AFD_Spillway_Safety_Barrier_(AFD_Construction_Report).pdf

PEND OREILLE RIVER, IDAHO

FALLS ·DAM

CONSTRUCTION REPORT

ON

FOUN0ATl0N rQF SPILLWAY DAM

CORPS OF ENGINEERS, U.S. ARMY

SEATTLE DISTRICT, SEATTLE, WASHINGTON

d d'

Amendment 0002

GONSTRUCTION REPORT

OF

EOUNDATION TREATMENT

AT THE

A. L B E N I F A L L S D A M P R O J E C T

A L B E N I F A L L S, I D A H 0

INTRODUCTION • • . . .

PURPOSE AND SCOPE

INDEX

AUTHORI'IY • • • • • • • • . . . . . . . . . • • •

LOCATICN

GENERAL DESCRIPTION •

SAFETY ON THE JOB • •

GEOLOGY OF THE DAM SITE • • • • • • • • • • • • • • •

GENERAL • • • •

LOCAL GEOLOGY .

PHYSICAL PROPERTIES OF' FOUNDATION ROCK. • • • • •

PETROGRAPHY 0� FOlTIWA'IICN ROCK. • • • • • • • • •

Granodiorite Gneiss.

Schist • • • • • • •

Porphyroblastic Rock . . . . . . . . . • • •

Brecciated Rock

Weathered Rock .

FOTJNDA1ION EXPLORATION

EXPLORATION PRIOR TO CONSTJ.UCTION • • • • • • • •

E,XPIORATION DURING SPILL1•:Jl.Y CONS_ q 'GTION. •

EXPLORATION DrRINO FO· �R'40llSE CONSTRICTION • • • •

WORK P RFORHED UNDTi'R FI ST STAGE CONTRACT. • • • • • •

Gtt-JERAL D SCRIPTION .

PLAN O'<' \·;Orn<. • • • •

Pao-e C, No.

L

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__ ono_itn No. " • ono ith No. 6 • • • • • • • • • • • • • • • •

?a6a No.

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:::,1 l.J;., .1onolith No. 7 . . . • • • • • •

Honolith };o. 8 •

1.,onolith .o. 9 .

onol.:. t,I: 1.u. 10

I.ior.olith No. 11

. onolit.h no • 12

.doi.oL b 1�0 • 13

.. o.,olit� , . •. o. 14

· :onol:'._ th No. 15 r-1or.olith No. lt>

_ onolith J,o • 17

,. ono2.i t.1 I\O • lu

.. o;.o 1 · t.1 ., �\.I • 19

... or.olith rio. 20

• ..iOllOl: �.h .. ,o. 21

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.:onol.;.t,l: No. 25

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• • I •

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?age No.

• ;:4

• • 3'1:

• • JS

• • 35

...,5

• • 36

�7

• • 37

• • 58

• • 56

• • 35

• • 3:;

• • 39

. • 3�

• • 39

• • 40

• • 40

• • 40

. • 40

• • 10

• • 41

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Page No.

4.7 so

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�B r rL'S • • • • • • • • • • • • • • 51

C-enertl . •

Luit l\O+ 1

Unit I�o. 2

Lnit i'o. 'Z V

Uo.i t No. '

Un::_t No. 2 un.:.t .�o. '7 V

A .:) __ ( G.

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L

(Jntc']<L) . •

(Int·ke) . .

(IntakP.) . •

(Draft T .... t:)

( Dr� ft 'rube)

( ir• 1t .i.t:.bc.)

(IL

l<'OtrNDA'IION DR}1.INS • • • • •• • • • • • • •

GROUTING ( CU'f O?F CUR1AIN).

RAILROAD SPUR • • • • • . .

STRUCTUi-tAL B.\CKFILL ANt COMPACTED 1:.JaANKJ:'<l.!NT • • • • • • •

LOG CHUTE • • • • • • • • • • • • • • •

POWERHOUSE COF!-'ET1.DAHS • • • • • • • • •

ACKN OWLE .)GEMEl� TS. • • • • • • •

APPENDIX

PETROGRAPf!IC REPORT

GENERAL FLO'I FLAN • • • • • • . . .

FOUNDATION .!iXPLORA TION PL�J-J" • • • •

FOUNDATION J.XPLORA'.I'ION LOG R.c,coRDS. • • • • •• . . . • •

FOUNDATION Ex-PLORA'HON LOG REC 1RD.S.

FOUNDAT!ON EXPLORATION LOG RECOROO.

FOUNDATION EXPLORATIOI� LOO RECORDS.

SPILLWAY GSOLOGICAL FOUND,�TIOr- fvlAP.

POWERI OUSE GEC,LOGICAL fi'OlJNDA'f'ION HAP • • • • • • • • • • •

Fc:.q;e No.

Drawing No.

ILLUcJTRA'T'IONS

Palc'.'e No.

Aerial View of Alneni Falls Pam Site prior to Con::truc tion. • • • L

General Vieu of Upstream Snillway Cofferdam. "'howin- the Solid Rock Section • • • • • � • • • . . . .. • . • • • • • • • • • • • • 16

Series of Pictures Showi.ne 1ypical ,Joint P2.ttern in lipstream Cofferdam • • • • • • • • • • • • • • • • • • • • . • • • • • • • 16

View of the North Channel Dnri.np- Preliminary Excav::n.ion of the Right hbutment. • • • • • • • • • • • • • • • • • • • • • • • • • 17

Powder Crew Loaciing !-!oles on Small Island in the North Charmel. • 17

Aerial View of Spillway Cofferdams and E�c�vation During the First Sta9;e Construction. • • • • • • • • • • • • • • • • •

View of Prelim.inary Excavation of Spillway Sec ti on, Looking 'I'owarcs the Right Abutment. • • • • • • • • • • • • • • • •

T'.\rpica] Sec-tions of Line Drillinr:r in the Spillwa:v Key 'Jrench • • • 2L

View of Sr.d 11-;-·a�; Key 'Trench Di•r:i ni:; Excavation Ooerations. • • • • 27 iiiew of Completed Spillway Key Trench Prior to Placin!! of Concret� • . • • • • • • • • • • • • • • • • • • • • • • • • • • • 27

View of Right Abutment Showing Joint.ea Rock Prior to .E.xcavation for the Spillway Key 1rench • • • • • • • • • • • • • • • • • • • 28

Pruiorama of Left Abutment Shmr.inp; 'fypical Jointing of the Grani t,e f'oundat ion Rock • • • • • • • • • • • • • • • • •

View of Water Worn ::'oundation Rock in the Soui.h Channel, Monol i. th �)o L, of the Spillway. • • • • • • • • • • • • •

Major Fault Plane 'ihrour;h Monolith No. 6 of the Spillway Showing Hani:ring Wall and i'Jidth of Gouge Filled ?ault Zone • • • • 33

Gneissic Granodiorit,e i;1 Monolith No. 10 -:)howin!?' Scat.iered ?11enocrysts in the 0anoed Grounamass. • • • • • • • • • • • • • • 35

Gneissic Granodiori te Showing 1ano ri Structure a.YJ.d _nclus ·on�, Monolith �o. JO . . .. . . . . . • • • • • • • • • • • • • • • • • 35'

Foundation Rock Monolith No. 13 Showin� Fracturinrr of the Gneissic Granite • • • •

Foundation Rock Monolith No. 17 Showing- Ty-pical Jointing in the Granite Rock. • • • • • • • • • • • • • • • • • • • •

Page No.

TY!-)ical Gneissic Granodiorite in Spillway Monolith No. 16. • 38

Closeup of Gneissic Granocliorite in Spillway Monolith No. 16 Showing banded structure. • • • • • • • • • • • • • • 38

Closeup of Foundation Rock Showin� Cl�ster of Large Feldspar Phenocr;sts in the Gneissic Groundmass Monolith No. 7. , • • 40

Foundation Rock in Monolith No. 22 with Xenoliths and Pheno-crysts in Homogeneous Groundmass . • •

Panorama View of Powerhouse Excavation in the North Channel

Looking Upstream • • • • • • • • • • • • • • • • • • • • • • 48

View Showing Turbine Pi ts a, d Intake Jenc-h of the Powerhouse Prior to Concrete Placing. • • • • • • • • • • • • • • • • • 48

View of Intake Bench (Elev. 1988)and Left Abutment Showing Cleanup Operations of the Area • . • • • • • • • • • • • • • 51

View of Cleanup Operations of Pounoation Rock by Draaline and Hand Work in Draft Tube Area • • • • • • • • • • • • • •

View of the Rieht Abutment of the Powerhouse Showing the Major Fault in the Area ano Ft-actured Condition ot the Rock

Wall • • • • • • • • • • • • • • • • • • • • • • • • • • • • 52

View of Left Abutment Showing the Major Fault in the Powerhouse Area. • . . • • . . • . . . . . . . . . . . • . •

Major Fault Plane Exposed on the n.ight Abutment. • • • . • •

Foundation Rock in Upstream Wci.11 of Turbine fit Unit No. 1 •

!foundation Rock in Upstream Wall of '1urbine Pit Unit No. 2 •

Joundation r1ock in Upstr0am ••all of 'lurb·ne Pit Unit No. l _, .

View Showing fypical Foundation Rock in the Po;:erhouse Area RiP-nt Abutment • . • . • • • • . . • • • . . . • . • . • . .

View Showine Fractl!red Condit.ion nf tl e iP.ht .Abutrne.:it Downstream -.rom Centerline of Fowerhouse Units • • • • • • •

Page No.

Closeup of an Intensely Shattered Zone of Foundation Rock on the Right Abutment of the Powerhouse • • • • • • • • • • • 62

View Showing the Jointed Structure of the Foundation Rock Exposed on the Abutments of the Powerhouse • • • • • • • • . 63

Aerial View of Albeni Falls Dam Showing Completed Powerhouse and Spillway Structure • • • • • • • • • • • • • • • • 73

CONSTRUCTION REPORT OF FOUNDATION TREATMENT

ALBENI FALLS DAM PROJECT

INTRO ID CTI ON

PURPOSE ANr· SCOPE

This report is assembled as a permanent recor d for the purpose of describing all of the foundation treatment, and operations during the construction of Albeni Falls Dam Project. In general this report will cover the follow.ing operctions:

a. Preliminary foundation investigations to determine character and condition of foundation rock.

b. Treatment required to handle the foundation.

c. Excavation of spillway and powerhouse floor and abutments.

d. Shallow low pressure grouting of t he structure 1 s foundation and enlarging of the right channel.

Inclu ded in this report is a detailed description of the methods employed, difficulties encountered in performing all pertinent work, and condition of the rock before concrete was placed. Photographs, maps, and drawings o.f the work accompany this report.

The construction of the project was accomplished by four prime con tractors in f our· separate stages, consisting of the following: first stage, preliminary excavation; second stage, spillway construction; third stage, powerhouse construction; and fourth stage, generator installation.

AU 'l'HORL!!

The Albeni Falls Project was authorized by the Flood Control Act of

1950, approved 17 May 1950 (Public Law 516, 81st Congress, 2nd Session).

Work on the dam was started on 4 January 1951 and continued until completion of the structure. This foundation report was prepared in accordance With letter from Di vision Engineer, North Pacific lli:vision, Corps of Engineers, Subj ect: Foundation Reports, dated 22 December 19h8.

LOCATION

The Albeni Falls Dam Project is situated in Bonner County, Idaho, on

Pend Oreille River, approximately 25 miles below the outlet of Lake Pend

Oreille. It is two miles east of Newport, Washington, on the Newport

Priest River Highway, u. s. Highway No. 2. The main line of the Great

Northern Railway gives ready access to the si 1,e, passing through a cut, in the left abutment of the spillway dam at Elevation 2080.2 feet above mean sea level. A spur track off the main line gives rail access to the right abutment.

GENERAL DESCRIPTION

The spillway unit is a concrete submerged type gravity structure, 805 feet in length with a normal height of 83 feet above the stream bed.

However, in the south channel of the stream, the height of the structure is 1 23 feet. Th e spillway consists of 10 bays with �Umited flow capa-city, controlled by two leaf vertical lift gates, each 40 feet wide with an overall height of 32 feet, supported by eight foot wide piers. Eleva tion of the spillway crest is 2033.0 feet, and the bridge deck is 2097.0 feet, producing 1,153,000 acre-feet of usable storage.

The powerh�se unit consists of three generator units and the assembly bay located across the north channel. The total length is

301 feet, with an overall height of 188 feet, elevation of the generator floor 2060.0 feet. 'Ihe principal elements of the powerhouse structure are the turbines, generators, control gates, shop facilities, and control floor, with all necessary operating equipment. Total generating eapacity is 42,000 ldlowatts. Appurtenant features connected with the powerhouse structure are service area, transfomer yard., swi tchyard, and log chute.

Ref er to Drawing No. l, Plan of the Dam Site.

SAFETY ON 'lHE JOB

The excavation of the foundation for the structure necessitated that safety regulations be strictly enforced due to type of work and the weather conditions encountered. The clearing of the north channel of small islands and the diverting of the river had to be accomplished under hazardous winter conditions and extreme care was used to protect the work men and safety precautions., such as walkways ., ringbuoys, and safety lines were used to full extent.

The abutments o.f the spillway and powerhouse were potentia.1 safety hazards, but safety belts were used extensively by the workmen and abut ments were kept free of loose rock. The contractors, ',,lflile not required by regulations, employed a full time safety engineer. This is an indica tion of the good relations in safety matters., that existed between Govern ment and contractor personnel. Excellent safety records were made by the contractors during all phases of construction.

L_

Aerial vie� of Albeni Falls Dam Site prior to construction

GEOLOGY OF THE DAM SITE

GENERAL

The geological past has left its mark on the countryside with its rugged hills and deep valleys. The sedimentary rock of the area was deposited during the pre-Cambrian age. These sediments were later in truded by acid and basic intrusions during the Cambrian, Ordovician and

Tertiery periods. Scattered outcrops of these intrusive rocks are found throughout the area. Faulting and f<?lding is also well pronounced in the area, along with erosion by streams and glaciers.

The ltlai.n features of the area were formed by the structural growth of the motmtain ranges and valleys caused by the faulting and folding with interspersed periods of erosion. The Pleistocene glaciation also played a major role in the forming of the present topography of the area and controlling of the present drainage pattern of the basin. Pleistocene glaciers scoured out Lak e Pend Oreille and at the same time another lobe of the ice mass moved south down the pre-glacial river bed which followed closely the present course of the Little Spokane River.

Through glacial erosion and outwash, which filled the old channels, the river was diverted to its present course where it remained after the receding of the glacier, so that present drainage is entirely post-glacial.

The pre-glacial stream of the present Pend Oreille valley was flow:i..ng in a southerly direction and was reversed by glacial scouring of the divide near the Canadian border and debris filling the southern half of the drainage valley.

LOCAL GEOLOGY

The geologic structure at the dam site is composed o.f a grano diorite (hereafter called granite ) ridge extending across the valley, with exposures on both abutments and om the numerous islands located in the river channel. Outcrops have been noted for several miles to the north and south of the site. The ridge slopes steeply upstream and down stream from the site, making an excellent barrier across the river.

The rock is a hard granite, which is moderately to closely jointed with varying degrees of weathering and some faulting. Three master faults were found to be passing through the spillway section at right angles to the axis. In the powerhouse area a major fault passes through the abut ments and floor foundations on approximately the centerline of the uni ts and dips downstream. 1'vidence indicates that there are areas of closely jointed and softer granite both downstream and upstream from the ridge.

PHYSICAL PROPER:rms OF FOUNDATION ROCK

The foundation rock is generally a unifo� grained granite which shows varying degrees of alteration and weathering. Minor portions of the foundation are composed of schist, porphyroblastic and brecciated rock.

The granite (granodiorlte) is a gray-rock w ith unifonn gneissic structure and contains plagioclase and orthoclase porphyroblasts up to two inches in size. Small inclusions of hornblende-biotite schist are also found throughout the foundation rock. Pronounced kaolinization of the plagioclase feldspars and complete chloritization of the biotite minerals is prominent in some areas of the foundation. Representative samples of the predominant rock types encountered in the exploration drilling were selected for compressive strength of the foundation. The results of these tests are as follows:

Hole No. Depth Ft.

16 90 19 95 19 85 35 90

43 95 43 62 43 74 45 20 46 68 48 170

Type of Rock

Granodiorite Gneiss Quartz Latite Quartz Latite Weathered Altered Granodiori te Granodiori te Granodiori te Granodiorite Fresh Granodi6rite Brecciated Granodiorite Fresh GranoJiorite

Compressive Unit Weights Strength PSI Lbs/Cubic Ft.

17,424 175.7 10,758 178.7 18,648 165.7 18,746 164.3

11,758 174.2 14,451 163.4 6,764 164.e

16,012 168.1 11,711 166.8 25,144 170.7

The average bearing strength for the sample tested was 15,139 'J.�.i.

The te�t specimens usually failed alone the pre-existi�g joint planes that were filled with sacondary mineralization.

During the stages of excav.J.tion for the spill.my and powerhouse it was noted that physical changes in the rock occurred with definite lines of control. Fracturing plays an important part in the foundation rock with major faulting located in both the spillway section and parallel to the centerline of the turbines i� the powerhouse. The exposed foundation rock of Albeni Falls Dam is more than adequate to support the low head structure.

PETROGRAPHY 0:::-' FOUNDATTO�. ROCK

The foundation rock for Albeni .tt"al�s Dam is composed pri;-,cipally of a granodiorite rid6e tr at is exposed oy the river channel. The lithologic character of the rock is in general a granodiorite gneiss, with varying extent of alteration and weathering. A minor area of dacite porphyr-.r was also found in the foundation.

The following petrographic descriptions are based on detailed micro scopic examination of thin sections prepared from representative samples obtained during the exploration drilling o: the dam site. The analysis was made by Arthur W. Schmidt, Chief, Petrography Branch, North Pacific

Division Laboratory in June 1952.

a.- Granodiorite Gneiss. The minerals, oligoclase, orthoclase, hornblende, biotite and quartz are predominant with aci..:essory minerals of magnetite, titanite, allanite, clinozoisite, and apatite which occur as traces. Alteration minerals are chlorite, kaolin, and sericite in the feldspars with veinlets of calcite, quartz, feldspar, a!1d epidote.

Hematite and pyrite m:i.nerals were also noted in minor quantities. The crystals are generally anhedral to subhedral with noted alteration pro ducts present. Zoning and twinning are also present in some crystals.

The gneissic rock varies in degree of alteration, brecciation, vreather ing and the number of prophyroolasts.

b. Schist. In the areas where the structure is on the schist side, the sample contains more hornblende in proportio:1 to the amount of feldspar present. The mineral biotite has been altered to its secondary product chlorite. Some hornblende shows alteration to actino lite.

c. Porphyroolastic rock. The porphyrobl�sts enclose many small k:J.olinized plagioclase crystals which are very pronounced. Biotitc minen.1., are eo,n. letoly ch ... oritizec1, an� iron oxi.ae mi.1erals filled t 1e rn.inute _·r'lvtu.res.

d. }b::cciate::d 1tock. 'l''.te urecciab� l rock campl..!s are filled .vi th the iror, oxide rociucts and alteratiun ;;! t;1e pla6ioeJa.se t., kaolin and oiotite to chlo_·ite a:1d some ho:t!'!blende to ,;;Ctinolite is present in i:.he specimens.

e. .ieat 1ere_g_�. l':ie weathere:i s�mpl3s all show advanced al teI' ation of all the 1n.inerals present.

A ..ietailerl pe:.ro• raphic repo�·t .:...n:!. p•1otograpn or core sa�ples .may oe found. .:.:1 the appen.:.ix of ':.his report.

lOUID1H�ON c.XPLO.c .l'lON

Ini :..:.al explor�Lion we\s done on tne site in 1943 .rhen nine hole::, -..ere drilled in Jhe i1ortn cham.el b.r ,he Portland Di3trict. ifo furt:Ocr work 7m.s ctone until 5 July 1950 when the Seautle Dis .rict, Corps of

.C:ngin�ers, explorar.ion protfram was started. This proc-ram ;;as complet::,d

7 D3cem::,er 1950 aft'e_' drilling 39 NX hol•1.J on t. E: siue anl t'he completion of 10 te3t it� -r, the aF , r::: -ate site. 1 •v driliin ::as performed uj'

Lynch rot.tcrs Dri lli ._ Compcil�Y, Se ti:;le :i.M. 11all fal 1 Disc.rict, Corps of Enpi 1ecr.J, . .1nder cor.tr ct ,,o t. e '>eattl� Dic.trict, and te5t its by

Government forcas of the Seattle Ji.3,.,ri�c.

�--=: lor- uion dril .i , consi.:n:.:,i of oo un vertictl nei an�le hole3 dri � ,rJ tnrcu .10 1t thG site. IL · core ... J.°r IT! t ,� nol-s ,1, r� :!..o cd 1.nd cores stored for future reference at the District Office. F.ach hole was pressure-tested for leaks in the foundation.

The holes were located on three lines intersecting the axis of the spillway dam and two lines parallel to the downstream cofferdam locations. A few locations not on these base lines were drilled to complete the infonnation. A complete report of the preliminary investi gations by the Corps of Engineers is on file at the Di.strict Office, Seattle, Washington. Refer to Drawing No. 2 for location, and Drawing

No. 3, 4, 5, for a detailed description of the explor atory holes com pleted prior to construction af the dam.

EXPLORATION DURING SPILLWAY CONSTRUCTION

Due to the excellent condition of the foundation, as revealed on completion of the excavation to grade, extensive exploration drilling was considered unnecessary. NX holes 50 feet in depth were located on the centerline of each pier. Under the odd-numbered piers, the NX holes are located on the axis line, and under the even-numberea piers on a line 30 feet downstream from the axis. Eleven vertical holes totaling

553.3 feet were drilled with excellent core recovery of dense granite at each location. The rock varied from the pink porphyritic granite near the right abutment, grading into gneissic granite towards the left abutment. Cores show that the rock joints are extremely tight except within minor areas of higb]y fractured rock. Fractures show that hydro thennal alteration has taken place with the deposit of chlorite on the faces. A detailed examination of all cores was made for record purposes.

Re.fer to Drawin[ i'Jo. 6 for detailed ir�or,1:.ation.

On the basis of the exploration cited above ;i_nd the Gxcellent conJition 01 the excavatec �·oundDtion surface, plus the design of the spillway stru,·ture, for 100 percent uplift, it v,as <iecideo that the foundation was 11tore than adequate for t is type of structure and that no spillwa;f curtain ;routing was necessar;y. All curtain grouting was deleted from tne specifications in Change Order No. 2 of tr.e second stage contract.

EX?i.ORATION Dl RD,Li ru,;;i lll-!Oll.:3E CONSTRL CTI Ol1

Sxploration of the "Owerbouse area l'Jrior to construction gave com plete information on the found;;it:i..on ar d onlJ a lim:.. ted • rogram was r,eeded to r.iake a final check. .3�;� NX hole3 were drilled in the powerr.ouse area.

l'wo drill noles were pl ·ced i..n each unit. Une 50-foot vertical nole was loGatea under tr.e c6nter 01. each g•,meratin_ unit anu one €0-i'oot angle hole was orilled 93 f,;;et downstream on the centerline o~· each unit. 'l'he

:.lovm�tream holes were drilled on a €0-Jegr�e angle downstream. The total footage for the six nol e;:; was 333. 6 feet wi vh excellent core recovery in each hole. The rock cores consisted of gneissic granite with minor varia, l;ions to a p:..nk porphyritic gr«nite. fhe dip of vne fonnation is in a dor,nstr..,am direction tov.ar� the left abutment. Cores show a moderatel;y

.:·.::-acturecl roch ,it. small areas ,;hich ax·e hi_hl;\ s:1,;1.tt:ered. Seams are

:er.erall;,r tight, oei:i _.illeo wi.,L gouge 1n.ater al or s�conlary ae_,osition o! h;rdrotterrnal cilterat.ion pr·o:tucts. A lL.ited num:.er of the ir..ctures are op,::n, allovtin�· � water coa:-::;e tc u'.:lV'lop. An .:..nsr,..,ction )_ cores was made and a detailed log was completed on each core. Refer to Drawing No. 6 for detailed information.

Ole to the excellent quality of the oores and the exposed founda tion, it was decided that no further exploration would be necessary in the powerhouse area.

WORK PERFORMED UNDER FIRST STAGE CONTRACT

GENERAL DESCRIPrI 00

The first stage contract was executed by the Macco Corporation of

Paramount, California, consisting of the preliminary excavation of the spillway section, construction of two earth and rock filled cofferdams, and unwatering of enclosed area, excavation to enlarge the north channel for diversion purposes, and opening of necessa:cy borrow areas.

The contractor furnished all the necessary equipment to do the job and work was performed in a satisfactory manner in strict accordance w.i. th the specifications.

Work commenced in January 19.51 and was accepted by the contracting officer on 2.5 May 1951.

PLAN OF WORK

The plan of construction invol ved two main operations that were performed concurrently, consisting of enlarging of the north charm.el and construction of the spillway cofferdams.

Work began in the north channel with the excavation of the right abutment and the small islands to the minimum el evation of 2020 feet.

This operation continued throughout the duration of the contract.

The building of the cofferdams began with the borrowmg of material from the right abutme nt for the downstream cofferdam. This opera.ti.on met with several minor setbacks before completion. The upstream coffer dam was then started, but several attempts had to be made bef' ore a closure was made.

While the above work was being carried on, the contractor star ted excavation operations in the spillway section to Elevation 2022 feet.

A large percentage of this material was used as core material for the cofferdams.

Suitable borrow areas were opened for impervious material and gravel blanke ts, as required.

IDewatering of the enclosure was started as soon as the filters and s eals were completed on both cofferdams.

CONSTRUCTION OF COFFERDAMS FOR SPILLWAY SECTION

The problem of building cofferdams for the spillway section was rather unusual at this project. Two channels existed through the area with a large island in the center which had to be removed to enable spill wq- construction. To facilitate cofferdam construction , the island was incorporated in t he upstream and downstream cofferdams along with the extensive use of the excavated material from the spillway area to dam the middle and south channels. In the upstream cofferdam, a section of the island was left as a solid rock wall and in the downstream cofferdam the toe of the island was blasted to Elevation 2018 feet with the material being left 1n place.

DOWNSTRE.l\M COFFERDAM

Dmmstream cofferdam construction began with the removal of spoil material from the left abutment and borrow area and placing it in the south channel. Simultaneously, work began on the south island, and the excavated rock was placed in th e south channel. In the section of the cofferdam passing across the toe of the island, the rock was excavated to Elevation 2035 feet. The area was then drilled to Elevation 2018 feet and shot. This material was left in place to be removed with the coffer dam. Approximately 3,000 pounds of powder were used in the shot. Wash ing action of the river in the south channel caused the cont ractor quite a little trouble in making a closure of the south channel. Fifty feet of the fill washed out at one time due to the large wave set up by the heavy blasting on the island.

On the closure of the downstream cofferdam, which occurred after the upstream closure was made, the rock fill cofferdam was eKtended to the middle island. Closure of the middle channel was done in a routine manner and without difficulty.

The cofferdam was then raised to Elevation 206o feet with the recµire ed slope of 1-1/2 to 1. A filter blanket of pit run gravel was placed on a 2 to l slope on the river side. Mini.mum thickness was three feet.

Covering this was the impervious blanket on a 2 to l slope, ranging from four feet in th.:.c1rnes.s aLove Elt,v;,t.:.on 2030 .... 0et, to _.n _ · gnt foot thicime.:;s below. A one-foot r'il ter blanket and. three-.:oot rip rap blanket were placed on the i nperviou3 bla.rJ.:et a.oove the 2030 elevation for protect" on a.§;:iinst 11ave actioa.

In the area of the south channel, it v. s nece3sary to place an adLlitional 10,000 cubic yar·ds of i.np,,::;rvious r;iateri:u aaove the speci£:i0d requirements to of fee,; a sr tisfs.c tory a�al o:..· the coffcrci.2Jll.

A o.:.vcr· �ms u�t:d to inspect the co.1.·.l.·crda111 for large leaks durine the sealin,; operations. LEiakage through the cormstream co.L·;erd.3.In con s:L:;ted of .;eneral seepa .e o•rer the whole &..reo. vir,h r.1ctjor leal:age through a sec�ion of the south ci"l.JJ111cL A 12, EDO .;allon-rer-:tinute pnmp wa3

U3Cd to h<J.11dlc t .e seepoi,_,'e ,;ith the :1p ro:xi.Iri.c. -:iv leci:a e o� 10,000 gallons per minute.

It v;a3 r:oted ciurj Pc a t __ .r orar�• flooc.it\., of the cofi'erdrun that the impervious se2li1.g mat .ri.::l act00 ;:,, ; a valve a .. u. allo·m d acloi..tional seep age. On ciewr.�ri11g of ':.r1e _r.closure, tlte i.n e1•yious tll3.teritl s�aJ.ed the cofferdam ti&ht.l;.,.

The con::;tru�t:.on of the up3tred!ll co1f::-rua1 .. ,raJ -ttorr.pted OJ placi11g tnc rock e:.c..,vated from t:e ~ ilh, y jr,t0 the ..,01t1 ch:cnt1(.;]. Th·� IJ10t od

1.a r.:-it satL.,.1- ctor;i 1ue: u tr e l 1�"'"' u . . cunt of !3.ve.·i l :..ieing wa.:meu dovmst1E!�m. l'ne c01.tr.--ctor tne!'l rlaceo r_ co_f¥ roaru. upstream, known a the: mior co_f,r.� .m. i'nc c,;·:iftne __, of tLe r.:.\· r e, . . �·ta.tcd 1 ge oou�:.kr� to ,_,_: ...:ui it. s 1:.,-__ s L.' . .,,�·acto ., ·lo�i..::e was made. After closure, 'he junior cofferdam w;;s wicened a...'16 incor porated into the upstream cofferdam. The main cofferdam WAS placed across the channel with a 1-1/2 to 1 slope downstream from the junior cofferdam. The channel between the cofferdams was then clean€cJ with a dragline to bedrock. A gravel filter was placed on the upstrearn face of ths main cofferrlam and then the impervious seal was placed bet.ween the two rock cofferdams. �.n excellent job was obtained in shutting off the water int.he south channel with the two cofferdams.

After clos11re of the upstream cofferdam the contractor was acle to comple1 e t.he downstream cofferdam across tt.e s-::-uth cnannel.

The closinp of the middle channel was accomplished without any c:lii'ficulty due to the small amount of water. A rock fill was placed across the channel on a 1-1/2 to 1 slope. It was then blanketed with a r,ravel filter, impervious seal, and covered with r.ip rap according to specU'ications.

The center section of the upstream �offerdam between the t�o channels consisted of that part of the island wM ch was left in place forming a solid rock wall with a m1 nimum thickl'less of 30 feet.

This section w.,s removed to Elevation 2028 along wi t,h the removal of the rock fills to the same elevation.

Leakag-e of the cofferdams was very limited and all water could be hanc.leri efficiently. The ll;:'Strearr. cofferdam w-as sealed t.tght.ly except for one leak near the base of the seal in the south channel.

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1. General view of the upstream spillway cofferdam showing the solid rock seotion.

2. thru 7. Series of pictures showing the rook section of the upstteam. spill\118.y cofferdam. The blocky structure and joint pattern is typical of the entire foundation rock.

,----....�1-

- •• I. ... i

1. General view of the upstream spillway cofferdam showing the solid rock seotion.

2. thru 7. Series of pictures showing the rock section of the upstteam spillway cofferdam. The blocky structure and joint pattern is typical of the entire foundation

I_

1. General view of the upstream spillway cofferdam. showing the solid rock seotion.

2. thru 7. Series of pictures showing the rook section of the upsttea.m spillway cofferdam.. The blocky structure and joint pattern is typical of the entire foundation

1. General view of the upstream spillway cofferdam showing the solid rock section.

2. thru 7. Series of pictures showing the rock section of the upstberun spillway cofferdam. The blocky structure and joint pattern is typical of the entire founda.tion

1. General vi0w of the upstream spillway cofferdam showing the solid rock section.

2. thru 7. Series of pictures showing the rock section of the upstteam spillway cofferdam. The blocky structure and joint pattern is typical of the entire foundation

' •• �. ' • 1-· •

,r !�

1. General view of the upstream spillway cofferdam showing the solid rock section.

2. thru 7. Series of pictures showing the rook section of the upstbeam spillway cofferdam. The blocky structure and joint pattern is typical of the entire foundation

1. General view of the upstream spillway cofferdam showing the solid rock seotion.

2. thru 7. Series of pictures showing the rock section of the upstbeam spillway cofferdam. The blocky structure and joint pattern is typical of the entire foundation

EXCAVATION OF THE NORTH CHANNEL

Work in the north channel consisted of rock remoYal to provide adequate area and gradient for diversion of the river during flood stages.

The two small islands were removed and a section 100 feet in width was taken off the right abutment to Elevation 2020 feet.

Elevation of rock on the right abutment section before excavation ranged fran 2060 to 2070 feet in elevation.

Elev.ation of rock on the two small islands was 2050 feet and had to be removed to approximately 2030 feet elevation. In the excavation of the north channel the contractor was allowed maximum flexibility in blasting and excavation.

Since the working area on the small islands was limited, the contractor elected to shoot the islands in two major bl asts, one on each island.

Holes were drilled to a depth of 24 feet which took them approximately three feet below grade. These holes were loca ted on six-foot centers and loaded very heavily to insure good breakage of rock. Approximately one and one half to two pounds of 60 percent dynamite was used per cubic yard of rock blasted. The largest shot was on the north island consist ing of 2,934 cubic yards, using 5,000 pounds of dynamite tamped into 450 holes. The snaller island, consisting of 1,514 cubic yards of rock was blasted using 3,000 pounds of 66 percent dynami. te in 300 holes.

Due to the size of the blasts, every precaution was taken to clear the danger area completely. All rail and highway traffic was stopped during the blasting operations. A small blast was made in connection with the small island to clear a projecting ann from the main tsland.

View of the north channel during preliID�nary excavation of the right abutment eowder crew loading holes on small island in the north channel

The bla sted ,naterial was washed int� the pot hole of the nor th channel by the river. No excavation was necessary to remove blasted rock.

The section on the right abutment was removed in a series of blasts across the area. The first lilt of rock was highly weathered and material was extremely easy to remove. Holes on thi s lift were

18 feet in depth on six-foot centers. Approximately one pound of dyna mite per cubic yard was used. In some local areas the rock could be re moved by the shovel lii.thout blasting.

A second lift was taken across the section to an elevation just above the water level and material was removed to the disposal area upstream or pushed into the river to provide a working area for th e underwater cut through the section.

The final lift necessitated the use of extra equipment for drilling.

Sinc e a l.Jirge par t of the area had to be drilled through shot rock, the contractor first brought in a diamond drill to work the loose material.

This was found to be too light a rig for this work and it was abandoned.

The contractor then used chum drills to work the overburden which proved satisfactory and enabled the contractor to drill the solid rock shelf below water surface. On completion of a chum drill hole, a wagon drill was used to drill the rock shelf five feet below grade, Elevation 2015 feet, using a JO-foot steel.

At one time three churn drills were being used to speed up the work.

The river was rising slowly and at times the equipment was working in a foot of water. The ccntractor kept building up the working area w ith shot rock to stay above the river.

Holes were placed on six-foot centers and loaded with approximately two pounds of dynamite per cubic yard to insure good breakage.

The abutment was excavated on a quarter to one slope with 36,438 cubic yards of material being removed by an 80D Northwest shovel above the river surface and by a dragline below the surface. Material was removed to the disposal area by dumpsters and ten cu bic yard Euclid dump trucks.

'Work in the north channel was started on 28 January 1951 on the top of the right abutment and the small isla nds in the channel. On 2S March

1951 wet excavation was started on the right abutment section. All exca vation was completed in this area on 24 April 1951.

EXCAVATION OF THE LEFT ABUTMENT (2097 Bench)

Excavation work on the left ab utment consisted of rock removal of the abutment to an elevation of 2097 feet between the south channel and the railroad right-of-wey.

D.le to the proximity of the Great Northern mainline on the abutment, the method of blasting and excavation of the area was subject to approval by the railway. The Great Northern Raih;ay also required that the track be planked for 600 feet through the cut to fac ilitate rock removal after blasting. The Great Northern Railway had to be notified when each blast was to occur and trackage inspected by their maintenance foreman on completion of rock removal. All blasts were set off during the greatest lapse of time between trains so that normal service would not be interrupted.

The method used and approved by the Great Northern Railway con sisted of blasting the area in a series of light blasts. Two lifts were made and each lift was shot in three sections, leaving a 20-foot berm along the right-of-way to protect the track as much as possible. This berm was taken out in two lifts using small blasts on co mpletion of the other blasting on the bench.

The rock excavated on th e right abutment ranged in ele vation from

2120 to 2097 feet, the holes were placed on six-foot centers with the average depth of 12 feet. Each section blasted was approximately an area 100 feet long parallel to the right-of-way and extending to the south channel. Approximately one pound of 40 percent Dupont gelatin dynamite per cubic yard was used. Average amount of dynamite per blast was 900 pounds. All blasts were delayed towards the railroad, with five d elays being used. The 20-foot benn was shot using lif ters with a very light charge.

This method proved very satisfactory for the excavation of the rock.

HOW'ever, on one blast on 20 March 1951., the railroad cut was filled with approximately 500 cubic yards of material. Excavated material was removed by an BOD Northwest shovel loading into two Koehring dumpsters and two ten cubic yard Euclid trucks. Material was placed in both upstream and downstream cofferdams when needed or taken to disposal area parallel to the Great Northern Railwey mainline. The total quantity of rock removed fran the left abutment was 11,986 cubic yards. Work began on the left abutment 7 February 1951 and the final cleanup was completed 31 March

1951.

EXCAVATION OF SPILIWAY SECTION

Work in the spillway section consisted of the rough excavation of the area, known as the south island. Due to the necessity of removing the island for construction of the spillway, a major portlon of the first stage contract work was done in this area.

Since the south island was incorporated in the upstream and do-wnstream cofferdams, the excavation of the spillway was done in conjunction with them. The upstream of the island was left as a solid rock cofferdam and the downstream toe located under the downstream cofferdam was excavated to Elevation 2035 feet. It was then drilled to Elevation 2018 feet and shot but left in place as part of the cofferdam.

Labor crews began clearing the island of trees and vegetation on

2 February 1951 in preparation for drilling operations. The job consisted of complete removal of all rock between Elevation 2092 feet and 2065 feet, also the excavation to Elevation 2028 feet, across the island from the spillway axis to the rock wall of the upstream cofferdam, a distance of

85 feet. From the spillway axis to the doTtmstream cofferdam, a distance of approximately 150 feet, rock removal went to Elevation 2022 feet, across the island.

Since construction time was a major problem, the contractor ren ted a barge and boats to transport equipment and men to the island before any cofferdam closures were made in order to get rock removal underway at the earliest possible date. Actual drilling operations started on 16 February

1951 at the southwest corner of the island.

The area was worked in a benching operation across the island to the required grade. Each bench was blasted in approximate]y six sections to

Aerial view of spillway cofferdams and excavation during the first stage construction

L

View of preliminary excavation of spilh1ay section {south island), lcoki'ng to-wards the right abutment facilitate drtlli�g, blasting, and loading operations in the area.

The contractor was allowed the maximum flexi.bili ty in blastinr, of the rock; on all mass rock removal the contractor loaded all the holes heavily to insu re maximum breakage over the section. Up to 5,ooo pounds of czynamite were used per blast, with sufficient delqs to obtain good results. The approximate charge ranged from one and one-half to tw pounds per cubic yard. Holes were placed in a pattern on six-foot centers with the average depth of 24 feet.

Blasting of the final l ift was done in a similar manner. Al l holes were drilled to grade and a limit of one pound of czynami.te per cubic yard was set by t he contractinst officer. This was <i>ne to limit shattering of the rock below the grade lines.

Excavation of the 105,350 cubic yards of material was accanplimed

'With a Northwest BOD shovel and dragl ine, loading into six-cubic yard dumpsters and ten-cubic yard Euclid trucks. Material was used as coffer dam fill on the upstream and downstr eam corferctams or taken to the disposal areas shown on the general plan.

Work on this phase was completed on 25 May 1951. This also completed the contract for th:! first stage construction. The contract:i ng officer released the Macco Corporation as of that date and accepted their ..ork in accordance with Goverrunent regulations.

BORROW ARF.AS

Borrow areas for the impervious blanket and gravel filter were located and approved by the Government on tbe s outh side of the river.

Since these areas were located on private property, the cont ract.or made his own settlement with the owner. 'The !'.'rice of lS cents per cuoic yard for both the jmpervious matGrial anc p:ravel W<'IS ap;reed 11pon oy :r-:acco

Corporat:i_on and the Froperty o.-.-ner, J:r. Zimmer.

The borrow areas were cleared of all ve'1et.at.:.on e1nd stripped of the cverb-e.rden. Material was rernoveci by a on� and one-half cubic yard shovel loading into eip-ht-cutic yard trucks. �he total q_uanti ties taken from the respective. borrow areas for use in the cofferc1;:;ms were 28,760 cubic yards of i::;ravel and 2!.i, 121 cubic yards of impervious material.

ACCESS ROAfS

Access roaos to both sices of the river were available to the con t,ractor in accordance with the snecific&tions. Gn the north side of the river, the access road was on Government land and used by the contractoro

On the south bank the ccmtract.or elected to build his own access road from the county road west of the gravel borrow area, due to the location of the impervious borrow area and the !"r·wel borrow areao

Since necess;,ry h2ul roa.cs would have to be built from the borro"K pits, the contractor deciced to incorporate all the roacs into one.

Approval was attained from the contract,ini; officer and. the contractor made an agreeable settlement wi. th Mr. '3immer, the o.-mer of the property.

The road was built at the contractor's ex:rense and maintained through out the cont ract o

This road wc>s later .acquirE:d by the Gove.rnrr,ent as a pBr:nanc-nt access road to the south sirle of the cam.

WORK PERFO:t.1'2D UNDER SE::::mm STAGE CONTRA.CT

GEIERAL DiSCRIPTION

The second stage contract v,as executed by the Donovan Construction and james Construction Companies of St. Paul, Minnesota and their sub contractors, with Donovan Construction Company as the project sponsor.

1Nork consisted of the final excavation of the non-overflow and spillways sections; construction of !';i1e spi_llway and non-overflow structures;

construction of the powerhouse coff0rdams; and removal of the spillwa;:,r cofferdams.

The contractor furnished all the necessary e4uipment and materitls to perform the work which was done in accordance with the specifications and in a satisfactory manner.

Work on the second st:ige contract was commenced by Donovan-Jarnes

Company on 13 March lGSl With continuous operation until 9 June 1952.

On this date the contractor was released from the contract and the spillway structu.re acc0pted by the contracting ofi'icer.

PLAN OF WORK

1fiork by the contractor began with the construction of the necessary facilities on the site, such as warehouse, office building, carpenter shop, batch plant, etc. Wo1�k in the spillway section began with the rock excavation of the spillway abutments and the key trench to Elevat::_on 2014 feet. This oper,,.tion w.:1s followed by rock cleanup.

The second and main phase consisted of spillway construction which began on 1 August 1951, and continued until completion and installation of all equipment.

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Typical sections of line drilling in the spillV1ay key trench

1. Upstream wall monolith# 7.

2. Upstream wall monolith# 9.

3. Upstream wall monolith#= 13.

4. Upstream wall monolith# 15.

5. Upstream wall monolith# 15.

6. Upstream wall monolith# 17.

:SI

'lf\!a( '

I::', � � I 1 I - t2\

Typical sections of line drilling in the spillway key trench

1. Upstream wall monolith# 7.

2. Upstream wa.11 monolith# 9.

3. Upstream wall monolith# 13.

4. Upstream wall monolith# 15.

s. Upstream wall monolith# 15.

6. Upstream wall monolith# 17.

Typical sections of line drilling in the spillway key trench

1. Upstream wall monolith# 7.

2. Upstream wall monolith# 9.

3. Upstream wall monolith# 13.

4. Upstream wall monolith# 15.

5. Upstream wall monolith# 15.

Typical sections of line drilling in the spill�m.y key trench

l. Upstream wall monolith# 7.

2. Upstream vmll monolith# 9.

3. Upstream wnll monolith# 13.

4. Upstream �ull monolith# 15.

5. Upstream wall monolith# 15.

Typical sections of line drilling in the spill�my key trench

1. Upstream wall monolith# 7.

2. Upstream wall monolith# 9.

3. Upstream wall monolith# 13.

4. Upstream wnll monolith# 15.

5. Upstream wall monolith# 15.

6. Upstream 1mll monolith# 17.

Typical sections of line drilling in the spillvm.y key trench

1. Upstream wall monolith# 7.

2. Upstream wall monolith# 9.

3. Upstream wall monolith# 13.

4. Upstream wall monolith# 15.

5. Upstream wall monolith# 15.

6. Upstream 'Wall monolith# 17.

'l'he third majo:· ph2.:;e o:· the s,3conc.i s r, ,ge M3.S l'.''c!moval of ti1e 1p-

15t:ream and dowastrear-1 co .. :.:.,,rdarns o.' the spill.·.a�,. '.lnd con:,tructiiJn of the powerhou::1c co:..:erfl;:u:is. Thas'9 jt)b::; 1Tere <lone sim.ultqneo,.1Sly to faci.i.i;:.ate the rivJr d�V,L'.:;ion t..nro1. :. t,:e :spil .,ay.

Excavatj_on consisterl o:· :3. 01.-.f0ot 1'::i.:le kej• trei1ch .:or th·:: oase of the .3t,ructure a:; the predetermined ,:;rade elevation of 2014 feet, and the cutting b,::;ck 01 the a.but;nc:n t.s to •:ma" o le construction of :.an i'o .·ty foot bay3 .::..nd eleven eif.'1t-foot piers. T'lasc exc3.vation lirai ts were governed b;r req_uirements of design, and the fluctuation of -i;:ie river

Level. The rock ·.vas v�I"J excellent and rrore than adequate i'or ;:.t·ie de-sign of ti1e stru :;ture.

In tt;e key r.rench tnc walls v;er() li�1e dril �ed ,-.i t!1 a tolarance lirni t for vertic;,il linc:.J not to e1,ceed u.25 1'i:;et. A t.1rce-i:1.ch drill bit v1a.s

,_wed wi,;h the holes on six-inch cant�rs. Depth of tJv::! UCJstrea.m line ,J �::

fom·teun f:rnt, an(l '1 cie_.,t•L 01 ":;i !lt :: et on t1,e rlOY.'ItSv.!'ua.rn line. Ten thousand ei[:lt hundred thil·ty ono sc._uo.re i'-.::et of line drilling wa.J done al.,n:· the two lines of 'vhe l:-::.;1 trench. Satisfa�tory r.;s 1lt:::: -;'.'ere out1.:.n0d;

Since vertical faccG ·Nere desired and S" . .::.tit.o!'i:lf of tne i'onndat::.on held to a .ninim1un due to blas ti.'1 , t;1<c! .3 pacinr; a!1;;. l :,adin:; 01 holes ·,ws clor,cly controll0d.

Line drilline on :.!'le abutments and non-o,re.cflo11 section wa.J de-lE:ted as S:!tisfactory .::'o:.in::.ations cou2.J be obtained by rou".;ir:.e excav.:,t:on.

),Ii

The key trei:-ich ·,·;a.2. olestad iri two 1.u·ts aul rock r0:r,oved oy an BOD

Nort,lwrest. sr.ovel lc·,ci.inc.. into thr..::c �.:.,i:;ht-cubic :•mru '\Vh:.. Gt:.' du1np trucks.

�terial w�:c; stocl:�)i l2d for use in t:ie iowr.s ::.rec? ... m _;owcr,"l n.1.oe co.:'i'crduia.

In tne are.? of t,he soT�h charircJ, no e:;:c5.vc1.tion we.s ,.E:cBssary to

3ecure .::deq;w.te foundation 1·0ck.

Rock remov3.l cetan on 25 L::y 1951 31:d �-:-ac: co .. ,plE:ted on 28 September

1951. Twenty one t,housand twer.ty five cllbic :,'ard:. of rock we:x .. renoved from the spillw£,y unJe::- the second sts.ge cont,ract.

DHI.LLING AND EL..!..�lll\JG

To insure the best results o.f rock bre;::,ka, e r,hroughout the key trench, ttrce test sections SO feet in len5th were drilled and bla!,ted to obsern:: tr..e results.

In te:::t section Ho. 1, the holen were dl'il L d p;11·2.llel on £'our-foot centers, 1.0 fcc=;t ir. depth .�p•;t,rea.m ft·o,. a:ds :1.nd si:� .fe..:t ir, C:eptn ,.,own-stream and 103.deJ with tnrec-quurt.e.r�i �onnd 01 fortJ pc1·cer.t dyLa..rnite per cubic � a1'cl. Powcier ·:;a,; p!.c:.ced 1:st he bottor.:, two r�ct !'ron '�he oottom, and t,vo feet fro1:i �he tor of the no.Le. ;.lilli-secor..d del.-i.y.:: Y,e:r-c used fron t}�e ce1.ter to the sides with t'"le la1.:t row c:· clast holes fou1· .fe8t .! ;:om the v·ertical line dril :.in5•

Breakage on 'Gr.is shot ,·1:3.s 1;er:.er;:iJ...:.:r '.:,ooci; liowever, ,'.1.C higitl.y blocky ri:;ck CD.used considerable over-br-eak paf;t the line �rtl.iin,·.

l:1 tc:;t section No. 2, the r...olc::. ·,!'.::re placed \:,o tiw nw-1e o.er.t .• but or! par·al lel pattern oi three-foot CE nters.

'lC:

foJ.1c s were loaned w5.. th one-half pnuno of for:ty percent dynamite per cubic ya:ra, "OWdEr was placed at the bot.tom anc mic cle of the hole. The bl2st 1-:as ciel&yed from the center to ti-Je sj des.

'l'his shot only broke fair to the vertical line drilling with some over-break in the shattered rock.

Test section r'.o. 3 1r1as drilled on four-foot cent.ti1,s in a stago;ered pattern to the same depths as sections one ano. two. One-ha.lf pound of forty percent dynami i e l-.""as used per cuoic yard of material and placed in the middle and bottom of the hole.