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Two dimensional finite element modeling for the multi tier pile wall with anchor shoring sysytem

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2019
Özyürek, Yunus Emre
For deep excavations (such as greater than 20-25 m excavation depths) in urban areas, where there is strict deformation limits, multi-tier pile wall shoring system with soil anchors is becoming more widely used, since the system with one level of piles becomes insufficient or unfeasible. In this study, parameters affecting the behavior of multi-tier pile wall retaining system is investigated via two-dimensional finite element method. Firstly, a 30 m excavation is carried out with a multi-tier shoring system supported by prestressed ground anchors in an area with Ankara clay soil. This shoring system is analyzed by two-dimensional finite element method and the results are compared with the inclinometer measurements in the field. General deformation behavior measured by inclinometer could not be captured by any of the constitutive models. The “closest” pile horizontal deformation behavior to inclinometer measurements is obtained by using the Hardening Soil Model and drained geotechnical material parameters. Furthermore, the effects and the importance of overconsolidation ratio of clay in the results is demonstrated. Then the effects of various parameters by using two - dimensional finite element method (using Plaxis 2D software) on multi-tier shoring systems supported by prestressed ground anchors are investigated. These parameters are embedded length of upper pile, embedded length of the lower pile (socket length), effect of having an anchor at the overlap zone between two piles, the horizontal distance between upper and lower piles, interface friction coefficient between pile and soil, higher and lower intensity anchor placement (i.e. anchors per m2 plan area of wall). When the anchor in overlap length of upper and lower piles is canceled, displacements increase significantly in the socket zone of upper pile and in top of lower pile. Therefore, in the multi-tier pile wall retaining system, construction of the last row anchors of upper pile must be completed (together with pre-stressing and cross beam construction) before starting to the forage of the lower pile. It is concluded that for horizontal distances greater than or equal to H/3 (where H is the total depth of excavation) anchor lengths of two walls can be designed separately. The results of this study could be useful for safe design of multi-tier pile walls.