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Source: FOUNDATION ENGINEERING HANDBOOK

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GEOTECHNICAL ENGINEERING

Downloaded from Digital Engineering Library @ McGraw-Hill (www.accessengineeringlibrary.com) Copyright © 2010 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.

GEOTECHNICAL ENGINEERING

Downloaded from DigitalEngineering Library @ McGraw-Hill (www.accessengineeringlibrary.com) Copyright © 2010 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.

Source: FOUNDATION ENGINEERING HANDBOOK

CHAPTER 2

SUBSURFACE EXPLORATION

2.1 INTRODUCTION
As discussed in Chap. 1, the first step in the foundation investigation is to obtain preliminaryinformation on the project and to plan the work. The next step is typically to perform the subsurface exploration. The goal of the subsurface investigation is to obtain a detailed understanding of the engineering and geologic properties of the soil and rock strata and groundwater conditions that could impact the foundation. Specific items that will be discussed in the chapter are as follows: 1. Documentreview (Sec. 2.2) 2. Purpose of subsurface exploration (Sec. 2.3) 3. Borings (Sec. 2.4), including a discussion of soil samplers, sample disturbance, field tests, boring layout, and depth of subsurface exploration 4. Test pits and trenches (Sec. 2.5) 5. Preparation of logs (Sec. 2.6) 6. Geophysical techniques (Sec. 2.7) 7. Subsurface exploration for geotechnical earthquake engineering (Sec. 2.8)8. Subsoil profile (Sec. 2.9)

2.2 DOCUMENT REVIEW
Prior to performing the subsurface exploration, it may be necessary to perform a document review. Examples of the types of documents that may need to be reviewed are as follows: Prior Development. If the site had prior development, it is important to obtain information on the history of the site. The site could contain old deposits of fill,abandoned septic systems and leach fields, buried storage tanks, seepage pits, cisterns, mining shafts, tunnels, and other man-made surface and subsurface works that could impact the new proposed development. There may also be information concerning on-site utilities and underground pipelines, which may need to be capped or rerouted around the project. Aerial Photographs and Geologic Maps. During thecourse of the work, it may be necessary for the engineering geologist to check reference materials, such as aerial photographs or geologic maps. Aerial photographs are taken from an aircraft flying at prescribed altitude along preestablished lines. Interpretation of aerial photographs takes considerable judgment and because they have more training and experience, it is usually the engineeringgeologist who interprets the aerial photographs. By viewing a pair of aerial photographs, with the aid of a stereoscope, a three-dimensional view of the
2.3 Downloaded from Digital Engineering Library @ McGraw-Hill (www.accessengineeringlibrary.com) Copyright © 2010 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website.

SUBSURFACEEXPLORATION 2.4
GEOTECHNICAL ENGINEERING

land surface is provided. This view may reveal important geologic information at the site, such as the presence of landslides, fault scarps, types of landforms (e.g., dunes, alluvial fans, glacial deposits such as moraines and eskers), erosional features, general type and approximate thickness of vegetation, and drainage patterns. By comparing older versusnewer aerial photographs, the engineering geologist can also observe any man-made or natural changes that have occurred at the site. Geologic maps can be especially useful to the geotechnical engineer and engineering geologist because they often indicate potential geologic hazards (e.g., faults landslides and the like) as well as the type of near surface soil or rock at the site. For example, Fig....
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