Boone Dam Hydro-Geo Model and Seepage Remediation · 12/1/2015 · BOONE DAM HYDRO-GEO MODEL AND SEEPAGE REMEDIATION AIChE EAST TENNESSEE LOCAL SECTION 01 DECEMBER 2015 Boone Hydro-Geo

Boone Dam Hydro-Geo Model and

Seepage Remediation

Patrick V. Kiser, PE GCP&S Manager, Civil Engineering

01 December 2015

BOONE DAM HYDRO-GEO MODEL AND SEEPAGE REMEDIATION

AIChE EAST TENNESSEE LOCAL SECTION

01 DECEMBER 2015

Presentation Overview

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I. Background

II. Elements of the Geologic Model

III. The Boone Dam Hydro-Geo Model

IV. Remediation Strategy



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Background: Sinkholes and Turbid Discharge

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Background: Sinkholes and Turbid Discharge

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2012 Sinkhole

Oct. 2014 Sinkhole

Oct. 2014 Muddy Discharge



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Muddy Seep in Tailrace

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10/30/14 ▪ 18:42 ▪ Units Off ▪ HW 1372.7 11/03/14 ▪ 14:32 ▪ Units Off ▪ HW 1367.4



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2012 Sinkhole

Oct. 2014 Sinkhole

Oct. 2014 Muddy

Discharge



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Idealized Cross Section and Foundation Treatment

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Cut Off Trench Alignment

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Grout Curtain Alignment

Cut Off Trench Excavation



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Site Geology - The Underlying Issue

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Elements of the Geologic Model Complex Structure



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Elements of the Geologic Model

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• Bedrock

– Competent rock

– Epikarst

Epikarst

Competent Rock



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Epikarst

Foundation Soils



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Alluvial Cap

Residual

Foundation Soils



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Right Abutment Section along Grout Curtain

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Right Rim – Station 20+00 to 25+00

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Geological

Elements

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Exposed Top of Epikarst Alluvial Deposit in

Foundation Soils

Foundation Soils

Competent Rock

• Foundation Soils

• Epikarst

• Embankment Fill

Photographic

Definitions



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Geological

Elements

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Competent Rock


• Epikarst

• Embankment Fill

Photographic

Definitions

Foundation Soils

Epikarst

Embankment Trench Fill



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Geological

Elements

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Competent Rock


• Epikarst

• Embankment Fill

Photographic

Definitions

Foundation Soils Epikarst

Embankment Fill



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Core Trench Placing Clay

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Investigations – Exploration Borings

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Investigations – Geophysics

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Hydro-Geologic Model Overview

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Boone Hydro-Geo Model Thesis Statements

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1 • An extensive, subsurface drainage network existed in the epikarst prior

to construction of Boone Dam.

2

• The right rim provides a constant source of head under the embankment. Recharge in the right rim causes surges in volume and pressure to the epikarst and foundation, which have continued to develop the drainage network.

3 • Increased gradients from the reservoir have exploited weaknesses in

the cutoff trench and tied headwater to the drainage network.



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1 • An extensive, subsurface drainage network existed in the

epikarst prior to construction of Boone Dam.

Supporting Evidence:

Preconstruction site topography and

geologic mapping indicate features of a

well developed drainage network including

draws, alluvial deposits, springs, and

sinkholes.

Preexisting Drainage Network Hydro Geo Model Thesis 1. Drainage Network

2. Right Rim Contribution

3. Reservoir Contribution



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Preexisting Drainage Network

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Preconstruction

site topography

and geologic

mapping indicate

features of a well

developed

drainage network

including draws,

alluvial deposits,

springs, and

sinkholes.

Hydro Geo Model Thesis 1. Drainage Network





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Elev. 1260’

Elev. 1330’

Elev. 1275’

Elev. 1425’

Elev. 1500’ Preexisting

topographic

draw



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Preexisting sinkholes and

natural springs

Depressions prior

to construction

Spring prior to

construction



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Consolidation Grouting

Required



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2

• The right rim provides a constant source of head under the embankment. Recharge (high infiltration) in the right rim causes surges to the epikarst and foundation, which have continued to develop the drainage network.


• Extensive weathering present in right abutment

• Piezometric data indicates heads significantly higher than headwater in the

right rim and flow paths toward the toe.

• A French drain was required during construction to deal with excessive

flows from springs

• Confined aquifer like behavior observed during drilling of several boreholes.

• A number of piezometers increase in total head following high infiltration

events.

• Following high infiltration event on March 5, 2015 muddy seeps were

observed along the upstream face of the dam

Right Rim Contribution Hydro Geo Model Thesis 1. Drainage Network





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Artesian well in reservoir

indicates higher head from

regional groundwater

recharge

Dam Site

Right Rim



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Extensive weathering in right abutment, Section along grout curtain between

Sta. 15+00 and Sta. 25+00

Karstic Vadose Zone Measured Head in

Right Rim 1384’

Current HW 1352’

Embankment

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Piezometric data indicates heads significantly higher than headwater in the right rim and

flow paths toward the toe. B-27, shown below, is ~ 20 feet higher than the current

headwater.

Upstream of cutoff

Tip in Epikarst from Elev. 1389 to 1364



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The piezometric

contours indicate

flow paths in the

epikarst from the

right rim toward

the toe



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A French drain

was required

during construction

to deal with

excessive flows

from springs in the

area shown below.



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A French drain

was required

during construction

to deal with

excessive flows

from springs in the

area shown below.

Piezometers

with response

to high

infiltration event

Soil Boring (Embankment & NQ/HQ Rock Coring)

Sonic Boring

Observation Trench

Piezometer(s) Installation

Slope Inclinometer Installation

Proposed Boring Locations

Completed Boring Locations

Existing Borings

Stantec Boring Legend

Approximate Location of Seepage Piping Outlet

Approximate Location of Sink Hole



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A French drain

was required

during construction

to deal with

excessive flows

from springs in the

area shown below.

Piezometers at downstream toe respond to high

infiltration event



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A French drain

was required

during construction

to deal with

excessive flows

from springs in the

area shown below. Piezometer elevations

following high infiltration

event

Piezometer elevations

during dry period

Vibrating wire piezometer B-23D

fluctuates at higher elevations

following high infiltration event



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A French drain

was required

during construction

to deal with

excessive flows

from springs in the

area shown below.

Open standpipe piezometer B-6

fluctuates at higher elevations

following high infiltration event Piezometer elevations

following high infiltration

event

Piezometer elevations

during dry period



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A French drain

was required

during construction

to deal with

excessive flows

from springs in the

area shown below.

Following a high infiltration

event on March 5, 2015

muddy seeps were

observed along the

upstream face of the dam



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A French drain

was required

during construction

to deal with

excessive flows

from springs in the

area shown below.

Following a high infiltration

event on March 5, 2015 muddy

seeps were observed along the

upstream face of the dam



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A French drain

was required

during construction

to deal with

excessive flows

from springs in the

area shown below.

Seep #2

Video



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3

• Increased gradients to the reservoir have exploited weaknesses in the cutoff trench and tied headwater to the drainage network.


• Several PZs respond to changes in HW with small lag times

• B28 dye test pushed dye from downstream of cutoff to the upstream of the cutoff

• Grouting of the B30 instrument likely pushed grout from D/S of the cutoff to the

reservoir

• B-44 dye test (U/S) resulted in dye in B-28 (D/S), B-42 (D/S), and H/W

• PZs temperatures and water conductivity testing indicate that reservoir water and

right rim groundwater are intermixing underneath the dam

• PZ temperatures indicate water under the embankment is colder than regional

groundwater but warmer than reservoir.

• Conductivity indicates the same

• Open soil pipe at the U/S Toe of the dam

Reservoir Contribution Hydro Geo Model Thesis 1. Drainage Network





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3. Reservoir Contribution Instrumentation Response to HW

PZs respond to

changes in HW with

small lag times



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Grout Show

Location

B-30 Boring

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3. Reservoir Contribution B-30 Grout Event

Grouting of the B30

instrument pushed

grout from downstream

of the cutoff to the

reservoir



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Reservoir Contribution B-30 Grout Event

Grouting of the B30 instrument pushed grout

from downstream of the cutoff to the reservoir



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3. Reservoir Contribution B-28 Dye Test

B28 dye test from

downstream of cutoff

had a detect to the

upstream of the cutoff



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Reservoir Contribution B-28 Dye Test

B28 dye test pushed dye from downstream of

cutoff to the upstream of the cutoff



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B-44 dye test (U/S)

resulted in dye in B-28

and B-42 (D/S) epikarst

and headwater



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B-44 dye test (U/S)

resulted in dye in B-28

and B-42 (D/S) epikarst



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3. Reservoir Contribution Temperatures in Embankment Soils

Temperature closely

matches regional ground

temperature and indicates

very little flow through the

embankment soils

Normal ground temperature in the project area is 57oF

Reservoir Temperature is 43oF



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Pipe and Tank Illustration Hydro Geo Model Thesis 1. Drainage Network



TAILRACE

RESERVOIR

RIGHT RIM



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Pipe and Tank Illustration Hydro Geo Model Thesis 1. Drainage Network



• Simplified model of the existing drainage network

• Demonstrates the constant source of head from the Right Rim

• Exhibits the potential for large fluctuations in the system dependent on

water surface elevation in both Right Rim and Reservoir

• Illustrates the increased gradients due to the Reservoir



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Potentially Active Failure Modes

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Erosion through an open channel or pipe that connects to the reservoir, through the epikarst or embankment soils, with a resulting flowrate that quickly undercuts the embankment.

Erosion channels transmit high water pressures from the upstream lake to the downstream dam face, inducing a large slope failure in the embankment.

Sinkholes develop under the downstream face causing a series of slope failures that leave a deep gap in the embankment crest.



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Recent Conformations of Hydro-Geo Model Right Rim



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Recent Conformations of Hydro-Geo Model Reservoir Connections – B-60



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Recent Conformations of Hydro-Geo Model Reservoir Connections – B-60



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Remediation Plans



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Remediation Plans



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Remediation Plans



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Remediation Plans



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Remediation Plans



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Current and Upcoming Activities

• Test Grouting Program

• Exploration Grouting Program

• Composite Wall Design

• Environmental Assessment Completion



01 DECEMBER 2015

Questions

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Documents

Boone Dam Hydro-Geo Model and Seepage Remediation · 12/1/2015 · BOONE DAM HYDRO-GEO MODEL AND SEEPAGE REMEDIATION AIChE EAST TENNESSEE LOCAL SECTION 01 DECEMBER 2015 Boone Hydro-Geo