Consider a 2-D object consisting of two triangle compartments, as shown in Figure P9.4. Suppose a solution containing a 511 KeV gamma ray emitting radionuclide with concentration f = 0.5….

## How many layers of geogrid are needed and the vertical spacing of each layer.

A mechanically stabilized earth (MSE) wall is needed to retain a

10-m-high earth fill. Geogrid is used as reinforcement. Lab testing

shows the ultimate tensile strength of the geogrid is 80 kN/m, and

the external friction angle between the backfill and the geogrid is 30°.

The earth fill material will be compacted at 95% of its maximum dry

unit weight (dmax = 21 kN∕m³) at the optimum water content. Under

typical field conditions, the moisture content of the backfill is 5%.

Direct shear tests indicate the effective friction angle of the backfill is

30 degrees, and the effective cohesion is zero. No surcharge is on the

backfill. Use reduction factors of 1.5, 2.5, 1.2 for installation damage,

creep, and chemical/biological degradation. The foundation soil

beneath the MSE wall is silty clay; its moist unit weight in its natural

condition is 19 kN∕m³, the internal friction angle is 10 degrees, and

the cohesion is 25 kN∕m². Between the geogrid and the foundation

soil, the external friction angle is 9 degrees, and the adhesion is

22 kN∕m².

Determine:

(1) How many layers of geogrid are needed and the vertical spacing

of each layer.

(2) Geotextile embedment length of each layer.

(3) Geotextile overlap length of each layer.

(4) The external stability in terms of overturning, sliding, and bearing

capacity of the MSE wall you designed in (1)–(3).