S55_Geosynthetic Stabilization for Wet Subgrade_LTC2013

7/29/2019 S55_Geosynthetic Stabilization for Wet Subgrade_LTC2013

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Geosynthetic Stabilization forSoft Subgrade- Instrumentation and MEApproach

Xiaochao Tang, Ph.D.Louisiana Transportation Research Center

Murad Abu-Farsakh, Ph.D., P.E.Louisiana Transportation Research Center


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ACKNOWLEDGEMENTS

Financial Support from LA DOTD, Tensor, TenCate

Assistance from PRF


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BACKGROUNDLouisiana soil: soft subgrade soil leads to excessive deformation

Treatmentsfor soft subgrade:

o Thicker base (constraints of resources, high cost)

o Cut and fill (considerable expense of excavation and transportation)

o Chemical stabilization (lime-reactivity and environment, cement-

shrinkage cracks)

An alternative mechanical treatment: geosyntheticsplaced at base-

subgrade interface

Asphalt

SUBGRADE

Base


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Extruded geogrids: a polypropylene (PP) or polyethylene (PE) sheet,

punched and drawn (Biaxial &Triaxial)

Woven / welded geogrids: polypropylene (PP) or polyester (PET)

yarns, woven or welded

Geogrids

GeosyntheticsManufactured from polymeric material, used with geotech engineering

projects such as slopes, retaining walls, embankments, and pavements;

Includes geotextiles, geomembranes, geonets, geocells, and geogrids.

WovenBiaxial

GeotextilesPermeable textile structures: Woven & Nonwoven

ExtrudedBiaxial

ExtrudedTriaxial

Woven

Geotextile


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Evaluate and quantify effectiveness of geosynthetic

reinforcements for pavements built overnatural softsubgrade

Examinepre-rut

effects on geosynthetics performance

Incorporate effects of geosynthetic reinforcement into

pavement MEPDG design

RESEARCH OBJECTIVES


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EXPERIMENTAL PROGRAM

Cross Section

A total of 6 test sections

Two control sections: sand embankment and unreinforced

Triaxial geogrids: double-layer & at interface

High-strength geotextiles: 12-in & 18-in base at interface

Heavy clay (A-7-6), Mexico Limestone, Level 2 Superpave mixture

GeotextilesGeogridsGeogrids

Test Sections


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Pavement Instrumentation

HMA

Aggregate Base

Soil Subgrade

3''

10'

RS580 iGeotextile

CL

5''

1.5''

Potentiometer

Earth Pressure Cell

Piezometer

TDR Strain Gage

LVDT

2' 2' 2'2'4'2'2'

1'

8'8'

2'2'

1'

Thermocouple (Note: thermocouple will be installed at the edge between Sections 5 and 6)

North

Load-associated:

stress, strain, & deformation

Environment-associated:

water content & temperature

What to measure ?

Where to measure ?

Critical responses:

top of subgrade, base, bottom of

AC


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Pressure Cell (Top of Subgrade)

Hydraulic type with semiconductor transducer

Measures total stress and dynamic stress

Earth Pressure Cell

Pavement Instrumentation (contd)

Piezometer

Piezometer (Top of Subgrade)

Measures static and dynamic pore water pressure


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LVDT (Top of Subgrade)

Spring-loaded type with a contact disk of 2 in diameter

Measures both elastic and permanent overall subgrade deformations


Customized potentiometer

Potentiometer (Mid-Base)

Measures strain over the length

Both elastic and permanent

Customized LVDT


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Foil Strain Gauge on Geosynthetics

On opposite sides of geosynthetics, along transverse direction

Measures permanent and dynamic strains


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TDR (Top of Subgrade & Mid-Base)

Moisture content

Thermocouple (Subgrade, Base, & Asphalt Layer)

Spatial and temporal variations of temperature


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Cable protection and organization

Sensor labeling


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Site Characterization

Subgrade and Base

LWD, Geogauge, Nuclear Gauge, DCP, and FWD


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Accelerated Loading Facility (ALF)

About 100-ft long and 55-ton

Unidirectional, dual wheel, half of a single axle

Adjustable axle load: 9,750 lb to 18,950 lb

Nominal speed: 10.5 mph,

40-ft wheel path, wander covering 30 transverse distance


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Testing and Data Collection & Processing

Pre-rut on base & APT on AC

At select intervals: transverse rutprofile, instrumentation data (static &dynamic)

Data processing: eliminating outliers,data smoothing, identifying peaks

and valleys

Laser Profilometer


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PRELIMINARY RESULTS

Mechanistic modeling: calibration and validation

Subgrade resilient deflection by LVDT

83

83.5

84

84.5

85

0 0.5 1 1.5 2

Defle

ction(mm)

Time (s)

10

20

30

40

50

60

70

80

90

0 0.5 1 1.5 2

Vertica

lstress(kPa)

Time (s)

Vertical stresses atop subgrade measured by pressure cell

Response Measurement


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Increaseof dynamic vertical stress at the top of subgrade

Indication ofdecreaseof base modulus corresponds to LWD & Geogauge

As opposed to current MEPDG using constant modulus, possible to update

pavement layer properties along with traffic loading

Vertical stresses atop subgrade measured by pressure cell (section 6)

Response Measurement (contd)

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

0 500 1000 1500 2000 2500

Verticals

tressontopofsubgrade(k

Pa)

Applications of axle load


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After 1000 passes

Majority of rutting attributed to base

Accumulated subgrade permanent deformation

Performance Measurement (contd)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0 500 1000 1500 2000 2500

Accumulatedsu

bgradepermanentdeformation(mm)

Applications of axle load


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SUMMARY AND FUTURE WORK

Six test sections: geogrids and geotextiles, various structures

Pavement instrumentation

Interpretation and use of instrumentation data

Future work: continue APT testing, integrate instrumentation data in

design & analysis, incorporate effects of geosynthetic

reinforcements into MEPDG

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S55_Geosynthetic Stabilization for Wet Subgrade_LTC2013

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