Evaluating and Mapping the Stability of Slopes in Napa County

with a GIS-based Model

Dongyuan Wang

Ph.D candidate in geotechnical engineering

The University of Texas at Austin

December 7, 2000

Outline Outline Objective Background Data Preparation SINMAP Model Implementing SINMAP Outputs of SINMAP Discussions Acknowledgement

ObjectivesObjectives

Make the evaluation results visualized and accessible to the people.

Through this showcase, explore the feasibility of applying GIS in geotechnical engineering;Show how to evaluate and map the stability of slopes with SINMAP, a GIS-based model.

BackgroundBackground

Why Napa County?

•Development require more Lands;

•Landslide is one of main natural disasters plaguing the people in every country.

Why slope stability?

Why GIS?

Landslides in USALandslides in USA

Landslides in USALandslides in USA

Data Preparation(1) Data Preparation(1) DEMs: from USGS website

Only part of Napa CountySDTS GridScale:1:24000UTM projection

Soils: from USDA website SSURGOUseful files: comp,layer,

mapunit“Unifiled” field in “layer”

Data Preparation (2)Data Preparation (2)

Landslides: from USGS websiteIn geographic coordinates systemConvert it to UTM;Landslide PointsAdd “type” filed to

the shapefile

SINMAP SINMAP

An ArcView extension to calculate and map stability index of slopes based upon geographic information, primarily on DEMs.

Theoretical BasisInfinite slope model Topographic wetness index, R/T ratioDistribution: Uniform

Implementing SINMAP (1)Implementing SINMAP (1) Model Parameters

Gravity constant: 9.81 m/s2

Soil Density: 2000 kg/m3 Water Density: 1000 kg/m3·

Number of points in SA Plot: 2000 Calibration Parameters

T/R ratio: 2000-3000 m Dimensionless cohesion: 0.0-0.25

Angle of internal friction: 30-45 degrees

Lower wetness line percentage: 10%

Select DEM Grid Calibration area

Use “comp” file in soil date to create a calibration area; Clip “unifiled” field in “layer” to “comp” manually.Add landslide points;

Analyze Stability by adjusting calibration parameters

Implementing SINMAP(2)Implementing SINMAP(2)

Outputs (1) Outputs (1)

Outputs(2)Outputs(2)

DiscussionsDiscussions

1. Can we apply GIS in geotechnical engineering ?

2. Does SINMAP work well ?

3. Future work ?

AcknowledgementAcknowledgement Dr. Maidment at UT Dr. Tarbonton, Bob Pack and Craig Goodwin

at USU