A practical treatise on foundations, explaining fully the principles involved : with descriptions of all of the most recent structures, accompanied by numerous drawings ...

Front matter

I

EXPLAINING FULLY THE PRINCIPLES INVOLVED.

WITH

Preface

In a work on Foundations, theories and formulae are of little value ; therefore but little space is given to the discussion or criticism of either. The more common formulae are given without any attempt to explain the laws or premises upon which they are based ; a few examples are worked out in order to show the actual or relative values of the terms entering into them, and to compare the results with those used in practice. I do not do this either to ignore or underrate the value or im¬ portance of theoretical investigations; if the formulae deduced in themselves do not have practical value, they incidentally lead to comparisons with actual results, and induce the publica¬ tion of a large mass of more or less accurate records of observed facts. Theory and practice should go hand in hand ; but it is to be regretted that in many institutions claiming to be schools of engineering so great a preponderance in time and energy is given to the theoretical side of the question, even almost to the exclusion of practical instruction, whereby many erroneous ideas and principles are instilled into the minds of young engineers, to eradicate which years of labor, blun¬ dering, and mortification are required, causing loss and delays to their employers, loss and injustice to contractors by onerous and useless requirements and exactions, which could have been saved by a knowledge of a few facts and methods found in

IV

PREFACE.

common and every-day practice; theorists claiming that the “costs of labor, materials and construction, and also rules of practice ” are of no value to the student of engineering, as these will be acquired after leaving college, and that “ prin¬ ciples alone are necessary to be taught.”

Having been a professor for over six years, I have fully realized the need of suitable books, by which I could temper the almost painfully scientific, abstruse, and purely theoretical books that I was compelled to put into the hands of the student in engineering, which could only be partially supple¬ mented from a few years’ prior experience in active practice, during which the full force of what I have stated above was full)7 realized.

With the above experience and the experience derived from eighteen years of active practice, a very large portion of which was devoted to bridge construction in many parts of the United States, building on a great variety of soils, necessarily requiring a great variety in the designs and methods of con¬ struction, I have undertaken to write the following pages. The descriptive portions of this volume have been to a large extent based upon my own experience, the facts of which are taken from records made at the time and still in my possession ; they can therefore be relied upon as accurate. The drawings, with few exceptions, are taken from my own designs, and are accurate representations of the actual structures used ; in these my only aim was simplicity in design, convenience in construc¬ tion, combined with cheapness, strength, and suitableness for the purpose in view. Unusual sizes and shapes of the parts were studiously avoided, as only adding to the cost of material and construction without any compensating practical advantages.

I have only given prominence to these, as I believed they can be fairly well taken as typical designs, and with a few modifica¬ tions in the details can be readily converted into the designs of other engineers for the same purposes. Full descriptions, how-

PREFA CE.

V

•ever, have been given of all of the latest and largest structures, which can be readily understood when taken in connection with the drawings given. I have collected from all available sources facts in connection with this all-important subject that have been published up to the present date, such as the actual loads and pressures on every variety of material, accu¬ rate descriptions of all designs and methods of construction, all useful knowledge of the qualities, properties, and strength of the materials used. Believing that the want of familiarity with the costs of materials and construction, the usual dimensions and forms of parts, and the quantities of materials required in the more common structures, as expressed in bills of material and records of actual and comparative costs of structures, is a most fruitful soures of waste of money in making contracts, as designing contractors, by magnifying the costs of materials and •construction, and the difficulties and risks to be incurred, im¬ pose upon the credulity, ignorance and fears of engineers, there¬ by securing enormous profits on their works, for these reasons I have devoted more than the usual space to these matters. I have expressed opinions, made suggestions and (I hope) kindly criticisms, knowing full well that if they are erroneous or not justified by the facts presented they will be corrected, for which kindness I desire to express my thanks in ad¬ vance. No one need be misled by opinions, as the facts are present in full. I have endeavored in writing this volume to confine myself as closely as possible to matters pertain¬ ing to the subject of foundations, by which I mean those parts of structures resting on and directly supported by the materials of the earth, and these materials themselves in regard to their capacity to support the loads or pressures resting upon them. There has always been some confusion as to the mean¬ ing of the term Foundation: it is difficult, if not impossible, to separate that which supports a pressure from that which produces it. We must know the magnitude, the direction, and

VI

PREFACE.

the point of application of a force; and all three must be known. If the force is distributed, we must know the nature of the distribution, whether uniform, uniformly varying, or ir¬ regularly varying, so as to provide proper supports and resist¬ ances, with the requisite strength and at the required points. Except in so far as these considerations enter, I think that I have confined myself within the limits of the subject. To avoid confusion or too much repetition, I will always call the natural materials, of whatever nature, upon which the structure is founded or built, the Foundation-beds ; all else will be called Foundations or Substructures, these being the parts of the structure under the surface of the ground or water. Those portions above are only described or illustrated where it could not be avoided either for a clearer understanding or for sake of valuable comparisons. Where tables and other data have been taken from books, I have endeavored to give the authors the credit in the description. I am, however, largely indebted to the editors of the Engineering News, who kindly granted the free use of the columns of their valuable and wide-awake magazine. I am also under obligations to Mr. C. A. Brady. C.E. ; Mr. I. E. A. Rose, architect ; and Professor R. A. Marr, of the Virginia Military Institute, for valuable aid in prepar¬ ing the drawings. I have been greatly assisted in other ways by Col. E. W. Nichols, Prof, of Mathematics, Virginia Military Institute.

The volume is divided into three parts; it is further sub¬ divided into articles and paragraphs. The articles are numbered continuously throughout the volume, the paragraphs are only numbered continuously through each part. Par. I is at the beginning of each part.

W. M. Patton, C.E.

Lexington, Va., May, 1893.

Part First. Article I

PAGE

Foundation-beds: — Of rock, clay, sand, gravel, and silt — Rules for prepa¬ ration of — Bearing resistance of — Practical deductions — Tables of resistance to crushing of stone— Practical determination of bearing resistance of — Failure of structure mainly due to defective . . 1

ARTICLE II.

Foundations: — Means adopted in constructing — Of concrete— Composi¬ tion of concrete — Methods of mixing — Consistency of mortar in — Proportions in, of stone and mortar— Methods of mixing for the Ohio, Susquehanna, Schuylkill, and Tombigbee river bridges — Kinds of stone suitable — Broken bricks and shells in — Rules and principles in making — Proportions, mixing, etc., under Washington Monument — Absolute rules for proportion of quantities useful and practicable in certain cases — Impracticable when handling large quantities with limited time and money available . 9

ARTICLE III.

Concrete: — Uses and advantages of — Under walls of houses, bridge piers and abutments, and retaining- walls — Crushing strength of . . 80

ARTICLE IV.

Building Stones: — Granite, marble, limestone, slate, and sandstone — Prop¬ erties of, structural and chemical — Stratified and unstratified — Quarry indications as to quality — Siliceous, calcareous, argillaceous — Stones that harden by exposure, stones that disintegrate or deteriorate on exposure — Resistance to acid and atmospheric influences — Resistance

vii

TABLE OF CONTENTS.

viii

PAGE

of, to heat — Capacity of absorbing water — Durability of, and suitable¬ ness for building purposes . . . 23

ARTICLE V.

Quarrying: — Rules and principles — Drilling by hand and by machinery— Economical conditions of— Blasting with powder and dynamite, pre¬ cautions necessary to avoid injury to stones in — For face stones, for backing, rubble and concrete . 28

ARTICLE VI.

Stereotomy: — Only simple forms required for ordinary work— Useful for architectural and ornamental purposes, requiring complicated forme and shapes — Tools used — Methods used in cutting and dressing ordi¬ nary stones — Requirements as to beds and joints— Examination and inspection of stone — Chisel-drafts, pitch-lines — Models and templets — Necessary and unnecessary requirements . ... 34

ARTICLE VII.

Masonry: — Stones used in — Granite, marble, limestone, and sandstone — Classified — Dry stones, rough rubble, rubble in courses, block-in-course, ashlar — Stone suitable for — Relative dimensions of stone in — Facing and backing — Headers and stretchers — Dimensions and proportions — Bond in — Bed and side joints in — Ashlar, rubble, and concrete back¬ ing compared — Grouting walls of — Footing-courses, neat work, string¬ courses and coping, raising stones— Appearance of masonry on face no indication as to kind or quality of — Uses and advantages of chisel-drafts and-pitch-lines — Proper position, length, and other dimensions of headers . . . 97

ARTICLE yin.

String-courses and Coping: — Uses of — Projection of — Kind of masonry in — Position of — Shape of piers in plan— Square, circular, elliptic, and triangular ends— Templets for — How laid and constructed — For what purpose — Proportions of length and breadth of ends — Cutwater or starling proper . 46

ARTICLE IX.

Ice and Wind Pressures: — Velocity and force of wind — Formula for — How estimated on piers and trusses — Pressure of ice — Force of wind — How estimated— Various theories and assumptions — Moment of over¬ turning forces on trusses and piers — Moment of resistance to over-

TABLE OF CONTENTS.

IX turning— Ice and drift gorges — Effect of, on structures — Dimensions of piers required determined by other conditions, and always suffi¬ cient to resist these external and unusual pressures — Examples given, 49

ARTICLE X.

Retaining- Walls: — Stability of masses of earth, frictional — Cohesion and adhesion destroyed by exposure— Angle of repose — Natural slope — Uses of — Resultant pressure on — Magnitude, direction, and point of application of resultant — Moment of overturning force — Moment of stability or resistance to overturning — Resistance to sliding or fric¬ tional stability — Formulae and practical rules for thickness of walls — Pressure of water or quicksand on, and thickness required — Con¬ struction of — Kind of masonry in — Face, backing, and footing courses — Position of centre of pressure or resistance with respect to centre of figure of base — Plan and Section — U, T, and wing abutments and walls . 52

ARTICLE XI.

Retaining- Walls Formulae for stability — Rankine’s, Trautwine’s,

Moseley’s— Practical examples and rules . 57

ARTICLE XII.

Arches: — Theory of — Mathematical and graphical methods — Depths of arch-ring at keystone and springing— Centres of pressure — Lines of pressure — Masonry in arch-ring — Abutments— Spandrel walls — Back¬ ing — Flat and pointed arches, manner of giving way — Backing to prevent failure — Stability of — Resistance to crushing, overturning, sliding— Definition of terms used — Full centre — Elliptical and seg¬ mental . 64

ARTICLE XIII.

Skew Arches: — Definition of — String-course and ring-course joints — De¬ velopment of soffit — Usual construction of . 72

ARTICLE XIV.

Arches: — Formulae for depth of keystone— Examples under — Lines of pressure . 73

ARTICLE XV.

Brick:— Brick walls and piers— Brick-making— Uses and advantages of— English and Flemish bond— Construction and strength of— Durabil-

X

TABLE OF CONTENTS.

ity of — Stability of — Failure of — Mortar, adhesion to — Use below ground or water not recommended unless cement mortar is used — Slate between courses — Importance of being kept wet — Thickness of walls — Compressed brick — Dimensions — Measurement of — Sewers — Pavements . . 75

ARTICLE XVI.

Brick Arches: — Usually built in rings — Headers should be used— Two methods of building— Thickness of joints at intrados and extrados — Slate in joints — Use and advantage of hoop-iron — Used in lining tun¬ nels — Thickness of lining— Uses of —Stability of — How estimated and paid for . . 8£

ARTICLE XVII.

Arches: — Summary of theories and their practical applications— External forces — Assumptions made — Lines of pressure — Precautions necessary in constructing — Centres for arches . . . 85

ARTICLE XVIII.

Box Culverts:— Uses, dimensions, and construction of — Kind of masonry in— Thickness of walls — Height — Covering stones — Precautions in tilling over aud around culverts and arches — Rules and principles of masonry construction .......... 8®

ARTICLE XIX.

Cements and Hydraulic Limes: — How and where obtained — Kind of stones— Percentage of lime, clay, or silica, etc. — Temperature required in burning — Mixture of different grades of stone — General properties and qualities — Portland, heavy slow-setting — Rosendales, light quick¬ setting — Hydraulic activity and energy — Set not well defined — How determined — Proportions sand, cement, and water — Tensile strength of — Requirements of — Simple tests as to fineness, set, etc. — Slake slowly — Quick lime obtained from pure carbonates, or those contain¬ ing small per cents of clay, silica, etc., and will not harden under water — Process of slaking— Mixing with water — Quantities of mortar obtained per barrel of cement aud lime — Quantity required in mason¬ ry and concrete — Proportions of sand and water in mortars. . . 91

ARTICLE XX.

Mortar: — Definition of — Proportions of cement, or lime, sand, and water — Proportions of, in masonry — Cement and lime mixed economical —

Test of quick-lime and slaking of— Cement and quick-lime stones —

'TABLE OF CONTENTS.

Chemical and mechanical compositionof — Percentage of beneficial and injurious ingredients — Proper cements to be used — Tests of — Brands of — Tensile tests of briquettes— Hardening of lime and cement mor¬ tars— Deposited under water should have some set first, unless deposited in bags — Lime mortars not used under water — Pozzuolaua — Definition and uses of — Freezing of mortars not considered injurious Experiments on — Salt in mortars — Pointing mortars. Also see Sup¬ plement . 96

ARTICLE XXI.

Sand: — Uses of, in mortar — Proportions — Qualities necessary — Sizes of grains — Tests for cleanness and sharpness — Salt-water sand — River and pit sand — Cleanness and sharpness of grain most important requirements . 106

ARTICLE XXII.

Stability of Piers: — External pressures — Current, ice, drift, and wind — Expansion and contraction of ice — Effects on piers — Ice and drift gorges, and flow of— Destructive effects of — Tearing and crushing resistance of ice — Protection of piers, cutwaters, etc . 107

ARTICLE XXIII.

Water-way in Culverts: — Formulae for— Practical rules — Dimensions of, and how determined practically — Terra-cotta pipes— Iron pipes — Uses of culverts . 113

ARTICLE XXIV.

Arch Culverts: — Dimensions and construction of — Thickness of abut¬ ments — Formulae for — Practical examples — Lengths of span — Plans and sections — Surcharged walls — Formula for — General remarks . 115

ARTICLE XXV.

Cost of Work: — Remarks on — Brick-walls and piers — Trestle work, framed and pile — Timber, masonry, caissons, cribs and coffer-dams — Conditions in contracts . . 120

ARTICLE XXVI.

Cost of Work: — Tables of — Cost of quarrying, cutting, laying, sand, masonry, brick-work, rubble, concrete, paving, brick, arch stones, cement, lime, etc . . 123

TABLE OF CONTENTS.

xii

ARTICLE XXVII.

IAGB

Dimensions, Quantities and Cost: — Examples — Ohio, Susquehanna, Schuylkill, Tombigbee river bridges— Tables of quantities and costs — Cost of sinking caissons as usually estimated, also by cubic yard of displacement . 126

ARTICLE XXVIII.

Definitions and Tables: — Of parts of arches, piers, and retaining-walls, etc. — Tables — Of resistance to crushing, tearing, cross-breaking — Of -weights per cubic foot of materials — Of angles of repose — Of various materials — Of bearing resistance of soils— Uses of, and practical ex¬ amples . . 136

Part Second. Article XXIX

Timber Foundations: — Why used— Under walls of houses — How con¬ structed— Under New Orleans custom-house — Under towers — Unit pressures should be same under all parts— Piles often preferred in soft and silty soils— Cribs and grillages under piers — Construction of — Sinking of — Dangers of beds of sand and gravel — But often used — Example, Parkersburg bridge— Cribs sunk on rock — Precautions to be taken — Cribs sunk on rock— Coffer-dams of earth, and dimensions of — Remarks on . . 147

ARTICLE XXX.

Coffer Dams of Timber: — Double walls with clay-puddle — How con¬ structed — Dimensions — Remarks on — Single wall coffer-dams, tongued and grooved — Construction of — With vertical timbers — With timbers and plank in horizontal layers— Crib coffer dams — Construction uses and advantages— Puddle for— Pumps — Exca¬ vation — Size of dam important — Bracing— Precautions for safety — Coffer-dams with inner cribs — Construction — Uses and advantages of — Examples — Preparation of foundation-beds . 151

ARTICLE XXXI.

Open Caissons:— Construction of— Preparation of bed by dredging— By piles_For what depths useful and economical — Sides of, single wall coffer-dams, and removable— Bottom crib or grillage forms part of

TABLE OF CONTENTS.

xin

PAGE

permanent foundations — Generally simply resting on bed — Can be secured if necessary . 162

ARTICLE XXXII.

Cushing Cylinder Piers : — Construction and uses— Piles actual supports —Cylinder casings for concrete — Use of concrete — Depths sunk — Manner of sinking — Piers wanting in stability — Are economical, and often used — Cylinders often sunk without piles — Require constant watching and large quantities of riprap— Examples — Tensas River bridge — Full description and dimensions — Sinking— Shell concrete used-— Contract prices for, etc . 164

ARTICLE XXXIII.

Sounding and Borings: — Importance of— Common neglect of — Making —Errors and waste resulting from neglect of — First method, driving solid rods, uncertain, unreliable, and unsatisfactory— Second method, sinking large terra-cotta or iron pipes more satisfactory, but more or less uncertain— Third method, sinking small iron pipes by water-jet and force-pump, rapid, economical, reliable, and satisfactory— Descrip¬ tion of processes in sand and gravel and silt. Also see Supplement . 166

ARTICLE XXXIV.

Timber Pierr:— -Construction and uses— Ad vantages and disadvantages . 170

ARTICLE XXXV.

Framed Trestles:— Construction and uses — Designs and dimension of parts . . 172

ARTICLE XXXVI.

Properties of Timber: — Kinds commonly used — Pine, oak, cypress — Effects of bleeding or turpentining pine-trees . 177

ARTICLE XXXVII.

Durability of Timber: — Defects of, cracks, shakes, crippling, dotimess, sponginess, decay, and rot where developed in frame structures —Examinations for — Repairs and renewals— General remarks . . 180

. ARTICLE XXXVIII.

Preservation of Timber:— Character of defects— Effect of, on timber — Natural seasoning — Protection of bridge trusses — Artificialseasoning —

XIV

TABLE OF CONTENTS.

Preservation by solutions of metallic salts, creosoting, vulcanizing — Durability as affected by time of cutting down and by age of trees — Constantly immersed in water, favorable for durability — Asphalt and other paints — Discussions and remarks. Also see Supplement . . 182

ARTICLE XXXIX.

Framed Trestles: — Two types not often used, but good designs — Joints, weak points in . 187

ARTICLE XL.

Joints and Fastenings:— Mortise-aud-tenon— Disadvantage of— Square abutting joints with iron straps — Advantages of — Dovetail joints — Strut and tie — Longitudinal bracing— Fish and scarf joints —

Uses and designs — Actual and relative strength of joints — Formulae and examples of relative resistance to crushing, tearing, and shearing — Strength of connections should equal strength of main parts — Weak¬ est part determines strength of entire structure — Joints in king and queen trusses — Rules and principles to be followed in all joints and fastenings— Joints for lengthening — Ties, struts, ties and struts, and beams . 188

ARTICLE XLI.

Trestle Foundations: — Mud-sills— Masonry pedestals — Piles — Advan¬ tages and disadvantages of — Framed trestles divided into four classes — Comparative strength and economy of construction — Kind of stresses on main members— How connected to resist — Formulas for and examples of relative and actual strength and dimensions — Posts, caps, sills, stringers, struts, and braces — Explanation and use of formulae — Tables of resistance to crushing, tearing and cross-breaking — Ulti¬ mate and working stresses, factors-of -safety — Formula for long columns — Bill of timber and iron for four story trestle . . . . 196

ARTICLE XLII.

Timber Piles: — Uses of — Long and short — Kind of timber used, and com¬ parative value — Preparing piles for driving — Squaring butt — Pointing end — Square ends preferred in driving — Method of driving — Precau¬ tions to prevent splitting — Excessive brooming — Bands and shoes of iron — Remarks on driving — Great damage to piles in driving — Useless hammering on piles — Value of formulae discussed — Reliance mainly on experiment and experience — Experiments on bearing power of piles (also see Supplement) — Practical conclusions — Peculiarities in

TABLE OF CONTLNTZ.

XV driving in different soils— Remarks — Usual formulae and examples under them — Rankine's, Trautwine’s, banders’ . 207

ARTICLE XLIII.

Timber Piles -.—Engineering News formula — Latest and doubtless the best — No formula considered of practical value depending on weight of hammer, fall and penetration — Formula suggested for bearing re¬ sistance based on bearing resistance of soil and frictional resistance on exposed surface of pile — Only formula applicable to piles sunk by water-jet or otherwise forced in ground without blows of hammer — Examples under — Several forms of pile-driver used— Description and discussion — Hand, horse, and steam-power. Also see Supplement . 219

ARTICLE XLIV.

Piles: — Purposes for which driven — Long and short — Sand piles — Under houses, piers, wharves, and dikes — Pile-trestles extensively used — Dis¬ cussions of three and four pile bents, with vertical and batter piles — Designs of floors or decks — Economical considerations — Piles in differ¬ ent kinds of materials— Piles on rock bottoms — Cribs often substi¬ tuted for — Construction and sinking of cribs . 226

ARTICLE XLY.

Comparative Estimate of Costs Framed and Pile Trestles: — Tres¬ tles mainly temporary expedients, intended to be replaced by iron, masonry, or earthen embankments — Relative cost and quantities in framed and pile trestles — Timber and iron — Tables of iron, with drift-bolts — Straps — Mortise-and-tenons — Importance of — Discussion of economic length of span for low and high trestles— Calculations and comparisons — Manner of estimating and paying for trestles — Useless requirements — Local customs important to observe — Cutting piles off under water — Divers — Cross-cut and circular saws — Structures resting on piles — How secured — Proper alignment of piles— Remarks . . 235

ARTICLE XL VI.

Embankment of Earth on Swamps: — Supporting power of swamp crust — Depth sunk in underlying soft silt — Logs and plank used to support — Objections to these methods — General remarks on earth-work — Ma¬ terials for — Form and dimensions of embankments — Grades— Settle¬ ment of banks — Borrow-pits — Side drains — Caving in of slopes — 'Prevention of — Ballast for — Cross-ties— Pine, oak, and lignum vitae — Hewn and sawn cross-ties — Costs of — Recent methods of embanking,

XVI

TABLE OF CONTENTS.

PAGE

as compared with older — Swampy material unfit for embankments — Formula for bearing power of soft materials, to be used with caution — Soft stratum underlying a firmer one, and vice versa . . . 251

Part Third. Article XL VII

Deep and Difficult Foundations: — Open crib and pneumatic caisson methods — Crib-methods — Discussion and examples— General designs for timber and iron constructions — Methods of sinking— Examples — Poughkeepsie, Hawkesbury, Morgan City bridges — Discussion — Advantages and disadvautages — Difficulties — Costs and quantities . 262

ARTICLE XLVIII.

Pneumatic Caissons: — Air an essential element — Plenum and vacuum methods — Uses of — Principles and practical applications— Working chambers — Air-locks — Uses and position of— Shafts, pipes, etc. — Safety precautions — Number of men required— Effect of com [tressed air on men— Selection of men — Precautions for their comfort and safety — Paralysis and death in caisson work — Means of preventing, suggested — Signals — Immediate effect of reducing air pressure — Ma¬ chinery . 274

ARTICLE XLIX.

Pneumatic Caissons:— General designs and construction — Examples — New York and Brooklyn — Missisippi at St. Louis and Memphis — Diamond Shoals Light-house — Ohio River at Cairo — Susquehanna, Schuylkill, Tombigbee caissons — Quantities and cost — Full discussion of each structure— Cribs and coffer-dams on caissons — Full details of construction, sinking, and costs— Accidents, precautions against — Cribs not absolutely necessary — Masonry may be commenced on roof of caisson — Coffer-dams should always be provided — Designs and construction of cribs and coffer-dams — Uses and advantages. . . 281?

ARTICLE L.

Caisson Sinking: — Sand and mud pumps, and blowing-out process for excavating material — Precautions necessary in removing material from under cutting edges — Some difficult cases — Excavating below cutting edge in sand, clay, and silt — Filling cribs and working cham¬ bers with concrete — Precautions in passing concrete through supply

TABLE OF CONTENTS.

XVll shafts— Mixing concrete for— Considerations requiring caissons— Causes of some accidents— Difficulties and costs — Lessons to be learned — Discussions of — Frictioual resistances on outside surfaces . . 302

ARTICLE LI.

Combined Crib and Caisson: — Design, construction, and uses — First as a caisson, second as a crib, third as combined crib and caisson — Con¬ sists of an ordinary caisson or open crib, provided with one or more removable roofs, by means of which it can be sunk to any desired depth as a pneumatic caisson— One or more roofs removed, and sink¬ ing continued if desired by open crib process — Use in small depths— Requiring only one or, better, two roofs — After sinking, and sealing up working chamber, roof removed — Concreting is completed in open air or under moderate pressure — Better, more rapid, and satisfactory work — Substituted for ordinary coffer-dams — Construction and sinking described— Safety and comfort of men provided for — Economy, cer¬ tainty, and rapidity in sinking — When sunk to depths of 100 ft. by pneumatic process, piles can be introduced and driven, or sinking continued by open crib method to any greater depth — Average lift of dredged material decreased, and also cost, as compared with open crib process — Constructed of timber or iron, or both combined, in any of designs already given — General remarks on — Unnecessarily sized and shaped parts — Cost and increased difficulties in construction of caissons — Poor designs, etc . . 311

ARTICLE LII.

All-Iron Piers: — Of wrought-iron columns resting on masonry piers or pedestals — Description — Advantages, dangers, risks — Precautions necessary — Screw-pile piers — Full description and discussion of designs — Methods of construction — Sinking piles — Both by turning and by water- jet— Advantages and disadvantages .... 321

ARTICLE LIII.

Location of Piers:— By triangulation and direct measurements with tapes or wires — Instruments required — Base lines— Remarks on loca¬ ting bridge sites — Reasons controlling same — Examples of some of the longest spans and highest piers . 325

ARTICLE LIV.

Poetsch Freezing Process: — Details and discussions — Description of method — Considered as the best method of sinking through quicksand. 338

XVI 1(

TABLE OF CONI ENTS,

ARTICLE LV.

PAGE

Quicksand defined — The most difficult material to deal with in putting in foundations — Old methods of sinking through — Freezing process applicable — A more recent method — by injecting cement grout under pressure through pipes into the quicksand, which on setting converts quicksand into an artificial stone— Discussion and description of this last method— Sinking hollow cylinders of brick, concrete, or iron through — Methods and examples . . 336

ARTICLE LVI.

Foundations foe High Buildings: — Unit weights allowed on sand, clay, aud silt — Usual methods on sand and clay — Sinking through soft materials, by shafts, cylinders, etc., to rock, or by driving piles — The three methods compared and discussed— Economy controlling factor — Masonry on concrete — Iron rails or beams imbedded in concrete — Formulae for projection of successive courses — Timber platforms or grillages on natural material or beds of concrete — Some examples of actual loads — East River Bridge — Capitol building at Albany— Bridge at London — Washington Monument — Tay Bridge, Scotland — Hudson River Tunnel— Eiffel Tower, Paris— City Hall, Kansas City— Audito¬ rium Building, Chicago — Bearing resistance under piers and frictional resistance on surface of caissons as given usually uncertain and unreliable— Examples of— Cairo, Bismarck, Susquehanna rivetbridges — Methods of determination different— Importance of accurate determinations and full records— Effects of compressed air in caissons and escaping under cutting edge reducing frictional resistance— Resist¬ ance to pulling piles less than that to force them down, with reasons for same— Examples of frictional resistances— Records few and uncer¬ tain . 343