G1-Lecture17-Soil-Improvement

G1-Lecture17-Soil-Improvement - CEG-4011 Geotechnical...

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CEG-4011 Geotechnical Engineering I Lecture #17 Soil or Ground Improvement 1) Compaction 2) Pre-loading (surcharging) 3) Dynamic compaction 4) Jet Grouting 5) Soil-Cement Pile/Column 6) Geotextiles © L. Prieto-Portar, 2008
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Soft Soils Soft Soils Soft Clays Soft Clays Organic Silts Organic Silts Dredged Dredged Material Material Bearing Capacity Bearing Capacity Failures Failures Excessive Excessive Settlements Settlements Other techniques, in addition to compaction, seek to improve soft soils so that structures placed upon them do not fail through bearing capacity or excessive settlement. The rest of this lecture will show a few other methods of improve soils.
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Ground Ground Improvement Improvement Soil Reinforcement Deep Compaction Preloading Dynamic Compaction Resonance Compaction Vibro-flotation Cohesive soils Granular soils
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1. Compaction
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The oldest method of improving soil strength is the millennium old technique of compaction . This topic is so important that it is treated exclusively in our next lecture.
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2. Preloading (or surcharging)
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Advantages of prefabricated vertical drains: Increases the rate of consolidation. Reduces the pre-construction time. Increases the stability of slopes. Cheapest and easy to install. Preloading, surcharging or pre-compression is a process where a site will be loaded before construction begins. The additional stress to the soil increases its early settlement, thereby reducing settlements when the actual building is placed on the site. The preloading drives out water from the compressible soil voids, and the water is removed from the site via pumps or open channels. The voids previously occupied by the water now disappears, and the summation of the voids produce the net settlement of the ground surface. One of the methods used to accelerate the drainage of water is to decrease the path that the water particles have to take to exit the soil. A grid of vertical wicks (drains) is an effective method, as outlined below:
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Advantages: Reduce Post- Construction Settlement Reduce Secondary Compression Densification Improve Bearing Capacity
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Vertical Drains 2 v v drain c t T h =
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Typical arrangements of the vertical drains
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Types of Vertical Drains Types of Vertical Drains Sand drains Sand drains Sand wicks Sand wicks Plastic band drains Plastic band drains Driven displacement drains Driven displacement drains Bored drains Bored drains Prefabricated vertical drains Prefabricated vertical drains
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Prefabricated vertical drains. Geotextile fabric Drain pipes
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Installation of prefabricated drain wicks Setup the equipment Setup the equipment Drive the mandrel Drive the mandrel Extract the mandrel Extract the mandrel Cut off the drain wick Cut off the drain wick
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surcharge surcharge drains drains
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easily, and quickly drained using this special adapter to a regular back hoe. It installs a length of geotextile wick, that serves as a drainage path for the groundwater in the soil. This setup is
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This note was uploaded on 09/11/2011 for the course CEG 4011 taught by Professor Staff during the Summer '10 term at FIU.

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G1-Lecture17-Soil-Improvement - CEG-4011 Geotechnical...

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