Improving site soils for foundation use

6.1 Introduction

 A significant increase in bearing capacity may be achived by altering the soil properties of -, cohesion, and unit weight -. Settlements may be reduced by increasing the density with the resulting decrease in void ratio from particle packing. Particle packing also increase the stress-strain modulus in most cases so that the "immediate" settlements are reduced.

The modification of soil properties may be done in a number of ways such as:

Compaction. Usually most economical

Preloading. Primarily to reduce future settlement but may also be used to increase shear strenght.

Drainage. Used to speed up settlements under preloading but may also increase shear strenght since -, in particular, depends on water content.

Densification using vibratory equipment. Particularly in sand, silty sand, and gravelly sand deposits with - under 50 to 60 percent.

Grouting. Both to reduce voids and to stiffen soils.

Chemical stabilization. To stiffen soil.

Use of geotextiles. primarily as reinforcement but sometimes in other beneficial modes.

The above methods of soil improvement will be taken up in some additional