Building Collapse Due to Shallow Trench Excavation
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Missouri University of Science and Technology
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Building collapse due to shallow trench excavationS.J. Vion
R.C. Brown
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roceedings:
Third
International Conference on Case Histories
in Geotechnical
Engineering St. Louis Missouri
June
14 1993 Paper No. 8.10
".;..: "
uilding Collapse Due
t
Shallow Trench Excavation
S J. Vitton
Assistant
Professor of Civil
Engineering The
University
of
Alabama
Tuscaloosa Alabama
R C Brown
Professor of
Civil Engineering
The
University
of
Alabama
Tuscaloosa
Aalabama
SYNOPSIS: A
bui lding co l lapse i s inves t iga ted in which
a sha l low
t rench,
excavated along
t he l eng
of
the
bui lding,
resu l ted
in
the bu i ld ing s col lapse. An inves t iga t ion
indica ted
t ha t the t rench h
been
excava ted within
1
ft
(0.3 m)
of
t he foundation
and t ha t the
foundation
had been const ruc ted
approximately 7 f t (2.1 m) o f
s o f t s i l t y clay with
the bottom
por t ion of
th i s so l
highly sa tu ra te
The bear ing capaci ty of the foundat ion, pr io r to excavat ion,
was
es t imated to have a
safe ty
f ac to r
low as
1.5 . As a
r e su l t of
t he
proximi ty of the
t rench to
t h e
foundat ion
and the so f t s o i l s , t
t r ench
collapsed. soon
a f t e r
excavat ion. t i s bel ieved t h a t
t h e lower por t ion o f
the so i l
flowed
in
the t r e ~ c h c ~ u s ~ n g a l o s s .o f b e ~ r i n g capac i ty . An unders tanding
of
the geologic se t t i ng o f
t
f o u n d a t ~ o n
s o ~ l s
coupled
w ~ t h
s o ~ l s
information
from
t he
USDA s Soi l
Conservat ion
Service
ind ica t
the hazards o f excava t ing in t h i s s o i l .
INTRODUCTION
on Ju ly 16, 1989
a shallow t rench
was
excavated
along t he
l eng th
of a s ing le - s to ry
bui ld ing
located in the
c i t y
o f Tusca loosa , Alabama. The
t r ench was
being excavated fo r the
in s ta l l a t ion of
a
sewer
l i ne to provide service
to
a r ea r por t ion
of the bui lding. The t rench was
approximately 3
ft
( 0. 9 m) wide,
s t a r t i ng from the
southwest
corner
of
the bui lding and extending past the
nor thwest corner o f the bu i ld ing as shown in
Figure
1 . t
was
es t imated
tha t
t he
t rench
was
excava ted to a depth of between 5 and 6
ft
(1.5
to 1.8 m).
A
major i ty of the excava t ion
was
completed
in
a four hour
per iod by
a s ing le
backhoe opera tor . The co l lapse o f the bu i ld ing
occurred
approximately
one
hour
a f t e r the opera to r
completed the excava t ion and
was
on a
break.
Fortunate ly , no i n ju r i e s
resul ted
when
t he
bui ld ing col lapsed in to t he t rench . A
major i ty
o f
the
west wall
of
the bu i ld ing ro ta t ed in to the
t rench r e su l t ing in the
col lapse
of the bu i ld ing s
roof .
Ensuing l i t i g a t i o n resul ted
in
t he con t rac to r in
charge
o f the excava t ion being re spons ib l e
for
damages.
Although t he cause and
e f fe c t
r e l a t ionsh ip of
the
col lapse appeared obvious, the
ex ten t and nature of the damage i nd ica t ed t h a t t he
foundat ion
so i l s
were
in
a
r e l a t i ve ly weak
s t a t e
pr io r to excavat ion.
Consequently,
a pre l iminary
study
was
conducted
to determine
t he
fac to rs t h a t
lead to t he
col lapse
of
t he
bui ld ing
as wel l as
ways o f iden t i fy ing such s i t e s tha t may be
suscep t ib le to col lapse from
shallow
t r ench
cons t ruc t ion ,
thus he lping to prevent s imi la r
inc idence .
1177
SITE CONDITIONS
The City o f Tuscaloosa i s located in the wes
cen t r a l p a r t of Alabama and
has a
popula t ion
o
approximately
75,000.
The
cl imate
in
Tuscaloos
i s inf luenced by the Gulf of Mexico r e su l t ing i
r e l a t i ve ly warm humid
summers accompanied
b
r e l a t i ve ly mild winters .
The
average summer t im
tempera ture i s 80F
1
and t h e average winter t im
temperature i s
46
F with an average annu
prec ip i t a t ion
of
52 in .
The
major
phys iographic
fea ture
o f
t he
area
i s
t h e
Black
Warrior Rive
Basin
and
t he Black Warrior River.
The
Blac
Warrior River , which f lows through Tusca loosa
provides
a
major t ranspor ta t ion l ink with
t he Gu
of
Mexico
and has
two r i ve r
lock systems with
the corpora te l im i t s o f Tuscaloosa. The c i t y i
loca ted
on
t he south bank
of
the Black Warrio
River on a t e r r ace approximately 50 to
75
ft (1
to 23 m)
above t he
r iver s maintained
l eve l o f 12
f t
MSL
(37.5
m). Beyond
the banks o f the Blac
Warrior River ,
Tuscaloosa
tends from
r e l a t i v e l
f l a t
t e r r a in
in
the
West
to
r e l a t i ve ly steep
h i l l
to the Eas t .
The col lapsed bui lding
i s
loca ted wi thin
a
mixe
resident ia l /commercia l
sec t ion of Tuscaloosa in
southwest s ec t i o n o f
t he
c i t y a t the i n t e r sec t io
of two s t r e e t s as i s shown in Figure 1 . T
bui lding
was
used
by
an
e l e c t r i c a l contrac tor
a
both an
of f i c e
and warehouse a t
t he
t ime o f
t h
col lapse . The a rea surrounding t he bu i ld ing i
charac ter ized
as
a
topographica l ly low
a rea
b
wi th in
a
r e l a t i ve ly
f l a t sec t ion
of
Tuscaloosa
The bu i ld ing was of c inde r
block
cons t ruc t io
with convent ional s t r i p
foot ings,
which
we
placed a t grade l eve l .
The
ex te r io r wal ls o f th
bui lding
were
load bear ing wal ls
as
wel l a s
center
wal l const ruc ted along the length o f th
bui lding. The e a s t pa r t of the bui lding, which i
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7/25/2019 Building Collapse Due to Shallow Trench Excavation
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s t i l l in use as a
storage building,
has a 10
f t
(3.0 m)
high f la t roof, while
the
west one half
of
the building was used as a
warehouse
with a
16
f t
(
4.
9
m)
roof. The remaining concrete
floor on
the
west side
of
the building
i s now used
as an
outdoor storage area. The
footings were measured
a t 16
in.
(406
mm)
in width
and
18 in . (0.5
m)
in
depth,
while the combined bearing loads on the
footings were estimated to be 325 psf (16 kPa).
I t is believed
tha t
the
building
was
bui l t
in the
la te
1940s or
early 1950s.
NORT
L
Parking rea
Figure 1 Plan
view of the collapse
building
s i te .
GEOLOGIC CONDITIONS
Geologically, Tuscaloosa i s
located on the fa l l
l ine that separates the Southern Appalachian
Mountains (Appalachian Plateau
Province) and the
northern Gulf of Mexico
coastal plains
(Coastal
Plain Province). The f a l l l ine i s so named
because
i t
marks
the
area where
r iver
navigation
from
the
Gulf of Mexico typical ly ends due to an
increase
in gradient
of
the
r ivers in
Appalachian
Mountain areas. In t h i s region the Appalachian
Plateau
Province
consis ts of re la t ively
horizontal
Paleozoic sedimentary
rocks,
while the
Coastal
Plain Province consists primarily of
sedimentary
Cretaceous materials
overlain with
younger
Tertiary and
Quaternary
soi l s and
rocks
(Adams, e t
a l . ,
1926).
The surface
geology of
the Tuscaloosa area
consists
of
a very young
unconsolidated
sedimentary
layer
believed to be
of Pleistocene
age
and
described
local ly
as terrace deposits .
These terrace deposits
are
al luvial deposits from
the nearby Black Warrior River and in the
Tuscaloosa
area l i e unconformally on the
Pottsvil le Formation of Lower
Pennsylvanian age
(Wielchowsky, 1975)
.
These
deposits are believed
to
have e ~ n deposited during the melting
of
the
great continental
ice
sheets during the
f ina l
phases of
the l a s t
ice sheet
(Wisconsin)
some 10
to 30 thousand years ago.
The
terrace deposits,
which are 40 to 100 f t (12 to 30 m) thick in the
Tuscaloosa area, are marked by coarse gravel a t
the bottom and become
l ess
gravelly and more sandy
vert ical ly
unt i l
the upper layers are largely f ine
sand. The
upper
half s sandy
in
the lower
part ,
yielding to red
clayey
soi l s
n e a ~
the top
red clayey soils are characteris t1c of
later1t1c
weathering (Adams, e t a l . ,
1926).
1178
SOILS
INVESTIGATION
Field Invest igat ion
The f ie ld
invest igat ion
consisted
of
a s i te
invest igat ion
conducted within days
of
the
col lapse and a l a te r investigation
to
obtain
.samples for soi l
tes t ing .
During soi l
sampling,
however, it was found
t ha t obtaining undisturbed
so i l samples from the s i t e was dif f icul t . The
f i r s t dif f icul ty
was in
obtaining
undisturbed
samples
in
close proximity to the excavation. As
is
shown
in
Figure
2,
the
building
was
located
within
6 f t (1.8
m) of
an
adjacent property
and s
bounded by s t r ee t s and a parking lo t
in the
rear
of the
building.
The
soi ls
in the region of the
collapse were
a l l
highly disturbed
due to the
collapse and could not
be
adequately sampled.
Consequently, so i l samples
were
taken from the
rear
of the building
in
the
parking area.
Six
auger holes were
placed
through
the
surface
of
the
parking lo t . The
second
dif f icul ty encountered
was
tha t
a t about 40
in .
(1 m)
of
depth very soft
satura1;ed
soi ls
were
encountered. While the soils
~ e r e eas i ly penetra ted with a shelby tube, the
saturated so i l would not remain in
the
tube upo
extract ion.
In
fact , the auger hole
i t se l f
did
not stay
open
on
account
of the highly saturated
so i l s . Undisturbed samples
were,
therefore
obtained only for the top 40 in of the soi
column. Auger
holes
were also placed in
the
are
of the
excavation
to confirm the presence of
th
sof t
saturated
soi ls . These auger holes also
encountered very wet, saturated conditions wit
standing
water
a t
about 40 in . (1m). However
since the t rench had considerable debris placed in
it af ter the col lapse, th i s may
have
increased the
permeabil i ty of
the backfi l led
trench area
allowing water to col lec t in th is
area.
Class i f ica t ion
of
the
soi l s
was based on
the
following tes ts : Atterberg l imits, grain size
analysis ,
natural
water
content,
and uni t weigh
t e s t s .
st rength
measurements were obtained
from
uniaxial compression
t es t s . The
foundation
soils
were
found
to be a clayey
s i l t
CL-ML
in the top
40
in . (1
m)
tending
to a
low
plast ic i ty
clay
CL
in
a lower zone of 40 to 80 in . (1 to 2 m). Th
l iquid
l imits of the
soi ls ,
ranged
from
16 to 40
while the plast ic indexes were estimated to range
from 1 . 5 to 18 .
Void
r a t ios for the
undisturbed
samples
varied between
0. 55 and o.
70.
The
natura
water
content
ranged
from
15
near
the top
of the
so i l column
to 30
near
the
bottom of
the column
The unconfined
compressive strength
of
the soils
in the
upper
40 in. averaged 1060
psf
(50 kPa).
At
a depth of about 8 0 in . ( 2
m)
, a very s t i f f
clay,
d i f f icu l t
to
auger
through, was
encountered
in a l l
of the
s ix
auger holes completed. Figure
2
i l lu s t ra te s
a cross-section of the building, i t s
foundation
soi l s and the estimated location
of
the
exca.vation r ~ l t i v e to
the
building.
Exist ing Soils
Information
Since the foundations
are
relat ively shallow and
the
s t r ip footings located a t a depth of 18 in.
(457 mm), the
USDA Soil
Conservation Service soil
survey
of
Tuscaloosa county (1981) was
reviewed
for addit ional information
concerning
the area 's
soi l s . This survey had been issued
in
August of
1981,
with the major f ie ld work being
conducted
from 1971 to 1979. Figure 3 below shows the
general
so i l map for the area of the building
collapse.
As can be
seen
from Figure 3,
the
building
s
located
a t
the contact
of
a so l
type
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Remaining
Portion of
Building
14ft
roperty
Line
igure 2
Cross-sect ion o f co1lapse bui lding
s i te .
ident if ied
as
a number 2 and described in the s o i l
survey as
a Adaton
s i l t loam. According
to the
so i l survey, the
Adaton se r i e s
cons is t s
o f
deep,
poorly
drained,
s lowly permeable
so i l s t ha t
formed
in s i l t y f luv ia l sediments.
In
addi t ion,
the so i l
survey
provides information
fo r planning
land
uses
related to
urban
development such as bui lding
s i t e
ievelopment
and
engineering
index proper t ies .
For
building development, the Adaton so i l s were
: : lassified as being severe for bui lding
shallow
excavations and
dwe1lings without
basements.
This
NaS pr imar i ly due to
the
s o i l ' s wetness and
low
strength. Figure
4 l i s t s the
engineer ing index
properties
of
the Adaton s o i l ser ies .
t
can
be
seen from Figure 4 tha t the bas ic engineer ing
property t es ted
confirmed
the
f i e ld
t e s t
previously
reported.
WALYSIS
s i t e invest igat ion immediate1y
following
the
: :ollapse
found tha t the
t rench
for the
sewer
l i ne
1ad
been placed with in
1
ft o f
the foundation.
rhis was done due to the close proximity of
the
ouilding to an adjacent
property l ine , where
only
. 6
f t
1 . 8 m
s t r i p
of
land
was
avai lab le fo r
'lacement of the sewer
l i ne .
Based
on
t h i s
inding, the excavation was in
vio la t ion of
.pplicable
bui lding codes,
which
r equ i re tha t
:xcavations for any purpose near s t ruc tu res
should
.ot extend with in
1
f t (0.3 m
o f
the angle of
epose or
natural
slope of t h e
so i l
under
any
1179
foot ing
unless the s t ruc tu re s
f i r s t properly
underpinned or protected against
sett lement
(Southern Standard Build ing Code, 1961).
Based
on
the
so i l s t rength
measurements obtained, couple
with
the
in formation provided
in the USDA soi
survey o f
the
area , it i s highly
unlikely tha t
th
bui ld ing ' s
foundat ion so i l s
would be
able to
suppor t a 5
to
6 f t excavat ion within 1 f t of th
foundation.
To
address t h i s issue,
the
geologica
se t t i ng
of t h e foundation
so i l s ,
a
bearing
capaci ty analys i s
pr io r t o
the
excavation,
th
probable
co l lapse mechanism,
and
compliance
wit
exis t ing
building
codes
are
discussed .
Geologic Considerat ions
A s igni f icant fea tu re
of
the so i l s in th
Tuscaloosa area i s t h e a l luvia l orJ.gJ.n of
th
unconsolidated t e r race sediments deposited by th
Black warrior River . A well known charac ter i s t i
of a l luvia l depos i t s
i s
the extreme ver t i ca l an
hor izontal heterogenei ty
of
the
so i l s . due to
stream
migrat ion as well
as f lood
wate
depos i t ion. The USDA
Soi l
Conservation survey
presented in Figure 3,
shows t h a t
the
building
wa
cons t ructed
a t
the
edge
of
a pod-l ike sect ion
o
Adaton s i l t . However, so i l sampling revealed tha
a
majori ty
of the building,
pa r t icula r ly th
sec t ion
t ha t
co l lapse ,
was constructed
ove
approximately
7
ft (2 .1 m o f Adaton s i l t .
Othe
locat ions
in
t h e
Tuscaloosa
area in
which
th
Adaton
silt i s
found are primari ly in stream
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Figure
3
Soil
conservation
Service
soi l
survey.
l
Classification Percentage
paaslng
I
Soil
name and
map
symbol
Depth
I USDA tex ture
I
I
.... 1
' '
' '
Unified
2---------------- 0-7 Sil t loam--------IML, CL,
Adaton J I CL-ML
7-961Silt loam, s i l ty ICL, H
clay loam, s i l ty t
I
clay.
I
'
'
AASHTO
tA-4
I
IA-6
A-7
1
0
--...,,r:s.::ci :..:v:.::e__:nr ' m : : : . b e , . , r - = - ; . ; : ~ - - - 1 L
i
I 10 I
j
0
I
2 I
' ......_
' '
I I I
Plas
t i i t y
index
100
198-100190-100184-1001
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founda t ion so i l s ,
a
bear ing
capac i ty ana lys i s was
conducted
assuming a s t r i p foo t ing supported by a
two- l aye r soi l . A
recen t ly proposed semiempirical
equat ion by Azam and Wang
(1991)
fo r dete rmining
t he
u l t i m a t e bear ing capaci ty of a
two-layer
c-
s o i l was used in the ana lys i s . The proposed
bear ing capaci ty equat ion
i s given as fo l lows
where
q
0
u l t imate bear ing capaci ty of a s t r i p foot ing
over a two- layer so i l ;
q,
=
u l t imate
bear ing capaci ty of the foot ing
suppor ted
by
an
i n f i n i t e l y
t h i ck top - layer
s o i l , computed by the
t r a d i t i o n a l
bear ing
capac i ty
equat ions using
fac tors
recommended
by
Vesic (1975);
q u l t imate bear ing capaci ty of the foot ing
suppor ted
by an
i n f i n i t e ly t h i ck bottom-layer
s o i l , computed by
t he same method
as q,;
m l aye r fac to r ,
which
i s
o .17-o. 2 3 fo r two
layers
of clay (use o f
the
lower value
i s
recommended
if one c lay
l ay e r i s highly
compress ible) ;
H
1
=
d is tance between
the
base
o f
the s t r i p
foo t ing
and
the
top o f
the
bottom l ayer ;
B = width
of
the s t r i p foot ing.
Azam
and
Wang
analyzed
four d i f fe re n t
l ayer
combinations
with one
of
the
combinations
a s t i f f
clay under la in by a so f t c lay . While
the
over lying so i l
in
t h i s
analys i s cannot
be
c l a s s i f i e d
as s t i f f ,
as compared to
t he
proper t i es
of the s o i l s
t e s t ed
by Azam
and
Wang, t he
analysis
was used in hopes
o f
providing a lower bound
es t imate
o f t he bear ing capaci ty o f t he
foundation
pr io r to
t h e
excavat ion. In add i t ion ,
i ns t ead o f
computing
t he
bear ing
capac i ty us ing
fac to rs
recommended by Vesic
(1975),
a
lower
bound
es t imate
of and
q was made
assuming a
simple
un iax ia l s t re s s f i e ld below t h e foot ing
which
gives
%o
=
2c
(Chen
and McCarron, 1991). The
r e su l t ing
bear ing
capac i t i es are as follows
1060
psf
(51 kPa)
100 psf (5 kPa)
According
to
Azam and
Wang's
proposed equat ion,
the
u l t imate bear ing capaci ty of t h e
s t r i p
foot ing
over
t he two- layer so i l
i s
495 psf (23
kPa)
Since t he es t imated bear ing load
on
t h e foot ing
was 325 ps f (16 kPa) , the foundat ion
had
a safe ty
fac to r
of
approximately
1 .5
agains t
bear ing
capaci ty
fa i lure . According to Vesic (1975),
however, s i tua t ions in which
sa f e ty
fac to rs a re
less
t h an
2.0 should
be
avoided .
Consequently,
l:he foundat ion was below a
minimum
recommended
sa fe ty
f ac to r p r io r to
excavat ion of
the
t rench.
rn add i t ion ,
Vesic
also
recommends
t h a t removal
e x i s t i ng
overburden
by scour
o r
excava t ion
s h o ~ l
be
given
adequate
cons idera t ion . It s
m l ~ k e l y tha t
t h i s
was contemplated a t
t he
t ime
o f
:ons t ruc t ion of the bui lding o r tha t
an
analys i s
ll'as
performed.
1181
Collapse Mechanism
Based on t he above ana lys i s and informat io
gathered a t t he s i t e ,
t he
most probable co l l ap
mechanism
was
t h a t
once
the t rench was excavate
t he
bottom so i l , which was
high ly s a t u ra t ed an
possibly near
its
l i qu id l im i t , flowed i n to t h
t rench, t hus
undermining
the
upper
bear ing s o i
and
r e su l t ing in
t h e
col lapse
of the
bu i ld ing
This may a l so
account
for the
t ime
l ag t h a
occurred between t he complet ion of the t rench an
the co l lapse ,
which
was
about
1 hour.
Azam and Wang
a l so
studied t h e p l a s t i c
f lo
behavior o f foundat ion so i l s
us ing a
f i n i t
element technique to gain i n s igh t in to t h
progress ive y ie ld ing of
these
so i l s . The
analysis
of
a
s t i f f c lay
under la in
by
a
weak c la
revealed t h a t t h e y ie ld zone extends deep
i n to th
weaker
bottom l ayer
and
t ha t the
y ie ld
pat te rn
i
typ ica l o f a punching shear o f
the
top l aye
fol lowed by a
gene ra l
shear
f a i l u re of the
botto
layer . Although
the col lapsed
bu i ld ing
foundation
s o i l s
were considerably weaker
t ha
those s tud ied by Azam and Wang,
it
i s poss ib l
t ha t progressive
y ie ld ing of
the bottom so i l
a l s
accounted not only for the co l lapse bu t a l so t h
t ime delay o f
the
col lapse.
Building
Codes
According t o the s tandard bui lding
code
sec t ion on
excavations,
t he
excavation
had been placed too
c lose to
the
foundat ion s ince it was
not
a t
l e a s t
ft
(0.3
m
from the angle of
repose
o f the
s o i l
o r from the na tu r a l slope of t he so i l . Since t h e
angle
of repose
o f
a
so i l genera l ly
r e fe r s
to
a
granular mater ia l in loosely packed s ta te , t he
excavation
angle would have
to
have
been
based on
t h e
natura l
angle
o f
t h e so i l .
However, t h i s i s
a
d i f f i c u l t
parameter
to
determine since the s o i l s
were a so f t
sa tura ted s i l t y
c lay .
I f
it i s
assumed t ha t the so i l s
were a t
or
c lose
to
t h e i r
l iqu id
l im i t ,
then t he natura l s lope would be very
low
and
would r esu l t in la rge
d i s t ances
requ i red
from the foundat ion fo r the excavation. Thus, t he
only possible
so lu t ion for
t h i s
excava t ion would
have been to
prope r ly
underpin
o r
to prevent t he
bottom so i l s from f lowing in to the
t rench, both of
which would
have been
d i f f i c u l t
to complete given
the l imited space avai lab le as well as the c o s
involved.
An
add i t iona l
considera t ion n
t he
co l lapse s
t ha t al though t he con t rac to r was in
v io la t ion o
ex is t ing codes for excavation,
t h e i r pr io
experience wi th other ' excavations in t he
Tuscaloosa area ind ica ted
tha t there should be
no
problem
with t he excavation,
since they ha
excavated shal low t renches next to
o r
near t h
foundat ion without resu l t ing in a co l lapse of t he
t rench. Therefore , no considera t ion was
given
to
f i r s t t e s t ing
t he
so i l s to determine
if they
wer
s tab le to excavate . In addi t ion, t h e backho
operator observed
the
lower
so i l s
in
t he
t r enc
slowly f lowing
i n to the
t rench
but ye t
did
no
:consider
t h e
s i t ua t i on
as dangerous. Whil
t ra ining of t he opera to r was lacking in t h i s case
information
d id
e x i s t
from the USDA s o i l surve
fo r t h i s area t h a t
was
read i ly obta inab le and t h a
would
have
ind ica ted the
possible dangers
i
excavating these
so i l s . In addi t ion,
knowledge
o
the geologic or ig in
o f
the s o i l s in t h i s a re
would also he lp a l e r t opera tors
to
t h e occurren
of
po ten t i a l ly d i f f i c u l t
so i l s ,
s i n ce
in t h
case , the
a l l uv i a l
natu re of the s o i l s should b
r e l a t ive ly apparent given t he i r loca t ion to
t h
l a c ~ warr ior River .
-
7/25/2019 Building Collapse Due to Shallow Trench Excavation
7/7
CONCLUSION
Conclusions concerning the
building collapse can
be
summarized
as
follows:
1. The
building had
an
estimated
bearing
capaci ty
SF 1.5 pr ior
to collpase.
2. Bearing so i ls
were
found to
be
a low
plas t ic i ty s i l ty
clay overlying a
saturated
low
plas t ic i ty
clay.
3 A
trench
was placed
within
1
f t
(0 . 3
m of
the
foundation
and
in
violat ion
of applicable
building
codes
for excavations.
4 .
Insufficient
space
was
available between the
foundation
and an
adjacent property to place
the
trench and meet
exis t ing
codes for
excavations.
5 . Collapse of the building
i s
believed to have
resulted from the lower saturated clay
flowing
into
the
trench, thus undercutting
the overlying
so i l and causing a
loss of
bearing capacity.
6.
No investigation of so i l condit ions was made
prior to
the
excavation
nor
were
indications
of imminent fai lure
of
the
trench taken into
consideration.
7.
Information from the USDA
Soil
Conservation
Service
so i l
survey
showed tha t the
building
probably
was
located
on
di ff icu l t
soils
which
may cause problems with excavations,
especial ly
near
foundations.
8. A significance of th i s collapse i s
that
other
structures in the
Tuscaloosa area are
also
constructed
on
similar
so i ls .
Since
information exis ts tha t
can
identify these
types of
soi ls , t
can be used to
help
ident i fy foundation
so i ls tha t
are
potent ial ly
susceptible
to collapse from
adjacent shallow excavations.
REFERENCES
Adams, G.I . ,
Butts , c . ,
Stephenson, L.W. and.W.
cooke
(1926)
Geology of Alabama, G e o l o g ~ c a l
Survey
of Alabama, Special Report 14, p.
25.
Azam, G.
and
M.C. Wang (1991), Bearing
Capacity
of s t r ip Footing Supported by Two-Layer
c-
so i l , Transporta t ion
R e s e ~ r c h
R e c ~ r d
1331
TRB, National
Research
c o u n c ~ l W a s h ~ n g t o n
D.C.,
pp.
56-66.
cassagrande, A.
(1932), Rc;search
on
the Atterberg
Limits
of
Soils ,
P u b l ~ c
Roads Vol. 13,
No.
8 , pp. 121-136.
.
Chen,
w.F.
and w.o. McCarron
(1991), "Bearu -g
capacity
of Shallow Foundations, F o u n d 7 t ~ o n
Engineer ing
Handbook
2cd., Y. Fang, e d ~ tor ,
Chapter 4, Van Nostrand R e ~ n h o l d pp. 144-165.
Southern Standard Building Code,
1961, Southern
Building code Congress, Birmingham,
AL, Section
1301,
pp.
1-3.
USDA (1981),
so i l survey
T u s c a ~ o o s a
County,
Alabama, so i l
C o n s e r v a t ~ o n S e r v ~ c e
and Forest
Service, pp.
118.
vesic A.S. (1963), Bearing Capacity of Deep
o u ~ d a t i o n s
supported in
Sand,
"
Highway
Research Record 39
HRB,
National Research
council,
Washington, D.C. pp. 112-143.
vesic , A.S. (1975), Bearing
Capacity of
Shallow
Foundations,
Foundat ion
ngineer ing Handbook
1s t
edn.,
H.F.
Winterkorn and H.Y.,
Fang
(eds.) ,
Chapter
3,
Van Nostrand
Reinhold
Company,
Inc. ,
New York,
N.Y.
wielchowsky,
c .c . (1975), Cri ter ia fC?r
Distinguishing Pleistocene(?) A l l u v ~ a l
Terrace
Deposits from the Coker Formation in ~ h e
cottondale,
Alabama, Area, M.S.
T h e s ~ s
submitted
to
the Univers i ty of Alabama, p. 238.
1182
