Micropiling in Karstic Rock: New CMFF Foundation Solution Applied at the Sanita Factory

Abstract

The new Sanita factory is a 2 story factory warehouse covering an area of 10,000 m 2 located in Zouk-Mosbeh, Lebanon. The warehouse is composed of 140 reinforced concrete columns supporting a one way pre-stressed concrete slab designed to carry 25 kN/m 2 of industrial live load plus a future steel structure. The soil substratum consists of 1 to 4 m of silt on top of the bedrock. The bedrock is hard karstic limestone with cavities and fissures. Because of the karstic nature of the rock, the original design called for a strip foundation on top of the rock with a maximum allowable bearing pressure of 400 kPa. Combined Micropiles and Footing Foundation, CMFF, is a new foundation system that was created by the International Institute for Geotechnics and Materials, iIGM, and implemented as an alternative solution for this particular project. This new system was designed utilizing a finite element model. There were two major concerns regarding this solution. The first concern was with respect to the loadsettlement performance of the micropile in the karstic terrain. The second concern was to prove the advantages of the CMFF system considering the particular conditions of the project. Two static load tests were performed on the micropiles with different methods. The results of the tests permitted modeling the soil/structure interactive foundation system. CMFF in karst offered many technical advantages over classical methods. A cost saving of about 40% was also accomplished in the foundation system without compromising safety. This paper summarizes the results of the load tests and the advantages of CMFF in this particular project. The paper also presents the different phases of the foundation system by covering the design details, construction aspects, performance evaluation, and cost analysis.