that the bulkhead depicted in Figure 1 is commonly constructed dredged
bulkhead for which sheet piles are driven into soil, whereafter the anchorage
is installed and the soil mass in front of wall is removed by dredging. The
dredge bottom refers to mudline after dredging.
UTEXAS2 calculates limit equilibrium of slopes by one of four procedures. The
Spencer procedure, a rigorous procedure that evaluates both moment and force
equilibrium, is the recommended procedure to estimate stability of
bulkheads.
UTEXAS2 allows an engineer to model driving forces (weight of soil,
piezometric conditions, and surcharge load) and resisting forces (soil shear
strength, weight of water in front of bulkhead and lateral pressure exerted by
water on bulkhead). The geometric configuration of bulkhead system, including
soil layers, sheet piles, and water, is input by means of coordinate system.
The sheet piles are modeled by using specific weight of piles as input and by
using a high shear strength for the piles to prevent the critical circle from
going through the piles.
For circular searches, 'the engineer provides center
coordinates for the initial circle and grid spacing. It is recommended that a
grid spacing of 1% of the slope height be used. (The slope height is the
vertical distance from dredge bottom to top of bulkhead.) Generally an
engineer specifies backfill of granular material to be placed immediately
behind bulkhead to preclude development of extremely large lateral pressures
due to high groundwater level inside the wall after the free water on the
front side has lowered and specifies a bituminous or portland cement concrete
splash apron to be placed over the backfill to prevent damage due to over-
topping. Such design features for a steel sheet-pile bulkhead are shown in
Figure 1. Any profile configuration can be specified in UTEXAS2. The splash
apron should be modeled as a surcharge load.
PROGRAM INPUT:
1. Profile line describing geometry of granular fill, underlying clay, sheet
pile wall, and water body by means of x,y coordinates.
2. The material properties required include unit weight, cohesion and
friction angle for each type of material.
Unit weight is the total weight of
the soil including the soil moisture per unit volume. Cohesion of a soil is
all of the shear strength not due to friction. The friction angle is a
property of the soil used to compute its shearing strength as a result of
friction between the particles.
Surface pressure exerted by the splash apron
is the increase in pressure transmitted to the underlying fill due to the
weight of the concrete or asphalt pavement of which the splash apron is
constructed. (There are several different ways to specify the cohesion and
friction angles.)
3. Piezometric line by means of x,y coordinates
4. Surface pressure exerted by splash apron
5. Initial estimate of x,y coordinates at center of critical circle
6. Initial estimate of critical circle radius
7. Required accuracy (such as to nearest 0.5 ft)
8. Minimum elevation below which critica1 shear surface not allowed to pass.
9. Procedure to be used; Spencer method is recommended.
Note that input data is free format controlled by command words and that the
program is batch oriented requiring the data file be generated beforehand.
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