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Date: April 15, 1996 Author: Gerardo Osegueda Gine, CPK Consultores, S.A. San Salvador, El Salvador Subject: Shot Crete Retaining Wall with MANTA RAY® Tie Backs Description of Problem: In a residential area a decision was made to lower the level of the street by 7 mt. from the project level causing an increase in the height of the cut from the levels that were all ready occupied by residence. Design Procedure: Several design procedures were studied and used to rule the design. Due to the fact that MANTA RAY anchors work in true tension, only the modified Davis and the German Method for design were preferred. A check was done using observed performance of other soil nailed walls
and AASHTO information regarding design principles for tieback walls. The soil conditions were identified by performing
an SPT test 4 mt. into the slope. It determined a soil internal friction angle ranging from 32 to 34 degress. The
type of soil found was "silty sand" with some volcanic ash. Construction Procedure/Installation Equipment: Since the cut was already made, we proceeded to level off the surface of the embankment and protect it with a lite water cement seal and installed the MR-2 anchors with the hydraulic unit. The soil wa very hard; therefore it was difficult to drive anchors. By using pre-drilled holes almost to full depth of the anchors using a 4 inch diameter hydraulic auger, C.P.K. Consultores managed to install up to 16 anchors per day using the 18 HP hydraulic power pack and hammer. We covered the embankment with a reinforcement mesh and cast a 5 cm. shotcrete coat, proceeding afterwards to post tension the anchors to 12,000 pounds. A final 5 cm. shotcrete cover was applied. This shotcrete included seeds which will grow and make the final edifice look like a grassy wall. |
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