CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 1

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

Wabasha Street Rock

Slide

Slides prepared by Itasca Consulting Group May 30, 2018 Summarized for presentation by City of Saint Paul Public Works June 1, 2018

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 2

• Rock slide, investigation, factual findings

Recent events

Background information (geology, groundwater, etc.)

Site investigation & findings

Key factors creating rock slides at Wabasha Street

• Remedial Actions

Topics for Today

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 3

• Initial site visit, and development of an investigation plan

• Collect site geometry (photogrammetry and laser scanning)

• Collect information about the rocks and soil

Weathered limestone

Fresh limestone

Limestone joints

Shale character

Sandstone strength and joints

• Collect information about surface and groundwater

• Initiate a monitoring program

Site Activities Summary

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 4

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 5

Soil

Heavily Weathered Limestone

Limestone

Shale

Sandstone

Site Geology

Dry-Stack

Concrete “Walls”

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 6

• These apply to past, recent and future rock slides:

Weathering and karst at geological time scale

Vertical joints and horizontal seams in the Platteville limestone

Likely quarrying of the Platteville limestone

Surface runoff

Shale and sandstone raveling (water & freeze/thaw)

Past attempts at slope stabilization on private property (dry stack, cables, etc.)

Key Factors at Wabasha Street Site

Surface &

groundwater,

freeze-thaw

Sandstone and

shale raveling

Limestone blocks are

undercut & topple off

Vertical joints form

limestone blocks

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 7

• Sandstone/shale

raveling

The Key Factor

About 2’ limestone has

fallen off

Shale

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 8

Current Status

Block

that fell Overhanging

block

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 9

5 6 7

8

9

10 11

12

13

14

17 15

16 18 19

17 15

12

14

10

Limestone joints numbered

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 10

Joints are dashed because the

length and orientation are uncertain

PRIVATE PROPERTY

PRIVATE PROPERTY

PRIVATE PROPERTY

Site Map

Block that fell in late April Overhanging block

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 11

1. Limestone blocks

2. Upper (weathered) limestone

3. Limestone-shale-sandstone interface

4. Upper Soil

5. Lower Soil

6. Prior slope stabilization

Specific Site Features (Categorized into Types)

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 12

Specific Site Features

1 1 1

1 1

6 2

3

4

5 5

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 13

• Immediate threat treatment to permit Wabasha Street to be re-opened

• Longer-term treatment

Two Phases (at least)

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 14

• Overhanging weathered

limestone, dry stack & soil above

recent block fall

Immediate At-Risk Features (immediate threat)

1a 1c 1b

2-4-6 2-4-6

• Overhanging limestone blocks

1a—Must be removed

1b, 1c—Likely to be removed (due to removal of 1a or because of instability)

Overlying weathered limestone, soil, dry stack, etc. also removed

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 15

Considerations Leading to the Longer-Term Treatment

Soil

Limestone

Shale

Sandstone

Surface &

Ground

Water

Site Geometry Land

Ownership

Remedial

Actions

Service Life &

Maintenance Risk Cost Constructability

Monitoring Aesthetics

Landowner

Impacts

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

May 30, 2018 Wabasha Street Rock Slide Slide 16

CIVIL ● MANUFACTURING ● MINING ● OIL & GAS ● POWER GENERATION

Wabasha Street Rock

Slide

Slides prepared by Itasca Consulting Group May 30, 2018 Summarized for presentation by City of Saint Paul Public Works June 1, 2018