To investigate the mechanical properties of shale under different strain rates

then to provide scientific guidance for the exploration of shale gas

the uniaxial compression experiments of shale samples have been conducted under strain rates of 5×10-4/s

1×10-4/s

1×10-5/s and 1×10-6/s

respectively. The experimental results show that the strain rates affect obviously on elastic modulus

peak strength and fracture morphologies

etc. of shale. Elastic modulus and peak strength gradually decrease along with the inclining of strain rate from high to low

but the decreasing speed becomes gradually smaller and smaller. The fitting relationship of elastic modulus (also peak strength) versus minus logarithm of strain rate largely adapts to the power function

whereas a higher fitting degree occurs if the mean values are implemented. Relatively speaking

the elastic modulus has a higher strain rate reaction. The fracture modes are obviously affected by the strain rate: under high strain rate

sample rapidly split into several large pieces and the entire skeleton ruptured; with the decreasing of strain rate

the fracture mode gradually transfers to main splitting failure with local shear failure; under the lowest strain rate

the main fracture mode is still splitting fracture but with many transverse cracks inserting the lateral surface; that is to say

the fracture mode under lowest strain is characterized by occurrence of cracks-net. In a word

the strain-rates affect the fracture morphologies most obviously

which performs mainly the relatively mean fracture and cracks net. Thus

these features of strain rate effect can provide important enlightenment for the parameters determination and hydro-fracture plan-design of shale.