After breaking ground on a multi-million dollar addition, Lake Forest High School realized the specified conventional foundation system would not work. Some of the most unsuitable soils for deep foundation construction lie along Lake Michigan just north of downtown Chicago. Fill material, silty clay and till are present down roughly 190’ until bedrock is encountered. It was determined that 110 kip capacity micropiles offered the best solution.

Thirty-eight (38) piles were to be located on the exterior of the structure with no overhead restrictions. A 5.5” diameter pile installed to depth of 109’ was used. The top 74’ utilized a 5.5” steel casing with a wall thickness of 0.4”. The bottom 35’ would be the uncased bond zone. A 50’ section of 1.25” steel rod was then installed to provide load transfer from the cased portion of the pile down through the uncased bond zone. The entire pile was filled with a 4000 PSI grout.

There were also fourteen (14) piles to be installed within the basement of the existing structure where overhead clearance was severely limited. For the interior locations, a 73/53mm hollow bar was used in conjunction with a 7” diameter sacrificial drill bit. The hollow bar is advantageous in low overhead environments due to lower installation torques required, thus allowing smaller drill rigs to perform the installation.

Although this was a major change in the scope of work, no additional time could be added to the construction schedule. The foundation portion of the job was on the critical path and had to be completed in an expedited fashion. MixOnSite employed the use of two drill rigs, one for high production outside work and the other for the limited access inside work. The installation was completed 1 week ahead of schedule!