While technology significantly transformed our lives, we tend to forget the civil engineering paved the way for advancement much before the evolution of technology. We even forget to thank the giant role civil engineering played in helping every necessity turn to reality. Right from bridges to pavements to irrigation projects, we owe to the civil engineering for whatever we enjoy today.
As the civil engineering field advanced, a new design cropped up to support the existing demands from the public at large throwing major challenges at geo-technical engineers. Be it the extra basements to support the multi-level parking or to create an underground road passage, the need for deep excavation popped-up.
Why do we call it a challenge?
The reason is simple—when a geo-technical engineer performs deep excavation, the foundation drilling machine encounters with different layers of soil—including and not limited to rock. At times, dynamites might be used to break the rocks. The vibrations and impact caused due to the same can show a negative impact on not just that structure but even the surrounding structures.
A 13-storied huge building collapsed in Shanghai during a deep excavation process in 2009 and went into history as one of the worst building collapses. The studies ascertained that the building wasn’t constructed properly and that there was no study nor analysis done before going ahead with deep excavation. There were many such incidents that were reported even in the United States. Since then extra care has been taken and authorities have clearly laid out the norms for deep excavation. Every civil engineering company that undertakes a deep foundation must necessarily have a registered Professional Engineer (P.E) who would roll out the blueprint of the entire project and process post which the following things need to be adhered to:
- Site Characteristics: A geo-technical engineer is required to examine the site and understand the soil properties. A thorough lab examination of the soil needs to be conducted besides understanding the length of the pile and its type. Needless to mention, the age of the structure also matters. Deep excavation of a dam or a heavy structure that’s 10+ years is risky.
- Dimensions: The excavation should be done through a proper plan without causing any damage to the structure or its foundation. It is pertinent that the site engineer has the blue print of the original structure plan to assess and plan the dimensions for deep excavation.
- Surveying Adjacent Soils: In case deep excavation is carried out in sandy soils, the structure is prone to damage. Same is the case with silty soils although certain measures can be taken regarding the later. Clay soil is ideal for deep excavations and hence it is the duty of an engineer to survey the adjacent soils and prepare a report based on which further action should be taken.
- Surveying Adjacent Structures: If a deep excavation is to be carried out near a dam, an engineer must ensure that there are no heavy structures within a radius of 500 meters failing which it would impact the foundation of the adjacent buildings. A no objection certificate from the adjacent structure owners or from the authority should be obtained if required.
Excavation support design is a sensitive job and should be carried out only be a P.E who has expertise in geotechnical and structural engineering. Further, deep excavations should be supported by:
- Conventional retaining walls
- Sheet pile walls
- Braced walls
- Diaphragm walls