GeoInstitute Seminar

Colorado Association of Geotechnical Engineers

DEFORMATION OF COMPACTED FILLS

Iraj Noorany, Ph.D., P.E., G.E., F. ASCEConsulting Geotechnical Engineer

Professor Emeritus, San Diego State University

September 12, 2018

Structural Fills and Embankments- Support structures

- Support improvements- Walls, fences, pools, hardscape, landscape

- Tolerable differential movement

- Stable slopes

Design Challenges

Unsaturated soils are complicated

- Soil properties change Post-construction wetting from landscape irrigation, precipitation, underground seepage, and underground leaks change soil suction, water content, dry density, RC, degree of saturation, strength, moduli, etc.

- Fill’s geometry changes-Heave, settlement, lateral fill expansion (LFE)

Focus

Compacted structural fills

Expansive soils

Fill deformation due to wetting

Slope deformation due to wetting

Practice in California and Southwest U.S.

Not includedElastic deformationDeformation due to instability of slopesDeformation caused by earthquakeCreep deformation

Other methods and practices

Scope

Part 1- Types of wetting-induced fill deformation

Part 2- One-dimensional fill deformation- Laboratory swell-collapse tests- Deformation analysis

Part 3- Lateral deformation of slopes- Laboratory swell-collapse tests- Deformation analysis

Part 4- Mitigation of deformation of compacted fills

Part 1TYPES OF WETTING-INDUCED FILL DEFORMATION

- Significant differential movement of slabs and foundations- Heave- Settlement

- Cracks in structures and slabs

- Lateral stretching of fill embankments (LFE)- Separations and cracks in hardscape, parallel to descending slopes- Separations and cracks in side yard walls and top of the slope fences- Damage to appurtenant structures in the vicinity of the slope

From Brandon, et al. 1990

WETTING PATTERN

Placement, 1984 1996

Typical Inclinometer Data Showing LFE

Part 2ONE-DIMENSIONAL HEAVE AND SETTLEMENT

Step 1- Laboratory tests- Classification and compaction- One-dimensional swell-collapse tests

Step 2- Adjustment of the measured swell-collapse strains- n1, n2, n3

Step 3- Analyze heave, settlement

Step 1

One-dimensional Swell and Collapse Test

Tests in a large mold using the total fill material

Tests in small molds using the fill’s finer fraction

One-dimensional Swell and Collapse TestsASTM D 4546-14

- Method ATests on laboratory compacted specimens- Fill design stage, for predicting fill deformation- Forensic inverse analysis of fill deformation

- Method BTests on intact “undisturbed” samples- Forensic analysis of existing fill, and estimating the amount

of the remaining heave or settlement

- Method cFor loading-after-wetting cases; new loads on old fill

Test Method A - Design Phase Wetting-after-loading test

Use finer fraction of the representative fill material and prepare four or more laboratory-compacted specimens. Use water content and dry density of the finer fraction :

𝒘𝒘𝒇𝒇 = 𝐰𝐰𝐭𝐭 − 𝐏𝐏 𝐰𝐰𝐜𝐜𝟏𝟏 − 𝐏𝐏

𝜸𝜸𝒅𝒅𝒇𝒇 = 𝟏𝟏 − 𝐏𝐏 𝑮𝑮𝒄𝒄 𝜸𝜸𝒘𝒘𝑮𝑮𝒄𝒄 𝜸𝜸𝒘𝒘 − 𝐏𝐏 𝜸𝜸𝒅𝒅𝒅𝒅

This equation is reasonably accurate for: + No. 4 oversize fractions up to 40% (P up to 0.4), or +3/4” oversize fractions up to 30% (P up to 0.3).

Test Method A – Inverse Deformation AnalysisWetting-after-loading test

Take intact samples of the fill from forensic borings. Remove the oversize. Reconstitute specimens using the placement water content and dry density of the finer fraction.

𝒘𝒘𝒇𝒇 = 𝒘𝒘𝒅𝒅 − 𝑷𝑷 𝒘𝒘𝒄𝒄𝟏𝟏 − 𝑷𝑷

𝜸𝜸𝒅𝒅𝒇𝒇 = 𝟏𝟏 − 𝑷𝑷 𝑮𝑮𝒄𝒄 𝜸𝜸𝒘𝒘𝑮𝑮𝒄𝒄 𝜸𝜸𝒘𝒘 − 𝑷𝑷 𝜸𝜸𝒅𝒅𝒅𝒅

This equation is accurate for+ No. 4 oversize fractions up to 40% or +3/4” fractions up to 30% .

•

Corrections for testing system deformationsAll deformation readings must be corrected for system compliance

If filter paper is used, correct for compression of the filter paper in both dry and wet conditions.

ASTM D4546-08, Method ASwell/Collapse Tests on Multiple Samples

Wetting-induced Strains

Initial height of specimen = h

Amount of dry compression = ∆ h 1

Height of specimen before wetting = h1 = h - ∆ h 1

Amount of swell or collapse deformation = ∆ h 2

𝜺𝜺𝒔𝒔 = ∆𝒉𝒉𝟐𝟐𝒉𝒉𝟏𝟏

swell strain

𝜺𝜺𝒄𝒄 = − ∆𝒉𝒉𝟐𝟐𝒉𝒉𝟏𝟏

collapse strain

Step 2- Strain Adjustment Factors

n1 = Reduction factor for partial wetting effect

n2 = Reduction factor to account for the presenceof the inert oversize material in the fill

n3 = Empirical factor to account for the interference of the oversize fraction with volume change of the finer fraction

Partial wetting parameter, n1

𝑛𝑛1 = 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑤𝑤𝑤𝑤𝑃𝑃𝑃𝑃𝑃𝑃𝑤𝑤𝑤𝑤 𝑠𝑠𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑤𝑤𝐹𝐹𝐹𝐹𝑃𝑃𝑃𝑃 𝑤𝑤𝑤𝑤𝑃𝑃𝑃𝑃𝑃𝑃𝑤𝑤𝑤𝑤 𝑠𝑠𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑤𝑤

How to Estimate n1

- Based on lab partial wetting tests, coupled with forensic water content or degree of saturation data in the field

- Based on lab suction-controlled tests and soil-water characteristic tests, coupled with field measurements of matric suction

Parameter n3

- Empirical factor for the effect of interference of the large amount of oversize particles with volume change of the finer fraction

- Additional research is needed for testing large compacted specimens including the oversize

- Use n3 = 1 for soils with + No. 4 oversize fraction up to 40%, or +3/4” oversize fraction up to 30%

εadjusted = n1 . n2 . n3 εmeasured

Step 3 Compute Heave and Settlement

- Using the fill’s as-compacted bulk density, calculate vertical stresses at various depths; include surcharge pressures if any.

- Select the corresponding strains from the swell-collapse curve.

- Plot a curve showing the swell and collapse strains with depth.

- Calculate the cumulative deformation of the ground surface.

Test Method B- ASTM D4546-14Forensic analysis of a partially wetted fill

Take intact “undisturbed” samples from forensic borings; assemble samples in consolidometers; apply to each sample a single stress equal to the overburden stress plus the effect of surface loads, if any; unload and reload, measure dry compression. Any difference between dry compression after the first and the second load application is indication of sample disturbance;

Inundate each sample with tap water and measure the wetting-induced strain;

Plot the wetting-induced strains versus fill depth, and compute the remaining heave or settlement of the fill. Apply adjustment factors n1, n2 and n3, if any;

Using additional intact samples, measure the in-situ water contents and plot the forensic water content profile with depth. Plot the final water contents of the tested samples with depth. Also, using the fill placement records, plot the profile of the placement water contents.

Test Method CLoad-induced deformation after wetting-induced heave or settlement. Additional fill or new loads on top of an existing fill.Loading-after-wetting test.

The first part of the test is similar to Method A (reconstituted specimens), or Method B (intact samples). After inundation and after completion of swell or collapse, apply additional loads as in a consolidation test.

Plot the load-induced strains versus fill depth, and compute the fill deformation due to new loads.

Some ComplicationsOther methods that use Method C or variations of Method C instead of Method A

- Loading-after wetting consolidation test on a single specimen

- Swell-consolidation (SC) test and constant swell (CS) test

- Swell-consolidation (SC) test and empirical estimation of Swell Pressure

- Other

Method C- Multiple loads on one specimen(loading after wetting)

Method A- Single loads on multiple specimens(wetting after loading)

Comparison of Method A and Method C (Noorany 1992)

Nonlinearity of Method A data in Semi-Log Plots (Rosenbalm 2013)

Part 3LATERAL FILL EXPANSION (LFE)

LFE Method

Step 1- Triaxial swell-collapse tests on compacted specimens;measure wetting-induced vertical and radial strains for a range of K values

Step 2- Plot two sets of curves: wetting-induced vertical and radial strains versus major principal stress

Step 3- Adjust the vertical and radial strain curves by usingn1, n2, n3 as applicable

Step 4- Calculate vertical and lateral deformationof different points using a finite-element or a finite-difference code

Results of Triaxial Swell/Compression TestsSoil FV-1, w=15.0%, RC=90%

LFE Computation Codes

1992, “SWELL” by Joel Sweet- Noorany et al., 1992

1999, FLAC by ITASCA- Cundall, P. and Detournay C. 1999

- Noorany et al. 1999

Results of LFE AnalysisVertical and horizontal deformation for any point

Differential vertical and horizontal deformations

Calculations with different assumed K values

Calculations with different partial wetting assumptions

Lateral movement data for different setback distances from the slope crest

Part 4MITIGATION OF HEAVE, SETTLEMENT AND LFE STRUCTURAL FILLS AND EMBANKMENTS

Mitigation of Deformation of Fills- If feasible, use different soil types for different fill zones

- Different “performance-based” compaction specifications for different fill zones (….subject of another talk)

- Analyze different fill geometries and wetting conditions

- Structural design for thick slabs and deep foundations(Nelson, et al.; Briaud, et al.)

- Wide setbacks on top of descending slopes

- Landscape and hardscape layouts that can accommodate LFE

• Shortcuts based on local experience

• Cost

• Benefit

Summary

Additional InformationSee the attached list of references.

Questions

Comments

REFERENCES

ASTM D 4546-14 "Standard Test Method for One-Dimensional Swell or Collapse of Soils", ASTM Book of Standard Specifications, Designation: D 4546-14.

ASTM D 4718- 87 “Standard Practice for Correction of Unit Weight and Water Content for Soils Containing Oversize Particles”, ASTM Book of Standard Designation: D4718.

Brandon, T., Duncan, J.M., and Gardner, W. (1990), “Hydrocompression Settlement of Deep Fills”, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 116, No. 10.

Briaud, J.L. et al., (2016), “Stiffened Slab-On-Grade on Shrink-Swell Soil: New Design Method”, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 142, No. 7.

Cundall, P. and Detournay, C. (1999), “A FLAC Implementation of Noorany Method to Model Swell/Collapse Caused by Wetting”, Itasca Consulting Group, Inc. Minneapolis, MN

Houston, S. L., and Houston, W. N. (1997). “Collapsible Soils Engineering,”. Geotechnical Special Publication No. 68, Unsaturated Soil Engineering Practice, ASCE, New York, NY.

Houston, S. L., and Houston, W. N. (2017). “Suction-Oedometer Method for Computation of Heave and Remaining Heave”, Proc. ASCE Pan Am Unsaturated Soils Conference, Dallas, Texas.

Justo, J. L., Delgado, A., and Luiz, J. (1984). “The Influence of Stress-Path in the Collapse-Swelling of Soils at the Laboratory,” Proc. 5th Int’l. Conf. on Expansive Soils, Adelaide.

Nelson, D.N., Chao, K.C., Overton, D.D. and Nelson, E.J. (2015). Foundation Engineering for Expansive Soils, John Wiley & Sons, New York, NY.

Noorany, I. (1992). "Stress Ratio Effects on Collapse of Compacted Clayey Sand", Discussion, Journal of Geotechnical Engineering, ASCE, Vol 118, No.9.

Noorany, I., Sweet, J. A. and Smith, I. M. (1992). "Deformation of Fill Slopes Caused by Wetting". Proceedings of the ASCE Conference on Stability and Performance of Slopes and Embankments II, ASCE Geotechnical Special Publication No. 31, Berkeley CA.

Noorany, I. and Stanley, J. V. (1994). "Settlement of Compacted Fills Caused by Wetting" Proc. Vertical and Horizontal Deformations of Foundations and Embankments, ASCE, Vol 2 ASCE Settlement '94 Conference, College Station TX.

Noorany, I. and Houston, S. (1995). "Effect of Oversize Particles on Swell and Compression of Compacted Unsaturated Soils". Geotechnical Special Publication No. 56, Static and Dynamic Properties of Gravelly Soils. ASCE, New York, NY.

Noorany, I. and Scheyhing, C. (2015). “Lateral Extension of Compacted-Fill Slopes in Expansive Soils”, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 141-No. 1.

Noorany, I. (2017). “Soil Tests for Prediction of One-Dimensional Heave and Settlement of Compacted Fills”, Proc. ASCE Pan Am Unsaturated Soils Conference, Dallas, Texas.

Rosenbalm, D. C. (2013). "Volume Change Behavior of Expansive Soils Due to Wetting and Drying Cycles", Ph.D. Thesis, Arizona State University.

Stark, T.D., and Wilks, S.T. (2017). “Post-Construction Deformation of Compacted Fills Caused by Wetting”, Presented at ASCE Geotechnical Frontiers 2017, Geotech. Special Publication 280.