Making the case for geotechnical instrumentation of landfills

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with our clients and employees.

Making the case for geotechnical instrumentation of landfills How instrumentation can save your site

Rob Holmes, P.E. – Client Manager

April 29, 2014

Overview

• Why monitoring can be an important tool

• Instrumentation options

• Design/Construction

• Operation

• Expansion/Closure/Post Closure

• Case Study – Pennsauken Landfill

© 2014 Cornerstone. All rights reserved. |2

3

The Independent –

Online – Ashalnd,

KY September 6,

2013

SkyHi News,

Winter Park,

Granby and

Grand County,

CO, February 23,

2012

The Morning Call –

Lehigh Valley’s

Newspaper, March 14,

2013

( DONNA FISHER / THE

MORNING CALL / March

13, 2013 )

(Express-Times File

Photo | MATT SMITH)

Equipment/Options

• Inclinometers

• Horizontal

• Vertical

• Piezometers

• Extensometers

• Pressure Cells

Inclinometers

Multiple readings measuring

displacement at surface Vertical Inclinometer

• Used for measuring settlement and horizontal strain

• Magnetic plates/indicators…..

• …or, anchors set at specified depths, with measurements to reference head by micrometer/electric sensor

• Some equipment can be installed post construction

• Foil strain gauges for flexible membranes

© 2014 Cornerstone. All rights reserved. |

Extensometer/Strain Gauges

• Piezometers measure pore-water

pressure and ground water levels

• Standpipe

• Pneumatic

• Vibrating Wire

• Direct access not required

• Remote reading

• Immediate response


Piezometers

Pressure Cells

• Measures total pressure in earth fills and

embankments

• Changing earth pressure squeezes plates together

causing increase of fluid pressure

• Pressure read with vibrating

wire pressure transducer


Case Study – Pennsauken Landfill

• Phase V Cell – 10 acre site

• Soft tidal deposits/organic clay

• Designed 2002

• Constructed 2003

• Geotechnical monitoring required

• Stability considerations

• Settlement monitoring for strain


Instrumentation program

• Stability

• Pneumatic Piezometers (8)

• Vertical Inclinometers (2)

• Survey Monuments

• Settlement/Strain

• Horizontal Inclinometers (3 runs – up to 350’ long)

• Extensometers (installed on outside of inclinometer

casings


Phase V – Instrumentation Plan

Horizontal Inclinometer

w/register pointSurvey Control Benchmark Vertical Inclinometer

• Original construction

• Confined space entry

• Age of equipment

• Long-term durability of

equipment/installations

• Transition of

institutional knowledge


Challenges

Opportunities – “Age of equipment….”

• Extensive data set to verify original design

• Understanding of pore pressure response during lift

placement

• Used for future operational decisions

• Settlement/Strain

• Permit conditions based on worst case assumptions (although

original report had included a range)

• Data showed significantly less settlement


12’

/9

6’ fill – 36 months






Settlement Model – Worst Case Consolidation Parameters (HI-1)

Point

Predicted

Total

Settlement, ft.

Modeled

Total

Settlement,

ft.

Modeled

Interim

Settlement,

ft.

Actual Interim

Settlement, ft.

Ratio (%) -

Actual Interim

Settlement to

Modeled Interim

Settlement

HI 1.1 1.76 1.75 1.70 0.35 20.5

HI 1.2 3.85 3.84 3.37 1.43 42.5

HI 1.3 5.00 4.99 4.17 2.61 62.6

HI 1.4 4.95 4.96 2.70 2.10 77.7

HI 1.5 3.69 3.69 2.64 1.88 71.3

Actual Settlement only 44.5% of modeled settlement for all points

Actual Settlement only 54.5% of modeled settlement (HI-1)

Settlement Model – 50% or ‘Average’ Consolidation Parameters (HI-1)

Point

Predicted

Total

Settlement,

ft.

Modeled Total

Settlement,

(Average

Parameters) ft.

Modeled Interim

Settlement

(Average

Parameters), ft.

Actual

Interim

Settlement, ft.

Ratio (%) - Actual

Interim

Settlement to

Modeled Interim

Settlement

(Average

Parameter)

HI 1.1 1.76 0.52 0.48 0.35 72.9

HI 1.2 3.85 2.39 2.02 1.43 70.8

HI 1.3 5.00 3.47 2.80 2.61 93.2

HI 1.4 4.95 3.43 1.66 2.10 126.5

HI 1.5 3.69 2.93 2.02 1.88 93.0

Actual Settlement was 104.9% of modeled settlement for all points

Actual Settlement only 91.1% of modeled settlement (HI-1)

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

0 50 100 150 200 250 300 350

Set

tlem

ent (

feet

)

Distance Along Profile (feet)

Modeled/Predicted TotalSettlement

Actual Interim Settlement

Modeled Interim Settlement(Average Properties)

Modeled Total Settlement(Average Properties)

Settlement - HI-1 ProfileThrough September 2013

Let’s not forget about strain…Extensometer E-1 (@ Horizontal Inclinometer HI-1)

Magnet

Number

Baseline Readings Oct.

2003

(feet)

Q3, 2013 Readings Sep.

2013

(feet)

Difference

(feet)

Incremental Strain

(%)

1 33.71 33.78 0.07 0.2077

2 53.78 53.83 0.05 -0.0997

3 73.78 73.80 0.02 -0.1500

4 93.57 93.55 -0.02 -0.2021

5 113.57 113.49 -0.08 -0.3000

6 133.58 133.55 -0.03 0.2499

7 153.52 153.49 -0.03 0.0000

8 174.30 174.27 -0.03 0.0000

9 194.44 194.43 -0.01 0.0993

10 214.45 214.41 -0.04 -0.1499

11 234.39 234.40 0.01 0.2508

12 254.80 254.87 0.07 0.2940

13 274.78 274.83 0.05 -0.1001

14 294.87 294.96 0.09 0.1991

15 314.76 314.87 0.11 0.1006

16 334.89 335.04 0.15 0.1987

Closing Opportunities – Instrumentation

• Maintain Compliance

• Risk Reduction

• Site System Understanding

• Design Refinement

• Expansions/Modifications


Documents

Making the case for geotechnical instrumentation of landfills