A vacuum-refilled tensiometer for deep monitoring of in-situ pore water pressure

Document Type : Article


1 Department of Civil Engineering, Sharif University of Technology, Tehran, Iran

2 Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Professor, Hohai University, Nanjing, China

3 Department of Civil and Environmental Engineering, Chair Professor, Hong Kong University of Science and Technology, Hong Kong


Real-time measurement of soil water pressure has been recognized as an essential part of investigating water flow in unsaturated soils. Tensiometry, amongst different measuring techniques, is a common method for direct evaluation of water pressure. However, the lower limit of measurable water pressure by a conventional tensiometer becomes even more limited by increasing its length in the vertical installation. This paper describes development of a vacuum-refilled tensiometer (VRT) for monitoring soil water pressure independent of installation depth. This is achieved by fixing the distance between pressure sensor and ceramic cup together with incorporating an ancillary vacuum-refilling assembly into its design. The assembly allows for more efficient replacement of diffused air into the ceramic cup and reservoir with water. The new tensiometer is designed to withstand both negative and positive water pressure of up to almost one bar. In addition, the response time of the tensiometer to a change in negative water pressure for its working range (≥ -80 kPa) is very quick, in the order of seconds and one minute at most. The long-term performance of the new tensiometer is evaluated through a five-month monitoring program in the laboratory, simulating cyclic wetting and drying in the field.


Main Subjects

1. Livingston, B.E. A method for controlling plant
moisture", The Plant World, 11, pp. 39{40 (1908).
2. Or, D. History of soil science who invented the
tensiometer?", Soil Sci. Soc. Am. J., 65, pp. 1{3
3. Tarantino, A., Ridley, A.M., and Toll, D.G. Field
measurement of suction, water content, and water
permeability", Geotech. Geolo. Eng., 26, pp. 751{782
4. Marinho, F.A.M., Take, W.A., and Tarantino, A.
Measurement of matric suction using tensiometric
and axis translation techniques", Geotech. Geolo. Eng.,
26, pp. 615{631 (2008).
5. Stannard, D.I. Tensiometers-theory, construction,
and use", Geotech. Test. J., 15, pp. 48{58 (1992).
6. Bianchi, W.B. Measuring soil moisture tension
changes", J. Agricul. Eng., 43, pp. 398{399 (1962).
7. Watson, K.K. A recording eld tensiometer with
rapid response characteristics", J. Hydro., 5, pp. 33{39
8. Hubbell, J.M. and Sisson, J.B. Advanced tensiometer
for shallow or deep soil water potential measurements",
Soil Sci., 163, pp. 271{277 (1998).
9. Sisson, J.B., Gee, G.W., Hubbell, J.M., Bratton,
W.L., Ritter, J.C., Ward, A.L., and Caldwell, T.G.
Advances in tensiometry for long-term monitoring of
soil water pressures", Vadose Zone J., 1, pp. 310{315
10. Faybishenko, B. Tensiometer for shallow and deep
measurements of water pressure in vadose zone and
groundwater", Soil Sci., 165, pp. 473{482 (2000).
11. Raj, M. and Sengupta, A. Rain-triggered slope failure
of the railway embankment at Malda, India", Acta
Geotech., 9(5), pp. 789{798 (2014).
12. Garg, A., Li, J., Hou, J., Berretta, C., and Garg, A. A
new computational approach for estimation of wilting
point for green infrastructure", Measurement, 111, pp.
351{358 (2017).
13. Ridley, A.M., Dineen, K., Burland, J.B., and Vaughan,
P.R. Soil matrix suction: Some examples of its measurement
and application in geotechnical engineering",
Geotechnique, 53, pp. 241{253 (2003).
14. Hubbell, J.M. and Sisson, J.B. Portable tensiometer
use in deep boreholes", Soil Sci., 161, pp. 376{381
15. Oliveira, O.M. and Marinho, F.A.M. Suction equilibration
time for a high capacity tensiometer", Geotech.
Test. J., 31, pp. 101{105 (2008).
16. Liu, J., Chen, R., Sadeghi, H., and Ng, C.W.W. A
eld study of stress-dependent soil-water characteristic
curves and permeability functions of a loess soil for
land ll covers", The 1st Int. Conf. on Geo-Energy and
Geo-Environment, 1, Hong Kong, pp. 118{119 (2015).
17. ASTM Standard practice for classi cation of soils
for engineering purposes (uni ed soil classi cation
system)", ASTM standard D2487, Am. Soc. for Test.
and Mat., West Conshohocken, Pa (2006).
18. Ng, C.W.W., Sadeghi, H., and Jafarzadeh, F. Compression
and shear strength characteristics of compacted
loess at high suctions", Can. Geotech. J., 54(5),
pp. 690{699 (2017). https://doi.org/10.1139/cgj-2016-
19. Ng, C.W.W., Baghbanrezvan, S., Sadeghi, H., Zhou,
C., and Jafarzadeh, F. E ect of specimen preparation
techniques on dynamic properties of unsaturated negrained
soil at high suctions", Can. Geotech. J., 54(9),
pp. 1310{1319 (2017). https://doi.org/10.1139/cgj-
20. Sadeghi, H., Hossen, S.B., Chiu, A.C.F., Cheng, Q.,
and Ng, C.W.W. Water retention curves of intact and
re-compacted loess at di erent net stresses", The 15th
Asian Reg. Conf. on Soil Mech. and Geotech. Eng.
(15ARC), Geotech. Soc. Spec. Publ., 2(4), Fukuoka,
Japan, pp. 221{225 (2016).
21. Ng, C.W.W., Sadeghi, H., Hossen, S.B., Chiu, A.C.F.,
Alonso, E.E., and Baghbanrezvan, S. Water retention
and volumetric characteristics of intact and recompacted
loess", Can. Geotech. J., 53(8), pp. 1258{
1269 (2016). https://doi.org/10.1139/cgj-2015-0364
606 H. Sadeghi et al./Scientia Iranica, Transactions A: Civil Engineering 27 (2020) 596{606
22. Ridley, A.M., Marsland, F., and Patel, A. Tensiometers:
their design and use for civil engineering
purposes", Proc. of the 1st Int. Conf. on Site Charact.,
2, Atlanta, pp. 851{856 (1998).
23. Whalley, W.R., Lock, G., Jenkins, M., Peloe, T., Burek,
K., Balendonck, J., Take, W.A., Tuzel, I.H., and
Tuzel, Y. Measurement of low matric potentials with
porous matrix sensors and water- lled tensiometers",
Soil Sci. Soc. Am. J., 73, pp. 1796{1803 (2009).