THESIS APPROVAL The abstract and thesis of William J.

156 Pages·1999·11.92 MB·English

THESIS APPROVAL
The abstract and thesis of William J. Burns for the Master of Science in Geology
presented January 7, 1999, and accepted by the thesis committee and the department.
COMMITTEE APPROVALS: __________________________________________
Kenneth Cruikshank, Chair
__________________________________________
Scott Burns
__________________________________________
Marvin Beeson
__________________________________________
Trevor Smith
Representative of the Office of Graduate Studies
DEPARTMENTAL APPROVAL: __________________________________________
Ansel Johnson
Department of Geology
ABSTRACT

An abstract of the thesis of William J. Burns for the Master of Science in Geology
presented January 7, 1999.
Title: Engineering Geology and Relative Stability of the Southern Half of Newell Creek
Canyon, Oregon City, Oregon.

This study investigates the engineering geology and relative slope stability of the
southern half of Newell Creek Canyon, Oregon City, Oregon, located partially inside the
urban growth boundary of Portland where there is increasing pressure for development in
areas of geologically hazardous terrain.
Within the study area, features associated with landslides were mapped and
categorized according to their relative age (active, inactive-young, and inactive-mature)
and the depth to the failure plane (deep or shallow-seated). These features were then
examined and 79 landslides were identified. Sixty-five of the slides were classified as
shallow-seated or having a failure plane £ 4.5 meters below the ground surface. Most of
the 14 deep-seated landslides in the study area were classified as inactive-young and
inactive-mature and generally had a much greater area (1,600m2 to 256,000m2) than the
shallow-seated slides (40m2 to 6,100m2).
One deep-seated landslide, representative of most of the deep-seated slides, was
examined in detail and a stability analysis confirmed the current, relatively stability and
the potential for reactivation. The Spady Landslide, a typical shallow-seated landslide,
was examined in detail by mapping the slide after its initial failure in 1996 and then
again after it grew in size from 2,200 m3 to 14,600 m3 in order to examine how these
types of slides grow and the resulting stability of the area immediately adjacent to these
slides. Finally, a stability analysis was performed on all of the residual soils to evaluate
potential shallow-seated landsliding.
From the record of landslide features and geologic conditions, the Engineering
Geologic Map was constructed. This map, along with the stability analysis on existing
landslides and areas with no existing features resulted in the construction of the
interpretive Relative Stability Map. This Relative Stability Map was divided into three
zones with the following percents of the study area: moving ground (5%), potentially
unstable ground (56%), and stable ground (38%). The two maps resulting from this
study along with the text serve as an engineering geologic report for use by engineers and
planners in making educated decisions for future development.
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
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Acknowledgments

I am very grateful for all the assistance given to me, without which this study
would have been very difficult to complete. Dr. Kenneth Cruikshank suggested the
research topic and methods for analyzing the problems. His insight on field mapping,
landslide mechanisms, and stability analysis have proven to be very helpful. Dr. Scott
Burns proved very helpful by suggesting the study area and providing an excellent
background on slope stability in this area. Dr. Marvin Beeson helped me with
delineating the highly irregular stratigraphy within the Troutdale Formation and the rest
of the geologic units within the study area.
Many fellow students here at Portland State University have helped to complete
some of the detailed mapping needed for this study. David James and Tom Braibish
mapped the Spady Landslide with me in 1996 and did some of the soil analysis and
drafting of the detailed map. Stuart Cowburn, Glenn Gettemy, Robert Schlichting, and
Sean Wilson mapped the Spady Landslide after the second failure in 1997. Their help
proved essential for the completion of this study.
I am indebted to the city of Oregon City, especially Jessica Schriever, who
provided the digital data for the creation of the base map used throughout this study.
Bob Pinotti spent many hours helping create this base map and setting the stage for the
creation of the paper and digital output maps. I am also indebted to Sha Spady for letting
me run around her property mapping and taking soil samples for several months. Ron
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Jennison, at the Oregon Department of Transportation, graciously gave me bore hole
logs and aerial photographs taken during the construction of Highway 213.
Last but certainly not least, I wish to thank my family. My wife, Amy, helped me
with field work and spent many hours proofreading. She has lent moral support
throughout my studies here. My sister, Tonia, also helped me with field work and
continues to lend her moral support. My uncle, Gary Quinn, is an excellent mentor who
sparked my interest in slope stability studies. I’d also like to thank my brother and sister
in law, Greg and Audrey Brown-Spitz, for their final editing. Finally, I’d like to thank
my parents, Joe and Kay, who gave me tremendous moral support and financial help,
without which this would have been infinitely more difficult, if not impossible.
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TABLE OF CONTENTS
Acknowledgments.................................................................................................................i
Table of Contents................................................................................................................iii
List of Tables........................................................................................................................v
List of Figures.....................................................................................................................vi
List of Plates........................................................................................................................ix
Chapter 1: Introduction........................................................................................................1
Chapter 2: Description of Study Area.................................................................................2
Geology..........................................................................................................................4
The Columbia River Basalt Group..........................................................................7
Sandy River Mudstone and the Troutdale Formation.............................................7
The Boring Lavas....................................................................................................9
Willamette Silt.......................................................................................................10
Residual Soils........................................................................................................10
Man-Made Fill.......................................................................................................11
Chapter 3: Methods............................................................................................................17
Literature Review.........................................................................................................17
Base Map Acquisition and Creation............................................................................18
Field Mapping..............................................................................................................18
Detailed Mapping of the Spady Landslide..................................................................19
Laboratory Work and Stability Analysis.....................................................................20
Creation of Digital Data Maps....................................................................................20
Creation of Interpretive Maps......................................................................................21
Chapter 4: Landslide Features and Their Relative Ages...................................................22
Landslide Features.......................................................................................................22
Extensional Features..............................................................................................22
Shear Features........................................................................................................28
Shortening Features...............................................................................................30
Associated Features.....................................................................................................31
Morphological Changes of Landslide Features with Time.........................................33
Active Features......................................................................................................38
Inactive-Young Features........................................................................................39
Inactive-Mature Features.......................................................................................40
Chapter 5: Causes of Landslides in the Study Area..........................................................42
Material Properties.......................................................................................................43
Shear Strength Reduction......................................................................................46
Geometry-Effect of the Shape in a Landslide.............................................................48
Chapter 6: Types of Landslides Identified in the Study Area...........................................51
Deep-Seated Landslides...............................................................................................53
The Highway 213-Morton Road Landslide..........................................................54
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The Highway 213, Mile Post 2.1 Deep-Seated Landslide....................................61
Deep-Seated Landslide Conclusions.....................................................................62
Shallow-Seated Landslides..........................................................................................63
The Spady Landslide.............................................................................................65
The 1996 Failure of the Spady Landslide ...................................... 68
Growth of the Spady Landslide: The 1997 Failure......................... 74
Discussion of the Spady Landslide................................................ 79
Conclusions for Deep and Shallow-Seated Landslides..............................................81
Chapter 7: Delineating Potentially Unstable Areas...........................................................83
The Engineering Geologic Map..................................................................................83
The Relative Stability Map..........................................................................................84
Stable Ground........................................................................................................85
Potentially Unstable Ground.................................................................................85
Moving Ground.....................................................................................................87
Residual Soils Stability Analysis..........................................................................87
Chapter 8: Conclusions......................................................................................................92
Suggested Engineering Geologic and Geotechnical Investigation.............................93
Suggested Land Use Planning.....................................................................................94
Suggested Further Study..............................................................................................94
References..........................................................................................................................96
Appendix A......................................................................................................................100
Appendix B......................................................................................................................109
Appendix C......................................................................................................................129
Plates.......................................................................................................................In Pocket
v
LIST OF TABLES
Number Page
Table 1: Residual soil properties examined through the soil series in the study area
(after Gerig, 1985) (* Indicates no data available)...............................................13
Table 2: Residual soils engineering properties examined through the soil series in
the study area (after Gerig, 1985) (* Indicates no data available)........................14
Table 3: Description of morphological feature changes with time (after McCalpin,
1974)......................................................................................................................37
Table 4: Highway 213-Morton Road Landslide Stability Analysis Results, assuming
undrained conditions.............................................................................................59
Table 5: Material properties for residual soils and bedrock units (beds) within the
extent of the Spady Landslide...............................................................................71
Table 6: Generalized material properties for the three catagories of residual soils..........87
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LIST OF FIGURES
Number Page
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).......................................................................3
Figure 2: Miocene to Pleistocene stratigraphy of Newell Creek Canyon (after
Schlicker and Finlayson, 1979; Tolan and Beeson, 1984).....................................5
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).............................................................................................6
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).........12
Figure 5: Location map of man-made fill, large cut-slopes, and current development
within the study area (after Oregon City, 1997; METRO, 1997).........................15
Figure 6: Block diagram of typical landslide, illustrating landslide features and their
spatial relationships (after Cruden and Varnes, 1996)..........................................23
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 (8(cid:212) · 11 inch field notebook for scale)....................................25
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.......25
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).............................................................................27
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.................................29
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..............................................................................................................34