Rockery Design and Construction Guidelines

摘要

Rockeries, also known as dry stack walls, consist of earth retaining and/or protection structures typically comprised of rough onsite rocks stacked in an interlocking fashion with no mortar, concrete, or steel to retain cut or fill slopes. They are context sensitive solutions that in many cases are also relatively low cost. Several rockeries exist as historic or cultural features on many Forest Highway and National Park roads. Many were apparently built in the Civilian Conservation Corps (CCC) era of the late 1930's; some are still performing well and others have required extensive maintenance or have failed. Generally, rockeries have not been designed according to the ASSHTO standard specifications or other accepted wall design procedures. On the other hand the wide range of implementation suggests excellent performance can be expected when certain conditions are met. There is little guidance available to standard acceptable design and construction guidelines and to what conditions need to be met. A rationally based and tested design procedure therefore is needed to provide designers and owners with the confidence that these structures can be used in modern highway engineering. Commercially, rockeries have been constructed in several northwestern states for the past four decades. As rockery design procedures tend to vary regionally, the Federal Highway Administration - Central Federal Lands Highway Division (FHWA-CFLHD) contracted Sanders & Associates to research and evaluate the existing methods by which rockeries are designed and constructed, with the eventual goal of developing comprehensive design and construction procedures. The existing design procedures were also compared using several typical rockery design cases to determine how the resulting rockery designs differ and to determine the methods most appropriate for use by the FHWA's Federal Lands Highway Divisions (FLH) as a design approach. Based on the research performed by the contractor, a design methodology was developed to evaluate rockery stability as a function of the rockery geometry (height, base width, and batter), rock properties and placement, and lateral pressure imposed by the backfill materials. Guidelines are presented for analyzing, designing and constructing rockeries, and for conducting quality assurance during rockery construction.