Soil Improvement in the Construction Industry

During construction, engineers encounter different kinds of soils. Some are tightly packed and compact while others are loose.

To ensure the quality of the construction, soil improvement must be carried out. So, what is soil improvement?

In this post, you will learn what soil improvement is and how soil can be improved in the construction industry.

Why Soil Improvement is Important

Soil improvement is a process in which soil is improved in a site to enhance the prospects of on-time and safe project delivery.

Soil improvement is crucial in the construction industry due to the following.

It enhances the density and stiffness of the soil; hence, preventing liquefaction which can damage the structures around earthquake-sensitive regions.
Soil improvement prevents excessive settlement of reclaimed land when it is being used for roads, bridges, airports, and other construction purposes.
It stabilizes contaminants in dredged soil to mitigate and consequently eliminate environmental impacts.
Soil improvement can improve the shear strength of the soil; hence, preventing slips failure and increasing the bearing capacity of the soil.

Soil Improvement Techniques

Many options exist when it comes to soil improvement. However, each technique has its own benefits and drawbacks with regard to time, performance, and cost.

Let’s check out the top-rated soil improvement techniques.

1. Compaction Piles

Compaction piles comprise pre-stressed timber or concrete that is installed in a grid pattern and is generally driven to a depth of up to 60 feet. Installing compaction piles caters to both densification and reinforcement of the soil.

2. Geotextiles

Installing geotextiles is an effective way of improving the soil. Certain geotextiles can be used to stabilize embankments and also improve the bearing capacity of soft soil foundations on marine projects.

Engineers use geosynthetics during construction to increase safety by preventing underground failure and reducing the settlement of the subsoil foundation.

3. Prefabricated Vertical Drain Installation

Prefabricated geotextile filter-wrapped plastic strips with molded channels can be more effective when combined with other soil improvement techniques.

It is ideal in case of liquefaction hazards reduction where the drainage capability of the soil has to be increased.

This technique involves the installation of drains of sand, gravel, or synthetic materials. Sand and gravel drains are usually installed vertically while synthetic wick drains can be installed at various angles.

The accumulation of excess pore water pressure will be reduced if the pore water within the soil can drain freely.

4. Cement Soil Mixing

The cement soil mixing method is very effective in places where soft subsoil poses a serious threat to maritime construction.

This method is also called cement deep mixing, soil mixing, auger mixing, rotary mixing, or soil-cement columns/piles.

The cement deep mixing method is often applied for the foundation of:

breakwaters, revetment, and wharfs
seismic reinforcement of marine structures
foundations of roads, railroads, bridge piers, tanks, buildings, and river dikes
countermeasures for liquefaction

5. Compaction Methods

Compared to other methods of soil improvement, compaction methods take a shorter time.

a. Dynamic compaction

Densification in dynamic compaction is performed by dropping a heavyweight of concrete or steel in a grid pattern from 30 feet to 100 feet tall.

Dynamic compaction provides an economical way of soil improvement for the mitigation of liquefaction hazards. Experts carry out local liquefication beneath the drop point to make it easier for the sand grains to densify.

Additional densification occurs when the excess pore water pressure from the dynamic loading dissipates. This process is somewhat invasive as the surface of the soil may require shallow compaction with the possible addition of granular fill following dynamic compaction.

b. Vibroflotation

As the name implies, vibroflotation involves the use of a vibrating probe that can penetrate granular soil up to 100 feet deep.

As a result of the vibrations of the probe, the grain structure collapses thereby densifying the soil surrounding the probe. The vibroflot is raised and lowered in a grid pattern to treat an area of potentially liquefiable soil.

a. Dynamic compaction

Stone columns can be constructed by the vibroflotation method or the Franki Method. When vibroflotation is combined with a gravel backfill in the ground, it results in the formation of stone columns.

This process is not just an effective means of drainage; it increases the amount of densification and also provides a greater degree of reinforcement. In the Franki Method, a steel casing and a drop hammer are introduced.

The steel casing is driven into the soil and gravel is filled in from the top and tamped with the drop hammer as the steel casing is successively withdrawn.

Wrapping Up

The aim for most soil improvement techniques used to reduce liquefaction hazards is densification of the soil – a process in which drainage capacity is improved to reduce pore water pressure during earthquake shaking.

Other options include stabilizing subsoils or accelerating the consolidation of soils and dredged sediment for the construction of newly reclaimed land.

With the knowledge shared in this post, one can determine what soil improvement technique is the most suitable for the project.