presented for interpreting the in-situ test data in terms of the measured 

 sediment properties. The resulting technique should be considered as a 

 tentative method which needs to be substantiated by additional tests in a 

 greater variety of sediments and by the actual performance of foundations. 



TEST EQUIPMENT 



The in-situ plate bearing device, Figures 1 and 2, provides a remote 

 means for forcing a small spread footing into the seafloor at a controlled rate 

 and measuring the resulting load on the footing versus displacement. Mechan- 

 ically, the device consists of a moveable weight holder with a bearing plate 

 attached to it. The weight holder is supported and its vertical displacement 

 rate controlled by three closed-circuit, pressure-equalized hydraulic cylinders. 

 A tripod framework, supported on three articulated bearing pads, guides the 

 weight holder. The device is connected to its surface support vessel via a syn- 

 thetic rope which attaches to the top of the weight holder. When the line is 

 taut (during lowering or raising operation), the weight holder and bearing 

 plate are in the "test ready" or retracted position; when slack (after the 

 device is on the bottom), the weight holder moves downward forcing the 

 bearing plate into the sediment. The equipment can accommodate a variety 

 of bearing plates ranging in size up to 1 .5 feet in diameter and can apply a 

 maximum load of 6,000 pounds. 



The instrumentation system provides sensors for measuring load and 

 displacement of the bearing plate and vertical orientation of the device. The 

 load transducer, located immediately above the bearing plate, consists of a 

 strain-gaged element enclosed in an oil-filled pressure-equalized case.* The 

 plate displacement is measured using a linear potentiometer which is mounted 

 on the framework with the potentiometer's plunger connected to the moveable 

 weight holder as shown in Figure 1 . The vertical orientation of the device is 

 indicated by a pendulum mounted on a rotary potentiometer. The techniques 

 for measuring displacement and vertical orientation are essentially the same as 

 described in the performance evaluation report.^ The signal conditioning and 

 telemetry system has been modified considerably since last reported on how- 

 ever. The variable voltage signals from the sensors are converted to variable 

 frequencies and are transmitted acoustically to the surface as an FM signal on 

 a carrier frequency of 40 kHz. A hydrophone aboard the surface vessel is used 

 to sense the signal which is then discriminated to produce individual analog 



This unit replaces the spring and linear potentiometer method for load measuring which 

 was described in the initial evaluation report on the device.^ 



