MICROPILE INSTALLATION USING THE PREVENTER SYSTEM TO CONTROL THE INFLUX OF GROUNDWATER DUE TO A HIGH WATERTABLE-Paper

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The paper describes underpinning and ground improvement works at an eight-storey building in Deira, Dubai, where basement cracks and water ingress had raised concerns about structural movement. Although monitoring indicated that movement had stabilized and the building remained within acceptable structural limits, additional grouting and micropiles were designed to improve stability.<br /><br />The basement installation was complicated by a high water table: groundwater stood at approximately -1.46 m, while micropiles were installed from -4.45 m, requiring penetration of the waterproofed slab. To control water inflow without dewatering, contractors used a pneumatic preventer system. Its inflatable rubber insert allowed the hollow micropile tendon to pass through while restricting groundwater flow; a gate valve provided a secondary seal.<br /><br />A total of 312 TITAN 40/20 micropiles, each 15 m long, and more than 580 tube-à-manchette grouting tubes were installed. Micropiles were drilled, flushed, and dynamically pressure-grouted. Special grout mixes addressed groundwater sulphates and required strength and curing performance. A one-way valve was also used when necessary to limit water returning through the hollow tendon.<br /><br />Work took place in a confined basement with only 2.4 m of headroom. Tendons therefore had to be installed in short coupled sections, and an electric drilling rig was used to avoid fumes. Grout quality was tested, and all 16 preliminary tension tests met the design criteria.<br /><br />The preventer enabled safe and efficient installation while avoiding temporary dewatering, a significant advantage given the site’s proximity to a metro station. Its use was estimated to save nearly AED 2 million in dewatering costs.

Keywords

micropiles

ground improvement

underpinning

basement cracks

water ingress

Dubai

Deira

groundwater control

pneumatic preventer

grouting