8/9/2015

1

SOIL REINFORCEMENT PRINCIPLES AND SYSTEM

DESIGN PROPERTIES

Lessons PW 5, 6 and 7

RM Chapter 3

Lesson Plan PW Lesson 5 (RM Section 3.2)

– Properties of Reinforced and Retained Fill Soils

PW Lesson 6 (RM Section 3.3 – 3.4)– Soil-reinforcement interaction

PW Lesson 7 (RM Section 3.5)– Reinforcement structural design properties

– Steel corrosion, geosynthetic degradation, andlong-term design strength

8/9/2015

2

Properties of Reinforced and Retained Fill Soils

PW Lesson 5

RM Chapter 3.2

Lesson 5 – Learning Outcome

The participants will be able to:

Define the reinforced fill and retained backfill soil parameters required for design

Identify issues/concerns with marginal fills

Soil Properties

Foundation soil

, wc, Φ´, c´, cu , Cc, Cv

Reinforced fill

, Φ´, c´, k, D50, Dmax, electrochemical

Retained fill

, Φ´, c´, k, electrochemical

8/9/2015

3

Reinforced Fill Materials

Select backfill / AASHTO

Urban stone

Marginal materials

Select Granular Fill for MSEW

U.S. Sieve Size Percent Passing

4-inch (102 mm)* 100

No. 40 (0.425 mm) 0 – 60

No. 200 (0.075 mm) 0 - 15Plasticity Index (PI) shall not exceed 6

Soundness tests required

* ¾ in. for geosynthetics & epoxy or PVC coated steel unless construction installation damage tests performed

8/9/2015

4

GRADATION AND SHEAR STRENGTH

(From research on sand ; after Schlosser and Long, 1972)

Gradation & Drainage After J. P. Powers (1992)

“Construction Dewatering”

% Fines and Permeability

(from NAVFAC DM-7.1)

Free Draining

8/9/2015

5

MSEW Fill Gradation Max 15% fines for gravity drainage

and shear strength

Some fines needed to aid compaction

Limit top size to prevent reinforcement damage & for compaction

Beware of problem soils!

– Gap graded soils

– Soils with Cu < 4 or >20

– High strain soils (i.e., with mica, gypsum, smectite, montmorilinite)

– Recycled concrete or asphalt

Fine Grained Soil

MarginalReinforced Fill?

8/9/2015

6

Marginal Reinforced Fill Issues

Property Result

PI

Fines

Fines/PI

Marginal Reinforced Fill Issues

Property Result

Horizontal Stress

Load Transfer

PI Construction Deformations

Creep Deformations

Fines Drainage &

Water Pressure Problems

Fines/PI Corrosion

Reinforced Fill for RSS

U.S. Sieve Size Percent Passing

4-inch (100 mm)* 100No. 4 (4.76 mm) 100 - 20

No. 40 (0.425 mm) 0 – 60

No. 200 (0.075 mm) 0 - 50Plasticity Index (PI) < 20

* ¾ in. for geosynthetics & epoxy or PVC coated steel unless construction installation damage tests performed

8/9/2015

7

Reinforced fill

Contracting Agency should develop detailed backfill specifications that uniformly apply to all MSE wall systems

Backfill properties and specs do not replace QC/QA inspection

Reinforced Fill

For MSE wall

- use 34° friction angle

For RSS systems

- allow > % fines

- 28° reasonable, but run test

Retained Backfill

Run tests to obtain backfill properties or use conservative values (e.g., 28°)

8/9/2015

8

Reinforced Fill Electrochemical Properties

Steel Reinforcements

Resistivity > 3000 ohm-cm AASHTO T-288

pH > 5 and < 10 AASHTO T-289

Chlorides 100 ppm ASTM D4327

Sulfates 200 ppm ASTM D4327

Organic Content 1% maximum AASHTO T-267

Reinforced Fill Electrochemical Properties

pH Limits for

Geosynthetic ReinforcementsPET > 3 and < 9 AASHTO T-289

PP & HDPE > 3 AASHTO T-289

Lesson 5 – Learning Outcome

The participants will be able to:

Define the reinforced fill and retained backfill soil parameters required for design

Identify issues/concerns with marginal fills