Figure 12-5. Sediment densitometer 



Pore pressure gauges 



Instrument Description. Ten pore pressure gauges were used during 

 SUPERTANK. Each gauge is fabricated from a DRUCK precision pressure 

 transducer and an environmental enclosure fitted with a porous stone. 



240 



DRUCK model PDCR 10 total pressure transducers were used as sensors 

 for pore pressure measurements. The sensing principle is a strain gauge 

 bridge bonded to a silicon diaphragm. Each pressure transducer is 

 approximately 2.25 in. (5.72 cm) long by 0.69 in. (1.75 cm) in diameter. A 

 four-core shielded cable includes a ventilation tube for reference of total 

 pressure to local atmospheric pressure. 



Each pressure transducer was enclosed in a 1-in. (2.54-cm) aluminum pipe 

 to protect the molded cable attachment from environmental abuse. Carborun- 

 dum porous stone isolates the pressure transducer from the sand environment. 

 The enclosure eliminates soil pressure from the measurement, providing a 

 separate measurement of pore water pressure. 



Location. Each pore pressure gauge and housing was hose clamped to a 

 1-in.- (2.54-cm-) diam aluminum rod, which was threaded into the stainless 

 steel inserts in the walls of the wave channel. The sensor head was located 

 approximately 1.5 ft (0.46 m) from the wall. A representative in-place gauge 

 is shown in Figure 12-6. 



Chapter 12 Pore Pressure and Sediment Density Measurements 



