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.

What are vertical or wick drains, and vacuum consolidation

WHAT ARE VERTICAL OR WICK DRAINS?

Soil stabilization using Prefabricated Vertical Drains (PVDs) or wick drains are applied in areas with loose, compressible and water-saturated soils such as clay and silty clay. These soils are characterized by a very weak soil skeleton and a large pore space, usually filled with water (pore water). 

When a load such as a road embankment, a hydraulic fill or a dike, is placed on soft compressible soils, significant settlements may occur. These settlements can create serious problems. Any increase in load can also result in an increase of pore water pressure. In soils with low permeability, this water dissipates very slowly, gradually flowing from the stressed zone. Increased pore pressure may also cause soil instability and

slip plane failures may result. 

A vertical drainage system – drains are generally placed in a square or triangular pattern, spaced at about 1 to 3 meters – allows for faster removal of excess pore water, thus decreasing the risk of slip plane failure. The consolidation of soft cohesive soils using vertical drains can reduce settlement time from years to months ensuring that bearing capacity is adequate and construction can commence rapidly.

WHAT IS VACUUM CONSOLIDATION?

Vacuum consolidation is a process whereby vacuum pressure is applied to an area where PVDs have already been installed. The purpose is to potentially increase the drains’ effectiveness. 

Generally, this technique requires the application of a surcharge loading to squeeze water out of the soft clay soils. Such loading must be equal to or in excess of the service loading to which the developed land will be subjected. In vacuum consolidation, the vacuum pressure applied contributes to the surcharge loading, and therefore actual surcharge heights are reduced. 

An additional important advantage of the vacuum is the isotropic nature of the vacuum pressure and the correlated improvement of the stability under Pre-loading, reducing considerably the risk of slope failure resulting from the surcharge.

Note:this articles are excerpted from the iadc dredging, facts about soil improvement, and here we thank the authors give us the knowledge about dredging and soil improvement.

Cement mixing pile and soft foundation treatment

Cement mixing pile is an effective form of soft foundation treatment，just like vacuum consolidation and vibration. 

It is a kind of main agent that uses cement as a curing agent. The cement is sprayed into the soil by a mixing pile machine and fully stirred to make a series of physical and chemical reactions between cement and soil. To harden the soft soil and increase the strength of the foundation. Cement mixing piles are divided into single-axis, double-shaft and three-axis mixing piles according to the main construction practices. 

In the 1970s, the use of cement mixing piles to reinforce soft soil foundations has been around for more than 40 years. It uses a special deep mixer to force the soft soil and cement (curing agent) to stir, and uses a series of physical and chemical reactions between cement and soft soil to consolidate the soil to form a whole body, water. Stability and strength of cement soil piles. This process is mainly used for the treatment for soft soil foundations enhancement.

For more method and technologies about soft soil improvement, please take a tour at our official website at www.sunzo99.com .

pvd installation vedios

Introduction To Non-cushion Sand Layer Vacuum Preloading Method

The method relates to a large area soft ground treatment method, in particular to a vacuum preloading method without a drainage sand layer. 

Non-cushion sand layer it includes the following main steps: 

1) laying drainage plates on the treatment site according to the plum pile type; 

2) arranging the horizontal drainage system to replace the medium coarse sand cushion used in the previous vacuum preloading construction, two kinds of laying can be used One of the ways; 

3) Connect the main pipe of the horizontal drainage system to the vacuuming device, and then vacuum the construction after filming. 

The vacuum preloading method for the non-drained sand cushion of the invention is suitable for the reinforcement of large-area soft soil foundation, especially for the dredger fill and the newly deposited ultra-soft soil, and the utility model saves a large investment of laying the sand cushion layer. The vacuum transmission effect is good, and the horizontal drainage system of the wire spring tube + tube plate connector + drainage plate can realize large-scale finished product and normalized construction, and the laying time is short, and can be recycled and reused. The construction period is short and the unique advantage of economic saving.

The main purpose of the dredging projects

The main purpose of the dredging project is to excavate the harbor basin, the inbound waterway, etc., to fill the land to build the dock, the port area and the port industrial zone, the coastal city land and recreational land and land reclamation, the shore beach maintenance, the water conservancy and flood control and the reservoir area. Improvement of water environment such as dredging, rivers, lakes and seas, ecological restoration, construction and landfill of various underwater pipelines. The role of dredging projects in human social progress, environmental improvement and economic development is very important.

Use dredging methods to dig shallow sections of deep rivers or bays to improve navigation or flood discharge capacity; an economically viable primary method of landfilling dredged soils in excavation channels or harbor basins into nearby low-lying areas for land reclamation . 

Dredging has traditionally been treated in a manner that is abandoned or dumped in the waters adjacent to the project. The dredging project has created a new way of turning waste into treasure and comprehensively processing it, and then developed it into the use of dredged soil as building materials and materials for building buildings. The dredging project is also extended to excavate the bottom of the river or the bottom of the sea to bury the river or cross-sea pipeline (water pipes, oil pipes, transmission cables, communication cables, etc.); remove the sand and stone for hydraulic engineering with strong underwater displacement capacity. Material foundation and soft ground improvement; blowing sand to protect the beach and so on.

In the past few decades, human beings have increasingly demanded environmental standards. Preventing and reducing the pollution of waters and land by dredging activities has become an important issue that must be considered in dredging projects. Dredging methods are used to excavate underwater contaminated soils and carry out engineering. Processing has also become an important part of dredging projects.

What is Dredging and Its Application

Dredging is to dredge, widen or dig deep waters such as deep rivers and lakes, and use manmade power or machinery to carry out underwater earthwork or excavation works.

The generalized dredging includes the reef and the fried beach, which are carried out by the blasting method under water. A small river that is constructed by artificially breaking the flow. Various dredgers are widely used in mechanical construction, and onshore construction machinery such as rope shovel is sometimes used.

About the dreging history, the mechanical dredging began in 1600, and the prototype of the chain bucket dredger appeared in the construction of the port of Rotterdam, the Netherlands. China began construction of dredgers in the Huangpu River in 1889. In 1929, the Jiangnan Shipyard caused a chain bucket dredger. In the early 1980s, China had an annual capacity of about 300 million cubic meters of mechanical dredging.

Dredging works are widely used: 1, to excavate new waterways, ports and canals. 2, Deep, widen and clean up existing waterways and ports. 3, dredge the rivers, channels, and dredging of the reservoir. 4, Excavation of foundation pits for hydraulic structures such as docks, docks and ship locks. 5, Combine dredging to carry out landfilling, reclamation and other projects. 6, Clear underwater obstacles.