What is Soil Improvement and Its Importance in Dredging Industry

WHAT IS SOIL IMPROVEMENT?

In the dredging industry soil improvement is typically implemented to:

- prevent excessive settlement of reclaimed land when it is being used for construction purposes (roads, airports, bridge and other foundations);

- enhance the soil stiffness and density to prevent liquefaction

which can lead to damage to structures in earthquakesensitive regions;

- improve the shear strength of the soil to prevent slip failure

and increase the bearing capacity of the soil;

- immobilise or stabilise contaminants in dredged soil in order to mitigate and preferably eliminate environmental impacts.

Soil improvement techniques vary depending on the characteristics of the soils and subsoils. Some techniques are applied to consolidate existing loose subsoils and some are specifically for compaction of newly reclaimed soil.

WHY IS SOIL IMPROVEMENT IMPORTANT?

Typically, potential reclamation sites are shallow coastal zones or marshy lowlands. The soil in these areas often consists of thick layers of soft clay or silts. Reclamation work increases the load on these soft layers, causing widespread settling.

Waiting for the natural settlement of this land is time consuming and thus costly and may put a project in jeopardy if it cannot be accomplished in a designated period of time.

To accelerate the settlement process, dredging contractors have developed specialized solutions to consolidate these soft soils. In addition, newly reclaimed soil is often in a loose state and may not meet the demands of the planned infrastructure

and therefore needs to be improved.

WHAT IS THE DIFFERENCE BETWEEN CONSOLIDATION AND COMPACTION?

A distinction is made between consolidation techniques for cohesive soils (clay, silt) and compaction techniques used to solidify granular soils. The consolidation phase has become an essential part of soil improvement and several techniques have been developed to stabilise new ground. 

Amongst these are preloading or surcharging the area that is subject to consolidation with a temporary load of sand, using Prefabricated Vertical Drains (PVDs), sand drains and a system known variously as BeauDrain, Intensive Forced Compaction (IFCO) or Press-To-Drain (PTD) as well as vacuum consolidation. These are all methods in which soil improvement takes place over a longer period of time.

Compaction is done by methods such as smooth rollers, High Energy Impact Compaction (HEIC), or Dynamic Compaction (DC) – also known as heavy tamping – or Rapid Impact Compactors (RIC) and vibroflotation.