The Russian Practice of Assessment of Earth Dam Seepage Strength

ICSE6 Paris - August 27-31, 2012-Vadim Radchenko, Irina Belkova, Oleg RumyantsevFigure 2: Contact erosion of soila –coarse-grained soil – fine-grained soil; b - coarse-grained soil – clay (cohesive) soil; c –cracked rock – clay or finegrainedsoil; ϑ - angle between directions of seepage velocity and gravity force; D o –average size of coarse-grained soilseepage pores; d sp –dimension of (suffosion) fine-grained soil particles which may be carried out by seepage flow;k r – permeability factor of rock; k s – permeability factor of soil; b c – crack width.For this we, at first, determine the critical gradient of contact erosionI ,of fine-grained (or cohesive)soil. Its value depends on size of grain composition fractions of contacting soils. Then the obtained meaning(value) I ,is compared with concrete hydrodynamic conditions of the seepage flow in the structure or itscr celement. Experimental methods to define values ofnon-cohesive and cohesive (clay) soils were developed.VI.4.1cr cDetermination of critical gradients of contact erosion for non-cohesive soils.cr cI ,depending on sizes of their grain compositions forIf two nonuniform non-cohesive soils (or soil with cracked rock) contact between each other, the criticalgradient of fine-grained soil erosion and dimensions of carrying-out particles with the diameter d ≥ 3% isdetermined by the experimental equation [Pravedny, 1976 – 1991]:Icr , c=1 ⎛ dsp⎞ dsp⎛ ϑ ⎞⎜2, 3 + 15⎟ sin ⎜30+ ⎟ , (12)ϕ ⎝ D0⎠ D0⎝ 81⎠where: ϕ1–the coefficient accounting for the shape and roughness of soil fractions.At that the relation isdsp < 0.7. With the relationdsp ≥ 0.7 there is no erosion and carrying-out of fine-D0D0grained soil fractions. The average diameter of fine-grained soil seepage pores is determined by the equation(9).The equation (11) may be used to determine the critical gradient of fine-grained soil erosion on the contactwith cracked rock (Figure 2c), but the value bс, crack expansion in rock, should be substituted into theequation (11) instead of D0.VI.4.2Determination of critical gradients of contact erosion for cohesive (clay) soils.In case there are contacts between cohesive (clay) soil and coarse-grained material or with cracked rock(Figure 2b, c), the cohesive soil may be eroded.The value of the critical erosion gradient Icr , cat contact seepage: cohesive (clay) soil with plasticity indexIP- coarse-grained soil (or cracked rock), may be determined by the experimental equation [Pravedny]:Icr , c= 1− 0.75 , (13)maxDwhere:maxD – is determined by the equation (4) for coarse-grained soil, at that00spmaxD ≤ 0.018 m (with0maxD > 0.018 m the cohesive soil will be separated in pores of coarse-grained material, the contact erosion).0583

ICSE6 Paris - August 27-31, 2012-Vadim Radchenko, Irina Belkova, Oleg RumyantsevThe equation (12) may serve to determineI ,at the contact: cohesive soil – cracked rock (Figure 2c). Incr cthis case the maximum value of crack expansion should be substituted into the equation (12) instead ofmaxD .0VI.4.3 Determination of critical gradients of contact erosion for cohesive soils with plasticity index I P < 5.Many researchers observed that cohesive soils with plasticity index I P < 5 (2-4) – loamy sand, poor loamysand differ from more plastic soils by seepage-strength properties.On the base of experimental studies of clay soil with plasticity index I P ≤ 6 for contact erosion with gravelfilter, graphical equation of admissible contact erosion gradient was obtained:I cont sc adm = f (D о 60c, d ag ), where D о 60c – calculated diameter on the contact with loamy sand, d ag – calculateddiameter of soil aggregate forming at erosion. Numerical values of f can be found from diagrams in[Mishurova 1970, 1975].The admissible gradient shall be equal to:I cont.scadmcont.scInorm= , (14)1.5 ⋅ kwhere k –the coefficient depending on the slope of eroded surface, its values are determined by standrads.VII CONCLUSIONSPractically fail safe operation of earth and rock-fill dams, constructed in the USSR, Russia and othercountries for more than seventy-year period, demonstrates that the described method of local and generalseepage strength, used for dam designing, is justified and provides operational reliability of structures.VIII ACKNOWLEGMENTS AND THANKSWe are grateful to Dr. Valentina Burenkova for encouraging us and helping to write this paper.IXREFERENCES AND CITATIONSChugaev R.R. (1962). – Underground outline of hydroengineering structures. Publishing House“Gosenergoizdat”. Moscow-Leningrad.Chugaev R.R. (1965). – On calculations of seepage strength of dam foundations. “Hydrotekhnicheskoestroitelstvo” (Hydrotechnical Construction) Issue 2. Moscow.Chugaev R.R. (1968). – Earth hydroengineering structures (theoretical calculation basis). Energoizdat.Leningrad.Patrashev A.N. (1935). – Pressure flow of ground water carrying fine sandy and clayey particles. Isvestiya.B.E. Vedeneev VNIIG. Vol. 15, 16. Leningrad.Patrashev A.N., Pravedny G. Kh. (1965). – Manual on designing of reverse filters for hydroengineeringstructures. VSN-02-65/GPKE and E USSR.Pavchich M. (1961). – Method of determination of nonsuffusion soils grain size distributions. Isvestiya.B.E. Vedeneev VNIIG. Vol. 68. Leningrad.Pavchich M., Balikov B.I. (1976). – Methods to determine soil permeability factors. Publishing House“Energiya”. Leningrad.Pavchich M. (2006). Transition filters XIII Danube-European Conference on Geotechnical Engineering.Active geotechnical design in infrastructure development. Proceedings. Vol. 2 Ljubljana. SloveniaBurenkova V.V., Mokran B. (1983). – On substantiation of reliability of suffusion soil strength inhydroengineering structures. “Hydroengineering construction .Burenkova V.V. (1992). – Assessment of suffusion processes in loose inequigranulas soils. Int. Congressof filters and filtration phenomena in geotechnical engineering. Karlsruhe. Germany.Pravedny G.K. (1976). – Guideline on calculation of seepage strength of dams made of soil materials.Leningrad. Publishing House “Energiya”. 55-76 pPravedny G.Kh. (1991). – Recommendations on designing of reverse filters for hydroengineeringstructures.VNIIG. St.-Petersburg. 56-90 p584