Geotechnical Exam Question Set B Flashcards
List three (3) types of earth retaining structures and define how the structures
gain stability to retain the soil?
- Gravity walls rely on the stability of its self-weight
- Cantilevered walls rely on weight of soil retained above its base
- Sheet piles walls rely on embedment depth and horizontal restraining forces
State the two (2) main types of dewatering methods. Give an example for each
method stated.
- Removal methods: pumping from sumps / well pointing
- Exclusion methods: coƯerdam
Determine five (5) factors aƯecting the choice of materials for filling and
backfilling.
- The material will remain stable for the duration of the structure against which it is
being placed. - The material contains appropriate texture or consistency such that it can be
properly compacted. - The material is readily available.
- The material is as hard as possible.
- The material is not too wet, full of voids and liable to excessive shrinkage.
- The material is free from chemicals that will attack concrete or any surface of the
structure it is in contact with.
List three (3) advantages and three (3) disadvantages of using sheet piles in
trench protection.
- Advantages: high strength, readily available and continuous
- Disadvantages: flexible and can cause excessive ground movement,
- can only be
driven to limited depths - installation can be severely hampered by
obstructions in the ground
Name two (2) types of shallow foundation and describe each type
- Pad foundation: usually constructed to support structural reinforced concrete
columns, stanchions or isolated brick piers - Strip foundation: normally provided for load-bearing walls and for rows of
columns that are closely spaced
Determine the circumstance when strip foundation / combined footing should
be used instead of pad footing.
- When the distance between the adjacent pad footings is less than the width of
the pad footing.
- Piles could be classified by the method of installation and by the derivation of
bearing capacity. Briefly describe how the piles are classified:
a. By the way their bearing capacity are derived:
- Friction Piles: piles transfer load to the surrounding soil by means of
friction between the surfaces of the piles and the soil
- End Bearing Piles: piles transfer most of these loads to a firm stratum
on which their ends rest
b. By the methods of installation:
- Displacement Piles: pile displaces its own volume while it is being
installed in the ground
- Non-displacement Piles: Is formed by the placement of
reinforcement and concrete in a hole formed by removal of existing
soil from the ground
List ten (10) possible problems occurring during the installation of a pile.
- Overdriving the pile
- Driving the pile using the wrong hammer weight
- Deflected oƯ location by obstructions
- Ground heaving
- Tensile cracking during driving
- Consolidation in sand due to piling
- Confusion between chiselling and socketing
- Concrete placement and mix design
- Necking of pile due to incorrect casing withdraw method
- Boring in unstable soils may cause breakthrough of soil wall
State three (3) advantages of using dynamic load test over static load test of a
pile.
- Easy to set up as no concrete cubes are required.
- Easily mobilized as and when required.
- Can check integrity of piles.
.State the causes of deferential settlement
- The soil profile may not be uniform across the site
- The ratio between the actual load and the design load may be different for each
column - The ratio of dead to live load may be different for each column
- The as-built foundation dimensions may differ from the plan dimensions
Determine the purposes of ground improvement.
- To reduce the settlement of existing ground
- To increase the bearing capacity of the existing ground
- To increase/decrease the permeability of the existing ground, depending on the
project objective
12.Describe how dynamic replacement is carried out.
- It is carried out in three passes over the entire area.
- The passes are separated by time intervals depending on the rate of dissipation
of excess pore water pressure in the soil. - In the first pass, pounding is carried out at wider spacing followed by second and
third passes in which granular columns are installed in between those formed in
the first pass.
List four (4) functions of stone columns.
- To enhance the bearing capacity
- To reduce the settlement of soft soils such as peats
- To accelerate the stage of primary consolidation
- To reduce the liquefaction potential of sands
- To improve the stability of slopes
State three (3) disadvantages of Sand Compaction Pile (SCP).
- Substantial heaving of the ground during SCP installation.
- Not easy to control the positioning of the SCP to achieve the exact replacement ratio.
- Steel casing often irretrievable and are left in the ground.
