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SUBSURFACE EXPLORATION. M. Zoghi, Ph.D., P.E. Geotechnical Design Fall 2008. OUTLINE. Overview Literature Search – “Desk Study” Reconnaissance Survey Preliminary Investigation Detailed Investigation Geotechnical Report. I. Overview - Typical Project. Project Initiation

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Subsurface exploration

SUBSURFACE EXPLORATION

M. Zoghi, Ph.D., P.E.

Geotechnical Design

Fall 2008


Outline
OUTLINE

Overview

Literature Search – “Desk Study”

Reconnaissance Survey

Preliminary Investigation

Detailed Investigation

Geotechnical Report


I overview typical project
I. Overview - Typical Project

  • Project Initiation

  • Review Existing Data

  • Meet with Structural Engineer

  • Perform Subsurface Exploration Program

  • Perform Laboratory Analysis and Testing

  • Perform Design Analysis

  • Prepare Geotechnical Investigation Report

  • Review Final Plans and Specifications

  • Establish Construction Criteria

  • Troubleshoot Construction Problems


Subsurface exploration 1328947

Source: Cernica, 1995


Subsurface exploration 1328947

Source: Cernica, 1995


Objectives of site exploration
Objectives of Site Exploration

  • To identify the location & thickness of soil & rock stara

  • To verify the character and location of the GWT

  • To obtain soil/rock specimens for testing and evaluation

  • To determine the relevant engineering properties

  • To identify potential problems (expansive, collapsible…)

  • To establish construction procedures for altering subsoil conditions

  • To estimate settlement, bearing capacity, lateral earth pressure distribution, etc.

  • To determine the type and depth of suitable foundation system.


Uncertainties
Uncertainties

  • Predict subsurface conditions between the borings based on local geology

  • Observe and inspect soil conditions during construction and modify design as deemed appropriate along with a post-construction monitoring plan

  • Accept and acknowledge some risk of failure due to unforeseen conditions

  • Use higher factors of safety in design and apply appropriate conservatism


Project assessment
Project Assessment

  • Obtain the preliminary project data such as the building/bridge plan, column location, etc.

  • Identify the type of construction, structural loads, etc.

  • Obtain the existing topography and proposed grading

  • Establish allowable settlements


Ii literature search desk study
II. Literature Search – “Desk Study”

  • Geologic maps – such as the USGS maps

  • Soil survey reports – USDA reports for each county

  • Soil’s reports – existing nearby projects

  • Aerial photographs

  • Historic groundwater data – US Corps of Engineers, etc.

  • Public libraries



Subsurface exploration 1328947

Idaho is an igneous state, built from many different episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho batholith, a huge emplacement of plutonic rock of Mesozoic age, and the swath of lava beds across the south that marks the path of the Yellowstone hotspot.

http://geology.about.com/library/bl/maps/blidahomap.htm


Iii reconnaissance visual inspection of the site
III. Reconnaissance episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho – Visual Inspection of the Site

  • Inspect the general topography of the site and verify the presence of drainage ditches, vegetation, abandoned dumps and debris, or other material

  • Inspect the conditions of nearby structures …

  • Verify the types of exposed soil/rock at the ground surface

  • Inspect the soil stratification of nearby deep excavations

  • Inspect high-water marks on buildings and bridge abutments

  • Look for signs of distresses in pavements, other shrinkage crack patterns, and creep of slopes


Iv preliminary investigation

IV. Preliminary Investigation episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

AAA

Abandon

Adapt

Alter


V detailed investigation

V. Detailed Investigation episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

  • Spacing and depth of borings

  • Sampling

  • Groundwater

  • Other details


Subsurface exploration 1328947

Source: episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho Cernica, 1995


Spacing
Spacing episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

Source: Das, 2002


Minimum depth of borings
Minimum Depth of Borings episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

Subsurface Conditions Min. Depth of Borings

Poor 6S0.7+ D (m)

Average 5S0.7+ D

Good 3S0.7 + D

S = No. of Stories, D = Anticipated Depth of Foundation


Subsurface exploration 1328947

Hand episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho Augering and Core Sampling for Collection of Shallow Soil Samples

Auger to desired depth

Extract auger and insert core sampler

Drive core sampler

Extract core sampler

Remove split spoon from shaft

If shelby tube, cap and store

If split core, open and slide into sterilized collection jar

Wash equipment (steam clean, as required) prior to collection of next sample

http://www.cee.vt.edu/ewr/environmental/teach/smprimer/core/core.html


Subsurface exploration 1328947

Continuous Flight Augers episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

http://www.drilleronline.com/CDA/ArticleInformation/features/BNP__Features__Item/0,3643,138082,00.html


Subsurface exploration 1328947

Drill Rig episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

http://en.wikipedia.org/wiki/Site_investigation


Subsurface exploration 1328947

Truck-Mounted Drill Rigs episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho


Standard penetration test spt
Standard Penetration Test - SPT episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

  • The most commonly used in-situ test.

  • ASTM D-1586

  • Sampler is driven into the soil strata to a maximum depth of 18 in.

  • Via a 140 lb hammer.

  • From a height of 30 in.

  • No. of blows required to penetrate each of the successive 6 in. depths … to a total of 18 in.


Spt cont d
SPT Cont’d episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

  • The number of blows to drive the first 6 in. are not taken into account to avoid seating errors.

  • The field (raw) blow count value, N, is obtained by adding the numbers from the last two 6-in. penetrations.

  • The corrected N value:

    N60 = N(H BS R)/60


Subsurface exploration 1328947

A episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho R (%)= {[(D0)2 – (Di)2]/(Di)2}(100)

Where:

AR = area ratio (≤10% undisturbed)

D0 = outside diameter of the sampling tube

Di = inside diameter of the sampling tube


Boring logs
Boring Logs episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

  • Name & address of the drilling company

  • Driller’s name

  • Job description and number

  • Number and type of boring and boring location

  • Date of boring

  • Subsurface stratification, which can be obtained by visual observation of the soil brought out by auger, split-spoon sampler, and thin-wall Shelby tube sampler


Boring logs cont d
Boring Logs Cont’d… episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

  • Elevation of water table and date observed, use of casing and mud losses, and so on

  • Standard Penetration resistance and the depth

  • Number, type, and depth of soil sample collected

  • In case of rock coring, type of core barrel used and, for each run, the actual length of coring, length of core recovery, and the RQD

Das, B.M., 2000


Subsurface exploration 1328947

Source: episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho Cernica, 1995


Subsurface exploration 1328947

Source: episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho Cernica, 1995


Subsurface exploration 1328947

Source: episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho Cernica, 1995


Cone penetration test cpt
Cone Penetration Test - CPT episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

http://www.conepenetration.com


Subsurface exploration 1328947

Cone Penetration Testing episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

Advantages• Rapid data acquisition• No drilling mess• Immediate data availability• Detailed subsurface information

http://pubs.usgs.gov/fs/2003/fs028-03/


Correlations between q c and n values
Correlations between q episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho c and N Values

qc = 0.4 N (MN/m2)

Refer to Table 9.6, p-341 of textbook


Subsurface exploration 1328947

Rock Coring episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

Coring Bit


Rock quality designation
Rock Quality Designation episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

RQD = La / Lt

La= total length of intact hard and sound pieces of core of length greater than 4 in. arranged in proper position

Lt= total length of drilling


In situ rock quality
In-Situ Rock Quality episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

RQDRock Quality

90-100 Excellent

75-90 Good

50-75 Fair

25-50 Poor

0-25 Very poor

Source: Peck et al., 1974


Subsurface exploration 1328947

Groundwater Monitoring episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho


Subsurface exploration 1328947

VI. Geotechnical Report episodes of volcanism and intrusion, plus vigorous uplift and erosion by ice and water. Its two largest features are the great Idaho

  • Letter of transmittal

  • Cover page

  • Table of contents

  • Introduction – provides an overview of the project site along

  • with potentially serious problems encountered

  • Description of site investigation program

  • Inspection