As a basis of crack research of expansive soil

crack features of quantitative description contributes to further investigate the influence of cracks on engineering properties of expansive soils. Taking surface cracks of expansive soil as research objects

crack images are captured by using digital imaging

and parametes of crack features are obtained through optimizing and improving methods of crack image processing and crack feature extraction. For methods of crack image processing

it showed that improved local threshold binarization method could distinguish crack and background better than Ostu method. By marking connected areas

globally distributed noises on the crack binary image is eliminated effectively; and employing closing operation

tiny holes and gaps could be filled. The above methods make the crack binary image clearer and more reliable. For crack feature extraction methods

lookup table method is adopted to quickly identify crack endpoints and intersections

which helps count number of crack branches. Improved endpoints recognition algorithm was used to remove burrs from crack trunk

which makes the statistics of crack length more accurate. And improved minimum enclosing rectangle algorithm is used for statistics of crack width

which improves the calculation accuracy and saves the calculation time. Rose diagram is employed for statistics of crack orientation

which could be more intuitive to analyze the change law of crack orientation and number.