Contents preface (VII) introduction 1—37
Yüklə 18,33 Mb.
|
(v) Grouting Grouting is the process by which fluid cement pastes are pumped through small diameter drilled holes into crevices and joints in rocks for strengthening dam foundation. After setting, the cement paste forms an impervious barrier (or grout curtain) to the seepage water. This method is also used for creating grout curtain in alluvial foundations of embankment dams. However, it is difficult to force cement grout into pores of sizes smaller than about 1.0 mm. To overcome this difficulty, chemical grouts are used in place of cement grouts. Grouting of alluvial deposits is also difficult because of: (i) the necessity of keeping the hole open with casing, (ii) the impossibility of using packers, and (iii) the lack of a proper injection technique. Chemical grouts, used until recently, were costly and not much effective either. The ‘‘Soletanche’’ method (4), however, enables effective grouting of alluvial deposits. In this method, a row of holes (125 to 250 mm diameter) at a spacing of about 3.0 m are drilled through the alluvium up to bedrock by using drilling mud and suitable drilling bits. Grout pipes (diameter about 60 mm) having circumferential rows of holes at vertical intervals of about 300 mm are set to bedrock in the drilled hole. The circumferential holes were covered with 100 mm long, tightly fitting rubber sleeves. The annular space between the grout pipe and the drilled hole is filled with a brittle clay-cement grout (Fig. 15.16). Grouting of the alluvium is then carried out from the bottom up through each of the circumferential holes in the grout pipe. The grout mix is pumped into each circumferential hole under pressure through a smaller interior grout pipe which has a set of two rubber packers spaced 300 mm apart. In this way the grout pressure can be confined to the short length of the grout pipe opposite each of the circumferential holes and the rubber sleeve. ~ 325 mm
62.5 mm pipe with circumferential rows of holes each 325 mm ± Brittle clay-cement in annular space Packers inside 62.5 mm pipe Rubber sleeve ~ 325 mm Grout enters soil through cracks Grout pipe Holes in pipe Packers inside 62.5 mm pipe 85 mm hole Yüklə 18,33 Mb. Dostları ilə paylaş:
|