DOI: This dam is provided with an innovative and advanced system for quasi-3D thermal monitoring of seepage and erosion, which was used for temperature measurements. The herein reported analysis of the measurements showed high applicability of the thermal monitoring method in determining the severity of erosion and seepage processes using numerical modelling. Introduction Thermal monitoring methods are currently recommended and considered the most promising for the detection and evaluation of seepage and erosion phenomena in earth dams [3, 7, 8].
Changes in the thermal field caused by seepage and leakage through the dam body or foundation allow for the assessment of the intensity of these processes as well as an indirect analysis of the erosion processes. In the flood, a piece of downstream slope lost stability at the perimeter ditch.
These hypotheses are widely described in chapter 4. Due to the relatively low water level at that time, the first hypothesis could not be verified, and this article reports an analysis of the second hypothesis by the thermal monitoring method. Thermal monitoring offers a wide array of temperature measurement analysis tools [8, 15].
They also include thermal-hydraulic numerical models of the test object. Such a model of transient heat and water transfer was developed for piezometric cross section No. This cross-section is located in the area of the ditch slope failure.
The period from the 24th of May to the 4th August was modelled. It is a class II, 6 m high dam, built in and as a temporary facility for military purposes, i. Material for the embankments was not properly sorted, and the embankment density was neither proper nor controlled in the earthworks [5, 9, 17].
The dam body is made of sandstone and limestone fragments, sand and silt sand. Seepage in the foundation under the dam is limited by a wooden sheet pile set at the toe of the upstream slope. It connects to the inclined clay core, forming a m long waterproof element.
The clay core is protected by 1. The upstream slope is protected by 30—35 cm thick stone block paving laid on cement mortar Fig. Frontal dam seepage water is drained through ceramic drains in aggregate surround of three-layer gravel filter set in the downstream slope toe. Water from the drains flows to an open ditch running at 6 m distance from the drainage axis. On the upstream side, the crest is protected with sill made of prefabricated reinforced concrete slabs, combined with the tight pre-quaternary clay core.
There is an asphalt-paved road on the damn crest [9, 17]. This fully automatic system of quasi-3D monitoring continuous over the length of the dam and extended in chosen piezometric cross-sections was described in detail by Radzicki et.
Temperature sensors in piezometric cross-sections, the measurements from which are discussed here, are mounted along the entire length of each piezometer at 1 meter intervals Fig. On the upstream and downstream slopes of each instrumented piezometric cross-section, numerous temperature sensors are mounted for measuring external thermal loads.
Thermal monitoring of earth dams Thermal monitoring is used to detect and assess seepage and erosion processes on the basis of analysis of temperature measurements in earth dams. The methodology is intensely developed by some major research centers in the world, and in Poland by the Institute of Water Engineering and Management at the Cracow University of Technology. Thermal methods of analysis of water flow in the ground are based on the relation in the heat and liquid transfer processes, which are coupled.
These relations are described by the energy conservation equation. At zero water velocity, only heat is transferred, which is a relatively slow process. However, even only a change of soil moisture due to even minimal leakage causes local changes in the thermal front transition rate and disturbs the local isotherm pattern [4, 11].
This process is called advection and is predominant over conduction. As a result, the body temperature measurements and their analysis allow to identify leaks and to monitor seepage processes. Since the erosion process changes the structure and values of soil parameters, it affects the values and directions of water flow vectors in the seepage area, and, consequently, influences the soil medium temperature field.
Each type of erosion process causes characteristic disturbances of the hydro-thermal field, allowing its thermal monitoring exploration [4, 13, 14]. In summary, the thermal monitoring method enables the detection and analysis of the seepage and erosion processes.
As an example, Fig. The multi-year monitoring shows that one of the areas where significantly intense erosion and seepage processes have been observed is the section between and around piezometric cross-sections 6 and 7, of total width ca. Benchmarks located on the facility crest within this region showed subsidence therein by ca. Soil compaction probing carried out from the bench on the downstream side of the dam showed that, at the seepage curve level in the bench embankment, the soil compaction in most of the holes was described as loose and very loose in a ca.
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