Watertight Elements Research Articles

Strength and deformability of different types of geosynthetic barriers

Introduction. Water engineering facilities utilize geosynthetic barriers of various materials, but the most common are polyvinylchloride (PVC) and polyethylene (PE) considered to be the most efficient. However, the utilization of thermoset geosynthetics (PVC and PE) as watertight elements of the geosynthetic barriers of earth dams has also a number of drawbacks. In the course of time, PVC can lose its properties due to plasticizer loss, whereas PE is susceptible to cracking at thermal impacts. That is why it is necessary to consider geosynthetic barriers of other types as alternatives. For this purpose, we studied the deformability and the strength of geosynthetic barriers of thermoset material (chlorosulfonated polyethylene — CSPE), as well as of a rubber-type synthetic material (ethylene-propylene diene monomer — EPDM). Materials and methods. Sample testing of geosynthetic barrier materials for monoaxial extension was conducted by means of a tensile-testing machine, which records during the experiment the changes of the tensile force and the longitudinal extension. The changes of the cross-section area of the samples were measured by means of a digital side caliper. Results. It was determined that of the considered geosynthetic barrier types (PE, PVC, CSPE and EPDM) the strongest one is the reinforced CSPE type and the most deformable is the EPDM barrier. Reinforced CSPE geosynthetic barrier has a tensile strength above 100 MPa, it is approximately 5 times higher than that of PVC and PE barriers. By deformability, reinforced CSPE barrier is similar to PE barriers. An EPDM geosynthetic barrier has the linear deformation modulus around 1 MPa, it is capable of a multiple extension without loss of strength. Conclusions. By strength vs. deformability ratio, EPDM geosynthetic barriers can compete with PVC barriers.

A review on the development of reinforced ice for use as a building material in cold regions

Carrying building materials into remote cold regions makes construction in these regions difficult and rather expensive. The need for such materials can be reduced by the use of both ice and ice-soil composites. In cold regions ice is abundant and cheap. However, using ice as a building material has some limitations. It is a relatively weak material and shows an extreme creep behavior compared to conventional building materials; mechanical properties are strongly temperature dependent and melt protection is necessary even in the coldest areas. The behavior of ice can be improved by reinforcement. Ice composites have been applied successfully in engineering structures. In this paper the classification of various methods of ice (-soil) reinforcement is presented. Despite the fact that there are many studies on ice reinforcement, ice composites have a very limited application. At present there are only three types of reinforced ice structures: (i) ice roads reinforced by geomaterials, (ii) watertight elements in the dam of Irelyakh hydro system in Siberia and (iii) ice structures on an inflatable mold constructed in the winters of 2014 and 2015 in Finland. Currently ice reinforcement methods are not widely used in construction. The aim of this paper is to carry out research to further introduce ice reinforcement into the practice of construction when feasible. The authors show that there is a need to stimulate the development of a building method for ice composites.

Use of quick-setting substances in watertight elements for rock material dams

Use of quick-setting substances in watertight elements for rock material dams

Infilling of low-head rockfill dams

Harnessing small and medium rivers is important for the maximum use of the potential of local water resources. When assessing the possibility of constructing earth dams as part of small hydrodevelopments, especially in remote, difficultly accessible regions, it is important to be able to use local natural materials and technological schemes in which the construction of the bulk of the shoulders and watertight elements can be done independently. Of interest under such conditions is the use of the infilling method for reducing the permeability coefficient in the shoulders and foundations of dams composed of coarsefragmental soils. Insignificant volumes of fine-grained materials in the form of sediments or clay and sandy loam deposits can be used for this without the use of scarce building materials and complex technologies [1, 2]. The results of investigating the infilling process in interrelation with the temporal change in the permeability coefficient and parameters of the seepage flow on the basis of a probabilistic model are given below. This makes it possible to most completely take into account the characteristics of the particle-size distributions of the soils of the dam body and infilling material and their change during filling of pores. A variant of a rockfiU dam proposed for small Pamir hydrostations is examined as an example. Infilling is carried out after constructing the dam with complete or partial filling of the reservoir by delivering material to the upstream slope from floating pipelines. Calculation Method. The process of filling the soil pores of the dam and foundation with finer material (infiller) occurs in the form of movement of the particles of this material along the pores. The sizes of an individual particle and of the pore encountered by it have a random character. The mathematical condition under which the infiller particle is retained in the soil pores is written in the following form:

Some characteristics of the interaction of the Sayano-Shushenskoe dam with the surrounding rocks

1. In an analysis of the results of on-site investigations of high arch, archgravity, and statically indeterminate structures of dams, it is necessary to take into account the geostructural and geomorphological characteristics, discreteness of the properties of the surrounding rocks, and contemporary tectonic movements. 2. The problem of decompression of the foundation of the channel part of the Sayano-Shushenskoe dam requires a thorough study with the development of measures to stabilize the watertight elements and to prevent the development of a contact crack. 3. It is necessary to reexamine the recommendation of par. 9.8 of SNiP 2.06.06-85 concerning the construction of concrete aprons when designing transitions of arch dams with the foundation. 4. The stability of the separating wall should be checked for dynamic loads during passage of the design flood with consideration of the real load-bearing capacity of the foundation. 5. It is necessary to organize the observations specified by the design within the overflow dam.

Seepage at the contact of the clay core with the foundation made by the “diaphragm wall” method

Designs of the contact watertight elements of the body of an earth--rock dam with the watertight element in the foundation of the "diaphragm wall" type are often used in hydrotechnical construction. Designing of such a contacting component requires a thorough analysis of the performance of these watertight elements. The combination of the latter often requires the use of special structural elements, which depend on many factors: the relationship of the permeability coefficients of the core (facing), dam body, and material of the diaphragm wall, slope angle of the core (facing) to the vertical, depth of penetration of the wall into the core, etc. [i].

Polymer film materials in watertight members of earth structures

1. The small unit materials consumption of polymer, particularly polyethylene, watertight elements and high productivity of making them at practically any ambient air temperatures predetermine the effectiveness of their year-found construction regardless of the climatic region and area of the object being faced. 2. An urgent problem is the development of specifications and setting up the production of polymer materials intended specially for creating watertight elements of earth structures. Such materials can be PE panels with a thickness of 0.5–1.0 mm with protective layers, for example, of foamed PE with a thickness of 5–10 mm, applied on one or two sides.

Consideration of the stress-strain state in calculations of slope stability of earth dams

1. The stability of slopes of earth structures can be estimated directly from solving the appropriate boundary-value problem with modeling of the actual relations between stresses and strains. 2. Even in the simplest cases (a homogeneous “dry” dam under the effect of its own weight and a horizontal seismic load) the proposed method permits refining the surface of sliding and the value of the stability factor obtained by elementary methods. 3. Despite the fact that the VNIIG-Terzaghi method does not take into account the stress-strain state, it provides a comparatively high accuracy. In the investigated example the error in determining the stability factor is 10%. Apparently, in more complex cases for structures being constructed from various types of soils, with consideration of the seepage forces (especially unsteady), with consideration of consolidation in the watertight elements of the dams, and with consideration of their staged construction the divergences can be much greater.

Construction of dams on soils containing soluble salts

1. The experience gained by Soviet and foreign hydraulic engineering indicates the possibility in principle of constructing dams on foundations containing soluble rocks. 2. The construction of dams on foundations containing soluble rocks requires thorough surveys and the development of suitable protective measures to preclude the possibility of dissolution of the rocks in dangerous zones and to restore the reliable operation of water-tight elements. 3. The construction of earth dams from gypsinate soils is permissible provided that the gypsinate soil placed in the structure has a permeability coefficient of not more than 0.1 m/day. 4. Structures being constructed on foundations containing soluble salts should be provided with an inspection gallery and an extensive network of monitoring equipment for observing the seepage flow and timely detection of centers of leaching.

Watertight elements of earth hydraulic structures

Film facings are the most economic type of watertight element of those presently existing. However, this advantage of them is noticeably displayed in the case of small heads and need to protect large areas. As the head increases and the area of facing decreases the difference in the cost of film and other elements becomes less noticeable.

Operating conditions of earth dams on undermined territories

1. The operating conditions of a dam on undermined territories substantially differ from those under ordinary conditions (without undermining). This necessitates a special approach to the design and operation of such dams, since the use of the experience of conventional hydraulic engineering is not possible. 2. The occurrence of cracks in the foundation in the case of undermining unloads the soil mass adjacent to them. Further deformation of the mass occurs due to an increase in the size of the primary cracks (practically without the occurrence of new ones), which is the main characteristic of deformation of earth dams on undermined territories. 3. The use of nonsoil materials for watertight elements (WTE) of dams (asphaltic concrete, polymer films) cannot completely eliminate and cannot change the regular mechanism of cracking in their body, consequently disruption of the continuity of such elements is completely possible. Therefore the use of the indicated nonsoil materials as WTE, in principle, requires further investigation. 4. All the aforesaid brings to the forefront as the most promising direction of investigations the development of fundamentally new designs and technological measures to ensure reliability of earth dams on undermined territories.

Seepage regime in the medeo dam following accumulation of a mudflow

Field observations of the behavior of the dam during accumulation of a mudflow, geological investigations, and laboratory investigations lead to the following conclusions. 1. When designing mudflow-retaining dams made from the rock, construction of watertight elements on the upper pool side is practically useless, since the mud deposits themselves successfully form a facing and impervious blanket. 2. The seepage flow through the dam comes from a comparatively small layer of water accumulated on top of the mud deposits due to the river runoff following the mudflow. The mud deposits themselves contribute negligible seepage. 3. When placing earth in the dam by the combined method (blasting and filling) it is necessary to take into account the difference in the seepage properties of the zones constructed by the different methods. When earth is placed by heavy-duty trucks the permeability is considerably lower than in the case of an embankment constructed by blasting. 4. In view of the absence of experience in operating mudflow-retaining dams (excluding the 1973 mudflow) increased requirements must be imposed on the design of drains and discharges, provided the dam is not calculated for brief discharge of the water that seeped along the downstream slope. 5. Retention of the disastrous mudflow by the Medeo dam proved that it is possible to control this menacing natural phenomenon. 6. The insignificant settlement of the dam crest (about 10 cm) following rapid flooding of the dam soils indicates high operating qualities of the embankment constructed by the massive blasting method. 7. The construction of mudflow-retaining structures does not eliminate the need for other measures of controlling mudflows (lowering of the levels of morainal lakes, forest-improvement and channel-regulating measures, etc.). Only a combined approach will create a reliable protection system.

Construction of watertight elements of earth dams

Construction of watertight elements of earth dams