Upstream Saddle Dike Construction Case Histories

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by Barry Thacker, PE

Knoxville, TN 37909

Virginia PE Seminar 24 March 2016

Lebanon, VA

Schnabel E N G I N E E R I N G

Nolan Run Western Saddle Dike post-failure aerial photograph from MSHA Report of Investigation—

Date of failure = 30 November 2012

Aerial view in 1979 looking downstream at Nolan Run dam construction in background and surface mining in foreground

1980 view looking upstream during surface mining with area of western saddle shown in background

Western saddle el. 1268’

Western Saddle Dike from MSHA-Approved Stage IV Plan, which required that construction start before the surface of the fine coal refuse achieved elevation 1250 feet

Construction of the Western Saddle Dike began in April 2012 when the fine refuse was at about elevation 1247 feet with the pool at elevation 1255 feet. Thus, clarified water was about 8 feet deep above the settled fine refuse level when construction began.

Grading upstream slope of western saddle dike on November 15, 2012 (i.e. 15 days before the failure).

Orientation of dozer at time of failure based on eye-witness accounts.

Graded slope on southern face on November 16, 2012 (i.e. 2 weeks prior to failure), after pneumatic piezometer P-7 was installed in fine coal refuse at tip elevation 1225 feet

Access ramp onto crest of fill (Note difference in elevation between ramp and adjacent fill)

Staff gauge used to measure pool elevation

Pneumatic piezometer P-7

Sequence of events prior to failure:

1259.6’Identified as coarse refuse on P-7 driller’s log to el. 1234.5’

• 11/23/12 (i.e. 1 week before failure): 15 psi measured in P-7 corresponds to a water level at elevation 1259.6 feet or 4 feet higher than pool elevation.

• 11/16/12 (i.e. 2 weeks before failure): P-7 was installed at a reported ground elevation = 1264.5 feet.

• 11/30/12 (i.e. morning of the failure): 15 psi measured in P-7 was the same as the week before. Pool measured at elevation = 1255.42 feet.

• The project engineer said the CCR fill had reached about elevation 1271 feet on the riser guide pipe at P-7 on the morning of the failure.

According to the field engineer, “The scene then reminded me of the movie ‘Armageddon’ when the asteroid started breaking apart with spikes and canyons forming at the surface.”

“Thousands of clear bubbles”

“Lip disappeared”

“A ‘burp’ in the pond”

On the day of the incident, the field engineer and the project engineer met to discuss the measurements in P-7.

Aerial photograph taken during routine inspection by WVDEP on 11/29/12

“After the collapse, the current was

carrying us to the north.”

“Slurry mound”

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Northern Islands

Southern Islands

Whirlpool

Post-failure aerial

photograph

Z-Z Reference

Line

0’ 100’

Western saddle dike pre-collapse reconstruction and relic survey plan

Dozer

Pickup Truck (no camper with windows down)

Pickup Truck (camper with windows up)

Pickup Truck (camper with windows up)

Dozer

Pickup Truck (no camper with windows down)

LEGEND

(After 250,000 cy of CCR lost in failure?)

P-7 (Pre-failure)

500’

Profile through stable area of dike

--where fine refuse was

thickest

From MSHA Investigation

Report—

MSHA Conclusion: A failure occurred because... the coarse coal refuse (CCR) embankment was raised faster than the strength of the fine coal refuse (FCR) could increase.

MSHA’s failure model used estimated pore pressures in P-7… 10 times greater than the piezometer reading.

Note the coarse coal refuse and orange clay intrusions

in the fine coal refuse in BH-22A drilled at the location of the northern islands, which indicates failure through the

natural foundation clay.

CCRFCR

(Stable zone where boring B-108 was drilled)

No observations of failure on

north end, where construction was done uphill from

the natural bench. BH-16 Log

B-108

At BH-21, a sequence of FCR/orange-brown clay/

CCR/FCR was found.

Natural orange clay soil overlying CCR sandwiched between FCR in the impoundment at a distance of 400 feet from the original dike is indicative of multiple stages of failure involving the natural clay soil.

Aerial photograph at Nolan Run taken during a routine inspection by WVDEP on 11/29/12

Area that was low upstream of ramp as shown in 11/16/12 photo has been filled by 11/29/12.

(Site personnel said during interviews that fill placement was concentrated here during the week before the failure to widen the haul road ramp—area where the coarse refuse was thickest).

No change in pore water pressure readings at P-7 would be explained if the fill level here had been raised from elevation 1264.5 feet to 1271 feet between its date of installation and the date of its first reading, with no fill placed at P-7 after measurements began.

BH-24T-A

BH-15

Profile Z-Z at t = 60 daysFinal scarp

Initial scarp

“slurry mound” observed here at start of failure

SLOPE/W (PHSG method)

Initial failure location as verified by eye witness accounts and location with shortest construction time.

Fine Refuse In-Situ

Fine Refuse Upstream of Pushout

Failure No. 1The initial slide likely occurred due to elevated pore water pressures in the underlying natural clay foundation and FCR zones. With rapid loading on stiff clay, filling can continue without incident, because the clay can dilate as it is stressed, thus gaining strength. But when suction pressures dissipated, stiff clay ruptured and MOVED over the area of Boring BH-6!

BH-6

Note: Top of natural clay soil is now 6.5 feet lower in BH-6 than before the failure.

Sequence of failures as shown on western saddle dike pre-collapse reconstruction and relic survey plan

1. Initial failure occurred along Profile Z-Z, heaving the mass out over FCR/clay foundation soil upstream of the former dike at BH-6.

2. The newly loaded FCR deposit/ foundation soil underlying the failed mass experienced a time = 0 loading condition, causing it to “explode” at BH-6 in a secondary failure to the north and northeast, leaving a ‘sludge-filled void” in its place.

NOTE: The pick-up truck with windows up and a camper likely moved in line with the other pick-up truck initially, but then floated in a northerly direction with the current from the secondary slide to sink at its final resting spot.

BH-6

Note: Top of natural clay soil is now 6.5 feet lower in BH-6 than before the failure

3. The embankment adjacent to the initial failed zone slid into the “sludge-filled void” as a tertiary failure, adding weight to promote continued movement of the secondary slide.

Potential stability problems have been avoided at natural saddles in Virginia by filling hollows upstream of those saddles during earlier stages with CCR…

How do I suggest designing and building saddle dikes like the one shown below?

Raise fill in advance of rising FCR level

CCR

FCR

50’

Start pushoutconstruction sooner,

rather than later

Pushout construction at these saddle dike locations began when the FCR level was more than 50 feet in elevation below natural saddle level. Filling occurred in advance of the rising FCR level over a period of more than 7 years prior to raising the dikes above natural saddle level.

An example of that approach is shown here at Virginia Site No. 1

Future Saddle Dike Locations

Main Dam

Virginia Site No. 2 Virginia Site No. 3 Virginia Site No. 4

Virginia Site No. 5

Virginia Site No. 6

So, why am I dressed in Victorian-era attire?

Welsh miner/engineer David R. Thomas time travels from the past to teach students about the Coal Creek Labor Saga, which

is now part of Tennessee’s education curriculum.

David R. Thomas

Meeting of miners and business leaders at Thistle Switch in July 1891 to plot a course of action to end convict leasing after the Tennessee Coal Mining Company (TCMC) replaced striking miners with convicts at its Tennessee Mine in Briceville.

Col. Keller Anderson,

Commander of Fort Anderson on Militia Hill

www.coalcreekaml.com

STEM-historian Charles Darwin

Promote STEM as a living STEM-historian

In addition to being a living historian in the classroom…

…I serve as tour guide to historic sites associated

with the Coal Creek Labor Saga…

Barry Thacker, PE, 865-584-0344, bthacker@schnabel-eng.com

…Appalachian toothpicks