geotechnical engineering ecg 503 lecture note 12 4.0 ground improvement techniques

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GEOTECHNICAL ENGINEERING ECG 503 LECTURE NOTE 12 4.0 GROUND IMPROVEMENT TECHNIQUES

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Page 1: GEOTECHNICAL ENGINEERING ECG 503 LECTURE NOTE 12 4.0 GROUND IMPROVEMENT TECHNIQUES

GEOTECHNICAL ENGINEERING

ECG 503

LECTURE NOTE 12

4.0 GROUND IMPROVEMENT TECHNIQUES

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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.

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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

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for compacting very small areas

Vibrating Plates

effective for granular soils

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Smooth-wheeled Roller

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

Smooth Wheeled Roller

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Sheepsfoot Roller to Compact Clay Soils

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Provides kneading action; “walks out” after compaction

Sheepsfoot Roller

Very effective on clays

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Impact Roller to Compact the Ground

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

Impact Roller

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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)

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

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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)

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Vibroflotation

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Vibroflotation

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Blasting

Aftermath of blastingFireworks?

For densifying granular soils

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Earthmoving Equipment

Large Excavator (see minivan on left for scale)

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Grader for spreading soil

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Bulldozer for spreading soil evenly

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Loader

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Backhoe

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Crawler mounted Hydraulic Excavator

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Rock Breaker

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Filed Compaction

• Pneumatic rubber tired roller

Different types of rollers (clockwise from right):

Vibratory roller

Smooth-wheel roller

Sheepsfoot roller

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Big weights dropped from 25 m, compacting the ground.

Craters formed in compaction

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GENERAL BACKGROUND OF

SOFT CLAY

Malaysia Coastal Area – Not fully developed

Soft clay usually located around the coastal area

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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

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TWO DISTINCT ATOMIC STRUCTURAL UNITS

oxygen

silicon

0.29 nm

aluminium or magnesium

hydroxyl or oxygen

0.26 nm

Silicon Tetrahedron Aluminium Octahedron

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Micro-fabric particles in natural clay.

Flocculated Dispersed

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Flaky shape

Plate like structure

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ION EXCHANGE

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Ground Improvements for Soft Clay

• Stone Column (Vibro-Replacement)

• Prefabricated Vertical Drain

• Cement Column

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VIBRO-REPLACEMENT (STONE COLUMN)

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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

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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

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Stone Columns

vibrator makes a hole in the weak ground

hole backfilled ..and compacted Densely compacted stone column

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PREFABRICATED VERTICAL DRAIN (PVD)

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CEMENT COLUMN (CHEMICAL STABILIZATION)

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APPLICATION OF STABILIZE CLAY

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GROUTING TECHNIQUE

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EXAMPLE OF CASE STUDY FOR GROUND IMPROVEMENT

METHODS ON SOFT CLAY

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GEOTEXTILES