Hydraulic and earth engineering – Foundation – Columnar structure
Reexamination Certificate
1999-02-09
2002-03-12
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Foundation
Columnar structure
C405S237000, C405S238000, C405S239000, C405S240000, C073S784000, C073S011030
Reexamination Certificate
active
06354766
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to earth engineering, especially relative to short aggregate pier implementations. Specifically, this invention relates to methods and apparatus for improving the feasibility of short aggregate piers, improving the strength and load-bearing characteristics of the soil matrix in the vicinity of short aggregate piers, reducing the costs of constructing short aggregate piers, improving the construction of short aggregate piers, and employing short aggregate piers in engineering applications involving settlement control bearing capacity improvement, lateral load resistance, landslide control and uplift anchoring.
It is known to strengthen otherwise inadequate load-bearing capacity of soil by formation of short aggregate piers, such as those disclosed in U.S. Pat. No. 5,249,892, the subject matter of which is incorporated in its entirety herein by reference. Generally, short aggregate piers are constructed in situ by individually compacting a series of thin lifts or layers of aggregate within a cavity formed in the soil. When each lift is compacted, vertical compaction forces are transferred through the aggregate vertically and laterally outward to the surrounding soil. The pier resulting from a vertical “stack” of lifts, each compacted before the next lift is formed and each including aggregate elements which are not cohesive, is characterized by the ability to transfer a relatively large portion of the load outward and laterally into the adjacent, prestressed soil. Short aggregate piers have been recognized in the civil engineering field as revolutionary, partly because they provide for increased load-bearing capacity in soil environments which would otherwise tend to make construction of adequate foundations expensive or unfeasible.
Because short aggregate piers are a relatively recent development, much effort lately has been expended towards improving their feasibility, reducing their cost and expanding their field of use and improving their construction. The present invention provides several unique and novel techniques, which include novel methods and the use of novel apparatus that provide the advantages of improving the feasibility of short aggregate piers, reducing their cost, expanding their field of use and/or improving their construction.
Feasibility of short aggregate piers in certain soil environments is limited by the load-bearing characteristics of matrix soils. These characteristics include the soil shear strength, compression characteristics, compactibility, density and permeability or affinity for water. For example, it has been recognized that, especially in loose or soft soil environments, undesirable degrees of settlement may occur when the bearing load is applied to short aggregate piers constructed according to known techniques. It has also been recognized that in known short aggregate pier constructions, very soft subsoils may result in excessive material construction costs due, for example, to the absorption of a significant amount of aggregate stone into the bottom bulb of the short aggregate pier during the tamping or compaction step of construction. These shortcomings tend to limit the feasibility of known short aggregate pier techniques. Thus, it would be desirable to provide techniques which tend to favorably influence or improve the load-bearing characteristics of matrix soils and/or matrix soils in combination with short aggregate piers. It would further be desirable to provide for construction techniques for short aggregate piers which would tend to expand the feasibility of short aggregate piers across a wide range of soil compositions.
Another problem recognized since the development of heretofore known short aggregate pier techniques relates to “plastic” or “heaving” soil environments. These types of soil matrices are characterized by a high-volume change potential due to the absorption of water. Such soil compositions tend to create the potential for undesirable uplift forces on short aggregate piers and on surrounding matrix soils. Uplift forces are undesirable because supported structural members such as footings, mats, beams and slabs will tend to move upward, causing structural distress and/or cosmetic damage. It would therefore be desirable to provide short aggregate pier techniques which reduce the potential for uplift forces in plastic or heaving soil environments. Yet another limit on the feasibility of known short aggregate pier techniques relates to liquefiable soil environments (i.e. soils which tend to liquefy when subject to sufficient dynamic stress). Typically, engineering codes may require special aggregate drain gradation in structures formed in liquefiable soil environments. Present aggregate drain structures are not constructed in thin lifts and are, as a result, not as efficient in providing settlement control or soil liquefaction control as can be provided using known short aggregate technique with compaction of each lift (the short aggregate pier technique). It would therefore be desirable to provide short aggregate pier techniques which provide the ability to meet aggregate drain gradation requirements.
Another problem recognized with known short aggregate pier construction techniques is that in soft or unstable soil environments, the pier cavity may tend to distort, cave-in, or become otherwise damaged as the pier is formed in situ. It would therefore be desirable to provide for short aggregate pier construction techniques which reduce the potential for damage to the pier cavity during pier construction.
Yet another problem recognized with known short aggregate pier techniques is that the impact loading typically applied to compact each lift during construction of an short aggregate pier may be problematic in areas which are in close proximity to sensitive structures (i.e. older buildings) or buried objects, such as pipes, culverts or conduits. It would therefore be desirable to provide short aggregate pier construction techniques which do not present a danger to damaging nearby sensitive structures.
As short aggregate piers are desirable, in part, because they are economical, it is desirable to provide for construction techniques which reduce the cost of short aggregate piers compared to known construction techniques. It is also desirable to provide construction techniques which maintain the integrity of the matrix soils susceptible to damage during construction. Still further, because of the advantages recognized in known short aggregate pier techniques, it would be desirable to expand the field of use of short aggregate piers to earth engineering areas that include, for example, global stabilization, lateral load resistance, landslide control and uplift control. Finally, it would be desirable to provide methods and apparatus for obtaining stress distribution and other data from short aggregate piers which have been constructed.
SUMMARY OF THE INVENTION
The aforementioned problems and desired advantages are realized by the present invention, which provides several novel and unique methods and apparatus that improve the feasibility of short aggregate piers, improve the strength and load-bearing characteristics of the soil matrix in the vicinity of short aggregate piers, reduce the costs of constructing short aggregate piers, improve the construction of short aggregate piers, and employ short aggregate piers in engineering applications involving settlement control, bearing capacity improvement, lateral load resistance, landslide control and uplift anchoring.
A. Short-Aggregate Pier Construction Techniques for Improving Soil Characteristics.
One aspect of the present invention relates to methods for constructing short aggregate piers to improve the load-bearing characteristics of the soil and to short aggregate pier constructions made by such methods. These techniques include: 1) methods and apparatus for preloading soils and short aggregate piers; 2) methods for providing chemical additives to short aggregate pier constructions; and 3) methods for employing mesh reinfor
Bagnell David
Banner & Witcoff , Ltd.
Geotechnical Reinforcement Company, Inc.
Singh Sunil
LandOfFree
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