Environmental Engineering Reference
In-Depth Information
more dangerous than cuts made in level ground, even with the same cut inclination,
depth, and geologic conditions. The significant difference is likely to be seepage condi-
tions.
Side-hill fills
must always be provided with proper drainage, and on steep slopes reten-
tion usually is prudent.
Slope Activity Monitoring
Where potentially dangerous conditions exist, monitoring of slope activity with instru-
mentation is necessary to provide early warning of impending failures.
Hazard Zoning
In cities and areas where potentially dangerous conditions exist and failures would result
in disastrous consequences, such as on or near high, steep slopes or on sensitive soils near
water bodies or courses, development should be prohibited by zoning regulations.
Pertinent in this respect is a recent slide in Goteburg, Sweden (ENR, 1977), a country with
a long history of slope failures in glaciolacustrine and glaciomarine deposits. Shortly after
heavy rains in early December 1977, a slide occurred taking at least eight lives and carry-
ing 67 single-family and row houses into a shallow ravine. Damage was over $7 million.
The concluding statement in the article: “Last week's slide is expected to spark tighter con-
trols of construction in questionable areas.”
9.5.2
Regional and Total Slope Studies
Preliminary Phases
Objectives and Scope
The objectives of the preliminary phases of investigation, for either regional studies or for
the study of a particular area, are to anticipate forms, magnitudes, and incidences of slope
failures.
The study scope includes collection of existing data, generation of new data through ter-
rain analysis, field reconnaissance, and evaluation.
Existing Data Collection
Regional data to be collected include: slope failure histories, climatic conditions of precip-
itation and temperature, seismicity, topography (scales of 1:50,000 and 1:10,000), and
remote-sensing imagery (scales 1:250,000 to 1:50,000).
At the project location, data to be collected include topography (scales of 1:10,000 to
1:2,000, depending upon the area to be covered by the project, and contour intervals of 2
to 4 m, or 5 to 10 ft), and remote-sensing imagery (scale of 1:20,000 to 1:6,000). Slope sec-
tions are prepared at a 1:1 scale showing the proposed cut or fill in its position relative to
the entire slope.
Landform Analysis
On a regional basis, landform analysis is performed to identify unstable and potentially
unstable areas, and to establish preliminary conclusions regarding possible failure forms,
magnitudes, and incidence of occurrence. A preliminary map is prepared, showing topog-
raphy, drainage, active and ancient failures, and geology. The preliminary map is developed
into a hazard map after field reconnaissance. At the project location, more detailed maps are
prepared illustrating the items given above, and including points of slope seepage.
