The Baldwin Hills Reservoir Failure 1987 Engineering Geology

8/16/2019 The Baldwin Hills Reservoir Failure 1987 Engineering Geology

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Engineering Geology

24 (1987) 161--166 161

Elsevier Science Publishers B.V., Amst erdam -- Printed in The Netherl ands

Prepared i s c u s s i o n

THE BALDWIN HILLS RESERVOIR FAILURE*

S.D. WILSON

(Accepted for publication December 1986)

As Scott mentioned, I was engaged {along with Dr. Casagrande) by the

Standard Oil Comp any of California to assist th em in their defense of the

lawsuit that was instigated by the insurance carriers against the Standa rd Oil

Compa ny. Now it is inevitable th at when yo u are engaged by a client yo u do

your best to help him out and I am sure that my objectivity was somewhat

colored by that relationship, but, as Ron Scott also ment ioned, after the law-

suit was settled out o f court my relationship with Standard Oil Company

was terminated. I certainly at this point feel no obligation to the Standard

Oil Company t o d efend their position, and I hope that my viewpoint at this

time is a little more objective, perhaps, th an it was at the time. S cott says

that it was too bad the case was settled out of court, that we have no writ ten

legal opin ion as to the respon sibility for the failure. I am not so sure tha t I

agree with t hat stat ement . It is very diffic ult to reach a decision, a legal deci-

sion, based solely on technical matters. And I am not sure tha t legal deci-

sions are always based upon the correct int erpretat ion of technical facts. I

personally was somewh at relieved when th e case was settled ou t o f court. I was

not looking forward t o a long and difficult interrogation on the witness stand.

There are, of course, a numbe r o f areas of disagreement between t he various

principal investigators of the failure of the Baldwin Hills Reservoir, ye t certain

things are quite clear. It is clear th at t he fa ilure of the Baldwin Hills Reservoir

resulted fr om vertical offsets across the pre-existing faults which un derla y the

reservoir. These vertical offsets not only des tro yed the integri ty of the under-

drain system but also eventually permitte d water to seep through the r uptur ed

zone of the clay lining and ev entual ly to pressurize the underdrain in the fa ulted

zones with water under ful l reservoir pressure. It is also clear th at these vertical

offsets at the faults started t o develop duri ng the first filling of the reservoir and

tha t t hey conti nued to develop throu ghou t the life of the project. It is also clear

tha t during the life of the project the re was areal subsidence, tilting and stretch-

ing of the ground surface in an east/west direction. These ph eno men a were the

direct result of oil-recovery operati ons fr om the adjacen t Inglewoo d oil field and

there is no d isputing that. It is also clear that starting in 1957 floodi ng and repres-

surization of the oil producing strata not only slowed down the rate of settle-

ment, b ut eventually led to episodes of upward movem ent of the ground surface.

*Oral presentation.

0013 -795 2/8 7/$0 3.50 O 1987 Elsevier Science Publishers B.V.


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Now, since all these facts are well established, and apparently agreed to by

all of us, at least by most of us, it would appear th e cause of the failure and

the actual mechani sm of failure are also well under stood . This does not quite

seem to be the case. With respect to the causes of the vertical offsets across

the faults, the various investigators have published papers, reports and dis-

cussions th at offer at least 5 possible hyp othe ses as to wh y these offsets

developed.

(1) Areal subsidence concentrated at the three identified faults.

(2) Ground surface stretching leading to concentrated separation of the

material along the faul t traces forming deep open through-going cracks.

(3) Differenti al consoli dation unde r reservoir loading at initial saturation

of the fou ndat ion material on the west side of each fault resulting from

material in the do wnt hrust side having been loosened by the initial faulting

and vertical deformatio n.

(4) Tectonic movements along the faults.

(5) Differential fo un dat io n reb oun d on the east side of faults 1 and 2

resulting fro m high pressure water injection in the oil-producing zones under-

lying the area south of the reservoir.

With respect to tectonic movements, it appears to be well docu ment ed that

there have been no observed displacement s along the various faults in recent

times and therefore tectonic movements can be deleted from the above list.

Therefore, I am in complete agreement with the opinion expressed by Tom

Leps in his writ ten paper, in response to Prof. Leona rds' questions posted

before the meeting , as follows: Each o f the above reasons was active to

some ext ent in seriously deformi ng, cracking and separating the asphalt

sealing membrane, the pea-gravel drain blanket, and t he concret e cradle tile

pipe drains where the y crossed over the faul t traces. And each separately in

time could have caused the fatal piping ind epe nde ntl y. Leps also concludes

that it is improbable that a definitive quantification of the relative contribu-

tions of each of t he listed items will ever be possible, and that , f urt hermore ,

the value of such quanti fica tion in terms of the basic lessons to be learned

fro m this failure is at this time minimal. There seems to be no comple te

agreement as to the mechanism that triggered the failure. Leps presents some

very convincing arguments th at a sudden episode of vertical mo vemen t just

prior to failure heaved the east sub block but not the central sub block and

tha t this resulted in several inches of sharp diffe rential mov eme nt across

Faults I and II, which not only disrupted the subdrains system but also

fault ed the clay lining and initiated piping which perfo rate d the lining. In

my opinion the subdrain system was already disrupted and the stage was

already set for final piping along the fault system. In my 1972 paper submit-

ted to the ASCE Specialty Conference at this very same university, I pointed

out that the differential heave, which post-failure surveys found across

Fault I, could well have developed aft er the failure as a result of water enter-

ing the existing fault un der full reservoir pressure, thus relieving the existing

shear stresses. On the other hand, there is no question but that there was

some heaving prior t o failure resulting fro m the repressurization of the


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produci ng oil field. Leps refers to the 7/8 inch of heave at the water tank,

some 500 ft. s outh of the reservoir which devel oped prior to failure. This is

factual. But to the best of my knowledge th ere was no observable differential

vertical mov eme nt at the gro und surface across the nea rby proje ction of

Faults I and II. I believe Scott has just disputed that statement, and has said

that there were vertical displacements further to th e south and I am sure that

there were. Of course, the ground surface at that point was quite a bit above

the elevation of the fault i tself in the reservoir floor, and perhaps the move-

ments were masked. Likewise, there were no observable vertical offsets of

this magnitude visible at the g round surface either north or south of the

reservoir nor in explorat ion trenches excavated outside the reservoir. There

certainly were cracks, and those cracks had developed, b ut I do not reme mber

seeing the vertical displacement t hat Ron Scott refers to. The main evidence

indicating that there was some differential vertical mov emen t across Fault I

prior to failure presented by Leps is the consistent record of heave shown by

benchmarks on the inlet and outlet tunnels in contrast to zero movement at

(at least) one point in the inspection gallery west of the fault.

Although the data are factual and the evidence convincing, i t is worthwhile

noting that the inspection gallery was of rigid reinforc ed concrete, and that

the to tal differential move men t of the gallery was somew hat less than that

of the observed mov eme nt across the adjacent faults. Furt herm ore, the

movem ents o f crack openings in the gallery were quite erratic and showed

wide seasonal variations with temperature. Nevertheless, I am now prepared

to accep t the possibility, perhaps even the probability, that fault mov emen t

at Fault I may have occurred during the 24 hours prior to failure and, if so,

could have contr ib uted to the f inal incremented founda tion distort ion which

permit ted piping to commence.

At the same time I have difficulty in accepting the premise that fault

movements were the sole cause of the differential vertical movements across

the fault which developed during the life of the reservoir prior to failure. I

would like to present on ce more, some of the data which led me in 1972 to

state that these vertical differential movem ents were no t all the result of

fault movements.

During the life of the reservoir, the regional subsidence of the southwes t

corner of the reservoir was abo ut 1 ft ., and tha t o f the no rtheas t corn er was

0.5 ft. , th us the re was 1~ ft. of di fferen tial regional subsidence across the

reservoir. In addition to the above there were, of course, settlements of the

embankme nts resul ting from compression of the emban kment material , the

founda tion und er the emban kments, and set t lement of the f loor resul ting

from compression of the foundation materials under load. The maximum

combin ed t otal settle ment of the floor of the reservoir was 1.01 ft . Slide 1 is

a section throu gh the south circulator line and inlet tunnel on which there is

superimposed th e to tal settleme nt as measured after first fill ing (7/10ths of a

year), afte r draining th e rese rvoir in 1957 (61/2 years), and afte r failure (13.1

years). The difference between t he to tal set tlemen t and the regional subsidence

represents compression of the foun dati on's soils. Note the sharp offset across


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each of the two fault planes. The reason for this sharp differential compres-

sion across the two fault planes, in my opinion, is primarily that the founda-

tion strata on the west, do wnth rust side of each fault is badly sheared and

distressed. The n ex t slide is the same slide that Sco tt sho wed just a few min-

utes ago showing the obviously distressed strata on the west side of Fault V

which proba bly resulted f rom the original vertical displacement at the time

of the faulting, and the downdr ag caused the near surface strata to b ecome

badly fra ctu red and loo sened. Now at th e same time the reservoir was tilting

due to regional subsidence, and differential compression settlements were

developing across Faults I and V, the reservoir was elongating in the nor thea st

and south west direction. The total change in length from 1950 to 1964 was

0.86 ft . , or 0.065 ft . per year. The total elongation divided by the t otal

length, assuming the strains were uniform throughout, was 0.07%. Based on

strain gage measurem ents in the inspection chamber, i t was dete rmin ed th at

the inspection cha mber elongated app roxi matel y 0.6 inch, over a total length

of 100 ft. , which is an average of 0.05% strain. This strain is compara ble to

average strains of 0.037% measure d in east--west lines across the reservoir.

The measured horiz ontal elongation or stretch is most likely directly rela-

ted to the regional subsidence which caused the tilting of the reservoir. It is

equally obvious that the magnitude of the maximum average strain, 0.07%, is

so small that if it were distributed uniformly across the reservoir, it would in

no way adversely effect a well designed earth structure such as the dam or

reservoir. In fact the strain me asur ement along the crest of the south dam

showed elongation strains of the order of only 0.04% strain, which was com-

parable to average strain of 0.037% measured across the reservoir in the same

direction. The maximum tensile strain in the north dam was larger as a result

of settlement of the embankment itself. Strains in the north embankment,

however, were not critical because the original failure developed in the floor

of the reservoir and the final breach developed in the east abu tme nt adjacent

to the main dam but not in the embankment itself. It is possible that repres-

surization of the produ cing oil field to the south cont ribu ted to the lateral

spreading and t o gradual opening of the surface fault north and s outh of the

reservoir. It is also probable that water from the reservoir once it infiltrated

the fault under full reservoir pressure opene d up the fault to a width of per-

haps several inches. When this hap pen ed the vertical shear stresses across the

fault surface were reduced t o zero and the block on the east side of the fault

rebounded about 0.16 f t .

In summary, there is no question but that there was regional subsidence,

i.e. tilting, lateral stretching, and actual cracking of the ground. These acti-

vities undoubtedly contributed to the state of stress in the foundation of the

reservoir that ultimately resulted in vertical offsets across the fault. This off-

setting cracked the asphalt membrane and ruptured the drain pipes and thus

permit ted water f rom the reservoir to saturate the fou ndat ion soils adjacent

to the faults which in turn increased the differential compression and ulti-

mately led to failure.

Jerr y Leona rds has propo sed several questions for the discussers to answer.


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One of them reads as follows. Would more careful study and interpre tation

of crest settlemen ts, seepage flow rates, etc. have alerted t he designers to

impending failure before it was too late? Would modern metho ds of inter-

preting the data do a better job than was possible in 1963? If so how?

There were th ree bits of informa tion developed by the monit oring program

th at in hindsight appeared to give an indication o f worsening condit ions

altho ugh no t necessarily of imp ending failure. Horiz ontal and vertical move-

ments were measured by the DWP in the drainage inspection chamber, which

was a relatively rigid reinforced concrete box under the reservoir floor and

which crossed Fault I. The first crack in the inspection chamber was ob-

served in 1951 during first partial filling. At that time strain gauges were

established across the crack. The overall trend of increasing rate of crack

opening was somewha t obscured by th e erratic changes resulting fro m inter-

nal temper atu re changes. A comparison o f readings on a particular date wit h

those of the previous two or three readings would show only erratic readings

of no significance. However, a long term plot such as shown in the next illus-

trat ion, reveals quite clearly a rapid rate of increase in the crack opening

starting someti me prior to 1959. I have shown on this illustration in the

upper part three typical defor matio n time curves of clay samples from the

Panama Canal which were subjected to unif orm loads, the loads being held

con stan t for a period o f time. Several of them failed in a few seconds. One

of th em failed in the course of a year. But t hey all show a characteristic in-

crease in rate of deformation. In the lower part you see the plot of crack

opening of t he Baldwin Hills inspection gallery, the 13-year record. Yo u see

a similar rate o f curvature in there. I think it is possible that had one lo oked

at this entire record of crack deformati on and compared it with some oth er

data, one might have been a little bit alarmed th at somethi ng was going on

that needed to be looked at and examined more carefully. This particular set

of data by itself is not necessarily related to the u ltimate failure but it might

have served as a red flag had it been plotted and reviewed.

During t he first filling of the reservoir excessive leakage of up to 75 gallons

per minute developed throug h the lining adjacent to the intake tower. The

reservoir was drained and repairs were made, as Jansen described, and t he

reservoir was refilled.

The ne xt plot is a plot of the measured leakage vs. time af ter t he refilling.

It started out at about 23 gallons per minute, and then gradually decreased

up to about 1956 when it reached a low of about 6--8 gallons per minute,

held const ant for a while, and then starting abou t 1962 it showed a rapid in-

crease in rate of leakage. It was generally believed that the decrease in

leakage measured between 1951 and 1956 rep resented a self-healing of the

clay lining, and tha t th e sit uation was getting better. In all probabilit y it was

not getting better, it was merely the f act th at t he lower seal, the 1A -thick

asphalt seal, was being rup tur ed and the water was being permit ted to by-

pass the drains where the pipes were broken and to enter directly into the

foundation. In fact, it is even probable that the rate of total leakage was

actually increasing during this period and t hat this plot actuall y is a misleading


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plot. It was factual, but it does not represent the total leakage through the

lining, because certainly during all of this period some of it was escaping

straight into the foundation. The abrupt increase in rate of leakage in 1962

might have served as another red flag except, of course, it was far less than it

was during t he first filling and even less than it was at the sta rt of the refilling

process.

Settlement measurements were made around the crest of the dam period-

ically throughout its life. The interpretation of the settlement data was com-

plicated by t he fact t hat there was regional subsidence, variable compression

of the emban kment s and of the foun dati on soils and errors due to benchmark

subsidence. Careful post-failure analysis of the data, however, might permit

one to conclude that sharp differential settlements of 0.2--0.3 ft. developed

across Faul t I under lying the main dam duri ng the life of the reservoir, as

shown in the lower por tio n o f this figure. I do n ot consider any of the above

data t o be so obvious th at it should have alerted the designer to an impend ing

failure. Nor do I believe that modern methods of interpreting the data would

have led to dif fe ren t conclusions. Th e Baldwin Hills Reservoir was a very well

instrum ented dam, the instruments perf ormed properly, the da ta were re-

corded and observed. The designers recognized two things must n ot be per-

mitted to happen: water must not ever be permitted to enter into the founda-

tion strata and it was also accepted that fault movements could not be

tolerated. It is too bad that they could not have devised some sort of instru-

menta tion to measure directly whether or n ot there was leakage into the

foun dati on strata and whet her or no t sharp differential movements were

occurring across the faults. This was not t he f ault of the existing instru ments

because the instruments that were put in did their job, they measured what

they were supposed to do and they measured it correctly but, unf ortu nate ly,

the y did not measure the part icular parameters t hat were essential to eval-

uating the safety of the project.

The Baldwin Hills Reservoir Failure 1987 Engineering Geology

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