Variable Piedmont rock conditions in a Washington, DC Water Shaft - - PowerPoint PPT Presentation

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Feb 10, 2024 264 likes •559 views

Variable Piedmont rock conditions in a Washington, DC Water Shaft Geohazards 2018 Steve Mogilnicki WRA Acknowledgements Corman, DC Water, Davis, Bradshaw Outline 1. purpose 2. geologic setting 3. methods 4. observations 5. rock

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Variable Piedmont rock conditions in a Washington, DC Water Shaft Geohazards 2018 Steve Mogilnicki – WRA Acknowledgements Corman, DC Water, Davis, Bradshaw

SLIDE 2

Outline

1. purpose
2. geologic setting
3. methods
4. observations
5. rock reinforcement
6. conclusion

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1. purpose

C.S.O. Drop Shaft 21 Kennedy Center DC Water Clean Rivers Project

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Shaft in rock drill & blast 28 feet diameter 96 feet deep

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2. geologic setting

Coastal Plain Modified from USGS

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Schist

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USGS Wash. W. quad (1994) Fleming, Drake, McCartan

Melange of turbidite sediments metamorphosed into schist

fill Rock Creek Shear Zone

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Image from http://www.scotese.com PALEOMAP

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3. methods

strength & weathering foliation, joints, mineralization spacing/roughness/infill - discontinuities weak zones & faults strike & dip

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8 pre-blast visits, Aug. to Oct. 2017

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Approach Channel

A C B D

Quadrants

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blast hole drilling

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4. observations

Quadrant A Foliation dips

ut of cut

Steep joints (2)

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largest joint - planar

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wedge

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Discontinuities Foliation - strike NE, moderate dip SE, spaced 1 – 3 feet, rough Joints - strike often NW, steep dip, spaced ½ - 2 feet, smooth

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Quadrant C Foliation dips into cut Joints

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Clay on smooth joint

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Weak rock geohazard intensely fractured highly weathered

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Slickenside

n joint

fault strike N 15 W dip 70 NE

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foliation data strike NE dip SE regional shear

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joint data 2 sets NW

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5. rock reinforcement – bolts & mesh

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filler concrete - rockfall

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Shotcrete

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6. In conclusion