A Case Study of Multi-point Temperature Logging for Effective Groundwater Drainage in High Embankment

As is often experienced in the field of mountain ground disasters, groundwater in a formation is rarely uniformly distributed and flowing. Groundwater is composed of several fluidized layers, which are affected by the complex geological and soil conditions in the subsurface, and the water level and hydraulic head of each fluidized layer form the groundwater table. Without sufficient information on the location and depth of the groundwater flow layer, it is difficult to achieve effective results when implementing countermeasure works to lower groundwater. To prevent this from happening, it is very important to know the location of the groundwater flow layer in advance, both in plan and in three dimensions. The depth of the groundwater flow layer and its thickness can be obtained by performing a “multi-point temperature logging” developed by Dr. Atsuo Takeuchi. The greatest advantage of this logging method is that it can obtain information on the groundwater leachate layer above the borehole water level even when the water level in the borehole is extremely low. The commonly used method for detecting fluidized layers is the saline dilution method, but the information on fluidized layers is limited to the depth below the water level in the borehole. To solve this problem, logging while drilling exploratory boreholes in stages is another method, but it is quite difficult to apply because of its high cost and time burden. The built-up area under study is 30 m layer-thick embankment. Groundwater is present within the fill of this built-up area due to poor drainage. In order to ensure the stability of the embankment, groundwater exclusion using collection wells was considered. Multi-point temperature logging was conducted at two locations to determine the drainage pipe layout of the water collection wells. As a result of this survey, several groundwater seepage points and groundwater flow layers could be detected and effective drainage pipe placement could be planned.