Soil Mechanics MidTerm 2

Page 1

A Site investigation is typically (6) Steps:

Desk study - In this stage we are collecting and understanding information relating to the site such as:

- Location of area

- Details of the area including proposed/existing state

- Government regulations

Site Reconnaissance - A site visit is conducted to:

- Validate results of the desk study

- Take photographs

Planning a field program - What do we need to do and how?

- Determine the type of testing that needs to be done, the sampling method and frequency

- Determine the number of boreholes/pits

- Determine the type of equipment required

- Locate utilities

Executing the field program

Laboratory testing

reporting

SOILS EXPLORATION METHODS.

NON DESTRUCTIVE TECHNIQUES:

GROUND PENETRATING RADAR

SEISMIC SURVEYS

TEST PITS

SOIL IDENTIFICATION IN THE FIELD

Colour

Moisture

Structure

Shape

Smell

Feel

BOREHOLES REQUIRED:

<250m2 = 3min BH

250m2 < plan area < 1000m2 = 4 min for plat, 5 min for sloped

>1000 = every 300m2 --- if area is 4500m2 then 4500/300 = 15min

In-Situ (SITE) Testing

TYPES:

SPT Standard penetration test

CPT Cone penetrometer test

PMT Pressuremeter test

VST Vane Shear test

- Large variety of In-Situ testing, most commonly being the Standard penetration test (SPT) and Cone penetration test (CPT)

STANDARD PENETRATION TEST (SPT)

The number of blows required to penetrate 6" increments is recorded

N Value is # of blows to penetrate last 12"

Once blow counts are recorded, the split spoon is opened to take a disturbed sample for testing

Samples are typically collected every 1.5 meters

The N value can be used to characterize shear strength

A SHELBY TUBE WILL GIVE US AN UNDISTURBED SAMPLE

A SPLIT SPOON SAMPLER WILL GIVE US A DISTURBED SAMPLE

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LAB 1 HYDROMETER AND SIEVE ANALYSIS

LAB 2 LIQUID, PLASTIC AND PLASTICITY INDEX

Atterberg limit is moisture content of fine-grained soils as they transition from a solid to liquid state. Liquid limit and Plasticity index is used in soil classification. The plastic limit is the point at which a soil becomes too dry to be plastic or mouldable.

LIQUID LIMIT

Using the casagrande cup, a soil sample is placed and the device cranked until the line down the middle is closed. The number of blows is recorded.

A drier sample will take more blows than a weter sample.

PLASTIC LIMIT

Roll the mass between the glass plate and hand until a uniform diameter of 1/8" or 3.2mm is achieved. once a sample can be obtained without crumbling, weight the sample and dry. Water % can then be obtained.

LAB 3 SOIL CLASSIFICATION - VISUAL/MANUAL

Felt the material, dry, wet moise. Odour. Colour. Coarse or fine.

LAB 4 MEASURING PERMEABILITY USING CONSTANT HEAD AND FALLING HEAD TEST

LAB 5: MOISTURE CONTENT/VOLUME RELATIONSHIP W/ STANDARD PROCTOR TEST

Volume/mass of mould is recorded, mould is filled with loose soil 1/3 at a time with 25 hammer drops each time.

Mould + compacted soil is weighed. Soil is pushed out and mass is taken. a sample is taken to measure MC%.

LAB 7 UNCONFINED COMPRESSIVE STRENGTH/TRIAXIAL TEST

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SOILS EXPLORATION METHODS.

NON DESTRUCTIVE TECHNIQUES:

GROUND PENETRATING RADAR

SEISMIC SURVEYS

TEST PITS

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Page 5

MODULE 1: GROUNDWATER

CAPILLARITY: RISE OF WATER FROM SATURATED ZONE TO A DRIER ZONE

FLOW: MOVEMENT OF WATER WITHIN SOIL

FROST HEAVE: VERTICAL EXPANSION OF SOIL CAUSED BY FREEZING WATER

The smaller the grain size, the smaller the void space therefore the greater the capillary rise.

Homogeneous clays make the best barriers to prevent soil and groundwater contamination.

Frost action- As the top of a frozen soil thaws there is nowhere for the water to go but up because the layer below is still frozen.

Coefficient of permeability of a soil can be determined in the laboratory using permeameters and in the field using pumping tests.