Chapter 26 Rammed Aggregate Piers Are Created First Drilling

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Chap. 26 Ground Improvement

26.1 State the advantages and disadvantages of removal and replacement as a ground improvement

method.

Solution

The removed soil is usually replaced by compacted fill using the soil removed or imported soil.

Advantages:

1. The compacted fill will be much more uniform.

Chap. 26 Ground Improvement

26.2 State the advantages and disadvantages of precompression as a ground improvement method.

Solution

Precompression has many advantages, including:

• It requires only conventional earthmoving equipment, which is readily available. No

special or proprietary construction equipment is needed.

Chap. 26 Ground Improvement

26.3 Explain how vertical drains can be used to speed up consolidation of soils in situ.

Solution

Vertical drains installed in a regular pattern with horizontal spacings typically around 3 m can

speed up the consolidation of soils because the excess pore water within the soils now drains

26.4 Name four in situ densification methods and describe how each one works.

Solution

Vibrocompaction

One method of densifying deeper soil deposits in situ is to insert either a terra probe or a

Dynamic Compaction

Dynamic compaction (also called dynamic consolidation or heavy tamping) is another method of

in situ densification. It uses a special crane to lift 44 to 267 kN (5–30 ton) weights, called

Rapid Impact Compaction

Rapid Impact Compaction (RIC) is an in situ densification method that uses a hydraulic pile

Blast Densification

Blast densification is another method of in situ densification. This method consists of drilling a

26.5 Name four in situ replacement methods and describe how each one works.

Solution

Vibro Replacement or Stone Columns

With this method, a vibroflot is used to create a shaft that is backfilled with gravel to form an

Aggregate Piers

Aggregate piers, also called Rammed Aggregate Piers®, are created by first drilling a shaft in the

ground and then back filling the shaft with aggregate that is compacted in layers using a ram.

Vibro Concrete Columns

Vibro Concrete Columns (VCCs) are concrete columns that are constructed in situ using a

bottom-feed downhole vibratory probe following these steps:

1. The downhole probe is advanced to the desired depth.

2. Concrete is pumped through the tremie pipe in the probe with the probe moving up and

Rigid Inclusions

Rigid inclusions are similar to VCCs. They are concrete columns constructed using a vibratory

26.6 Name four types of grouting and describe how each one works.

Solution

Intrusion Grouting

Permeation Grouting

In permeation grouting high slump grout is pumped into soil to fill in the void spaces between

Compaction Grouting

Compaction grouting (also known as displacement grouting) uses a stiff (i.e., about 25 mm or 1

Jet Grouting

Jet grouting is a method developed in Japan during the 1960s and 1970s, and uses a special pipe

26.7 Describe the TRD method.

Solution

The TRD method was developed in Japan in the 1990s and uses a special full–depth vertical

Chap. 26 Ground Improvement

26.8 Describe how soil reinforcement improves soil properties. Name one soil reinforcement

technique that can be applied to foundation engineering.

Solution

Soil is relatively strong in compression but weak in tension. The placement of tensile

Chap. 26 Ground Improvement

26.9 A proposed medical office building is to be built on a vacant parcel of land adjacent to a hospital.

This site is underlain by 30 ft of loose sand that is prone to seismic liquefaction. To rectify this

liquefaction problem, the sand needs to be densified. Suggest an appropriate method of ground

improvement for this site and indicate the reasons for your selection. The groundwater table is at

a depth of 5 ft.

Solution

An appropriate method of ground improvement for this site is vibroflotation. With the patterned

26.10 Some ground improvement methods can be used to construct “intermediate” foundations that

have capacities that are between those of shallow and deep foundations. Name two of these

methods.

Solution

The in situ densification methods can be used to construct “intermediate” foundations. These