Si:einves:ica:ion or'ae C ianneUnne 3ri'isi 'erry'ermina

by ARNOLD AARONS", CEng, FICE, A. G. WEEKS), PhD, DIC, CEng, FICE, MIStructE, FGS,and R. D. PARKESt, MSc, CEng, MICE

THE PROPOSALS FOR the Channel Tunnelincluded the provision of a terminal at theBritish end at Cheriton near Folkestone.The construction of this terminal, whichwas to cover an area of approximately129ha, would involve the solution of a widerange of earthwork problems relating toapproach roads, a surface water storagelagoon and the main railway line forthrough traffic, as well as the terminal areaitself with its attendant landslips, notablyat Castle Hill and Cherry Garden Hill. Theextent of the area is shown in Fig. 1.

The terminal was to contain road andrail embankments and a cut-and-covertunnel loop for terminal rail traffic at thewestern end. To the east and just beyondthe terminal a second cut-and-cover tunnelwas to take both main line and terminaltraffic through the toe of the Castle Hill

landslip. This tunnel would then developinto a cutting passing through, but closeto the toe of the Cherry Garden Hill land-slip.

The vertical alignment of the ChannelTunnel itself, coupled with the restrictionson space within the terminal area left littlescope for manoeuvre so that the proposalswere directed by circumstances mainlyunrelated to the earthwork problems. Itwould therefore be necessary, in the eventof any instability, for the solution to in-volve landslip stabilisation rather than anymodification of the design proposals.

The site investigations for the terminalalso included a programme of testingthe properties of the spoil material fromthe tunnel which was to be used as fillmaterial for the regrading of the site. Itwas intended that 3 700 000m'f spoilfrom the English landward and seawardtunnelling drives be used in this operation,producing fill heights of up to 12m.

Project managers for the Tunnel wereRTZ Development Enterprises Ltd. Asconsultants to RTZDE, Building DesignPartnership were architects, civil andstructural, mechanical and electricalengineers for the British ferry terminal at

"Associate, Building Design Partnership.li t Senior Partner and Senior Engineer, A. G.Weeks tk Partners.

Folkestone. A. G. Weeks 8t Partners werespecialist soils consultants to BDP, andthe site investigation was carried out byGround Engineering Ltd., of Borehamwood,Herts.

Geology of the areaFig. 1 outlines the geology of the site

area. There are minor local differencesbetween this and maps published by theInstitute of Geological Sciences, but theseresult from the large quantity of additionaldata provided by recent site investigations.

Topographically the chalk escarpment,rising to just over 160m AOD, dominatesthe area to the north; the scarp face isindented by several coombes, notablythose at Cherry Garden and, further to theeast, at Holywell, which in cutting backhave isolated conical hills at Castle Hill andSugarloaf Hill. The hard basal beds of theMiddle Chalk (Melbourne Rock) cap theescarpment and the isolated hills; thescarp face is largely coincident withthe outcrop of the Lower Chalk (80mthick) and drops steeply to the flatterGault Clay vale at about 90m AOD.

The Gault Clay (48m thick) outcropsin a kilometre wide band running east-west parallel to the escarpment. Thestrata dip gently to the east and north-east.

Underlying the Gault, and thus out-cropping to its south, are the Folkestonebeds. These consist of sands with bandsof hard siliceous or calcareous sandstone,and they occupy a large proportion of thesouthern and western sections of the sitearea. The occurrence of the Gault Clayand Folkestone Beds at the surface iscomplicated at the western extreme, westof Frogholt, by the presence of faultingclose to the natural contact between thetwo strata.

During the Pleistocene and Holoceneperiods ('Ice Age'o present day) theescarpment suffered severe erosion andthere is strong evidence to show that thecoombes were largely cut in late and postPleistocene times (the last 15 to 20,000years). The rock debris thus producedhas sludged down the coombe floors,

spreading out in broad lobes over theGault outcrop. Head, or solifluxion, de-posits of this type, produced under peri-glacial climatic conditions, are broadlygrouped as Coombe deposits by theInstitute of Geological Sciences (IGS).The vigorous nature of the erosion pro-cess is illustrated below the Cherry Gardencoombe where Coombe deposits wereseen directly overlying unweathered,jointed Gault Clay, the weathered andcryoturbated material (see below) havingbeen removed. Commonly, the movementof the solifluxion lobes has induced slipsurfaces in the underlying Gault Clay;further, the Gault shows widely the effectsof cryoturbation, that is the disturbancein-situ due to severe frost action duringthe Pleistocene.

A striking and important feature of thescarp face is the occurrence of majorlandslips affecting the strata at and aboutthe Gault/Lower Chalk interface. The slipsare apparently stable under present con-ditions with no history of recent move-ments, present evidence suggesting thatthey were initiated towards the end of thePleistocene.

The lithological characteristics of thesolid formations and drift deposits arenow briefly outlined under the unitsmapped by IGS.(i) Lower Chalk (Cenomanian)

The lower Chalk has a total thicknessof 80m; it is an impure chalk with varyingproportions of clay, and broadly it is mostargillaceous in the lower 20m to 30mknown as the Chalk Marl. The lowerchalk calcium carbonate content rangelies between 30% and 90%, the lowervalue being obtained in the Chalk Marl.There is a grey marly Chalk with palerharder beds at regular intervals of 0.5m to1m. It is the horizon chosen as mostfavourable for the driving of the mainChannel Tunnel because of its relativeimpermeability, ease of cutting by con-tinuous machines and ability to stand fora time after tunnelling without support.(ii) Glauconitic Marl

A sandy marl packed with grains of themineral glauconite which give it a distinc-

,Zfhe

Pllltlllll&lllriJilÃi L-d l » Fault, crossmark indicates downthrow side—-—.—-- Geological Boundary broken line denotes uncertainty

IAlluvium

tB Head Sul>erficial

e Coombe Depositsj

h a Middle Chalkhsa Lower Chalkhs a Gault Clayh~ Folkestone Bedsh Sandgate Beds

Cretaceous

Fig. 1. General plan view of the site with geological outcrops and landslips shown

May, 1977 43

tool

90E

O0 80

70

50

40

26LowerChalk

Chalk Marl Chalk P17Marl P

Glauconitic Marl ---— —,Glauconitic Chalk p

-41arl 5~Ii surface GGault Clay

Clay

50 100 150 200

metres

250 300 350 400 450

Fig. 2. Section through the Cherry Garden Hill landslip

75

—70

65

—55

—50

—45

"0"

„0

Angular chalk GRAY

calcareous SILT ma

Light brown, clayey, calcareousSILT with chalk fragments

Light brown grey, fissuredclayey SILT

Pale grey, fissured and laminatedclayey SILT

Remoulded grey CLAY with manyslip surfaces

Hard, grey, fissured CLAY

P1B

failure zones at 61 3&

Stiff, grey. fissured, silty CLAY

Green grey, glauconit ic CLAY

=~~EGrey silly CLAY with manyslip surfaces

Slip surface

Hard, grey, fissured CLAY

p1cj

Drown clayey SILT

Ittle grey brown, fissuredclayey SILT

x-Grey and light grey, clayey SILT

===Remoulded grey CLAY with manyslip surfaces

Hard, grey, fissured CLAY

40 m A 0.D.

Fig. 3. Detailed borehole profiles in the Cherry Garden Hill landslip

tive green colour; it varies in thicknessfrom 0.75m to 2.5m in the area and formsa convenient marker for the base of theLower Chalk. It does not appear to benotably more pervious than the ChalkMarl, although several springs emerge inthe coombe heads at or slightly above thelevel at which it outcrops.(iii) Gault Clay

A stiff fissured overconsolidated clay,blue grey in colour, more or less silty,calcareous and with occasional bands ofphosphatic nodules.

Planar jointing is prominent in the un-weathered Gault Clay, and locally thematerial was seen to behave upon initialexposure in deep trial pits as a jointed'rock'ith boulder sizes up to 1m.

In some localities the upper beds of theGault take on a very similar lithology tothe Chalk Marl. Jukes-Browne (1900)divided the formation into 13 beds, severalof which are lithologically distinctive andcan be traced over the site area. Typicalof these are bed XII, 1m of 'dark greenargillaceous greensand of marly clay fullof glauconite grains'r bed Vll, 2m ofuniform dark grey very fossiliferous clay.

The thickness of the Gault is subject tosignificant local variation, due to thevarying amounts removed in the period oferosion represented by the Chalk/Gaultunconformity, but in the site area about48m are present. In contrast to theChalk Marl the Gault shows a propensity

44 Ground Engineering

to slip when exposed in cutting faces;natural slopes in the material seldomexceed 8'.(iv) Folkestone Beds

The Folkestone Beds constitute thehighest member of the Lower Greensandand consist principally of white, yellowishor ferruginous sands with widespreadlayers cemented by a calcareous, ferru-ginous or siliceous material to form hardbeds known as Folkestone Stone. Thedepth below the top of the formation towhich these beds extend decreases west-wards. However, they are present overthe whole of the Folkestone Beds outcropin the terminal area. The presence of theFolkestone stone beds give rise to atopography dissected by small steep sidedvalleys, notably those south of Frogholtand Newington.

The top of the formation is now takento be at the top of the 'Sulphur

Band'hich

is a bed of phosphatic nodulesowing its name to the yellow alterationproducts of pyrite, which locally encrustthe nodules.(v) Coombe deposits

The IGS include in this unit all depositslaid down in the coombe floors andspreading fanwise from their mouths. Thematerial is largely derived from the erosionof the coombes and includes chalk debrisfrom mud to gravel grade, flints, organicmuds and peaty soils, and sometimescalcareous tufa deposited by springs

emerging in the coombe bottoms. Hill-wash is largely consequent on the distur-bance of ground by human cultivation andclearance in the last 2000 to 3000 years.

The thin variable deposits of the coombefloors and debris fans have accumulatedover fairly long periods of time underchanging climatic conditions. The accu-mulation of calcareous tufa probably datesfrom a 'climatic optimum'f 6000 to 7000years ago when temperature and rainfallwere higher than at present. The over-lying loamy hillwash and chalk gravel mudsmark the deterioration of climate since the'optimum'nd more recently the disturbingeffects of human cultivation.

The severe cryoturbation effecting theupper surface of the Gault presumablydates from the severe cold of the LateGlacial periods.

Site investigationThe site investigation programme re-

flected the concern over the stabilityproblems and, of the total of 85 shell andauger boreholes and 29 trial pits, 54 bore-holes and 12 trial pits were located in theCherry Garden Hill/Castle Hill area. Ineach of these boreholes continuous un-disturbed sampling was carried out andeach sample was inspected to determinethe presence and depth of any slip sur-faces. In most cases this inspection wasconcurrent with the sampling and so itwas possible to install piezometers of the

Casagrande type at the position of themajor slip surface in the Gault Clay.

For the Cherry Garden Hill landslip, theboreholes were situated along three linesand a sample section, through BoreholeNos. P26, P17, P18 and P19, is shown in

Fig. 2, which gives an impression of thescale of the problem. Borehole logs fromBorehole Nos. P17, P18 and P19 are alsoshown (Fig. 3).

Although the Gault Clay en masse has avery low permeability, of the order of 10

'o

10 'm/sec., the piezometers stabilisedwithin about five weeks and showed arapid response to changes in the ground-water table. A sample graph of the read-ings (in Borehole P17) shows that therewas a significant rise in the water level of2m occurring within the space of oneweek in late September 1974. This risewas repeated in the majority of the bore-holes and the readings remained high forat least three months before reverting toabout the original level. During this time,however, the weather was abnormally wetand owing to the cancellation of theproject, it is not known what effect theprolonged dry spells of 1975 and early1976 have had on the groundwater levels.

The results of the borehole investigationenabled several conclusions to be drawnas to the nature of the landslips and inparticular the Cherry Garden Hill and CastleHill slips.

(i) The landslips are probably of Pleisto-cene Age and the materials withinthem consist of disturbed LowerChalk, Chalk Marl, Glauconitic Marland Gault Clay.

(ii) The water levels recorded in piezo-meters installed in the lower partsof the slips —both along the slipsurface and within the slipped mass—were close to ground level. It isalso likely that the groundwater tablecorresponded very closely to thepiezometric level. This informationcould be inferred from

drillers'ecords

during boring, the emergenceof several springs near the toe of thelandslips and also the flow of waterinto trial pits excavated in the area.

(iii) The principal basal slip surfaceswere approximately horizontal throughthe Gault Clay, with a steeply in-clined back slip surface rising upthrough the Chalk Marl and LowerChalk. Inspection of undisturbedsamples had shown the presence ofnumerous secondary slip surfaceswithin the slipped mass.

The precise position of the slip surfacesbeing known, along with the piezometricdata, an accurate assessment of thestability of the landslips could be made,although this depended on the shearparameters employed.

The shear parameters mobilised alongthe slip surfaces are the residual para-meters and these were measured usingboth cut plane residual shear box andring shear tests. It has been shown thatthe residual shear stress/normal stressenvelope is not a straight line but iscurved and passes through the origin, i.e.C'c = 0, but al'„varies. Tan ss'„at anypoint is taken to be the ratio between theshear strength and the effective normalstress (see Fig. 4), i.e. the slope of theline joining the origin to the relevant pointson the shear strength envelope.

The ring shear tests provide the lowerbound values of the residual parametersand it has been found that usually theactual field values are in excess of those

130

75

50

Ring shear

x ~Residual cut plane shear foi

25

/0 100 700 300 400 5IM Effective ftofmat stress700

(kfflm )

Gault Clay in the ring shear apparatus

resulting from the ring shear test. In Fig.4 it can be seen that the results from thecut plane residual shear box tests aregenerally in excess of those from the ringshear tests for Gault Clay, the percentagedifference in tan es',. (and tp'„) being 0at an effective normal stress of 100kN/m'-'o

15% at an effective normal stress of600kN/m'-'. Previous very limited data ob-tained for London Clay has indicated thatthe difference between the field case andthe ring shear test result approaches some20%. It was therefore decided that thecut plane residual shear box tests werelikely to give the closest approximation tothe in-situ parameters in this case.(1) Castle Hill

In conjunction with information gainedfrom previous investigations in 1968 and1973 a reasonably comprehensive pictureof the failure emerged. Piezometer read-ings taken over an 18-month period be-tween 1968 and 1970 indicated that theporewater pressure levels along the slipsurface/surfaces varied by no more than3m between their maximum and minimumvalues, and in most cases the variationwas less than 2m. Stability analysescarried out in 1974 showed that the factorof safety against failure was increased byapproximately 2.5% for each 1m loweringof the water table. Therefore, assumingthe mean variation to be 2m, then themaximum variation of the factor of safetyin normal conditions would be 5%.

To determine the three-dimensionalstability of the landslip, a series of eightsections was analysed using the Morgen-stern and Price analysis. These sectionswere spaced equally across the slip, andfor those sections along which no bore-holes were situated, the positions of theslip surface and pore water pressure levelswere interpolated from adjacent sections.The factor of safety of the entire slipcould then be estimated from the ex-pression:

F,.W,F =

W,where F, = the factor of safety of a

single slice.ily, = the weight of that slice.

This method of analysing the failureassumes the landslip to have occurred asa single operation in one direction, andthat any future failure would again occurin the same direction involving the wholemass as a single entity. It is probablethat neither of these assumptions is en-tirely correct as examination of trial pitsand borehole samples taken near the toerevealed the presence of several organiclayers. This would indicate that severallandslips occurred, probably as a result oferosion of the toe by stream or peri-glacial action.

The factor of safety of the whole CastleHill landslip, calculated on the abovebasis, was 1.2. The pore pressure levelsused in the calculations were the highestlevels recorded in the period 1968-1970,where applicable, and also the levels inthe later boreholes. This factor of safetywas not, of course, an absolute value, butit did show that further movement was apossibility, particularly when consideringthe proposed earthworks within the land-slip, such as the approach cutting, tunnel-ling and landscaping. It was estimatedthat these operations would lower margin-ally the stability, but it was the intentionthat, where such low values were con-cerned, the stability should, in all cases,be maintained if not increased. It wassuggested that the introduction of drainagewith the tunnel might aid the stability and,whilst it could not be guaranteed that itwould lower the pore pressure along theslip surface, it would almost certainly havea beneficial rather than adverse effect.(2) Cherry Garden Hill

This landslip, like the Castle Hill land-slip, had shown no sign of recent move-ment. The service reservoir near the headof the slip had shown no signs of distressand was still, apparently, acceptably water-tight (to the Folkestone Water Company).However, unlike Castle Hill, this landslipapparently occurred as a single failure asthere is no evidence of the multiple failurespresent near the toe of Castle Hill.

Stability analyses were carried out, asfor the Castle Hill landslip, using theMorgenstern and Price non-circular slipanalysis, on a total of nine sections (usinginterpolated values) and the overall factor

May, 1977 45

Fig. 4. Residual shear strength envelopes forand the conventional shear box

of safety for the whole landslip wouldappear to be as low as 1.02 when usingthe very high (October 1974) piezometerreadings. It was calculated that theexcavation of the cutting in the toe couldresult in a reduction of 7% of this value.It was therefore apparent that a movementof this landslip could be activated by theproposed earthworks, unless adequatestabilisation measures were employed.

Trial cutting and drainage installationAs part of the investigation a trial cut-

ting was excavated at the position anddepth of the proposed cutting in the toe ofthe Cherry Garden Hill landslip. It wasknown that the stability of this landslipwas very low and any reduction due tothe removal of toe weighting (excavationof the cutting) had to be balanced by anequivalent increase elsewhere. Some formof toe weighting was a possibility butcalculations had shown that, once thecutting had been formed, it was possiblethat the critical failure surface wouldbecome one emerging from the toe of thecutting. In this case, toe weighting on thedownslope side of the excavation wouldhave no effect. Thus, the most viablealternative would appear to be drainage.

The cutting, of which details are givenin Fig. 5, was some 80m long and wasdivided into two sections, one half withcounterfort drainage installed, the otherhalf without. In addition, boreholes weresunk and piezometers installed at themajor slip surface as before. In this way,it could be determined whether drainageof the water close to the ground levelwould affect the piezometric level on theslip surface, some distance below. Thecontrol section, without drainage, wouldenable the comparison to be made.

(a)

+++ +

++

+

E''

E

E"

p+ + +pE''

E

'ide

drainage trenches

44ttt4,.;, ~tj j ~J JJ I j~ExcavatedChalk Harl

approx. /4 In

+piezometer positions

(b)I'll'st sexcava

E

Second stage Impartedgravel

750mm

Fig. 5. (aj General plan view of the trial cutting. (b j Details of the drainage trenchesas dug

yegg P

@i@a trltrm 'c

fx 44rr'

Ble jer Wigrti

4

(4; ttddl

'.: rtet Jj

=0 Illj I

Fig. 6. Preparing to place ballast filter material —east trench

46 Ground Engineering

: ~ Nttkr~

20

19

17 75

165 10 15

moisture conlent (%170

Fig. 7. Dry density and CBR/moisturecontent relationship for Lower Chalk (BSlight compaction test)

Compaction trialsAlthough it was proposed that spoil

from the British tunnelling drive be used in

constructing the terminal area, the firstmaterial to become available was from theFrench excavation at Sangatte. It wasarranged that compaction tests on theLower Chalk/Chalk Marl should be incor-porated into a series of trials into the useof stabilised Upper Chalk being undertakenat Sangatte.

It was originally proposed that thecounterfort drains, which were to be 6mdeep, would be installed by excavating a6m deep by 0.75m wide trench backfilledimmediately with the granular drainagemedium. However, excavations over 3mdeep in the landslipped Chalk Marl werefound to be very unstable and unsupportedvertical faces would not stand for even ashort time. The final method of installingthe counterfort drains was for the top 3mto 4m to be excavated with side slopes of2 (vertical) on 1 (horizontal), the overallwidth of excavation being some 7m at thesurface. Where the Gault Clay was en-countered vertical sided trenches could betolerated. The drainage medium was thendeposited on one side of the excavation,whilst the remainder was backfilled withthe excavated material. This meant thatthe drains were only effective on one side,as the recompacted material was virtuallyimpermeable.

Piezometer readings taken from boththe drained and undrained sections of thetrial cutting showed that there had notbeen a measurable decrease in the porewater pressure at the level of the deepseated slip surface at the base of thelandslip.

It had therefore to be assumed thatthis method of drainage, allied with thecutting, would not be sufficient to ensurethat failure would not occur in the future.This was particularly relevant since afailure and consequent disruption at thispoint would have affected, and couldpossibly have closed, the entire project.

An alternative stabilisation method wassuggested, which would have involved theinstallation of about 70 pumping wellsclose to the head slope of the landslip andpenetrating to the slip surface. Unfortu-nately, this had not proceeded beyond thefeasibility stage when the entire projectwas cancelled.

At the time of the trial in the spring of1974, the Lower Chalk (Craie Bleu) hadbeen stored under protective sheetingthroughout the winter after being exca-vated during the previous October andNovember.

The spoil, which was graded from500mm downwards, had a moisture con-tent of 7%, having decreased from 13.7%during the winter.

The trial consisted of the laying of fourstrips of the material, 20m long by 3.5mwide. Two strips were made a total of600mm thick and two 400mm thick, one ofeach pair being laid at the natural stockpiledmoisture content and one in a saturatedcondition. Each strip was made of threelayers of the required amount with a faceshovel. The chalk was then reduced in

size to a nominal 80mm maximum usinga rotovator attached to a tractor, and themoisture content was adjusted by addingwater from a tanker with a spray barattachment. Compaction was then carriedout by an Albaret Sismopactor vibratingroller in four stages, each stage consistingof four passes.

In-situ testing and sampling was carriedout after each of the compaction stages,consisting of density and Menard pressure-meter tests and the extraction of 105mmdiameter undisturbed and bulk samples.

Both British Standard Light and HeavyCompaction Tests were carried out on thebulk samples and the results comparedwith the in-situ densities. In addition, ateach moisture content a CBR test wascarried out upon the sample in the BSCompaction Mould. Whilst this is not atrue CBR test, it does enable the sensi-tivity of the material to moisture contentchange to assessed (see Fig. 7).

The two strips for which it was intendedthat the material be completely saturatedproved to be intractable when the moisturecontent reached 22%. The strips wereallowed to dry until compaction waspossible in the normal way. The resultingfinal moisture content was found to bebetween 19% an 20%.

The results showed that:(a) The in-situ densities were close to

those obtained in the British StandardLight Compaction tests, and that therewas very little difference between theresults of 8 and 16 passes (96.5%and 97.5% of the Compaction testresults respectively) .

(b) Four passes of the roller were in-sufficient for moisture contents ofless than 17.5%.

(c) The 600mm layer was too thick, re-sulting in poor compaction of the base.

(d) Both the British Standard Heavy andLight Compaction Tests showed thata very rapid decrease in CBR occurredas the moisture content of thematerial increased. In the latter case,it decreased from 34% at 12%moisture content to 10% at 15%moisture content and then to 1.5%at 19.5% moisture content.

The conclusions to be drawn from theresults were that the spoil material wouldbe suitable as fill, provided the moisturecontent did not exceed 17%. The thick-ness of the layers should not exceed300mm with compaction by a vibratingroller and a minimum of eight passes.

The above conclusions would, of course,only apply to the French material andfurther work was proposed to confirmthese findings for the British end. It ispossible that this may yet be done.

&.Trade Literature

Milestones in Soil Mechanics, by tenRankine lecturers, ed. Jeremy P. P. Blanc,reprinted from Geotechnique by The In-stitution of Civil Engineers, 26-34 OldStreet, London, EC1V 9AD. 330 pp.;illus.; price, UK E5, overseas E6 post paid,from Marketing Dept., ICE.

This reprint of the written versions ofthe first ten Rankine Lectures is a happyreminder of many stimulating eveningsspent in listening to distinguished speakersof world renown, in alternate years fromoverseas. The Lectures were made possi-ble by the remarkable success of theFourth International Conference held inLondon (1957), and the British Geotechni-cal Society has greatly benefited theprofession by them.

Professor Casagrande opened in 1961with "Control of seepage through founda-tions and abutments of dams," whichgave a useful sense of proportion ontactics for dealing with both straightfor-ward situations and the problems causedby geologic accidents. Dr. Cooling, the'father'f British soil mechanics, spokeabout "Field measurements in soil mech-anics," on which his own Division haddone (and is still doing) so much work.Monsieur Mayer's Lecture on "Recentwork in rock mechanics" helped to unifythe approach to rocks and soils.

The Fourth Rankine Lecture, by Pro-fessor Skempton on "Long-term stabilityof clay slopes", probably had as muchinfluence on engineering practice and pub-lic safety as any single lecture in theEnglish-speaking world. His lucid explana-tions and easy style helped the conceptof residual strength to be widely recog-nised and used.

Professor Newmark (1965) dealt with"Effects of earthquakes on dams and em-bankments," a subject which could wellbe repeated in the future for its importance.Professor Bishop was the first UK lec-turer to have spent his early professionalyears designing and constructing civil en-gineering works. His comprehensive studyof "The strength of soils as engineeringmaterials" reflected research and creativeequipment design over many years.

The late Dr. Bjerrum's Seventh Lecture,on "Engineering geology of Norwegiannormally-consolidated marine clays asrelated to settlements of buildings,"showed a happy blend of ingenuity andpractical judgement in situations wheresoil properties were previously not wellunderstood. The lifelong practical experi-ence of Rudolph Glossop made his 1968Lecture on "The rise of geotechnologyand its influence on engineering practice"a useful contribution to historical per-spective. The "design-as-you-go" principlehe mentioned is possibly the greatestcontrast with conventional engineeringdesign.

Professor Peck's Ninth Lecture on the"Advantages and limitations of the obser-vational method in applied soil mechanics"was a reminder of Terzaghi's powerfulinfluence on his close associates. The

May, 1977 47