Engineering Geology Flashcards
7 cards from real ASBOG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Engineering Geology flashcards as text
Which type of fault movement is most likely to produce a pressure ridge in alluvium along a strike-slip fault?
Answer: Compressional restraining bend
A compressional restraining bend on a strike-slip fault forces material to converge and buckle upward, forming a pressure ridge in the overlying alluvium.
The Atterberg limit most relevant to the shrinkage and cracking potential of an expansive clay is the:
Answer: Shrinkage limit
The shrinkage limit marks the water content below which further drying causes no further volume change, and low shrinkage limits correlate with high swell-shrink potential.
In a triaxial compression test, if the deviator stress at failure is 200 kPa and the cell pressure is 100 kPa, the major principal stress σ1 at failure is:
Answer: 300 kPa
σ1 = cell pressure (σ3) + deviator stress = 100 + 200 = 300 kPa.
Swelling pressure in an expansive soil is best measured using which laboratory test?
Answer: Constant volume oedometer test
In a constant volume oedometer test, load is applied to prevent any swell, and the pressure required to maintain zero volume change equals the swelling pressure.
Which drainage pattern typically indicates a structurally controlled, folded terrain with alternating resistant and weak rock units?
Answer: Trellis
A trellis drainage pattern forms where main streams follow weak rock layers (e.g., valleys) with short tributaries cutting perpendicular through resistant ridges in folded rocks.
The critical height of an unsupported vertical excavation in a purely cohesive soil (φ = 0) is given by:
Answer: Hc = 4c / γ
Terzaghi's stability formula gives the critical height Hc = 4Su/γ for a vertical cut in undrained clay, where Su is undrained shear strength and γ is unit weight.
Which rock texture is most indicative of explosive volcanic eruption and rapid magma vesiculation?
Answer: Pyroclastic (scoriaceous or pumiceous)
Pyroclastic textures with abundant vesicles (scoria, pumice) form when gas-rich magma erupts explosively and chills rapidly, trapping gas bubbles as void space.