Hidrológiai Közlöny 1966 (46. évfolyam)

7. szám - Dr. Lipták Ferenc: Kolmatációval kapcsolatos laboratóriumi vizsgálatok

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BjiH5imie noKpi.iTiiíi rpyHTa H3 MejibKOaepHHCTbix vacTHU n0i<a3aH0 Ha (|)nrype 22, a iieííCTBHe nApa, ycTpoeHHoro B Tejie aaMÖbi H3 MeJibK03epHiiCTWX rpyHTOB, noKa3aHo Ha (})Hrype 23. <J>HJibTpannoHHbie pacxoabi, nojiyMeHHbie npn ;;BIIweHHM >iepe3 rpyHTbi oflHHai<oro 3epHOBoro cocTaBa, HO pa3JIHMH0H nOpiICTOCTH, 3HaiIITeJlbHO OTJlimaiOTCfl Me>KAV COŐOH. Ha ([inrype 24 ii3o6pa>I<aeTCíi BJNI^Hiie IIOPHCTOCTH npH HCn0JIb30BaHHH BOflH Öe3 H3H0C0B. no pe3yjibTaTa.w jiaöopaTopHbtx HCCJieAOBaHHii nojiyMeHw OTBeTM Ha MHoromicjieHHbie Boripocu no KOJibMaTanHH, OflHaKO ocHOBHbie AauHbie AJIJI npoeKTiipoBaHiiji MO>KHO aaTb TOJibKO nocjie ripoBe«eHn>i IICCJIEAOBAHHH no Kana-iy, nponycKaioiueMy Boay, TaK KaK npn ABiiweHHH BOflbi npHAeTcn ywHTbiBaTb H MHoromicjieHHbie ;ipyine ([LAKTOPBI H HX BJiHHHiie Ha KOJIBMATANMO. A Laboralory Study inlo Colmatation By Dr. F. Lipták The phenomenon and prooess bv which partieles of Huspended sediment, or artificially introduced suspension, which enter together with seepage water into the soil, settle in the voids of the latter, is referred to as colmatation. As a result of conseqnent sealing the seepage discharge Q is reduced. Colmatation is the combined effect of seepage and sediment movement, and is consequently a highly involved phenomenon. Laboratory studies on natural and artificial colmatation were carried out at the Chair for Water Resources Management, Technical University for Building and, Traffic, Budapest, Hungary. No discharge was conveyed during these experiments in the canal, i. e., the only movement of water was that due to infiltration. Permeabimeters of 40 cm internál diameter (Fig. 1) and a 4 metre long experimentál basin (III. 1) were used for these experiments. The materials in which the colmatation process was studied were coarse and a finer sandy gravel and silty sand (Fig. 2). The coarse sandy gravel layer was penetrated already under low hydraulic gradients (0.1) by a part of the sediment, whereas the other settled in the voids, or was deposited on the surface. Instead of filling the voids uniformly, the sediment förmed a characteristic system of passages (Fig. 3, Ills 2 and 3). No passages woro förmed in the silty sand. The process of colmatation resulting upon the introduction of natural sediment is illustrated in Figs. 4 to 8. In the coarse sandy gravel discharge dropped to 21% (Fig. 4) and 26 % (Fig. 6) of the initial value, whereas in layered soil the drop was 48% (Fig. 8). A further conclusion obtainable from Fig. 6 is, that the reduction of the initial discharge (taken as 100%) to 26% is due pritnarily to sediment settled in the voids and to a smaller extent only to that depositing on the surface. As will be perceived from Fig. 7, reversed flow at lower hydraulic gradients caused no dislocation and scouring of once settled partieles from the voids. The effect of materials used for artificial colmatation (clay and bentonites) is illustrated in Figs. 9 to 17. By introducing suspensions of these materials (mainly bentonite) into water, seepage discharge can be reduced quicklv and effectively. The greater part of clay was carried by seepage water deep into the sandy gravel layer and as a consequence of the system of passages developed it reached points at considerable distances from the infiltration surface. The greater part of bentonites settled on the surface of the soil and förmed a highly impervious sealing layer there. Seepage discharge was reduced to 1— 2% of the originál value. Almost the full pressure drop oecurred in the surface sediment and in the upper 2 cm thick layer. The impervious sediment film was capable of withstanding even higher hydraulic gradients (1.1). Results of experiments carried out in the seepage basin with natural sediment are illustrated by the <p — = (p/y) + z lines in Figs. 18 to 21. The progress of colmatation is demonstrated in Figs. 19—20, while the effect of the surface sediment in Fig. 21. The effect of the finegrained soil lining and of a core made of fine-grained material is illustrated in Figs. 22 and 23, respectively. Significant differences were observed between seepage discharges passing through layers of the same grain size distribution, but of different porosity. The effect of porosity is illustrated for the case of clear water in Fig. 24. From the results of laboratory investigations positive information could be obtained on numerous probléma related to colmatation, but design eriteria can be derived from experiments conducted with flowing water only. In the case of water flowing in a canal the process of colmatation is influenced namely by numerous additional factors.