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Hydraulic Fracturing Stress Measurements and Their Implication for the Design of the First Concrete Lined Pressure Shaft in Sri Lanka



Author(s)

Hadi Barghamadi1, P. Nater1 and P. Huwyler2

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DOI:10.17265/2332-8215/2016.01.007

1. Mahab Ghodss Consulting Engineering Co., Tehran, Iran 2. Pöyry Switzerland Ltd., 161 8037 Zurich, Switzerland

The Uma Oya Multipurpose Development Project (UMDP) is a water transfer, hydropower and irrigation in the south-eastern part of the central highland region of Sri Lanka. During geotechnical site investigation program 42 hydraulic fracture tests and 42 impression packer tests were carried out in 3 boreholes to about 840 m depth. Based on the stress measurements the minimum and maximum horizontal stress ratios were calculated. In situ stress computations at all the tests were based on the assumption that the principal stress components were vertical (v) and horizontal (H and h, the maximum and minimum, respectively). The results of the measurements had a direct impact on the design of the major openings bearing a high overburden—the underground powerhouse and the transformer cavern—and revealed a significant optimization potential concerning the selection of the lining system of the pressure shaft.

Hydraulic fracturing, stress measurement, in situ stress, vertical stress, horizontal stress, pressure shaft