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Sealing should be accomplished in one continuous operation. Where the sealing interval will exceed 100 feet (30.5 metres) in length, consideration must be given to the collapse strength of the casing. Further, because of the weight of such extensive seals, consideration must also be given to the installation of stronger retaining devices and a to staging the placement of the seal (as, for example, the i installation of a short segment of rapid-setting sealant in 8 advance of the main body of sealing material; the former becomes a foundation to support the extensive seal). • ' b 8.,.,"• $ Sealing Methods , : L� t 5 0�7 The following methods can be used to seal the upper portion of the annular space. Except for the first, these 9 methods are illustrated on Figure 10. The first method is ag tr frequently used where short seals, under 20 feet (6 metres) ;W& W deep, are placed in dry material. �t < a Gravity Installation (Without Tremie). In this 0 method sealing material is poured into the annular space 4C without the use of a tremie or grout pipe. It cannot be used where the annular space contains water and is limited to � intervals less than 30 feet (9 metres) deep. When used, - u visual observation (with the aid of a mirror or light) should A be made during placement of the seal. L'a aJ Grout Pie Method. In this method, the seal is * ' � laced in the annular space by gravity through a grout p13. or tremie) suspended in the annular space (see Figure 10 W 1. Drill the hole large enough to accommodate the grout pipe (at least 4 inches or 100 millimetres, greater W in diameter than the diameter of the casing). €n 2. In caving formations, install a conductor p casing. _ _ U_ 3. Provide a packer or grout retainer in the a ❑ annular space below the interval to be sealed. � O 4. Extend the grout pipe down the annular a: ua space between the casing and the wall or conductor to near w the bottom of the interval to be sealed just above the a retainer. ; 5. Add grout in one continuous operation, beginning at the bottom of the interval to be sealed. The bottom end of the grout pipe should remain submerged in the sealing material during the entire time it is being placed. {` The grout pipe is gradually withdrawn as the sealing material is placed. Where a conductor casing is used to hold back =Y caving material, it may be withdrawn as the sealing material _ ¢ i r � u� is placed. _ Q W Pumping-Exterior Placement. For this method the -'.i. .: Q� same procedure as described for the Grout Pipe Method (above) is followed except that the material is placed by pumping instead of by gravity flow. The grout pipe must always be full of sealing material and its bottom end must remain submerged in the sealing material until the interval has been filled. . 68 - -