16. Geotechnical & Pavement Flashcards
What is the Resilient Modulus?
the measure of the subgrade material stiffness via the triaxial test.
What is the California Bearing Ratio (CBR) test?
An indirect measure of soil strength based on resistance to penetration (by a standardized piston moving at a standardized rate for prescribed penetration distance).
What is the Resistance Value (R-value) test?
A material stiffness test that expresses a material’s resistance to deformation as a function of the ratio of transmitted lateral pressure to applied vertical pressure.
What does the dynamic cone penetrometer measure?
The direct correlation between the strength of a soil and its resistance to penetration by solid objects.
What does the modulus of subgrade reaction for Richard Pavement measure?
The stiffness of the foundation soil
What are the two widely used methods for pavement design?
Empirical Method (1993 AASHTO guide) and Mechanistic-Empirical Method (NCHRP 1-37A)
What is the difference between they two methods of pavement deisgn?
Empirical Method is based on empirical observations; MEPDG method uses theory of mechanics.
What are the three major stages in the MEPDG design method
(1) Evaluation, (2) Analysis, (3) Stratey Selection
How are structual respones (stresses, strains, and deflections) calculated with MEPDG?
Mechanistically, based on material properties, environmental conditions, and loading charactersistics. Thus using theory of mechanics. Aka Pavement Response Model.
Input: pavement geometry, environment, material properties, traffic
Output: stress, strain, displacement
How are the preformace predictions calculated with MEPDG?
Empirical models. Aka Performance Model.
Input: stress, strain, displacement
Output: cracking, rutting
Causes of alligator (bottom-up fatigue) cracking.
- Loss of base, subbase or subgrade support (poor drainage)
- Stripping on the bottom of the HMA layer
- Increase loading (unanticipated loads)
- Inadequate structural design
- Poor construction (inadequate compaction)
Causes of longitudinal (top-down) cracking for rigid pavement.
- Poor lane joint construction
- Temperature cycling
- Reflective cracking in base layer
- Volume changes in subgrade
Causes of rutting (permanent deformation).
- Insufficient compaction of HMA layers
- Subgrade rutting (as a result of inadequate pavement structure)
- Improper mix design
Causes of thermal cracking (transverse).
Heating/cooling cycles in the asphalt. (i.e., surface cools faster and with more intensity than the core of the structure)
What are the distress in rigid pavement?
- Bottom-Up Transverse Cracking (JPCP)
- Top-Down Transverse Cracking (JPCP)
- Joint Faulting (JPCP)
- Punchouts (CRCP)
What are the four characteristics of pavement condition for evaluating pavement rehabilitation?
(1) Pavement Roughness (rideability)
(2) Pavement Distress (surface condition)
(3) Pavement Deflection (structural failure)
(4) Skid Resistance (safety)
What is settlement?
Settlement by means of elastic deformation, immediate settlement.
What is primary consolidation settlement?
Reduction of soil volume as a result of pore water expulsion.
What is secondary consolidation settlement?
Reduction of soil volume as a result of plastic adjustment of the soil structure.
What does compaction do to the soil?
Increases the density of an unsaturated soil by reducing the volume of air in the voids; instantaneous process; water content does not change.
What does consolidation do to the soil?
Increase the density of a saturated soil by draining out some of the water; time dependent process; water content decreases.
What are the purposes of ground modification (soil stabilization)?
- Increase shear strength
- Reduces permeability
- Reduces compressibility
What are the two categories of soil stabilization?
- Mechanical: blending different grades of soil to obtain required grade
- Chemical: blending of the natural soil with chemical agents.
Type of soil stabilization methods?
- Soil Replacement: removal and replacement; displacement
- Water removal (consolidation); wick drains/sand drains
- Site Strengthening: deep or shallow vibratory techniques or dynamic compaction
- Grouting or Compaction Grouting
