BULK INFILL GROUTING DESIGN GUIDANCE

Transcription

1 Preferred Design Procedure No FHWA design procedures are currently in existence for Bulk Infill Grouting (BIG). Despite the lack of a standard design procedure, various design procedures have been developed and implemented in projects across the United States in both transportation and nontransportation related applications. The design methods, as well as construction methods, for BIG include flush grouting, karstic cavity grouting, and grout columns. The use of each design procedure depends on the application for which BIG is required. Flush grouting and grout columns are used to prevent subsidence from subsurface mine workings while karstic cavity grouting is used to prevent subsidence from sinkholes and other karst terrain. These methods are not proprietary. Summaries for each of these methods are included in this document. Table 1 provides a list of the typical inputs and outputs for design and analysis procedures. Summary of Design/Analysis Procedure: Flush Grouting Reference(s): Andromalos and Ryan (1988) Ohio Department of Transportation (1998) Okonkwo et al. (1988) Stump (1988) Woodward (2005) This procedure comprises the backfilling of a mine working within the treatment zone using a weak grout. Holes are drilled from the ground surface into the subsurface voids and grout is pumped into the voids. The grout is typically a low-slump yet still fluid grout that allows it to fill nearly the entire system of mine voids. The treatment zone is usually taken as the project area projected downwards at a 15 angle of influence outside the structure. Holes are drilled around the perimeter, typically on 15- to 25-foot centers. The perimeter is grouted first to contain the grout that will be subsequently pumped in the central area. A thicker grout or crushed stone may be used on the perimeter to help prevent excess grout from flowing out of the treatment zone. Once the perimeter barrier has been established, interior holes are drilled, usually on 20- to 25-foot centers, and a weak grout is flushed into the mine until refusal. The grout used for this application should be designed to withstand crushing by the weight of overburden. November 2012 Page 1 of 5

2 Summary of Design/Analysis Procedure: Karstic Cavity Grouting Reference(s): Fischer and Fischer (1997) Madrid et al. (2005) Waltham et al. (2005) Watson et al. (2003) Woodward (2005) Karstic cavity grouting involves the injection of grout into karstic voids and cavities to mitigate the formation and development of subsidence sinkholes. Grouted voids are typically cavities existing at the soil-rock interface where the overburden is susceptible to piping and, therefore, the development of subsidence sinkholes. For pretreatment purposes, a grid of injection points is placed over a treatment area since karstic cavities are unpredictable. Subsurface conditions are used to approximate the total amount of grout take for a treatment area. If the grout injection attains a certain grout take, more grout injection holes may be drilled. For mitigation purposes, grout is injected directly into the throat of the sinkhole. In general, design of a grouting program in karst is heavily reliant upon the engineer s professional experience with both karst and grouting. November 2012 Page 2 of 5

3 Summary of Design/Analysis Procedure: Grout Columns Reference(s): Stump (1998) This procedure entails the placement of low-slump grout columns in mine workings. The columns act as pillars for mine voids resulting from room and pillar mining. Holes are drilled to the depth of the voids and are subsequently used to inject the grout to form typically conical columns. Decisions on the placement of grout columns rely heavily on knowledge of the layout of the mine void. Grout columns are required to withstand overburden pressures to prevent crushing. November 2012 Page 3 of 5

4 Table 1. Typical inputs and outputs for design and analysis procedures. Allowable settlements Performance Criteria/Indicators Bearing capacity Stratigraphy Voids: type, size, extent, depth Lithology Subsurface Conditions Ground water level Permeability Chemistry of rock, groundwater Loading Conditions Layout (angle of draw) Grout cement-water ratio Grout mix/additives Grout permeability Material Characteristics Grout compressive strength Total grout take volume Bleed/stability Borehole drilling and injection grouting Construction Techniques Verification of filling efficiency Grout injection hole spacing Geometry Width of stabilization work Injection depth November 2012 Page 4 of 5

5 References Andromalos, K.B. and Ryan, C.R. (1988). Subsidence Control by High Volume Grouting. ASCE Geotechnical Special Publication 19: Mine Induced Subsidence: Effects on Engineered Structures, Fischer, J.A., Fischer, J.J. and Ottoson, R.S. (2003). Grouting in Karst Terrane Concepts and Case Histories. ASCE Geotechnical Special Publication No. 120: Grouting and Ground Treatment, Madrid, L.D., Stach, R., Murphy, B.K., and Chinault, M.W. (2005). Estimating Grout Quantities for Residential Repairs in Central Florida Karst. ASCE Geotechnical Special Publication No. 144: Sinkholes and the Engineering and Environmental Impacts of Karst, Ohio Department of Transportation. (1998). Manual for Abandoned Underground Mine Inventory and Risk Assessment. May 15. Okonkwo, I.O., Judd, W.R. and Altschaeffl, A.G. (1988). A Review of Some Aspects of Grouting for Mine Subsidence Control. ASCE Geotechnical Special Publication 19: Mine Induced Subsidence, Stump, D.E. (1998). Grouting to Control Coal Mine Subsidence. ASCE Geotechnical Special Publication No.80: Grouts and Grouting: A Potpourri of Projects, Waltham, T., Bell, F. and Culshaw, M. (2005). Sinkholes and Subsidence: Karst and Cavernous Rocks in Engineering and Construction. Chichester, UK: Praxis Publishing Ltd. Watson, B.H., Devilbiss, T., Fischer, J.A and Fischer, J.J. (2003). Grouting Roadway Sinkholes. ASCE Geotechnical Special Publication No. 122: Sinkholes and the Engineering and Environmental Impacts of Karst, Woodward, J. (2005). An Introduction to Geotechnical Processes. Glasgow, Scotland: Bell & Bain Ltd. November 2012 Page 5 of 5