Stabilization of Foundation Slab with Micropiles
Newport Beach South of Los Angeles, California, is witnessing a flurry of new construction projects. One of them is the Newport Bay Marina, a bayfront mixed use project that is built at a former World War II shipyard site.
When completed, Newport Marina Bay will provide 1,394m² (15,000ft²) of retail space below 1,951m² (21,000ft²) of office space. The project also includes a new 23-slip marina and a public plaza.
Since the job site is at the waterfront below sea level, the entire perimeter of the project is enclosed by a combination of sheet pile walls and secant pile walls with a series of de-watering sump pumps running continuously until the waterproofed concrete walls over the sheet piles are complete. The design engineer selected DYWIDAG Micropiles to resist the uplift force on the underwater concrete slab and to prevent structural damage due to high potential of soil liquefaction in the event of an earthquake. A total of 624 double corrosion protected (DCP) 57mm Ø DYWIDAG Micropiles were installed in a grid pattern at approx. 3.66m (12ft) spacing for this project.
One of the reasons why Vertical Earthworks, Inc. was successful in winning the contract was the fact that DYWIDAG produced the 170t of DYWIDAG Micropiles in customized lengths of 12.2m (40ft). This way, the contractor was able to make a cost efficient offer because the bars, which are normally supplied in standard lengths of 18.3m (60ft), did not have to be cut, and consequently, no material had to be wasted.
Drilling in the local soil, mainly silt deposit and alluvium, was a challenge. After experimenting with different micropile installation methods including the vibratory method with pre-drilling, full displacement auger etc, the contractor selected a partial displacement auger using the pre-drilling method. The boreholes were pre-drilled with a 61mm (24”) diameter auger and then re-drilled with a slightly smaller diameter auger. In order to keep the drilled hole from collapsing, premixed slurry grout was tremie pumped through a grout port at the bottom of the auger bit as the auger was being extracted from the hole. Afterwards, the DYWIDAG Micropiles were inserted into the slurry filled drilled holes.
In addition to supplying the micropiles and associated hardware, DYWIDAG also provided stressing equipment for pile testing in order to prove the suitability of the chosen system for the conditions on site. The micropiles were successfully installed in January 2015 and the entire project is scheduled for completion in 2016.