Abstract
The paper reports a groundwater-flow-related failure occured to a homogeneous sandfill dam, 20 m high, and describes in detail the analysis of the leak occured during the first impounding under a head of 3.6 m only. After an examination of various hypothesis, piping as the failure mechanism is proposed and checked with numerical analysis derived from Schmertmann’s theory as well as with a field test. Back analysis is extended to explain what happened after an uninterrupted pipe established between reservoir and the toe of the dam.
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Abbreviations
- B :
-
Horizontal segment of seepage path (ft)
- B ur :
-
Bulk unloading—reloading modulus
- C i :
-
Flow concentration coefficient (overall)
- C jt :
-
Flow concentration coefficient for a pipe
- C IP :
-
Flow concentration coefficient of the flow net in the horizontal plan
- C IS :
-
Flow concentration coefficient of the flow net in the vertical plan
- C 2n :
-
Flow concentration coefficient at outlet, normal to the axis of the pipe
- C ap :
-
Flow concentration coefficient at outlet, parallel to the axis of the pipe
- €3:
-
Flow concentration coefficient for 3D flow condition
- C.ir:
-
Flow concentration coefficient for a 3D pipe
- Cr″I:
-
Required cohesion
- C,s :
-
Shape factor for the pipe’s cross section
- GI,:
-
Uniformity coefficient
- D :
-
Thickness pipeable
- d oo :
-
Diameter 10 % passing
- d fto :
-
Diameter 60 % passing
- d ave :
-
Characteristic diameter controlling the deposition process
- D ur :
-
Edometric (constrained) unloading–reloading modulus
- e :
-
Void ratio
- F 3 :
-
Proportionality factor for a semicircular pipe (ft/min)
- FSH:
-
Factor of safety against hydrofracturing
- FSP:
-
Factor of safety against piping
- FSS:
-
Factor of safety against shear
- F v :
-
Water volume factor representing the dilution of the water/soil suspension
- G s :
-
Specific gravity of grains
- h :
-
Head (ft)
- H I :
-
Actual maximum head existing along any given pipe segment (ft)
- H niax :
-
Maximum allowable head (ft)
- I :
-
Seepage gradient
- i c :
-
Critical seepage gradient
- i v :
-
Vertical seepage gradient
- k :
-
Coefficient of permeability (ft/min)
- k h :
-
Horizontal coefficient of permeability (ft/min)
- k j :
-
Coefficient of permeability of generic segment (ft/min)
- k rp :
-
Coefficient of permeability proper of the reference segment in a direction parallel to the pipe axis (ft/min)
- k v :
-
Vertical coefficient of permeability (ft/min)
- k an :
-
Coefficient of permeability normal to the slope a (ft/min)
- k ap :
-
Coefficient of permeability along the slope a (ft/min)
- L :
-
Pipe segment length
- L′:
-
Transformed pipe segment length taking as reference the coefficient of permeability k rp of the reference segment
- L 2 :
-
Transformed pipe penetration length
- L YD:
-
Thickness factor
- I′/L′:
-
Pipe development
- LJ:
-
Length of generic segment
- n :
-
Manning’s roughness coefficient
- N F :
-
Number of flow channels
- NI I:
-
Number of head drops
- p :
-
Dynamic water pressure
- q :
-
Flow
- R :
-
Hydraulic radius (ft)
- R c :
-
Lane’s weighted creep ratio
- RH:
-
Scour velocity reduction factor
- S :
-
Degree of saturation
- S :
-
Slope of piezometric surface
- T :
-
Overall time for piping
- t :
-
Vertical segments of seepage path
- v :
-
Velocity of the flow in the pipe (ft/s)
- Vti3:
-
Lower bound transport velocity (ft/min)
- vs:
-
Velocity required to scour a uniform particulate material (ft/s)
- vt:
-
Velocity required to drag a uniform particulate material (ft/s)
- w :
-
Water content
- z :
-
Pipe diameter (mm)
- DH:
-
Minimum head difference needed to maintain the lower bound flow velocity (ft)
- (DH/L′)cr:
-
Critical local gradient
- AT:
-
Time for the pipe to move across each segment L of the path (min)
- a :
-
Dip from horizontal
- f :
-
Friction angle
- Y d :
-
Dry unit weight
- y t :
-
Total unit mass
- Y :
-
Unit mass
- s h :
-
Horizontal stress
- a v :
-
Vertical stress
References
Krumbein WC, Sloss LL (1963) Stratigraphy and sedimentation. W.H. Freeman & Co., New York
Lambe TW, Whitman RV (1969) Soil mechanics. Wiley, New York
Schmertmann JH (1957) Effect of seepage on scour at wall face. In: Proceedings of 6th conference on coastal engineering, Gainesville, Florida
Schmertmann JH (1980) Notes and calculations for “a quantitative piping theory”. Appendix B to Special Board of Consultants Report for Florida Power & Light Company
Sembenelli P, Biondani E (1984) Analisi degli Effetti prodotti dall’Invaso sulle Dighe in Terra e Roccia. Rivista Italiana di Geotecnica, Anno XVIII, N. 2, Aprile-Giugno
Sembenelli P, Sembenelli G, Ruffini A (1997) Internal erosion around relief wells in fine sand. In: Proceeding XIX international Congress on large dams, vol II, pp 715–722
Sherard Jl, Dunnigan LP, Decker RS (1976) Identification and nature of dispersive soils. ASCE J Geotech Eng Div 102(GT4):287–301
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Sembenelli, P. (2016). A Case of Piping in Sand Under a Dam and Its Back Analysis. In: Rao, V., Sivakumar Babu, G. (eds) Forensic Geotechnical Engineering. Developments in Geotechnical Engineering. Springer, New Delhi. https://doi.org/10.1007/978-81-322-2377-1_21
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DOI: https://doi.org/10.1007/978-81-322-2377-1_21
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