Introduction to Site Characterization

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Introduction to Site Characterization

• Prof. Jie Han, Ph.D., PE
• The University of Kansas

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Outline of Presentation

• Introduction
• Boring and Sampling

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Introduction
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Site Characterization

• Site investigation (or site exploration)
• Laboratory testing
• Insitu testing

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Site Investigation

• Determining the locations and thickness of the
  soil strata
• Visually classifying soil types
• Determining the location of the ground water
  table
• Soil sampling
• Providing soil profile

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In-Situ Testing vs. Soil Laboratory Testing

• Advantages
• Testing the soil in-situ and less disturbance
• Less expensive and quick test
• Some testing techniques can provide a continuous
  profile
• Advanced testing techniques can obtain a number
  of properties at the same time
• Disadvantages
• No sample is often obtained
• Most use correlation to estimate soil properties
• Most correlation was developed based on the soil
  laboratory test results
• Less control over stress and drainage conditions

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Disturbed vs. Undisturbed Soil Samples

• Disturbed soil samples for soil classification
  and Proctor compaction tests
• Undisturbed soil samples for soil strength and
  modulus tests
• - No truly undisturbed soil sample because of
  shearing and compressing the soil during the
  process of inserting the sampling tool
• - Relieving the sample of its in-situ stresses
• - Possible drying and desiccation
• - Vibrating the sample during recovery and
  transport

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Preliminary Design Information

• Site map (including elevation contours)
• Proposed site location and dimensions
• Finish floor elevation and basement depth
• Type of structure, design loads, and allowable
  settlements
• Options of foundations - shallow or deep
  foundations
• Local building code requirements

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Existing Subsurface Information

• Geologic history of the site (rock and soil,
  faults, old rivers or creeks or ponds, sinkholes
• Existing soil profile and properties nearby the
  site
• Existing underground structures (including
  utility lines)

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Field Reconnaissance

• Visually inspecting the site and surrounding
  area
• Determining the accessibility of the site
• Evaluating the drainage conditions
• Verifying the existing grading with the site map

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Boring and Sampling
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Type of Boring Techniques

• Hand auger
• Bull sampler
• Flight auger or bucket auger
• Hollow-stem auger
• Rotary wash boring

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Soil Sampling

• Obtain representative soil samples for soil
  profile and laboratory tests
• Standard split spoon sampler for insitu standard
  penetration tests and disturbed soil samples
• Shelby tube sampler (a thin walled seamless
  steel tube, typical diameter of 3in.) for
  undisturbed soil samples

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Hand Auger Sampling
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Hand Auger Drilling
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Bull Sampling
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Solid and Hollow Auger Flights
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Solid Flight Auger
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Hollow Stem Auger
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Pitcher Barrel Sampler
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Split Barrel with Soil
Courtesy of Mayne
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Split Spoon Sample Liner
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Preparing to Extrude Samples from Core Barrel
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Shelby Thin-Wall Tubes
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Rotary Wash Boring
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Rotary Wash Boring Bits
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Drill Rig
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Boring Spacing and Depth

• Typically at least one boring per 230 m2
• Hand auger for investigating the local site
  condition (such as old rivers or ponds)
• Limited depth of bedrock
• Below the influence depth of the proposed
  shallow foundations
• Depth of end-bearing soil layer for deep
  foundations

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Rough Guidelines for Spacing Exploratory Borings
Area for each boring (m2)
Subsurface conditions
Poor quality / erratic
100 - 300
Average
200 - 400
High quality uniform
300 1,000
Coduto (2001)
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Guidelines for Depths of Exploratory Borings for
Shallow Foundations
Min. depth of borings (m)
Subsurface conditions
Poor
6S0.7 D
Average
5S0.7 D
Good
3S0.7 D
S number of stories
D depth of foundations
Sowers (1979)
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Groundwater Monitoring

• Install observation wells to monitor the
  groundwater conditions

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Advance Groundwater Sampling Tool
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Groundwater Monitoring Well Installed by Direct
Push Method
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Schematic of Direct Push Installed Monitoring
Well
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Test Pit

• Dig test pits using a backhoe
• Limited to a shallow depth (typically the upper
  3m)
• Cost effective

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Soil Profile (Boring Log)

• Typical soil profile contains the following
  information
• - Project name, boring log number, location,
  ground elevation, groundwater depth, date
• - Elevations and/or depths of soil layers, soil
  description and classification, Atterberg limits
  or moisture content, unit weight, blow counts,
  and undrained shear strength

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Boring Locations
A
B-1
B-2
105
A
20ft
B-3
100
95
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Soil Profile (Boring Log)
100ft
95ft
B-1
B-2
B-3
El. 103
El. 105
El. 98
El. 99
100
95
Silty sand (SM)
90
85
80
Medium to fine sand (SP)
75
70
Clay (CH)
65
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