dry working area of 12m width by its perpendicular direction
(estimated to be 1-2km) footprint area is required as shown in
Figure 1. The water level is 3.5 m above riverbed level, and pumps
must be provided to keep the working area dry. The riverbed
consists of 6m of silty sand, overlying low permeability marine
clay. The silty sand has a permeability of 8 ×10-5 m/s. The total
unit weight γt of the silty sand is 18 kN/m^3.
The cost (per metre run) of supplying (for the required
duration), installing and removing a single line of sheet piles
varies with the depth d of sheet pile penetration, as shown in
Figure 2. The cost of supplying and operating pumps (for the
required duration) is $2000 for each litre/s of pump
capacity.
Draw flownets for sheet pile penetrations of 1m, 3m and 5m.
Hence suggest an optimum depth of sheet pile penetration d,
by:
1) attempting to minimize the combined cost of pumping and sheet
pile provision;
2) ensuring that the average upward hydraulic gradient in the zone
of soil enclosed by the dashed line in Figure C1 is less than 60%
of the critical value associated with a quick condition.
- To Facilitate Construction Works A Sheet Pile Cofferdam For A Dry Working Area Of 12m Width By Its Perpendicular Direct 1 (47.01 KiB) Viewed 46 times
- To Facilitate Construction Works A Sheet Pile Cofferdam For A Dry Working Area Of 12m Width By Its Perpendicular Direct 2 (179.78 KiB) Viewed 46 times
Figure 2 1800 1600 1400 1200 1000 Cost of sheet piles (SGD/meter run) 800 600 400 200 0 0 1 2 3 4 5 6 Sheet pile penetration, d (m)