184S. 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



to leave the soil in an unstable equilibrium, which the presence of water will 

 readily destroy. 



Chalk is a material, which, in those parts where it first crops out, that is, 

 !!„!>■! '"''"f,"'^ stratum, has frequently given much trouble, from its in' 

 rZlJ, ""?K f'-fq''«'«;y of pot-holes of loose gravel, which, when unduly 

 charged w, h water, have at times broken awav the surrounding chalk, when 

 near the edge of a cutting; lower down, where it is more compact chalk 

 will st,and at a very steep slope, allowance being still necessarv for the eftect 

 of wea her. riie fear sometimes fell, of deep chalk cuttings, is one for 

 whic 1 there would appear to be but slight cause, the very fact of their depth, 

 usually involving their greater solidity. There is nolhing in the nature of 

 pure chalk, which should render it liable to heavy falls, excepting where it !s 

 exposed, unprotecte.l, to some constantly [undermining action, such as that 

 of the sea breaking at the foot of clilTs. 



The diluvial strata are, from their nature, the least compact, and therefore 

 require the greatest slopes in excavations and embankments ; the alteration 



distorted the original horizontal strata, renders them more liable to further 

 change of form by facilitating the operation of water the element to which 

 neouCu. "?■?',"'" '!fP''f' <""• ""<• *° ^'''ose continued action they seem 



h, wbi/) • '"'=^P '"''• ^f """ s'^"*"' ""= »«»' ^oliJ are gravel and sand, 

 ^1,T^« ,, '• u^",- °"S ?"'' "^''^"^ """ '^"P'-' »f excavations may he left steep, 

 m, inlr'r '""''!"S.a''J unsubsiding qualities render them the most suitable 

 Z ex.t,,!^l'. ! n"^ ' permanent way. The other soils of this class 

 f m^rK T ■ . " ' ' 1°"'' "^ "^' ''"■" """ «™ »"'' '^"'"^i»"s ; others, of 



a D overb.niw ' r '"''J'f' '" "''"' "■''"'= q^'^l'^""'!^ ""d peat are soil of 

 a proverbially treacherous character. 



vJi^^'TZV! '''iVr'' ""■','"'/' "^"''•'' "'" P''"?" '"elination for slopes, 

 imits al.o I e height of embankments and the depth of cuttings. It would 

 he impossible however, in a general sketch to give any definite nles 

 for either, as they depend on minute differences of soil, as well as the va ion 

 concomitant circumstances of the case. >aiiuus 



In rock cuttings, many instances may be adduced of the sides of excava- 

 tions ditrcring very slightly from the |,erpendicular, while the correspoi ding 

 embankmen , may have slopes of about J horizontal to 1 vertical. Excava- 

 tions in chalk are commonly made (when the chalk is solid,) with slopes 



bo1e"'Fmb %*" ' l"^ *°i \'t"'' ^'°'" ''^'"g -"eased when iL materia 

 loose. Embankments in chalk may have slopes from I to 1 to 1 S to ] 

 Excavations in gravel will stand sometimes at a slope of J to 1 but more 

 frequently at to 1. Embankments of gravel, if good, will stand wel/ at U 

 or 14 to 1. Lxcavations and embankments in strong sand will stand at in 

 clmat.ons rather greater than in gravel. Very few clays can be trusted, eitl e^ 

 in excavation or embankment, at a less slope than 2 to 1. Both quicksand 

 and peat require the aid of draining before excavation is praetica le and the 

 great quantity of earth which th.y invariably swallow up renders b; forma! 

 tion of an embankment upon cither a work of great difficulty, unless The 

 surface to bo covered is previously prepared by means of fascines or hu dies 

 to support the superincumbent mass. "uruies 



In materials of a rigid and unyielding character (such as rock and chalk) 

 the practical limit to the depth of a cutting, or to the height of an em lank 

 ment, goes far beyond that point, at which a tunnel or%iaduet would be 



A Vellow clay. P[ j^j 



5 Blue clay 10 /"t. to 15 



C Rolled flint shingle 1 iJJ 



V Fine sand ' " ' q .^ 



f jr's""^ ■. :::::;:::: o oi 



p Fine sand . , 



G Ferruginous sand w.th fossils 

 H Loose grey sand with fossils. . 

 I Strong blue clay . 

 K Black clay and san 



L Black dirty sand g 



M Dark sand with fossils, oysters, &,c n 



N Stone with fossils .'.".'.'.'.'.'.'.*.' o 



O Decomposed stone and sand with fossils 

 P Plastic clay. 



25 



more economical In such materials, too, it does not hccoiue necessary to 

 augment the mehnation of the slopes, with an increased height of et^baU. 

 ment, or depth of cutting; a step which is essential in soils of a j"g 

 character, and becomes more necessary in proportion as the rigiditv dimin^ 

 isbes. In yielding soils there is a limit of safety, in the heiKbt of en Tnl 

 ments and the depth of cuttings. The reason of't'bis L oS ; the r ' "in- 

 of an unyielding sod, will admit of mass lying upon mass, like a wall, until 



.VM'^,N'"""'n-" «'■""? r '" ""^'' ""■ ''^'^« bvthcsuperincunle 

 weigh ; while a yielding sod has not sullicient tenacitV to support its own 

 weight, to any great height, but sinks down bodily and spreads out at the 

 Ides. Gravel or sand will not. in general, permit with perfect safely a cu! 

 ting of much above 70 feet to 80 feet in depth, or an embankment rnuch ex 

 ceedmg ,^,0 feet or fiO feet in height ; and i,l clay the lin its of afetTa fir' 

 more contracted In some cases, an embankment mav be carried to a much 

 greater height than it otherwise could, bv forming it' in several lifts abovs 

 each other and thereby allowing time for the weight toseUle^adua Iv, and 

 to distribute Itself equally over the base. The speading of the foot of the 

 embankment may be frequently prevented by cutting stc^sTu po tion of the 

 revetm;nt" '"'""'"^ "^ ' '^ "^ '°'"' """' "^id soil, in Ihe form of a 



The consideration of the variable law, which regulates the slopes required 

 in yielding mate.ials, according to the depth of the cutting, or the Slit of 

 an embankment (increased height or depth requiring increased inclination of 

 slopes), may, perhaps, fairly lead to the conclusion, that where the height or 

 depth IS considerable the inclination of the slopes should not be in a regular 

 straight hne, but rather in a curve, so as to have the greatest incHnation at 

 the bottom, where there is the greatest pressure, and the least at the on 

 this system would approach nearest to the analogy of nature, where riRid 

 angular lines are found only in the unyielding rocky crags, while all the 

 slopes of the more yielding soils are undulating. 



In partial illustration of these preliminary remarks, the author then pro- 

 ceeds to give the result of his observations on the soils upon the Croydon 



BOTTOMOE LONDON CtfviT 



:S^>^^v^'^'"Z7:h 



Sg^S^-^ ^yg^' f ygr J ^^Sr^J. -.^ A yj^^k^C** 'T 1 



Fig. 2,— Potltion of tta< Slip Inthg New Cross Cutting, JnJ Novunlju, 1-1 



