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The soil-cement cushion represents a compacted and stabilized layer of the soil base, built under the foundation, which is intended to replace a part of the collapsible layer, to increase the bearing capacity of the soil base and/or to play a role of engineering barrier against migration of harmful substances in the geoenvironment. The soil-cement...
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Context 1
... the respective curing period the test specimens were immersed in water for 4 hours before the testing of their unconfined compressive strength. An electromechanical compression machine (Figure 3a) with precise electronic control of the loading rate was used to conduct the test (in the particular case 1 mm/min according to the requirements of ASTM D 1633) and constant digital recording of load and deformation (Figure 3b). The results are presented in Table 5. ...
Context 2
... the respective curing period the test specimens were immersed in water for 4 hours before the testing of their unconfined compressive strength. An electromechanical compression machine (Figure 3a) with precise electronic control of the loading rate was used to conduct the test (in the particular case 1 mm/min according to the requirements of ASTM D 1633) and constant digital recording of load and deformation (Figure 3b). The results are presented in Table 5. ...
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Citations
... The optimum cement content of the loess-cement layer beneath the radioactive waste repository was defined to be 5% (by the dry weight of soil) of Portland cement type CEM I 42.5 N -SR 5. The selection was based on a particular classification and physico-mechanical tests of a set of loess-cement mixtures (Karastanev et al., 2016). Laboratory measurements of the geotechnical parameters showed that the selected loess-cement mixture, prepared at W opt and ρ ds after proper curing, possesses strength and deformation characteristics that fully meet the design stress-strain requirements to the soil-cement cushion beneath the repository foundation (Tchakalova and Karastanev, 2017). ...
... The quantities of loess, Portland cement and water, necessary for one filling of the mixer, were determined on the basis of these values. In view of reaching the optimum water content W opt = 17.0% of the ready loess-cement mixture (with 5% of Portland cement), as determined previously (Karastanev et al., 2016), and taking into account the atmospheric conditions during the cushion construction, the following quantities of the ingredients were defined for one mixer charging: ...
The construction of a compacted and stabilized layer with local soil from the excavation, mixed with Portland cement, is a soil improvement technique widely applied in foundation works in collapsible loess ground in Bulgaria. Commonly, the role of that cement-modified layer is to replace a part of the collapsible ground, to increase the bearing capacity of the soil base, and/or to be an engineering barrier against migration of harmful substances in the geoenvironment. A multi-barrier near-surface short-lived low- and intermediate-level radioactive waste repository is under construction in Bulgaria. A cement-modified soil layer beneath the disposal cells is going to be built by in-situ compacted mixture of local loess and Portland cement. The cement-modified layer (indicated as loess-cement cushion) is not a continuation of the foundation, but it is a part of the soil base and performs two main functions: to be an engineering barrier against eventual migration of radionuclides in the geoenvironment and to increase the bearing capacity to restrict deferential settlement of the soil base. The present paper describes a field experiment aiming to verify the strength and deformation characteristics of a selected optimum loess–cement mixture by implementation of in-situ cement-modified loess ground. After 28-day curing at in-situ conditions, the loess-cement did not exhibit any fissuring or other disturbances. The allowable bearing capacity qa of the cement-modified loess ground exceeded 900 kN/m2, and it possessed the following strength and deformation characteristics: deformation (plate) modulus EPLT = 500 MPa; coefficient of sub-grade reaction ks = 2158 МPa/m, and unconfined compressive strength qu = 2.00 MPa.
... A loess-cement cushion beneath repository cells is going to be built by in-situ compacted mixture of local loess and Portland cement, prepared in a central mixing plant. Based on the analysis of the results obtained from classification and physico-mechanical tests of a set of loess-cement mixtures, prepared with optimum water content W opt and maximum (standard) dry density ρ ds of loess and Portland cement, it has been proposed optimum cement content for the construction of the compacted loess-cement cushion beneath the radioactive waste repository to be 5% (by the dry weight of soil) of Portland cement CEM I 42.5 N -SR 5 (Karastanev et al., 2016). ...
... More detailed information about the mineral, chemical, and grain-size composition of the used loess soil can be found in Karastanev et al. (2016). ...
... The classification index means Portland cement of type I (i.e., with 96-100% clinker content); strength class 42.5 (standard compressive strength at the 28 th day ≥42.5 MPa and ≤62.5 MPa), normal strength growth; sulphate resistant. The reasons for the choice of this type of cement can be found in Karastanev et al. (2016). ...
Soil-cement cushions are compacted and stabilized layers of the soil base, built under the foundation. Usually, they are constructed with local soil from the excavation, mixed with Portland cement. In Bulgaria, this soil improvement technique has been applied in foundation works in collapsible loess ground, aiming to replace a part of the collapsible layer, to increase the bearing capacity of the soil base, and/or to play a role of engineering barrier against migration of harmful substances in the geoenvironment. A multi-barrier near-surface short-lived low-and intermediate-level radioactive waste repository is under construction in Bulgaria. A loess-cement cushion beneath repository cells is going to be built by in-situ compacted mixture of local loess and Portland cement. Based on the results from classification and physico-mechanical tests of a set of loess-cement mixtures, it was proposed optimum cement content of the loess-cement cushion beneath the radioactive waste repository to be 5% of Portland cement. The present paper aims to assess the following geotechnical parameters of the selected loess-cement mixture after proper curing: unconfined com-pressive and flexural strength; shear strength parameters; static and dynamic elastic constants; and hydraulic conductivity. The results obtained prove that the mixture prepared at W opt and ρ ds of local loess and 5% (by the dry weight of soil) of Portland cement type CEM I 42.5 N-SR 5 possesses strength and deformation characteristics that completely meet the design stress-strain requirements to the soil-cement cushion beneath the repository foundation.
With the development of civil engineering in Bulgaria, in the northern part of the Danube plain, several problems related to the collapse (quick subsidence and self-compaction) of the loess soils during wetting are established. The collapsibility of loess soils, the causes, and the prevention of this dangerous phenomenon for construction, are the subject of many studies. One of the most widely used methods in construction for stabilizing a loess ground is the cement-soil cushion (CSC). The main task of the present study is to select an effective technology for the construction and adequate composition of the cement-soil (loesscement) cushion under the foundations of buildings in the city of Kozloduy, founded on collapsible loess.
