Groundwater Flow Characterization Using Different Hydraulic Methods in Large and Deep Earth-Slide Rich in Clay

Abstract

Since 2013 some different hydraulic tests were conducted and replicated in a large earth-slide characterized by a landslide body rich in clay and with a mean thickness of 30 m, located in the Northern Apennines. All the tests were finalized to estimate the hydrogeological properties of the landslide and successively to design future mitigation measures. To define geometry of the sliding mass more than 15 boreholes’ stratigraphy were analyzed. Successively, the boreholes were equipped with inclinometers and open-standpipe piezometers. According to the stratigraphy, the landslide body is characterized by the presence of gravel layers in a clay-rich matrix. The research compares the results of the different used techniques, which are realized in 2 boreholes, 5 open-standpipe piezometers and using 1 couple well-piezometer. The used techniques and the number of the tests are: 31 slug tests (ST), 4 falling head tests (FT), 5 low-flow pumping tests (PT), 1 point dilution test (PD), 2 aquifer tests (AT). Moreover the tests are elaborated with different solutions: the STs with the Hvorslev and KGS solutions; the FHs with the AGI and Hvorslev solutions; the LPs with the Muskat solutions; the ATs with the Theis, Cooper-Jacob, Neuman, Moench and Tartakosky-Neuman solutions; the PD with the classical solution where Darcy velocity is calculated as a function of the rate of dilution. The results show a variability of hydraulic conductivity (K), Storativity (S) and Specific storage (Ss) in the horizontal and vertical directions (K between 1.0E-5 and 1.0E-8 m/s; S between 4.0E-3 and 5E-5; Ss between 1.0E-3 and 3.0E-3 1/m). The horizontal and vertical variation are correlated with the lithologic heterogeneity highlighted by the borehole stratigraphy. Moreover, all the hydraulic tests conducted on the landslide body given results of high performance and redundancy. The comparison between results derived from different methods are comparable each other and only in some cases it shows differences of one order of magnitude.