Building with Compressed Earth Block within the Building Code

Abstract

Despite the use of earthen materials in building construction for thousands of years, many engineering properties of earthen walls are not well understood, documented, or regulated. California and New Mexico have adopted building codes allowing earthen structures through prescriptive methods that rely on rules of thumb to limit heights and spans of construction. Furthermore, California restricts earthen structures to very limited areas on the basis of soil type. Overall, the prescriptive methods have led to uncertainty about reinforcing requirements. There is a belief among builders who use earthen materials that reinforcement is required only in areas of high earthquake hazard, implying that a geographic area is either seismic or not. In reality, all locations are prone to some seismicity. On the basis of the probability of seismic activity and soil conditions at each locale, every site has a risk that ranges from very low to very high probability of earthquake damage. Energy compliance and structural adequacy are two areas of concern to city officials. This article delineates the processes required to build with compressed stabilized earth blocks (CSEBs) within the building code. The authors determined that the compressive strength of CSEB walls is sufficient in most residential applications, but wall shear strength is more critical. To determine the wall in-plane and out-of-plane shear strength, the authors conducted laboratory tests to investigate the shear strength of CSEB wall assemblies, first without reinforcing (which proved insufficient) and then incorporating geogrid (sometimes referred to in the industry as geofabric) on interior and exterior wall surfaces as a method of lateral reinforcement. The resulting unreinforced wall shear strengths were used to determine where unreinforced CSEBs can be used to meet code strength requirements. The following data demonstrate that CSEBs are viable material for residential construction but are acceptable only for use in limited areas without reinforcing due to assembled wall mass and the seismic loads they create. In addition, this article reviews the energy-compliance process required when designing earthen structures.