The land subsidence is one of the main geological disaster in Suzhou

China.Owing to long-term extraction of groundwater

the land subsidence area has continuously extended which hinders the development of local economy.A series of experiments have been carried out in this study.In order to study the mechanism of land subsidence

the experiment combines the quantitative analysis of soil microstructure with the macroscopic mechanical test

and the soil samples were taken from a 200 mborehole in Shengze

Suzhou.A larger number of SEM images were obtained after using the method of vacuum freeze-drying.The imaging analysis software PCAS was used to acquire the parameters of soil microstructure and the fiber Bragg grating（FBG）techniques were used to monitor the soil layers in the borehole.The data in liquid and plastic limit tests

quick consolidated tests

the quantitative analysis of microscopic structure and the data of distributed fiber optic sensing indicate that the moisture content

the liquid index and the compression coefficient get smaller and the microstructure orientation become more obvious with the depth of strata increasing.There is a large number of microscopic pore structures in the waterbearing sand layer of the second confined and the volume is big enough

which causes a great potential of subsidence in the future and this remains to be investigated.