Geological Investigations for Projects Questions and Answers

Answer: A

Bearing capacity, settlement, stability, water and excavatability are all questions about behaviour under the works rather than about the ground as it stands. Everything in the investigation should be directed at answering them.

Answer: B

Published maps, memoirs, aerial photographs and records of neighbouring works cost almost nothing and shape everything that follows. Starting with boreholes means drilling without knowing where the problems are likely to be.

Answer: C

Correct answer: identifies likely problems and guides where to explore

The desk study costs very little and is done before anyone goes on site, so its value lies in telling the investigation where to look. Maps, memoirs, old plans and records of neighbouring works reveal what ground to expect and what has gone wrong nearby, and the boreholes are then placed to answer real questions rather than scattered at random.

Answer: D

Correct answer: observing the present condition of the ground and its surroundings

The walkover puts the desk study against what is actually there: seepages, hummocky ground suggesting old slips, cracked walls on adjacent buildings, made ground, the state of the drainage. None of it is measurement, and that is not its purpose - it is the check that the records still describe the site.

Answer: A

Correct answer: lineaments, drainage patterns and old landslides

Aerial photographs show the ground as a whole, and features invisible from within the site read clearly from above: fault lineaments, drainage anomalies, the lobate form of an old landslide, differences in vegetation over shallow rock. Stereo pairs add the relief. What they cannot give is anything quantitative about the material itself.

Answer: B

Travel times of waves refracted along interfaces give the velocity and thickness of each layer, so rock head is mapped continuously. It requires velocity to increase downward, which a soft layer beneath a stiff one violates.

Answer: C

The method assumes velocity increasing with depth, so a soft layer under a stiff crust is a hidden layer that the travel times cannot reveal. A weathered zone beneath a hard cap is the classic case and a dangerous one.

Answer: D

Correct answer: the water table and variations in saturation

Resistivity depends strongly on the amount and salinity of the pore water, so a saturated horizon contrasts sharply with a dry one above it. That makes the method well suited to locating the water table, tracing saline intrusion and mapping clay content. It says nothing about strength or structure.

Answer: A

Correct answer: rapid attenuation in clay and saturated ground

Radar depends on the ground being electrically resistive, and clay and saline water are conductive: they absorb the signal within a metre or two. In dry sand or clean gravel the same equipment reaches ten metres or more. Penetration is therefore governed by the material rather than by the instrument, which is why a trial line is worth running before the survey is planned.

Answer: B

Correct answer: density

A gravity survey measures very small variations in the earth’s gravitational field caused by density contrasts at depth. A cavity or a buried valley filled with soft deposits shows as a negative anomaly, a dense intrusion as a positive one. It is the method of choice for detecting voids in limestone, where nothing else works over large areas.