New York City College of Technology
Department of Construction Management and Civil Engineering Technology
SOIL MECHANICS PROJECT
CMCE 2456 – Fall 2020
A homeowner want to level a rear yard. You visit the site and realize that the work will require the
construction of an about 5-ft-tall retaining wall. Your subsurface exploration indicates that the soil
in the yard is homogeneous medium to fine SAND with trace amounts of silt (USCS Classification
SP) to a depth of 25 ft below ground surface. N-values suggest that the material is classified as
NYC Building Code Class 3b material; groundwater was not encountered. Laboratory tests
indicate that the sand has a moist unit weight of 122 pcf and an angle of internal friction of 33°.
PROBLEM STATEMENT
Size the retaining wall such that it has a geotechnical factor of safety against sliding and
overturning of 1.5.
Assumptions
 Assume a vertical surcharge of 300 psf is applied on the high side of the wall.
 The wall foundation must bear 4 ft below the lowest grade for frost protection.
 The stem of the wall must be a minimum of 12-inches thick.
 The wall footing must be a minimum of 12-inches thick.
 Ultimate friction factor for mass concrete against clean fine to medium SAND is 0.4.
 Consider passive pressure in the analysis.
 Lateral pressures due to the surcharge have a uniform distribution based on a pressure
equal to 50 percent of the vertical pressure.
 Unit weight of reinforced concrete is 150 pcf.
Assignment
1) Produce an engineered-quality scaled drawing.
2) Include your calculations showing your assumptions, pressure diagrams and resultant
forces.
3) What is the applied bearing pressure under the wall?
4) Is the applied pressure less than the Building Code allowable?
5) If passive pressure is discounted, what is the resulting factors of safety?
6) Provide a cover letter with your submittal.
NOTE: Your calculation must be on engineering paper, they must be neat and without
scribbled corrections.