Types and Characteristics of Ground Improvement Techniques (2)

Ground Improvement Techniques
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In our previous discussion, we briefly explored ground improvement methods for weak soils.

(Please refer to the previous post for more details.)

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Today, we’ll enhance our understanding by providing concise explanations for each method.

Before We Start: Understanding Clayey and Sandy Soils.

1. Clayey vs. Sandy Soils

Accurate definitions can be elusive, but let’s simplify:

Clayey Soil : Think of it as clay. According to “Grim,” clay is a soil that exhibits plasticity when mixed with a certain amount of water. Particle size is typically less than 2μm.

Sandy Soil : Though not exactly sand, it’s helpful to consider it as having similar properties, often referred to as “non-cohesive soil.”

1-1. Differences in Drainage:

Clayey Soil : Composed of very fine particles, including clay minerals with electrostatic properties, leading to poor drainage.

Sandy Soil : Coarser particles with ample void spaces, allowing for rapid drainage.

2. Drainage Methods for Clayey Soils

2-1. Sand Drain Method

(1) Overview

Sand drains are installed in weak clayey soils to serve as permeable columns that facilitate drainage and expedite soil consolidation.

(2) Installation

Uses compressed air casing, water jet casing, rotary boring, or earth auger to install sand piles. Load is applied to the treated ground, which enhances consolidation and drainage through the sand columns.

(3) Advantage

– Effective drainage.

– Applicable up to soils with N-values of 25.

– Sand columns resist lateral soil movement.

– Long-term drainage efficiency remains stable.

(4) Disadvantages

– Potential disturbance to surrounding soil.

– Requires high-quality, expensive sand.

– Slow construction speed.

– High cost due to extensive material and labor needs.

2-2. Paper Drain Method

(1) Overview

Uses synthetic cardboard sheets instead of sand piles to expedite consolidation in very weak clayey soils.

(2) Features

– More cost-effective than sand drains.

– Faster installation.

– Effective drainage.

– Uniform drain cross-section over depth.

– Minimal disturbance to surrounding soil.

(3) Cardboard Requirements

– High permeability compared to surrounding soil.

– Prevents passage of fine particles.

– Sufficient strength to avoid breakage.

2-3. Pack Drain Method

(1) Overview

Involves placing sand in a special fibrous mesh to form permeable columns in weak soils.

Allows for simultaneous installation of multiple drains.

Since it is wrapped in fiber, it is less likely for the drain to be cut compared to sand drains, and the amount of sand required is reduced.

(2) Advantages

– Faster than sand drains (four drains at a time).

– Mesh prevents sand column breakage.

– Reduces sand quantity needed.

– Smaller diameter installation possible.

(3) Disadvantages

– Potential mesh twisting during installation.

– Long-term drainage efficiency concerns.

– Specialized equipment needed.

– Difficult depth adjustment in irregular ground.

3. Sand Compaction Pile Method for Sandy Soils (& Clayey Soils)

(1) Overview

Uses vibration or impact to drive sand into the soil, forming large, compacted sand columns to stabilize the ground.

(2) Effects

– Forms composite ground with properties of both sand and clay.

– Increases bearing capacity, reduces settlement, enhances shear strength.

– Accelerates consolidation and mitigates liquefaction.

4. Vibroflotation Method for Sandy Soils

(1) Overview

Inserts a vibratory probe into sandy soil, using water jets and vibration to compact soil and fill voids with gravel.

(2) Advantages

– Deep compaction achievable from the surface.

– Unaffected by groundwater levels.

– Fast and cost-effective.

– Particularly effective for structures subject to vibrations.

5. Dynamic Compaction Method for Sandy Soils

(1) Overview

Involves repeatedly dropping heavy weights (10-40 tons) from heights (10-30m) to consolidate soil through impact and vibration.

(2) Advantages

– Treats large areas.

– Effective at considerable depths.

– Significant improvement in soil properties.

– Can manage obstacles within the ground.

– No special chemicals or materials required.

(3) Disadvantages

– Potential damage to nearby structures.

– Environmental issues due to noise, vibration, and dust.

– Excess pore water pressure in saturated clay.

– Possible delays in construction.

6. Conclusion

We’ve expanded on various ground improvement techniques, providing a comprehensive overview of their applications and benefits. We’ll discuss more in future posts.

Feel free to reach out with any questions or for further details. Thank you, and see you next time!

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