environmental risks for 30 years after closing. Mining the landfill eliminates the need for
closure while producing moneymaking power and reducing the storage volume needed
for a specific amount of trash. So before soil consolidation tests are made for a landfill,
plans for its possible mining should be reviewed.
SETTLEMENT OF FOOTING
An 8-ft (2.4-m) square footing carries a load of 150 kips (667.2 kN) that may be consid-
ered uniformly distributed, and it is supported by the soil strata shown in Fig. 18. The
silty clay has a compression index of 0.274; its void ratio prior to application of the load
is 84 percent. Applying the unit weights indicated in Fig. 18, calculate the settlement of
the footing caused by consolidation of the silty clay.
Calculation Procedure:
- Compute the vertical stress at middepth before and after
application of the load
To simplify the calculations, assume that the load is transmitted through a truncated pyra-
mid having side slopes of 2 to 1 and that the stress is uniform across a horizontal plane.
Take the stress at middepth of the silty-clay stratum as the average for that stratum.
Compute the vertical stress (T 1 and (T 2 at middepth before and after application of the
load, respectively. Thus: (T 1 = 6(116) + 12(64) + 7(60) = 1884 lb/ft
2
(90.21 kPa); (T 2 =
1884 + 150,000/33^2 = 2022 lb/ft^2 (96.81 kPa).
FIGURE 18. Settlement of footing.
Woter
table
Sand
and
gravel
Silty clay
Rock
