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Shield tunneling is a popular tunnel construction technique for its efficiency and speed. However, uncertainties associated with site soil conditions, past loading histories and analytical modeling, can result in performance issues. To monitor shield tunnels and ensure performance and safety, fiber optic sensing technique is proposed. Based on Brillouin optical frequency domain analysis, the technique can monitor the opening and closing of segmental joints in shield tunnels with high sensitivity. To determine tunnel lining segment displacement, different fixed-point spacings have been tested in the lab. The test results show that the difference in fixed-point distances had no impact on the test accuracy and the sensing cable with 0.9-mm polyurethane sheath coater has the best performance. For demonstration, the Brillouin optical frequency domain analysis-based monitoring technique is applied to the Suzhou Metro Line 1 tunnel for tunnel lining segment joint monitoring. The technique detected minor deformation of the segment joints in tunnels in operation and located leakages within the tunnel. The technique further identified that the minor deformations of the segment joints and track bed expansion were closely associated with temperature variations. [ABSTRACT FROM AUTHOR]

In-situ thermal response testing (TRT) has become the most effective way to determine ground thermal parameters before developing renewable geothermal energy systems. However, these parameters may not be static when some hydrologic conditions in porous formation change with time. In this paper, we propose a method for evaluating the ground heat exchange performance using the active distributed temperature sensing (A–DTS) technology, which infers soil moisture by a thermal response caused by active electrical current. We evaluated the feasibility of this method by several lab experiments and a field thermal response test (TRT). Using this method, the relationship between thermal conductivity and soil moisture content was established for silt, clay, organic soil and sand, respectively. To quantitatively evaluate the sensitivity of soil thermal conductivity to moisture content, a new parameter called relative thermal conductivity ( β ), is defined to describe the effect of water bridges among soil solid particles on thermal conductivity. The lab test results demonstrate that soil moisture content has significant influence on thermal conductivity when the soil is nearly dry ( β  >  β (cri) ), but its effect becomes less evident when the soil is moist ( β  ≤  β (cri) ). It is found that the relationship between soil moisture content and thermal conductivity can be well fitted by the Johansen model. The results of the field-scale TRT demonstrated the ability of the proposed technique to detect the effects of rainfall on soil thermal conductivity near the ground surface. The field test results also suggest that the soil thermal conductivity measured by in-situ DTS is larger than that obtained from soil samples in lab. However, for rock, the thermal conductivity acquired by DTS is less than the values collected in lab. [ABSTRACT FROM AUTHOR]