GEOTECHNICAL ENGINEERING

ECG 503

LECTURE NOTE 11

TOPIC : 4.0 GROUND IMPROVEMENT TECHNIQUES

MARCH 2009

LEARNING OUTCOMES

Learning outcomes:

At the end of this lecture/week the students would be able to:

Understand natural slope and made engineered soil slope assessment which include rainfall induced failure and role of suction.

TOPIC TO BE COVERED

Objective and Principles of Ground Improvements

Types of Ground Improvements With Respect of Cohesionless and Cohesive Soil

Mechanical Methods and Objective; Stone Column, Dynamic Compaction, Vibrofloatation and Vibro Compaction.

for compacting very small areas

Vibrating Plates

effective for granular soils

Smooth-wheeled Roller

Compacts effectively only to 200-300 mm; therefore, place the soil in shallow layers (lifts)

Smooth Wheeled Roller

Sheepsfoot Roller to Compact Clay Soils

Provides kneading action; “walks out” after compaction

Sheepsfoot Roller

Very effective on clays

Impact Roller to Compact the Ground

Provides deeper (2-3m) compaction. e.g., air field

Impact Roller

Dynamic Compaction- pounding the ground by a heavy weight

Suitable for granular soils, land fills and karst terrain with sink holes.

Crater created by the impact

Pounder (Tamper)solution cavities in limestone

(to be backfilled)

Pounder (Tamper)Mass = 5-30 tonneDrop = 10-30 m

Vibroflotation

Vibroflot (vibrating unit)Length = 2 – 3 mDiameter = 0.3 – 0.5 mMass = 2 tonnes

Practiced in several forms:

vibro–compaction

stone columns

vibro-replacement

Suitable for granular soils

(lowered into the ground and vibrated)

Vibroflotation

Vibroflotation

Stone Columns

vibrator makes a hole in the weak ground

hole backfilled ..and compacted Densely compacted stone column

Blasting

Aftermath of blastingFireworks?

For densifying granular soils

Earthmoving Equipment

Large Excavator (see minivan on left for scale)

Grader for spreading soil

Bulldozer for spreading soil evenly

Loader

Backhoe

Crawler mounted Hydraulic Excavator

Rock Breaker

Filed Compaction

• Pneumatic rubber tired roller

Different types of rollers (clockwise from right):

Vibratory roller

Smooth-wheel roller

Sheepsfoot roller

Big weights dropped from 25 m, compacting the ground.

Craters formed in compaction

GEOTEXTILES