Lecture 8: Geologic Investigations Flashcards
aims to foresee problems that may
arise and figure out possible ways to address them.
Site investigation
Data needed for Site investigation
- Soil and rock underlying the site (kinds, properties, probable issues)
- Groundwater level
- Extent of weathering
- Hazards (landslide, earthquake, etc.)
3 General Phases of Site Investigation
- Desk Study
- Preliminary Reconaissance
- Site Exploration
Aims to gather and study all available literature and data related to the site
Desk Study
maps that show the geology of an area including data related to the rock units and distribution in the area, geologic structures, age relationships of the rocks, as well as cross section view of the map.
GEOLOGIC MAPS
shows mainly the elevation data
related to the map. It uses contour lines to show which areas are at the same altitude/elevation and thus allows for visualization of flat areas vs slope areas and how steep slopes are.
TOPOGRAPHICAL MAPS
show data and distribution of soil in an area.
Soil Maps
shows the site’s susceptibility to various
hazards like earthquake or liquefaction
Hazard Maps
based on the expected structure, one can estimate how much load will be transferred to the ground
POSSIBLE LOADS
certain important structures have stricter rules in design and construction
IMPORTANCE
some structures can have deformation like settlement of floor while some like factories that require precision (due to machine connections to each other) may have more stringent design considerations related to deformations.
TOLERANCE TO DEFORMATION
The amount of effort put into desk study must be based on several factors. What are these factors
- Project complexity
- Project extent/size
- Site conditions (possible issues based on material on site)
desk study should provide you with a list of_____________
This ensures efficiency.
what data is still
needed and what exploration tests will be needed to get them.
In 2D Topographic maps, if a slope is steep, you will see _____ as it increases its height
quite quickly
closer lines
A _________usually covers very large
areas. Provides a bigger picture of the site
geologic map
USGS maps, they range from scales of ______ to _________
1:20,000 to 1:2,500,000
Limitation of Geologic Maps
Does not necessarily have quantitative properties that we want to know about our site.
Geologic Mapping
Scientific process to map geologic features in the area concerned and create maps of it.
Process of Geologic Mapping
- The first step is the traditional field visit where a geologist walks around and takes FIELD NOTES which will then be used to make geologic maps.
- These data can be supplemented by aerial images and remote sensing and other technologies.
Map of SURFACE GEOLOGY
shows data about material
occurring at ground surface including alluvium, mud, and other materials.
it shows materials that have been “drifted”
and covers the more solid units underneath
Drift Edition
Map with no drift shown (like looking at ground if drift material are removed), only the SOLID geology underneath
Solid Edition
SUBSURFACE GEOLOGY MAPS
ISOCHORE MAPS ISOPACHYTE MAPS HORIZONTAL PLANE MAPS STRUCTURAL CONTOUR MAPS GEOPHYSICAL MAPS
ISOCHORE MAPS
Isochore maps show the vertical thickness of geologic units using isochore lines (lines that join points with same vertical thickness)
ISOPACHYTE MAPS
Uses isopachyte lines that join points of same
stratigraphical thickness rather than vertical thickness. This is more complicated and more used by geologists than engineers.
HORIZONTAL PLANE MAPS
maps the geology at some horizontal plane
below the surface. Visualize chopping off certain thickness from the surface and mapping what you see afterwards.
STRUCTURAL CONTOUR MAPS
maps structural surfaces (faults,
unconformities) and the contours is based on the dip value of the surface being illustrated.
GEOPHYSICAL MAPS
maps from geophysical methods (discussed later on)
showing information based on the data gathered from whichever geophysical method was used
Key information you must understand from the geologic maps
AGE OF UNITS, STRUCTURAL RELATIONSHIP OF UNITS, make 3d maps by making geologic maps at different levels and stacking them, geological sections
shows the relative ages of strata in a map and is usually found at the margin of the map
STRATIGRAPHIC COLUMN
TECHNOLOGY FOR MAPPING
- GIS
- GPS
- Remote Sensing
- Aerial Images
Technology that allows easier management of spatial data. Used for data capturing, storing, retrieving, editing, analyzing, comparing, and displaying.
Geographic Information System
Other data that can be used in GIS
remote sensing, aerial
images, and other maps from geophysical methods (gravimetric maps, aeromagnetometry maps, etc.).
GLOBAL POSITIONING SYSTEM
• Allows determination of precise location.
• This gives geologists the ability to assign a structure/unit of
importance to a coordinate easily
Uses aircraft or satellites to measure reflected and
emitted radiation to monitor physical characteristics of an area or structures in an area.
REMOTE SENSING
The data measured from Remote Sensing can
take the form of __________
1 acoustic waves
2 other electromagnetic spectrum waves
Two main Systems used in Remote Sensing
- Infrared Lin Scan
2. Side Looking Airborne Radar
uses emitted electromagnetic
radiation related to temperature of objects.
Infrared Lin Scan
Pulses of energy are shot from an aircraft, bounces off the ground, and is received by the aircraft again. This allows creation of photographs from
recorded data. One of its advantages is that it is not affected by cloud cover.
Side Looking Airborne Radar
The images from remote sensing can:
• Help in study of landforms, their characteristics, which may
provide information as to what comprises them.
• For places with limited maps, it can be useful in creation of
other maps related to the terrain or geology, among others.
reflects lasers to create ground elevation maps
Light Detecting and Ranging System
Applications of Remote Sensing in Civil Engineering
• Water resources studies and modelling • Disaster risk management related research for natural calamities • Environmental observation • Urban monitoring and studies
• Image usefulness depends on its quality as well as what can be shown in the photograph, can be used with a stereoscope to make a 3D
ground surface model, which can then be used to make topographic
maps.
Aerial Images
Its done to supplement the desk study and give a better
report.
PRELIMINARY RECONAISSANCE
site inspection or walkover
survey
PRELIMINARY RECONAISSANCE
A report is made summarizing all details related to the project and site, the possible issues (and solutions), as well as future work suggestions to further determine feasibility of project or rule-out possible issues and data to be used for design phase.
PRE-SITE EXPLORATION REPORT
