Interlocking CSEB buildings Nepal Performance and failure behaviour investigated by masonry prism and triplet shear testing

Abstract

Nepal is situated in-between the Indian and Eurasian tectonic plates resulting in a long standing history of seismic activity. The company Build up Nepal, was founded as a response to the major 2015 earthquake in Nepal and works with interlocking Compressed Stabilised Earth Blocks (CSEBs) which are made up from soil, sand, cement and water which are compressed and cured. Build up Nepal works with engaging communities, creating jobs and helping people build their own house as well as providing engineering services. Modern interlocking CSEBs present a viable alternative in reconstructing seismic resilient houses in a economical way, yet its complex structural behaviour lacks universally established building codes. Build up Nepal seeks to make this construction method standardised in Nepal and get further government approval for the system. In order to achieve approvals, more reliant data on the performance of their system is needed. Based on the system implemented by Build up Nepal, this thesis investigates methods of testing and possible improvements for interlocking CSEB masonry. By exploring how testing can be done in a simple way, which parts of the system contribute to overall strength, and what improvements are feasible in rural Nepal, this thesis aims to support Build up Nepal’s goal of standardising this construction method. The standard Determination of initial shear strength was adapted for the equipment available in the workshop connected to Build up Nepal’s office in Kathmandu and a testing plan was developed. Together with experimental testing a field trip to constructions sites in western Nepal was conducted to understand the circumstances and context. During testing, several limitations of the setup were acknowledged. The precision of certain testing equipment was low, indicating that a future step for the company is to move testing to a laboratory environment. A key issue with the test setup was the unintended increase of pre-compression loads; these are supposed to remain constant, which proved impossible with the current equipment. The results from the experimental testing demonstrate that increasing the cement content in grout and adding bed mortar improves overall system strength. However, insights from the site visit show that grout mix might be varying and application of bed mortar potentially is a challenge. The interlocking keys do not only support alignment during mason but also provides a 83% gain in shear strength compared to specimens without the keys. The recommendations are to continue using the interlocking keys and to further investigating bed mortar before widely adopting it in construction. Moreover, the cement to sand ratio of one to three should be used and simple measuring equipment should be provided to ensure consistency in batch size and mix proportions.