Be prepared! The importance of pre-construction site investigation - by Stephen Lampard

As we all know, when working within the boroughs, it is inevitable that one of your projects will end up with an adjacent structure neighboring the property line. This situation is unique to most but for New York builders, developers, and design professionals, it is nothing we have not encountered before. That being said I would like to share a few recent experiences that have occurred on job sites to remind us all of the challenges that may arise when working in such conditions.

Please see below the specific scopes of work which have been gathered in various stages and or facets of a new construction project. 

Sub Surface Investigation

• The more information the better! As developers and construction professionals, you are always better off spending a little more for additional borings and the front end analysis of the site and surrounding sites existing soil conditions.

• Believe what the geotechnical engineer is presenting. In most cases, the soil investigation can show that the soils beneath the existing structures can be pretreated prior to any work commencing. This can be used as a means of mitigating adjacent property movement.

• Understand the water table and how it can affect proposed construction activities. Have a game plan that deals in the reality of water conditions will go a long way in mitigating neighboring building movement.

Drilling of Piles and Caissons

Plan, develop, and purchased into the contractors scope a drilling technique that mitigates issues during the drilling process. The most common method used is known as “Duplex Drilling.” This is a process by which the roller hammer used for cutting through the soils stays a minimum distance up inside the steel casing. This ensures all drilling fluid and/or air passes from the roller but back up and out the top of the casing.

The redirecting of drilling fluid away from adjacent property foundations is essential. By doing so, one can avoid over-saturation of soil beneath foundations of adjacent structures and thereby reduce risk of soil characteristics becoming altered and consolidating in an unpredictable manner.

The following construction activities, on their own or combined together, create an environment for which the changing of soil characteristics is an unavoidable conclusion and thus making building movement a reality:

• Air loss outside the casing into soil during drilling of piles/caisson.

• Loss of drilling fluid outside the casing into soil during drilling of piles/caisson.

• Over saturation of the project site via drilling fluid

•Being prepared is the only way to be proactive and productive.  Spending more up front to investigate your site and your adjacent property will save you in the end.

Stephen Lampard is vice president of technical services at Domani Inspection Services, Valley Stream, N.Y.