A Field Investigation Into the Performance of Inclined Strutsconnected to Adjacent Buildings During Excavation

Geotechnical designs are commonly based on several assumptions. Regardless of limitations caused by the inherent variability of soil and its unknown behavior، field measurements by the site instrumentation provide opportunities to have a safe and efficient design. Therefore، instrumentation has an important role in geotechnical research and professional studies. With the development of urban construction، excavations adjacent to buildings have increased dramatically. With large changes in stress distribution due to excavation، displacements may occur in the adjoining buildings and the soilmass. In urban excavations، the control of displacements created in soil and adjacent buildingshave always been an important issue due to the risk of damages. An optimum design and safe operation of the supporting system require a full understanding of the load distribution and displacement patterns in it. A simple traditional method in protecting the excavations is the use of inclined struts. This method،commonlyusedinIran،is the use of inclined strutsto support the adjacentbuildings. This method is not merely used in large excavations، but it is very popular for small to medium size excavations because of long-term traditional uses in Iran. Althoughthe mentioned method has practical applications but it is not fully investigated. It is necessary to investigate the presented method to determine itsadvantages and disadvantages as well as the limitations and the appropriate scope of its application. Some theoretical and numerical studies have been conducted in this regard and in fact the primary understanding of the performance mechanism of inclined struts and the loads acting on them are based on numerical studies. Thispaper reports the results of aninstrumentation undertakenon inclined struts during excavation and presentsvaluable informationaboutthe performance of such struts. In addition، a two dimensional numerical modelingwas performedand calibrated in order toverifythe mechanism ofstruts performance observed in thefield monitoring. The results proposethe mechanismof the inclined struts during excavation beside existing buildings as follows: (a) Partofthe load of the adjacent building ispassed to the bottom of the excavation through theinclined strutand consequentlyless pressure is exertedonthesoilbeneath the foundation. Therefore the amount of settlement beneath the foundation decreases. This mechanism suggests that inclined struts act as underpinning. (b) The inclined strutreduces the horizontal displacements of the excavation wall and the neighboring buildings due to the lateral constraintsit creates. As described below، the reduction of horizontal displacement has a significant impact on reduction of damage in neighboring buildings. Moreover، the paper in troduces a set of simpleinstrumentations which are designed in the course of the presented study andcan beusedin common engineering practice for small to medium size excavations. Monitoring is commonly neglected in small or medium projects but the use of proposed set of monitoring tools could play an important roleto increase safety and also in the investigation of excavations in urban areas.