Low-Level Concrete Bridge Over the Mary River, Maryborough, Queensland.” by ALFREDBARTON BRADY, M

246 BRADY ON MARYBOROUGH CONCRETE BRIDGE. [Selected

(Paper No. 3184.) ‘‘ Low-Level Concrete Bridge over the Mary River, Maryborough, Queensland.” By ALFREDBARTON BRADY, M. Inst. C.E.

THE old high-level timber bridge, 1,456 feetin length, erected across theMary River, Naryborough, in 1874, having been partially destroyed bythe abnormal floods which occurred in February, 1893, thus cutting off the means of communication by road between Maryborough and Tinana and the important gold- field of Bympie, it was decided by the Queensland Government and the Maryborough Bridge Board to construct a low-level bridge of a permanent character on the downstream side of the old structure, and to take down, and remove from the site, the standing portion of the old timber bridge, the traffic meanwhile being provided for by a steam ferry. Alow-level bridge, it was considered, wouldserve allpur- poses and would be much safer during floods. It had been amply demonstrated during floods in various parts of the colony that floating logs, trees, and heavy masses of debris are not usually carrieddownstream inany considerable quantityuntil bridges built at low levels have become entirely submerged, and then all drift timber can float harmlessly over them. A low-level bridge would also necessarily be so much shorter between the banks-in thisinstance 843 feet shorter-and the cost of maintaining the roadway and the bridge generally would be correspondingly reduced. After some timespent in making surveys, taking soundings and borings, and preparing and considering various schemes, the Author’s design for a concrete bridge was finally approved by the Bridge Board and the Government; tenders were invited and a contract was let in September, 1894. The Author was induced to recommend a concrete bridge, as it ensures a structure of very great strength, almost everlasting in character, and the annual expenditure in maintenance isconsequently reduced to a minimum. New Bridge.-The dimensions of the new bridge, Fig. I,

Plate 4,are:-total length, 613 feet ; waterway between faces of abutments, 595 feet;width of roadway betweencurbs, 20 feet 8 inches; width between faces of arches, 22 feet 8 inches. The level of the roadway on the bridge is 12 feet 6 inches above high water of ordinary spring tides, when the depth of water at the bridge is 28 feet ; the maximum flood-level, namely, that attained in February, 1893, is 33 feet above high water. There are eleven concrete spans, or arches, each 50 feet in the clear, carried upon ten concrete piers in the river and two abutments,Fig. 1, Plate 4. The rise of each arch is 4 feet, or G5 of the span; the thickness of concrete at the crown of each arch is 20 inches at the centre of the roadway and 18 inches at the curbs, the thickness at the haunches along the centre line being 5 feet 8 inches, Figs. 3 and 4, Plate 4. Abutments.-The abutments,Figs. 2, Plate 4, are constructed of Portland cement concrete, composed of 5 parts of hard stone broken to a 2-inch gauge, 2 parts of clean sharp sand, and 1 part of Portland cement, and are carried upon ironbark piles shod with 28-lb. wrought-iron shoes driven to a solid foundation, those in the Maryborough abutment to an average depth of 26&feet, and those in the Tinana abutment to an average depthof 29 feet below low- water level, the piles being spaced 4 feet 6 inches apart, centre to centre. Piers.-Each of the piers is constructed in tworectangular sections or columns below low-water level, arched over between low and high water and then carried up solid to the springing of the arches, Figs. 3 and 4, Plate 4. Each section of the pier foundations is 10 feet 4 inches by 5 feet 6 inches in horizontal cross-section, and all were sunk to a rock foundation, the maximum depth below high water being 55 feet 8 inches. The piers have semicircularends above low waterand are battered above the plinthat the rate of 1 in 24, the sides or faces of each pier being battered at the rate of 1 in 48, to a thickness at the impost, or string-course level, of 4 feet 6 inches, Figs. 3 and 4, Plate 4. The sections or columns, twenty in number, were sunk by means of wrought-iron caissons. The cutting lengths, 7 feet long, were formed of external bottom plates, 4 inch thick by 3 feet wide, and top plates 3 inch thick by 4 feet wide, with an internal pocket formed of +inch plates, 3 feet 3 inches wide, having 2 inches by 2 in ches by ',-inch angles at tbe top, Figs. 5, Plate 4. The angle- bars at the jointsof the cutting lengthswere 24 inches by2& inches by 3 inch, and acted also as stiffeners. The cutting edge was also stiffened with a flat bar, 8 inches by Q inch, double riveted. The

Downloaded by [ University of Sussex] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. 248 BRADY ON MARYBOROUGH CONORETE BRIDGE. [Seleoted intermediate caissons, each 4 feet in length,were formed of &inch plate, jointed, stiffened and stayed with 2 inches by 2 inches by 4-inch angle-bars throughout, Figs. 6, Plate 4, and were left in place on completion of the work below low-water level. The caissons were designed to be of the least expensive construction possible, all smith-work or forging of angles being avoided, except inthe cutting lengths, where the cornerswere welded. In all other lengths of the caissons, the angles were cut off square, the corners being formed with stiffening pieces of 2 inches by $-inch flat iron, and the joints were made up with pine-wood filling. Al- though this plan was adopted to cheapen the cost of manufacture, it is questionable whether the extra cost of making a superior jointat the corners of the caissons bybending the angle-bars would not have been more satisfactory in the end, as the slight amount of leakage encountered in sinking the piers, at no time exceeding 300 gallonsper hour, which evidently came through atthe corners, mighthave been entirely avoided. The slight countersink left in punching the plates was found to be sufficient to hold the plates together, the rivets being simply “nobbled,” and the work was practically flush-riveted on the outside, without the necessity for any countersinkingof the holes in theplates. The method adopted in sinking thepiers was the following :-A temporary staging of piling, securely braced, was prepared on the site of each pier, Figs. 9, Plate 4 ; the bottom- or cutting-length of each caisson was slungto four wrought-iron rods, 2 inchesin diameter, screwed $-inch pitchfor 10 feet of their length, and operated by nuts withcross bars having armsof 3 feet 9 inches in length, and provided with anti-friction rings underneath. Cement concrete, gauged 5, 2 and 1, was then carefully packed into the pockets and brought up to the top of the caissons, the interior cavity being formed by removable panels of lt-inch rough pine, strutted as shown in Figs. 5, Plate 4. The first and second lengths of the intermediate caissons were then bolted on to the top of the cutting length, the joints being made with a chunam of coal-tar and quicklime, and the concrete lining was continued to the top. The caissons were then lowered by fleeting ” the screw hangers, for which purpose strong clamps (a), Figs. 9, Plate 4, were provided, additional caissons being fixed and the concrete lining being continued until the weight was taken on the bed of the river, when divers released the hangers by driving out the bolts which secured them to the cuttingedge. Sinking then proceeded in the ordinary way by dredging where practicable, but the bulk of the excavation proved to be a tenacious and compact mixturo of

Downloaded by [ University of Sussex] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. Papers.] BRADY ON MARYBOROUGHCONCRETE BRIDGE. 249 sand, graveland clay, withsmall shells, quiteunsuitable for dredging, and removable only by divers. On reaching the rock, the weight of the column, amounting to 60 tons, was again taken on the screws, the suspending rods being transferred to the inside of the column, and a length of eachrod beingbuilt into the concrete for suspending the column, Figs. 9, Plate 4. The surface was then levelled to a fixed depth gauged below the cutting edge by divers, and the column was finally lowered into position upon bags of fine concrete laid carefully under the cutting edges. Into thesethe caissons bedded themselves, forming a tightjoint to exclude leakage when fillingin the concrete core withinthe column. The shaft was then sealed by the deposition of concrete through the water inself-releasing skips up to about 10 feet below the bed of theriver at the pier. The concrete aboutthe cutting edge, gauged 4,1+and 1, was laid bya diver and carefullypacked round the bagsto it depth of 4 feet. Theremainder of the seal was gauged 5, 2 and 1. After allowing the core to set for 2 or 3 days, or longer if convenient, the water in the shaft wasremoved by a canvas baler worked from a steam winch. The baler was made of No. 1 canvas, and measured 2 feet 4 inches in diameter, and 4 feet in depth, being provided with strong hoops of 1;-inch round iron at the top andbottom, covered with leather to preventchafing, and discharged on an average about 3,000 gallons, or about 35 lifts, per hour. The remainder of the concrete core was then laid, carefully packed and rammed, in the dry, to a level of about 8 feet below the full height of the concrete casing, thus forming a key for the upper portion of the concrete pier, Figs. 7, Plate 4. Some leakagehad to becontended within getting in this portion of the work; the amount, however, was not considerable, averaging between 200 gallonsand 300 gallons per hour. By mixing and laying with two full gangsof men, with separatesteam derricks to each gang for lowering the concrete, the core was got inwith sufficient rapidit,yto enable the packersto keep well ahead of the leakage, and so prevent the watercoming through the surface of the concrete. In one or two instances, when through mismanagement thisdid occur, considerable diEculty was ex- perienced in removing the water, whichaccumulated without dis- turbing the cement. To avoid such acontingency, the resident engineer had a sump formed of ordinary drainage tiles, 10 inches by 6 inches, of horseshoe shape, laid in the corner of each shaft as the core wasbrought up, and into this the suction-pipe of a Goold semi-rotary pump was inserted ; bythis means the

Downloaded by [ University of Sussex] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. 250 BRADY ON MARYBOROUOH CONCRETE BRIDGE. [Selected level of thewater was kept at anytime below that at which the concrete wasbeing laid, withoutdisturbing the cement or interfering with the packers. This sump was carried up to the level of the plinth andwas afterwards filled in solid with concrete. The top of each column, forming the plinth of the pier, was laid with 4,1& and 1 concrete in temporary iron caissons, similar to the intermediate lengths of the permanent caissons, but having all the angles fixed externally.These temporary caissons werecarried up toabove high-water mark andwere supported by timber shores, Figs. 9, Plate 4. The shores were arranged to be easily knocked out and removed as theconcrete reached the topof the plinth of the pier. To provide for any overturning action resulting from the flood pressure upon the face of the bridge producing a tensional stress in theupstream columns of the piers, a railway rail,Bignoles pattern, weighing 60 lbs. per yard, and 20 feet in length, with suitable cross bars attached, was built into the concrete, Fig. 4, Plate 4. The matrix for constructing the piers above plinth level was then formed, having framed moulds for the circularends and for the arch connecting the sections or columns, and Itinch pine boards supported on studding for the intermediate flat surfaces, all pro- perly stayed against the false works used in sinking the columns of the piers. The work of layingthe concrete, gauged 5, 2, and 1, was commenced immediately the falling tide had left the surface at the plinth level. Thesesurfaces had been previously thoroughly cleaned end picked over, and were well grouted with 1 to 1 compo, to receive the upper concrete work, the first few gauges deposited being made richer in cement to secure perfect adhesion. Thepacking of the concrete wascarried on 'well in advance of therising tide, to the height of the string course, which was subsequently laid of 4, If and 1 concrete in framed moulds. The whole of the concrete in the piers was deposited in self-discharging skips, Figs. 6, Plate 4, worked from a punt on either side of the pier. Thetemporary wrought-iron caissons, from the river-bed up to low-waterlevel, were by an arrangement with the contractors, left as a permanent protection to the concretepiers. Theaverage pressureupon the foundations, makingdue allowance for frictionand buoyancy, amountsto 4.14 tons per square foot. Superstructure.-The concrete in the arches or superstructure of the bridge is composed of 4 parts of broken hardstone of 2-inch gauge, l& partclean sharp river sand, and 1 part of Portland cement. The segmentalarches are strengthened by means of a

Downloaded by [ University of Sussex] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. Papers.] BRADY ON YARYBOROUGH CONCRETE BRIDGE. 251 continuousframework formed of steelrailway rails, Vignoles pattern,weighing 414 lbs. per linearyard, spaced 2 feet apart inthe arching, Figs. 2, 3, and 4, Plate 4. Thereare eleven skeleton frames in all, eachconsisting of two members only, viz.,a horizontal top member, continuous for theentire length of the bridge, and a curved or segmental lower member, follow- ingthe curvature of thearch in each span, Fig. 3, Plate 4. The frames are bolted to cast-iron chairsor bed-plates on each pier and abutment, and on the latter the chairs are well anchored down to the concrete by long bolts and plates, Figs. 8, Plate 4. There are two cross ties to the framing in each span and one over each pier, each tie being 23 inches by 2% inches by #-inch iron angle-bar rivetedto the flange of the upper member of the skeleton framing, Fig. 3, Plate 4, chiefly for the purpose of stiffening and giving lateral support to the framing during the deposition and ramming of concrete inthe arches. The concretewas laid on wood centering,and the steel skeleton framing was completely embedded. The whole surface of concrete exposed to view above low-water level, including soffits of arches, was floated to form a uniform surface, with 1 part of Portland cement to 2 parts of sand laid on in two thicknesses, and finished to not less than $-inch thick ; the whole then received a coat of cement-wash, composed of 6 parts of cement to 1 part of sand, mixed fluid in buckets close to where it was required and used immediately afterwards. In constructing the arches formingthe superstructure of the bridge, a considerable amount of forethought had to be exercised to ensure the joints beingplaced in thepositions least detrimental to the ultimate strengthof the structure, considered in relation to the flood stresses, as well as to those resulting from the maximum superimposed load, and also to secure the deposition of the greatest quantity of concrete practicable during daylight-which was not more than 11 hours-as the contractor’s arrangementsdid not admit of continuing work through the night. With this object in view, it was decided to lay a half width of a complete span each day, andthis arrangement was adhered to, the wholesuper- structure being laid in 22 days, with the exception of the parapets, whichwere built subsequently. Toassist the transverse joints betweencontiguous arches, two cavities, each 4 feetby 2 feet 6 inches, were left along thetops of the piers and extending the full depth of the haunches of the arch ; these cavities were afterwards filled in with a richer concrete gauged 3, It and 1, formingkeys which materially assisted thejoint to withstand flood-stresses.

Downloaded by [ University of Sussex] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. 252 BRADY ON MARYBOROUGH CONCRETE BRIDGE. [Selected The falseworks forlaying the arches were of pinetimber throughout, and consisted of six ribs, 4 inches thick, in the width of the arch, supported on capsills carried on three piles driven into the river-bed at the centre of each span, theouter ends being carried on the staging of the piers. Each rib was 2 feet deep at thecentre and 1 foot atthe ends, andwas formed of two flitchessecurely bolted togetherwith $-inch bolts. Theribs were laid with 14-inch pine planking, wedged at the ends to the required levels, andafterwards securely strutted on topiling. The mould was then completed by the erection of the sides, of li-inchboarding on studding,strutted by longitudinals from thepiers to the centre capsills, Figs. 7, Plate 4. The whole of the concrete for the archeswas gauged 4, If and 1 ; it was mixed on a largeplatform, laid on theabutment on the Maryborough side, the stone being carted from it heap 400 yards away and tipped direct into the gauge boxes, and the sand being wheeled from a heap close at hand. The mixed concrete was conveyed from the platform tothe packers in side-delivery tip-wagons running on a temporary tram- road, fromwhich it wasdischarged on to concrete boards and shovelled therefrom into the work, being well cut in with spades, and rammed solid, aspecial form of rammer being provided for packingunder the bottom rails of theskeleton framing. The concrete wasmixed moderately wet, it being found thatany excess of waterdrained off readilythrough the cleading of the mould, withoutcarrying away cement, the waterwhich escaped beingperfectly clear andlimpid, whilst the concrete laid better together and could berammed without difficulty. As it was thought probable that during floods an upward thrust might be brought to bear upon the arches on the upstream side by trunks of trees or logs of timber becoming jammed under them, a nest of six steel rods, each $-inch in diameter, was built into the concrete across thefull span of each archand parapet curb, along the upstream side of the bridge only, to resist the stresses induced by such an upward thrust, Fig. 10, Plate 4. Steel rail dowels were also used at intervalsto connect the concrete parapet curbing to the arching. The average number of men employed in forming the arches was as follows :-Seventeen labourers filling gauges and mixing concrete, sixlabourers filling trucks and running them to four packers and rammers ; also four labourers loading stone and sand, six horses and drays with drivers, andone carpenter; or forty men

inall, who mixed and laid, on an average, 11 cubicyards of concrete per hour. Stone.-The only cut stone in the bridge is the sandstone coping to the blockings of the parapets at each end of the bridge, the bedstones to the lamp pillars, and the porphyry margin stones to the gully gratings,Figs. 2, Plate 4. Roadway.-The roadway on the bridge was formed of iron-bark block paving, 5 inches deep, sawn from 9-inch by 3-inch planks. The blocks were coated with boiling tar and were laid with close joints directly on the surface of the concrete superstructure, which was finished with a camber or rise of 2 inches along the centre of the roadway for drainage. The blocks were cut and stackedfor seasoning sixmonths before beinglaid, and after laying, the joints were completely filled and made watertight with a boiling mixture of asphalturn coal tar, and clean sharp grit or river sand. When completed, the whole surface of the wood paving received a thorough coating of well-boiled tar, and was afterwards covered with a layer of sharp sand. Four rows of blocks were laid longi- tudinallyagainst the curbs on either side of the bridge, the paving between the longitudinal rows being laid transversely. A space or seam, 18 inch wide, was left next the curbs, and was filled with mastic to allow for theexpansion of the blocks in wetweather. A disastrous flood, however, which occurred inJanuary 1898, did so much damage to the roadway, washing off about two-thirds of the wood blocking, andthe whole of themetalling on the approaches, that it was decided to remove the remaining portion of the wood paving, and to lay the entire length of the bridge and its approaches, a total length of 1,071 feet, with tarred metalling, composed of twoparts of hard blue metal brokento a %inch gauge, two parts to a l-inch gauge, and one part of blue metal screenings or chippings to pass through a ;-inch mesh, the whole thoroughly dried by heat and then well mixed with boiling coal- tar and stacked to allow the superfluous tar to run off, after which it was spread uniformly, to an average depth of 6 inches, well punnedor rammed, brought to an evensurface, andthen well rolled with a &ton roller untilthoroughly consolidated, and formed to the proper convexity. Theentire area of tarredmetalling was afterwards coated uniformly with fine grit sifted from the blue metal screenings. The coal-tar waskept continually boiling for atleast 3 hours before being mixed withthe metal or screenings, andtarred metalling was prepared and laid down duriog fine weather only. ‘l’llis work was conlpleted satisfactorily in November 1898. The

Downloaded by [ University of Sussex] on [16/09/16]. Copyright © ICE Publishing, all rights reserved. 254 BRADY ON MARYBOROUGH CONCRETE BRIDGE. [Selected surface drainage from the roadway on the bridge is provided for by two gully chambers every 54 feet in the length of the bridge, formed in the concrete of each span, covered with wrought-iron surfacegratings in cast-iron frames, protected with hardstone margins, and having outlet pipes, 4 inches in diameter, through the arches, discharging directly into the river,Fig. 1, Plate 4. Parapets.-The handrailing of the bridge consists of removable wrought-iron stanchions fitted with turned ends into galvanised cast-iron sockets, set in the concrete curbs. Through the forged stanchions pass three rails formed of gas tubing, screwed together at the joints, the two uppertubes being li-inch ,bore andthe lower tube $-inch bore. The parapets are made in sections, four to each span, or 13 feet 6 inches in length, having threestanchions in each, for convenience of removal, and with special semicircular sections on the four intermediate escapes over the piers. It was demonstrated by the resident engineer before the opening of the bridge, that, with the aid of three men, the entire handrailing could be removed in sections, replaced and keyed up again and fixed perfectly rigid in 3 hours ; thus showing that, in the case of a sudden rise in the river, no fear needbe entertained for the security of the handrailing. The lighting of the bridge is provided for by four gas-lamps fixed on the upstream side, the end lamps having three lanterns carried on cast-iron standards,and the two intermediate lamps having one lantern each, carried on 3 inches by 3 inches by ;-inch arched angle-barstandards. The lamps are fixed with special connections, so as to be easily removed in the wet season to leave the surface of the bridge clear for the passage offlood waters over it.Several floods occurred duringthe construction of thebridge, that on the17th February, 1896, risingto a level of 85-39 feet, or within14-46 feet of thegreat flood in 1893; and since the completion of the bridge two heavy floods have passed over it, doing no damage whatever to the structure of the bridge, which stood the severe tests admirably, the only damage sustained being to the roadway as already described. The total cost of the bridge andapproaches, including engineer- ingand supervision, amountedto 525,000. Thefirst contractor havingfailed financially in May, 1895, before muchwork was done, a second contract for the construction of the bridge had to be let ; the successful tenderers were Messrs. McArdle and Thomp- son of Brisbane, who signed their contract on 26th July 1895, the time allowed for the completion of the work being 15 months. The contractors completed their work within contract time in a

highly creditable manner; the bridge being novel in character, and the river subject to frequent floods, the work was not carried through without some difficulties, which, however, were success- fully overcome. The bridge was formally opened for traffic with some ceremony on the 30th October, 1896, by the Hon. David Ray Dalrymple, M.L.A., Minister for Public Works, in the presence of a large and representative assembly of the public, and the structure was named the Lamington bridge, in honour of His Excellency the Right Hon. Baron Lamington, K.C.M.G., Governor of Queensland. In concluding this Paper, theAuthor has muchpleasure in acknowledging theable assistancerendered bythe Besident Engineer on the works, Mr. Alfred J. Goldsmith, M. Inst. C.E., to whose fertility of resource, engineering skill, painstaking and vigilance, extending over a period of 2 years, must be attributed in a large measure the successful completion of the structure, the first of its kind in Australia.

The Paper is accompanied by four drawings and four photo- graphs, from a selection of which Plate 4 has been prepared.

APPENDIX.

The followinn are the prices paid for the different descriptions of work in the bridge and appioaches :L e S. d. Excavation inabutment foundations . . 0 3 0 percubic yard. ,, ,,,, pier foundations(including cost of staging' and wrought-ironcaissons. 5 0 0 1, I, ,* also levelling surface of rock bottom) . I Ironbark piles for abutment foundations . 0 3 6 ,, linear foot. Sawn hardwood in capsills and planking . 0 3 G ,, cubic ,, Wrought iron in pile shoes and spikes . . 0 0 4 ,, lb. Cementconcrete (5 stone, P sand, and 1 15 0 ,, 1 cement) in abutments .....l cubic yard. Cement concrete in piers (5, 2, and 1) . . 2 3 0 ,, 1, I, ,, ,, imposts (4, 13, and 1) 2 7 0 7, ,, >I $9 ,, ,, arches (4, l+,and 1) . 3 1 0 ,, >, 9, ,, parapets, copings, &C.> 2 10 0 ,, 1, (Z, 14, anci'l) ...... ,, Rubble stone backingto abutments . . 0 4 0 11 ,, 9, Freestone coping and lamp bases ... 0 9 0 ,, ,, foot. Cast-ironchairs to skeleton framing , . l 0 0 ,) cwt. Wroughtiron in bolts, nuts, &c. ... 0 0 5 ,, lb. .. ,, ,, anglesand rivets ... 1 o 0 ,, cwt. ,, gully-frames,gratings, cramps, dowels, &c...... S 0 0 1, ,, Steelrailway rails to skeleton framing, 9 0 0 ,, ton. straight ...... Steelrailway rails to skeleton framing, I curved aud forged- ...... 1 14 o 0 ,, ,, Steel in fish-plates, and cover# to all connections ...... } 30 0 0 ,, ,, Hardwood block paving on bridge ... 0 1% 0 .. square yard. Excavation for approaches ..... 0 2 0 .. cubic .. Htone pitching 7 inches deep on embank- ,, superficial yar11. ments ...... } o 4 o Metalling on roadways of approachca . . 0 9 0 ,, cubicyard. Wages of labourers ...... 0 0 9 .. hour.

* The cost of staging was equal to about 8s. per cubic yard of excavation: the actual cost of the wrought-iron caissons, including conveyance from the banks of the river, fixing and jointing, and cost of lowering gear, was equal to about S2 168.3d. per cubic yard of excavation.

QUANTITIESOF PRINCIPALITEMS m BRIDQE. Excavation in foundations of piers and abutments . 1,250 cubio yards. Piles in abutmentfoundations ...... 565 linear feet. Wroughtiron in pileshoes ...... 532 lbs. Portland-cementconcrete in bridge . . . . . 4,270 cubic yards. Castiron in chairs to skeleton framing- . . . . 3.53 tons. Steel andironwork in skeleton framingto super-} 88.11 structure ...... 9, Wrought iron in anchor bolts, plates,gullies, sockets, cramps, dowels,&c...... ] 2.63 ,,

[THE INBT. C.E. VOL. CXLI.] d

F-3:10. LONG! SECTION OF CUTTING LENGTH.

SECTION. ELEVATION,

PLAN. PLAN OF CUTTINGLENGTH PLAH.