geotechnical engineering ecg 503 lecture note 12 4.0 ground improvement techniques
TRANSCRIPT
GEOTECHNICAL ENGINEERING
ECG 503
LECTURE NOTE 12
4.0 GROUND IMPROVEMENT TECHNIQUES
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
Mechanical Methods and Objective; Stone Column, Dynamic Compaction, Vibrofloatation and Vibro Compaction.
Physical and Chemical Methods and objective; Grouting and cement column
Hydraulic Methods and Objective of Vertical Drain and Preloading
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
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
GENERAL BACKGROUND OF
SOFT CLAY
Malaysia Coastal Area – Not fully developed
Soft clay usually located around the coastal area
The soft clay have been a source of difficulties for many years. The soft soil can cause settlement which can give a lot of problem and damage in several way. This is the reason why Malaysia’s coastal areas are not generally developed
TWO DISTINCT ATOMIC STRUCTURAL UNITS
oxygen
silicon
0.29 nm
aluminium or magnesium
hydroxyl or oxygen
0.26 nm
Silicon Tetrahedron Aluminium Octahedron
Micro-fabric particles in natural clay.
Flocculated Dispersed
Flaky shape
Plate like structure
ION EXCHANGE
Ground Improvements for Soft Clay
• Stone Column (Vibro-Replacement)
• Prefabricated Vertical Drain
• Cement Column
VIBRO-REPLACEMENT (STONE COLUMN)
Vibro-Replacement
•Also known as stone column. The technique are similar to vibroflotation/vibrocompaction except the granular fill materials which used is sand is replaced by gravel stone sizes ranging from 50mm to 100mm
Soil Layer
-Increase in density
- Increase in bearing capacity
- Radial drainage (help to improve settlement)
- Shear strength of soil improve
- Reinforcing the soil by applying rigid member (stone column) inside the soil
Stone Columns
vibrator makes a hole in the weak ground
hole backfilled ..and compacted Densely compacted stone column
PREFABRICATED VERTICAL DRAIN (PVD)
CEMENT COLUMN (CHEMICAL STABILIZATION)
APPLICATION OF STABILIZE CLAY
GROUTING TECHNIQUE
EXAMPLE OF CASE STUDY FOR GROUND IMPROVEMENT
METHODS ON SOFT CLAY
GEOTEXTILES