Mechanism of Sinkhole Formation Above the Retsof Salt Mine

POSTULATED SINKHOLE MECHANISMS

• Piping

• Dissolution

PIPING CONCEPT

• Rock Remained in Place• Rock Fractured• Water Flow Downward through Fractures• Glacial Sediment Piped through Fractures• Voids in Glacial Sediment• Periodic Collapse of Voids

INITIAL EVIDENCE OF PIPING

• Episodic Sinkhole Growth

• Glacial Sediment Deep in Rock

• Excessive Drop of Surface

DISSOLUTION CONCEPT

• Dissolution of Salt Below Rock

• Loss of Rock Support

• Drop of Rock and Glacial Sediment

DISSOLUTION EVIDENCE

• Abundant Soluble Material

• Seismicity Related to Rock Breakage

INVESTIGATION OBJECTIVES

• Assess Collapse of Rock

• Determine Soluble Material Thickness

• Determine Source of Sediment in Rock

• Assess Strength of Glacial Sediment

INVESTIGATION OF ROCK COLLAPSE

• Drilling Data

• Seismic – Reflection Surveys

• Correlation of Subsidence Data

2YS

11YW

SCALE IN FEET

4000

9448

9446 9428

9568

94069410

9416

94279407

9426

94179430A94329431

94199425

94189430

94209421

94099413

9404

942394229424

9433

940594119412

9415 9414

94049408

N

SCALE IN FEET0 300

SCALE IN METERS91

.

.

Rock SurfacePrior to 3/12/94

March 12, 1994

N

-0.1

-0.5

1.0

-0.1

Surface SubsidenceAs of 3/28/94

SCALE IN FEET0 300

SCALE IN METERS91

N

Rock SurfaceAfter 3/12/94 and Before

4/6/94 Sinkhole

0 500

152

SCALE IN FEET

SCALE IN METERS

N

Rock Surface Drop 3/12/94 – 4/6/94

0 500

152

SCALE IN FEET

SCALE IN METERS

N

Seismic Survey Results (3/22 – 3/23/94)

N

0 500

152

SCALE IN FEET

SCALE IN METERS

Surface SubsidenceAs of 4/6/94

SCALE IN FEET0 300

SCALE IN METERS91

N

Rock Surface After 4/6/94

Sinkhole Formed

0 500

152

SCALE IN FEET

SCALE IN METERS

N

Rock Surface Drop After 4/6/94 Sinkhole Formed

0 500

152

SCALE IN FEET

SCALE IN METERS

N

Surface SubsidenceAs of 4/14/94

0 500

152

SCALE IN FEET

SCALE IN METERS

N

Surface SubsidenceAs of 6/13 and 6/15/94

0 500

152

SCALE IN FEET

SCALE IN METERS

N

Seismic SurveyResults 7/6 – 7/10/94

=

400 8000600

400

200

-200

0

-400

-600

GENESEE VALLEYFILL

SCALE IN FEET

CARBONATES

SHALE

SYRACUSE SHALE &DOLOMITE

UNIT D

VERNONSHALE

MINEOPENING

YIELD-PILLARPANEL

WATER MOVEMENT

CARB O NA T E S

S H A L E

SY RA CUS E S H A L E &DO LO MI T E

VERNONS H A L E

UNIT D

MINEOPENING

YIELD-PILLARPANEL

= W A TE R MOVE MENT

G ENE S EE VA LLE YFI LL

SCALE IN FEET0 400 800

600

400

200

-200

0

-400

-600

G ENE S EE VA LL EYF ILL

CARB O NAT E S

S H A L E

SY RA CUS E S H A L E &DO LO MI T E

VERNONS H A L E

UNIT D

MINEOPENING

YIELD-PILLARPANEL

= W ATER MOVE MENT

SCALE IN FEET0 400 800

600

400

200

-200

0

-400

-600

POSTULATED SINKHOLE MECHANISMSPIPING CONCEPTINITIAL EVIDENCE OF PIPINGDISSOLUTION CONCEPTDISSOLUTION EVIDENCEINVESTIGATION OBJECTIVESINVESTIGATION OF ROCK COLLAPSE