This paper presents the development of a shallow foundation system consisting of mat foundations for support of all structures including heavily loaded, settlement sensitive structures at a recently completed Polysilicon Plant in China. The site grading for the 700 by 700 m (2297 by 2297 ft) site included up to 15 m (49.2 ft) of fills and 18 m (59.1 ft) of cuts. The soil conditions consisted of native residual stiff clays overlying siltstone/mudstone and conglomerate bedrock. Soft soils were present in the canyon bottoms and at the contact between stiff soils and bedrock.
Settlements of native soils and bedrock were measured during site grading when up to 15 m (49.2 ft) of fill was placed to achieve the finished site grade. These measurements provided accurate assessment of compressibility of the native soils and fills. Full-scale test fills measuring 20 by 20 m (65.6 by 65.6 ft) (top dimensions) by 6 m (19.7 ft) high were placed at the finished grade to measure compressibility of both native soils and fill. Where settlements were unacceptable (in deep fill areas and where soft soils were present), surcharge of up to 10 m (32.8 ft) was placed to reduce the compressibility of the soils and post-construction foundation settlements. The entire plant was supported on shallow mat foundations designed for settlement using compressibility data obtained by full-scale settlement monitoring of test fills. The mat foundations traversed variable soil conditions consisting of deep fill, residual soils, and bedrock. Measurements of settlement were made during construction of major structures and tanks and these values compared favorably with predicted settlements.