The Seventh Terzaghi Lecture

8991

J une, 1972

SMb

Journal of the SOIL MECHANICS AND FOUNDATIONS DIVISION Proceedings of the American Society of Civil Engineers

THE SEVENTH TERZAGHI LECTURE Presented at the American Society of Civil Engineers Annual and Environmental Engineering Meeting, New York City, New York October 19, 1970

. WILLIAM LAMBE

INTRODUFTION OF TERZAGHI LECTURER By James K. Mitchell

In honor of the "Father of Soil Mechanics," Dr. Karl Terzaghi, the Soil Mechanics and Foundations Division established the Terzaghi Lectureship in 1960. At about yearly intervals the Executive Director, upon recommendation of the Executive Committee of the Soil Mechanics and Foundations Division, invites a distinguished geotechnical engineer to deliver the Terzaghi Lecture. This invitation is considered one of the highest honors that can be bestowed on a member of the soil mechanics fraternity by his colleagues and, at the same time, it serves as a living memorial to the late Dr. Terzaghi. The six previous Terzaghi Lectureres are: 1963, Ralph B. Peck 1964, Arthur Casagrande 1966, Laurits Bjerrum

1967, H. Bolton Seed 1968, Philip C. Rutledge 1969, Stanley D. Wilson

When outstanding individuals are introduced we very often hear the cliché, 'He really needs no introduction." However, to properly appreciate the magnitude and scope of the contributions of this year's Lecturer, the facts are as follows: He received the Bachelor of Civil Engineering degree in 1942 from North Carolina State University. After a period in engineering practice he joined the faculty of the Department of Civil Engineering at the Massachusetts Institute of Technology. In 1944 he was awarded the S.M. degree, and in 1948 the Doctor of Science degree from that institution. He advanced rapidly through the academic ranks and served from 1956 until 1969 as Head of the Soil Engineering Division. In 1969 he was appointed the Edmund K. Turner Professor of Civil Engineering, the first person to hold this new chair. In the early 1950's he directed his research activities at problems in soil technology, soil stabilization, and frost action in soils. He has been generally recognized as one of the pioneers in the application of physico-chemical principles and compositional considerations to the study of soil behavior. Just as Karl Terzaghi recognized in the early stages of his career in soil mechanics that the solution of important problems required improved knowledge of the physical properties of soils, our speaker tonight recognized that many facets of soil behavior can only be understood by probing into the compositional and structural characteristics of soil as an engineering material. Throughout these years he engaged in an active consulting practice and became recognized as an outstanding engineer who could identify problems and who wasn't afraid to try innovations in their solution. Starting in the last half of the 1950's he began to direct his research and consulting efforts more and more towards the use and evaluation of soil mechanics methods for the prediction and assessment of the field performance of engineering structures. This research has resulted in major advances in techniques for settlement and stability analysis, improvements in construction practice, and extensive developments in field measurement techniques. One of his best known and most significant contributions from this work is the Stress Path Method for analysis of deformation and stability problems. Also evolving from these studies has been the ICEP, or Integrated Civil Engineering Project, concept, which is the subject of tonight's lecture. His many important consulting projects ah over the world have served as excellent case studies for the development of this approach. Our Lecturer has authored or coauthored some 70 papers on a variety of topics in the field; he is the author of the book Soil Testing for Engineers, which is known around the world; and he is a coauthor with R. V. Whitman of the recently published book Soil Mechanics. He is a registered Professional Engineer in Massachusetts and in Vermont, and a member of several professional societies. His service to ASCE has included the chairmanship of the Soil Properties and Session Programs Committees of the SMFD and service on the Executive Committee, where he was chairman in 1967. His awards are many, including from ASCE, the Collingwood Prize (1951), the Wellington Prize (1961), and the Norman Medal (1964). He has twice received the

Desmond Fitzgerald Medal of the Boston Society of Civil Engineers, and has been twic cited by the National Aeronautics and Space Administration for contributions to Th Apollo program. These are the facts about Thomas William Lambe. To those who know him there i, considerably more. Almost 20 yr ago, in the summer of 1951, I began as an eager nes graduate student and fumbling research assistant under the supervision of Bill Lambe Our association has been close since. His inspiration and guidance over the years have (been of inestimable value to me. I am sore these feelings are echoed by all those who (have been his students. His enthusiasm, energy, and zest for Life serve as an outstanding example. He brings an intensity and efficiency to his work that are matched by few others. Jf present to you Professor Lambe, the Terzaghi Lecturer for 1970. 1

'I HE INTEGRATED CIVIL ENGINEERING PROJECT By T. William Lambe,' F. ASCE

NATURE OF THE INTEGRATED CIVIL ENGINEERING PROJECT The Integrated Civil Engineering Project—ICEP—is an approach to civil engineering that my MIT colleagues and I have evolved during the last decade and a half. Fig. 1 summarizes the essentials of the Integrated Civil Engineering Project. The objective of ICEP is to create and to utilize a constructed facility to meet specified criteria of function, economy, life, safety, and compatibility. All of these criteria except compatibility are well under-stood by the civil engineer. The term compatibility means that the constructed facility must harmonize with and complement its environment. It must not offend nature and life near the facility; it must obtain public acceptability. The underlying principle of ICEP is: in order to obtain a constructed facility that meets the specified criteria, it is essential to integrate the components of the project. These components range from project conception to project completion and include: (1) Establishment of the need of a facility: (2) financing; (3) planning; (4) investigation and evaluation of sites; (5) design; (6) construction; (7) surveillance; (8) operation; (9) maintenance; and (10) alteration. The whole point of the ICEP concept is to overcome the isolation of project components. ICEP was devised to help ensure that the components were integrated, to ensure that the boundary conditions employed in the various components were consistent, and to ensure that the engineers' efforts were used most effectively. Of course, I am not the first engineer to worry about treating a project in its entirety, i.e., as a system. Terzaghi himself worried a great deal about the lack of cooperation between designer and builder. In his paper "Consultants, Clients, and Contractors" (1958) he deplored the usual situation of little cooperation between the designing department and constructing department of a company. Rutledge in his Terzaghi Lecture lamented the lack of close cooperation between the planner and the designer. The Observational Method, developed by Terzaghi and by Peck, attempts to tie design and construction together. Surely other engineers have worried about the lack of integration of the components of a project. The key feature, in fact, the heart, of ICEP is the way in which the project components are integrated. The execution of ICEP is: evaluate each important prediction and use this evaluation to improve the present facility and future facilities. Thus the essential actions of ICEP are to identify and check the Note.—Discussion open until November 1, 1972. To extend the closing date one month, a written request must be filed with the Executive Director, ASCE. This paper is part of the copyrighted Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 98, No. SM6, June, 1972. Manuscript was submitted for review for possible publication on September 28, 1971. ' Edmund K. Turner Prof. of Civ. Engrg., MIT, Cambridge, Mass.

ENGINEERING PROJECT

various predictions made during the course of the project and then to employ the results of these checks. In the typical project, many of the predictions critical to the planning and designing can only be checked by observing and measuring actual conditions encountered during construction and operation of the facility. For example, when designing a dam, the engineer uses the results of subsoil exploration to predict the dimensions and properties of the various soil strata. During construction he may find the thickness or permeability of one of the layers quite different from that predicted. He should then use this information obtained during construction to alter the design and method of construction as required. Thus, using data obtained during construction, the engineer integrates the design and construction phases of the project.

ICEP DEFINITION An Approach to Civil Engineering. OBJECTIVE To c r e a t e a n d u t i l i z e o C o n s t r u c t e d Fa c i l i t y t h a t m e e t s s p e c i fi e d C r i t e r i a o f Fu n c t i o n , E c o n o m y, L i f e , S a f e t y & C o m p a t i b i l i t y.

PRINCIPLE A close integration of Project Components is required to obtain Objective.

EXECUTION Evaluate Critical Predictions and use evaluation on present facility - ICEP PRACTICE - and on future facilities -ICEP RESEARCH.

I'IG. 1.—ICEP ESSENTIALS On civil engineering projects the engineer's predictions are almost never precisely correct. Among the reasons these predictions are incorrect are: 1.

Subsoil conditions are generally ver y complex and difficult to characterize accuratel y on the basis of a reasonable exploration and testing progra m. 2. Facility loadings arising from nature's action—earthquakes, wave forces, storms, etc.—defy precise predictions. 3. Construction procedures, especially those involving soil are highly dependent on conditions encountered at the site, weather conditions, human behavior, etc. 4. Alterations in the environment caused by the presence of the constructed facility are very difficult to predict. Un fo rtun at el y, fe w eng ine er s re al ic e how unr eli abl e the ir p red ic tion te chniqu es ar e and how gene ra ll y poo r a re the dat a used in th ei r pr edi ct ions.

TERZAGHI LECTURES

Even worse, few engineers know the extent that their work is based on predicted conditions. Further, because the engineer seldom checks his predictions in actual practice, he generally builds up an unjustified confidence in his procedures. There are, of course, predictions that cannot be readily checked. For example, the effects of a design earthquake or design flood on a structure can rarely be fully checked because the earthquake or flood is not likely to occur. Even so, a partial check can be obtained by measuring and interpreting the performance at a loading less than the design loading. ICEP is based on evaluating the critical predictions made during the project and using the results of the predictions. In ICEP Practice, the prediction evaluation is used on the project at hand or on a similar project in the same area, typically for the same owner. In ICEP Research, the prediction evaluation is used to check and, hopefully, improve prediction techniques, i.e., improve the state of knowledge for use on facilities to be constructed later. A sharp boundary does not exist between ICEP Practice and ICEP Research. In carrying out ICEP practice one frequently also does ICEP Research. To execute ICEP Practice requires both that the predictions be evaluated and that the evaluations be used. In executing ICEP Research, the main effort is devoted to evaluating the predictions. To use effectively the results of prediction evaluation on a current project, i.e., to carry out ICEP Practice requires: 1.

Obtaining, processing, and interpreting appropriate information, usually field data, very expeditiously. 2. Close communications among the various organizations and engineers within the organizations involved with the project. 3. A project setup that is responsive enough to utilize the results from checking predictions. The difficulties associated with obtaining accurate field data and using it expeditiously are much greater than many engineers realize. One cannot help but suspect that filing cabinets are bulging with incorrect field data and field data that have never been utilized. This presentation describes several illustrations of ICEP. After the ICEP examples, some general findings are presented and discussed.

AMUAY RESERVOIRS Project Description.—An excellent example of ICEP Practice consists of the oil storage reservoirs built by the Creole Petroleum Corporation at Amuary, Venezuela. In 1955, Creole built its first fuel oil storage reservoir— FORS-1 and in 1956 built its second—FORS-2. (FORS comes from Fuel Oil Reservoir Storage.) In 1962, FORS-1 was expanded from its original volume of 4,000,000 barrels to 11,000,000 barrels by raising the dam from 13 my high to 24 m high. [Measured volumes of the reservoirs in 1970 were: FORS1 volume = 11,363,010 barrels; FORS-2 volume - 9,490,400 barrels; and FORS-3 volume - 7,874,000 barrels. (One barrel = 42 gal = 5.610 ft 3 0.610 m 3 )] The third Amuay Fuel Oil Storage Reservoir—FORS-3—was built during the summer of 1969. FORS-3 was formed by constructing a dam

ENGINEERING PROJECT

230 m long and 22.3 m high (at its maximum height) to enclose a natural quebrada, i.e., a small ravine. The fuel oil storage reservoirs have proved to be spectacular successes. In comparison with conventional storage in steel tanks, open reservoir storage has certain inherent advantages, i.e.; 1. 2. 3. 4.

Much greater storage capacity per unit area of real estate. Simpler pumping facilities needed. Shorter time required for design and construction. Much cheaper per unit storage capacity for both initial cost and maintenance cost. These technical and economic advantages for a reservoir far outweigh the technical advantages of tank storage, i.e., steel tanks permit more flexible operation of the refinery and result in lower oil loss from evaporation and leakage. The oil retention capacity of the reservoirs is based on the phenomenon of Interfacial tension. A fine grain soil properly compacted at a high water content will retain oil with zero leakage. Using the setup shown in Fig. 2, one can demonstrate that until the pressure of oil exceeds the oil entry pressure, no oil will invade the water-wet soil sample. Critical Predictions.—among the many predictions required in the creation and utilization of the oil storage reservoirs were two critical ones, namely: (1) the soil lining the reservoir would retain the oil; and (2) the soil slopes would remain stable. Field exploration and extensive laboratory tests indicated that a local plastic clay would satisfactorily retain oil with no leakage under a head of 30 m. Laboratory tests were run to measure the strength characteristics of both undisturbed and compacted soil. Stability analyses were based on the laboratory determined soil parameters and predicted values of pore pressure. Evaluation of Predictions.—Creole's sudden need for a large amount of storage for fuel oil placed a severe restriction on the time available for planning, investigation, testing, and designing. The time available, a few months, was much too short for conventional steel tankage to be built. This fact significantly influenced Creole's decision to employ the untried scheme of an earth reservoir to store fuel oil. The severe time restriction precluded an adequate field exploration program. Because of this fact and because the scheme of storing oil in an earth lined reservoir was untried, Creole agreed to a field surveillance program. To execute surveillance and maintenance programs for an oil storage reservoir was logical for Creole, an organization that normally carries out inspection and maintenance programs on its steel storage tanks. Fifteen years of experience at Amuay have shown that surveillance and maintenance of oil storage reservoirs costs much less (per barrel of oil stored) than does the Inspection and maintenance of steel tanks. The surveillance program consists of installing and reading field measuring devices (oil detection wells, water wells, piezometers, inclinometers, bench marks from which vertical and lat eral movement could be detected, stress cells, and temperature measuring devices), sampling periodically the embankment and natural slopes, and periodic inspections by an engineer. The field measuring system was installed gradually over a long period of time.

TERZAGHI LECTURES The evaluation of fi eld perfo rmance has shown that the compacted clay core in the earth embankments has retained oil with zero leakage. On the other hand, measurements made in the oil detection wells and examinations

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FIG. 3.—WEST-EAST SECTION, REFINERY AREA made in test pits have revealed that oil has penetrated cracks in the natural soil slopes of FORS-1 at least as far as 30 m. In the abutment areas oil penetration into cracks of natural soil caused concern both from the view of

ENGINEERING PROJECT

oil loss and from the view of slope stability near the abutments. The natural slopes that formed three sides of both FORS-2 and FORS-3 were lined with compacted clay based on the experience at FORS-1. The most troublesome aspect of the stability studies made in connection with the design of the oil storage reservoirs was the prediction of pore water pressure that would exist in and under the embankments, and in the natural hillsides. We predicted that pore water pressures in the embankments would be negative and in the foundations of the embankments the total head would average less than 13.5 m, corresponding to an excess pressure of 12 tons/m 2 . (See Lambe, 1963, for a discussion of stability studies on FORS-1.) Field measurements have indicated that negative pare water pressures do exist in the embankments and the excess water pressures in the foundations are far below 12 tons/rn 2 . In studying the stability of the natural hillside, the engineer predicted that the phreatic surface would remain at El. 1.5 m, as determined from borings made during the exploration for the projects. This prediction turned out to be incorrect—in fact, horrendous! Fig. 3 shows measured total heads. There exists a perched water table trapped above El. + 10 by the layer of fat clay. There appear to be two sources of the perched ground water. First, the extensive construction of refinery structures, roads, and asphalt sheets to retard erosion have significantly reduced the evaporation of ground water; second, leaks in the refinery drainage system and especially in the pipes carrying water for fire protection have introduced large quantities of water into the ground. Use of Prediction. Evaluations.—Prediction evaluations have been used in nearly every component of the FORS projects. In planning FORS-3, consideration was given to selecting a site with a minimum of cracks in the natural hillside. In designing FORS-3, the entire reservoir was sealed with a clay core in the embankment and a clay liner over the floor and along the natural hillside. Further, a drain and water collection system was installed at FORS-3 to facilitate the lowering of pore water pressures in the natural hillside. On several occasions the field measuring system has been used to guide the safe operation of the oil storage reservoirs. For example, during 1969 the permissible minimum level of oil in FORS-3 was based on readings from the piezometers in the east wall of the reservoir. Rising piezometer levels in the north abutment of FORS-2 during 1967 and 1968 led to the decision to execute a surface drainage maintenance program behind FORS-2. This surface drainage program resulted in a lowering of subsurface pore pressures. Other examples could be cited to show that the results of field measurements and performance evaluation have been and are now extensively used in the planning, design, construction, maintenance, operation, and alteration of the oil storage reservoirs at Amuay. MIT FOUNDATIONS Project Description.—in 1960, MIT began a major expansion of its physical plant. Because of the high cost of foundations and construction delays attributal to foundations of campus buildings, MIT initiated in November, 1962 the program, "Foundation Evaluation and Research—MIT" called, FERMIT. The

TERZAGHI LECTURES

E XC A VAT ION

purposes of FERMIT are: (1) To ensure that building foundations constructed on the MIT campus perform satisfactorily; (2) to reduce the chances of foundation construction damaging existing structures; and (3) to reduce the cost and construction delays associated with foundations. The heart of FERMIT is the evaluation of field performance, i.e., evaluation of the important predictions made in the planning, design, and construction of the MIT foundations.

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Critical Predictions. —The design and construction of foundations built be-fore the mid-1960's were based on the following three critical predictions: 1. Dewatering for the construction of a given foundation would lower the water table only in the vicinity of that excavation.

ENGINEERING PROJECT 2.

Foundations of long end-bearing piles would perform better than shallow floating foundations, i.e., undergo less total settlement and less differential settlement. 3. The construction of foundations on long piles would cause less dis-turbance to adjacent saructures than would the construction of floating foundations . There were a number of other predictions made, some of them being used TABLE 1,—MIT BUILDINGS Foundation type

Number of buildings

Number of stories

Settlement, in inehes

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7 5

6 to 29 6 to 30

1 Lo 2 1/2

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Materials Space Refrigeration

Life Selences Student CAES Chemistry MaeGregor

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190

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TERZAGHI LECTURES to arrive at the three critical predictions. For example, predictions of the rate of bottom heave of an excavation and settlement following foundation construction were employed in the prediction of behavior of floating foundations. Evaluations of Predictions.—Observations at many wells around the MIT campus have proved that the first prediction was very bad. The data in Fig. 4 indicate that dewatering for an excavation can depress the ground-water piezometric level for a very large distance from the excavation—greater than 1,000 ft. Extensive field measurements have shown that foundations on end-bearing piles do perform better than buildings on floating foundations—however this Superiority in performance is very slight. The data in Table 1 indicate that foundations on bearing piles settled about 0.5 in. whereas floating foundations settled up to 2 in. Data on differential settlement presented in Table 2 indicate that the floating foundations have behaved about as well as the pile foundations Extensive field measurements have shown that Prediction 3 is not correct. Pile driving causes greater disturbance to adjacent structures than does a Properly mute excavation for a floating foundation. As indicated in Fig. 5, Pile driving, even in preaugered holes, develops large excess pore pressures in the foundation clay. During pile driving adjacent structures heave and, as the excess pore pressures dissipate, the structures settle. The field data in Fig. 6 illustrate this point. On the other hand, settlements resulting from nearby excavations have been minor--less than 0.04 ft. Use of Prediction Evaluations.—Extensive use has been made of the results from FERMIT. The evaluations of the three critical predictions have resulted in several actions by MIT. Unrestricted ground-water pumping on the MIT campus is no longer permitted. Engineers and. contractors must submit dewatering schemes to MIT for review and approval. The evaluations of Predictions 2 and 3 have led to the conclusion that floating foundations on the MIT campus are superior to foundations on bearing piles. In addition to this technical superiority, floating foundations have a distinct economic advantage over deep pile foundations. Thus, MIT is going more and more to floating foundations. Only for unusual situations will MIT approve a proposal involving a deep pile foundation. Both engineers and contractors have requested that FERMIT participate on their projects—a true measure of the value of FERMIT.

LAGUNIL LAS PRELOADS Project Description.—in early 1960 the Creole Petroleum Corporation was faced with the necessity of constructing three very heavily loaded tanks on weak sub soils at Lagunillas, on the east coast of Lake Maracaibo, Venezuela. The three tanks were part of a dehydration process and would operate at capacity. A foundation analysis based on in situ undrained shear strengths showed a factor of safety for each tank less than unity, in fact, about 2/3, Close to the area where the three tanks were to be built, another oil company had constructed a tank on subsoil conditions presumably similar to those at the Creole site. During the test loading of the tank, the foundation suffered a complete shear failure. At the time of the foundation failure, the applied surface load was about 1/2 of the design load for the tanks Creole proposed

ENGINEERING PROJECT to build. This other company founded their rebuilt tank on piles. An engineering Study revealed that Creole could save considerable money by employing a preload technique for their tanks rather than installing a pile foundation. Fig. 7 shows the size of preload used at two of the tank sites. The preloading was successfully carried out. Lambe (1962) describes certain aspects of the Lagunillas preload project. ti - 28.3

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FIG. 8.—LAGUNILLAS PRELOAD S—II Critical Predictions.—On the Lagunillas preloads there were two critical predictions, namely: 1. 2.

The preload could be fully built in a reasonable time. The weak and compressible foundation could be adequately improved in a reasonable time. Since the preload was to be built at such a rapid pace that essentially no dissipation of pore pressure was expected at the center of the clay layer, the Lagunillas project offered an excellent opportunity to examine available

TERZAGHI LECTURES techniques for predicting pare pressures developed under undrained conditions. Evaluations of Predictions. — the results of the field measurements shown in Fig. 8 proved that both of the critical predictions were correct. The full

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preload was placed in a little over a 3-rnonth period without a foundation failure occurring. Settlements were very large, almost a meter, during loading. The data in Fig. 8 also indicate that a large portion of the excess pare

ENGINEERING PROJECT 'FABLE 3.—SHEAR STRESS AT P1EZOMETERS (Ao. -

Piezometer nurnber

)/2 by elastic theory, in pounds per square foot 1,220 1,290 1,360 1,390 1,460

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FIG. 11.—GENERALIZED SOIL PROFILE

TERZAGHI LECTURES

pressure in the foundation was dissipated during the preloading period. Originally it was thought that only 6 months were available for improving the foundation by preloading. The process engineers had difficulty in debugging the dehydration process and the preloads were thus permitted to remain in place almost 3 yr. Thus the second prediction—that the foundation could be improved during the available time for preloading—was correct, but in fact the actual time was far greater than initially thought. Fig. 9 presents the results of field vane shear tests run in the foundation soils during the preloading period. These data indicate a considerable strengthening of the soil, especially in the upper boundary. On the basis of subsoil exploration and laboratory tests, the engineer predicted that the clay layer was freely drained both at the top and the bottom. Piezometers installed in the silt layer above the clay confirmed that the silt served as a free drainage layer for the clay. The prediction of free drainage at the bottom of the clay was checked by the insertion of Piezometer P-31. As can be seen in Fig. 8, the clay was not freely drained at the bottom. Fig. 10 presents a comparison of predicted and measured pore pressures at the center of the clay for an undrained loading. The details of these predictions are described elsewhere (Lambe, 1962). The comparison shows a very close agreement between predicted and measured pore pressures. The closeness of this agreement is remarkable in view of the fact that the computed shear stress at most of the piezometers far exceeds the shear strength of the clay (see Table 3). Note that techniques 4 and 5 gave precisely correct predictions of the pore pressure at P-21 even though both techniques are based on elastic theory. Elastic theory predicts a shear stress of 1,220 psf for the clay which has a shear strength of 400 psf to 500 psf, as indicated in Fig. 9. Use of Prediction Evaluations.—The Lagunillas preloads actually served two purposes. First, by using a preload which subjected the foundation to a more severe loading than did the fully loaded tank, the preloads served as test loads. If the preloads could be satisfactory built to full height, it was then almost certain that the tanks could be built without causing a foundation failure. The preloads were built at a rate determined by stability analyses for partially drained foundation conditions, tempered by judgment from the field measurements. Thus the performance evaluations proved that the stability techniques used worked for the Lagunillas conditions. The stability techniques were then applied with confidence to the three tanks for which the pre-loading was done and for later construction at Lagunillas. The evaluations of predictions were also used to design and construct the tank foundations and to guide the tank test loading.

KAWASAKI RECLAIMED LAND Project Description.—the desperate shortage of land available in Japan for industrial development has necessitated extensive site construction by reclamation of underwater areas. Fig. 11 presents a generalized soil profile of two sites developed by the Toa Nenryo Company. Aspects of this project are described in detail in Lambe (1969). Critical Predictions.—The development of the Toa industrial sites involved two critical predictions, namely:

ENGINEERING PROJECT Cfn

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SITE 300 15 cm

20 cm

SITE 400

2 5

cm

3 0

c m

33 cm

40 cm

0

7

FIG. 12.-KAWASAKI SITE SETTLEMENT, JULY 1963 TO FEB. 1965

a.

'1

.cr a. a - I^ SETTLEMENT

2 0.5

z w

1

.1° a.

1- W W m

W cc z Z 0 u

o

u. o

u

1.0

1

Feb. 1963.

la • 0 z  1, 1

1.5

1962 I 1963

LEGEND 9

E

18-4-

17

- A

19

18

-

19-2 -

20 cm/yr

- 2 - 43- 19-4 -

30 cm /yr

18

18 -3 - 19 20 I

-

O

10 cm/yr

1964

1

1955

1967 SETTLEMENT OF REVETMENT — StTE 400

FIG. 13.-SETTLEMENT OF SITE 400

1966

1968

TERZAGHI LECTURES

1. The subsoils were in static equilibrium. 2. The hydraulic fill required no special drainage. Evaluations of Predictions.—the initial planning and design for the Kawasaki industrial sites were based on the assumption that conditions were static. Because of the recent placement of the hydraulic fill and because of the well-known pumping of water from the subsoils for industrial use, the engineer predicted that conditions were not static. Settlement devices and piezometers were installed throughout the two sites. Figs. 12 and 13 proved that the Kawasaki area was not in static equilibrium but was settling at a rapid rate. Fig. 24 compares predicted and measured values of total head for Site 400. This figure indicates that considerable excess pore pressure still exists and that continued settlement can be expected. Attempts to limit the o le)

4 -

4 , 4

FI LL 7 0

20

CLAY 1

z 210 z o CL AY II - 40

36.0 CLAY

III

46.0

- 60 0

+10 TOTAL HEAD IN METERS

FIG. 14.—TOTAL HEAD AT SITE 400 (19(38) pumping of ground water may prove to be effective in reducing the general site settlement. To check the need for special drainage in the fill and to evaluate the relative effectiveness of paper and sand drains, the load test shown in Fig. 15 was carried out. By having settlement observation points at the top and bottom of fill in each of the three treated zones, a determination could be made of the effectiveness of the drains. The settlement of the fill is shown in Fig. 16. These data show that the fill consolidates almost as rapidly as the test load was built and there was no significant difference in settlement behavior among the three zones. Pore pressure readings in the fill confirm that essentially no excess pore pressures were developed by placement of the load test.

These measurements of settlement and pore pressure confirm that Prediction

ENGINEERING PROJECT

El

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INCUNOMETER

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15.—LOAD TEST SITE 400

-

TERZAGHP LECTURES

Center of Load S 1 -5 2 No Treo ?mear

5

9 - ST

— O Sond Orme

5,3

0.1 z

o

O,

NOV

DEC.

JAN.

OCT.

FEEI 1 MAR.1 APR 1 MAY 1 JUNEJ111Jef AUG l SEP 967

1

1966

FIG. 16.-SETTLEMENT OF FELL TIME 3

.119631

19645

1

IN

YEARS

4 119651

SET TLEMENTS

2

1

5 119661

6 119171

7 119581

P R ED IC T E D SI T E SE T T LE M E NT (Fr o m fi n p l o c e m e n 1 o n d p u m p oo fr o m d e e p p i c u yi

S E T T L E M E N T O F TA N K SHELL

Tonk 3.

Ilion, Sheil Sel7le1nen1 Tonel, Average 5he11

elllement

11.6rn - atter 25 Yo r k 2 , Av e r a g e — iSheH Senlement

P R E D I C T E D S E T T L E M E N T , S I T E + TA N K

yeorsl

(2.5 fr- oft tv 25 veces)

FIG. 17.-COMPARLSON OF PREDICTED AND MEASURED TANK SETTLEMENTS

ENGINEERING PROJECT 2—no drains needed in fill—was correct. Fig. 17 shows a comparison of predicted settlement and measured settlement for the large crude oil storage tanks built at Site 200. The field data show that Tanks 1, 2, and 3 settled almost the same amount and the prediction of tank settlement was correct. The close agreement between predicted and measured tank settlements is remarkable in view of the fact that the engineer used the wrong tank load in making his settlement prediction. Based on information supplied to him, the soil engineer predicted that for the first few years the tanks would operate at near capacity. He thus made his settlement predictions on the basis of a tank full of oil. The actual loading history of one of the large tanks indicated that the tank operated close to half capacity. The engineer making the settlement prediction should have somehow approximated the predicted loading with a cyclic load, averaging hall capacity, rather than a static load of full capacity. DIFFICULTIES WITH ICEP The initiation and execution of ICEP has encountered both technical and nontechnical difficulties. To obtain and install field measuring devices usually required considerable time and money. Even though there have been recent developments in field instrumentation, the profession is a long way from having reliable devices to obtain all of the types of data needed for performance evaluation. When a device goes bad on a field project, the consequences are generally more serious than would be true in a laboratory experiment. One seldom gets a second chance on an actual project whereas a laboratory experiment can usually be repeated. The most troublesome of the nontechnical problems is the difficulty of obtaining the opportunity to do ICEP. Many owners are understandably reluctant to finance ICEP because of its preventive rather than its remedial or curative nature and because of the uncertain results of the performance evaluation. Owners are much more receptive to programs of field measurements after serious troubles have developed. The systems normally employed to create and operate a constructed facility are not ideal for the close integration of project components. On the typical complex project the large number of organizations involved, the system of payments, the allocation of responsibilities, etc., combine to make it very difficult to obtain maximum value out of a performance evaluation. ICEP IN THE UNIVERSITY The conduct of ICEP Research and the study of examples of ICEP Practice are of great value to the student and to the profession. ICEP has developed knowledge and fed it directly into the classroom, thereby making courses relevant and, in fact, exciting. Many of today's students want the opportunity to apply recently learned fundamentals to real field cases. They want and need the perspective which can be gained from studying the integration of project components on a constructed facility. For the last couple of decades the university has been the most important source of research in civil engineering in the United States. A disproportionately high percentage of papers published by the ASCE are authored

332

TERZAGHI LECTURES

by educators and further a disproportionately high percentage of ASCE Prizes awarded for research and publications are won by educators. For example, during 1969 there were a total of 95Q authors of papers published in the Journals of the American Society of Civil Engineers. Sixty-six percent of these authors were educators; a group that constitutes 8 % of the total membership of the ASCE. Two reasons why the university is such a powerful force in civil engineering research are: 1. 2.

A major objective of the university is to produce and disserninate knowledge. The university has a continuous flow of students who question the accepted and then search for the answers to questions that they (and their professors) raise. Unlike industry, the university does research primarily to contribute to knowledge, not to produce proprietary products and techniques. Publication of the results of research is encouraged—maybe over encouraged. ICEP Research constitutes an ideal format for university research. It gives the professor and his students real cases lo study. It indicates to the professor those aspects of prediction techniques that are deficient. ICEP thus gives the professor and his student the opportunity to select significant problems—those most in need of research. ICEP Research would seem to offer a solution to the problem of a growing percentage of published papers being theoretical, whereas the percentage of case studies is declining. A potential problem with ICEP Research is the tendency for the researcher to be drawn into the engineering of the project on which the research is being conducted. Having field performance data, the professor and his research team are prime candidates for helping the engineer and contractor solve problems which arise during the project. This potential problem can be pre-vented by the professor's maintaning close communication with the project engineer, supplying him field data as he needs them. At the present time, both engineers and contractors working on the MIT Campus request that ICEP Research be conducted on projects with which they are involved. I consider this solid proof of the success of ICEP!

CONTRIBUTIONS OF ICEP Successful.—On the whole, both ICEP Research and ICEP Practice have proved highly successful. The ICEP format was developed to attack and hopefully salve some of the shortcomings, weaknesses, and neglect in civil engineering research and practice which I myself have done and have observed others do. ICEP was intended to help: (1) Identity the most significant aspects of a project, and indicate where the engineer should concentrate his efforts; (2) ensure that the correct model was used in the design analysis: (3) ensure that the facility was built according to the design; and (4) evaluate the judgment decisions which had been made during the planning and design. Fifteen years of experience with the ICEP approach has shown it to be successful beyond my fondest hopes. Field performance evaluations have been made on a number of types of

ENGINEERING PROJECT structures. including: A breakwater; buried structures; braced excavations; open excavations: earth dams; embankment foundations; building foundations; and foundations for refrigerated structures. Publications cited in the Appendix —References, and others, describe some of these specific cases. Preceding parts of this paper illustrate aspects of four ICEP's. In addition, there are several general findings from ICEP's which are of interest. These are described in the following paragraphs. Documented Field Cases.—A well-documented field case, even without full interpretation, can constitute a worthwhile contribution to the profession. Terzaghi many years ago pointed out the importance of field observations to our fundamental knowledge. At the 1936 First International Conference on Soil Mechanics and Foundation Engineering he stated: ". Our theories will be superseded by better ones, but the results of conscientious observations in the field will remain as a permanent asset of inestimable value to our profession .." Well-documented field cases are useful to the researcher who develops a new prediction technique and to the engineer pre-paring a state-of-the-art evaluation of a topic. For example, H6eg et al. (1969) used the reported Lagunillas Preload data to help develop their method of estimating in situ shear strength from measured pore pressures. Further, considerable use has been made of FERMIT data (e.g., Fig. 5) by engineers doing foundation work in the Boston area. Correct Prediction Does Not Prove Technique is Correct.—ICEP Research has shown on several occasions that, even though some prediction technique correctly predicts performance, the technique may not be a sound one. For example, a very close prediction was made of the pare pressure at the bot-tom of the excavation for the CAES Building, Lambe (1968). This correct prediction resulted to some extent from a cancellation of errors—an under-prediction of the head drop due to the excavation was offset by an under-prediction in the rate of pore pressure dissipation. Further, pore pressures developed in the foundation of the Lagunillas preloads were predicted very closely by a method based on the theory of elasticity even though shear stresses predicted by elastic theory were as much as two to three times the shear strength of the soil. Importance of Initial and Final Conditions.—Field performance evaluations have repeatedly emphasized that initial and final subsoil conditions may be far different from those typically assumed by the engineer. For example, the assumption that static ground water exists before the construction of the facility and will exist when equilibrium has been reached can be seriously in error. The Kawasaki and Amuay cases are striking examples of nonstatic equilibrium ground-water conditions. On important projects, the engineer should measure ground movements and pore pressure prior to construction. A measurement of lateral soil stress as a function of depth would also be very valuable; however, instrumentation for this measurement is not yet available. Importance of Construction Details.—IC EP experience has repeatedly shown the great importance that details in construction procedures can have on performance. This fact is especially true on braced excavations. The lateral movements of sheeting and the magnitudes of strut loads depend very greatly on such things as the sequence of excavation, the timing of construction operations, the extent of strut preloading, the extent of dewatering, etc. Need for Improvements in Project Management.—there is a great need

TERZAGHI LECTURES to develop and teach principles of project management.. ICEP experience has repeatedly shown potentially useful field performance data were not used to maximum benefit. Field data must be obtained and processed rapidly, portrayed, and interpreted correctly, and—most importantly—the significant interpretations must be put at the disposal of the engineer making decisions. Experience has repeatedly shown the difficulties of processing field data rapidly and feeding them back to the decision maker. Partly as a result of experiences with ICEP, MIT plans to initiate a program in Project Management. This program of education and research will focus on the three major aspects of producing constructed facilities— preconstruction planning, construction management, and post construction surveillance and evaluation. The program will emphasize integration of the entire management process through improved information processing and use. The ICEP theme, prediction evaluation, will be central to the program. ACKNOW LEDGMENTS By its very nature ICEP is a team effort. Many of my past and present colleagues and research students have contributed to the development of ICEP and to the execution of many successful projects. Credit is due to these many people who have so greatly contributed to ICEP. David J. D'Appolonia helped interpret the data from a number of projects. Harry Horn helped initiate FERMIT. L. A. Wolf skill has worked closely with all of the ICEP projects for the past 7 yr. His tenacity and skill enabled us to obtain accurate field data. Able and progressive management at the Creole Petroleum Corporation and MIT has substantially aided the ICEP effort. Deserving special credit are: S. J. Mathis, formerly of Creole now of Standard Oil of New Jersey; R. W. Willmon, former Manager of Creole's Amuay Refinery; William R. Dickson, Associate Director of MIT's Department of Physical Plant; and Philip A. Stoddard, MIT's Vice President-Operations and Personnel.

APPENDIX.—RE FERENCES

1. Hdeg, K.. Andersland, O. B.. and Rolísen. E N., "Lindrained Behavior of Quia Clay . Under Load TeL at Asrum,"