Hydraulic fracturing has been used for the stimulation of petroleum and geothermal reservoirs, measurement of in-situ rock stress, waste injection, the remediation of soil and groundwater aquifers. However, due to different field geology, in-situ stress state and rock properties, the process of hydraulic fracturing becomes hard to predict and measure in field conditions. Moreover, there are still many problems related to hydraulic fracturing that need to be investigated, especially in the crack-tip zone. For the above reasons, all hydraulic fracture tests were conducted on hollow cylindrical specimens with 15mm in inner diameter, 100mm in outer diameter and 95mm in length and without pre-existing crack to produce experimental data for investigation of hydraulic fracture propagation and evolution of micro cracks.
Four different types of specimens were used in this research, such as coarse sand with or without fly ash and fine sand with or without fly ash. The crack propagation direction was controlled by applying a slight point load to the specimen. The pumping system together with automatic monitoring system could control the fluid driven rate to get the post-peak behavior. Two nondestructive testing techniques (acoustic emission and shear interferometry) were applied to monitor the micro behavior. In this study, fluid-driven fracture test was performed to simulate mode I tensile fracture, and instrumentation of the experiments (injection rate, tensile stress, evolution of micro crack, crack propagation) and testing procedures were presented. Finally, stress paths of experimental results were shown and the micro crack evolutions were plotted in two dimensions with three points of views.

Hydraulic fracturing has been used for the stimulation of petroleum and geothermal reservoirs, measurement of in-situ rock stress, waste injection, the remediation of soil and groundwater aquifers. However, due to different field geology, in-situ stress state and rock properties, the process of hydraulic fracturing becomes hard to predict and measure in field conditions. Moreover, there are still many problems related to hydraulic fracturing that need to be investigated, especially in the crack-tip zone. For the above reasons, all hydraulic fracture tests were conducted on hollow cylindrical specimens with 15mm in inner diameter, 100mm in outer diameter and 95mm in length and without pre-existing crack to produce experimental data for investigation of hydraulic fracture propagation and evolution of micro cracks.
Four different types of specimens were used in this research, such as coarse sand with or without fly ash and fine sand with or without fly ash. The crack propagation direction was controlled by applying a slight point load to the specimen. The pumping system together with automatic monitoring system could control the fluid driven rate to get the post-peak behavior. Two nondestructive testing techniques (acoustic emission and shear interferometry) were applied to monitor the micro behavior. In this study, fluid-driven fracture test was performed to simulate mode I tensile fracture, and instrumentation of the experiments (injection rate, tensile stress, evolution of micro crack, crack propagation) and testing procedures were presented. Finally, stress paths of experimental results were shown and the micro crack evolutions were plotted in two dimensions with three points of views.

Adachi, J.I. and Detournay, E. (2008). ”Plane strain propagation of a hydraulic fracture in a permeable rock.” Engineering Fracture Mechanics, Vol. 75, pp. 4666-4694.
Amadei, B. and Stephansson, O. (1997). Rock Stress and Its Measurement, 1st edition, Chapman & Hall, London.
Berumen, S., Tiab, D., and Rodriguez, F. (2000). ”Constant rate solutions for a fractured well with an asymmetric fracture.” J. Petrol. Sci. Eng., Vol. 25, pp. 49-58.
Brady, B. and Brown, E. (1985). Rock Mechanics for Underground Mining, George Allen & Unwin, London.
Bray, D.E. and McBride, D. (1992). Acoustic Emission Technology, Non Destructive Testing Techniques, New York.
Bunger, A.P., Detournay, E., and Jeffrey, R.G. (2005). ”Crack tip behavior in near-surface fluid-driven fracture experiments.” C. R. Mecanique, Vol. 333, pp. 229-304.
Bush, D.D. and Barton, N. (1989). ”Application of small-scale hydraulic fracturing for stress measurements in bedded salt.” Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. Vol. 26, No. 6, pp. 629-635.
Chen, Z. (2012). ”Finite element modeling of viscosity-dominated hydraulic fractures.” J. Petrol. Sci. Eng. Vol. 88-89. Pp. 136-144.
Delaney, P.T. and Pollard, D.D. (1981). ”Deformation of host rocks and flow of magma during growth of Minette Dikes and Breccia-bearing Intrusions near Ship Rock, New Mexico.” Geological Survey Professional Paper 1202, U.S. Government Printing Office, WA.
Garagash, D.I. and Detournay, E. (2000). ”The tip region of a fluid-driven fracture in an elastic medium.” Trans. ASME: J. Appl. Mech., Vol. 67, pp. 183-192.
Hayashi, K., Sato, A., and Ito, T. (1997). ”In situ stress measurements by hydraulic fracturing for a rock mass with many planes of weakness.” Int. J. Rock Mech. Min. Sci., Vol. 34, pp. 45-58.
Haimson, B.C. (1989). ”Standard test method for determination of the in-situ stress in rock using the hydraulic fracturing method.” Annual Book of ASTM Standards, 04/08, 851-6.
Haimson, B.C. (1993). ”The hydraulic fracturing method of stress measurement: Theory and Practice.” Comprehensive rock engineering, Vol. 3, pp. 395-411.
Hubbert, M.K. and Willis, D.G. (1957). ”Mechanics of hydraulic fracturing.” J. Petrol. Techol., Vol. 9, pp. 153-166.
Hung, Y.Y. and Hovanisian, J.D. (1972). Exp. Mech. pp. 454-460.
Hung, Y.Y. (1999). ”Applications of digital shearography for testing of composite structures.” Composites Part B: Engineering, Vol. 30, pp. 765-773.
Hunt, J.L., Frazier, K., Pendergraft, B.P., and Soliman, M.Y. (1994). ”Evaluation and completion procedure for produced brine and waste-water disposal wells.” J. Petrol. Sci. Eng., Vol. 11, pp. 51-60.
Ito, T., Evans, K., Kawai, K., and Hayashi, K. (1999). ”Hydraulic fracture reopening pressure and the estimation of maximum horizontal stress.” Int. J. Rock Mech. Min. Sci., Vol. 36, pp. 811-826.
Leendertz, J.A. (1970). ”Interferometric displacement measurement on scattering surfaces utilizing speckle effect.” J. Phys. E., (J. Sci. Instrum.), Vol. 3, pp. 214.
Leendertz, J.A. and Butters, J.N. (1973). ”An image-shearing speckle-pattern interferometry for measuring bending moments.” J. Phys. E, Vol. 6, pp. 1107-1110.
Lockner, D.A. and Byerlee, J.D. (1991). ”Precursory AE patterns leading to rock fracture.” In Proc., 5th Conf. on Acoustic Emission/Microseismic Activity in Geology Structures and Materials. Pennsylvania State Univ.
Maji, A.K. and Shah, S.P. (1989). ”Application of acoustic emission and laser holography to study microfracture in concrete.” In Nondestructive Testing, Sp-11, pp. 83-109. Amer. Concrete Inst., Detroit, Michigan.
Maji, A.K., Tasdemir, M.A., and Shah, S.P. (1991). ”Mixed mode crack propagation in quasi-brittle materials.” Eng. Fract. Mech., Vol. 38, pp. 129-145.
Murdoch, L.C. and Slack, W.W. (2002). ”Forms of hydraulic fractures in shallow fine-grained formations” J. Geotech. Geoenviron., Vol. 128, pp. 479-487.
Pollard, D.D. and Aydin, A. (1988). ”Progress in understanding jointing over the past century.” Geol. Soc. Am. Bull., Vol. 100, pp. 1181-1204.
Pollard, D.D., Segall, P., and Delaney, P.T. (1982). ”Formation and interpretation of dilatant echelon cracks.” Geol. Soc. Am. Bull., Vol. 93, pp. 1291-1303.
Raaen, A.M., Skomedal, E., Kjorholt, H., Markestad, P., and Okland, D. (2001). ” Stress determination from hydraulic tests: the system stiffness approach.” Int. J. Rock Mech. Min. Sci., Vol. 38, pp. 529-541.
Thomas, A.L. and Pollard, D.D. (1993). ”The geometry of echelon fractures in rock: implications from laboratory and numerical experiments.” J. Struct. Geol., Vol. 15, pp. 323-334.
Wu, R. (2006). ”Some fundamental mechanisms of hydraulic fracture.” Ph.D. Thesis, Georgia Institute of Technology, GA.