Offshore Pile Grout Monitoring Method

Abstract

An electrical conductivity method of monitoring offshore pile grout isdescribed. By using this method, the initial appearance of the grout, itscontinued presence, the subsequent extent of set, and its quality can bemeasured remotely. Introduction The connection between the seabed and offshoresteel platforms is achieved by using tubular steel pileswhich are passed through the main leg and/or theskirt pile sleeves. The piles are either driven to final penetration or cemented in predrilled holes.Although piles passing through the main legs may beconnected to the structure by welding at the deck level, in many structures the anular space betweeneach pile and leg or skirt pile sleeve is filled to somepredetermined elevation with cement grout. Thepresence of annular grout can significantly enhanceplatform strength. This strength enhancement canbe included in platform design considerations if thedesigner can reasonably assume a given degree ofgrout coverage and quality. Ref. 2 specifies minimum 24-hour compressivestrength for grout at 1500 psi (1034 kPa). API RP 2A(Section 6.12) also specifies that a "means should beprovided to determine that the spaces have been filledas required."The method described in this paperoffers a technique for satisfying the API standards, as well as providing other measurementsi.e.,the identity of the resident fluid in the annular space(fresh water, seawater, or air);the arrival of thecement top at predetermined elevations;the occurrence of cement "fallback" in the event ofpacker failure;the set of the cement; andthequality of the set cement. In previous practice, visualobservations, diver-collected samples, andmonitoring of the volume of grout pumped havebeen used for these purposes. For example, in the grouting of the piles of theCognac platform "the overflow of the grout at thetop of the pile sleeve was observed with the remote-control vehicle (RCV). The diver caught two samplesfrom the overflow in plastic bottles. The volume ofgrout pumped was about 40% in excess of thevolume of the annulus." These methods are limitedto practical diver operating depths and, with regardto the use of the RCV and the collection of overflowsamples, information is generated regarding only thegrout that overflows the annulus. Knowledge of thepermanent level of the grout and the quality of thegrout inside the annulus is lacking. JPT P. 2234＾