Load Transfer System

Abstract

This is a new type of pile foundation for support of structures. It uses a new method of forming concrete around the steel rebar prior to installing the rebar. Concrete is molded in an undulating fashion to improve load transfer to the adjacent hole backfill. The backfill is densified in place and grouted to maintain the dense configuration. The grouting is injected into an unlined hole. If temporary casing is used during drilling, it is removed prior to grouting. The basic premises are that grouting the hole backfill to the surrounding soil provides a better load transfer at that interface. And, beyond a few inches past the steel rebar, grouted dense sand and gravel are adequate for the load at that point. Timing of the grouting is more flexible than typical ready-mix concrete delivery systems. This method also allows for real time testing of the pile capacity.

1 . First claim of this application is that the pile will function the same if the concrete is only placed around the rebar for a few inches, and the remainder of the hole is filled with dense sand and gravel. Due to the lower stress level as discussed above the grout locking the dense sand and gravel in-place does not need to be as strong as Portland cement. The other advantage to grout is a quick set time allows for real-time testing to ensure the load capacity of the pile. What is necessary is to mold the concrete in an undulating fashion so that the sloping surface places a compressive load on the dense sand and gravel. Second claim is the grout will penetrate the surrounding soil thus giving the pile the capacity of a larger diameter then the drill size of the hole. The amount of penetration is dependent upon the soil condition and the type of grout that is being used. Third claim The load transfer process described herein works just as well in reverse. The transfer of load from soil to steel rebar is just as efficient as load going from rebar to foundation soil. This load transfer makes it possible to support soil where lateral support soil is being removed. This commonly occurs with temporary or permanent excavations. If the soil adjacent to the proposed cut is first vertically supported then the cut is stable because the supported soil has become a gravity wall. Fourth claim using multiple piles drilled and set in an area adjacent to a proposed cut for a retaining wall will result in lower load on the wall. This is due to the grouted piles providing vertical support for the soil adjacent to the cut. Vertical support for the soil adjacent to the cut reduces or eliminates the driving force that creates the load on the retaining wall, temporary shoring. In the case of temporary shoring it is possible to use threaded rebar and mold the concrete around a threaded sleeve. Once the temporary excavation is backfilled the threaded rebar can be unscrewed from the shoring pile and reused. Fifth claim The same load transfer system can be accomplished using smaller bent rebar attached and around the main load carrying rebar. Two examples of this type of system are provided herein. One uses small rebar twisted to form a spiral node and the other uses multiple bent rebar to form a node. The main advantage to these systems are they can be formed on site using standard rebar and be put into use immediately.