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