Factors Affecting Lubrication of Pipejacking in Soft Alluvial Deposits

Inadequate lubrication during pipe ramming can result in exaggerated jacking force leading to damages to the jacked pipe string and adjoining properties. However, a consensus due to limited studies has not yet reached. This study describes a method that can be used to evaluate the lubrication performance by the reduction in the frictional coefficient mu as a function of injection mode, soil and lubrication natures, and pipe deviation. The results of an application of the method to a pipe ramming project in soft alluvial deposits are presented. Compared to 0.4 kPa of the 2-8 m section of the gravel, the excessive pipe deviation, while spanning through the 8-21 m section of the same gravel at Drive C, increases the frictional stress tau(ld) to 12.5 kPa, thereby reducing the reduction in the frictional coefficient mu to 71%. At Drive D, the combined effects, resulting from the excessive pipe deviation and the varying face resistance induced by driving into the 11-24 m section of clayey gravel, contribute to the growing frictional stress tau(ld) of 4.0 kPa and are deemed as being the major cause leading to the low reduction of 84%. While pipejacking through the 24-31 m section of clayey gravel, the occasional gravel leads to the inability of developing lower face resistance causing the misleading reduction of 60%. To summarise, the excessive pipe deviation and/or the varying face resistance largely affects the percentage reduction in the mu value despite the excessive volumes of injected lubricant. The occasional gravel leads to the misleading reduction.