Data Quality Quantification for Time Domain IP Data Acquired along a Planned Tunnel near Oslo, Norway

Abstract

SUMMARYTests were done measuring resistivity and time domain induced polarisation using standard multi-core cable spreads and a special layout with separate cable spreads for transmitting current and measuring potentials. For both types of cables spreads both normal and reciprocal measurements were done in order to estimate the measurement errors. The tests were done along a planned tunnel stretch outside Olso in Norway. The electrode contact was variable with resistances in the range 0.6 -25 kΩ. The results gave low median error levels for both types of cable spreads, but the single cable spread showed a significantly larger variation with more scatter in the IP data. Data for both types of spreads gave models that are consistent and appear to delineate the complex geology in a useful way. It is concluded that the single cable spread gives surprisingly good IP data considering the large layouts at this site, which is adequate for inversion of the integrated full decay. If on the other hand the data were to be used for spectral IP inversion of the decay curves for recovering the Cole-Cole parameters the extra effort of measuring with separated cable spreads would probably be well motivated. Near Surface Geoscience 2013 -19th European Meeting of Environmental and Engineering Geophysics Bochum, Germany, 9-11 September 2013 Introduction Combined resistivity and time-domain induced polarisation (IP) surveying can provide data that is very useful in engineering investigations (e.g. Dahlin et al 2010). Measuring IP in the time-domain with relatively compact multi-channel multi-electrode systems is attractive because of the simplicity of the procedure and thus its efficiency in the field. However the use of this technique is sometimes discouraged by the bad quality of the measurements in cases of high electrode contact resistances which can render data interpretation infeasible or at least unreliable. Electromagnetic coupling in the multi-core electrode cables can have a significant role in creating this problem (Nielsen 2006). In such cases separation of current and potential circuits by using separate multi-conductor cable spreads can yield significant improvement in data quality (Dahlin and Leroux 2012). The procedure is relatively simple and can be implemented with common resistivity and time-domain IP equipment. The results presented using this approach show improved results compared to measuring with a single cable spread. We have carried out systematic measurement tests at a number of sites in order to do such quantification, and results from one of the sites are presented here.

Improvement of coarse root detection using time and frequency induced polarization: from laboratory to field experiments

“…Acquisition of time domain IP data is technically similar to ERT (it provides data on resistivity and chargeability at the same time), but it is much more difficult from the standpoint of measurement due to the much smaller signal (Dahlin et al, 2013). The principle of time domain IP involves injecting a direct current (Figure 1) into the subsurface by using two injection electrodes.…”

“…Unfortunately these electrodes polarize, adding noise to soil signal. However, Dahlin et al (2013) and Hördt et al (2007) showed that the use of non-polarizable electrodes in-situ with TDIP does not give better results when: (1) the study site has low electrical resistivity; (2) the electrodes used for injection are not used immediately for the following potential measurement. The TDIP approach appears easier to implement on a dike.…”

“…The electrodes (9 cm stainless steel nails) were fixed on a support to ensure constant distance and penetration in the soil. According to Dahlin et al (2013) and Hördt et al (2007), the system formed by the two injection electrodes and the two others used only for measuring the potential could lower electrode polarization effects. Four 1 m-long linear transects were Author-produced version of the article published in Plant and Soils, 2017, 417, 1-2, 243-259.…”

Improved characterisation and modelling of measurement errors in electrical resistivity tomography (ERT) surveys

“…Much recent work has been done to improve quality of IP measurements. For example, Dahlin et al (2013)…”

Mapping tree root system in dikes using induced polarization: Focus on the influence of soil water content

“…The first interval started after 10 ms corresponding to the initial time delay. IP measurements used a WennerSchlumberger configuration implemented following the recommendation of Dahlin et al (2013) i.e. not measuring on the same electrode the potential directly after an injection to prevent electrode polarization (as with a dipole-dipole configuration).…”