Optimal Design of Anchored Walls for Seismic Performance in Excavation Support Systems

The primary objective of this study is to probe an optimum pattern of anchor distribution to improve seismic behavior of a series of anchored walls as a temporary excavation support system, without increasing the cost of their preliminary static design. To this end, the related literature including both nail and anchors as reinforcement was, firstly, thoroughly reviewed to shed light on the probable successful scenarios. It is concluded from the literature that the bottom rows of reinforcement play an important role in providing seismic stability, while the top rows reduce seismic displacement of the walls. Additionally, in the absence of liquefaction or cyclic softening of the soil, the seismic stability of nailed walls has been satisfactory in all previous seismic events due to their conservative design. Thus, control of seismic displacements is crucial. Furthermore, it has been pointed out by numerous studies that partly the interaction of the anchors and the wall with the soil and partly the amplification of the seismic waves through the wall require a numerical analysis to be simulated properly. Secondly, detailed calibration of a 3D numerical model was accomplished by simulating a previously conducted centrifuge modeling of a nailed wall as an excavation support system, experiencing cyclic loadings. Subsequently, different patterns of anchors with the same overall length were tried in the calibrated numerical models and their seismic performance were presented in terms of wall movement and settlement of the soil surface behind the wall. The primary finding of this study indicates that increasing the length of the anchors to 0.9 times the excavation height, while positioning them at a depth equal to one-fourth of the excavation depth, considerably reduces seismic wall displacement and settlement in sandy soils of the models studied herein. Moreover, though different models exhibited similar displacements under static conditions, their seismic displacements varied significantly. Notably, the above-mentioned configuration led to the least seismic displacement of the anchored wall investigated in this research.