Hydraulic and earth engineering – Earth treatment or control – Chemical
Reexamination Certificate
2000-01-12
2002-03-19
Pezzuto, Robert E. (Department: 3673)
Hydraulic and earth engineering
Earth treatment or control
Chemical
C405S128100, C405S129450
Reexamination Certificate
active
06357968
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
BACKGROUND OF THE INVENTION
This invention relates generally to the field of containment of underground hazardous wastes and more specifically to a method and apparatus for constructing an underground barrier wall structure using a jet grout injector subassembly comprising a pair of primary nozzles and a plurality of secondary nozzles, the secondary nozzles having a smaller diameter than the primary nozzles, for injecting grout in directions other than the primary direction, which creates a barrier wall panel having a substantially uniform wall thickess.
An important goal of environmental remediation is reducing or preventing underground hazardous wastes from migrating outside of contaminated sites. Examples of hazardous wastes include pesticide contaminated groundwater, benzene vapors, or non-aqueous phase liquids, such as gasoline leaking from a buried storage tank. An underground structure, such as a barrier wall, can be used to contain or redirect the flow of groundwater contaminated with hazardous wastes. A barrier wall is typically made of a substantially impermeable material that prevents the flow of these hazardous materials through the relatively permeable surrounding ground (soil, sand, etc.). Cement-based grout (a well-known mixture of Portland cement, sand, and water), sometimes mixed with the surrounding soil, is commonly used as a ground-hardening material to fabricate impermeable underground barrier walls.
Alternatively, the underground barrier wall can be constructed of materials that include permeable reactive materials (PRM's). As the hazardous wastes flows through the permeable barrier wall, the wastes are removed, captured, or modified by the action of various active agents contained within the PRM's. The PRM's react with the hazardous wastes by chemical, physical, or biological processes, or combinations of these. Treated groundwater is then returned to the aquifer.
Underground barrier walls can be fabricated in-situ by jet grouting. The term “jet grouting” refers to the use of high-pressure jet spray nozzles, which are located on an injector subassembly attached to the end of a drill string, to inject a slurry of material at relatively high velocity into the surrounding soil. The jet spray simultaneously masticates and erodes the surrounding soil, while mixing the loosened soil with the injected slurry to form a soil/slurry mixture that replaces the eroded cavity. If the slurry is primarily made of grout then the mixture of soil and grout subsequently hardens into a solid, substantially impermeable material (sometimes called “soilcrete”). If the slurry contains PRM's, then the mixture of soil and slurry forms a permeable reactive barrier wall.
In this application, the term “soil” is broadly defined to include any mixture of soil, sand, clay, gravel, organic materials, or other granular materials, either naturally occurring or man-made, which can be loosened and eroded by the action of the jet spray. The phrase “jet grouting” is broadly defined to include injection of slurries containing (1) grout or other ground-hardening materials; or (2) permeable reactive materials (PRM's). The terms “slurry” and “grout” is herein broadly defined to include mixtures of solid materials with any liquid, including water; and with any gases, including air. The terms “slurry” and “grout” also comprehends 0% of solid materials, including: (1) injection of only liquids; (2) liquids plus gases; (3) gases only; (4) or any combination of solids, gases, and liquid that can be injected from a spray nozzle, e.g. “jet grouted”. In this application, the terms “slurry” and “grout” are used interchangeably, as defined herein above.
Jet grouting typically occurs when the drill string is being withdrawn from the drill hole. If the jet injector subassembly is not rotated during withdrawal, then the jet spray creates a thin “diaphragm wall”. The injection of “grout” as it was broadly defined earlier, from each jet nozzle, as the nozzle is removed from a single hole, acts to create its own thin diaphragm wall segment. The number of segments equals the number of jet nozzles. For example, operation of two jet nozzles would result in two panels. Each segment is connected to each other segment by grout which is deposited and fills up the central void space left when the drill string is removed from the drill hole.
The jet injector subassembly traditionally has only two nozzles (e.g. orifices) that typically that face outwards in diametrically opposite (e.g. 180 degrees opposed) directions. Nozzle diameters typically vary from 2 to 3 mm, but can be larger, or smaller. The slurry is injected at high pressures (up to 6000 psi) through these two nozzles, in a direction radially outward from the center of the subassembly. As illustrated in
FIG. 1
, the high velocity jet spray creates a panel whose width, R
max
, is greater than the panel's maximum thickness, T
max
. Depending on the soil conditions, R
max
can be at least 2 meters; the maximum thickness T
max
can be at least 20-30 cm; and the minimum thickness T
min
can be at least 8-10 cm.
An interconnected barrier wall can be made by drilling a second hole close to the first one and repeating the jet grouting process, as many times as necessary to provide adequate coverage.
FIG. 2
illustrates a series of interconnected thin diaphragm wall panels using this technique. Typical distances between adjacent holes are 1-3 meters, but can be larger or smaller depending on the soil conditions and requirements.
Conventional jet grouting processes that use only two (non-rotating) nozzles create barrier walls that have a non-uniform wall thickness. This results because the natural shape formed by a jet spray is an expanding cone. Consequently, when two nozzles inject slurry from diametrically opposed positions, a “bow-tie” shape results. The “bow-tie” shape can be seen in
FIGS. 1 and 2
.
The problem with this “bow-tie” shape is the thin, weak region located directly adjacent to the drill hole. This thin region is more prone to cracking, separating, and/or tearing than the thicker region at the end of the jet spray. Cracking may be caused by non-uniform shrinkage of the solidifying grout or surrounding media. Also, the thin region may have a non-optimum mixture of grout plus soil, when compared to the thicker region at the end of the jet spray.
FIG. 3
shows that cracking of the thin section can create uncontrolled leakage of hazardous wastes, thereby defeating the integrity of the containment barrier.
The problem of weakness associated with the bow-tie shape is also present in permeable reactive barrier walls constructed of permeable reactive materials (PRM's). Any large differences in the wall thickness of a porous reactive barrier wall (T
max
>>T
min
) would likely result in non-uniform rates of waste treatment, and non-optimum utilization of the PRM's. Likewise, cracking or tearing of the porous reactive barrier wall would reduce the overall effectiveness of the waste treatment process because untreated wastes could flow directly through the cracked region.
A need remains, therefore, for a simple and easily deployable solution to the problem of weakness and non-uniform thickness caused by the bow-tie shape associated with jet grout injection using conventional dual-nozzle technology. Against the background just described, the present invention solves this problem by using at least four additional secondary nozzles to simultaneously fill in the thin, weak region by injecting slurry in directions other than the pair of diametrically-opposed primary nozzles.
FIG. 4
shows that this method produces a filled-in zone, 72, that creates an optimum underground barrier wall structure having a substantially uniform wall thickness. Throughout this application, the phrase “substantially uniform” means that the variations in the wall's actual thickness are small when compared to the wall's average thickness.
BRIEF SUMMARY OF THE INVENTION
The present i
Dwyer Brian P.
Dwyer Stephen F.
Stewart Willis E.
Addie Raymond W
Pezzuto Robert E.
Sandia Corporation
Watson Robert D.
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