The long-lived debate on the principle of effective stress is rooted in the obscure physical significance of stresses. For the sakes of clarifying stress concepts and establishing a reasonable principle of effective stress, unsaturated soil is divided into six phases and the bearing structure of it, named generalized soil structure, is defined based on considering soil as a special structure. Then the essence of effective stress equation, named stress relation equation, is derived according to analysis of interphase interactions and independent-phase equilibrium. The stress relation equation indicates the corresponding relation between two series of stress variables used in mixed and multiphase continuum models, respectively. Furthermore, a reasonable concept of suction stress is redefined to describe interparticle connection properties. Then, a generalized stress framework is constructed by associating stress relation equation with suction stress. After demonstrating the concept of neutral stress, a generalized principle of effective stress is established and the total soil skeleton stress is searched out, which is the predominant stress controlling the strength and deformation of soil. Finally, the collapse phenomenon is analyzed and the time- and spatial-dependent stress frameworks are developed.
Self potential (SP) and electrical resistivity tomography (ERT) methods are used together with the results of groundwater samples hydrogeochemical analysis to assess the impact of the water leak from the landfill garbage site at NamSon located in Northern Hanoi on causing pollution to the surrounding environment and affecting geological structure. Selected survey area covers an area of 180 × 300 m lying in the low land of the NamSon site with a slope ranging about 8 m in direction NW–SE. There are three geophysical measurements lines denoted as T1, T2 and T3. Processing 180 SP data points has allowed to draw maps of equipotential epoch in the two periods in 2015 and 2016. The maps show four zones of SP positive anomalies with maximum amplitudes of about +20 mV where the groundwater flow direction is downward and five zones of SP negative anomalies with minimum values in a range from ?180 to ?260 mV where the groundwater flow direction is upward. Resistivity values of the subsurface layers of soils and rocks have been aquired from 2D inverse model for measuring ERT in March 2015 and March 2016. The results of the ERT allowed to define the low resistivity in the range 15–20 Ωm related to leachate plume from NamSon landfill site. Results of the physico-chemical analysis of groundwater samples from the existing six boreholes show increases in concentration of the measured pollutant parameters indicating contamination of the groundwater as a result of solid waste leachate accumulation. This result is affirmative evidence for the survey results by geophysical technique. The rapid decrease in quality of groundwater over the last year is probably due to the influence of the leachate from the NamSon landfill site. 相似文献
