پایپینگ

صفحه 1:
In the name of God Piping in Teton Dam 

صفحه 2:
Introduction on Piping 

صفحه 3:
HYDRAULIC ۵ = Darcy’s Law predicts that under normal conditions, the volume of water that flows through a porous medium increases in direct proportion to the hydraulic head = Terzaghi (1929) asserted that the moment that the seepage pressure becomes equal to the force of gravity (effective stress), the discharge increases abruptly, because soil particles begin to be lifted apart and dispersed. 

صفحه 4:
CRITICAL HYDRAULIC GRADIENT = Terzaghi defined the critical hydraulic gradient as that value of pressure head which equals the ratio between effective normal stress acting on the soil and the pore water pressure. When these values become equal, the effective stress becomes zero because the seepage pressure equals the submerged weight of the soil. = The percolating water can then lift particles of soil into suspension and transport them. « This process is known as hydraulic piping 

صفحه 5:
GENERAL ASPECTS OF THE CRACKSTOPPER THEORY Zowe ABOVE TaLWATER musT BE A Aypotherrca/ crack upstream ni chy care filters Jwo EssenTiat ELEMENTS 7. CRACK Won'T GET LARGER 2. CRACK WILL PLUG WITH FIL7ER MIL. — Wo GUARANTEE oF VaLioITy — = Graded filters are intended to restrict the migration of fines on either side of the impervious clay core of an embankment dam 

صفحه 6:
GRADED FILTER CRITERIA 100) Suitable filter material Percent passing «| / 005 01 02 OF 10 20 5.0 10 Sieve opening. mm = Filtration criteria were initially explored by Terzaghi in 1922, then refined by experiments of the Bureau of Reclamation, published in 1947 (shown here). The purpose of filters is to prevent migration of soil particles under a positive hydraulic gradient; a process referred to as ‘hydraulic piping”. 

صفحه 7:
Some Reasons of piping Weak controlling during construction Low density of concrete adjacent the pipes Cohesionless or less cohesion soils Dam-foundation interaction Cracks due to Heterogeneous soils foundation and embankment Pipes cracks Sliding in dam Waves effects in upstream Caves which are dugged by animals Drying the surface of embankment during construction Drying the downstream Downstream deformation Arching effect Layers with high permeability ¥ Improper compacting layers ANN 5 باج بك ابوك 1 بد 

صفحه 8:
ال رمه(ا) مدص ]” duce GS, (OPO ۰ 06 hited Cruel) sound euqarertoy ‏اس‎ ‎* OCuuse oP Pothine — Durn Pil toodequately posepacted, tow dey = Pravtuned bedrock cbutwe — Cxcessive ‏ما‎ vo yout barrier — Cipro erosiog of tucks by teckiccy ‏رت‎ 

صفحه 9:
Geology characterization & Compaction Materials 

صفحه 10:
= Teton Dam was built on the Teton River, one of the principal features of the Teton Basin Project of the US Bureau of Reclamation funded in 1964. It was intended to supplement irrigation of 112,000 acres of farm land in the Upper Snake River Valley and generate 16,000 Kw of electricity. The plain above the gorge is covered by 30 feet of wind-blown loess. 

صفحه 11:
= Teton Dam was designed with a triple line grout curtain beneath the earth embankment. But, the grout curtain ended up being built as a single-line because the grout take was more than double what had been allotted for the project. 

صفحه 12:
bas! is ete ۹ Teton Dam was designed as an earthfill embankment using wind blown loess as the principal fill material (seen here as light colored material) with river sand and gravel (shown as grey color), as the free draining material. 

صفحه 13:
= The dam’s abutments were comprised of a perversely fractured welded ash-flow tuff (rhyolite), with beds of lapilli tuff and basalt. Large voids associated with volcanic fumaroles were detected during construction 

صفحه 14:
Prominent and very abundant zones of low-angle platy joints Blocky, with closely to widely spaced moderately to steeply dippi (30° to 60°) joints dominant, some low-angle joints in upper part Blocky, massive, with moderately abundant near-vertical and low- angle Joints A 35۳ ۳6 7 SARS 1 The three principal flow units identified in the dam abutments are shown here. Unit 2 was observed to be intensely jointed, with joint apertures of as much as 6 inches. Although many of the largest joints were filled with concrete slurry, no filter was placed between some of the open joints and the silty loess fill in the abutment keyways 

صفحه 15:
و ‎gyre womns‏ اسه ‎ ‎Site ‏سر‎ ‎LAKE ano srReam Ns f Lane ano STREAM ‘oerosirs ‏مر‎ 0 ۱ ۱ 1 Rout = 0.308 Meters ‎amo PROFILE OF TETON DAM ALONG THE GROUT CAP ‎= The exposure of so much jointed and blocky rock led to a major design change, calling for the excavation of deep seepage cutoff trenches, or keyways, in each abutment. The grout curtain was extended to the depth indicated on this vertically exaggerated elevation view. 

صفحه 16:
= Asingle line of grout holes was utilized beneath the embankment because the grout takes were more than double what had been allotted for the project. The portion of the right keyway trench that failed is shown in red cross hatching. 

صفحه 17:
اس موی ‎I‏ 1 aus A cue es os ai Fore sissies 1 ‏مه مه‎ of 207 Steet هد نم لإالك ۵ ۱۵۵۵۵ 5 او ایس ی ۳ ۱ اا ‎Zan tea‏ = Design section through Teton Dam, showing the five principal fill zones. There were only three kinds of on-site materials: 1) wind blown loess (silt); 2) river gravels and sands; and 3) disaggregated rhyolite tuff from the abutment excavations 

صفحه 18:
compacted wrth CAT B25 sheepshat ۶ ۸ ۰ This zone compacted with fives af Euclicl TD-74 dump trucks SECTION THRU ABUTMENT KEYWAY FILLED WITH CompacTeD ZONE L FILL = By changing from the TD-74 dump trucks to the CAT 826, the compactive effort was increased more than five-fold. = A much stiffer wedge of fill was thereby created above lower density fill in the base of the keyway trench 

صفحه 19:
When the reservoir filled, the compacted loess would have been wetted. Low density loess compacted dry-of-optimum moisture content would be more susceptible to hydrocompaction. Hydrocompaction-induced settlement may have contributed to the formation of voids and subsequent hydraulic fracturing between fill of contrasting density, as sketched here. 

صفحه 20:
Failure Sequence On June 5, 1979 

صفحه 21:
= Newly-completed Teton Dam as it appeared in mid-May 1976, as the reservoir was filling at the rate of 3 feet per day. The rate of filling is usually limited to no more than 1 foot per day. This view is looking towards right abutment 

صفحه 22:
a Leakage was initially noted around 7 AM on Saturday June 5, 1976. This view shows a dozer being sent down to fill in the hole at elevation 5200 around 10:45 AM 

صفحه 23:
. Sm =< = The dozer is lost in the expanding hole, around 11:20 AM on June 5‘. Note turbid nature of outflow along the abutment 

صفحه 24:
ly deteriorating situation as it appeared around 11:30 AM. A massive hole has developed in the downstream face of the embankment and is migrating upward 

صفحه 25:
= The hole continues to enlarge and rise toward the crest of the right abutment. This is about 11:50 AM 

صفحه 26:
= Dam crest 666 10 ay at 11:55 AM on Saturday June 5, 1976. Note increasing discharge. 

صفحه 27:
= Maximum flood discharge emanating from gap in dam’s right abutment, just after noon on June 5th, 1976 

صفحه 28:
a The final breaching is filmed from a helicopter that was sent out to warn people downstream of the imminent failure. Amazingly, one of two men fishing a half mile downstream survived! 

صفحه 29:
A 1$ billiard Dollar Flood 

صفحه 30:
The flood inundated the towns of Sugar Rexburg, only © 6 because of the advance warning The loss ended up costing the federal government close to $1 billion dollars At 350 feet high, Teton was the highest dam to ever fail It’s untimely failure signaled an end to the era of big dam building in America 

صفحه 31:
= View looking upstream the day after the failure. The piping failure initiated on the right abutment, between elevations 5190 and 5230. 

صفحه 32:
= Telephoto view of crest of right abutment, showing remains of the right abutment keyway, crest embankment and spillway gates. 

صفحه 33:
Post Failure Analysis 

صفحه 34:
» 7 ۳ = Looking at the right abutment and the remains of the grout cap (arrows). The 60 foot deep V- notched keyway was swept away during the flood 

صفحه 35:
= Detail of right abutment keyway area, showing zone between elevations 5190 and 5230 underlain by blocky Unit 2 rhyolite = This is the fatal seepage zone, where water appears to have jumped across the keyway, i i hydraulic p Zone 1 loess fill 

صفحه 36:
= Cross section of right abutment keyway and crest embankment where the keyway trench was between elevations 5165 and 5220. The hydraulic piping appears to have initiated at this elevation in the keyway, based on observations the morning of the failure. 

صفحه 37:
Soil Properties « Results from finite element analyses at U.C. Berkeley showing contours of ratio between vertical stress in embankment to overburden pressure in the keyway trench at Sta. 15+00, before wetting of the loess fill. The analysis suggests the load of the embankment was being arched across the steeply-inclined keyway trench. 

صفحه 38:
و صسه = Computed values of normal stress on cross section of right abutment at Sta. 13+70. The highlighted areas are where the predicted hydrostatic pressure exceeds the sum of the transverse normal stress and tensile strength of the Zone 1 fill. These zones would have been susceptible to hydraulic fracturing. 

صفحه 39:
= This shows the enormous cut severing the left side of the main embankment fill, exposing the inclined Zone 2 gravel drain. This is how the dam appears today. 

صفحه 40:
= View looking downstream in 1977, after channelization of the outbreak flood debris choking the channel. 

صفحه 41:
CONCLUSIONS + Teton Dam was constructed with numerous shortcomings, any number of which may have combined to cause its untimely demise during its initial filling. These deficiencies include: « Inadequate grout curtain; « Lack of filter or sealer between core loess and open fractures in abutments; - Excessively steep side walls in abutment keyways, promoting arching and likelihood of hydraulic fracturing; » Gross inconsistencies in compaction techniques and soil conditioning (wet seams) which may have led to asymmetric hydrocompaction, which could have caused open voids to form in the abutment keyway. 

صفحه 42:
CONCLUSIONS = Acalculated Factor of Safety less than 1.0 does not, in of itself, mean that a structure failed via the precise mechanism analyzed. « All manner of failure mechanisms should be evaluated without prejudice. This is difficult to do, for we are all prejudiced by our life’s experiences. 

صفحه 43: