Investigation on in situ test and measurement technique of groundwater level in vacuum preloading

Groundwater level (GWL) plays a significant role in theoretical studying of vacuum preloading. The evolution pattern of GWL under the negative pressure condition, however, is still not well understood, and conflicting views continue to be disseminated as a result of insufficient measurement technologies. In this paper, the conventional method, Zhang’s method, and the newly proposed floating ball method (FBM) were employed in the vacuum preloading process for reclaimed land to gain critical insight into the GWL change characteristics according to the in situ distinguishing performances exhibited by the three techniques. Testing results show that the FBM exhibits the best measurement performance; linear decline of mean GWL is reasonably predicted according to the water level change in the pipe during vacuum preloading in this field test. The preconditions and influencing factors of GWL testing in vacuum preloading are elucidated. Local GWL waveform distributions around the water pipe, mainly caused by both the airtight effect and the vertical lifting effect, are highlighted, which can make the water level in the pipe and the average GWL changes out of sync under negative pressure condition. A possible improvement of the GWL measurement is also proposed based on the advantages and disadvantages of the current methods.