The document summarizes a landslide early warning system project that aims to more accurately model slope stability for Hawaii DOT. It describes testing new instrumentation for soil characterization, including laser diffraction for grain size distribution and tensiometers for field suction measurements. Results found laser diffraction and tensiometer measurements matched well against standard tests and could provide reasonable estimates for slope stability modeling.

1. Landslide Early
Warning System
Wyatt Bartlett- UH Manoa
John Nihi- UH Manoa
Melia Iwamoto - Graduate Student Advisor
Phillip Ooi - Faculty Advisor
UH Mānoa Geotechnical Engineering Lab

2. Overview
1. Objectives
2. Project Locations
3. Field Instrumentation
4. Lab Methods
5. Results
6. Discussion of Findings
7. Summary & Conclusions

3. Objectives
1. Soil Characterization
• Hydrometer (standard) vs.
Laser Diffraction (new)
2. Suction Characterization
• SWCC = w% vs. suction
• Theoretical vs. Lab vs. Field
Create more accurate slope stability models for Hawaii DOT

4. Project Locations
Likelike Highway Pali Highway

5. Monitoring Instruments
• Inclinometer – Lateral Displacement
• Tensiometer – Suction
• Water content sensors – Water content
• Rain gage - Precipitation

6. Datalogger
• Program collection frequency
• Collects data remotely
• Powered by solar energy

7. Lab Methods
1. Grain Size Distribution
• Wet Sieve and Hydrometer (Conventional)
• Laser Diffraction (New and being studied)
2. Soil Water Characteristic Curve
• Pressure Plate - Lab
• VSA (Vapor Sorption Analyzer) - Lab
• Tensiometers - Field
• SoilVision - Theory

8. Grain Size Distribution
Hydrometer Laser DiffractionWet Sieve
4 days 15 minutes1 day

9. Suction in the Lab
Pressure Plate Vapor Sorption Analyzer

10. Suction in the Field
• Tensiometer to measure suction

11. Results - Grain Size Distribution
0
10
20
30
40
50
60
70
80
90
100
0.000010.00010.0010.010.1110
%Passing
Diameter (mm)
Wet Sieve and Hydrometer vs. Laser Diffraction
Horiba4 Hydrometer4

12. Discussion of Findings
Hydrometer vs. Laser Diffraction
• Compared to Di Stefano, et al. (2010)
Di Stefano, C., et al. (2010) Comparison between grain-size analyses using laser diffraction and sedimentation methods. Biosystems Engineering 106 (2010) 205-215

13. Results - Suction
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
1 10 100 1000 10000 100000 1000000
GravimetricWaterContent
Suction (kPa)
Soil Water Characteristic Curve
Soil Vision (B2-11)
Measured (Field MPS-6)
Measured (Lab - VSA)
Measured (Lab - PP)

14. Summary and Conclusions
Grain Size Analysis
• Laser diffraction provides a reasonable estimate of the
soil grain size distribution compared to wet sieve and
hydrometer tests
Soil Water Characteristic Curve
• Suction measurements in the lab matches well with
those in the field
• They also match well with theoretical curves
These findings will be useful in development of the LEWS

15. Acknowledgements
• Special thanks to:
• NSF SEE 3 Program
• Melia Iwamoto
• Marica Ottorogram
• Phillip Ooi
• Yogi Kwong Engineers
• HDOT

16. Q & A

17. References
• Di Stefano, C., et al. (2010) Comparison between
grain-size analyses using laser diffraction and
sedimentation methods. Biosystems Engineering
106 (2010) 205-215
• Jotisankasa, A. and Vathananukij, H. (2008)
Investigation of soil moisture characteristics of
landslide-prone slopes in Thailand. International
Conference on Management of Landslide Hazard
in the Asia-Pacific Region