Western Loop Road Retaining Wall
Greensboro, NC


Location:
Greensboro, NC

Contractor: Archer Western

Owner: North Carolina Department of Transportation

Wall Designer: Foster Geotechnical, Woodbridge, VA

A new retaining wall built; as part of the $116 million North Carolina Department of Transportation (NCDOT) Greensboro western loop project, was constructed using STALITE expanded slate lightweight aggregate as a backfill. The project is located just north of West Vandalia Road near the intersection of West Vandalia and Groometown Road. The area where the retaining wall was placed had compressible soils and limited area for over excavation. The combination of site conditions made the use of the lightweight fill an attractive option for the NCDOT. Foster Geotechnical, who designed the wall, said the incorporation of lightweight fill (at the NCDOT’s request) into the project was not complicated and they often use lightweight aggregate fill for similar applications over poor soils.

The lightweight aggregate was shipped directly to the project from Carolina Stalite Co.’s Aquadale plant, located just outside of Albemarle, NC. The material had a gradation meeting ASTM C-330 (3/4” to #4) requirements and the damp loose density averaged 53 lb/ft3 when shipped from the plant. A total of 4200 tons of lightweight aggregate was shipped for the project from December 2004 through June 2005. Below is a chart of typical values for design using lightweight aggregate fill. As you will notice in the chart the lightweight aggregate has several advantages over typical fill. The high internal angle of friction (40°-46°) paired with the low maximum compacted in-place density (62 lb/ft3 wet, 59 lb/ft3 dry) makes STALITE lightweight fill an option in solving many poor soil problems on construction sites.
 

Aggregat

Property

Measuring

Method

Test

Method

Commonly Used

Specifiactions for

ESCS

STALITE Expanded

Stalite Lightweight

Aggregate

Typical Design

Value for

Ordinary Fills

Soundness

Loss

Magesium

Sulfate

AASHTO

T 104

< 30% 0.23% < 6%

Abrasion

Resistance

Los Angeles

Abrasion

ASTM

C 131

< 40% 26% 10-45%

Chloride

Content

Chloride

Content of

Soils

AASHTO

T 291

< 100ppm 37 ppm  
Grading

Sieve

Analysis

ASTM

C 136

Comment No. 1 ASTM C-330 ASTM C 33

Compacted

In-Place

Bulk Density

(Unit Weight)

Density

Test

ASTM D-698

Comment 2

< 70 lb/ft3

62 lb/ft3

59 lb/ft3

100-130 lbs/ft3

Stability

(Phi Angle,

Ф)

Direct Shear
Test

Consolidated

Drained

Triaxial-

consolidated

Drained

ASTM D 3080
Comment 3

Corps of

Engineers EM

1110-2-1906
Apendix X
Comment 3

Comment No. 3 40°-46° 30°-38°
(fine sand-
sand & gravel)
 
Loose
Bulk Density
(Unit Weight)
 
Loose ASTM C 29 Dry < 50 lb/ft3
Saturated < 65 lb/ft3
 
48-55 lb/ft3 89-105 lb/ft3
pH pH Meter AASHTO
T 289
 
5-10 6.95 5-10

Comments
1. Grading: ESCS aggregates are available in a wide variety of grading, therefore it is essential the specifier contact the ESCS supplier for the gradings that are available in a given location. Some common gradings are ¾” to No. 4, ½” to No. 4, 3/8” to No. 8, 3/8” to 0, 2” to ¾”, 2” to 0 or blends of these. ESCS aggregate suppliers can be found on ESCSI’s website at www.escsi.org. (LINK TO http://www.escsi.org)
2. Several methods have been used to determine the in-place moist bulk density (unit weight) of a given aggregate, therefore contact the ESCS producer for recommendation on local practices.
3. ESCS lightweight aggregate has been tested by both Direct Shear and Triaxial test methods. With either method, the phi angle will vary in both ordinary and ESCS fill, depending on test procedure, aggregate grading, particle angularity, amount of compaction and amount of consolidating stress applied during the test. Design and specify the minimum phi angle appropriate for the project design and material(s) that are contemplated for use in the project. Contact the ESCS supplier(s) for specific properties of their materials.

 

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