Normally a strain gauge installed in a test pile is used to determine how does a applied load be transfered from top to bottom. The principle is based on elatic shortening theory of a single pile. Meanwhile there should be have an another set of tell-tale (or extensometer)to measure the displacement profile along the pile shaft. The purpose of tell-tale is to determine the elastic compression of pile and subsequently a t-z relationship for soils may be established. Somehow I found there is inconsistent for the elastic shortening of pile using the strain gauge and tell-tale. Anyone has the same experience before? What would be the possible reasons behind ?