Geological Investigations for Projects Questions and Answers

Answer: A

Correct answer: the site is covered by deep uniform soft clay

An adit is driven to examine a rock mass in place, so it has no application in deep soft clay, where boreholes and sampling give everything an adit could and the excavation would need support throughout. The other three are the standard justifications: seeing the discontinuities, testing at the level of the works, and the scale of a cavern or dam abutment.

Answer: B

Correct answer: a core stone has been mistaken for rock head

Spheroidal weathering leaves rounded corestones of sound granite floating in decomposed material, and a hole stopped on the first hard thing it meets may have stopped on one of them. The foundation is then designed on rock that is a metre thick with weathered granite beneath. Proving a hard layer by drilling several metres into it is the standard precaution.

Answer: C

A weathered zone beneath a hard cap violates the method's assumption of increasing velocity, so the interface it reports is the cap rather than true rock head. Boreholes calibrate the geophysics precisely to catch this.

Answer: D

Correct answer: both the assertion and the reason are true and the reason explains the assertion

Both are true and the reason gives the mechanism. Geophysics measures velocity, resistivity or density, none of which identifies a material on its own - the same resistivity may mean a saturated sand or a clay. A borehole at one point on the traverse ties the measured property to the actual ground, and the survey then extends that identification along the line.

Answer: A

Correct answer: the assertion is false although the reason offered is a true statement in itself

The reason is quite true - published records do contain a great deal - but the conclusion drawn from it does not follow. The desk study directs the investigation; it cannot supply the ground conditions at a specific site to the accuracy a design requires, and treating it as a substitute for exploration is how sites come to be built on unrecorded made ground.

Answer: B

Correct answer: preserves the observations for later reinterpretation

Facts and opinions are separated deliberately. The interpretative report will be superseded as the works change or as construction reveals more, but the logs and test results remain valid, and keeping them in a document of their own means a later engineer can form a different view from the same evidence.

Answer: C

Correct answer: a geophysical traverse across the site

This is the essential complementarity between the two families of method. A borehole, a penetration test and a laboratory test each give detailed information at a single point. A geophysical traverse gives continuous but indirect information along a line - which is why the two are used together, the boreholes calibrating what the traverse measures.

Answer: C

The correct match is a-ii, b-iv, c-i, d-iii.

• Standard Penetration Test: a dynamic test done inside a borehole, mainly in granular soils (ii).
• Probing penetration test: driving a probe to estimate penetration resistance with depth (iv).
• Cone Penetration Test: measures the soil's response to a cone pushed continuously into the ground hydraulically (i).
• Field vane test: gives the undrained shear strength of soft cohesive soils (iii).

The first code gives the probing test the cone description, and the second and fourth misplace the SPT, which is the dynamic borehole test.

Answer: D

The additive is Fly ash.

Expansive soils such as black cotton soil contain swelling clays like montmorillonite. Stabilising them with lime or cement plus fly ash, a pozzolanic waste from thermal power plants, forms cementing compounds through the pozzolanic reaction. This reduces plasticity and swelling and raises strength, and it uses a waste product cheaply.

Bitumen is used to waterproof or bind granular soils, not to cut swelling of clays. Anhydrite swells itself when it hydrates to gypsum, and bauxite is an aluminium ore, not a stabiliser.

Answer: A

Buff bricks come from clay with about 2 to 3% iron oxide.

The colour of a fired brick depends mostly on its iron content. Clay with little iron oxide, around 2-3%, fires to a buff or cream colour; higher iron contents give the familiar red, and still higher iron, especially with overfiring, gives dark red to purple and brown bricks.

Clays with 3-6% or more iron oxide therefore produce red rather than buff bricks, so the higher ranges are wrong.