Geotechnical and Pavement

What the road sits on and what it is made of: soil sampling, testing, evaluation and stabilization, soil properties, compaction and earthwork balance, and the traffic loading, design and rehabilitation of flexible and rigid pavements. It carries 6–9 of the 80 questions on the Transportation exam.

What the problems look like

Mostly calculation, from a lab report, grain-size curve or cross section. Recurring shapes — AASHTO classification and group index; phase relations (dry unit weight, relative density, shrinkage limit); effective stress, consolidation time, triaxial shear strength and permeability; earthwork with swell and shrinkage, average end areas and the mass diagram; ESAL loading; AASHTO-93 layer thicknesses and the flexible design equation; asphalt volumetrics (VMA, absorbed and effective binder); and which field test gives which parameter.

By exam day you should be able to —

• classify a soil by the AASHTO chart and compute its group index;
• work phase relations and effective stress, including standing water above the ground;
• find degree of consolidation from time, drainage path and cv;
• convert earthwork among bank, loose and compacted volume and read a mass diagram;
• build design-lane ESALs by vehicle class;
• size flexible layers from structural numbers and check capacity with the design equation;
• compute VMA and effective asphalt content.

Where people lose points

• Classification order: work the AASHTO chart left to right and stop at the first group that fits; read percent passing at the named sieve, not a neighbouring one. Granular A-2-6 and A-2-7 soils take the partial group index, and F is always the No. 200 fraction.
• Effective stress: subtract pore pressure from both principal stresses. Water standing above the ground adds to total stress and pore pressure equally — include it in both or neither.
• Drainage path: Hd is half the layer only when both faces drain; unfractured (impervious) rock or an impervious clay below is not a drainage boundary. Interpolate U from Tv rather than taking the nearest row.
• Earthwork states: swell relates bank to loose; shrinkage relates bank to compacted. Split average end areas at the grade point.
• ESALs: when the load equivalency factor is given per axle, multiply it by the axles on each vehicle; a tandem or tridem factor applies once per axle group.
• AASHTO-93: ΔPSI is the loss, p0 − pt; layer design subtracts the structural number the rounded upper layers provide; each layer keeps its own coefficients.
• Asphalt specific gravities: VMA uses the aggregate's bulk (oven-dry) value; effective specific gravity comes from Gmm, not the apparent value.

Have these at your fingertips

Classification charts, phase relations, the U–Tv relation, earthwork definitions and asphalt volumetrics — and where they live in the Handbook. The pavement standards — the AASHTO Guide for Design of Pavement Structures (1993) and the AASHTO MEPDG (3rd ed., 2020) — are the same editions before and after April 2027. Know the MEPDG's input levels.

Going deeper

• Which PE Civil exam should you take?
• Drainage — the water a drainage layer has to pass

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