Subsoil influenced by groundwater flow

Abstract

Even though the soil mechanics has rapidly evolved within last 80 years of its modern history, due to numerous phenomena which influence soils behaviour and are based on its natural characteristics the room for improvement exists. However, most engineering problems, regarding saturated and even unsaturated soils behaviour, can be resolved with sufficient accuracy using powerful numerical models and methods. Although even models which approximate the reality perfectly have to be supplied with material parameters obtained from either laboratory or in-situ experiment when both classes affect only limited surroundings.This thesis focuses on two important areas of research connected with the presence of liquid phase in the soil. First, there is an internal erosion problem of saturated soils when subjected to groundwater flow. Second, the behaviour of soils in unsaturated state under is part of the research. Here the thesis focuses on suction cancellation followed by additional settlement of foundation structures in fine grained and coarse grained soils. However, the last mentioned class is commonly referred as unaffected by suction cancellation. The area of interest was restricted to "hydro-mechanical" point of view and does not involve any chemical interactions between the phases inside the soil or between the surrounding and solved domain. Predominant part of the thesis concentrates on the experimental analysis and its evaluation followed by recommendations. Stand for full scale experiments with varying groundwater table was designed and constructed allowing for observation of all the phenomena and possibility of estimating the effects in situ due to selected measuring technique, i.e. static plate load test. The results obtained from the full scale experiments proved to be very useful in understanding and evaluating of the processes through which the groundwater influence the behaviour of the subsoil. Some of the results obtained challenge the general assumptions, such as fine particle loss due to groundwater flow or negligibility of the effect of suction for coarse soils. The results were also used to calibrate and confirm the ability of professional codes to approximate the soils behaviour during plate load tests and suction cancellation. The success of the last mentioned simulations was very limited despite the enormous computational time used.Part of the thesis is devoted to search for a simple solution with large variety of use available and understandable in common engineering practice. Here, the elastic layer theory with adopted varying influence zone theory providing for fast analytical solution is employed. The thesis also contains recommendations for flood risk assessment, and several comments on practical issues regarding the infiltration policy for large impermeable areas and the influence of hydraulic structures and channel improvements on adjacent areas

Even though the soil mechanics has rapidly evolved within last 80 years of its modern history, due to numerous phenomena which influence soils behaviour and are based on its natural characteristics the room for improvement exists. However, most engineering problems, regarding saturated and even unsaturated soils behaviour, can be resolved with sufficient accuracy using powerful numerical models and methods. Although even models which approximate the reality perfectly have to be supplied with material parameters obtained from either laboratory or in-situ experiment when both classes affect only limited surroundings.This thesis focuses on two important areas of research connected with the presence of liquid phase in the soil. First, there is an internal erosion problem of saturated soils when subjected to groundwater flow. Second, the behaviour of soils in unsaturated state under is part of the research. Here the thesis focuses on suction cancellation followed by additional settlement of foundation structures in fine grained and coarse grained soils. However, the last mentioned class is commonly referred as unaffected by suction cancellation. The area of interest was restricted to "hydro-mechanical" point of view and does not involve any chemical interactions between the phases inside the soil or between the surrounding and solved domain. Predominant part of the thesis concentrates on the experimental analysis and its evaluation followed by recommendations. Stand for full scale experiments with varying groundwater table was designed and constructed allowing for observation of all the phenomena and possibility of estimating the effects in situ due to selected measuring technique, i.e. static plate load test. The results obtained from the full scale experiments proved to be very useful in understanding and evaluating of the processes through which the groundwater influence the behaviour of the subsoil. Some of the results obtained challenge the general assumptions, such as fine particle loss due to groundwater flow or negligibility of the effect of suction for coarse soils. The results were also used to calibrate and confirm the ability of professional codes to approximate the soils behaviour during plate load tests and suction cancellation. The success of the last mentioned simulations was very limited despite the enormous computational time used.Part of the thesis is devoted to search for a simple solution with large variety of use available and understandable in common engineering practice. Here, the elastic layer theory with adopted varying influence zone theory providing for fast analytical solution is employed. The thesis also contains recommendations for flood risk assessment, and several comments on practical issues regarding the infiltration policy for large impermeable areas and the influence of hydraulic structures and channel improvements on adjacent areas