Grouted Liners

1 The design development of steel liners for PCRVs over the years has led to the currently acceptable principle of bonding the liner to the concrete with a multitude of closely spaced stud or hook anchors. 

4 One possible method of Isolating the liner from the concrete vessel until some stage after vessel prestress Is applied Is the formation of a small construction gap between the liner and the vessel concrete. This gap would be approximately 300mm wide and on completion of the prestress period would be grouted up. See figure 39. 

5 There are two ways In which this gap could be formed. Either erect the liner first and construct the vessel walls, including gap, or construct the vessel walls first and lower the liner in position maintaining the gap. 

6 The first method follows the current approach to construction of a PCRV. The liner Is erected on the vessel bottom cap with the penetrations attached. The vessel walls are constructed using the liner to support formwork for the Internal face. Formation of the construction gap could be achieved by using a permanent or built In shutter. The liner would be stiffened by continuous rolled sections and these could be used as 

7 The second method involves conventional construction of the pressure vessel walls using removeable formwork to both faces. Through wall penetrations would be cast In and could be accurately located by making the Internal wall shutter a template. Uhen the walls are complete to the underside of the top cap level the liner would be lowered In one piece Into the void. Connection between the liner and penetrations would be done after prestressing and could be as shown In figure 40. 

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Preliminary work on the grouted liner concept has identified the likely main problems, typically, construction methods, connecting up cooling pipes and standpipes, assessment of degree of liner anchorage required and so on. It Is recommended that further work on this concept should be carried out to determine whether or not It Is feasible. It Is also recommended that the previous work on the freestanding liner concept be followed up. 

Slurry walls, grout curtains, sheet piling, biobarriers, reactive barriers Grout injected liners... 

The prestressing of a typical PCRV would take about nine months to complete and of course some of the early life creep will take place during this period. If the grouting operation was delayed for six months after completion of prestress this would eliminate about 70% of the strain due to long term creep on the liner. 

Proposed detail of Junction between grouted main liner and gas duct. 

Fig.AO. PROPOSED DETAIL OF JUNCTION BETWEEN GROUTED MAIN LINER AND GAS DUCT...

There will be a period of relaxation and thermal equilibrium before the liner is ready to be grouted. Check manufacturer recommendations on how long you should wait before sealing the annular space between the liner and the existing sewer. 

In addition to grouting between the liner and the sewer, you will also have to seal the annular space between the liner and where it enters and exists a manhole. A rule of thumb is to install a sealant for a distance equal to 1 times the pipe diameter of the liner. Wait until relaxation and thermal equilibrium has settled in. Normally, this will not take more than 24 hours, but check manufacturers recommendations to confirm a satisfactory waiting period. 

The next step is sealing the open space between the old sewer and the grout or liner. This reqnirement prevents invasion of ground water, backfill material, and other debris. Once this is done, yon are ready to backfill the work area. 

Figure 3.13 Installation steps (a) lightweight pipe is hand-carried into the host pipe, (h) beveled end, (c) fabric band is saturated to complete the joint, and (d) small annular space between the liner and host pipe can be grouted.

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