Engineering Geology And Relative Stability Of The Southern Half of Newell Creek Canyon, Oregon City, Oregon

by
William J. Burns

A thesis submitted in partial fulfillment of the
requirements for the degree of

MASTER OF SCIENCE
in
GEOLOGY

Portland State University
1999

This page is the index to the HTML copy of the thesis. The thesis is also available in the following format:

Table of Contents

List of Tables

Table 1: Residual soil properties examined through the soil series in the study area (after Gerig, 1985) (* Indicates no data available)

Table 2: Residual soils engineering properties examined through the soil series in the study area (after Gerig, 1985) (* Indicates no data available)

Table 3: Description of morphological feature changes with time (after McCalpin, 1974)

Table 4: Highway 213-Morton Road Landslide Stability Analysis Results, assuming undrained conditions

Table 5: Material properties for residual soils and bedrock units (beds) within the extent of the Spady Landslide

Table 6: Generalized material properties for the three catagories of residual soils

List of Figures

Figure 1: Location of the study area in the southern half of Newell Creek Canyon, Oregon City, OR.  Boundaries include: Morton Road (north), Molalla Avenue (west), Beaver Creek Road (south) and Holly Lane (east) (after Oregon City, 1997; METRO, 1997)

Figure 2: Miocene to Pleistocene stratigraphy of Newell Creek Canyon (after Schlicker and Finlayson, 1979; Tolan and Beeson, 1984)

Figure 3: Geologic map of the study area displaying the contact between the Sandy River Mudstone/Troutdale Formation and the Boring Lavas where many of the landslides are located (after Schlicker and Finlayson, 1979; Oregon City, 1997; METRO, 1997)

Figure 4: Soil series map of the study area displaying the distribution between the Xerochrepts and Haploxerolls (92F) and Helvetia (37D) Series containing steeper slopes with thinner soils and the Bornstedt (8B, 8C), Jory (45B, 45C), and Woodburn (91B, 91C) Series with low to moderate slopes and thicker soils (after Gerig, 1985; after Oregon City, 1997; METRO, 1997)

Figure 5: Location map of man-made fill, large cut-slopes, and current development within the study area (after Oregon City, 1997; METRO, 1997)

Figure 6: Block diagram of typical landslide, illustrating landslide features and their spatial relationships (after Cruden and Varnes, 1996)

Figure 7: Fresh tension crack located above head scarp of the Hilltop Avenue landslide, located at the dead end of Hilltop Avenue in the southwest section of the study area (8½ ´ 11 inch field notebook for scale)

Figure 8: Transverse cracks formed as a fill failure flows over the lesser disturbed natural stratigraphy.  View looking down at west R & B Leasing landslide

Figure 9: View looking up at head scarp of the Spady Landslide after the February 1996 failure displaying a continuous escarpment of bare soil with a concave downslope shape.  This is typical of a fresh head scarp on an active landslide (plane table survey rod = 15 ft)

Figure 10: Change in vegetation size, from large (older) trees in the foreground (left side of picture) to smaller (younger) trees in the background (on landslide), divided by a shear zone marked by a small gully.  This slide is located in the northern portion between Newell Creek and Highway 213

Figure 11: View down the debris flow filled channel below the Spady Landslide after the first failure (February 1996), displaying marginal levees and creek channel filled with soil/debris.  It is approximately 15 meters wide and extends for approximately 60 meters beyond the large, downed tree in foreground

Figure 12: Ponded channel caused by debris flow from the second failure (March 1997) of the Spady Landslide

Figure 13: Block diagram of idealized landslide features displaying morphological changes with time: A) Active, B) Inactive-Young, and C) Inactive-Mature Features (after McCalpin, 1974)

Figure 14: Infinite slope diagram illustrating parameters and equations for the factor of safety and the critical slope thickness for a slope with seepage parallel to the slope

Figure 15: Method of slices (modified Bishop Method) parameters and equation for calculating the factor of safety: (A) general diagram displaying circular slip surface and slices and (B) detail of forces acting on a single slice.  Side forces not included in Bishop Model, added in Janbu (Bishop, 1955)

Figure 16: Histogram of Frequency versus exposed scarp for all the landslides in the study area.  Note the dividing depth between shallow-seated and deep-seated at 4.5 meters

Figure 17: Plan view of surficial features identified for The Highway 213-Morton Road Landslide, a deep-seated landslide

Figure 18: Cross-section A-A' through the Highway 213-Morton Road, deep-seated Landslide displaying the Bishop stability analysis calculated failure plane for the current conditions and the generalized stratigraphy and approximate material parameters from bore-hole and well logs

Figure 19: Reactivation of the Dewey-Warren Street, deep-seated landslide with destroyed (red tagged) house in the background.  An 8 ½ inch by 11 inch size field notebook is on the scarp for scale.  Displacement measured on the scarp only totaled 0.3 meters of horizontal and 0.5 meters of vertical

Figure 20: Oblique arial photograph of the active, shallow-seated Highway 213-mile post 2.1 landslide on the toe of the larger deep-seated slide.  This slide occurred during construction of the highway in the summer of 1984 and is indicated by arrows.  Also noted is the rock buttress located in the cutslope above the slide (after ODOT, 1998)

Figure 21: Map of the entire Spady Landslide after the 1996 failure.  Includes the extent of the debris flow and outline of the 1997 failure (James et al., 1996)

Figure 22: Histogram of monthly precipitation for Oregon City from 1996 to 1997 (August) (after National Weather Service, 1998)

Figure 23: Map of the entire extent of the 1997 Spady Landslide failure. Includes the debris flow section of the landslide and the ponded channel (Wilson et al., 1997)

Figure 24: Graph of the factor of safety versus slope angles for the residual soils in the study area with a constant water table at a depth of 0.5 m.  Note the critical slope angles for each category, above which the factor of safety falls below 1.5

Figure 25: Map of actual slope angles within the study area and the relation to the residual soils

Figure 26: Map of residual soil series with factors of safety less than 1.5 and the approximated outlines of mapped shallow-seated landslides

List of Plates

Plate 1: The Engineering Geology Map of the Southern Half of Newell Creek Canyon, Oregon City, Oregon

Plate 2: The Relative Slope Stability Map of the Southern Half of Newell Creek Canyon, Oregon City, Oregon

Plate 3: Maps and Cross-Sections of 1996 and 1997 Spady Landslide: Growth of a Shallow-Seated Landslide, Newell Creek Canyon, Oregon City, Oregon

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