In this study

semi-diagenetic rock specimens of the Xigeda Formation in Zhaizi village on Jinshajiang River were investigated. The mineral composition of the specimens was determined by X-ray diffraction (XRD)

and the microstructure and change of mineral particles in natural and saturated states were observed by scanning electron microscopy (SEM). The influences of water and confining pressure on the strength and deformation of semi-diagenetic rock of Xigeda Formation were determined using triaxial compression test. And the microcosmic mechanism was also discussed. The strength characteristics of the semi-diagenetic rocks of Xigeda Formation different from that of the soil and the soft rock were revealed by statistical analysis of the relationship between the strength indexes and water content of rock

soil and soft rock. On the basis

engineering classification suggestions for the semi-diagenetic rocks of Xigeda Formation were given. Based on the above research

some conclusions are as follows. 1) The microstructure shows that the semi-diagenetic rock of Xigeda formation has weak cementitious structure which is obviously different from that of soil and rock. The cementation structure is easy to be destroyed after saturation. 2) The cohesion and friction angle of semi-diagenetic rock decrease with the increase of water content. The average modulus increases with the increase of confining pressure at high water content

it decreases with the increase of moisture content when the confining pressure is constant. 3) The order of cohesion is soft rock> semi-diagenetic rock of Xigeda Formation>soil. The sensitivity of the cohesion to the water content is soft rock> semi-diagenetic rock of Xigeda Formation>soil. The sensitivity of the friction angle to the water content is soil > semi-diagenetic rock of Xigeda Formation> soft rock. 4) The rocks or soils should be classified as hard soil-soft rock

with the uniaxial compressive strength between 0.2 and 3 MPa

and cohesion between 30 and 200 kPa

measured from a standard specimen (Φ 50 mm×100 mm). It is suggested that it should be distinguished from rock and soil in practical engineering application.