ALICC Method for Long-Term Control of Subsidence of Soft Ground
Deep mixing soil stabilization
Conventional ground improvement
Ground improvement by ALICC
(Area and volume to be improved can be reduced.)
Concept of arch effect
(The appropriate pile interval can be designed.)
1. ALICC (Arch-action Low Improvement ratio Cement Column) Method
When roads are built in Japan, high embankments are often constructed on ground which contains very deep soft soil layers. Serious subsidence is likely to occur to those roads and affect the surrounding houses or farmland.
As a solution, deep-mixing soil stabilization, a technique to inject cement into the ground and agitate it to form cement piles and build the foundation for the embankment above the ground, is often used to improve the soil.
But the conventional procedure, which constructs cement piles mainly on the slope of the embankment, requires a wide area or a greater volume for improvement, and therefore is very costly.
Considering these circumstances, the team developed ALICC, a new soil improvement method that features the use of the arch effect to realize a reduction in area or volume for improvement. Incorporation of the arch effect into the design allows for improvement of the ground entirely under the embankment at an equal interval. Reduction in cost and construction period is thus realized by reducing the area or volume for improvement.
2. Arch Effect
ALICC is based on the design theory that the phenomenon of stress concentration, in which the embankment load acts on cement piles as the embankment builds up, is assumed as the embankment load acting in an arch-like way. Application of this theory allows us to determine appropriate intervals relative to the strength of the ground or embankment and realize more economically efficient design.
This method is currently used in various parts of Japan. We intend to continue diffusing technologies in the future.
(Contact: Construction Technology Research Team)
Engineering Manual for Construction and Management of Roads and Other Structures
on Peaty Soft Ground Published
Manual on Countermeasures for Peaty Soft Ground revised in March 2011
Typical Hokkaido fibrous peat
Road surface unevenness caused by
long-term settlement of soft peaty ground
What is peaty soft ground?
Peaty ground is found widely in cold areas. It is produced when reeds, sedges and other plants in marsh, lake and other wetland habitats fall, decay and accumulate. Under certain topographic conditions characterized by low temperatures and high humidity, naturally accumulating layers of partially decomposed plants begin to build up to form peaty ground. In Japan, massive peat bogs are found in Hokkaido and Aomori, with smaller ones dotted around the country. The peat layers frequently seen in Hokkaido are approximately 3 - 5 m in thickness, and sit on top of accumulated soft clay layers often measuring more than 20 m in thickness. Soil with an accumulation of peat in the top layer and a thick accumulation of soft clay below is referred to as peaty soft ground. The existence of the thick clay layer, in combination with the distinctive characteristics of peat, makes it more difficult to work with this type of ground.
Characteristics of peat
The plant fibers in peat are interwoven, forming a sponge-like material with the consistency of a loofah. Peat is seen as a distinctive soil that is wholly different from other types. Its high porosity makes it very water-retentive, meaning that even light loads can cause major immediate deformation in addition to the worse problem of long-term settlement. As peat is also particularly low in strength, it can collapse under the weight of earth piled on it.
Key points in the revision of the manual
As outlined above, peat has a unique set of characteristics, meaning that standard methods cannot be applied in related testing, surveying and analysis. Against this background, the considerable expertise and the body of study results obtained so far were summarized to create standards for testing, design and construction relating to peat. These were published in the form of the Manual on Countermeasures for Peaty Soft Ground in March 2002.
The March 2011 revision focused on the reduction of life cycle costs, including those incurred in construction and maintenance related to embankments on peaty soft ground. For the construction of roads that allow safe, convenient travel over peaty soft terrain, appropriate measures based on the predicted extent and duration of settlement are needed. In this regard, a method to accurately calculate long-term settlement in such ground - a task previously considered extremely difficult - was developed. In addition, information on countermeasures involving improved design and construction management methods as well as new survey and design techniques that take seismic factors into account were added to the manual in order to enhance its content.
CERIs Geotechnical Research Team plans to continue studies related to peaty soft ground and share information on practical technologies as needed. We hope the manual will help engineers in the field as a useful technical guide, and that it will become even more widely used.
(Contact: Geotechnical Research Team,CERI)