In the context of this thesis, the possible application of qualified soil improvement in river dike construction is investigated. The design of river dikes is based, in addition to the basic force balance, on a probability and costbenefit analysis for determining the design flood level. Through various influences, these fundamentals can change in the course of the service life. This means that the river dike must be adapted to the new boundary conditions. The aim of this investigation is to examine the suitability of the technology of soil improvement, which is already used in road construction, accessible to river dike construction. In this way, dyke cubature with steeper embankment inclinations could be realized, thereby enabling the saving of space. In addition, the possibility of using the same technology for the design of overflow sections or reconstruction or boosting of dikes is examined and described.
To achieve this, various investigations were executed on a sectional model of a one-zone dike with a qualified soil improvement (mixed binder consisting of lime and cement) in the hydraulic laboratory and on soil samples in the geotechnical test laboratory of the TU Darmstadt. Based on the results of this study, recommendations for the practice are formulated.
In the hydraulic model tests, a distinction was made between impoundment, seepageflow and overflow tests as well as combinations of these tests. In total, the sectional model was impounded for 377 days and overflowed for 49 hours. In the overflow tests, additional variations were carried out landside. Tests were carried out with and without hydraulic jump at the foot of the landside slope of the dike. Before and after each test, the surface of the dike was inspected and, based on further measurement data, conclusions on the dike stability were drawn.
To determine the stresses on the dike, hydraulic parameters (water depth, flow rate, flow velocity) were measured in the sectional model during the tests and transferred by application of a one-dimensional numerical model interpolated to a higher resolution. On the basis of these data stability investigations were carried out (partly using computer software). In addition to the physically depicted test dike, six different cubatures and three different materials were compared with each other, whereby one of these materials was the material not mixed with a binder and therefore served as a reference for comparison.
It can be stated that improved soil material generally showed significantly lower efficiency rate than the original material, unless, a different component (such as the subsoil or a surface layer) than the improved soil is decisive for the verification. In this case the improvement does not change the efficiency rate. A comparison of the tests with simultaneous changes in the cubature (steeper, more compact cubage, 1:3 1:1.5) allows the following further conclusions to be made: By means of soil improvement most of the tests can reach the same or lower efficiency rate (depending on the type and quantity of the mixed binder). Due to the smaller contact area, the deportation’s efficiency rate and the settlements increase in comparison (both independent of the building material). The improved dike can resist remarkable loads that would otherwise require the use of concrete systems. Furthermore, it could be proven that the improved soil can be covered with grass in combination with a topsoil layer. This allows the dike to integrate well into its surroundings and to receive the additional reinforced protective layer. At the same time, the improved material has proven to be resistant to burrowing animals.
Finally, the present work provide practice-relevant information on the use of the construction material under investigation in practice and makes recommendations for further action of investigation up to its inclusion in the state of the art. | English |