Licture_2 - 2 Sub surface Exploration Topics 2.1...

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Unformatted text preview: 2. Sub - surface Exploration Topics. 2.1. Introduction. 2.2. Subsurface Exploration Program. 2.3. Exploratory Boring in the Field. Chapter 2 2.4. Procedures of soil sampling. 2.5. Observation of Water Tables 2.6. Vane Shear test. 2.7. Cone Penetration test . 2.8. Coring of Rocks. 2.9. Preparation of Boring Logs. 1 2 Subsurface Exploration Geotechnical Investigation steps 1. Assessing the underground conditions & Engineering properties of soil strata. This is called Site Exploration. Site a. Drilling an exploratory borings. b.Obtaining soil samples. c. Testing soil samples into laboratory. d.Conducting tests in-situ. 2. Perform engineering analysis based on the data gained from step 1. 3. Use the analysis results to develop geotechnical 3 input for design purposes. Geotechnical Investigation a) boring and collecting soil samples 4 b) laboratory tests 1 To Avoid this Subsurface Exploration good quality site investigation program is needed? Why Why 5 6 and this and this 7 8 2 Purposes of Site Investigation Obtain Information that will help Geotechnical Engineer in the following: 1. Selection of the type and depth of foundations. 2. Determining the soil bearing capacity. 3. Prediction of settlement. 9 4. Establish the ground water table depth.10 5. Prediction of lateral earth pressure for structures like retaining walls, sheet piles, and braced cut. 6. Determination of foundation problems (for example expansive soil, collapsible soil, organic soil, and so on…) 7. Establishment of construction methods for changing subsoil conditions. 8. Determine the foundation remedial actions (Existing structure). Subsurface Exploration Program Phase 1 1. Collection of Preliminary Information: 1. Structure type and use. 2. Approximate column load and spacing. 3. Local building code. 4. Basement requirements. 5. Span and length for bridges. 6. Type of soil in the structure surrounding area. 12 11 3 2- Field Trip or Site Visit: To provide the following: 1. General topography of the site. 2. Possible existence of drains, ditches, etc. 3. Existence of cracks or failures of nearby structures. 4. Soil stratification from nearby deep cuts. 5. Ground water level from nearby wells or water marks on nearby buildings 13 Phase 2 Site Investigation: To perform the following: 1. Planning numbers and locations of the boreholes. 2. Performing test boreholes. 3. Collecting samples at the desired depths of the boreholes for observation, classification, and laboratory testing. 14 Minimum depth of borings (ASCE) Determine the net increase in the stress ∆σ’ Estimate the variation of the vertical stress σ’o D1 at ∆σ’= q/10 D2 at ∆σ’= 0.05 σ’o Chose the smaller of the two depth 15 Important Notes: 1. The depth can be changed during the drilling operation depending on the subsoil encountered. 2. For Excavation, the depth of boring should be at least 1.5 times the depth of excavation. 3. If a bedrock is encountered the minimum depth into the rock is about 3 m. 16 4 Borehole Spacing Types of Projects Multistory building One-Story Industrial building Highways Residential subdivision Dams and Dikes Spacing (m) 10 - 30 20 - 60 250 - 500 250 - 500 40 - 80 17 5 ...
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