GDM do not allow axial resistance on casing (more on this later). Design initially based on GDM equations and historical load test data. Lots of historical load test data including Ravenel Bridge, Cosgrove Ave, and US 78. See Camp and Gieser for very good summaries of skin friction in marl. Skin friction ranges from 3 to 5 ksf, with most values above 3.5 ksf (a few < 3 ksf) Skin friction is constant with depth. So designing with 3 ksf is reasonably conservative, right? End Bearing historical load test data. See Camp for a very good summary of end bearing in marl. End bearing ranges from 40 to 80 ksf within depths (i.e., effective stress) of interest. End bearing increase with overburden effective stress. So designing with 40 ksf is reasonable, right? 20 The Load Test
A.H. Beck built a beautiful 60-in.-dia., 111-ft-long shaft, AFT ran a fine bi-directional, O-cell load test, and Mother Nature does not really care what scholarly publications have to say about skin friction. You then realize that Load Test is two 4-letter words Skin Friction Results Peaked mobilized unit side shear resistance ranged from 1.7 to 3.7 ksf in the marl. No matter how you parsed the data, you end up with an average marl skin friction of 2.5 ksf. You contemplate saying a third 4-letter word, but you refrain because engineers are professionals and would never do such a thing. End Bearing Results The load test confirmed the 40 ksf was, in fact, rather conservative. Test mobilized 60 ksf. 21
Alls Well That Ends Well Luckily, only a few shafts had reached final design, and none were in the ground. So the design was revised using 2.5 ksf and 50 ksf, and disaster was averted. In the end, most shafts were controlled by lateral fixity and were overdesigned for axial load cases. 22 Geotechnical Design Piles Skin Friction Piles included open-end steel pile, steel HP sections, and composite prestressed-concrete.
Design based on GDM equations and historical load test data. Lots of historical load test data from hundreds of SCDOT and commercial projects in the greater Charleston area. Skin friction for overburden soils predicted with GDM equations and considered seismic soil strength lose where appropriate. Overburden contributed an insignificant Skin friction of 2.6 ksf was used for piles bearing in marl. End Bearing in Marl historical load test data. End bearing of 26 ksf was used for design. End bearing was considered for PSC and HP sections. Full end bearing was not considered for the large-diameter OEP piles Large diameter OEP pile may behave as plugged at low strain, but PDA testing is a high-strain test and generally does not see a plug. 23 PDA Testing To date, 83 test piles have been testing using high-strain, dynamic testing (PDA) method. 20 pile testing on installation.
63 restrikes. All piles types have been tested. Testing to date has confirmed the initial pile design. Only one end bent was lengthened by a few feet. The composite piles on BBC were reconfigured to improve driveability. PSC section tip elevation was raised to reduce marl penetration and bounce, and HP section was lengthened, but original design tip was maintained. A number of piles required a second restrike to confirm capacity due to slow set up in marl. Marl is a fine-grained soil and generates very high excess pore-water pressure during pile driving. Required driving resistance are not achieved at installation. Pile must sit idle for a period of time to allow excess pore-water pressures to dissipate Pile is restruck with PDA to confirm required driving resistance. 24 Marl Behavior and PDA Testing 160% 140%
% of Req'd Ultimate 120% 100% ML B1 NB10 Linear (ML B1 NB10) ML B4 SB1 Linear (ML B4 SB1 ) ML B7 SB1/ SB6 Linear (ML B7 SB1/ SB6) ML B9 SB6/
SB10 80% 60% 40% 20% 0% 4 6 8 10
12 14 16 18 20 22 24 26 28
30 32 34 36 38 40 42 44 46 48
Idle Time (Days) 25 Marl Behavior and PDA Testing 160% 140% % of Req'd Ultimate 120% 100% ML B1 NB10 ML B4 SB1 ML B7
SB1/SB6 ML B9 SB6/SB10 ML B11 NB5 ML B11 SB5 ML B13 NB5 ML B13 SB5 BC B28 P7 80% 60% 40%
20% 0% 4 6 8 10 12 14 16 18
20 22 24 26 28 30 32 34 36
38 40 42 44 46 48 Idle Time (Days) 26 The Trials and Tribulations of CSL, & You have to actually build what is on the plans. Remember that you cant use skin friction on the casing rule? Well
Two issues required a bit research into skin friction on the casing: CLS showed that some axial controlled shaft had a bullet nose and <100% end bearing. A few shafts were constructed with casings that were too long (one was way too long). Review of the project load test and lots of other load tests in the marl indicate: The overburden soils above the marl provide some skin friction, but the percentage of the total is so small, it is reasonable to ignore it. (And if it all liquefies, you ignore it anyway.) The marl does provides skin friction on the casing, but it is much less than the uncased shaft. Vibratory hammers and displacement tooling remold the marl to a residual su value. Load test data indicates a value of 1.7 ksf is reasonable. 0.8 ksf made the shafts work on paper, so that is what we recommended, and all parties agreed rather the remove and rebuild option or the Frankenpile option. 27 Pictures 28 Pictures
29 Pictures 30 The End Thank you for listening. Questions? Hearing none, lets eat. 31
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