Vrednotenje koeficienta prepustnosti za napovedovanje nabrekalnih lastnosti zbitih ekspanzivnih zemljin

The swelling behaviour of expansive soils is significant in geotechnical engineering since it causes severe damage to civil structures. The swelling characteristics need to be well known for satisfactorily safe and economic engineering designs. A direct determination of the swelling characteristics requires considerable time and money, involving serious experimental effort. Alternatively, several indirect estimation techniques developed using empirical regression models available in literature are widely used in practice. These empirical estimation techniques have generally been assessed as a function of the soil properties, i.e., consistency limits, density, moisture content, clay fraction and type, and cation-exchange capacity. This paper describes the dependence of the percentage swell (S%) and the swell pressure (σsp) obtained from a free-swell (FS) test and a constant-volume swell (CVS) test, and the primary swell time (PST), in which almost 90% of the swelling occurs as strain, which is considered as a new swelling characteristic in this study, on the hydraulic conductivity (k) controlled by a change in the gradation of compacted expansive soils. In addition, the rate of primary swelling (Cps), which is the primary swelling phase’s slope of the curve of percentage swell vs. log time, and the ratio of (Cps/k) were used to analyse their relationships with the swelling characteristics. This study provides the empirical methods that can be utilized to obtain indirect estimations of the percentage swell (S%), swell pressure (σsp) and primary swell time (PST) depending on k, Cps and Cps/k, in addition to, or with, the conventional parameters. The correlation coefficients of the regression analysis, having high performance, and indicating strong relationships between the swelling characteristics and the indices proposed in this study, state that these empirical prediction equations can be used safely in engineering practice.Nabrekanje ekspanzivnih zemljin je zelo pomembna lastnost v geotehniki, saj lahko povzroča visoko škodo na gradbenih objektih. Za projektiranje zadostno varnih in ekonomičnih inženirskih projektov morajo biti nabrekalne lastnosti dobro znane. Neposredna določitev nabrekalnih lastnosti zahteva veliko časa in finančnih sredstev ter vključuje resen eksperimentalni napor. Druga možnost je, da se uporabi ena od tehnik za posredno ocenjevanje, ki so bile razvite s pomočjo empiričnih modelov regresije, le te so na voljo v literaturi ter pogosto uporabljene v praksi. Te empirične tehnike ocenjevanja so bile na splošno podane kot funkcija lastnosti zemljine, te so: konsistenčne meje, gostota, vlažnost, količina in vrsta glinene frakcije ter kationska izmenjalna kapaciteta. Članek opisuje odvisnost odstotka nabrekanja (S%) in tlaka nabrekanja (σsp) dobljenega iz preizkusa prostega nabrekanja (FS) in preizkusa nabrekanja pri konstantnem volumnu (CVS) ter primarnega časa nabrekanja (PST). V pričujoči študiji predstavlja primarni čas nabrekanja, novo karakteristiko nabrekanja, v katerem skoraj 90 % nabrekanja nastopi kot deformacija, koeficient prepustnosti (k) pa je nadzorovan s spreminjanjem granulometrije zbitih nabrekljivih zemljin. Poleg tega sta bila stopnja primarnega nabrekanja (Cps), ki predstavlja naklon krivulje odstotka nabrekanja (S%) v odvisnosti od logaritma časa v območju primarnega nabrekanja, in razmerje (Cps/k) uporabljena za analiziranje njunih zvez z nabrekalnimi lastnostmi. S pomočjo empirične metode te študije je mogoče, dodatno ali skupaj s konvencionalnimi parametri, posredno oceniti odstotek nabrekanja (S%), tlak nabrekanja (σsp) in primarni čas nabrekanja (PST) v odvisnosti od k, Cps in Cps/k. Korelacijski koeficienti regresijske analize kažejo na trdne odnose med nabrekalnimi lastnostmi in indeksi predlaganimi v tej študiji, ter potrjujejo, da se te empirične enačbe lahko varno uporabljajo za napoved v inženirski praksi