GEOTECHNICAL ENGINEERING ECG 503 LECTURE NOTE 12 4.0 GROUND IMPROVEMENT TECHNIQUES

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