Investigation of the effect of heavy construction nearby bench‐marks

Abstract

The investigation under discussion has resulted from a growing conviction on the part of some of us in the Section of Leveling of the Coast and Geodetic Survey that, in many cases at least, poor checks obtained in repeat leveling, when starting or tieing out new lines of levels, result from lack of stability of the bench‐marks instead of “sloppy leveling” as is often assumed. It seems only natural to be skeptical of the stability of a bench‐mark in the top of a concrete post extending 3‐½ or 4 feet into the ground and to believe that a bench‐mark in the foundation of a large building or a heavy bridge‐abutment will maintain its original elevation. However, we have gradually been forced to the conclusion that not all is stable that looks that way and in order to test, under controlled conditions as far as possible, the possibility that massive structures can undergo changes in elevation, we started wishing for a big construction job, conveniently located on which we could experiment. About that time the new War Department Building across the Potomac River was proposed and we began scheming to make this gigantic building produce a by‐product of possible interest to the surveying profession.