Detailed geologic mapping an essential step in foundation design for karst sites
This presentation is the property of its rightful owner.
Sponsored Links
1 / 14

Detailed Geologic Mapping: An Essential Step in Foundation Design for Karst Sites PowerPoint PPT Presentation


  • 74 Views
  • Uploaded on
  • Presentation posted in: General

Detailed Geologic Mapping: An Essential Step in Foundation Design for Karst Sites. Eric J. Seksinsky, P.G., P.E. Bashar S. Qubain, Ph.D., P.E. Jianchao Li, P.E. GeoStructures, Inc. King of Prussia, PA. GSA Northeastern Section, 49 th Annual Meeting Lancaster, PA March 24, 2014.

Download Presentation

Detailed Geologic Mapping: An Essential Step in Foundation Design for Karst Sites

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Detailed geologic mapping an essential step in foundation design for karst sites

Detailed Geologic Mapping: An Essential Step in Foundation Design for Karst Sites

Eric J. Seksinsky, P.G., P.E.

Bashar S. Qubain, Ph.D., P.E.

Jianchao Li, P.E.

GeoStructures, Inc.

King of Prussia, PA

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Outline

Outline

  • Geologic mapping for geotechnical investigations

  • Pennsylvania Turnpike widening project

  • Site geology and sinkhole setting

  • Preliminary and final data

  • Rock conditions and bridge foundations

  • Conclusions

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Geologic mapping for geotechnical investigations

Geologic Mapping for Geotechnical Investigations

  • Confirm published geology

  • Focus test drilling

  • Translate relative dips of rock structure in cores to actual orientations

  • Project test boring profiles along the strike of beds when drafting subsurface sections

  • Explain faulted contacts and inconsistencies in published maps

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Pennsylvania turnpike widening project

Pennsylvania Turnpike Widening Project

  • Valley Forge to Norristown: 3-mile widening project built in late 1990s

  • 1 major bridge + 2 smaller bridges

  • Pennsylvania Turnpike Bridge over the Schuylkill River

    • New, independent, 6 span bridge 1,225 ft long, 70 ft high

  • Alongside original (1952) 11-span bridge and 19th c. RR bridge

NEW BRIDGE

1952 BRIDGE

RR BR.

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Site geology and sinkhole setting

Site Geology and Sinkhole Setting

  • Site is along eroded “feather edge” of the Triassic Unconformity

  • Triassic Stockton over Cambrian Ledger and Antietam-Harpers

  • Cambrian carbonates:

  • Altered, fractured and deformed

  • Subjected to several geologic time periods of exposure, intense erosion and karst development

  • Sinkholes!

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


And there are many sinkholes in king of prussia

And There are Many Sinkholes in King of Prussia…

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Available geologic map fairly simple right

Available Geologic Map: Fairly Simple, Right?

CAMBRIAN

TRIASSIC ERODED BEDS

  • Only 3 formations, no faults or folds

TRIASSIC

UNCONFORMITY

Ref.: Berg, T.M., Geologic Map of Pennsylvania, Bureau of Topographic and Geologic Survey, Harrisburg 1980.

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


34 preliminary borings

34 Preliminary Borings

Found Ledger dolomite and Harpers phyllite but also hit...

  • Un-mapped phyllitic dolomite of the Cambrian Vintage Fm.

  • Un-mapped Triassic basal limestone conglomerate

  • Large subsurface voids and remnant dolomite ledges

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Exploration for final design

Exploration for Final Design

  • Assistance from Structural Geology Dept. at Franklin & Marshall

  • Insight from technical publications by Cloos and Pettijohn

  • 87 more borings + mapping in quarries and road cuts

  • Primary geologic objective: differentiate Vintage from the Ledger

  • Why?...Not just a geologic exercise!

  • Assess karst hazards affecting each bridge

  • Vintage is not cavernous like the Ledger

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


A complicated geologic picture

A Complicated Geologic Picture

STOCKTON

SANDSTONE

LIMESTONE CONGLOMERATE

THRUST FAULT

SIMPLE-SPAN

BRIDGE

VINTAGE DOLOMITE

(BLUE)

NORMAL FAULT

2-SPAN

BRIDGE

HARPERS PHYLLITE

NORMAL FAULT

LEDGER DOLOMITE

OVERTURNED ANTICLINE

SCHUYLKILL RIVER BRIDGE

SCHUYLKILL RIVER

RR BRIDGE

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Rock conditions bridge foundations

Rock Conditions & Bridge Foundations

  • 6-Span Bridge

    • Sloping rock with voids and fingers

    • For foundation engineering  top of rock is top of Vintage not Ledger

    • Rock socketed caissons in the Vintage w/permanent casing through Ledger remnants to avoid load transfer to voids and fingers

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Rock conditions bridge foundations1

Rock Conditions & Bridge Foundations

  • Simple-Span Bridge

    • Cavern in Ledger below Triassic Unconformity

    • Spread footings on rock- limestone conglomerate

    • Cave grouted (3,000 CY)

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Rock conditions bridge foundations2

Rock Conditions & Bridge Foundations

  • 2-Span Bridge

    • Sloping rock, no voids

    • Driven H-piles

    • Pre-drilled into the Vintage and Harpers where rock surface slopes > 26°

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


Conclusions

Conclusions

  • Don’t assume accuracy of available maps; work by private firms can have a role in updating the state geologic maps

  • Detailed geologic mapping is essential to develop accurate subsurface sections and assess karst risk

  • An understanding of complicated karst features such as the steeply inclined Ledger remnants and voids would not have been possible without geologic measurements

  • Correlation of boring data with detailed mapping optimized foundations

GSA Northeastern Section, 49th Annual Meeting

Lancaster, PA March 24, 2014


  • Login