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

of a gravity lock monolith at Locks No. 27 on the

Mississippi River. Guidance on finite element

modeling and the application of fracture mechanics

is described in detail.

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