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  19 Grouting in Tunnels and Shafts 19.1 INTRODUCTION In Chaps. 16, 17 and 18, the applications were primarily either water shutoff  or strengthening a formation. In tunnel and shaft grouting, generally bothpurposes must be served. In addition, tunnels and shafts (because of theirgreater depth below grade) often involve the use of much higher pressuresthan the projects detailed in the previous three chapters (except for minewaterproofing, which may also take place at substantial depths). Further,tunnels and shafts are often very large projects and (like large cutoff walls)are often preceded by extensive soil investigation. This permits prediction of possible water problems and the detailed preplanning of how thoseproblems will be handled. The procedures used in grouting tunnels andshafts are much the same regardless of project site and can be illustrated bycase histories of relatively small projects as well as large ones. 19.2 SHALLOW TUNNELS The tunnel shown in Fig. 10.4 is typical of conditions (unexpectedlyencountered in small, shallow tunnels) which require remedial measures. Ithad been anticipated that mining would take place in clay, using steel Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.  supports and lagging. However, a fine, dry sand statum was intercepted forabout 300ft along the tunnel line. It might have been possible to continuemining by using a shield and liner plates. Alternatively, the sand could bestabilized by grouting in order for mining to proceed without danger of lossof ground. Grouting was selected as the more economical procedure. Groutpipes were driven from the surface as shown in the vertical section in rows6ft apart. (Grouting in tunnels is often done from the tunnel face. Groutingfrom the surface, however, permits continuous mining and for this reasonmay be cost-effective even through longer grout pipes are needed.) Asilicate-based grout was used to create an arch about 3ft thick. The groutvolume placed averaged 100gal per lineal foot of tunnel.Another project where grouting from the surface proved the mostfeasible took place in Harrison, New Jersey, where two 12-ft-diameterconcrete tunnels were to be constructed under 13 sets of live railroad trackswithout interrupting railroad traffic.The tunnel invert was located 17ft below track level, and the lowerhalf of the tunnels was in clay. Above the clay was 2 to 4ft of sand overlainby meadow mat about a foot thick. Mixed cinder and sand fill were abovethe meadow mat. Two shafts were put down by driving sheet piling. Theywere 270ft apart, spanning the tracks. Concrete pipe was to be jacked intoplace, forming the tunnels. Figure 19.1 shows sketches of the jobparameters.A surface area 38ft wide by 15ft long (in the line of the tunnels)adjacent to the shaft was treated from the surface. Drill rods (E size, pluggedwith a rivet) were to be driven to the top of the clay stratum, and groutingwas done by withdrawing in 3-ft stages. After this work, holes were cut inthe shaft sheeting, and the jacking operation was begun. After about 17ft of progress (the limit of the grouted zone) excessive water flow occurred, andquick conditions developed. At this point it was decided to grout the entiretunnel length. The grouting was started with holes and rows spaced 3ftapart. Spacing of holes in each row was increased to 4ft after experienceproved that this spacing gave adequate stabilization.The project was done with an acrylamide-based grout. The formationwas stabilized to the extent that cave-ins and quick conditions wereprevented, and the inflow of water was reduced to the point where it couldbe readily handled by pumping. The entire grouting operation wascompleted in 27 working days, using a total of about 34,000gal of grout.Pipe jacking was also involved in a 4000-ft pipeline in Alameda,California [1]. Five-foot-diameter concrete pipe was being laid by cut andcover methods. The pipe had to penetrate a 65-ft-high levee, where cut andcover could not be used. After jacking got underway a short distance, sand,gravel, and boulders ran into the pipe, leaving a large open cavity above it. Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.  Rather than risk the possibility of the cavity extending itself to the surface of the levee, the contractor chose to stabilize the formation by grouting. Asilicate-based grout was selected, since the formation was mainly sands andgravels.At the heading, 0.5inch steel pipe was driven by air hammer to a depthof 10 to 11ft at five locations, arranged in a half-circle pattern flaring outslightly from the upper concrete pipe circumference. Each grout pipe waswithdrawn in 1ft increments, with an average of 10gal of grout injectedevery foot. Pumping pressures were generally in the 100 to 120psi range,and gel times of about 2h were used. (Much shorter gel times could alsohave been used effectively.) Grouting was done by a night shift and pipe jacking and mucking during the day. F IGURE  19.1  Plan of grouting for jacked tunnels. Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.  Similar procedures in tunnel stabilizations are detailed in Refs. [2–5].Although these jobs date back 20 to 25 years, the procedures used then arestill valid and in use today. The procedures were new at that time andtherefore newsworthy. Similar work done today is generally not reported inthe technical press.In more recent work, the grouting patterns for tunnels have becomemore complex and sophisticated. A case in point is the stabilization of arock–soil interface detailed in Ref. [6]. Other references to tunnel and shaftgrouting can be found in Ref. [7]. 19.3 EUROPEAN PRACTICE In Europe, chemical grouting in tunnels is ‘‘automatically considered as partof the tunneling plans rather than looked upon as an esoteric tool’’ (Ref. [8],part 1, p. 9; the several descriptions of tunnel work that follow are takenfrom the same reference). As a result, a much larger volume of work andexperience exists in Europe, and domestic practice tends to follow theprocedures and techniques developed overseas.A schematic of the subsurface conditions along the axis of a sewertunnel in Warrington, England, is shown in Fig. 19.2. The tunnel is insandstone until the surface of the sandstone dips downward; then for about F IGURE  19.2  Tunneling conditions for grouted section of sewer tunnel,Warrington new town development. (Note: This schematic is not to scale.)(From Ref. 8.) Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.

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Jul 23, 2017
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