Shear strenght properties of waste material several years after disposal

• Autorzy: Suchnicka H.

Warianty tytułu

PL

Wytrzymałość materiału zawałowego po kilku latach od zdeponowania

• Języki publikacji: PL

Abstrakty

PL

Przedmiotem szczegółowej analizy - przede wszystkim dotyczącej cech wytrzymałościowych, ale też i stanu fizycznego - są wyniki badań laboratoryjnych materiału zwałowego, zalegającego od ponad 5 lat, na głębokości 20-50 m. Porównywane są one z rezultatami wcześniejszych badań, Przeprowadzonych na próbkach pochodzących w prawdzie z większego obszaru i z większych głębokości, lecz niestety o węższym zakresie. Badania zostały wykonane na próbkach o naturanej wilgotności, w warunkach trójosiowego ściskania, z pomiarem ciśnienia wody w porach. Wymuszenie zadawane było w pomieszczeniach, z prędkością (4,5-5,3) mm/h, przy ciśnieniu bocznym (w komorze aparatu) zbliżonym do panującego w warunkach naturalnych. Podczas interpretacji wyników badań, dużą uwagę poświęcono ocenie wpływu na wartości parametrów wytrzymałościowych wyboru warunku, jaki oznaczałby przejście materiału w stan graniczny. Potwierdzona zastała ogromna - losowa - niejednorodność materiału zwałowego, manifestujaca się nie tylko w dużych rozrzutach wartości parametrów fizycznych, ale też różnymi stanami materiału (niejednokrotnie próbki pochodzące z tego samego otworu wiertniczego wykazywały tak różne stany, jak np.: zwarty i półzwarty, czy miękkoplastyczny, a nawet płynny). Pewnym zaskoczeniem był fakt, odnotowany zarówno w badaniach ostatnio przeprowadzonych, jak i wczesniejszych, że mimo ogromnej zmienności bezwzględnych wartości oporu ścinania zwałowego, oceny jego wytrzymałości, przeprowadzone w nawiązaniu do wartości naprężeń efektywnych, okazały się tak dokładne. Wyjaśnienie tego zagadnienia wymaga dalszych, pogłębionych studiów, a nade wszystko badań i to badań "in situ", zarówno samego oporu ścinania, jak i ciśnienia wody w porach materiału.

EN

The primary objective of the study was to examine the strength properties of the waste material. So far, these properties have not been sufficiently well recognized and, what is more, they are known to vary with time and with the increasing thickness of the overlying material. This is mainly due to the ever changing structure of the material. At the first stage (I) the material assumes a two-storey structure (Fig. 1 a), which changes with time elapsed through stage II (Fig. 1 b) until the process of transformation has been completed at stage III (Fig. 1 c) to produce a breccia-like structure. The scheme of relations between successive stages (vertical stresses [sigma] and strains [epsilon] or shear stresses [tau] or density (Q)) are plotted in Fig. 2 (solid lines). The same relations for undisturbed soils are shown in the same figure (dashed lines). The laboratory tests were carried out on samples of waste material (set S) disposed of on a spoil heap about 5 years earlier and collected at the depth of 20 to 50 m. Those were unconsolidated undrained triaxial compression tests under strain-controlled conditions (at a strain rate ranging from 4.5 to 5.3 m/h) and at a cell pressure approaching that occurring in the waste heap. Particular consideration was given to a detailed identification of the physical properties of the material. The variability of the basic physical parameters (w, q) in the S-set (sample 7) for three regions differing in size is shown in Table 1. To support the experimental material for the needs of further analysis, the results of some previous tests were used in this paper. These previous tests were carried out on samples collected at the same spoil heap about 5 years earlier. The samples represented a much larger region because they were obtained from 15 boreholes at the depth of 5 to 90 m, although the scope of recognition of the physical properties was significantly simpler. This set of specimens is referred to as Set T. The larger number of specimens in Set T allowed statistical analysis of the effect of age and pressure on the water content and density values in the distinguished subsets. The results of the investigations into the physical properties (for both sets) are plotted in Figs 3, 4, and 5. Successive figures (Fig. 6 for specimen 4 and Fig.7 for specimen 6 of Set S) show typical results of the strength tests. All shear strength data for this set are plotted in Fig. 8. For clarity, Fig. 9 includes only extreme values of the shear strength for the much larger sample set T. The scattering of shear strength results for Set S and Set T is very large if the description is made in terms of total stresses, and surprisingly small if shear resistance is described in terms of effective stresses. It is the inhomogeneity of the material that should be blamed for the failed attempt to estimate the values of apparent strength parameters for each set of three specimens collected at the same depth. Only sometimes it was possible to estimate effective strength parameters (Table 5). Figure 10 shows the distribution of shear resistance (q_{f) for the specimens of Set S in the vertical profile. On the left-hand side there are values of the cell pressure [sigma]0 at which each test was carried out, as well as the values of the pore pressure (u0) involved by this cell pressure. To compare these two quantities with the pressures generated by the self weight of the soil or water the values of the latter were shown in Fig. 10 by two lines - solid for soil and dashed for water. There is no clear relationship between pore water pressure and current stress state irrespective of whether the loading is isotropic or anisotropic (i.e. at failure), Figs 11 and 12. And this means that Skempton's pore pressure parameters are very difficult to estimate (if at all), especially in the case of parameter A. The test results are summarized in Fig. 13 and Table 6. The plots show areas of shear strength scattering for Set S, Set Tand natural (undisturbed) soil displaying a physical state and plasticity similar to those of the waste material. Figure 13 also includes the resultant lines (lines with points). Summing up, the investigations of the waste material even from the same borehole evidenced a strong random inhomogeneity, which manifested not only in the physical state (varying from very stiff or hard to very soft or even liquid) but also in the values of absolute shear strength, i. e. those described in terms of total stresses. On the other hand, it was surprising to find that both in the present test (Set S) and in our previous studies (Set 7} the description of the shear strength in terms of effective stresses was incredibly precise. The problem calls for further reconnoitring (both laboratory and in situ) investigations. In situ investigations should primarily aim at measuring and describing the pore pressure distribution in the waste material But is another major question which calls for answer: Does the age of the waste material and the pressure of the overlying strata affect the physical and mechanical properties or not, if the material has overlain the spoil heap for several years? In situ investigations should also aim at providing data on the position of the weakness zones in the heap. Penetration tests seem to be best suited for this purpose.}

Słowa kluczowe

PL

grunty zwałowe; badania laboratoryjne; wytrzymałość

EN

waste material; laboratory tests; shear strength

• Wydawca: Instytut Mechaniki Górotworu PAN
• Czasopismo: Archives of Mining Sciences
• Rocznik: 2000
• Tom: Vol. 45, nr 1
• Strony: 47--71
• Opis fizyczny: Bibliogr. 8 poz., wykr.

Twórcy

autor

Suchnicka H.

• Instytut Geotechniki i Hydrotechniki, Politechnika Wrocławska, Wybrz. Wyspiańskiego 27, 50-370 Wrocław