ETL 1110-2-344
31 Dec 93
APPENDIX A: FRACTURE MECHANICS BASED ANALYSIS OF
A GRAVITY LOCK MONOLITH
1. Introduction
a. Traditional practice. Traditional design
practice for evaluating structural stability of gravity
structures is currently based on an approximate
technique (see paragraph 2) which produces conser-
vative results in the prediction of cracking. A frac-
ture mechanics based analysis is an improved
method which may be used to predict cracking and
to perform a structural evaluation. ETL 1110-8-
16(FR) states that a fracture mechanics analysis
should be performed if current stability and strength
criteria indicate that major structural rehabilitation is
necessary because overturning instability and crack-
ing are predicted. In this enclosure, a fracture
mechanics based analysis combined with a finite
element structural analysis is described. A specific
example using fracture mechanics analysis is pro-
vided for the evaluation of the strength and stability
Figure A-1. Locks 27 monolith 7E cross section
of a gravity lock monolith at Locks No. 27 on the
Mississippi River. Guidance on finite element
2.
Current Design Practice
modeling and the application of fracture mechanics
is described in detail.
a. Analysis. Current design practice to deter-
b. Locks No. 27, Monolith 7E. Locks No. 27
mine sliding and overturning stability of concrete
are located at mile 185.1 (km 298.01) of the Missis-
navigation structures is to perform a static, rigid
sippi River navigation channel. The locks are part
body equilibrium analysis (subsequently referred to
of the Chain of Rocks Canal which allows river
as the traditional analysis). This analysis is gener-
traffic to bypass the Chain of Rocks low water dam
ally performed assuming that no tensile forces can
(Dam No. 27). These locks consist of a 1,200-ft-
be transferred across the concrete/rock interface at
long main lock and a 600-ft-long auxiliary lock,
the base of the structure. The effects of uplift,
both with 110-ft-wide chambers. The lock walls
bearing, backfill, backfill saturation, lock chamber
water level, and the geometry of the structure
consist of gravity monoliths founded on rock. The
should be considered. The static, rigid body equi-
analyses were performed on monolith 7E because
librium analysis, coupled with the assumed pressure
traditional analysis indicated that this monolith was
distributions, is used to find both the base compres-
the most critical. Monolith 7E is located on the
sion area and the soil/rock bearing pressure. For
east landwall of the main lock approximately 200 ft
the current study (monolith 7E), typical loads and
downstream from the upstream lock gate. Mono-
the assumed uplift and bearing pressure distributions
lith 7E is 34.5 ft long, and a typical cross section is
are shown in Figure A-2. Full uplift due to hydro-
shown in Figure A-1. The monolith is constructed
static pressure was assumed to act under the tension
in a 3-ft deep key as shown in Figure A-1. For the
(cracked) area of the base, and a linear distribution
examples described herein, the effect of the key is
for uplift forces was assumed under the compres-
ignored; and it is assumed that the foundation inter-
sion area.
face is at elevation 340 ft.
A-1
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