:cr:PICI.ENCY OF SELJ=.:CTED sa.l\PI:S

by

Cx>aig Van Hatta

Th{~s.i.s s1J.br.litted to the Graduatl:! Faculty of the

Vi:i:,ginia Polytechnic Institute

in candida.oy for• the deg1:>ee of

MAS'I'Bl~ OF SCIENCE

Sanitary Engineering

-2-

TABLE QF CONT:CHT'.:; Pa.g:e

I. Introduction. • • • 0 • • • • • • • • • 5

II. Fr~tfiew of I.ti teI.,ettl1i~e 0 • • • • • 7

III. Hetho<ls a"'lc1 Materials • .. • • • • 9

IV. Pesults • • .. • ~ 0 • 0 0 .. 0 ,. • " • 20

v. DisGussion of I{r.:sn1lts 0 " • • 0 • • • • trn

VI. Conclusions • .. • • • 0 0 0 0 e • 0 • 48

v:r.1. Surnn1::11"')y • • 0 • v • 0 • 0 • • • C> • 49

_.,.VIII. Acknowledgments .. " • • • • • • • • • 0 • 50

IX. Bibliography 0 • $ • 0 .. • • • • • • • 51

x. Vita • • • .. • • • • • • • • • ~ • • 52

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LIST or TABLES

Page

Table I. Weir Calib:r:Y~t ion Data • • • • • • • • • • • 14

Tu]:)le II. List of Si.eves Used to Obtain Grit Particles 16

Table III. Results of Experiment I - Trough 1 • • • • 25

Table !V. Results of Experiment II- Trough 3 • • • • 25

Table v. Results of Experimr.:mt III - Trough l • 0 • 26

IT able VI. Results of Experiment III - Trough 2 • • • 27

. Table VII • Results of Expe:i:•.tment III - Twugh 'l 28 v • • • k

Table VIII. Results of Expe1"'iment IV - Trough l • • • • 29

'l'able IX. Results of Expe1~iment IV - T°!'OUgh 2 • • • • 30

Table x. Results of Expe1:• iment IV - Trough 3 • • • • 31

Table XI. Rasul ts of :Experiment IV R - Trough 1 • • • 32

I'ig\1!"0 1.

Figure 2.

Figure 3.

r· .. : 1gure 4 •

Figure 5.,

Figure 7.

Figure 8.

F. i.gu:r.•e 9.

Figure 10.

figUI>e 11.

Figure 12.

figure 13.

T .. I ST \ QF fIGUHI!S

Sketch of apparatus • • • • • . . . -· . Page ... 17

Trough dimensions and typical particle flow patteI'l18 • • • • • • • • • • • • • • • 18

Weir calib1~ation curve • e • • .o • • • • • 19

Velocity vs. per cent grit passing trough for Expe.rinien.t III, 0.2 mm •••••••• 33

Velc,clty v--s. per cent grit pass:i.ng trough fol' Exper:i.1ne.nt IV, 0 .1 n:rrn • • • • • • • • • 31+

Compa.r•ison of repeat series with ori~final series • • • • • • • • • • • • • • • • • • 35

Bar graph comparisons of per cent grit passing trough for '£roughs 1 11 2, and 3; under ldentical conditions • • • .. ~ • • • 36

Per cent passing vs. selected vm1iables for 0,05 ft. weir setting. • • • • • • • • 37

Per cent passi.ng vs. selected variables for 0.10 ft. weir setti.ng .. .. • • • • • • 38

Per cent passing vs. selected Vi'lriables for 0.15 ft. we:i.r setting • • • • • • • • 39

Scoux• w,:locity vs. particle diameter • • •

Difference in per cent passing fo:r 0.1 and 0.2 mm particles vs. selected variables. • li5

Per cent pa1;;sing vs. Tieynolds no. <.i.t. constant Froude no. for 0.2 mm p.'::lrrticle size •• .• • • 0 • • • • • • • • • • .. . . Pe1~ cent pass!ng vs. I1oynolds no. at constant rroude no. for 0.1 mm part.:i.cle size •• . . ' . . . . . . . . • • • • • • 47

-5-

I.. INTRdDUC'l'lON

In a sewage treatment plant it is desil~abie to remove hard,

gritty material such as sand and gravel from the sewage flow in

order to save weal:' on pumping equipment, and to reduce the

qmmtity o:f matter which must pass through the complete treat-

mcnt process.. Bar screens are used to remove large gvavel or

stones, but generally some form of grit chamhei~ is used to ramove

smaller stones, sand and similar particles of high density and

hardness.

It is not de:sd.:t~able, however, to remove all grit particles

because in attempting to remove ver-J small diameter particles

certain decomposable organic constituents in the sewage would

also be trapped. This decomposable mat·ter, .i.f dumped iu; the

open without tr<:~atment along with the grit mci.teria.l, ·would pose

a serlou.s health probleri-i- It is, therefore, desirable that a

grit chambex• have the ab:i.lity of selective sedimentation in

that it should trap coarse pal"'ticles but pass fine particles.

Most commonly a grit chamber is desibtned to trap a 0.2 'fll.m

diarneter parti<.:1.e of sp.ecific gravity 2 .65 but pass particles

f 11 ,;i• (3) o ·· sma er uiarneter.

Many grit cham.bers are somewhat elaborate structures

utilizing mechanical equipment, but in small plants wheI'e the

flows ar-e not great the grit chamber will in actuality he little

more than a wide section of the pipeline whel."e the velocity of

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flow is decreased to the poin-t where the grit settles to the

bottom and is t?'apped by a trough. This trough is then pumped

clean at pe1"'iodic 5.nt·,?::'vals and th€ S<'lnd and gr.it is disposed

of 1 generally by using it as a fill material.

At the pX'esent time the1"e is no generally accepted method

for the design of gr5.t chamber t:r.oughs other than to provide

sufficient ca1)acity for the expected volum(~ of grit including

a. suitable safety :factor. These troughs usually al'e designed

with sloping sides so that the grh will nettle to a central

point to be dra"m off by a pipe 01"' some type of screw mechanism,

but the1·,e is no criteria now in use for the design of an overall

shape that w:i.11 trap the desiwd particles and paBs the rest.

Th<:"! objective of this investigation was ·to exai11ine cartain

specific shapes of grit collection troughs to determine the

efficiency of the sections for the selective collection of grit.

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II o REVIEW OF LITERATUPJ:

1\n :investigation of the literature pr•oduced info1"'rnation which

fa~ll b<:ts:tcally :tnto two categoric~s, sedimentation ·theory and grit

chamber desi;.:;n. Ltte:r.'atu:r.'e on secllmentation theo1"y dealt with

the theory of settling of discrete particles er with the movement

of bottom loads in streams, canals or chamber·s, and therefore, was

not directly related to the subject being investigated •

. r '. -ff , ( 5 ) d • ., .Pl d • . ' • ' 1 h. t''.l• f,01"'ris stu :i.eet ,;: ow ov{~X' a . eprass1on in i-11.s neve op-

ment of relationships in quasi-smooth flow but was concerned only

with ver7 small squ<:u."'e-shaped depr~'1ssions. These depressions were

too small to be analogous to the large troughs used :i.n this in-

vestigation.

Ar,.dcles tleal:i.ng with grit chamber design invariably were

concerned. with d1";veloping the most efficient flow ci•oss section

rathe1~ than collection trough; a.'1d in every case a mecha:.riically

cleaned grit chaillber was discussed r>ather th<.'l..n tbe simple collection

tr,ough which was the object o:f this investigation.

Im indication of the pr•oblem, bo1-Jever 9 was given by Bramer

ancl l·ioak(l) uho stated, 11 In practice, sedimentation basins are not

often designed; they arc sized on the basis o:f past experience. n

Th:i.s would evidently app.ly to gr•it chambe1"'s as well as sedi-

mentat:i.on basins since thet'e is a g!'eat similarity in. the two.

Metcalf ai'ld Edd/ 4 ) again attet1ted to the 11ruJ.e of thumb"

practices employed in trough design 1-1hen they stated, "In some of

the early trough and hopper bottom8 the slopes were too flat

for the grit to slide down them and there is some evidence that

the inclination should be at least forty-five deg:r.,aes." They

indicate, therefore, that the hopper sides should be steep, but

they provide no des.:i.gn criteria for a mo:rie definite slope.

The ravlew of literature thus showed that ve-:r..,y little work

hC1.s been done on the design of non-mechanically cleaned grit

chambers, leaving the subject open for investigation ..

-9-

III. NE'l'HODS AND HA'rERIALS

Tii.e means by which datum was obtained in this investi•

ga.tion was th~ construction of a scale motlel grit chamber to

obtain purely empirical values. The chamber was constructed of

plywood and plastic according to the dimensions shov..rn in

Figure 1.

This investigation was confined to the comparfoon of th~:e

troughs as shown in Figure 2. 'I1·H~ troughs were made of Plexiglass

Acrylic Plastic so that particle :movement in the trough could be

readily observed. The remainder• of the gr·it chamber was ma.de of'

plywood utilizin3 'i/JOotl screws, with w<1tet"pr>oof gluG being used

as a sealant and to provide added strangth. Wing nuts and bolts

were used to connect the plastic sections to the plywood section 11

with Vaseline petroleW! jelly being used to seal the joints.

Petroleum jelly turned out to be an em;ellent sealing material

since it was waterproof, clean, very workable, and never dr>ies

out. The plywood secti.on of the chamber was painted with marine

var,nish to waterproof the surfaces and J.'>!'event warping.

Normally, a Parshall flume or a sedimentation tank would

follow a grit chamber in actual usage, thereby controlling the

depth in the chamber but since flow f:l'om the model had to be

immediately channeled away a weir was u.sed to control the height

of the water surface and as a mee.ns o:f measurfog the quantity of

!flow. The weJ.r was placed at the end of a short sta.bi.Hzation

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section which followed the trough. The stabilization section

was needed because if the weir were plr1ced directly behind the

trough, a large number of particles would hit the bottom of the

weir and drop into the trough. The stabilization section pro-

vided a. means for the particles which did not settle fast enough

to be trapped by the trough to continue past and not be de-

n<:?cted downward.

The wei!' was rectangular wlt:h a piece of sheet metal tacked

across the bottom edge to provide a sharp crest. Calibra.tion of

the weir was accomplished by passing a constant flow of water

through the chamber and trapping and weighing that portion

which passed in a measured ti.mr~ interval. By measuring the temp-

erature of the water, and the:rieby knowing the density, the volume

was easily determined; this divided by the time interval gave the

quantity in cubic feet per second.

Two rulers were used to read the depth cf flow 9 one located

on the inside face of the weir measured the height of the weir

crest a.hove the bottom of the channel 9 and the other located

about ten inches ahead of the weir on the wall of the channel

measured the height of the water surface above the channel bottom.

The difference in these two :readings was plotted against the

kno-vm quantity on log log graph paper. The calibration points

are listed in Table 1 and plotted in Figure 3. The resulting

graph •~as then used to determine quantities of flow during the

-11-

various experiments by simply taking the difference of the two

depths and :i::•eading the flow from the graph.

An approach channel was used to direct the water in the

proper dh~ection before it ~nte:roed the char,1ber proper. 'fhe

approach channel was made nar:riower than the chamber in order to

maintain a velocity which would not permit grit to settle out

before reaching the cha:mber. 'Hater entered vertfoally downward

at the upper end of the a.pproach channel through a £'ire hose

from a town water connection.. Water passing over the weir was

funneled directly into a floor drain to the sewer system.

Grit was introduced to the flow hy use of a funnel w.i:th a

rubber hose and clamp attached to the bottom. The funnel was

suspended over the upper en.d. of tha approach channel and when the

clamp on the hose was Faieased the mixture of water ai'ld sand pass-

ed down into the flow at a nearly constant rate. Chasiak and (2) Burger had exper.:i.ence in using sand in testing grit removal

apparatus and they minimize the effect of the rate of sand feed.

They st:ated 9 "The rate of feeding of sand, which varietl ft>om

ahout two to ten pounds pe!' minute, did not affect the f3ff iciency

Ordinary construction sand \~as used as g:r•it during: the

entire investigation i4lth a range of particle sizes being used.

Grains of a uniform slz.e were obta.:tned by passing the raw sand

through a seriies of standard sieves as indicated· in. Tal:)le 2.,

-12;;;

level of ~t leat'.lt two inches abo"J~~ th«; sm;d :J'lrt1 foc.:~ in th•! i .·

.; !.

i

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When all of the grit had been introduced to the flow the

valve was closed, thus ceasing operation of the chamber. All

of the grit which had settled out before reaching the tl"Ollgh was

then swept d.own into the tr•ough with a small paint brush to be

rem()vGd and measured. P.:n.y grit which had passed the trough and

settled in the stabilization section was not included in the

measurement; ln other words, the chambe1 .. and tt>ough sections t-n:~re

considered as a unit in developing efficiencies and all grit

settling in both were included in the measurement. The gI•it was

then removed from the trough by siphoning -with a plastic labora-

tory hose. 'l'he siphoning action was quite efficient and all of

the grit was quickly and easily removed. After removal ~om the

troilgh the mixture was poured into the graduated cylinder for

final measurement.

At one poirtt in the investigation a baffle was installed i.n

the approach channel to prevent rippling, a pr«iblam ·which will be

discussed late~, but was unsuccessful. The baffle was four

inches high and placed on the bottom of the approach channel about

ten inches from the upper end. 'l'he baffle was somewhat useful

at low flm,ts but seemed to ir.icr-ease rippling at high flows and

had to be removed.

p IJ. .d T:dill ft. ft.

0.10 0.225 l 0.10 0.225 2 0.10 0.225 3 0.10 0.225 ·~ 0.10 0.225 5 0.10 0.225 6 0.10 0.225 '7 OolO 0.225 8 0.10 0.225 9

0.10 0.208 l 0.10 o.2os ::.? 0.10 0.208 3 0.10 o.:zos It 0.10 0.208 5

0.10 0.245 1 0.10 o. 2!~5 2 0.10 0. 2!.J..$ 3 0.10 0. 21.~5 !~

0.20 0.365 ~

J..

0.20 0.365 2 0.20 0.365 3 0.20 0.365 4 0.20 C. 3frG 5 0.20 o.:~65 6

0.20 0.1+05 1 0.20 0.405 '?. 0.20 0.405 3 0.20 O. LI05 lj.

TAr:JI.:C I

Uelr ('.a.libration Data

Weight lh"' J.)o;>.

500 500 500 500 500 500 500 500 500

400 iwo 400 400 1}00

500 500 500 500

500 500 500 500 ~00

500

500 500 500 500

Ternpex•aturo of water - 23°C

Density of 11ater at 23° C :':". 62.28 lbs./:ft."

v Volume

wt./62.28 cu.. .ft.

80028 8.028 8.028 8.028 8.o:rn B.028 8.0.~8

8.028 8.028

6.423 6.4·23 6.423 6.lJ.23 6.423

8.023 8.028 8.028 H.023

3.028 8.028 H.028 8.028 8 .. 028 B.028

a.o:rn 3v028 8.028 8.02E

T Time

secondi:l -157.,S-!: 137.9*' 131. 91: 129 .6~'1 128. g·!~ 127 .1.p': 129.0 123.5 129. 1.p':

133.5 135.0 135.9 136.?. 137.3

10i+.3fc io2.e~·~

100.2 100.9

. ~:}9.Gf•' s1.1.p'i: 8t.t.5i: s3. a~·( 82.7 82.5

si~.o~·e

53. 7'i: 58.2 57 .11

-Flc;w

V/T. av Hate erag;e /sec. cu.ft.

0.06 23

0;;04

OoC'i

o,og 72

O.,l.3 B9

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'i'l\BLE I

Wei!' Calibration Data (continued)

.. . , p H Trial Weight Volume T Flow Rate

ft. ft .• lbse wt./62.28 Tirn.e V /T av~n."'age

cu.ft. seconds cu 0 ft. /Bee. ..,, ·=--

0.20 0,.350 1 soo 8.028 92. 7.;~ 0;,20 o.35o 2 !)00 s.02s 94-.3 0 .. 20 0.350 3 500 8.028 1;J5 .• 5 0.20 Oo350 4 500 8.028 95.8 0 .• 20 0~850 5 500 8.028 94.7 0.0844

0.20 o.319 l 500 8.028 139.5 0.20 0.319 2 500 8.028 140.L~

0.20 0.319 ') 500 89028 11~2 .5 .., 0.20 0~319 4 500 8~028 162. 71: 0.20 Oo319 5 500 2.028 140.2 0.0571

Oo20 0.281 1 200 3.211 118.5~~

0.20 0.281 2 200 3.211 93.5* 0.20 0.281 3 200 3.211 98.4 0.20 0~281 4 200 3.211 100.6 0.20 0.281 5 200 3.211 109. a~·~ 0.20 0.281 6 200 3.211 102 .1+ 0~20 0.281 7 200 3.211 97.9 0.20 0.281 8 200 3.211 103.6 0.0319

0.20 ' 0.,380 1 500 8.02B Bl. 5 f: 0.20 0.380 2 500 8.028 78.3{: 0~20 o.3so 3 500 8.028 76.2* 0.20 0.380 4 500 8.028 75.31':' 0.20 0.380 5 500 8.028 73 .1.p·~ 0.20 0~380 6 500 8.028 73.0 0•20 0.380 7 500 8.028 73.o 0.110

-

~Walues not used j_n computing T average

-15-

LI.st of Sieves tlsed to Obtain G1.,j.t Partir:l<~s

u. S., Sle'lle Number

20

40

50

60

120

DiaTileter of P'articl~ Passing Sieve, m i11:tmet:er~1

o.2s1 -ut/ 0.250

0.,125

Av-e:r>np:e Dlameter of Part:Lcle Obtatned

m:i.ll:tmetfH'3

o.,. 72

0.3G

0.20

0.10

s' -a ,, /'- o" 2, ~ 4 J " 2 '· a " / , -o '' < ~~ t - t >t~

LH§:'. --- l a·-3" _'flt i i _t ~~========================~~ Qt I I

Approach Channel J---= I.. Ch_gmbe~ --:,~Stab ..

~

... ... ~ -...

I -()

PLAN ·Secfion

• t:i· rlaslic section 1 '

:: <() •I C)

5 E.CTI ON A

, Figure 1 : 5kefch of opporafus

Trough no. 1

y 3"

Trough no. 2 .. <.o

3" 4"

-:::::...

Trough no. 3

3" 8 ,, Scour

Figure 2: Trough dimensions and typical particle· flow patterns

0.201 i !

-;__ ~

~ 0./0 "+-

c:: 0.08 --(\_'

0.06 I

=t

0.01

0.02 0.04 0.06 0.06 0.10 0.20

Flow, 1n cubic feet per second

Figure 3 : Vve1r calibrat1on ci1r11e

-20 ...

IV. RESULTS

The investigation was dlvided into :four el{periments which

were run accoxiding to the method descvlbed in Section !I! •--

Methods and Materoials it the differenca being tl1at a differ>Emt

sand part:iele size was used for em:~h expel".'iment;.

'l'he pre.liminary e}(perin1ents employed sand grain sizes of

0. 72 and O • 36 mm. 'I'he resu..t ts of these e~per:tments, presented

in Tablas !H and IV, sh.owed 100 percent '.l'.'emoval afte:r. several

test m.ms. Experimentation was shlfted to smallel" sand sizes

upon evidence that thE! experi.mental unit was not pe1..,forning the

function of seleeti'lre sediment4tion.

The results of Experiment III* where a 0.2 mm grain size was

uaed 9 _at:e given in tab\llar form in Tables V tJ VI a.nd VII and

plotted in Fig1.1re lJ.. The results of Experiment IV 11 where a O. l

mm grain size W'as used, are given in tabular form in 'fables VIII,

IX and X and plotted in figure 5.

Data points were obtained within the widest range of veloci-

ties which were praet.f.cal for each experiment. At lower

velocities nea~ly all the grit would settle out in the chamber

before t>eaching the tr~ugh, and at high velocities :ripples would

form on the water surface that ma.de it difficult to read the depth

in the chamber.

'fhese rS.pples occurred du:r·ing the weir calibration runs,

however$) and did not seem to have any marked effect upon the

-21-

results, as can be seen i.n Figure 3 in which nea'l.'J.y all points

plot on a straight lim:i.

The patterns of particl.-~ flow wh:ich we:t'.'':3 observed in the

troughs a:r.•e shown 5.n Figure 2. 'l'he troughs a:re numbron"Bd J.,. 2

and 3, .:1 notatlon wh:tch i~s used throughout t:h1s work.

A doubl·~ v-ortex fol"med in Trough l as shown in "figure 2,

the smaller vortex l'Ota.t5.ng at a :faster rate than the la:r.\gex> one.

The ~mall WJ'.!'tcx did not nppe.;ir to produce an~! f2couring ef:fect

upon the collected zrit beneath :tt. In Trough 2 the fi'l'.'it

co.llect1::-id 5.n the: corners 11 r.t.8 shown in Figure 2 5 c;nd in a thin

layer across the bottom. Onlv T1?ough 3 showed clear evidence of

scouri.ng acti.onj} however.r-, it did not appear> that the sr..?oure<l par·-

tfoles wel'.>c di".'iven up into the flow of the vortEm but were s:tmply

pushed to a ::i~w position on th€ bottom nearer to the opposite

,,,all. In o.11 threr~ 'troughs it appeai'.>Cd thay any particle wh.ich

hit the sid,ls or bottom did not re-enter the flow patter•n.

In general the grit wa.s caught :i.n the trough in two ways.

First~ a certain amount of g:r>ii: whi.ch settl·;~d out just before

rr.ia.(~hing the trough would bG pushed along the bottom by -'che flow

to thl! edge of th1z trough and slid.s down. Only ~ snall percent ...

age would be pieked up <:>t the ~Jdge and carried in.to the vortex.

Secondly 9 a certaJ.n portlon of the grit would strik~; the opposite

wall and slit:1.e do:·m to the bottom. Grit seemed ·to collect in the

bottom of 'r·.~ouu;bs '.:? a.nd 3 :i.n ~pproximately equal amounts at both

ends, lndfoating that the two trapping mechanisms just described

-22-

were ,:o..)ach responsible for nearly the same amount of grlt being

trapped by the trough.

The curves in Figure 4 compare VE'ilod.ty w.ith the percent of

grlt which passed the trough. Th1~ee weir height settings were

selected to be used for· comps.rison, 0.05 ff;et, 0.10 feet 9 and

0.15 feet. P.s can he seen the 0.05 fer;:t curve pr>edominantly

appeared to the leftt the 0.10 feet curve ne'Kt, and the 0.15 feet

curve to the right in relation to each other. The o.o5 feet

curves have a characteristically steeper slop0, followed by the

0.10 feet curves, with the 0.15 feet curves starting out very

steep but quickly leveling off. 'fhese cha.ract:eristics t:t:t:•e not

nearly so prominent in Figure 5 whi.ch plots the :t'asults c:f

Experiment IV in which a smaJ.1 grain size of 0.1 mm was used.

Experiment IV a wider divergence of data points meide the con-

struction of a reasonable line through the points :more difficult.

Table XI gives the Fesults of Experiment !VR, a repeat of

one series in Exper:i.ment IV. It was felt that since sand fo1 .. any

one run during the investigation was obtained by uslng sand which

was trapped in the previous l"Un plus some extra sieved sand f01'."

wakeup, that possibly the sand was. ncJt constant in its nature

from one r•un to the next• In Experiment IV~ for ernample ~ the

mrel:'age grain size used wag 091 mm but actually varied from 0.07'-l·

mm to 0.125 mm. It was felt that ~- possible error was being in-

troduced in that the smaller particles wer13 pr-obe.bly being removed

-2s-

roo!'0 than the la:r.•gr:~'r po.l'tic1es 3.n the range. When the sand was

then retrieved to be used again the average size could possibly

For the repeat series a lal'.'ge quantity o:f r>aw :smnd was

run through the p,rH chamber at the highest velocity which was

to be usod. The sand :r.'et1•ieved Wt'rn then set aside as a. source

of supply for makeup sand to be used in the repeat series.

'I'his r.;hould have prc;vidt;i<l a r.1ore constant grit supply and have

had the ef:fect of increasing the aver.•age diameter. The results t

however, did not show a. significant change from data obtained

p1'eviously and. 9 :tn fact, varied both higher and lower indicat-

:i.ng no trend owe wuy ot• the other. 'I'he results ol)tained from

the ·N~peat S<Jries are plotted in Figure 6 whlch also presents

the previous results.

Fif:ure 7 is a. bar graph which gi.ves the percent capture of

sand for' the three: troughs under equal conrH:tions of weir beight 9

velocity, and particle size.. One relatively high velocity a.nd

one :N:latively low velocity o;1e1•c chosen for comparison... The

percent passing v;_'tlUet:> plotted in the bar gr•aphs wet·e taken from

the jl';r.>aphs in Fiip:wes 4 an<l 5.

t\n effort to compa!'e the variables effecting gr-it: scour

with the percentages of grit passing the unit during the e;i:peri ...

ments is shown in F'lgure:s 8, 91 and lC, for welr settings of

0.05 :feet, 0.10 feet, and 0.15 foet, respectively.. In these

-24-

figures the percent grit passing thi:~ trough is plottGd against

the three variables,, Reynolds ntll1:be1"' (NF<) !I f:i:•oude number (NF) 9

and the depth in the chamber (H) ll which were thought to e:ffec·t

scouro The depth va:.dable Na.s div:i.ded by the w:tdth cf the

channel in ordet" to create a dimensionless 1>2n'.'arneter to ccx"res-

pond to the I~eynoJ.ds and Frou<le numbers. As ca.n be seen in

Figures

indicating a linear va.1'.'iatiot1 of the 8(-:lected variables w:i.th

percc.;:nt passing or performance.

figur-es 8 s 9, and 10 also give an indication of the or,der

of importance o:f the throe var.iables in that the vari.abl.e which

is effective ove:t' trw.~ t..iidest I'cmge of values can be eJ~pei'.::-ted to

have the most p:romirKmt tota.1 effect. In other wor•ds e the

parameter- which va.·.des the most ca:.n be e~rpecte<l t:o have the gretit-

est effect on perform.:m.ce., The Izeynolds number can be seen to

show the g!'eate::'t range of V<.">.x•iati.on 11 with the From.le number

-25-

TABLE III

P..esul ts of Experiment I - Trough 1

Particle size o. 72 mm

' p H velocity grit grit percent

ft;. ft. ft./seco added trapped passin1~ ml ml

-·

0.10 0.225 0.570 133.5 133~5 -0.10 0.280 i)~ 803 131.J..O 1.34.0 -0.10 0.300 o.soo 135.o 135.0 -

Experimentldiscontinfe<l

'rABI,E IV

Results of Experiment II - T1~ough 3

Particle sh::e 0.36 mm

p H i?eloclty grit grit pericent ft. ft. ft. /sec. add~d ti:•apped passing

ml. ml

0.,05 0.15 o.ss1 1.76.0 176.0 -0.05 0.17 0.695 175.0 175.0 -0.10 0.28 0.803 175.0 175.0 1.0

Experiment discontinued I I

p H ~relod:ty

fl:. -f ....... ,.- .... .ft./scc ..

o.os 0.1.3 0.1}92

0.,05 0,.15 0,.587

0.05 0.17 O,.G95

0.10 0 .. 20 o.1p+o 0.10 0.22 o.sss

!

0.10 0.24 o.ti2s 0 .. 10 0.26 o.ns 0.10 0,.25 0.,715

O.lO o.2a o.aos 0.10 0.23 o. 80~l

'

0.15 0.21 o.1.i31

0.15 0.29 o.s2i1-o.1s o.31 0.606

0.15 0 -'.)~~r: • "v...; o. 716

TABLE V

Rcsu.1 ts of f.;{pEn:•:tmmrt :i: n ... 'l'.\"p1..l.gh 1

Pnrticle s.:1.ze o,. 2 mm

n:eynolds 1-':r:-oude gr:'i:t mrnhc:r l111mber ;ziiichI?d

Nn N't~ 1~1. .t~ •. ..

o.533 it 10 It.

(t. 057H 132.0 ir..1~ 0.871 't .... 0.0113 131.0

1.169 x 10 l~

0,.0882 128.0

0.870 x 10 !~ 0.0~01 130.0 IJ

1.16!~. x 10' o. Ol~Ot~ 127.0 1. i~a1!. x io 1~· o.osos 121.0

ti l .. 839 x 10' 0.0611 153.0 •• p•:>r> 104 ..!.. • . :»);:f :;.{ fl.0611 isii .• o

2. 2'.211 :~ 104 0.0?15 1!12.0 . 1.t

2.221.~ ~: 10' 0.0715 JJ.~2. 0

l.lf.'? x lOi~ o. 02?.0 . l!t6.0

1.503 x 104' o.02si+ lt}l}. 0

1 n1.-R 101.J. +O·.h'- X ...... o.osos lHO,.O 2 "7" 101t .0 "· x . 0.01+75 1'29,0

---~· ....

grit t:ra.pped

:ml ..

131,.0

128,.0

lJ.9.0

127 •. Q

121.0 109,.0

12tt.O

131..0

113.0 105.0

11-~ii. a J-1.i.o.o

129.0

97.0

percent nassing

o.a 2.3

7.,0

2.3

~. 7

9.9

19.0

14,.9

20.1.t

26.l

J..l~

2.3 7.9

2LJ .• 8

i

"' Cf)

'

;

' p H velocity

ft:. ft. :ft.ir~ec.

o.os 0.13 o. 11s2 ' 0,.05 0 .. 15 0,.587

' o .. os 0.11 o.sg5

0~10 0~20 0.492

0.10 0.22 0.535 0.10 o.2i~ o.l~25

. 0.10 0.26 o. 715

0.10 0.28 o.&os 0.15 0.21 0.11-37

0.15 0.29 o.524

0.15 o.31 0.606

0.15 0.33 o.682

TABLE VI Results of Exper:i.ment III - T:r.ouff.h 2

Particle size 0.2 mm

Reynolds rroude grit number number added

n·P H ml. ·' ''r

o.6~53 x 104· 0.0578 170.0 0.871 x 10 l.f. 0.0713 170.0

• i~ 1.169 x J.0 o.ons2 164.0 !~ 0.;870 x 10. 0~0301 154 .. 0

l.;161.} x 104 Q.040LJ. 153.0 l.L~84 X J.0

!~ o.osos 11.i.s.o 1 s~0 10!~ . • ..J ... 1 x. t 0.0611 148.0

!• 2. 22l~ ~ 10 t o.011s 1.26.0

1.167 x 1011· 0.0220 1'-l5.0

1.503 x 10 4 0.,0294 l!.1-3.0

J..858 Y- io1·t· 0.036$ 139.0

2.226 x 104 0.94313 129.0

grit trapped

ml.

170.0 164.0

152.0

153.0

ll~5.0

126.0 126.,0

%.O

143.0

139.,0

129.0 100.0

percent pass in~

---3,.5

7.3

0.6

5.2

13.l

14.9 23.6

2.1 2.B 1.2

22.s

I !'\) -..3 I

TABLE VII

Results of Eltper·iment III - T1~ough 3

PID.~ticle size 0.2 rnm

.,-, f-! velocity Reynolds Fron.de gl"it r:

:ft. ft. ft./sec. number number added H F ml. -~..., 'Z""I '·'r l'.

-o.os 0.13 o.ti.~2 o.633 1~ 10

!~ 0.057B 161+. 0

o.os G.15 0.587 0.871 x 10 l\.

0.0713 J)~l. 0 1J.

0.05 0.17 0.695 1.169 x 10. 0.0882 136. ()

0.10 0.20 0.1+1~.o 0.870 x 10 It

0 .. 0301 1611-.0

'' 0 .. 10 0.22 0.535 1.164 x 10 i~ o.o4o4 175.0

0.10 0.24 0.625 1. Lj.f)!~ X 10 l.}

0.0505 169.0 0.10 D.26 o.11s 1.839 x 10

ii 0.061.l 150.0

0.10 o.n 0.003 2.2211. x 10 4 0.0715 130.0 I' 0 1 i· 0.21 o.1rn1 1.16'7 )~ 10 ·+ o.o?.20 152.0 ·-:,)

0.15 0.29 0.521~ 1.503 i< 10 4 0.0291.J. 147.o

0.15 0.31 0.606 1.853 " 10 1.j.

o.o36B l~-0. 0

0.15 0.33 O.GB2 2.226 x 10 I~

O.Ott38 121.J..O

~~rit t1.,apped

ml.

151.0 13G.O

128.0

151~.o

169.0

J.50.0

130.0

lot:•. o

JJ~7.o

lli2 .o 221.~.o

7H.O

p~"!r-cent

passing

l.B 3.5

.5.9

-ii. G

11.2

13.3

18-5

3.3 3.t~.

11.U. ~i1 .1

I

'" (';:J I

TABIJE VIII

Results of E:>tJ;H:n'l.ment IV - Tr•ough l

Pal.'ticle s.i.ze 0.1 mm

t p ;,i '. velocity Reynolds Fx•oude g:vit

ft. ft. ft./sec. nrnnber numbe1"' added ,, u rnl. !"L:> n,... J., r:

t1. o.os 0.11 0.3% 0.1.~31 }{ 10. 0. Ol~l~3 128.0 o.os 0.12 0.417 O.IJ.95 x 10 4

0.0450 135.o 0.05 0.12 0.1117 0.495 ~ 10

l.J. 0.0 1~50 134.0

0.05 0.13 o.i~92 0.633 x 10 4 0.0578 127.0 ~t o.os 0.13 o. i~92 0.633 x 10. 0.0578 126.0

0.15 O.lt~ o.536 O. 7W2 x 10 4 0.063'7 131.0 o.os 0.15 o.587 0.211 x 10

!J. 0.07.13 ll~3. 0

0.10 0.19 0.395 O. 711·2 x lO i.~

0.0255 129.0 0.10 0.20 o.4tW 0.870 x 10

$.~ o.oso1 135.0 0.10 0.21 0.490 1.01n ,~ 10

l~ 0.0355 137.0

0.10 0.22 o.535 - . .. }.~ ..1..164 }I; l,0 0.01~01+ 125.0 0.10 0.23 o.ss1 1.335 ~ 10

lj. 0.04.55 122.0

o.1s o.2s Oo396 1.018 x 10 IJ.

o.01a1 128.0 o • .15 o.,'.27 o.i137 1.167 x 10

!~ 0.0220 133.0

0.15 o.2s 0.1~32 1.335 x 10 ti o.02sa 130.0

o.1s 0.29 0.521+ 1.503 % 10 t}

0.0294 132.,0

gr•it trapped

ml.

115.0 na.o

108.0 103.0

102.0 88.0

86.0

110.0 io1.o

93.0

80.0

02.0

105.0

99.0

90.0

B2.0

pe:t"cent ·past~ir1g~

9. t~

3!i·. 8

19.4

18.9

19.0

32.8

39.9

lt1 .• 7

20.'7

32.l

36.0 LHJ~:l

18.0

25.6

30.8

37.9

I l\) tP

'

TABLE IX Results of Expex•.iment IV - Trough 2

Particle size 0.1 mm

p H velocity Re5molds l:roude grit ft. ft~· ft. /sec. numht:r number added

N l) N.,.., ml. .I.'\. t

LJ. o.os 0 .. 11 o.396. I O.lt31 x 10' o.oi+43 130.0

o.os 0.12 0.1~17 : o.i~gs x 10 tf.

0.01.~50 131~. 0

o.os 0.12 o.ta7 0.1195 x 10 L~ o.o45o 138.0

o.os 0.125 c.4lrn o.ssl.!- x 10 4.

o.oi~99 130.0 o.os 0.13 o.492 0.633 x 10

11. o.os1s 11~2 .. 0

o.os 0.14 o.536 0 .. 11.12 :'{ 10 !~

0.0637 137.0 o.os 0.15 o.sa7 0.871 x 10

L~ 0.0713 144.0 ..

0.10 0.19 0.395 0. 7L~2 X 10 •; 0.0255 119.0 0.10 0.20 0.1+40 0.870 x 10

1.j. 0.0301 132.0

0.10 0.21. o.490 O.OJ.B x 10 It 0.0355 135.0 0.10 0.22 0~535 o.164 x 10

1.j. 0.011.ott 130.0

0.10 0.23 o.ss1 . l~

1.3:35 x 10 .. 0. (JL~65 125.0 I~ o.1s 0.26 0.395 1~_018 ~< 10. 0.0187 133.0

o.1s 0.21 0,.437 ... N. i-- 0- 4¥' J.. Hi 7 x ,.LO 0.0220 131.0 o.J~S .0 .. 28 0:1rn2 I 4 . 1.335 x 10 o.02ss 136.0

o.1s 0.29 0 • 521I . 4

1.503' x 10 0.0299 136.0

grit tj.'apped.

ml.

120.0

108.0

97.o ·106.0

108.0

· 101.0

88.0

103.0

101.0

87.0

,'7<;,l;O

Gl.O

111.0 103.0

98 •. 0

81.0

per>cent passing

7.7 19.5 29.7

Hl.5

23.9

26.3

38.9

13.4-

18.9

28.7

39.2

51.2

15.5

21.4

27.9

40. l~

I w 0 I

TA .. BLE i{

fa~sults o:f Experiment: IV - T1'.•ough. 3

P2.rticle size 0.1 mm

p H veloc.ity Heynolds Froude g:r)it ft. f·t. :ft./sec. number n-umbe1" a.dded

.NR frr ml.

l~ 0.05 0.12 0 .11.17 O.i.!95 x 10. O.OLJ.50 135.0 0.05 0.13 o.1~,92 0.633 x 10

4 0.0578 138.0 l!.

0.05 0.13 O.l.J-92 0.5:33 x 10. o.os?s 128.0 o.os 0.14. o.536 0.7L}2 X 10 ll· 0.0637 131o0

o.os 0.145 o.566 0 «•2 - 104 •'-',.,Lo. ... x ....._, o.068G 136.0 o.os 0.15 0.587 O.f.i?l }t J.0 1 ~ 0.0113 156.0

0.10 0.20 o.440 o. 8'70 :x: 10 ll 0.0301 164.0 ti

0.10 0.21 o.i~go 1.018 x 10.,. 0.,0355 in.o I•

0.10 0.22 0.535 l.16ll X 10 r 0.0401~ 129.0

0.10 0.225 o.s6o le 2Lfp :'°' 10 I.~

o.oi~a3 13:3.0

0.10 0.23 o.ss1 1 ':'• 3 r.; • l () l~ ....... v ... ., x \ 0.,0%5 l!.!-l~. o J•

0.10 0.24 O.G25 1. 50~:l :l': 10 '1' 0.050S 132.,0

0 .1t; G.27 0.!}3.7 1 . .., ~ '""'f -~~ ·i n 4 ... ~ .. ~~· ,,,, l ;1.·,. ...... "' I"\ "'')"-'""' ;_•. j '- "',; l~jO. 0

l• 0.15 o.2a o.tJ.82 1.335 % .10 r 0,0258 132.0 0.15 0.2\':i 0.5211. c-n-:> . ll l.,,,_,., x 10 0.0291-f. 130.0 0.15 o.so o.ss7 , ""': -~"' . if.

·•·• >:-l:IL. ;< .lO 0.0333 H2.0 '

grit trappGd

ml.

109.0 98.0

CJS.o 93.0

97.0

38.0

123.0 86.0

88.0

77.0

70.0

57.o

~"h ('\ ...to.V·--•.• ,...

gg.o

83.0

n.o

perc~!nt

passJ.ng:

:rn.o 29.0

23.4

29.0

28.1 1{3.0

25.0

30.0

~H.8

112.1

51.L?.

56.B

l")t\ ('\ <4V•V

25.0 35.2

14.5.3

.

I <P 1--1 I

-32-

TARLE XI

Results of Exner5.ment. IVR - Trough 1

:Repeat of E'tperiment IV Using Washed Sand Nakeup

Pc:rticle size 0.1 rnm

---....... .-...... . ._,,..., .. __ '1u,:.- - -.--.. ~~ .. ~ .. ·.~.:..c-_,, ............ 1 ........... .,... .oir:

grit g~it

P. ,, ,, velocity added trapped percent ft .• ft. ft./sec. ml. ml. passing

0.10 0.19 o.395 130.0 110.0 15.4 0.10 0.20 0.4'+0 136.0 lOL~.0 23.5 Oo10 0.21 O.IJ.90 137.0 97.0 29.2 0.10 0.22 o.535 J.25.,0 77.0 38.4 0.10 0.23 0.587 122.0 64.0 47.5

0.8

~ ,/

:'.::J'I 0 ,:::. ,/ " " "

""1--... .u <;J c I /)

C) / r.f:.

0

~ o.s~{j) r I s a4 ~1 _·_· --'----l....'----'-----'-'-----J..----L.'---L-----1-iTi-r_o--1.u_q_h---1.•n __ o_. _1 __ __

0.8

0.8

.. '::J'I o. 6

"'\-... ...... '-> ~ o.s ~ I &

I I

' I

10 20 .30 40 so

I ¢

/:::,. _-a----- .

Trough no. 2

10 20 30 40 so

--e------A ---~

~

Trough no. J 0.4.._ __ ...._ __ ..__ __ ...__ __ _._ __ _._~....__ __ ....._ __ ~ __ _._ __ _._ ______ _

10 20 .30 40 so Percent of grit passing. trough

0------0 0.05 ft weir heiqhf-A .ci. O. / 0 ft. weir heiqht m-----8 0. JS ft. weir h~iqht

Figure 4: Velocity vs. percent gn~pass1nq frouqh for Experiment Ill, 0.2mm.

0.7

v) 0.6

8-~0.5

-!----. u () 0

Trough no. J ~ 0.41·-o.3~. ~-'-~-'-'~-L..~-L..'~-'-~_._,~_._~__._1~__._~__..1~~

0.7r v) ~ !

::·:~~ "'i- .

....._

~ 0.4t

10 zo 30 40 50

-0 ..- --.,.,. jY' ·,

;;...-

-~ r-- 0 -0--7~-

__ -0 !.:,

Trough no. 2 ~ I 0.3.__~L--~.I--~"'--~-'--~-'--~-'--~_.__~_._~__._~_,_~

0.7

<r) 0. 6

~

10 20 30 40 so

Trough no. J

10 20 .30 40 so Percent of grit passing trough

0------0 0.05 ft. weir heiqht t:i. A 0. 10 ff. weir heigh f [J---o 0.15 ft. weir heiqhf

Figure 5: Velocdy vs. percenf grit passing trough for Expenment N, 0.1 mm.

0.7

<I) 0.6 Q..

<;..: o . .s

Trough no.1 Weir heiqnf = 0. 10 ff. 0---0 Experimenf IJ[R 11r---e. E xperimenf IJl

10 20 30 40 so Percent qr1f possinq trough

Figure 6: Comparison of repeat series with oriqinal series

,.- • '~11-,· oz c xpe r/rnen t J_J_ - . rnra. i// I 0,-/:: v2.10C!TU = .:J 7s

J 2 O~ Wo ~ bi~

Trouoh -> / 2 3 ./

T\ I! 00,.-_(.!. Ljeprn - . .:J 1 1.

3.5Js 2.0% P2

2 0 '5 (!. , I ,T I.

3.Z~~

~~~~~~~~~~~~~~~~~~~~~~~-

Experiment JI[ - 0.2 mm. Veloc1 fLJ = 0. 7 Ys

7. 5?a 7. 5% 6.oz

rJ t1 f3 Trouah -... / z 3 J

Depfh _,,_ 0. 0 5 Fi.

Experimenf IJZ- O!m1n. Ve I oc if y = 0. 4 ~ 1e.s5<>

Trou9h ~ / Depth ~ ..

11.oz

2 3 0. 05 ft.

Ex1oerlme.nf IJT- O.lmn1 Ve i o c / t lJ =- 0. 5 Z £s

27.S~ 27.0fb

/i·ouah __,,,.. / 2 3 .J

Depth - 005 ft.

30.0J;

/3.5% iS.5% /J.7%

j 2 3 2 3

0. JO ff 0.} 5 ff.

21.0}; I 9.0'k . ·D /"'Qt:· I. /o i6.D0

2 3 2 3

0. J 0 ff. 0.15ft.

35.0~ 3?.0~

38.5%'

~ I

2 3 2 3 0. /0 ft. OI L) f"l . ...,., n.

Flqure 7 : Bar qroph comparisons of percent qrii pass1n9 trouqh for Trouqhs J> 2) & 3> under ideniical conditions. ~

40

0

... 25

-V) 20 V)

15

I I 0 I

5 .... I

o! 5 I 0 I 2 o,N (10 -4

a l.....____.......______ ___ _ __ J __

0 06 08

R I N ~ 10 -1 iJ o ~ no.

- -0

1 2 3

U er gr Lo er r

0 05 07 0(9 Fr o 1 e no I ,,

I

? I· I ~

I I ,,

4

_ __ L_~-.J--___,_-~_..__ _ _ O C4 0 c -

hj 0 2 " ' 111 p , r I 5 1 e ,5 0 I r. in r 51 z

0 ?2

0..? O?

I '/ ' ,,

V.5 . s fo r

,/1

JO

0 25

20 0 0 -V) ....a .0 V) /" / ,..-::; / /

/~/ 15 //~/ Ii;. ,,,"'~ 0

-.,...... /'.:/' 10

\J

0 '-+=~-'-~--'-~---L- __J

0{!, J O 1z 1.4 I 6 I 8 20 Z.2 0. 2 05 06 0 7 0. 4 0. 5 06 RelJ ol s n o. I NR ,. ;0 · 4 (! o , NF ( /0 Oep f / w 1dt h/w

55

50

4 5

;G f1 ? I JI I ~/ I 1J..

/ .

I lh I

lj I '/;

I

40

35

3 0

'i..... 25 ~ v

20

~ 15

10 07 08 0 10 I I I 2 J 3 I 4 02 0 4 0. 0 0. 0 04 o 4 Z 0. 4

Reyno! s no , NR ' 10-4 no, Nr .. ;o D f I h , Yiv 0 0 Ti O U 1

TJ O U 2 Up 5 = 02 J size F1 e 9 · Per e ~ - - - -.::. Lowe s : Olm sele e 0 9r p . por SJ?e 0- --0

" l u J 0 .10 ft w

35

JO

25

V) 20 V)

15

10

5 1 r 8- - - . Ir" - -

ol_· _, __ -· - ·- ·' - --I . I 13 I 5 I 7 I 9 2 1 2 25

Re y1 olds no., NR i /0 -4

45

4 0

5

0

25

20

15 _ _ ___ _ -- - -- __ , 10 I I I 2 I 6 I 7 0 01

R e o/ 1 10 1

N R · /0 - 4

0----0 Up e Lo r

- --- 6. J

0--{]

- - --00

Fr o

L -co

c:J r I I I I I I I I I 'f I t

I '/ I ,' I I I '/

' I 'I

~ ~~

' -oo · ae

I

Ol4 005 0

n I NF De

/

tS

0 5 62 0 70 I / V\. 1 I I

7/w

~

I ~ I '0

I fJ/ I I

I

./ I I~ I

/I ---·-_ , __ .____..__ __ ..__

1.J 0 3 5 2 0 5 4 0 5 6 0 5 0 6 0

l'J;- D;J lh/vt11dfh, Yw s = 0 · 1n p.Jr F1qure l :J P cenl

selec l e 15 I s - 0 I 1 rr1 , s 1 e

-4-0-

v. DISCUSSION or RESULTS

The cm'ves plotted in I'iguren 4 and 5, for velocity versus

per cent passing, show the same gene:r.•al con:figuration for each

trough ntudied and~ therefore, gi•1e little indication of relative

perfo:r.mance.. The p:redominance of the o.o5 feet weh' height curve

to the ll:::ft and the 0.15 feet curve to the right was expected

since a.t the shallowe:t" depths the grit particles had a shorter

distance ·to travel to l"each the bottom than at deeper depths.

The bar graphs in Figure 7 also do not give an indication that

any one tr1ough trappc~d more grit than the others.

Becaur..ie it is desh1able, hoi.-1ever, that a grit chamber have the

ability of selectiv-e sedimentation a comparison was made to indi-

cate the ability of the chambe:t:' to trap 0 • 2 mm particles and pass

the 0.1 mm particles. In order to 1J,3st determine th<:.~ selective

sedimentation px'Operties of ea.ch trough the per cent passing values

fo:r. the 0.2 mm particle size were subtracted. from. the values for

the 0.1 mm pID".'ticle sizf), and the :t'esu.lting values were plotted

against the parameters effecting scour. namely, Reynolds numbe1",

F'roude numbe1"', and depth. Th.is analysis most clearly evidenced the

selective sed.i.mentation pr•ope1"ty of each trough because taking tbe

dlfference of the ti;ro pe1"'c1.mtages indicated which trough was

operating over the widest range. A trough with a wide rang~1 at

any one velocity would hmre a. high per cent passing for small

... 4J.-

partlcles coupled with a low per cent passing for large particles,.

A fair comparison could not be made 1 however, unless the

th1.>ee troughs wex•e compared under. identical scoul" conditions. In

order to accomplish this .it was necessary to select a particle

size and determine the corresponding scour velocity for each weir•

setting. A particle size of 0 .15 mm 1 an ave1"age of the two par-

ticle sizes actually used, was selected and the Shields equation

(1) was used to deteI'Illine the particle diamete1., which would ba

scoured hy all of the velocities >ihieh were recorded during the

experiments

(1)

V - scour velocity 0

k - constant for coarse sand, 0.04

f ... fric:t ion ±~actor from Moody cm."ves using sand diameter- as .

absolute rough~ess and lJ.RH as equivalent diameter

s - specific grovlty of particle, 2. 74 9 deter·;nined by .l\S'l'M

test 9 designation D8511·-58

d - diameter of .pal':'ticle

Once these particle diameters were obtained they were plotted

against their respective scour velocities for each weir setting in

Figurie 11. The plot in Figure ll enabled a. scour v~locity to be

read fol'.' the choHen o •. 15 mm particle diameter for each weir setting.

The scour ·;relocity thus obtained was used fo Figures 4 and 5 to

read an actual per cent passing value at that velocity. 'l'he

<liffe1 .. ences fo the peI>centages of the two pal':'ticle sizes taken

-42-

from Figures 4 and 5 are plotted against the selected scoul'.'

parruueters in Figure 12.

Figure 12 shows that the difference in per cent passing is

gl'eatest fo!' '.!.'rough 2 at the extremes of the range and nearly equal

for all three troughs at the midpoint of the range. 'l'hi.s i.ndicated

that Trough 2 had a high capture of large p9.rtic:tes along with a

low captur•e of small pa17ticles in comparison to the other troughs.

Therefore, the ability of selective sedimentation appeared to be

greatest in Trough 2.

An attempt was a.lso made to determine a ~::,:diction equation

which would describe the phenomena occur:l'ing in the chamber. There

were four variables which were felt would enter into a dev·alopment

of a prediction equation, Reynolds number, Froude number, depth,

and per cent passing. Since four- variables are very difficult to

work with in a dimensional analysis one was chosen to be eliminated.

As stated previously• Figures 8, 9 and 10 showed that the depth

variable was last in order of .i.mportnnce, so it was neglected in the

analysis.

The three remaining variables were plotted in Figures 13 and 11~

.in an effort to determine how the parameters combined, in addition

Ol:' in mul't ipli.cat ion. The Reynolds number was plotted against per

cent passing and the Fl'."oud.e number indicated at aach :r.esl.llting point.

An interpolation between the varying values of Froude numbers was

then performed to produce two series of points for two constant

valueB of F:r.•omie number. If the two resulting constant Froud'2

number lfo.es were para.llel 9 then the remaining two Vi:i1~iables would

be knmm to eon1b:i.11e In o.ddition. If they were parallel when plotted

in a J,oga1>ithmic plot, thay would have been known to eombine :i.n

multiplication.

Figu:r·e 13 shows that the constant Froude number points have no

semblence of order• about them for the 0.2 mm particle s.rne. A rough

logarithmic plot did not bring about ai.<y improvement•

In Pigm"e 11+, how"vor, the points produced two constant F'"t.,oud.e

numben."' lin(;is which were closely parall•.:il. This gave e·vid.ence that

the par.>ametel"'S would combine in addition, but a.n attempt was not

made to produce a prediction equation because the results in Figtu."'e

13 were contradictor'Y ~•d, therefore, a gen~ral equat:i.on could not

be evolved.

V)

s::s__ 0 ~ .7

Q O.?t (.._;

.....---..' ~ '- 0.6 ::::;,

-i-

G 0.!3 ~ ~ \ ....... 0.4 ~ () o.3' ~

-44-

Vveir seifinq = 0.05 ff.

0.06 0./0 0.14

Weir seffinq = Q/O ff.

0.5 25 I I I I I I

\!)I -.. ·I

01

0.06 0.10 0.14

g 0.7l ~ I Weir s e f fin CJ == 0. I 5 ff. ~ "'

t 0.6t_'?.·""-------- -------------~ 0.5~ I

~ I :

0./8 0.22 0.26

0. 18 0.22 0.26

~ 04: ;! V) 0.3~l~--'---~~l~~~~~l~~-'-~-'-'--'l~'--~~'~~-'--~-'-I~--'~

0.06 0.10 0. 14 0. 18 0.2 2 Porfic/e diameter, m.rn.

Figure 11 : Scour velocity vs. particle diamefer

40

36 ~ '32 f\.r

(\_<i I 28

....._ C) ~

.... 24 t)., ~ '"" ~ 20 {) Q_ ~ 16 t:: ~

(> 12

~ 8

0.0

\ \ ~

·E\ ~ '\. ~

'r.i\ '\..; ~ ~ \

'" \\.~ ,8 \

\ (!)

8-... ............. ""' ~

~' ~ ~

\ \ \ \V'" .\ b

\ \

b

_.___ _ _. __ _,__ _ _L ---1-. •• ---1-~~

0.02 004 0.06 0.5 1.0 l.S 0.1 0.2 0.3 Frouo'e no.J NF

0-- -----0 Trough 1 A .6. Trouqh 2 8---8 Trouqh 3

Rer;no/ds no. 1 NR )(10-4 Depf-h) h, ff.

F19ure I 2 : D1f ference 1n perceni poss1no for 01 & 0. 2 min. particles vs. selecfed

variables

• "" VI I

~ ...

{)'o c: .._ V) II)

~ Q.

"i-....

~ ~ ~

" ~

25

20

15

10 ~

r 5 L

1;. Froude no. -- 0. 040 © Froude no. :- 0. 060

li).030/

A ©

A

G

© 0.0713

A 0.02?0

© 0 0578

0.osos A 0

A 0 ·0882

0

~.040"l 0

0.0294

0. L_ 0. 6 0. 8 I. 0 /. 2 / 4 _...____/_._. 6_---1.

Fiqure /3:

Retjno/ds no., NR ~ 10-4

F'ercenf passinq vs. Re~;nolo's no .. of for 0. Z 1171n particle size

0.0611 ©

A 0.0368

...L. I I

1.8 2.0

constani froude no.

©

__J_

?.2

0.0115

}... (I\ t

so

40

~~

(J) . c: ~ 30 (/) t) Q.

--J.._ c: ~ \.) 20 ~

~

10

0 .01/3

0. 0355

('i).0450

<!> .0/87

/ 0.azss

(!) .01-43

0.016S

o'J ~~--0·

0 .040q

0.0ZS8

o.ono

'--~-'-~_._~-'-~-'-~--'-~~'--~-'-~-<-~-'--___J_ L.~~-

0. 4 0. 6 0. 8 I. 0 /_. Z I. 4 I. 6 Reynolds no. 1 NR x 10~4

Fiqure 14: Perceni pass1nq vs. Reynolds QO. at. constant froude no.· l'or 0. I tnn1. por/1cle size

J. "'1 t

-4B-

VIo CONCLUSIONS

'l"bis Investigation for1 to the :followlnE; conclusions:

l. A :rnod..ification of the appnratus to length~n the

o.pproach channel ~:md :.r:•<:Hluce rippling would produce hette'l'.' re-

sults in the high•Jt' V<-1loci.ty :ranges.

2. .Add.i.tfonal data is required in order to :formulate a

i•elationship betvu.wn the pm"'a.meters affecting grit capture.

3. Trough 2 was relatively mor."e efficient for the

selecti'i1<~ ca.pture of the grit pm .. ticl(1S used.

VIII. smmARY

The object of th.i.s investigation was to determin~ the

ef:f:i.ciency of three selected shapes of gyi t chamber troughs :for

the selacti.ve capture of grit.

A model grit chamber was constructed of wood with th1--ee

plastice l.ntercha.i.1geable trough sections. Water from a town

main was run th1~ough the appa.1..,atuG at various depths and velo•

cities. with sand of spec:ific particle si.zes being added to the

flow as it entered the model. Ordinary constr•uction sand was

used after being run through a series of sieves to obtain the

desired particle sizes. 1'.'he three troughs were of the same

general shape but with three dlfferent bottom lengths.

After all the grit had been added to tbe flou the process

was halted, end all the grit wh:i.ch did not pass the trough was

removed and measured. This mea.surernent when compared with the

known amount of grit which was added gave a per•centage capture

of gd.t for each run.

'l'he study showed that Trough 2, the medillli'l length trough~

was the most effect.lire for ·che selective ca.ptur-e o:f grit.

A.n rittempt was made to form11late an equation relating the

variables affecting grit remova1 9 but the data proved to be

contradictory.

-so-

VIII. ACl:C"!OWLEDGEMb"MTS

This thesis and the entil'e Master of Science graduate

program undertaken by the author were supported by a Public

Health Traineeship Award from·the Public Health Service,

u. s. DEPARTI-~ElfT OF HEALTH 1 EDUCATION 9 AND WELFARE. For this

at·1ard ·the author expresses his appreciation.

The author also eA-presses his appreciation to his thesis

advisor, Dr. William A. Parsons 1 for his encouragement,

guidance, and constructive criticism during the entir•e gra.duate

program; and to 1 for his assistance in the

hyclraul.ic aepects of this thesis.

-51-

IX. BIBLIOGRAPHY

i. Bva.'ner, H. c.,. • and Hoak• R. D .. , ''Design C:r•iteria for Sedimentatlon Basins.'' Industrial and Engineering ~?emlf?it;:x - Process Desisp and Development, !• 3 • 135 • . \July 1962).

2. Chasick 9 A. H. 0 and Burger, T. B., "Using Graded Sand to 'l'est Grit Removal AppaI:"atus." .Journal Water Pollution Control Federation, 36 1 71 890 9 (July 1964).

; -3.,. !"air1 G. M., and Geyer, J. c., Elements of Water Supplz

and Wei.ate ... Water Di~:pos~l 9 John Wiley. and Sons• :.tnc. , tic.~w Yo:r>k, 1958 9 p. 331.

5.

Metcalf, L. 9 and Eddy, H. P., American Sewe~age P~aatice 9 2_, McG!"aw ... f!f.11 Book Company, Inc., New York, 1935, P• ?.87.

Morris, H. M., .~nli-ed :f:!ydrat\lic!$. iri En!fu.ineerin_g, Ronald Press Comp;.my, :Hew York, 1963 9 PP• 5t.i. .. 59.

The vita has been removed from the scanned document

ABSTRACT

Efficiency of 8elected Shapes of Gr·it Chamber Troughs

Grit is usually removed from sewage flow just prior to

tI'eatment by sorne type of grit chamber, often little more than

a wide channel with a depressed trough to trap the gdt. Three

shapes of grit chamber troughs were studied in a model to deter-

mine which was the most efficient for the selective capture of

grit. The model was constructGd of wocd, with pla.sti.c, lnter-

ch.:-.mgeable troughs, and was six inches wide by about ten feet

long, including a thr>ee foot approach channel to the chamber'.

The three troughs were six inches deep wlth 2 :l,, side slopes and

diffe!'ed, thereforet only 5-n bottom length. Trough 1 tapered

to a point, Trough 2 had a frmr inch bottom length, and Trough 3

had an eight inch bottom length.

Watet' from a town main was run through the apparatus ci,t

velocities varying from 0.11. to 0.8 fps and. depths from 0.1 to

0.33 feet. Gvit was added, as the flow ente'X'(~d the approach

channel, through a funnel. Ordinary construction sand was used

as gI>it afte1"' be:i.ng sieved to obtain 0.1 and 0.2 mm diameter

part:tcles. When all the grit had been added the flow was stopped

and all g:r'h which had not passed the trough was r•emovrad and

measured. This measurement when cornpm."ed with the known amount

of grit which was added produced a value of per cent grit pasi;:.i.ng

the t1>ough for ench run.

'l'rough 2 9 the medium length trough., was :found to be

relatively most efficient for the selective captuN of grit.