24 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[January, 



an immense unbroken mass from the side of the hill, and not of a gradual 

 oreaking back of the groimd, as generally happens, where the slip is attribut- 

 able to a want of consisteniy in the stuff itseif. Subsequent examination 



and experience, however, satisfied the author that the origin of the niov 

 ment was seated deeper, and that a mass of the lias had separated from th^ 

 hill, somewhat in the form of the curve XYZ, in Fig. 1 ; and this idea was 

 subsequently verified, by the rising of the ground on the north side of the 

 railway (where it is supposed the curve came out) at X. The drift is stated 

 to be in a highly saturated condition, owing to the great extent of its sur- 

 face, its peculiar property of holding a considerable quantity of water, with- 

 out falling to pieces, and to its being seated upon the lias marl, which is 

 impervious. Hence it is contended, that the surface of the marl is the floor 

 of the water.seam, and the point to which drainage must be applied to be 

 effective ; and it is stated, that the weight of the drift was considerably re- 

 duced, by the means which were adopted to drain the eastern or upper half 

 of the cutting, to which, in the author's opinion, inui!t be attributed the non- 

 extension of the slip, beyond the part primarily affected. 



The author then proceeds to describe the means adopted with regard to 

 the moving ground, as well as the precautions taken afterwards, to prevent a 

 similar disaster taking place, where the ground was still firm. He states that 

 the removal of the broken ground, to a blope of l.J to 1, was finally had 

 recourse to, laying bare the slope A13, Figs. 1 & 3, for a considerable dis- 

 tance, and that all efforts to draw off the water from the drift, after it had 

 broken up, proved totally useless. Drains filled with nibble stone or faggots 

 were used ; but in most cases without effect, as they soon became choked by 

 the movement of the ground ; the further causes of their failure are com- 

 mented upon in detail, as well as the benefit derived from the experience 

 which they afforded, in pointing out the proper mode of treatment to be 

 pursued in future. The mode of proceeding which was at last adopted, and 

 which is stated to have been perfectly successful, is showii in Fig. 3. 



.Numii. FiK- 3. sotTii. 



Cross section, east ol the slip, higher up the val- 

 ley, ahowiug the headings, jh«lt8, and bench'mgs. 



It consisted, first, in removing a considerable portion of the drift, from 

 the area occupied by the cross section of the cutting, before the marl at its 

 bottom was touched ; and, secondly, in driving headings from the valley into 

 the hill, and connecting them by shafts sunk to meet them, from the high 

 ground south of the line of railway, which in their progress downwards, 

 necessarily pierced the water-bearing strata. These shafts and headings 

 were afterwards connected, by headings driven on the surface of the marl, 

 parallel to the railway, and thus the water was by degrees drawn oft' from 

 the drift, and its quantity sensibly decreased. Upon the eastern part of the 

 cutting, three benchings were cut, so as to bring the general line of the 

 slope of the cutting, within the point B on the ridge, w liich is formed by the 

 valley slope and the strata, and hereby, it was thought, a firmer base would 

 be obtained. 



Upwards of 1 ,500 yards of shafts and headings were driven, at an average 

 cost of about thirty shillings per yard forward. The drift is stated to stand 

 at present at a slope of 2 to 1, which is assumed by the author as a confir- 

 mation of his opinion, that the ground was radically favourable for railway 

 operations, but that it was affected by local peculiarities, which it was origin- 

 ally impossible to have foreseen. 



The necessity of attending to geology, as connected with engineering, is 

 insisted upon, as the author contends, that in almost all instances, the actual 

 surface of the country forms hut a jioor criterion, for judging of its original 

 formation. The paper concludes, with examination into the effects of water 

 upon clay, when in the ground and under pressure, and when exposed to the 

 action of the atmosphere. The author attributes the disintegration of the 

 clay by water, in the latter case, solely to the degree of pressure it is subject 

 to, and cites some instances which came under his observation, in support of 

 this opinion. 



The account embraces a record of the work, extending over a space of 

 more than two years, so that it is impracticable within the limits of an ab- 

 stract to give more than an outline of it. 



Mr. Lowe remarked, that the paper which had been read showed how inti- 

 mately the science of geology was connected with that of civil engineering, 

 and of what essential asistance the study was. This could not be too 

 strongly insisted upon, and it was very desirable that resident engineers on 

 railways should communicate to the Institution plain, but detailed accounts 

 of the events which occurred daily under their notice, and which, when illus- 

 trated by drawings like that which accompanied Mr. Thomson's paper, 

 would form invaluable records. 



Mr. Sopwith said, that the detailed account given by Mr. Thomson, derived 

 additional interest from the circumstance of its relating to the district, and 

 to the same series of rocks which first led to the examination and arrange- 

 ment of the strata of the British Isles, bj Mr. Smith, who bad been justly 

 named the father of geology. 



The vast masses of drift which frequently covered the regular stratification, 

 had only recently become a subject of investigation : and Mr. Thomson had 

 not only described the extent, nature, and effects of drift in this instance, 

 but he had also investigated with care the sources whence it originated. 

 This would often be found a study of practical value, as throwing a light on 

 the nature of the material to he dealt with. Mr. Sopwith instanced the 

 drift near the mouth of the river Tyne, which contained limestone brought 

 from a distance of full thirty miles, and granite from more than seventy 

 miles. The effect of masses of granite in displacing the stratified rocks was 

 also shown on the banks of the river Tyne, where the front of a quay that 

 was nearly perpendicular when built, was now, by the cH'ects of the super- 

 incumbent gravel of a ballast-hill, in a nearly horizontal position. The fact, 

 that the surface contour of a mass of drift, bore no relation to that of the 

 harder rocks beneath, was now well known ; and in the locality described by 

 Mr. Thomson, rocks reposed, in what was called " unconformable position," 

 upon the local strata. The paper just read, was a striking illustration of the 

 value of tlie railway sections, lately collected and placed in the Museum of 

 Fconomic Geology. 



Mr. Slate said, that there were some remarkable deposits of drift in the 

 Staffordshire coal-field. They had completely filled the spaces, which must 

 have been left, when the great down-tlirows or faults occurred. Between 

 Dudley and Birmingham, the coal and all the other strata had been thrown 

 down vertically nearly 100 yards, and yet there was not any appearance of 

 irregularity on the surface of the ground. 



March 26. — The I'hesident in the Chair. 

 Railway Cuttings and Embankments. 



" On Railway Cutlimjs and Embanhnents ; with an account of some Slips 



in the London Clay o« the line of the London and Croydon Ra.lway.'' By 



Charles Button Gregory, Grad. Inst. C. E. 



The formation of railways involving usually the excavation, removal, and 

 employment of large qnantities of earth, requires particular attention to the 

 practical geology of the soils used ; and the skill of the railway engineer is 

 tested by the application of his knowledge of the subject, to the safe and 

 proper forms and proportions, of cuttings and embankments. 



The material nature of every soil, assigns to it some particular slope, at 

 which if will remain in repose ; and this is not only as variable as the soil 

 itself, but it is also modified by every variety of circumstance to which it is 

 exposed. The principal change, however, for which provision is to be made, 

 is the influence of the alternations of weather, which will seriously diminish 

 the durability of a material, possessing in itself, considerable statical strength 

 and tenacity. 



All unstratified rocks, which are equal in their substance and free from 

 faults, may be excavated, so as to leave the sides of the cutting perpendicular 

 or nearly so, and the matciial excavated may form an embankment, nearly 

 approximating to the form of a rubble wall. In some such eases a tunnel 

 may be formed, by merely driving a heading through the rock, without the 

 protection of an arch of masonry. Many stones, whose strength and tex- 

 lure would enable them to stand at any slope, are still affected in their dura- 

 bility by moisture, and especially by frost ; with these, provision mnst always 

 be made for exfoliation to take place, without injury or obsliuction to the 

 works, by leaving a full margin at the foot of the slopes, trimming thera back 

 at a greater inclination, or forming steps or benches, upon which the falling 

 materials may rest. 



Stratified rocks, whose beds are horizontal, admit of a slope next in steep- 

 ness to the unstratified ; but in working through dipping strata and through 

 1 the shaly beds, which frequently lie above solid rock, care is necessary, not 



