Test Caisson Installation
This galleries of pictures shows the work sequence for the installation of three test caissons at Fajardo River Bridge (AC -019406). All test caisson were instrumented with Arc Welded Vibrating Wire Strain Gauges. Each caisson was provided at its 1/3 point with a stran gauges.
After welding the mounts of the VW to a 4 ft long No. 7 rebar, the rebar section is tie next to a structural rebar of the caisson. The VW is check prior to installation into the hole
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The length of 15 inch diamter test caisson was 48, 63 and 75 ft long.
An initial 16 inch case 5 ft deep is installed at each of the location. A slot 2 ft long 0.5 inch wide cut 1 ft from the top of the case is made to the initial case. The purpose of the initial case is to provide a lateral side exit to the instrument cables since during the load testing a hydraulic jack will load the caisson from the top. The 15" center hole is drilled to the requiered depth and a 12 inch diameter casing is intalled.
The steel cage is then lifted and place within the case hole.
A final check is made to the VW prior to placed the concrete.This picture shows the 12 inch casing and the 16 inch slotted casing.
A tremie pipe is lowered to the bottom of the case. In this phase of operation is were damages to the VW is most likely to occur.
The concrete mix is dump in to a concrete pump truck and pump to the bottom of the casing. A special connection call Heavy Duty Groove is used to connect the concrete pump 3" concrete hose (standard groove) to the trenie pipe (NPT). Almost certain that any other connection would have cuased a rupture of the connection between the concrete hose and the tremie due to the pressure used.
Water is displaced by the concrete as it lift from the bottom of the caisson. The pressure use for pumping the concrete will tend to lift the tremie pipe or event the steel rebar cage. This could be prevented by tie-in the tremie pipe to the steel case or by lifting the trimie pipe.
When the concrete reach the surface, the tremie pipe is removed and the 12 inch case is lifted.
The tremie pipe is re inserted since the concrete will displaced to cover the volume difference between the 12 inch case and the 15 inch hole. Some concrete will be lost within the formation. After the concrete reach the surface, the 16 inch case with single slot is lifted from the ground 1.5 ft , leaving a 6 inch long slot above ground 6 inch below ground to be able to extend the VW cable through the side of the test caisson.
The Finish Caisson
A load test is setup with dead weight above the caisson.
Heavy Beans are used to support over 250 tons in dead weight.
The results of the instrumentation of this particular test caisson is as follows: