**Civil Engineering**

CE4320/5367

HOMEWORK 2

**EXERCISE 1 (50 PTS)**

The following information pertains to a semigravity retaining wall with clean sandy soil as backfill (following page): Total height of wall stem H = 6 m, width of wall stem (top) = 1 m, width of wall stem (bottom) = 2m, J = 18.2 kN/m3 (moist unit weight), I’ = 28o (from CD triaxial test), c’ = 0 (sandy soil), G = 14o (soil-wall friction angle???D = 10o (inclined backfill), and E = 85o (same for the inside and outside faces). (A) Determine the Coulomb maximum active force per unit length of wall using the

trial-wedge based graphical method. (B) Compare the maximum active force obtained in part (A) with that calculated from

Coulomb’s analytical solution and draw a brief conclusion.

NOTE 1: You are required to redraw the cross section of the combined wall-backfill geometries to exact scale (the larger the better).

NOTE 2: For each trial wedge in part (A), you are required to draw a separate force

polygon to exact scale. NOTE 3: You are required to plot the change in the active force magnitude with

increasing trial-wedge angle T using MS Excel software. NOTE 4: You are welcome to use advanced plotting software, such as AutoCAD, for

the combined wall-backfill geometries and/or the force polygons, but is not required.

**EXERCISE 2 (50 PTS)**

The following information pertains to a cantilever retaining wall that is being designed as part of a recreational, open-channeled, waterways project as shown (following page): x H? = 10 ft (thickness of sandy soil) x H? = 15 ft (thickness of clayey sandy soil) x H? = 10 ft (lowest water table expected on the outside face of the wall) x J? = 110 pcf (moist unit weight), I’? = 30

o , and c’? = 0 (sandy soil)

x J? = 136 pcf (saturated unit weight), I’? = 28

o , and c’? = 215 psf (clayey sandy soil)

In addition, a surcharge load (accounting for parking and restroom facilities next to the wall) is being considered: x q = 1000 psf, a’ = 10 ft, and b’ = 8 ft Determine the Rankine net active force per unit length of wall. NOTE 1: The net active force is to be calculated based upon the resulting (combined)

lateral pressure distribution diagrams. NOTE 2: Hydrostatic pressures acting on both the inside and the outside faces of the

wall must be taken into account in calculating the net active force. NOTE 3: Use at least 5 equally spaced “depth intervals” in assessing the lateral pressure

diagram from the 1000-psf surcharge.

NOTE 4: You are required to plot the resulting lateral pressure distribution diagrams from backfill soils, surcharge load, and inside and outside hydrostatic pressures, to exact scale.

NOTE 5: You are required to follow the same step-by-step approach documented in

your class notes for solving similar examples, including calculation tables. NOTE 6: You are welcome to use advanced plotting software, such as AutoCAD, for

the pressure diagrams, but is not required.