Guy G. Loomis
Idaho National Engineering and Environmental Laboratory
Lockheed Martin Idaho Technologies Company
P.O. Box 1625
Idaho Falls, Idaho 83415-3710
(208) 526-9208, (208) 526-6802 (fax)

A proof-of-concept experiment was performed to demonstrate an alternate emplacement technique for creating a monolith out of a buried waste site using jet grouting. The technique is an improvement over the existing technique of nonreplacement jet grouting in that the drilling apparatus never touches the waste during the jet-grouting operation. Since 1994, the Idaho National Engineering and Environmental Laboratory has developed a technique for using nonreplacement jet grouting to both stabilize buried waste against subsidence and reduce or eliminate migration of contaminants by creating a monolith out of the buried waste. The state-of-the-art technique involves driving a drill stem with jet-grouting nozzles into the waste and then jet grouting while removing the drill stem. This jet-grouting process forms a monolith out of the waste. One of the issues involved in this technique is that the drill stem is contaminated and requires a special contamination control strategy to mitigate contaminant release when the drill stem is removed for repositioning. The technique eliminates contaminants on the drill stem in that the drill stem never comes in contact with the waste material. The technology is applicable for any buried waste but has been specifically developed for buried transuranic waste. At the Idaho National Engineering and Environmental Laboratory alone there is 2 million cubic feet of buried waste commingled with 6-8 million cubic feet of soil in shallow land burial. One of the options for this buried waste is to improve the confinement in situ, a process for which this technology is ideally suited. During the summer of 1997, a new alternative grouting technique was shown to have a positive proof of concept. The process involves driving thin-walled plastic sleeve pipes into buried waste, then grouting the surrounding material by penetrating the sleeve with high-pressure (6000 psi) grout. This is accomplished while keeping the drill steel above a short nozzle/seal assembly away from the contaminated waste. The testing described in this report shows that rotational grouting can occur while cutting the sleeve pipe and that even after cutting there is sufficient force to create a monolith out of an area of buried waste.

This document summarizes the results of a proof-of-concept test of an innovative nonreplacement jet-grouting idea for stabilizing buried waste sites. The target application for this technology is transuranic (TRU) pits and trenches at the Idaho National Engineering and Environmental Laboratory (INEEL) Subsurface Disposal Area. The test was performed in July 1997 at the facilities of Applied Geotechnical Engineering and Construction (AGEC) in Hanford, Washington.

The current technology (investigated by the INEEL during Fiscal Years 1994-1996 [ref 1-3]) involves using nonreplacement jet grouting that includes driving the drill stem into the buried waste and jet grouting while withdrawing the drill stem in precise increments. The upstage grouting technique has been developed to minimize grout returns; however, the contaminated drill stem is repeatedly withdrawn to the atmosphere and there is potential for contaminant spread. The alternative idea invented at the INEEL is to use drive points and thin-walled plastic sleeves driven into the waste to provide a shield for the drill stem during jet grouting as shown in Fig. 1.

The jet grouting involves a drill stem using dual nozzles located 90 degrees apart on the drill stem. The drill stem is rotated slowly such that the force of flow out of the jet nozzles first cuts through the plastic sleeve and then allows the grout to jet out into the buried waste matrix as if the sleeve was not present. The drill pipe and thus the two nozzles are rotated through 180 degrees such that a total of 360 degrees of the sleeve pipe is cut by the jetting action of the two nozzles.

Following grouting at one step, the continuously rotating drill stem is withdrawn a precise distance and the process is repeated. In addition, a specially designed seal near the bottom of the drill stem is employed to keep contaminants from coming to the surface through the drill-stem hole and further contaminating upper reaches of the drill-stem surface. This technology may be applied to over 2 million cubic feet of buried TRU waste at the INEEL for either long-term disposal or short-term interim storage with improved confinement followed by retrieval. The jet-grouting technique has been shown to be effective in creating monoliths out of buried waste sites. These monoliths can eliminate subsidence and provide added protection against migration of contaminants. This paper presents the results of the proof-of-concept experiments, with emphasis on the enhanced contamination control of the technology.

During the summer of 1997, testing was performed in full scale at AGEC facilities on the Hanford site. Apparatus included the CASA GRANDE C6S drill system, the CASA GRANDE JET-5 pump, and ancillary grout supply hoses and mixing apparatus supplied by AGEC. The test plan called for elaborate procedures to cut the sleeve. However, these procedures were not required since the force of the jet was capable of cutting the sleeve even in the rotational mode. This simplification allowed concentration on calibrating the flow through the nozzles as a function of time to rotate the nozzles through 180 degrees. What follows is a description of the sequence of events and procedures followed during the proof-of-concept testing.

Tests consisted of five demonstrations: sleeve cutting, driving sleeves into a soil site, column formation in soil by jet grouting, driving sleeves into a buried waste site, and monolith formation within a simulated test pit by jet grouting. All of the jet-grouting operations were performed at 6000 psi pressure, with the Portland cement mixed 1:1 by mass with water.

The sleeve-pipe penetration tests showed that not only could the 6000 psi pressure cut though the pipe, but the cutting could be accomplished in a rotational mode. The sleeve-pipe penetration testing was greatly simplified in that initial tests with water only showed that penetration of the sleeve pipe was almost immediate upon initiation of the 6000 psi of water flow. It was reasoned that water had poorer cutting characteristics than particulate grout (Portland cement mixed 1:1 by mass with water). Therefore, the sleeve penetration test could focus on optimizing the rotational speed of the drill balanced with the total delivered flow though the nozzles to achieve complete cutting of 360 degrees of the pipe. The test was performed in a 55-gal drum (see Fig. 2) such that the total flow emanating from the nozzles could be collected and volume measured for each cutting campaign. Optimization tests resulted in a nominal set of parameters to achieve complete sleeve-pipe cutting. This was an iterative process of trying different rotation times. Based on this optimization, the following parameters were established: 10 s per 180 degrees rotation of the pipe, 6000 psi grouting pressure, and a 5-cm step. In this manner, with two nozzles 180 degrees apart, in 10 s, grout will penetrate the entire circumference of the sleeve. The plastic pipe was PVC 1120 ASTM D2241-4 in. schedule (125 psi).

It was shown that the driving of sleeve pipes could be accomplished without fracturing the plastic sleeves. This was specially impressive considering the large (up to 1-ft diameter) cobble in the local soils. Sleeve pipes were driven into two locations as part of field trials. Driving the field trial holes involved rotopercussion for the entire 10-ft length of the insertion. Through the use of a special clamp arrangement, the sleeve pipe followed the drive point down without incident (no fracturing of the sleeve). Once inserted, the grouting proceeded with the parameters established during the sleeve-pipe cutting test. No grout was observed on the drill stem for the first hole; however, for the second hole grout leaked past the seal. It was determined that the keeper ring (located approximately 6 in. above the nozzles) slipped, allowing a loose seal. For the field trials, the keeper ring was simply tightened and the second field trial hole proceeded. Field trial hole 1 involved a 5-cm step and field trial hole 2 involved a 6.5-cm step. The goal was to inject approximately 0.4 gal/step (based on experience [ref 1, 2]). By adjusting the step size, it was hoped to obtain information on the effect of total injected grout/length of hole relative to the column created.

Once the field trial columns were emplaced, they were allowed to cure for 15 hours before excavation. Excavation showed the formation of typical grout columns with 20-24 in. average diameters. It was also determined that at several positions, the 10-s rotation for 180 degrees was giving some incomplete penetration. Therefore, it was determined that the parameters for grouting would be increased to 12 s on a step, with a step size of 7.5 cm, and that the 10 s per 180 degrees rotational rate would be kept.

A total of 10 holes were successfully drilled and grouted in the debris pit, with some cross communication of grout seen up adjacent holes. The sequence was to drive only one sleeve at a time 9 ft into the ground and grout out the bottom 7 ft. The debris pipe consisted of 30-gal drums loaded with simulated buried TRU waste (patterned after the material buried at the INEEL's Radioactive Waste Management Complex). In addition, each drum had dysprosium oxide tracer added as a stand-in for plutonium oxide at 110 g per drum. The pit was constructed using a backfill of INEEL soil (the soil was shipped to Hanford for this testing).

The debris pit was grouted with the final set of parameters established during the field trials (7.5-cm step, 12 s on a step, 10-s 180-degree rotation). The order of grouting is shown in Fig. 3, which represents a triangular pitch matrix. After grouting the first hole, it was observed that the seal keeper ring had again slipped, allowing grout to move past the seal to the drill stem. The "nozzle" assembly was removed, taken to a machine shop, and the keeper ring was tack welded. Following this action, there was no further leakage past the seal for any of the remaining 9 holes grouted. There were no grout returns observed for the first 6 holes. However, when grouting hole 7, grout began emanating up the interior of the sleeve for hole 6. For the final holes, grout returned up adjacent holes. When an extra drive point was placed on the top of the pipe that grout was emanating from, the flow stopped, indicating that grout returns could easily be controlled by sealing the top of the sleeve pipes.

The other technique that could be employed is to use an every-other-hole strategy. However, the testing schedule would not allow this strategy to be examined. During the grouting sequence, at no time did grout come up the outside of the sleeve. Rather, grout only emanated from the inside of the pipe. The average time to grout a hole was 28 minutes for this proof-of-concept test, which is comparable to past jet-grouting activities (ref 1, 2). Approximately 100 gal of grout was emplaced per hole, or a total of 1000 gal for the entire pit. However, only about 50 gal emerged as grout returns. This grout could fill a void volume of approximately 75% of the theoretical pit volume, which is comparable to other buried waste demonstrations performed at the INEEL.

A destructive examination of the grouted debris pit showed that, indeed, a monolith had been formed and that the sleeve-pipe idea shows a positive proof of concept. Grout penetration was total within drums and in the soils surrounding drums. Several of the retrieved adjacent holes showed connected column formation. A complete photographic record of the excavation is available from the author (ref 3). However, reproductions for this report are not of sufficient quality to evaluate the cohesiveness of the monolith.

An evaluation of tracer on the sleeve pipe following driving of the sleeve and on the drill stem above the seal following grouting shows that there is essentially no tracer detected. Table I gives a complete listing of the analyzed samples using inductively coupled plasma-mass spectroscopy (ICP-MS). Obtaining tracer concentrations for a variety of backgrounds including the drill stem, sleeves, and grease fittings was mandatory because prior grouting experiments at the INEEL involved dysprosium oxide tracer material in the simulated buried waste, and this identical equipment was used in the subject work. Additional smear samples using Whatman 4.25-cm hardened filter paper were taken on the top of the sleeve pipe following driving of the sleeves and on the drill steel above the seal ring. Examining Table I shows that for virtually all samples

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except three, the filter paper tested below the detection limit of the ICP-MS system. The detection limit can be expressed as 100% recovery for spiked samples of 100 ppb. One of the samples was of the returned grout material that came up hole 7 (see Fig. 3) when grouting hole 10. This positive sample of dysprosium tracer material is expected because the grout is returning up directly from the pit. For the sample on the drill steel above the seal for hole 5, the analytical laboratory note was that this sample had a superfluous result because there was no internal standard added. For the drill steel above the seal for hole 1, there was leakage past the seal. This was due to the keeper ring slipping, and high-pressure grout and mixed-in contaminants were found above the seal. Following this hole, the entire subassembly was removed and taken to a machine shop where the keeper ring was tack welded in place. Following this action, there was no further leakage past the seal. All drill-stem samples showed below instrument detection limits for all succeeding holes grouted.

It is concluded that using sleeve pipes and drive points can create monoliths during jet grouting and that the process can keep the drill steel free of contaminants when applied to buried debris. At 6000 psi, the JET-5 pump can cut through the plastic sleeve in a rotational mode and still provide sufficient force to create columns in soil and monoliths in buried waste. The sleeve can be driven into the soil and into buried waste debris without shattering, even in the rotopercussion mode of the CASA GRANDE drill system. Management of grout returns appears to be simply a matter of blocking the flow, possibly with above ground packer systems.

It is recommended that the control of grout returns be evaluated using a packer or other easily applied system at the top of adjacent sleeve pipes during grouting. In addition, it is recommended that the emplacement technique be examined for grouting materials other than Portland cement to determine if the technique can be extended to other fluids. Finally, it is recommended that this technique be incorporated into plans to perform a treatability study involving stabilization of TRU pits and trenches at the INEEL.

1. G.G. LOOMIS and D.N. THOMPSON, "Innovative Grout/Retrieval Demonstration," INEL-94/001, (January 1995).
2. G.G. LOOMIS, D.N. THOMPSON, and J.H. HEISER, "Innovative Subsurface Stabilization of Transuranic Pits and Trenches," INEL-95/0632, (December 1995).
3. G.G. LOOMIS, A.P. ZDINAK, and C.W. BISHOP, "Innovative Subsurface Stabilization Project3/4 Final Report (Revision 1)," INEL-96/0439, (July 1997).

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