whittle mit soil investigation

7/21/2019 Whittle Mit Soil Investigation

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SITE INVESTIGATION

Methodology, Stratigraphy and Groundwater Monitoring

TYPES OF PROJECT

- New works (siting criterion)

- Condition assessment of existing structures (repair, retrofit)

- Sources of suitable construction materials (disposal of waste materials)

TYPES OF SITE

- Compact: buildings, bridges etc.

- Extended: railways, roads, transmission lines, pipelines

INFORMATION FROM SITE INVESTIGATION

1. Stratigraphy

- geometry of subsurface deposits (areal extent, thickness, depth)

- identification of geological units

(need to establish resolution relevant to problem)

2. Location and character of bedrock

- type, fissured/jointed/intact. other features (faults, solution cavities etc.)

- importance of local geological environment

3. Location & character of groundwater

- hydraulic regime (aquifer and aquitard layers)

- factors affecting in situ pressures

- chemical composition

4. Engineering Properties of Main Soil Layers

Shear strength - cohesive and frictional components (drainage conditions)

Deformation (compressibility, shear stiffness)

Flow resistance (permeability/hydraulic conductivity)

Consolidation- links deformation of soil skeleton to displacement/flow of pore water

- controls rate of pore pressure dissipation

* Measure soil properties using laboratory tests on soil samples and/or in situ tests


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PROGRESS OF SITE INVESTIGATION

* Typically there are four phases of site investigation associated with a project:

1. Reconnaissance

- uses available information sources

(see list of geological sources from DM7)

- use for background/feasibility studies

2. Preliminary Investigation

- identify first order site characteristics

stratigraphy, bedrock character, groundwater regime

identify site specific problems

typically includes series of boringssome limited field testing for engineering properties

- Often this data forms the basis for Major Design Decisions

- Often constrained by budget and time

3. Detailed Site Investigation

- provide data for designer and/or contractor

- program of laboratory testing

- perform detailed analyses/interpretation of data

- Often this data arrives too late to affect major design decisions

4. Verification

- additional investigations performed during construction

- monitoring of field performance (part of observational approach)

* Cost of site investigation approx. 0.5-1.0% of project capital costs

SCOPE OF SITE INVESTIGATION

1. Low Level Projects

- Minimal site investigation (site visit; test pits?)

- Satisfy code requirements2. Normal Level Projects

- Geotechnical engineer defines scope of site investigation

- Addresses all main design issues (key engineering properties)

3. High Level Projects

- Intensive site investigation (minimize risk)

- Requires extensive soil property characterization


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RECONNAISSANCE; INITIAL SITE INVESTIGATION

Geological Information

(USGS, NOAA, USDA, GSA)

- topographic maps

- maps of subsurface and surficial geology

- water supply papers

- bulletins -- detailed geological descriptions

Aerial Photography

(USGS, NASA, Skylab, Eros)

- planning of large projects

Boring Compilations

- previous soils investigations

e.g. BSCE collection dates from 1914

- also available from state agencies such as Mass. Highway Dept.; MBTA etc.

Adjacent Facilities

- buildings (and their foundations), excavations, subways etc

- utilities (power, sewer, water supply etc.)

History of site

- pre-existing foundations/construction

- sources of contamination etc.


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From Rowe (1972)


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SOURCES OF GEOLOGICAL INFORMATION (FROM DM7.1)

Series Description of Material

U.S. Consult USGS Index of Publications from Superintendent of

Geological Documents, Washington, D.C. Order publications from

Survey Superintendent of Documents. Order maps from USGS,(USGS) Washington, D.C. Contact regional distribution offices

for information.

Geological Individual maps of each state showing coverage and sources

index map of all published geological maps.

Folios of Contains maps of bedrock and surface materials for many

the Geo important urban and seacoast areas. When out of print,

logical obtain folios through suppliers of used technical

Atlas of literature.

the United

States

Geological This series supplants the older geological folios

including

Quadrangle areal or bedrock geology maps with brief descriptive text.

Maps of Series is being extended to cover areas not previously

United investigated.

States

Bulletins, General physical geology emphasizing all aspects of earth

profes sciences, including mineral and petroleum resources,

sional hydrology and seismicity. Areal and bedrock geology maps

papers, for specific locations included in many publications.

circulars,

annual

reports,

monographs

Water Series includes papers on groundwater resources in

specific supply localities and are generally accompanied by description of

papers subsurface conditions affecting groundwater plus

observations of groundwater levels.

Topographic Topographic contour maps in all states, widespread coverage

maps being continually expanded.

Libraries Regional office libraries contain geological,seismological

information from many sources. Data on foreign countries

are often suitable.


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Series Description of Material

National Consult Catalog 1, Atlantic and Gulf Coasts; 2, Pacific

Oceanic and Coast, 3, Alaska; 4, Great Lakes; and 5, Bathymetric Maps

Atmospheric and Special Charts. Order from Distribution Service,

Administra National Ocean Survey, Riverdale, Maryland 20840.

tion (NOAA),National

Ocean Survey

(NO 5)

Nautical Charts of coastal and inland waterways showing available

Charts soundings of bottom plus topographic and cultural features

adjacent to the coast or waterways.

U.S. Consult list of Published Soil Surveys, USDA, Soil Conser

Department of vation Service, January 1980 (published annually). Listing

Agriculture by states and countries.

(USDA), Soil

ConservationService.

Soil maps Surveys of surface soils described in agricultural terms.

and reports Physical geology summarized. Excellent for highway or

airfield investigations. Coverage mainly in midwest, east,

and southern United States.

State Most states provide excellent detailed local geological maps

Geological and reports covering specific areas or features in the

Surveys/State publications of the state geologists. Some offices are

Geologists excellent sources of information on foreign countries.

Office

Geological Write for index to GSA, P.O. Box 9140, 3300 Penrose Place,

Society of Boulder, Colorado, 80302.

America (GSA)

Monthly Texts cover specialized geological subjects and intensive

bulletins, investigations of local geology. Detailed geological

special maps are frequently included in the individual articles.

papers, and

memoirs.

Geological Publications include general geological maps of North and

maps South America, maps of glacial deposits, andPleistocene aeolian deposits.


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PRINCIPAL SOIL DEPOSITS (from DM7.1, 1982)

Major

Division

Principal Soil Deposits Pertinent Engineering

Characteristics

SEDIMENTARYSOILS

Residual

Material

formed by

disintegration

of underlying

parent rock or

partially

indurated

material.

Organic

Accumulation

of highly

organic

material

formed in

place by the

growth and

subsequent

decay of plant

life.

Residual sands and fragments of

gravel size formed by solution and

leaching of cementing material,

leaving the more resistant parti-

cles; commonly quartz.

Residual clays formed by decomposi-

tion of silicate rocks, disintegra-

tion of shales, and solution of

carbonates in limestone. With few

exceptions becomes more compact,

rockier, and less weathered with

increasing depth. At intermediate

stage may reflect composition,

structure, and stratification of

parent rock.

Peat. A somewhat fibrous aggregate

of decayed and decaying vegetation

matter having a dark color and odor

of decay.

Muck. Peat deposits which have

advanced in stage of decomposition

to such extent that the botanical

character is no longer evident.

Generally favorable

foundation conditions.

Variable properties

requiring detailed

investigation.

Deposits present

favorable foundation

conditions except in

humid and tropical

climates, where depth

and rate of weathering

are very great.

Very compressible.

Entirely unsuitable

for supporting

building foundations.


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Major

Division


Characteristics

TRANSPORTED

SOILS

Alluvial

Material

transported

and deposited

by running

water.

Floodplain deposits. Deposits laid

down by a stream within that

portion of its valley subject to

inundation by floodwaters.

Point bar. Alternating depos-

its of arcuate ridges and

swales (lows) formed on theinside or convex bank of miti-

gating river bends. Ridge

deposits consist primarily of

silt and sand, swales are

clayfilled.

Channel fill. Deposits laid

down in abandoned meander

loops isolated when rivers

shorten their courses.

Composed primarily of clay;

however, silty and sandy soils

are found at the upstream anddownstream ends.

Backswamp. The prolonged

accumulation of floodwater

sediments in flood basins

bordering a river. Materials

are generally clays but tend

to become more silty near

riverbank.

Alluvial Terrace deposits.

Relatively narrow, flatsurfaced,

riverflanking remnants of flood-

plain deposits formed by entrench-

ment of rivers and associated

processes.

Generally favorable

foundation conditions;

however, detailed in-

vestigations are

necessary to locate

discontinuities. Flow

slides may be a

problem along

riverbanks. Soils are

quite pervious.

Finegrained soils are

usually compressible.

Portions may be very

heterogeneous. Silty

soils generally

present favorable


Relatively uniform in

a horizontal

direction. Clays are

usually subjected to

seasonal volume

changes.

Usually drained,

oxidized. Generallyfavorable foundation

conditions.


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Major

Division


Characteristics

(cont d)

Materialstransported

and deposited

by running

water.

Aeolian

Material

transported

and deposited

by wind.

Estuarine deposits. Mixed depositsof marine and alluvial origin laid

down in widened channels at mouths

of rivers and influenced by tide,

of body of water into which they

are deposited.

AlluvialLacustrine deposits.

Material deposited within lakes

(other than those associated with

glaciation) by waves, currents, and

organochemical processes. Deposits

consist of unstratified organicclay or clay in central portions of

the lake and typically grade to

stratified silts and sands in

peripheral zones.

Deltaic deposits. Deposits formed

at the mouths of rivers which

result in extension of the

shoreline.

Piedmont deposits. Alluvial

deposits at foot of hills or

mountains. Extensive plains oralluvial fans.

Loess. A calcareous, unstratified

deposit of silts or sandy or clayey

silt traversed by a network of

tubes formed by root fibers now

decayed.

Dune sands. Mounds, ridges, and

hills of uniform fine sand

characteristically exhibiting

rounded grains.

Generally finegrainedand compressible. Many

local variations in

soil conditions.

Usually very uniform

in horizontal

direction.

Finegrained soils

generally

compressible.

Generally finegrained

and compressible. Many

local variations in

soil condition.

Generally favorable


Relatively uniform

deposits characterized

by ability to stand in

vertical cuts. Col-

lapsible structure.

Deep weathering or

saturation can modify

characteristics.

Very uniform grainsize; may exist in

relatively loose

condition.


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Major

Division


Characteristics

Glacial

Material

transported

and deposited

by glaciers,

or by melt

water from

the glacier.

Marine

Material

transported

and deposited

by ocean waves

and currents

in shore and

offshore

areas.

Glacial till. An accumulation of

debris, deposited beneath, at theside (lateral moraines), or at the

lower limit of a glacier (terminal

moraine). Material lowered to

ground surface in an irregular

sheet by a melting glacier is known

as a ground moraine.

GlacioFluvial deposits. Coarse and

finegrained material deposited bystreams of meltwater from glaciers.

Material deposited on ground

surface beyond terminal of glacier

is known as an outwash plain.

Gravel ridges known as kames and

eskers.

GlacioLacustrine deposits. Mate-

rial deposited within lakes by

meltwater from glaciers. Consisting

of clay in central portions of lake

and alternate layers of silty clay

or silt and clay (varved clay) inperipheral zones.

Shore deposits. Deposits of sands

and/or gravels formed by the trans-

porting, destructive, and sorting

action of waves on the shoreline.

Marine clays. Organic and inorganic

deposits of finegrained material.

Consists of material

of all sizes invarious proportions

from boulders and

gravel to clay.

Deposits are

unstratified. Gener-

ally present favorable

foundation conditions;

but, rapid changes in

conditions are common.

Many local variations.

Generally present

favorable foundation

conditions.

Very uniform in a

horizontal direction.

Relatively uniform and

of moderate to high

density.

Generally very uniform

in composition. Com-

pressible and usuallyvery sensitive to re-

molding.


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Major

Division


Characteristics

Colluvial

Material

transported

and deposited

by gravity.

Pyroclastic

Material

ejected from

volcanoes and

transported by

gravity, wind

and air.

Talus. Deposits created by gradualaccumulation of unsorted rock

fragments and debris at base of

cliffs.

Hillwash. Fine colluvium consisting

of clayey sand, sand silt, or clay.

Landslide deposits. Considerable

masses of soil or rock that have

slipped down, more or less as

units, from their former position

on steep slopes.

Ejecta. Loose deposits of volcanic

ash, lapilli, bombs, etc.

Pumice. Frequently associated with

lava flows and mud flows, or may be

mixed with nonvolcanic sediments.

Previous movementindicates possible

future difficulties.

Generally unstable


Typically shardlike

particles of silt size

with larger volcanic

debris. Weathering and

redeposition produce

highly plastic, com-

pressible clay. Un-

usual and difficult



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Example of Uncertainties in Geological Mapping (after Baecher, 1978)


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UNUSUAL SITE CONDITIONS

check list - description given in DM7, Canadian Foundations Manual

PROBLEM SOILS PROBLEM CONDITIONS

Organic Soils

Normally Consolidated Clays

Sensitive Clays

Swelling and Shrinking Clays

Loose Granular Soils

Calcareous SandsMetastable Soils (e.g. loess)

Glacial Till

Artifical Fills

Residual soils

Soluble Rocks

Shales

Meander loops and cutoffs

Relic Landslides

Kettle holes

Mined areas

Permafrost

Noxious or explosive gasesExtremes of temperature

Sulphate soils and groundwater

Karst topography

Perched water tables

Artesian Water Pressures


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FROM CANADIAN FOUNDATIONS MANUAL (1985)

CHAPTER 5

UNUSUAL SITE CONDITIONS

5.1 INTRODUCTION

The following paragraphs give brief descriptions of the types of soil, rock,

or conditions, that require precautionary measures to achieve satisfactory

design and performance. Early recognition of these types of soil, rock, or

conditions is essential to allow sufficient time for adequate investigations

and the development of designs.

5.2 PROBLEM SOILS

5.2.1 ORGANIC SOILSSoils containing significant amounts of organic materials, either as colloids

or in fibrous form, are generally weak and will deform excessively under load.

Such soils include peat, and organic silts and clays typical of many

estuarine, lacustrine, or fluvial environments. Such soils are usually not

satisfactory as foundations for even very light structures because of

excessive settlements that can result from loading the soil.

5.2.2 NORMALLY CONSOLIDATED CLAYS

Organic clays of softtomedium consistency, which have been consolidated only

under the weight of existing conditions, are found in many areas. Typical of

these are the clays of the Windsor Lake St. Clair region and the varved clays

in the northern parts of Manitoba, Ontario, and Quebec. Imposition of

additional load, such as a building, will result in significant longterm

settlement. The magnitude and approximate rate of such settlement can be

predicted from analyses based on carefully conducted consolidation tests on

undisturbed samples. Such studies should be made before any significant

structure is founded on or above these clays, in order to determine whether

settlements will be acceptable, considering the characteristics and purpose of

the structure.

Driving piles through normally consolidated plastic clays may cause heave or

displacements of previously driven piles or adjacent structures. The bottom of

excavations made in such soils may heave, and adjoining areas of structures

may move or settle, unless the hazards are recognized and proper precautions

taken to prevent such movements.

Special precautions may be necessary in sampling and testing varved clays. Any

analysis should take into account the important differences in properties

between the various layers in the clays.

5.2.3 SENSITIVE CLAYS

Sensitive clays are defined as having a remoulded strength of 25% or less of

the undisturbed strength. Some clays are much more sensitive than this, having

a remoulded to undisturbed strength ratio of 1 to 20, or even 1 to 50, are


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known. Typically, such have field moisture contents equal to or greater than

their liquid limits, and such relations may indicate their presence.

Extensive deposits of sensitive clays occur in some areas, as for example, the

Champlain clays of the St. Lawrence and Ottawa River Valleys. Where such clays

have been preconsolidated by partial desiccation, or by the weight of

materials subsequently eroded, foundations may be placed on the clays,provided that the foundation load produces shearing stresses under the

foundations that are well within the shear strength of the clay, or else

excessive settlement and possibly catastrophic failure will result. Disastrous

flow slides have developed in the Champlain clays in a number of places, and

the hazard must always be considered. Deep excavations in sensitive clays are

extremely hazardous, because of possible severe loss in shear strength,

resulting from strains within the soil mass beneath and adjacent to the

excavation.

Determination of the physical properties necessary for evaluating the

significance of sensitive clays to a proposed structure requires taking and

testing of both undisturbed and remoulded samples of the clays and thorough

analysis of the possible hazards involved. Because of the extreme sensitivityof such clays to even minor disturbances, taking and testing undisturbed

samples requires sophisticated equipment and techniques, and should be

attempted only by competent personnel experienced in this type of work.

5.2.4 SWELLING AND SHRINKING CLAYS

Swelling and shrinking clays are clays that expand or contract markedly upon

changes in moisture content. Such clays occur widely in the provinces of

Alberta, Manitoba, and Saskatchewan and are usually associated with lacustrine

deposits. Shallow foundations constructed on such clays may be subject to

movements brought about by volume changes, because of changes of the moisture

content in the clays. Deep foundations supporting structural floors can be

damaged if the enclosing clay is confined. Special design provisions should be

made, which take into account the possibility of movements or swelling

pressures in the clays (see Chapter 17).

5.2.5 LOOSE, GRANULAR SOILS

All granular soils are subject to some compaction or densification when

subjected to vibration. Normally, this is of significance only below the

permanent water table. Sands above the water table, as a rule, will be only

slightly compacted by most building vibration, because of friction developed

between the grains from capillary forces. Usually for sands in a compact to

dense state, settlements induced by vibration will be well within normal

structural tolerance, except for very heavy vibration, as from forging hammersor similar equipment. However, if the sands are be in a loose to very loose

state, significant settlement may safely result from even minor vibrations or

from nearby pile driving. In some cases, earthquakes have brought about the

liquefaction of very loose sands, as occurred in Niigata, Japan. In this

event, structures supported above such soils may be completely destroyed.

Loose sands will settle significantly under static load only. Such settlements

may exceed allowable tolerance. Consequently, loose sands should be

investigated carefully and their limits established; densification or

compaction of such deposits may be essential before structures can be safely


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founded above them.

5.2.6 METASTABLE SOILS

Metastable soils include several types of soil, abnormally loosely deposited,

which may collapse on saturation. Such collapses will cause severe or even

catastrophic settlement of structures founded in or above these soils. Loessis the most common metastable soil. Because metastable soils are strong and

stable when dry, they can be misleading in investigations, and extreme care

should be taken to ensure identification and proper foundation design wherever

such soils occur. The open, porous structure, which is the usual means of

identification, may be completely collapsed by the boring techniques. Where

such conditions may be anticipated, borings should be done by auger methods,

and test pits should be dug, from which undisturbed samples may be taken for

determining accurately inplace densities.

5.2.7 GLACIAL TILL

Till is unsorted and unstratified glacial drift deposited directly by and

underneath glaciers. Its soil grains are usually angular and all sizefractions are normally present (Legget, 1962, 1979, 1983). Basal till

(consolidated under the full weight of the glacier) is normally very dense,

whereas ablation till (deposited from the glacier during ablation) may not be

dense. Till is generally a good foundation material, but problems have arisen

with the presence of soft layers and large boulders in some tills. Till may be

difficult to excavate. Finegrained till is generally frost susceptible.

5.2.8 FILL

An engineered fill placed under careful control may be an extremely dense

material, more uniform, more rigid, and stronger than almost all natural

deposits. When not placed under controlled conditions, it may be a

heterogeneous mass of rubbish, debris, and loose soil of many types totally

useless as a foundation material. It may, of course, also be some combination

intermediate between these extremes. Unless the conditions and quality control

under which a fill was placed are fully known, the fill must be presumed

unsatisfactory for use under foundations. Investigations must establish its

limits, depths, and characteristics throughout.

5.3 PROBLEM ROCKS

5.3.1 VOLCANIC ROCKS

Parts of the Canadian Cordillera and the Western Interior Plains have

extensive deposits of geologically young volcanic rocks. Some tuffs within

these volcanic sequences have high porosities, low densities, and low shear

and compressive strengths. These materials weather rapidly, in some places, to

smectites (swelling clay minerals; montmorillonite).

5.3.2 SOLUBLE ROCKS

Rocks such as limestone, gypsum, rock salt, and marble are subject to high

rates of solution by groundwater, and may contain solution channels, caverns,

and sinkholes, which may cave to the earths surface. These conditions present

special foundation problems (Calembert et al., 1973).

5.3.3 SHALES

Shales are the most abundant of sedimentary rocks and commonly the weakest


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from the standpoint of foundations. Two special problems with certain shale

formations have been identified in Canada.

In Western Canada, the Bearpaw Formation and other shales of Cretaceous age

have been found to swell considerably when stress release or unloading leads

to the absorption of water by the clay minerals, in combination with exposure

to air. Bearpaw shales also have a low frictional resistance, which may createslope stability problems for both excavations and construction on or near

natural slopes in Bearpaw shales. Special advice should be sought if Bearpaw

or comparable shales are encountered along deep river valleys.

In Eastern Canada, volumetric expansion of some shale formations, caused by

the weathering of iron sulphide minerals (mainly pyrite), accelerated by

oxidizing bacteria, has occurred in a few localities. Conditions leading to

mineralogical alteration seem to be related to lowering the groundwater table

and to raising of the temperature in the shale, particularly when the shale is

highly fractured. These conditions enhance bacterial growth and oxidation of

the sulphide minerals. Where these conditions are encountered, special

provisions should be considered to reduce heat loss from the building spaces

to the supporting shale. Shales often weather rapidly when exposed to air inexcavations. Special measures are warranted to avoid prolonged contact with

air.

As the effect of chemical degradation of foundation rock on the performance of

the structure may become obvious only several years after the completion of

the structure, the problem can only be avoided by recognition of potential

difficulties at the time of Site exploration and the taking of remedial

measures during design and construction phases of the project.

5.4 PROBLEMCONDITIONS

5.4.1 MEANDER LOOPS AND CUTOFFS

Meandering streams from time to time develop chute cutoffs across meander

bends, leaving disused, crescentshaped waterfilled channels, called oxbow

lakes, which later fill with very soft, organic silts and clays. Frequently,

these crescentshaped features can be detected in aerial photographs or from

accurate topographic maps. The soils filling these abandoned waterways can be

weak and highly compressible. It is necessary, therefore, that their limits be

determined and the depths of the soft, compressible soils be established.

5.4.2 LANDSLIDES

The possibility of landslides should always be considered. Whereas landslides

in an active state are readily identifiable, old landslides or unstable soils

in a potential landslide state are more difficult to detect. They may be

signalled by hummocky conditions, by bowed trees, by tilted or warped strata,or by other evidence of displacement. The presence of sensitive clays

increases significantly the risk of landslides. The stability of such an area

may be so marginal that even minor disturbances such as a small excavation

near the toe of a slope, or slight changes in groundwater conditions or

drainage, may activate a slide. It is simpler to take precautions to avoid

triggerring a landslide than to stop one in motion, but it is better still to

avoid the landslide or potential landslide area altogether.

The banks of actively eroding rivers are always in a state of marginal


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stability. This is particularly true of the outside bends of such rivers,

because active cutting is usually in progress, especially during periods of

high water. Ongoing sloughing of a slope is often an indication of incipient

failure (Eden and Jarrett, 1971).

When a potential landslide area is identified, care should be taken to

investigate it thoroughly and to adopt construction procedures and designsthat will improve the stability. Both the steepness and height of slopes are

important factors influencing the stability. Steepening a natural slope, or

excavating near the toe, or placing fill at the top of slopes, either

temporarily or permanently, will adversely affect the stability of the slope

and may result in slope failure. Proper design analysis is required whenever

such construction works are contemplated. In particular, the design must

consider the aspects of a seasonally varying groundwater regime, as well as

the effect of freezing and thawing of the ground. Arrangement for drainage may

be necessary, at both the top and the toe of the slope. High slopes may

require additional drainage placed horizontally in the sides of the slopes.

5.4.3 KETTLE HOLES

During the deposition of glacial outwash by the retreating continental icesheets, large blocks of ice commonly became stranded or trapped in the outwash

deposits. Upon melting, these blocks left depressions in the outwash mantle,

many of which were subsequently filled with peat or with soft organic soils.

Such depressions, known as kettle holes, range in diameter from a few metres

to several hundred metres. Usually, the depths of kettle holes do not exceed

40% of their minimum lateral dimensions; the depths are limited to the angles

of repose of the surrounding materials. Kettle holes are normally easily

identified as shallow surface depressions. In some localities, however, all

obvious surface expression has been destroyed by farming or levelling

operations. In such places aerial photographs will often reveal a difference

in vegetation cover.

5.4.4 MINED AREAS

Sites above or adjacent to mined areas may be subject to severe ground

movements and differential settlements, resulting from subsidence or caving.

For coal mines and other types of mines in horizontal strata, the zone of

disturbance generally does not extend laterally from the edge of the mined

areas for a distance more than half the depth of the mine below the surface.

There is little control of the solution process that occurs in potash or salt

mines, and subsidence may extend several hundred metres beyond the edges of

the mine or well field. Some evidence indicates that the solution may extend

farthest up the dip of the strata.

Investigations must be extremely thorough and all possible data on old mines

should be obtained wherever such differential settlement conditions aresuspected (sources of mine data are given in Subsection 4.9.10). While good

maps for active, or recently closed mines may be available, the accuracy and

reliability of maps or plans for long abandoned mines is frequently poor.

Furthermore, there are many minedout areas, especially in the older mining

regions, for which no records are now available.

5.4.5 PERMAFROST

Permafrost is the thermal condition of the earths crust and surficial

deposits, when its temperature has been below the freezing point continuously


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for a number of years. Half of Canadas land surface lies in the permafrost

region, either in the continuous zone where the ground is frozen to great

depths, or in the discontinuous zone where permafrost is thinner, and there

are areas of unfrozen ground.

The existence of permafrost causes problems for the development of the

northern regions extending into the Arctic. Engineering structures are, ofcourse, greatly affected by the low temperatures. Ice layers give soil a

rocklike structure with high strength. However, heat transmitted by buildings

often causes the ice to melt, and the resulting slurry is unable to

support the structure. Many settlements in northern Canada have examples of

structural damage caused by permafrost. In construction and maintenance of

buildings, normal techniques must, therefore, be modified at considerable

additional cost.

The accumulated experience from careful, scientifically planned and conducted

investigations makes it technically possible to build practically any

structure in the permafrost area (Rowley et al., 1975). Design and

construction in permafrost should, therefore, only be carried out by those who

possess special expertise in this area.

5.4.6 NOXIOUS OR EXPLOSIVE GAS

Noxious or explosive gases, of which methane is the most common, are

occasionally encountered in clay or silt deposits and in landfill sites

containing decaying organic matter. They constitute a hazard to workmen

constructing caissons or deep excavations. Gases may be found in shale or

other sedimentary rock deposits in various areas of the country. These may be

a special hazard in deep excavations, or where borings have encountered such

gases, which have discharged into the construction area. The history of the

local area of discharge of gas from borings, even if only for short periods of

time, should be especially noted and suitable precautions taken.

A particular problem may exist in tunnels or drainage systems where the

oxidation of iron sulphides by bacteria can deplete the free oxygen supply in

poorly ventilated areas so much that persons entering may be asphyxiated. Such

areas should be thoroughly purged with clean air before anyone enters, and

adequate ventilation must be assured while people are present.

5.4.7 EFFECTS OF HEAT OR COLD

Soils should be extremely furnaces or differential is necessary

be protected against contact with surfaces that will hot or cold. Desiccation

of clay soils beneath alongside ducts carrying hot gases will cause

settlements. Therefore, insulation and ventilation around hightemperature

structures.

To prevent the potential collapse of retaining walls in the winter due to ice

lens formation, the walls must be backfilled with nonfrostheave material for

a distance equal to maximum frost penetration. The extent of the backfill may

be reduced by means of insulation behind the wall. Also, proper drainage must

be provided.

5.4.8 SOIL DISTORTIONS

Soils distort both laterally and vertically under surface loadings. Lateral

distortion is generally not significant, but severe lateral distortions may


20/54

1.364 Notes: 2

2-20

develop in highly plastic soils toward the edge of surface loadings, even

where the loads are not sufficient to cause rupture or mud waves. These

lateral distortions may affect foundations, or structuresupporting piles, or

pipe trenches located in or adjacent to areas subject to highsurface loading,

such as along the edge of fills or a coal pile. Lateral distortions are a

special hazard if sensitive clays are present. In such soils, shearing strains

accompanying the distortions may lead to significant loss of shear strength orpossibly even to flow failures or slides.

Both lateral and vertical displacements may develop when displacementtype

piles are driven. Cohesive soils are especially subject to such displacement.

Previously driven piles or existing foundations may be displaced, or the soil

movements may result in excessive pressures on retaining walls, on sheeting

for excavations, or on buried pipes. Heaved piles may be redriven and used. If

there is significant lateral displacement, the piles may be kinked or bowed

beyond the safe limit of use. These hazards must be evaluated in the

investigation programme. Provision should be made in design and construction

procedures to ensure that other structures or piles are not damaged or

displaced by the driving of adjacent piles. Preboring through the cohesive

strata should be required if there is risk of disturbing existing structuresor previously driven piles.

5.4.9 SULPHATE SOILS AND GROUNDWATER

Suiphates in the soil and groundwater can cause significant deterioration of

Portland cement concrete. Because contact of concrete with sulphates

invariably is due to sulphate solution in the groundwater, isolation of the

concrete by interception or removal of sulphateladen waters will prevent

deterioration of the concrete. An alternative solution is to use

sulphateresistant cement in the concrete.

The presence of sulphates in the groundwater does not automatically justify

the use of sulphateresistant cement. Highquality watertight concrete is less

susceptible to deterioration by sulphates than lower quality concrete.

Furthermore, the use of sulphateresistant cement does not necessarily make

the concrete sulphateproof.


21/54

1.364 Notes: 2

2-21

BOREHOLES

Most commonly used site investigation technique for vertical stratigraphy

All sampling operations are carried out from within boreholes

Many in-situ tests are performed within boreholes

- Standard Penetration Test (SPT - all major classes of soil)

- Field Vane Test (FVT - especially in soft clay)

- Mnard Pressuremeter (especially in soft rock/very hard clay)

- Pumping tests (field permeability measurements)

- Geophysical measurements (e.g., cross-hole tests)

Installation of piezometers (monitoring groundwater)

Location depends on type & size of structure, local geology

W. Teng (1962)

Project Spacing of Borings (ft)

Uniform* Average* Erratic*

Minimum

Number

Multi-storey building 150 100 50 4

1-2 storey building 200 100 50 3

Bridge Piers, Towers 100 25 1 to 2

Embankments 1000 500 100

Borrow Pits 500 200 50

* Overall stratigraphic character of foundation soils:

e.g. glacial deposits in Boston are erratic, while many coastal deposits are very uniform.

It is usually good practice to locate and define the character of the bedrock.


22/54

1.364 Notes: 2

2-22

H. Aldrich (1972)

Structure Foundation Type Area per Boring (ft2)

Large 1 storey structure

(e.g. shopping centre)

Spread footings

Deep foundation

7500

5000

2-3 Storey Building

(e.g. light mfg.)

Spread footings

Deep foundation

5000

2500

Medium to high rise

building

(A >10,000ft2)

Spread footings

Deep foundation

2500 to 5000

1500

Spacing: General rules of thumb

- rarely less than 25ft

- rarely greater than 2000 - 3000ft

Depth: Guidelines for Different Situations - illustrated on subsequent pages

GENERAL RULE:

- Explore all strata which can affect structural performance and foundation design


23/54

1.364 Notes: 2

2-23

REQUIREMENTS FOR BORING DEPTH (FROM DM7.1)

Areas of

Investigation

Boring Depth

Large structure with

separate closelyspaced footings.

Extend to depth where increase in vertical stress for

combined foundations is less than 10% of effectiveoverburden stress. Generally all borings should extend

to no less than 30 ft below lowest part of foundation

unless rock is encountered at shallower depth.

Isolated rigid

foundations.

Extend to depth where vertical stress decreases to 10%

of bearing pressure. Generally all borings should

extend no less than 30 ft below lowest part of

foundation unless rock is encountered at shallower

depth.

Long bulkhead or

wharf wall.

Extend to depth below dredge line between 3/4 and

11/2 times unbalanced height of wall. Where

stratification indicates possible deep stability

problem, selected borings should reach top of hard

stratum.

Slope stability. Extend to an elevation below active or potential

failure surface and into hard stratum, or to a depth

for which failure is unlikely because of geometry of

cross section.

Deep cuts. Extend to depth between 3/4 and 1 times base width of

narrow cuts. Where cut is above groundwater in stable

materials, depth of 4 to 8 ft below base may suffice.

Where base is below groundwater, determine extent of

pervious strata below base.

High embankments. Extend to depth between 1/2 and 11/4 times horizontal

length of side slope in relatively homogeneous

foundation. Where soft strata are encountered, boringsshould reach hard materials.

Dams and water

retention

structures.

Extend to depth of 1/2 base width of earth dams or 1

to 11/2 times height of small concrete dams in

relatively homogeneous foundations. Borings may

terminate after penetration of 10 to 20 ft in hard and

impervious stratum if continuity of this stratum is

known from reconnaissance.


24/54

1.364 Notes: 2

2-24

Boring Depth Considerations for a Shallow Foundation


25/54

1.364 Notes: 2

2-25

Boring Depth Considerations (contd.)


26/54

2-26

Boring Method Procedure Utilized

Auger boring Hand or power operated augering

with periodic removal of

material. In some cases

continuous auger may be used

requiring only one withdrawal.Changes indicated by examination

of material removed. Casing

generally not used.

Ordinarily

exploration

partly satu

and soft to

May be usedbetween dr

when power

bucket auge

of hole. Ho

soils and

table.

Hollowstem flight auger Power operated, hollow stem

serves as a casing

Access for

undisturbed

hollow stem

with plug

suitable fo

in sand and

Washtype boring for undisturbed

or dry sample.

Chopping, twisting, and jetting

action of a light bit as

circulating drilling fluid

removes cuttings from holes.

Changes indicated by rate of

progress, action of rods, and

examination of cuttings in

drilling fluid. Casing used as

required to prevent caving.

Used in san

without bou

hard cohes

soils. Mos

subsoil exp

be adapted

locations,

swamps, on

buildings.

undisturbed

Rotary drilling Power rotation of drilling bit as

circulating fluid removes cutting

from hole. Changes indicated byrate of progress, action of

drilling tools, and examination

of cutting in drilling fluid.

Casing usually not required

except near surface.

Applicable

those conta

gravel, cobDifficult t

accurately

practical

locations b

mounted equ

application

TYPES OF BORING METHODS IN SOILS


27/54

1.364 Notes: 2

2-27

WASH BORING


28/54

1.364 Notes: 2

2-28


29/54

1.364 Notes: 2

2-29


30/54

1.364 Notes: 2

2-30

COMPARISON OF LAB AND IN-SITU SOIL TESTS

(modified from Jamiolkowski et al., 1985)

Laboratory Tests

Advantages Disadvantages

- Well-defined boundary conditions

- Strictly controlled drainage conditions

- Pre-selected stress or strain path

- Uniformity of stress and/or strain in the sample

(in principle)

- Soil nature and physical features fully identified

- Size of sample limited, (are properties

representative of in-situ soil mass?)

- Sample disturbance inevitable in some soils

- Non-uniformity of sample in practice.

Development of shear planes

- Expensive and time consuming

In-Situ Tests

Advantages Disadvantages

- Large volume of soil tested, therefore should reflect

more accurately in-situ fabric of soils

- Possibility of obtaining continuous record of soil

profile

- Can be conducted in soils which are difficult to

sample

- Soils tested in their natural environment- Cheaper and less time consuming

- Boundary conditions are poorly defined*

- Drainage conditions are not controlled*

- Large degree of disturbance caused by insertion of

device in the ground (leading to highly non-

uniform fields of stress and strains around the

test device)

- Complex modes of deformation and failure areimposed on the soil

-Interpretation of engineering properties primarily

empirical/ indirect**

- The nature of the soil is not examined directly+

* with the possible exception of the Self Boring PressureMeter (SBPMT)

+ with the exception of the Standard Penetration Test (SPT)

** with the possible exception of the SBPMT and cone penetration tests (CPT)


31/54

1.364 Notes: 2

2-31

CLASSIFICATION OF SOIL SAMPLES

Class Quality Identification Properties that can be

Measured

Footnote No.

1 Undisturbed a. Block samples

b. Stationary piston

samples

A, B, C, D, E, F, G, H, I, J,

K

1,2

2 Slightly disturbed Open thin-walled

tube sampler

A, B, C, D, E, F, G, H, J 3

3 Substantially

disturbed

Open thick walled

tube sampler, e.g.

split spoondriven samplers

A, B, C, D, E, G 4

4 Totally disturbed Random samples

from augers, test pits

A, C, D, E, G 5

5 Slurried materials Wash borings B 6

Properties:

A - Stratigraphy G - Water content

B - Stratification H - unit weight

C - Organic content I - Permeability

D - Grain size distribution J - Compressibility, Consolidation

E - Atterberg limits K - Shear strength

F - Relative density

Notes:

1. Certain materials such as clean sands cannot be sampled without disturbance except by using

special techniques such as freezing. Block samples are best when dealing with sensitive, varved

or fissured clays.

2. Samples should be stored in conditions of controlled humidity and temperature.

3. Samples of this type are currently also used for shear strength tests. This practice is not optimal,

but may be satisfactory for uniform, insensitive clays. Radiography can be used to select thebest quality samples for these tests

4. Best use of these tests for estimating engineering properties is through correlations using the

Atterberg limits.

5. These samples should be kept in air-tight containers.

6. Crude but effective interpretation of stratification can be obtained by visual classifications of

washings.


32/54

2-32

SOURCES OF SAMPLE DISTURBANCE IN COHESIVE SOIL

Heading Item Remarks

1. Stress 1.1. Change in stresses due to . Excessive reduction in o~ due Relief drilling hole ling mud causes excessive defo

extension

Overpressure causes excessive

in compression1.2.Eventual removal of in situ . Resultant shear strain shou

shear stress small

1.3.Eventual reduction (removal) . Loss of negative u (soil su

of confining stress sence of coarser grained mate

Expansion of gas (bubbles and

gas)2. Sampling 2.1. Sampler geometry: These variables affect:

Technique Diameter/Length Area ratio . Recovery ratio Clearance ratio Accessories piston, .Adhesion along sample walls coring tube, inner foil, etc. . Thickness of remolded zone alo

wall2.2.Method of sampler advance . Continuous pushing better than2.3.Method of extraction . To reduce suction effect at bo

use vacuum breaker

3. Handing 3.1.Transportation .Avoid shocks, changes in tempeprocedures

3.2.Storage.

Best to store at in situ tempeminimize bacteria growth, etcAvoid chemical reactions with

Opportunity for water migratio

with storage time

3.3.Extrusion, trimming, etc. . Minimize further straining


33/54

1.364 Notes: 2

2-33

Conceptual Models of Disturbance Below Base of Borehole (Hvorslev, 1949)


34/54

1.364 Notes: 2

2-34

Observations of Sample Disturbance (Hvorslev, 1949)


35/54

1.364 Notes: 2

2-35


36/54

1.364 Notes: 2

2-36


37/54

1.364 Notes: 2

2-37


38/54

1.364 Notes: 2

2-38


39/54

1.364 Notes: 2

2-39


40/54

1.364 Notes: 2

2-40


41/54

1.364 Notes: 2

2-41

Specimen Sizes Necessary to Obtain Representative Engineering Properties of Soils

(After Rowe, 1972)


42/54

1.364 Notes: 2

2-42

Theoretical model (Strain Path Method) Indicating the Minimum level of disturbance associated

with pushing a sampling tube in clay (Baligh et al., 1987)


43/54

1.364 Notes: 2

2-43

SEISMIC REFLECTION AND REFRACTION SURVEYS

Seismic reflection and refraction tests are widely used to find the depth to bedrock based on

measurements made at the ground surface. The seismic reflection test measures arrival times of

direct and reflected waves, while the refraction test measures the first arrival times of waves for a

linear array of receiver geophones.

In both methods, an impulse sends stress waves propagating into the underlying soil from

the Source. The two principal types of body waves are p-waves (Primary/compressional or

longitudinal) and s (Secondary/shear waves). P-waves are analogous to sound waves. They travel

through solids and fluids and cause particle motions (local compression or dilatation) parallel to

their direction of travel. In contrast, S waves cause shearing deformations in which the particles are

displaced orthogonal to the direction of s-wave travel. Fluids have no shear resistance and hence,

cannot transmit shear waves:

The direction of wave travel can then be used to sub-divide s-waves into SV and SH components

(describing movements in the vertical and horizontal planes respectively).

The velocities of wave propagation in an elastic medium are:

vK G

and vG

p s= +

=4

3

where is the mass density of the soil, K and G are the elastic bulk and shear modulus,respectively.

The p and s-wave velocities can be related through the Poissons ratio, :v

v

p

s

= ( )

2 1

1 2

(e.g., for= 0.3, vp/vs= 1.87)


44/54

1.364 Notes: 2

2-44

SEISMIC REFLECTION

- example of uniform soil over horizontal rock interface

- single receiver

The impulse at S generates stress waves (mainly p-wave) that propagate radially away from

the source. Figure (a) shows the hemispherical wavefront at selected time intervals. Some of thewave energy travels along the direct path from S to R with direct travel time, td, while another

fraction is reflected back from the horizontal rock interface, with travel time trto the receiver:

tx

vand t

H x

vd

pr

p

= = +

1

2 2

1

4

where x is the specified distance between S and R, vp1is the p-wave velocity in the soil layer.

The velocity of wave propagation can be determined from td, while the depth to bedrock is found

from the measured arrival times of the reflected waves, tr:

H t v xr p

= 1

2

2

1

2 2

The distance x must be carefully selected to avoid ambiguity in the interpretation of trand td

(see Fig. b).

Soil-rock interfaces are rarely horizontal and soil layers will have important depth variations

in vp(or vs). The principle of seismic reflection can easily be extended using multiple receivers.

For example an inclined rock interface can be identified with two receivers:

vx

t

x

tp

A

dA

B

dB1 = =

If x

zt v

v t t t t x

t v x

A

rA p

p rA rB rB rA B

rA p B

:

sin

=

=

= +( ) ( )

0

2

2

1

12 2

1


45/54

1.364 Notes: 2

2-45

SESIMIC REFRACTION TEST

The seismic refraction test measures the first arrival of waves (regardless of path) at each receiver in

a linear array. One of the receivers is always located at the source.

Simple case with uniform soil overlying a horizontal rock interface. The figure shows the

wavefronts at a succession of time intervals. As the wavefront reaches the rock some of the rays

will be reflected and other will be refracted according to the angle of incidence. There is a criticalangle of incidence, ic, (that is defined by Snells law: sin ic= v1/v2) at which the reflected wave will

travel parallel to the rock interface. As the rock is generally much stiffer than the overlying soil, v2

>> v1. Hence, the wavefront (at a selected time such as t9) has a portion defined by the direct wave

and a portion controlled by the head wave. Beyond a critical distance xcthe first arrivals at the

surface are from the head wave (i.e., the rays that are critically refracted at the interface). The travel

times for the head wave to reach the nth receiver can be written as:


46/54

1.364 Notes: 2

2-46

For xn> xc:

S R

x - 2Htanicn

ic

Soil

Rock

v1

v 2

The travel times for the direct and head waves to reach the nth receiver are:

tx

vdn

n =1

tH

v i

x H i

v

x

vH

v vhn

c

n c ncos

tan

= + ( )

+ 2 2

21 1

1 2 2 1

2

2

2

Assuming that sinic= v1/v2(Snell's law).

Hence, the two waves will arrive simultaneously at a critical distance xc:

x

v

x

vH

v vc c

1 2 1

2

2

22

1 1 = +

From which the layer depth can be found:

Hx v v

v vc =

+2

2 1

2 1

For a layered profile in which the stiffness (and hence, wave velocity) increase with depth, it is

possible to interpret the thickness of each layer:

xn

H


47/54

1.364 Notes: 2

2-47

In this case the thickness of the kth layer is given by:

Hx v v

v v

H

v

v v v v v v

v vkk

ck k k

k k

j

jj

kk k j k k j

k k

=

+ +

+

+ =

+ +

+

2

21

1 1

1

2 2

1

2 2

1

2 2

The interpretation of layered profiles become much more complex if the contrast in layer velocities

becomes small, or in situations where a layer of low velocity exists below one of high velocity.

Note: The ray paths of waves become curved in soil layers where the stiffness (velocity) increaseswith depth - such as sands, gravels and normally consolidated clays. For example if the velocity

increases linearly with depth (i.e., stiffness ~ z2), then the ray paths follow circular arcs:


48/54

1.364 Notes: 2

2-48

USE OF SEISMIC REFRACTION FOR MEASURING DEPTH OF WEATHERED GRANITE

(Lee & DeFreitas, 1990)


49/54

1.364 Notes: 2

2-49

THE PIEZOCONE PENETROMETER

(after Baligh et al., 1981)

- Piezocone has cross-sectional area, A = 10cm2or 15cm2

- Device is jacked into soil at a steady rate of penetration, U = 2cm/sec


50/54

1.364 Notes: 2

2-50

VERTICAL SOIL PROFILING USING THE PIEZOCONE


51/54

1.364 Notes: 2

2-51

ADVANTAGES & LIMITATIONS OF DIFFERENT TYPES OF PIEZOMETERS

(Dunnicliff, 1993)

Type Advantages Limitations and PrecautionsObservation well Simple, inexpensive, universally available. Can

be driven in place.Not applicable if perched or artesianwater tables present. Metal elements

may corrode. Long time lag.Open standpipe Simple. inexpensive, reliable, usually has no

metallic elements. Long performance record.Can be converted to pneumatic type. Self-deairing.

Porous filter can plug due to repeatedwater inflow and outflow. Long timelag. Tubing must be raised nearlyvertical. Cannot be used ifpiezometric level is above top ofstandpipe. Freezing problems.Subject to damage by constructionequipment and consolidation of soilaround standpipe.

Closed hydraulic Simple. Reliable. Long experience record.Less time lag and less prone to damage thanopen standpipe piezometer. Allows centralobservation system to be used.

Freezing problems. Tubing must notbe significantly above piezometricelevation. Periodic de-airing required.

Pneumatic Stable. Easy to read. Short time lag. Capabilityof purging lines. Minimum Interference toconstruction. Level of tubes and readoutindependent of level of tip. No freezingproblems. Can be adapted for continuousrecording. Allows central observation systemto be used. Continuous flow type hasmoderate dynamic response.

Durability in excess of 10 years notproven. Attention is necessary toseveral detailed features in makingselection -- see text in this Session,Section 3.5 and Session E, Section9.3. More expensive than abovetypes.

Vibrating wirestrain gage

Easy to read. Can be used to read negativepore pressures. Short time lag. Minimuminterference to construction. Level of wires

and readout independent of level of tip.Suitable for automatic recording. Allowscentral observation system to be used.Frequency signal permits data transmissionover long distances. No freezing problems.Version available with in-place calibrationcheck.

Sensitive to temperature if thermalcoefficients of body and wire are notmatched. Some versions subject to

zero drift. Not suitable for dynamicreadings. Overvoltage protection andgrounding system necessary inregions of thunderstorm activity.Similar cost to pneumaticpiezometers. Zero drift may occur ifsubjected to impact.

Semi-conductorstrain gage

Easy to read. Can be used to read negativepore pressures. Short time lag. Suitable fordynamic measurements and automaticrecording. Minimum interference toconstruction. Level of wires and readoutindependent of level of tip. Allows central

observation system to be used. No freezingproblems. Version available for estimating in-situ soil properties.

Some versions sensitive totemperature. Long term stability notyet verified. Data can be falsified iftransmitted over long distances.Overvoltage protection and groundsystem necessary in regions of

thunderstorm activity. Similar cost topneumatic piezometers. Zero driftmay occur if subjected to impact.


52/54

1.364 Notes: 2

2-52


53/54

1.364 Notes: 2

2-53

Pneumatic Piezometer


54/54

1.364 Notes: 2

Vibrating Wire Piezometer