Materials

What the project is built from and built on: soil classification and boring-log interpretation, soil properties and phase relationships, concrete, piping materials, and testing against a specification. It carries 4–6 of 80 questions on the WRE exam — mostly reading a table, chart or log correctly, then one careful calculation.

What the problems look like

Classification-and-lookup, with an exhibit. Recurring shapes — AASHTO and USCS classification; boring logs (N60, consistency, RQD, groundwater); phase relationships; gradation coefficients; concrete w/cm, maturity, exposure class and strength acceptance; pipe selection; and field compaction acceptance.

By exam day you should be able to —

• classify a soil by AASHTO and USCS from sieve and plasticity data;
• read a boring log: N60, the right sample for a given depth, consistency vs. relative density, RQD;
• move between unit weights, void ratio, water content and saturation;
• compute Cu and Cc from a gradation curve;
• compute a batch's w/cm with aggregate moisture, and concrete maturity;
• judge concrete strength tests and field compaction tests against a specification;
• pick pipe materials for aging, corrosion and sewer-gas service;
• select concrete cover from exposure and member type, and the right nondestructive test for the property in question;
• interpret permeability and strength test results for a soil sample.

Where people lose points

• Classification inputs: percent passing = 100 − cumulative percent retained; PI = LL − PL. In USCS the P in SP means poorly graded, and SM is coarse-grained — more than half retained on the No. 200 sieve.
• Boring logs: N is the second plus third 6-in. increments; a hammer below 60% efficiency lowers N60. Read the sample that spans the bearing depth, and use the clay correlation for a clay. Rate rock on RQD, not recovery.
• Phase relations: γd = γt/(1 + w), not γt(1 − w); know which unit weight you were given before you solve for e — and solve for e, not 1 + e.
• Gradation: Cc squares D30; Cu is a different number. The size axis is logarithmic and runs coarse to fine — count gridlines slowly.
• Concrete mix: mixing water changes by each aggregate's free moisture — total minus absorption — so a wet sand adds water and an aggregate below absorption takes it out; adding total moisture overstates the water. Maturity sums (concrete temperature − datum temperature) × interval duration, from casting — not air temperature, and not an unweighted average.
• Concrete acceptance: judge 28-day results (or the designated test age). Every average of three consecutive tests must reach f′c — not the overall average, and not rounded up — and no single test may fall more than 500 psi below f′c (0.10f′c when f′c exceeds 5,000 psi). Know when the field-cured 85% check applies and when the 500-psi margin removes it.
• Pipe and exposure: unlined cast iron loses Hazen-Williams C with age; crown corrosion over a septic flow is H₂S turned to sulfuric acid, not attack from the liquid. Match units when reading sulfate exposure limits, and let deicers move the freeze–thaw class up.

Have these at your fingertips

The AASHTO and USCS charts, the phase-relationship identities, the SPT correlations, the concrete acceptance, exposure and cover tables, and the Hazen-Williams C values by pipe material and age — plus where each sits in the Handbook. Pipe selection for corrosion and sewer-gas service is judgment, not a table.

Going deeper

• Soil Mechanics — where these properties go to work
• Hydraulics–Closed Conduit — the pipe you selected, in a hydraulic calculation
• A quarter of the WRE exam isn't water

Part of the Water Resources & Environmental exam. Practice this area with exam-real problems — the tutor walks any one you miss. → Start practicing free — free with an account.