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1. Planning, Conducting and Reporting
of Geotechnical
‫اول‬ ‫فصل‬
Transportation Engineering Master Program
1

2. THE NEED TO ASK THE RIGHT
QUESTIONS
• The French detective, Bertillon, have a statement: “We only
see what we observe, but we can only observe that which is
already in the mind’’.
• Experience in engineering site investigations show every
foundation failure and contractual dispute due to ‘changed
geological conditions. There are two types of questions,
namely:
• – engineering questions, which relate essentially to the
design, construction and operation of any structure of the
type proposed and
• – geological questions, which arise from understanding of
the site geological environment and its likely influence on
the design, construction and operation of the projects. 2

3. Geotechnical Engineering Questions
• For Transportation Engineering (TE)which are
intended to Highways and Railways and there
structures like bridge, Tunnels etc., it is obvious that
important questions must relate to the permeability,
seepage, strength and compressibility of the
foundations, slope stability. However, there are many
other equally important questions. 3 main processes
involved in TE, their principal effects on the site
environment, and some resulting questions for the
designer and site investigator, are as follows:
3

4. Continues…
1. Excavation: To reach suitable levels for TE
structures base and foundations and fillings,...
2.Foundation loading: Imposed by the structure,
raises questions of compressibility of the foundation
and its shear strength against sliding retaining
structures, filling subgrade and earthquake loading.
3. Inundation (
‫آبگرفتگی‬
) – Filling the storage: Causes
changes to the groundwater regime and dewatering of
the roads and railways alignments.
4

5. Geological questions
• The following notes highlight the importance of
asking and finding the answers to such questions, and
of relating them to other site factors such as climate
and topography and the proposed development.
1- Questions relating to rock and soil types, climate
and topography
• The relative importance of any one of the
engineering questions:
5

6. Continues…
• 1. Sources of materials, for the following purposes:
– Earthfill, for the core or other zones.– Filters.
– Rockfill.– Rip-rap.– Concrete aggregates.– Road
Pavements.– For each material: Location of
alternative sources, qualities/suitability’s, quantities,
methods for– winning and processing. Overburden
and waste materials and quantities.
Possible use of materials from required excavations,
cutting, other works and TE structure's foundations.
6

7. Continues…
3-Rivers
Levels and floods
Stability of slops inside an outside of embankment
Erodibility of soils
4- Embankment
• Location, Nature of materials to be excavated..
• Cutting and filling and dewatering
• Permeability, compressibility, shear strength,
settlements and Monitoring systems
7

8. Continues…
5- Pavement
• Type
• Material
• Dewatering
• Soil subgrade
6- HW-Bridge
Foundation
Pairs and abetments
superstructures
7- Railway tracks
• Soil subgrade
• sub blasts
• blasts
- Bridge- RW
Foundation
Pairs and abetments
superstructures
8

9. Continues…
7- De stressing
• Chemical weathering
of rocks and soils
• Deposition of cement
• Erosion of wind and
water
• Deposition (
‫نشین‬ ‫ته‬
‫شدن‬
) of sediment
• Creep, land sliding
• Subsidence (
‫فرونشست‬
)
• Pressure by groundwater
• Freezing
• Burrowing (
‫زدن‬ ‫نقب‬
) by
animals
• Growth of vegetation
• Rotting of roots of
vegetation/buried timber
• Seismicity, i.e. shaking, or
displacement on a fault
• Volcanism and
• Glaciation 9

10. Questions relating to geological processes, i.e.
to the history of development of the site
• It is not enough, during the design and
construction of a major TE projects, to know
simply what rock or soil types are present, their
engineering properties and their approximate
Distribution
• The most important processes are usually the
youngest, commonly those relating to the near-
surface.
• This is partly because they will have had a major
influence on the strength and stability.
10

11. AN ITERATIVE (
‫تکرار‬
) APPROACH TO THE
INVESTIGATIONS
• The following notes relate to the four phases on Figure
4.1.
• Phase 1. First, the objectives of the work, or questions to
be answered, are defined.
• Phase 2. Existing geological, geotechnical and other data
relevant to the site are collected and compiled to give a
tentative (
‫تجربی‬
) geotechnical model (or models).
• Phase 3. The investigations are planned to confirm the
tentative answers and tentative geotechnical model and to
answer the outstanding questions.
• Phase 4. The investigations proceed in stages as planned.
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12. 12

13. PROGRESSION FROM REGIONAL TO LOCAL
STUDIES
• The geological studies in Phases 1 to 4 start with
consideration of the site location in relation to the global
tectonic situation, and should include study of the geology
of a broad region surrounding the site.
• This is necessary to assess the effects on the project of
large scale processes, some of which (Table 4.2) may have
potential to damage it.
• The regional geological studies are followed by geological
and geotechnical engineering studies at and near the site,
on intermediate and detailed scales.
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14. Broad regional studies
• Objectives
• 1. Major geological processes
• 2. To determine the regional stratigraphy (
‫زمین‬ ‫شناسی‬ ‫طبقه‬
) and
geological structure.
• 3. To explain the geomorphology of the project area in terms
of the regional stratigraphy, structure and geological history.
• 4. To draw attention to important features, major faults or
landslides, occurring at or close to the site, but not exposed or
recognizable at the site.
• 5. To get an appreciation of the regional groundwater
conditions.
• 6. To form a logical basis for the location and proving of
sources of construction materials.
14

15. REPORTING
• It is important during all stages, that the geotechnical
facts, interpretations, conclusions and decisions made
from them are recorded regularly by a system of formal
progress reports.
• A comprehensive report is essential at the end of each
stage, setting out the answers to the questions of that
stage and with recommendations for the next stage.
• The report (or a separate one) should include the results
of analysis and design, e.g, stability analysis, design of
filters.
• A formal system for checking and certification is needed
for all drawings and reports.
15

16. THE SITE INVESTIGATION TEAM
• 1. Knowledge of precedents (
‫سابقه‬
) .
• 2. Knowledge of geology.
• 3. Knowledge of soil and rock mechanics.
• 4. Knowledge of geotechnical and civil
engineering design.
• 5. Knowledge of civil engineering and TE
construction.
• 6. Knowledge of direct and indirect exploratory
methods.
• 7. Above average application.
16

17. SITE INVESTIGATION TECHNIQES
• A fundamental requirement for the investigation and
design of any project is accurate location and level of all
relevant data.
• Topographic maps at suitable scales are essential with
establishment on site of clearly identified benchmarks.
• All features recorded during the investigation should be
located and levelled, preferably in relation to a regional
coordinate system and datum
• A local system may be established provided that at some
stage during the investigation the relation between the
regional and local survey systems is determined.
17

18. Count…
• Topographic maps at several scales are required:
• – Regional maps, 1:250,000 with 20– 50m
contours to 1:25,000 with 10m contours.
• – Catchment area, 1:25,000 with 10m contours
to 1:2000 with 2m contours.
• – Project area, 1:1000 with 2m contours to 1:200
with 1m contours.
• – Individual engineering structures, 1:500 with
1m contours to 1:200 with 0.5m contours.
18

19. PHOTOGRAPHS AND PHOTOGRAPHS TAKEN
DURING CONSTRUCTION
• Interpretation (
‫تشریح‬
) of satellite images:
Standard LANDSAT images are at 1:100,000 scale
but images at 1:500,000 and 1:250,000 are also
available.
• – planning of access routes to and within the
project area,
• – location of potential sources of construction
materials
19

20. Interpretation of aerial photographs
• Coverage
• Coverage or scale, it is best to take new
photographs with the following advantages:
• – the photographs will show present conditions,
• – the required scales and coverage can be
specified and
• - the photographs can be used to prepare
topographic maps.
• Aerial photographs taken at different dates can
indicate changes in site conditions.
20

21. Interpretation
• Photo-geological interpretation using a stereoscope forms a
major part of the initial appraisal of regional and local site
conditions during the pre-feasibility and feasibility stages.
• A major advantage of aerial photography is that distance of
observation is not impeded by relief.
• The interpretation of geological structure.
• Landforms which reflect the structure of folded rocks show
up well on aerial photographs.
• In horizontal strata, mesa forms are common and, in dipping
strata, dip slopes and scarps indicate the direction and dip of
the bedding (Figure 5.1).
21

22. Continuous…
22

23. Continuous…
(b) Sketch showing lineaments
Aerial photograph and sketch showing lineaments in an area underlain by gently dipping
sandstones.
23

24. Photographs taken during construction
• Any review of an existing TE project should include
a thorough search for photographs taken during
construction, and systematic review of the
photographs.
• They are particularly valuable as a record of
foundation preparation and clean-up and for
assessing matters such as segregation of filter and
transition zones.
24

25. GEOMORPHOLOGICAL MAPPING
• Before embarking on a subsurface investigation
program, which may be (a) expensive and (b)
provide limited information of dubious relevance, it
is recommended that the surface evidence should
be systematically recorded.
• The ground surface reflects both the underlying
geology and the geomorphological development of
the area.
• Geomorphological mapping of surface features can
provide an indication of the distribution of
subsurface materials, their structure and areas of
possible mass movement, e.g. landslides. 25

26. Use of existing maps and reports
• Some useful data can often be obtained from
existing maps and reports prepared for
• other purposes.
• Maps showing the regional geology on scales ranging
from 1:100,000 to 1:1,000,000 are usually available
from government agencies. Some mining areas and
areas of existing or proposed urban development may
have been mapped at larger scales. The regional maps
are often accompanied by explanatory notes which are
useful.
26

27. 27

28. 28

29. Geotechnical mapping for the project
• Regional mapping
• When published regional geological maps are
available they are usually able to provide the
regional geological understanding required for a
project
• Geotechnical mapping
• Geotechnical mapping at and near the sites of the
proposed works is the key to the success of the site
investigation
29

30. …
• The maps show the following types of factual information as
shown on Figure 5.6.
– ground surface contours,
– geomorphic features, e.g. slope changes, areas of hummocky
ground,
– geological surface features, e.g. areas of rock outcrops, scree,
boulders and soil,
– features (
‫خصوصیات‬
) of in situ rock, e.g. rock types and their
boundaries, attitudes of bedding and foliation, the nature,
location and orientation of important geological defects such
as sheared or crushed zones,
– groundwater features, e.g. springs, seepage, areas of swamp
and vegetation indicating moist or wet ground,
30

31. 31

32. …
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