Method and Apparatus for Ground Improvement Using Compacted Aggregate Columns

Abstract

An apparatus and method for forming compact aggregate columns. The apparatus includes an aggregate materials hopper; a hollow mandrel adapted to be driven into the ground; a plurality of rubber bearing isolators disposed between the mandrel and the hopper for reducing transmission of vibratory energy between the mandrel and the hopper, and a rubber seal encircling and moulded to the outer circumference of the mandrel for preventing aggregate leakage from the hopper; flow control means comprising a stone gate or hinged tip convertible between an open position and a closed position for controlling aggregate flow, one or more collars encircling the mandrel disposed along the length of the mandrel, each collar having an outer circumference greater than the mandrel circumference; a vibratory hammer attached to a vehicle for inserting and removing the mandrel into the ground; and a monitoring and control system in the cab of the vehicle.

1 . An apparatus for forming compact aggregate columns, the apparatus comprising:
 an aggregate materials hopper having a top opening and a bottom opening;   a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an aggregate receiving opening;   connection means between the hopper and the mandrel;   flow control means, for controlling the flow of aggregate from the hopper through the mandrel;   soil densification means disposed along the length of the mandrel;   a vibratory hammer for inserting and removing the mandrel into the ground; and   monitoring and control means.   
     
     
         2 . The apparatus of  claim 1 , wherein the connection means comprises one or more rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal between the mandrel and the hopper. 
     
     
         3 . The apparatus of  claim 2 , wherein the one or more rubber bearing isolators comprise  4  isolators. 
     
     
         4 . The apparatus of  claim 2 , wherein the one or more rubber bearing isolators comprise  8  isolators. 
     
     
         5 . The apparatus of  claim 2 , wherein the rubber seal encircles and is moulded to the mandrel. 
     
     
         6 . The apparatus of  claim 1 , wherein the mandrel has an enlarged diameter bottom section and the flow control means comprises a stone gate convertible between an open position to allow aggregate flow from the hopper to the mandrel, and a closed position to prevent aggregate flow from the hopper to the mandrel. 
     
     
         7 . The apparatus of  claim 1 , wherein the flow control means comprises a hinged tip connected to the bottom of the mandrel and convertible between an open position to allow aggregate flow from the bottom of the mandrel, and a closed position to prevent aggregate flow from the bottom of the mandrel. 
     
     
         8 . The apparatus of  claim 1 , wherein the soil densification means comprises one or more collars encircling the mandrel, each collar having an outer circumference greater than the mandrel circumference. 
     
     
         9 . The apparatus of  claim 8 , wherein the one or more collars are disposed at spaced intervals along the length of the mandrel. 
     
     
         10 . The apparatus of  claim 9 , wherein the one or more collars are disposed at intervals of  5  feet along the length of the mandrel. 
     
     
         11 . The apparatus of  claim 1 , wherein the vibratory hammer is attached to a vehicle. 
     
     
         12 . The apparatus of  claim 11 , wherein the monitoring and control means includes hydraulic systems monitored and controlled from the cab of the vehicle. 
     
     
         13 . An apparatus for forming compact aggregate columns, the apparatus comprising:
 a materials hopper having a top opening and a bottom opening;   a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an enlarged diameter bottom section and an aggregate receiving opening;   between 4 and 8 rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal encircling and moulded to the outer circumference of the mandrel;   a stone gate convertible between an open position to allow aggregate flow from the hopper to the mandrel, and a closed position to prevent aggregate flow from the hopper to the mandrel;   one or more collars encircling the mandrel disposed at spaced intervals along the length of the mandrel, each collar having an outer circumference greater than the mandrel circumference;   a vibratory hammer attached to a vehicle for inserting and removing the mandrel into the ground; and   a monitoring and control system in the cab of the vehicle.   
     
     
         14 . An apparatus for forming compact aggregate columns, the apparatus comprising:
 a materials hopper having a top opening and a bottom opening;   a hollow mandrel adapted to be driven into the ground, its upper end passing through the bottom opening in the hopper, and having an aggregate receiving opening;   a plurality of rubber bearing isolators disposed between the mandrel and the hopper, and a rubber seal encircling and moulded to the outer circumference of the mandrel;   a hinged tip connected to the bottom of the mandrel and convertible between an open position to allow aggregate flow from the bottom of the mandrel, and a closed position to prevent aggregate flow from the bottom of the mandrel;   one or more collars encircling the mandrel disposed at spaced intervals along the length of the mandrel, each collar having an outer circumference greater than the mandrel circumference;   a vibratory hammer attached to a vehicle for inserting and removing the mandrel into the ground; and   a monitoring and control system in the cab of the vehicle.   
     
     
         15 . A method for preparing compacted aggregate columns comprising the steps of:
 filling a hollow mandrel with aggregate from a hopper above the mandrel through an opening in the side of the mandrel;   closing a stone gate near the upper end of the mandrel to prevent aggregate from rising in the mandrel;   driving the mandrel into the ground with a vibratory hammer, wherein driving the apparatus into the ground displaces the soil outwardly and downwardly from the mandrel to create a hole extending downwardly from the ground surface, and compacts aggregate present in the hole into an aggregate column;   withdrawing the mandrel, thereby allowing aggregate to exit the mandrel into the hole;   opening the stone gate to allow more aggregate to fill the mandrel; and   repeating the above steps until a compacted aggregate column of a desired length is achieved.   
     
     
         16 . A method for preparing compacted aggregate columns comprising the steps of:
 filling a hollow mandrel of the type having a hinged tip at its lower end with aggregate from a hopper above the mandrel;   driving the mandrel into the ground with a vibratory hammer, wherein driving the apparatus into the ground displaces the soil outwardly and downwardly from the mandrel to create a hole extending downwardly from the ground surface, and compacts aggregate present in the hole into an aggregate column;   withdrawing the mandrel, thereby causing opening of the hinged tip to allow aggregate to exit the mandrel into the hole;   repeating the above driving and withdrawing steps until a compacted aggregate column of a desired length is achieved; and   adding aggregate to the hopper as necessary to maintain the mandrel full of aggregate.