PCGE - 4. Mechanical Git - Dynamic Compaction

Question 1

It is the densification of soil at a constant water content. During this, air is expunged from a partially saturated soil in response to the compaction energy (normally a dynamic load).

Answer 1

Compaction

Question 2

It is that which occurs beneath a surface-operated compactor such as a roller or plate compactor.

Answer 2

Shallow Compaction

Question 3

It is that which occurs in the region surrounding a vibrator that penetrates the ground surface, such as a vibrating probe.

Answer 3

Deep Compaction

Question 4

In shallow compaction, what is the most common form of delivering compaction energy in the field to cohesive soils and to cohesionless soils?

Answer 4

kneading (Sheepsfoot roller) and vibration (smooth-drumroller/platecompactor/rammer).

Question 5

is the method most employed test to evaluate the compaction characteristics of a soil (with the use of proctor mold and hammer).

This test determines the maximum dry density / unit weight and optimum moisture content.

Answer 5

Standard Proctor Test

Question 6

These are motor driven that causes the compactor to “jump” and ram the soil as it comes down. These compactors work best with a thin lift (<100 mm) and with granular materials. They weigh from 70 kg to 100 kg and has plate size of 0.1sqm.

Answer 6

Rammer (tamper, jumping jack)

Question 7

For greater compaction effort, vibratory plate compactors can be used These generally weigh from 100 kg to 250 kg, have a typical plate area of approximately 0.4 sqm. It is best for granular materials and may be suitable for some mixed materials having a small cohesive component.

Answer 7

Vibratory Plate Compactors

Question 8

It is similar to a smooth roller, but it vibrates, combining static and dynamic forces to increase the efficiency of compaction. The vibrations compact the soil, force the settlement and increase its density.

These are commonly employed for compacting granular soils

Answer 8

Vibratory smooth drum rollers

Question 9

Applies compaction stress to the soil from the tip of the spike (or foot). This roller work best when compactingsemi-cohesive soils whose particles stick together, because of silt and clay particle.

Answer 9

Sheepsfoot roller

Question 10

Considered as the universal compactor. it is typically consist of an axle with several tires, side by side. The space between the rubber tires provides the kneading action needed to compact clayey soils, and the weight provides the action to compact cohesionless soils.

Answer 10

Pneumatic tired compactors

Question 11

is a field compaction technique that can compact soils in place to depths of up to about 7 m. The technique uses a modified, hydraulically operated, pile-driving hammer impacting a circular, articulating plate.

Watts and Charles (1993) describe the compactor as including a 70 kN weight falling 1.2 m on to a 1.5 m diameter foot at a rate of 40 blows per minute

Answer 11

Rapid impact compaction (RIC)

Question 12

is one of the oldest soil improvement methods known, reportedly used by the Romans prior 100 AD and 1800s in the US.

Answer 12

Deep dynamic compaction

Question 13

is a cost-effective method of soil compaction whereby a heavy weight (tamper) is repeatedly lifted dropped from a height, impacting the ground surface with impact energy.

In this method, a tamper, normally weighing between 10 and 50 tons, is dropped onto the ground from a height between 10 and 40 m.

Answer 13

Deep Dynamic Compaction

Question 14

Explain how Deep Dynamic Compaction (DDC) works

Answer 14

The weight is normally lifted with a crane and dropped in free fall by releasing the lifting cable. The resulting momentum of the falling weight provides the compaction energy for each drop.

The weights are typically constructed to be durable by using steel plate, box-steel and concrete.

In terms of size, narrow weights have been recommended by engineers and researchers.

Question 15

Explain the Phases of Deep Dynamic Compaction

Answer 15

1st Phase: Compaction in deep layers
aimed at treating the deepest layer by adopting a relatively wide grid pattern and a suitable number of drops from full-height capability of the crane.
Then, Backfilling-

2nd Phase: Compaction of Intermediate layers
aimed treating the middle layer, often the midpoint of the first phase or half of the initial grid, with lesser number of drops and reduced drop height.
Then, backfilling-

3rd Phase: Compaction of surface layers (Ironing Stage)
aimed treating the surface layer with continual tamp of a smaller number of drops compare to 2nd phase from low heights on a continuous pattern.

Roller compaction phase