Rock Engineering - I-196 Westbound Bridge over the Grand River, Grand Rapids MI2015 Michigan Bridge ConferenceMelinda L. Bacon, PE

PRESENTATION OUTLINE

• History of rock in the Grand Rapids Area.• Geotechnical innovations performed to obtain

rock cores for the I-196 WB Bridge project.• Review of the current AASHTO Rock

Classifications including:o The AASHTO Rock Mass Rating (RMR) system

concepts; and,o How to determine the general classification of the rock

conditions.

History of Bedrock in the Grand Rapids Area

GYPSUM DEPOSITS

• During the Paleozoic Era, beginning about 600 million years ago and ending about 230 million years ago, gypsum invaded the Michigan Basin at least six times.

• As the seas receded and evaporated halite (rock salt), gypsum (calcium sulfate with water) and other deposits were left behind.

• The gypsum beds are in the Michigan Formation.

GENERALIZED GEOLOGY

• In 1827, an Ottawa Indian discovered a Plaster Creek that enters the Grand River.

• Gypsum beds in Grand Rapids are generally located near the surface. 0

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Data 1 Data 2 Data 3 Data 4

Series 1

Series 2

Series 3

GENERALIZED GEOLOGY… continued

• The area’s first commercial gypsum operation began in 1841.

• Miners used room and pillar mining.• Miners observed cavities in the rock.• Gypsum is soluble &

disintegrates when exposedto the elements.

Geological Survey of Michigan, Volume IX,1903 - 1904, Part II, Plate IIb.

MAP OF GYPSUM LOBE

Geological Survey of Michigan, Volume IX, 1903 - 1904, Plate III

PHOTOGRAPH OF GYPSUM CORES

ROCK CONTOUR ELEVATIONS

GENERALIZED ROCK PROFILE

Geotechnical Innovations for theI-196 Westbound Bridge Project

SITE LOCATION

GEOTECHNICAL EVALUATION GOALS

• Evaluate the presence of gypsum within new foundation areas.

• Determine if voids or cavities were present in the rock.

• Provide a geotechnical data report & a geotechnical engineering report with recommendations for design of new foundations (adjacent to existing) for larger loads due to bridge widening.

TEST HOLE LOCATIONS

FIELD EVALUATION HURDLES

• Weekend work only.• River too shallow & swift for

barge work.• Utilities strapped under

bridge.• OSHA required float or

paddle boat in river.• Distance from bridge deck

to river bottom about 58’.• River bottom consisted of

about 8” to 12” of sand, gravel & cobbles over rock.

CLOSE UP OF BRIDGE PIERS

FIELD EVALUATION INNOVATIONS

• Spartan Specialties LTD was hired to install rigid pipe (I.D. 5 1/8” & O.D. 5 5/8”) through the cored bridge deck into the rock.

• The pipe was installed in 10-foot sections with shorter sections near the bridge deck & overall lengths of 60’ to 65’.

• The pipe had a carbide tip which was seated 14” to 18” into the rock.

FIELD EVALUATION INNOVATIONS… continued

SME had to use a tri-roller bit with wash rotary techniques to clean out the bottom section of the pipes prior to coring. The bottom 2’ to 3’ of the pipes were filled with sand, gravel & crushed rock.

FIELD EVALUATION INNOVATIONS… continued

• The rock cores were performed by SME by extending a wire line core barrel into the pipe to the rock.

• The wireline core barrel was able to collect up to 20 feet of rock core.

• The core barrel had a tip with a diamond cutter.

PHOTOGRAPHS OF ROCK CORES

GENERAL ROCK CORE FINDINGS

• Gypsum rock or obvious indicators of significant solution voids or cavities were not encountered in the upper 20 feet of rock sampled at the site.

• Samples of intact rock had a median value for unconfined compression strength of about 620 ksf (4,300 psi) with strength ranging considerably from about 40 to 2,000 ksf (300 to 14,000 psi).

GENERAL ROCK CORE FINDINGS… continued

• Frequent fractures were observed in the rock, mostly in a nearly horizontal bedding orientation. Occasional angled and near vertical fissures were also observed.

• Larger fissures and cracks near the surface of the rock formation were observed to have some shale/clay infill and staining. Fissures and laminations in the lower portion of the rock were generally tight and without filler or staining.

GENERAL ROCK CORE FINDINGS… continued

• The rock layering encountered is relatively uniform across the site. Therefore, the site conditions appear to be relatively uniform and suitably represented by one overall condition.

• Using the AASHTO Rock Mass Rating (RMR) system concepts, we have assigned the rock formation across this site an RMR number of 31. This results in the general classification of Class IV = Poor Rock conditions.

Review of the Current AASHTO Rock Classifications

ROCK MASS RATING SYSTEM

• Rock should be classified using the rock mass rating (RMR) system described in AASHTO Table 10.4.6.4-1.

• The RMR should be determined as the sum of all five ratings & should be adjusted in accordance with the criteria in Table 10.4.6.4-2.

• Rock class number and description should be determined in accordance with AASHTO Table 10.4.6.4-3.

AASHTO TABLE 10.4.6.4-1

AASHTO TABLES 10.4.6.4-2 & 10.4.6.4-3

ROCK CLASSIFICATION

• Rock Type• Color• Grain Size and Shape• Texture• Mineral Composition• Rock Weathering• Rock Strength• Discontinuity Descriptors• Publication No. FHWA NHI-01-031- Subsurface

Investigations - Geotechnical Site Characterizations Reference Manual May 2002 Section 4.7

ROCK CLASSIFICATION… continued

THANK YOU!Melinda L. Bacon, PE – Senior Project Engineerbacon@sme-usa.com | 269-207-1584