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SLIDE 1

Engineering geology

in practice in Britain: 12

3a:a oresen:a:ion,

areserva:ion anc recovery

by ADRIAN P. HUMPHREYS", BSc, CEng, FIMM, MIWES, FGS, FlnstPet

'A

knowledge

• f geologicai

principles would tend

to secure credit to

the engineer and advantage to the

society

in which he was placed....'.

• B. Smith, 1849

TO BE WORTH HIS SALT the engineering

geologist must present the engineer

• r

client

with information

that

is intelligible,

accurate, dependable

and

if

possible repeatable.

It is vital

that

this informa- tion is preserved and easily

recoverable.

Site and dient requirements

Each s'ite is unique and needs its own individual

site investigation

based

• n the

efficiency,

safety

and econom'ic require- ments

for the structure proposed. There-

fore data

and information must

be aimed

to maximise

knowledge

• f the sub-surface

at that s'ite. However, each

cl'ient usually has stringently limited funds available

for the site investigation. At

this point

the

judgement

• f

the consulting engineer aided

by the engineer-

ing

geologist recommends those

'investi- gations which

wrl'I enable

him to complete

the design

stage

'in

the most reasonable time with the unknown

• r partially

known

factors reduced

to

the bare

minimum.

Subsequent

site

investigations

• r labora-

tory testing can

usually

be

arranged

to

perm'it

superficial modification

• r
• n-

going design readjustment during

con- struction.

Prev'ious

articles

in

this series have

• utlined

site

investigation methods,

indi-

cating areas where techniques are either already developed

• r evolving.

These

in-

clude geolog'ical

field

studies, rotary

drilling,

percussion boring, geophysics, seismology,

aerial photography, ground-

water geology, soil mechanics, rock mec- hanics,

field and

laboratory testing. Interpretation even from a

small

part

• f this

range

• f investigations

completed for a specific site could include records

from many different

sources

and require detai'led examination

• f complete,

repre- sentative

• r spot

samples. Conclusions are

drawn from a very

wide range

• f

field and

laboratory samples, notes, tests, plans, maps and reports.

To secure

efli-

cient,

• rderly

examination and preserva- tion

• f 'ecords,

etandardisation

in all

forms is

highly

desirable

and usually

attainable.

Standardisation

Engineering

geology standards

in

the

UK were

• riginally

set by

individual

en- gineers

and engineering

geologists

using both

classical symbolism

and other sym-

vConsulting

geologist,

Kerves Wale, Kerves Lane, Horsham,

Sussex

bols

• f their
• wn

invention. During the

1939-45 war

and

post-war years, there was

initially a slow, but accelerating

trend

in

civil engineering and

geology towards

an improved

standardisation

in

engineer-

ing

geology.

Since 1957 most

engineers and

geo- logists

have conformed

to

the recom- mendations

• utlined

in the

BSI Code of Practice

• No. 2001
• n Site Investigation,

which

'is at present in the

revision pro-

cess.

The International Organisation for Standardisation

(ISO)

has been working

towards

an acceptable

suite of standards for some years

and has drafted

some

preliminary

reports. These have not yet received wide circulation,

• pen discussion
• r much

general

acceptance

in the UK.

The next major advance was the pub- lication

in 1970 of the Geologice'I

Society

Engineering Group's Working Party

Re- port on the logging

• f rock cores for en-

gineering

purposes.

This is followed by engineering

geologists

and consideration is now being given

to

its

possible

modifi-

cation after

five years'ractical

usage.

In

1972

another Geological

Society

Engineering Group Working Party

Report was published

• n the preparation
• f maps

and plans

in terms of engineering

geology. Adherence

to

th'is

report

is

also wide- spread

and

copies of both these book- lets, obtainable

from

the Geological

Soc-

iety at minimal

cost, should be on every

reference

and working

bookshelf. With the potential rise of computerised data storage,

it

would seem

that

in-

creased standardisation

will

be

required for all records.

Record sources

Records cover:

1.

Field

measurements

and

• bserva-

tions

2.

Laboratory measurements and ob- servations

3.

Reports

and drawings

for the en- gineer

and

client.

Field measurements and

• bservations

are made by instruments

• r description

using field survey

notebooks, magnetic tape,

field maps, plans

• r standard

forms.

As

these are the

basis for interpreta- tion

and reporting

they

should

be

pre- served after the report is written. Unfortunately

these basic records are

• ften

lost to a epecific site as an

indivi- dual

moves

• n, taking

his

notebooks

• r

even

his field maps with

• him. Some basic

records are destroyed

when

the report

is completed merely

because the operator does

not wish

to store

them. Laboratory measurements

and observa-

tions are made

by

testing techniques, description

• r

a combination

• f

both

using laboratory

notebooks,

standard forms and sometimes computer print-outs. There

is more chance of record

preserva- tion

in the laboratory

than

in the field as

the former

remains

comparatively

static,

although lack

• f storage

space

is often

considered a problem. The formal reports to the client

usually

incorporate

a distillation and interpreta- tion

• f the

'information and

data

avail- able with

conclusions drawn

from

that material. Maps,

plans, drawings,

cross- sections,

photographs, diagrams, graphs, tables

and

in cases of complexity

actual models are prepared

to

facilitate the

understanding

• f the sub-surface

structure

and

the

problems

'involved

in

a project.

These

items are usually preserved, but not necessarily

in toto and

for posterity.

Types of records

The engineering geologist

initially

ex-

amines existing

sources

• f

information, verifying and evaluating

the data

relevant

to the

new

project.

He then

prepares notes

from natural and artific'ially made

rock

and soil outcrops

in the field,

from samples

• btained

by mechanical means such

as

test

pits,

drilling,

boring and

• ther

forms

• f 'investigetron

at the site. These

field

records are then collated, re- viewed

and interpreted

for the report.

Field

records are made

in

field

books,

• n to magnetic

tape

'in a pocket recorder

and on to field maps, plans or forms sup- plemented ideally by

coloured

ground and/or air photographs.

To facilitate the descriptive

work, standard description

sequences are employed

wh'ich

ensure that no

vital

fact

is

inadvertently

• mitted.

Pen

• r pencil

can 'be used to provide a clear and unequivocal end result.

On maps and plans

where pencil

'is used

it is ad-

visable to ink

in the

field slips

the same

evening, unless

the aspect

is interpre-

tative

and dependent

• n later information.

Field records may be coloured

as th'is will

• ften

clarify a map. Coloured geological maps

can

now

be quite cheapfy repro- duced

and

are generally preferable

to

black-and-wh~ite

maps. Copies

• f the original

fieldwork should

be kept:

(i)

by the engineer,

(ii) at site, and (iii)

by the engineering

geologist. Where rock or soil samples are taken as cores, cuttings

• r spot samples,

these

should

be kept

in appropriate

containers at s'ite, although the engineer may require

a suite of representative

samples at his

main

• ffice.

The description

• f rock
• r soil

in an

underground

• pening

should

be

entered

• n a borehole

log and a suitable

• ne for

most purposes is that recommended

by November,

1976 33

SLIDE 2

DRILLING METHOD

Shell and auger to 4.80m Rotary core drilling, water flush to 25.00m

GROUND METHOD +43.63m O.D. CO-ORDI

NATES

7268/5423

• BOREHOLE. No.

MACHINE Pilcon '20'nd

B.B.S10, truck

mounted CORE BARREL AND BIT DESIGN F design barrel, diamond bit ORIENTATION Vertical

SITE

CASTLECARY DEVELOPMENT 'O', GLASGOW

WATER DRILLING RECOV SOIL SAMPLES AND

(%) &

DEPTH AND TYPE CASING PROGRESS LEVEL

OOOO

N WEDCO

0.50— 0.96 U(10) 0.96

D

2.00— 2.46 U(10) 2.46

D

CORE

R ECOV.

R.Q.D.

& SIZE

OOOO OOOO

cv'rt (000

CV W (OCO I I I I I I I I

DESCRIPTION OF STRATA Stiff, becoming hard, brown

silty CLAY with

• ccasional cobbles and boulders

(Till)

• mO

0-

co

3.50— 3.96 U(10) 3.90

W

3.96

D

4.50

D

PERMEABILITY

cm/sec x 10 s

I I I I

10 20 30 40

13.2

22

'I7

23

%24

22.3.67 22.3.67

SF

HWF ~ —4.80 —11.00

Thick bedded pale grey and brown coarse strong SANDSTONE with fine pebbles and conglomerate

• bands. Steep clay lined joints 6.00 to 7.50m.

Dark brown fine conglomerate

9.05 to 9.60m.

Mudstone flakes at 10.15m. Very coarse at base

(KIRKHILL SANDSTONE)

38.83

: I..of

• 'J

I:o.l.

'o '.I

;;I: ..o'.:I;:

~, J:'o

• ::I:o -'.I::.

I::4 ..I.o'

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.p 'It.o.

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• ".

:y 'o'. I

'o'. J.o".'2

63 .:I:,'.

(o

3.5

Qs Thin bedded grey moderately weak MUDSTONE,

sandy to 12.4m, with ironstone nodules throughout

30.2 23.3.67

I I I I I I I I I

14.00

Medium bedded grey fine strong SANDSTONE becoming laminated

17.50to 18.70m

(Borehole continued to 25.00m)

29.63 ;:I::

:.I'.'.

. I'.I .

;:..I

'.

':i.

'I;

'.:.I:": ::.I:.:'I::

':.:

'I

.-I.':"

I

.I'..'

I::

I

'.'I:.::I::

I

'.'I '.

:':'.I.:::

::I::

III

I

.n'.:rI

KEY

D W

2 V U(10) — 0.1m dia. undisturbed

sample disturbed sample Casing depth water sample Borehole depth day ground-water depth first encountered morning water

level

rate of penetration (mm/min) REMARKS Borehole chiselled 1.05to 1.90m. 4.0 to 4.45m. LOGGED BY; SCALE

• M. Jones

BLOGGS BROS. INC. 1/100

CLIENT

STRATHCLYDE CITY CORPORATION REF.

MJ/7964/30

'ig.

• 1. Example
• f borehole

log (reproduced

by permission

• f the

Geological

society

from the Quarterly Journal

• f Engineering

Geology,

• vol. 3, No. 1)

SLIDE 3 I I I I I

I

/

+'+ J + .+'

J'IVTJ +++-

f ++

+'+ + f boulders

4

x3x2m

.g

Ls'G

ation / /

( kF

/~/

rd I

No exposures.

Discontinuity pattern

in gently

Few scattered granite dipping hornfelsed mudstones

// // 55

thinly bedded and closely lointed

l,;

W

I I I along all discontinuities

boulders

I +

/~+

++

/

• (R+

"

'G'++I++M+

/++

++++ /+++ ++++

+++++++++

++++++++

+ + +/+ + + + + +

++++++++

++

++++++

1'/gm granite

head /

n 2m W V granite-

+++++++++

++++++++

++

++++++

~ + + Many granit

++ + ++~+

• Fig. 2. Example
• f field slip

(from the Quarterly Journal

• f Engineering

Geology,

• Vol. 5, No. 4)

....MZ~'

hfCF<

/

,',

I

yl

go

/

'Discontinuity pattern

in steep hornsfelsed

Lower Carboniferous

57

1m pale greenish yellow

CIOSely tO Very Widely

r 'i/VT"..'+...

'.: rr

i M~;qihO

f

d=8

~

r

V'- r

CalC flinta, Weathered in calcareous strata.+

.> r

'<I

~::.'''

• .

Fault zone with

much brecciation

/

cele flinta exposed

in trial trench

+lie e + +

/irr '

Many

smiall outcrops,

soil thin (

/

~II

/

• Ground

disturbed by r.",ining about 1860

(

(

horn'felsed muds s, thinly bedded

I

) j!

"ji t

.---,:j';I

|.4;:4',

jj:::;~-~~>",.:$

'i,,'„

/

~

++M~

r

~ +

'+ ++ +++

r/~+++G. +++ d r~ ~ ~1%SO +++++++Jr

j

~ ~

~ M y h Id

I light

h

.

• lgdg

+ e + + + + + + s,r mediumMJrained

weathered granite

+ +

cTI

r+JJJ JJ

the Geological

Society

Engineering Group Working Party,

see

Fig.

• I. Further

exam- ples are given

in their

Report".

Examples

• f field

drawings are includ- ed

in the

Geological

Society

Engineering Group Working Party Report on maps and plans and a typical

fie'Id

slip

is

shown as

• Fig. 2. Further

examples

• f field

slips

and

maps are given

in this

Report».

Measurements and

• bservations
• n

samples

in

the laboratory are recorded

• n individual

forms and graphs not neces- sarily standardised

• utside

a particular

firm or company.

Computer print-outs ere

in a form

where retrieval

is only as good

as the

• riginal

data and recovery pro- gramme fed into the machine. Program- mes are already

in

existence for some aspects

• f

borehole data storage

and

could be extended to

form a bas'ic

system. Copies

• f the

laboratory work should

be kept:

(a)

by the Engineer,

(b)

at the site, and

(c)

by the

• riginating

I'aboratory. Models

are of several

• types. The most

usual

topographic models show the

land-

scaped features

around

the

finished

pro-

ject and those with

a series of transparent formers illustrate

the sub-surface geologi- cal structure.

Dynamically

scaled models are sometimes used

by engineers

to study

deformation

in dams

and their foundations.

The kinematic model

is a particularly

valu- able aid for use

in the

determination

• f

the critical weaknesses

in

jointed

and layered

rock masses

and

for the demon- stration of attributes

• f particular

geological structures. Reports are

usually a synopsis

• f the

available information and data which has been gathered

together. Maps,

plans, dia- grams, drawings,

sketches,

photographs, tables

and graphs

are some of the

illus-

trative methods used to depict facets

• f

engineering geology. Of these

the geo-

logical fnap

• f

an

area

is the

starting point of an investigation,

see Fig. 2.

In

any

report,

fact

and interpretation should

be clearly separated

and a state- ment

• f opinion
• n the

accuracy

• f the

data and

informat'ion

given.

(continued

• n page 38)

November,

1976 35

SLIDE 4

Data presentation

For all site investigations

it is essential

to have engineers

and engineering

geo- logists

communicating

in

the same

lan-

guage, thus facilitating the exchange

• f

information and

experiences. Therefore geological

information must be intelligible, comprehensible, prefer- ably repeatable and

presented

in

a

manner

to ease

comparison

with

• ther

similar material. Information may well be derived from

techniques

in

• ther

areas

• f

applied

sciences

and may require elucidation.

Accuracy

in engineering

geo-

logy is mostly given

in generalised

terms which are broadly

defined

in CP 2001 and

the

two

Geological

Society

Engineering Group Working Party

Reports. There

is now an

increasing trend towards quanti- fications especially where geophysical borehole logs are shown

• n

computer print-outs. The geologist must describe

his

sam- ples unambiguously both

• n

drawings and

in

the written part

• f the

specifica- tion,

preferably quoting his

standards. Those parts of a report

which are deduc- tive

• r

measured should

be

indicated

and

comments made

• n the accuracy.

If

loose

geological phraseology is put

• n

specification

• r
• ther

drawings,

it

can permit

a

wide interpretation

• f

those

phrases describing the conditions found

during

explorations. This can lead to legal

liability

situations, but apart

from

that

it behoves

the geologist

to stick to

his

standards

and

the engineer

to

ensure that he has done so. The report must represent the

best

work done by responsible engineeES, en- gineering

geologists

and technicians who have carefully prepared

the data after conducting

a

testing programme.

Often disclaimers

are

written into

reports,

but there is a strong

case

for

being more

positive

by indicating

to the client

and through

him to the contractor

the degree

• f accuracy

and dependability

• f the data
• btained

usually by

extensive technical effort

by professional men

at significant

Cost. It is worth

remembering

that on almost

all

sites

the amount

• f sub-surface

in-

formation available

at the time of bidding represented

by

the amount

• f

tangible rock or soil

in

the core or

hand

speci-

men

is very much less than

1% of the

total foundation area,

i.e. less

than

• ne

NX

borehole every three square metres. The

rest

• f

the rock(soil geometry

and nature

is interpretation based

• n

the

field

judgement

• f the

engineering

geologist. Geological

units and

descriptions are not always easily pigeon-holed, but use

• f the

existing standards with common-

sense

will

aid

the standard presentation

• f data

and information.

Data preservation

Much

basic

data

and information

is tom

up or thrown

away

• n the comple-

tion

• f

individual

reports

• r the

actual construction. This destruction

• f

rock

and soil samples,

• f notes, tables, graphs,

test results,

plans, even reports and oc- casionally record drawings

is carried

• ut

sometimes at the

whim

• f quite

a junior member

• f staff. The

usual

reason

given is shortage

• r lack of storage

space.

Preservation

• f the basic records at site

can:

(1) Illustrate

the geometry

and engin- eering

properties

• f the

rock

and

so'il

types exposed and/or excavated, 38

Ground Engineering

(2) Assist

the long-term evaluation

• f

the soil or rock behaviour,

(3) Be a starting

point for further

in-

vestigations,

e.g. for structure

enlargement

• r

construction claims,

(4) Be admitted

as evidence

in case

• f failure,

(5) Be

an

• n-site

record

in

case

• f

emergency,

e.g. tunnel

collapse,

and

(6) Provide

an

example

• f the

engin- eering properties

• f the soil or rock types

for comparison with

• ther sites.

At headquarters, with developing com- puter methods and

microfilm

data storage, there

is little

reason

to make the excuse

• f shortage
• f space.

A little

time and money spent by the engineer at the end

• f a contract

would ensure that the maxi-

mum

kn'owledge

• btained

during investi- gation and

construction

rema'ined avail-

able

in

his

• ffice,

at

site

and possibly

also

in

a

future national data

storage centre.

Using microfilm,

the average

file

contents

can be preserved

• n a few post-

card sized plates, but

w'ith

advances

in

micro-miniaturisation, the

records

• f

a large project could be preserved

'in a shoe-

box sized container.

A recent

groundwater feasibility study

in

southern England was facilitated by the examination

• f the geological

logs of

an

adit

and

several wells

beautifully drafted almost

100 years

ago and kept by the present water engineer

in

his

• ffice

records. Together

with

• ther

information,

these

provided

an

excellent starting point for the study. They were

a magni- ficent tribu'te

to the

• riginal

Victorian water engineer and

to the succession

• f

water engineers who

have stewarded the

records since that time.

Data recovery

It is ideally

necessary to be able to repeat

a record

if doubt arises or accident

• ccur

and

also

if a

later investigation requires preliminary information. Recovery can

take two forms:

(i)

The original samples,

and

(ii) The descriptions

• f and

test

results from those samples. To some extent the recovery function

is filled

by the client, the engineer, the con- tractor, the Institute

• f

Geol'og'ical

Sciences

and

technical papers. But there

is at present

no standard procedure for

full

preservation and recovery

• f data.

Personally

the author

would like to see the establ'ishment

• f a central

repos'itory for sub-surface

data,

perhaps

most suit-

ably housed under

the

wing

• f the

In-

stitute of Geological Sciences who already collect

and store some sub-surface

data. The repository

would have

the

legal

power

to:

(a) Obtain

a copy of every site

investi- gation report, with maps, plans, re- sults and samples from

these,

(b) Collect

all 'information

• n past,

pres- ent

and future

surface

and under- ground

• pen'ings,

(c) Institute

a

system

• f

storage

and retrieval

• f data,

and

samples,

and

(d) Prepare

dyeline prints

• f topograph-

ical maps

at say 1:10000 or

larger

scale

• n

which the geology and location

• f

data would be super- imposed. The suite

• f maps

would

cover the

UK and

be available at all IGS offices, the repository

and per- haps

• ther

locations against

pay- ment. Interpretation

• f this

data

and informa- tion would have

to be

undertaken by an engineering

geologist

appropriate'ly qualified

to

avoid potential legal liability problems.

Conclusions

Presentation

• f

accurate,

intelligible, credible,

standardised engineering geology information

and

data

should

enable the engineer, the client

and

the

general public

also to assess

and

appreciate the geological aspects

• f

any engineering problem.

Standardised systems already exist and should be used

until

such time as improvements are made or a universally accepted system

is devised and developed.

Preservation

and recovery

• f information

and

data are becoming

rapidly

more

es-

sential as the costs of obtaining informa- tion

increase.

The contrasting situation would be

to destroy

material

• ften

gained

at

high

cost and

energy expendi- ture. The computer and micro-miniaturisation have made many advances during the last twenty years and during

the next twenty

will

become

dominant

for the storage

and retrieval

• f information.

For example, the Ordnance Survey have com- menced a pilot programme

to

produce

large

scale

maps

at 1:1250 and

1:2500

so that

the

map

• f a city

will fit on

a standard

2 200ft

reel

• f

magnetic

tape.

Such a programme could reasonably be adapted

to

engineering geology work, master

tapes

made and up-dated when

necessary. The author believes that,

in v'iew

• f the

escalating volume of geo'logical information

and data

becoming available for engineer-

ing purposes, it is of paramount

import-

ance to produce

a computerable

working manual and establish a central repository for sub-surface data

soonest. The

latter could usefully

be under

the wing

• f the

Institute

• f

Geological

Sciences

• r

the tentatively proposed Institution

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