Evaluation of ground and building settlement near braced excavation sites by model testing

Abstract

Braced excavations inevitably result in deformation of the adjacent ground and settlement of adjacent buildings behind the wall. Building settlement is believed to exceed the amount of associated ground settlement because of the additional settlement under building weight. This is due to a decrease in stiffness of the foundation soil that is caused by lateral movement of the excavation face. To quantify the amount of building settlement, model testing was conducted to determine the magnitude of the additional settlement due to the structure and the effect of varying the building's depth in the ground and of its distance away from the excavation wall. The building's settlement, when at ground level, was found to be up to 500% more than that of ground with no structure on it. This is for the case when the building's centroid on the ground surface is located within Rankine's active zone. When the building was embedded in the ground the degree of additional settlement decreases very rapidly, becoming negligible if the building is embedded at more than one half of the excavation depth. Additional model testing was conducted to estimate the extent of the soil improvement zone required to protect structures adjacent to an excavation. From the model testing results, soil improvement should be performed to reduce building settlement when the building's centroid is located in the excavation influence zone. The zone for this soil improvement is determined by setting the distance away from the excavation wall to be equal to the depth of the excavation.Key words: braced excavations, model testing, ground settlement, additional settlement volume, angular distortion, soil improvement.