Associate Professor V. E. EVREISKOV.

COMBATING LANDSLIDES

IN THE NORTH CAUCASUS

AND ON THE BLACK SEA COAST.

Tomsk — 1929.

Associate Professor V. E. Evreiskov.

Combating Landslides in the North Caucasus and on the Black Sea Coast*)

I. The North Caucasus.

The North Caucasian railways in the foothills of the Caucasus Mountains and their spurs have numerous phenomena of varied deformations of the earthwork, dating from the time of construction. These phenomena are most sharply expressed on the main line on the section Nevinnomysskaya—Georgievsk, on the Armavir—Tuapse line, and on the Stavropol branches, of which one, begun by the construction of the former Armavir—Tuapse Railway Company, has not been completed.

On the main line of the North Caucasian Railways, landslides occur with particular intensity on the section from Nevinnomysskaya station to Kiyan junction and near Vinogradnaya station.

The struggle against landslides on the main line was begun by the former Vladikavkaz Railway Company. The material preserved in the Administration of the North Caucasian Railways indicates that the most widespread method of combating the destruction of embankments was protective drainage, in the form of stone galleries, and transverse drainage, in the form of stone cuts. The former Vladikavkaz Railway Company apparently made especially ready use of stone galleries, and, it may be supposed, sometimes without sufficiently taking into account the geological structure of the railway roadbed foundation. The types of protective stone galleries used are shown in Drawings 1 and 2. The type designed in 1907 and shown in Drawing 1 is undoubtedly obsolete, and it is not found in the later materials of the Vladikavkaz Railway Administration.

Drawing 1. Type of longitudinal drainage (1907).

We were unable to establish in which parts this gallery is composed of dry masonry and of masonry in mortar. Whatever masonry the wall a may have been composed of, it is impossible to expect that, with a thickness of 0.42 m and a height of 5.12 m, it will remain undestroyed within the mass of strata undergoing movement.

*) Report on the field trip, submitted to the Chief Professional Bureau in the summer of 1928.

The stone gallery shown in Fig. 2 was designed in 1924–25 for combating landslides near Vinogradnaya station.

From the materials of the Administration it appears that this type was modified and a gallery was used in the form of a normal retaining drain; i.e., on the side of the track the entire drainage system is enclosed by a wall of dense, tamped clay; the base of the drain is laid on a concrete cushion; and the walls of the gallery and the vault are made of dry masonry.

Fig. 3 indicates the type of gallery of the former Vladikavkaz Railway, made of masonry in mortar, with openings in the walls to receive groundwater; the latter type was designed in 1914 for combating a landslide on the Bogoslovskaya–Nevinnomysskaya section.

Fig. 2. Design of a stone gallery.

A later type of gallery, intended for the Armavir–Tuapse line, is shown in Fig. 4. The widespread use of drainage galleries, practiced up to the present time, indicates that galleries are the favorite type of retaining drain on the North Caucasus railways.

Fig. 3. Drainage gallery (1914).

The great advantage of the types of drainage stone galleries described above is the possibility of inspecting them, since, with the clear height of the gallery being 1.07–1.28 m, passage through the gallery is possible. But the considerable empty space within the body of the drain, constructed of dry masonry, is at the same time its disadvantage, since with the slightest movement of the strata the gallery will be destroyed, thereby disrupting its proper operation and the possibility of inspection.

Incidentally, in places along the line it was difficult to establish the condition of the galleries, but there were indications that many of them were in a destroyed state.

Fig. 4. Drainage gallery (design of recent years).

In strata where movement of the latter can be expected, it seems to us more rational …

to use simpler types of drains, usually employed under conditions analogous to those of the North Caucasus railways, and to a lesser degree suffering from soil movements. In Fig. 5 is shown the type of drain used in the reconstruction of the mountain sections of the Siberian Railway, at a depth of 4 to 9 m, and in Fig. 6—a type of inexpensive drain used where the water-bearing layer lies at a considerable depth. This type was used earlier on the lines of the Vladikavkaz Railway, on the Mineralovodskaya branch¹; at present it has been successfully used in the construction of the Black Sea Railway; the latter type is not, in the full sense, an intercepting drain, but converting it into an intercepting one would present no special difficulties.

Fig. 5. Intercepting drain of a reinforced type at a depth of 8.0 m.

The chief defect of crushed-stone and stone drains—namely, their capacity for rapid silting up (after 5–10 years of service)—is inherent to the same extent in stone galleries as well.

It goes without saying that, where water-bearing strata occur at greater depths, adits may be successfully employed.

On a broad scale, on the main line, transverse drains (often called cuts) have been used to combat ballast troughs in embankments. On the North Caucasus roads there is extensive experience in constructing cuts, and their own types of the latter have been developed here. Cuts, as a means of combating ballast troughs, were among the first used by the Vladikavkaz Railway, which became part of the North Caucasus railway network.²

Fig. 6. Type of deep drain.

The data from the questionnaire of O. R. Stetsevich, undertaken by him for the preparation of a report to the XIV Consultative Congress of Track Engineers in 1896 on the question of ballast troughs, indicate³ that on the Vladikavkaz Railway cuts had already been used by that time. In an article by engineer Borodaevsky, printed in the proceedings of the XX Congress (1903), it is stated that the formation of ballast troughs on the Vladikavkaz Railway occurred mainly on the main line between the stations Mineralnye Vody and Vinogradnaya and on the Mineralovodskaya branch. Engineer Borodaevsky, pointing to the good results from the use of drainage cuts, does not recognize the latter

Fig. 7. Type of cut.

Fig. 8. Cross-section along ab.

not a radical measure, since, as a result of clogging, they require relaying after 5–6 years. The type of cut adopted on the North-Caucasian Railways is shown in Fig. 7. The width of the cuts is 1–1.50 sazhen (2.13–3.20 m); the distance between them varies within wide limits, depending on local conditions; the end of the cut is faced in the form of a retaining mass, laid in mortar and extending beyond the outline of the embankment or the outline of its slip; along the bottom of the trench a concrete gutter is laid for the removal of water, and above the gutter, for the same purpose, a small tube of dry masonry is formed in the body of the drain (see section along ab in Fig. 8); the outer surface of the cut was faced with steps, which were coated on the outside with cement mortar¹. The trenches of the cuts are filled with stone, and recently in some cases with pebbles. At present the question has been raised of using sand as a draining material, bearing in mind that sand is not subject to silting up, whereas stone silts up over the course of 5–15 years. It must be noted, however, that the old dispute about the advantages of stone and sand in drains cannot be regarded as settled, since there are insufficient experimental data for this, although, it would seem, such data would not be difficult to obtain.

Cuts, as a means of combating ballast troughs and, in general, the destruction of embankments, have been widely used on the Main Line and the Armavir–Tuapse branch of the North-Caucasian Railways; they are also widely used on other roads—on the Tomsk line and on the Kazanburg line. Being a rather expensive measure, cuts at once produce a favorable effect in combating the slipping of embankment slopes, and this effect is, of course, the more significant the closer the neighboring cuts are located to one another. When the slopes of embankments slip because of poor-quality soil, because the body of the embankment is wetted by springs or by ground water entering from the slopes of the hillside or from the base of the embankment, cuts are also an excellent means of combat.

The most interesting landslide section on the main line lies between Nevinnomysskaya station and Kiyan siding, which we were able to inspect. The history of this section is highly instructive. The original construction alignment on the Nevinnomysskaya–Dvortsovy siding stretch (for a length of about 6 km) was completely abandoned and moved to its present position²; along the Dvortsovy siding–Kiyan siding section the construction alignment was abandoned in two places. The relocation of the trackbed was caused by considerable destruction of the earthwork. But the trackbed on the new alignment also proved unstable, as a result of which large sums were spent on combating deformations of the earthwork, which the measures adopted failed to stop; therefore, in the pre-revolutionary years a new variant was developed for relocating the alignment higher up the hillside. Over a distance of 6 versts implementation of the last variant was begun, but the works remained unfinished; in the pre-revolutionary years artificial structures were built on the last variant, and in some sections the alignment was partially moved to the new variant, while in the near future a complete relocation of the line on the indicated section is expected. The foregoing shows that on the section under consideration, whose alignment has repeatedly been altered, we are dealing with a very unstable roadbed, and bringing it into a stable condition is very difficult. The terrain along this entire section is a rather steeply descending slope of the wet Barsuki ravine. Even a surface inspection of the slope makes it clear that its upper deposits

are, or were in the past, in motion, sliding (or creeping) down the slope. Below the line, closer to the foot of the slope, a clearly expressed landslide relief is discernible in many places.

When the slope is in an obviously unstable state, any disturbance of its temporary stability—due to the construction of embankments, cuttings, or the dynamic action of passing trains—evidently leads to the manifestation of mobility in the upper strata of the slope. From the railway materials it appears that, on the section under consideration, there were indeed considerable movements of the slope, which also carried along the railway track. For example, the section chief reported in 1926 on the sliding of an entire slope and believed that draining it was impossible because the water-bearing layer lay at a considerable depth; he also indicated that the track was being maintained by raising it on ballast; in the area of one passing loop on the section under consideration, movement of the roadbed under both tracks was observed over a length of 120 m. At present the landslide phenomena on the Nevinnomysskaya–Kiyan section, within the limits of the present route, have become localized in three places. An extremely interesting manifestation of this mobility in the summer of 1928 could be seen opposite the abandoned old line, where the landslide had taken hold of the roadbed lying in a cutting and half-cutting. This landslide expressed itself in severe settlements of the roadbed, which were compensated by raising it on ballast. The phenomenon here has a very complex character. In Fig. 9 a plan is shown of the cracks that formed; the lines abc, def represent cracks that formed below the roadbed as a result of movement of the slope, the contour abcfeda representing the collapsed part of the slope; as can be seen from the sections along AB and CD (Fig. 10), the part of the slope below the line def is in motion down the slope, as is shown by the bulges m near the bottom of the side gully that flows into the main Barsuki gully, and also by the widened crack along the line def, indicating that a part of the slope K has torn away.

Fig. 9. Schematic plan of cracks.

Fig. 10. Schematic section through the collapse.

The geological primary cause of all the movements of the slope is unknown, since there are no drilling data. In general, the geological aspect of deformations on the North Caucasus Railways has so far not received sufficient attention, most likely because of the difficulty of obtaining appropriations for geological investigations, the cost of which is generally a large figure. But without geological investigations, the struggle against movements of the slope is being conducted blindly.

Recently, thanks to the energy and interest in the matter shown by the local section chief, drilling has been begun on the slope. From the nature of the deformation it may be supposed that the water-bearing horizon is located at a depth not exceeding 5–8 m and that, consequently, drainage works are possible with the use of comparatively simple drainage means.

An insufficient appraisal of the geological aspect is seen in the embankment of the abandoned route, located below the existing line. Here the former Vladikavkaz Railway, in combating the destruction of the embankment, carried out extensive¹ works to drain it.

The embankment is cut by a whole series of cuts, sometimes through-cuts; the upper slope of the embankment is supported by retaining walls with counterforts, forming a concrete flume (Fig. 11); there is a large and complex gallery (Fig. 12) and other elaborate reinforcements.

Fig. 11. Diagram of capital drainage works.

Judging by the large quantity of ballast on the slopes and within the slopes of the embankment, it appears that, during deformations, it was, as usual, filled in with ballast, which could have led to the formation of deep ballast troughs; and in that case the drainage works applied to the embankment had their justification. But since the principal cause of the destruction—namely, the movement of the native strata at the base of the embankment—was not eliminated, the former Vladikavkaz Railway was ultimately forced to abandon the roadbed and move it higher up the hillside, where it too suffers from destruction. It is obvious that the new alignment, which has partly been prepared, as stated above, is in analogous conditions; and if drainage works for the native water-bearing layers are not carried out after the appropriate geological investigation, there is every reason to assert that the roadbed of the new alignment will likewise be subject to destruction, while its cost over a length of 5–7 versts has been calculated at 228,500 rubles.

Phenomena of railway-roadbed landsliding have also long been observed near the stations of Vinogradnaya and Georgievsk.

The geological structure of the roadbed near Vinogradnaya station, as determined by mining engineer N. Kh. Platonov², is shown in Fig. 13, from which it is seen that within the thickness of the strata inclined toward the Kuma River there are water-bearing interbeds, along which movement of the overlying beds may occur. The sliding phenomena that began here at the time of construction are being combated by deepening the flume and constructing galleries on the upstream side, with the object of intercepting the flow

groundwater. Here, obviously, we also encounter an insufficient appraisal of the geological aspect of the question, since reaching the water-bearing strata by means of open flumes and galleries does not appear possible here.

With regard to the study of landslides, the Armavir–Tuapse branch is of considerable interest; on this line, from Komsomolskaya station to Goitkh station, the Construction Administration waged a persistent struggle against deformations of the roadbed, building a number of drainage devices and retaining walls; this struggle, on a comparatively small scale, is being carried on at the present time as well.

Fig. 13. Geological section near Vinogradnaya station.

On the Armavir–Tuapse railway, cuts, adits, and also, on a large scale, drainage galleries borrowed from the former Vladikavkaz Railway were used as drainage structures; but it may be said that the use of the latter is not always justified by geological data.

Certain incidental figures, such as it was possible to obtain from the Administration of the North-Caucasian Railway, indicate that deformation phenomena during the construction of the above-mentioned section of the Armavir–Tuapse railway were extremely widespread. For example, in 1915–1916, on the 2nd construction section, between versts 94 and 154 (100 km–164 km), the total volume of landslide fills and excavations reached 136,000 cubic m (14,000 cubic sazhen); on the 3rd section, between versts 155 and 209 (165–223 km), it was necessary to cut back slopes, in order to give them a more stable position, by 38,400 cubic m (3,935 cubic sazhen).

The number of drainage structures built to combat deformations is considerable. I cite the following incidental figures: within one of the sections of the line, in 1926, there were stone galleries alone amounting to 2,300 linear m (1,080 linear sazhen); within another section there was no smaller quantity. On the 2nd construction section, in 1915–1916, more than 6,000 cubic m of drains and cuts were laid, and more than 7,300 cubic m were designed and marked out for laying.

Fig. 12. Gallery according to the design of Nasypko.

Despite the large number of drainage structures, it requires a significant increase, since deformations of the roadbed continue. These deformations do not have

of a catastrophic character; in most cases they manifest themselves slowly, but continuously. This condition of the roadbed has recently given rise to proposals for the complete abandonment of the existing route on the Komsomolskaya–Khadyzhenskaya section and its relocation to the south, which, in our opinion, is not dictated by the circumstances.

This section, Komsomolskaya–Khadyzhenskaya, which we were able to inspect, is laid along the unstable slope of the Psish River, and it may be concluded that, in general, comparatively shallow strata are involved in movement here, the drainage of which is quite attainable by means of ordinary drainage measures.

Without touching upon the ordinary structures employed here, we shall point to the use of cribwork (the scheme in Drawing 14) for supporting the slopes of slipping embankments. In one case the outlet part of a pipe is protected by such cribwork, probably in order to safeguard it from destruction. It was not possible to obtain more detailed information about this interesting structure.

Drawing 14. Design for strengthening an embankment with weak soil (1917).

In the materials of the former Armavir–Tuapse Railway there is an interesting design for the temporary strengthening of embankments in weak ground, approved in 1917. The design was used on the Chicago Milwaukee & St. Paul road and was published in the Railway Review for 1916,¹ whence, evidently, it was borrowed.

The said design of the former Armavir–Tuapse Railway for the temporary strengthening of an embankment provides for driving two rows of piles along the shoulders of the roadbed, with a spacing between piles of 1.17 m (0.55 sazhen); each of the pile rows is tied by two longitudinal timbers 200 × 200 mm (8″ × 8″), and the two rows of piles are connected by two transverse tie-rods of round iron 25 mm (1″) in diameter. The length of the piles in the design is indicated as within the limits of 6.4–8.5 m (Drawing 15).² This method of strengthening an embankment can in fact be used only as a temporary one, since, without eliminating the primary cause of the landslide or of the spreading of the embankments, it cannot guarantee the embankment against deformation, owing to the presence of ballast troughs or poor-quality soil in the body of the embankment. Whether this strengthening was applied on the former Armavir–Tuapse Railway could not be ascertained.

The greatest interest from the landslide point of view is presented by the Komsomolskaya–Khadyzhenskaya section, where the line for the greater part of its length is laid along the unstable slope of the Psish River. The numerous landslides that occurred here during construction made it necessary, in order to determine the cause of the sliding—

Drawing 15.

¹ “Methode of Holding Soft Roadbed C. M. & St. P. Ry.” Railway Rev. 1916, Nov. p. 653.
² It is obvious that the length of the piles must be greater than the height of the embankment.

…the necessity of a thorough geological survey, such as was carried out by the geologist of the Geological Committee, S. I. Charnotskii¹.

The strata of the slope, composed in most cases of sandy-clayey beds, dip toward the Psish River and contain a number of water-bearing layers, which in turn cause the movement of the surface strata of the slope, drawing the railway track along in their movement; moreover, this movement is taking place in various places at the present time, owing to the inadequacy of the drainage structures.

During construction, in many cases, in order to reduce the load of high embankments on sliding beds, the line was shifted into the slope, replacing high embankments with zero embankments and cuttings; and in several cases ravines with unstable strata were crossed by viaducts. One of these viaducts, during operation, was exposed to considerable danger, since landslides of the Armavir slope seized the bank abutment, which was displaced from its position; but the ring drainage 1 2 3 4, enclosing the abutment (Figs. 16 and 17), stopped this movement.

In places along the line, in many cases, one observes a critical attitude toward a type of drainage structure long favored on the road—the stone drainage gallery; and in one case an unexpectedly successful solution of the question was reached. On one of the sections subject to sliding, on the slope of the Psish River, where the track was becoming disturbed especially often, it was decided to employ a drainage gallery. The head of the section, having decided first to investigate the geological structure of the slope, came upon two water-bearing beds (Fig. 18)—one at a depth of

Fig. 16. Diagram of ring drainage around a moving abutment.

Fig. 17. Geological section through points 1, 2, 3, and 4.

Fig. 18. Geological section, transverse to the axis of the line, through test wells.

about 9 m, and the other at a depth of about 17 m. Assuming that the cause of the slope movement was the first aquifer, it was decided to drain it by means of absorbing wells, letting the water down into the second aquifer. On the slope side, at a distance of about 4–5 m from the track axis, six concrete wells with openings in their walls were built. The effect proved very substantial—the movement of the roadbed ceased. An analogous solution was also applied in another case.

2. The Black Sea Coast.

The construction of the coastal Black Sea Railway, begun in the prewar period, is being carried out on the Tuapse–Adler section, 108 km long; on the rest of it, namely from Adler to the connection with the Transcaucasian railway network, work has been temporarily discontinued.

Even before the construction of the Black Sea Railway it was known with sufficient certainty that the coastal masses of the Black Sea along the route of the railway were in motion in a whole series of places, producing a large number of landslides of various kinds. The surveyors, already during the surveys, took into account the geological structure of the seacoast and possible complications in constructing the line.^1)

Geologist K. I. Bogdanovich,^2) who carried out the geological survey during the final surveys of the Black Sea Railway, indicates that on the Black Sea coast various types of landslides were found, caused by a combination of bedding conditions, both in the bedrock and in the already displaced rocks. In the bedrock all three types of landslides were present: type a, when movement occurs mainly along the bedding planes of impervious strata, or along fissures dipping in the direction of the dip of the beds (Fig. 19); type b, when the heads of beds move in the direction of fissures developing across the dip of the beds (Fig. 20); type c, when movement occurs along the bedding surface of two unconformably overlying series of strata (Fig. 21).

Fig. 19.

Fig. 20.

Geologist K. I. Bogdanovich pointed out the exceptionally difficult conditions for constructing the railway on certain sections of the Black Sea Railway (for example, on the Tuapse–Adler section—within Dagomys–Khosta), but did not consider construction of the railway roadbed hopeless.

Fig. 21.

The line of the Black Sea Railway, laid along the shore of the Black Sea approximately at an elevation of 4–8 m above its level, introduced a new negative factor into the stability of the coastal masses. The latter, in some cases being cut by excavations or loaded by embankments, began to move, and the first period of construction was characterized by a stubborn struggle with landslides. A case is known in which a landslide buried—

^1) A. Sergeev. “Washes, landslides, rockfalls, bulging of slopes, and other movements of the earth’s surface in relation to the construction of railway roadbed.” Inzhener, 1907, No. 6.

^2) K. I. Bogdanovich. “Several remarks on the geological conditions for the construction of the Black Sea Railway from Tuapse to Novo-Senaki.” Proceedings of the 2nd All-Russian Congress of Workers in Practical Geology and Exploration. St. Petersburg, 1913.

…an entire train was buried, and the interruption of traffic caused by the landslide lasted more than a month.

The line cut through a whole series of old landslides that had formed owing to the following causes: the dip of the strata toward the sea, the alternation of water-permeable and water-retaining beds, the fissuring of the marly rocks, the abundance of atmospheric precipitation (more than 1500 mm), and the destruction of the shore by marine surf. These areas of old landslides proved to be the most mobile and dangerous, producing secondary landslides.

The number of individual, more or less significant landslides that appeared on the Tuapse–Sochi section during construction reaches 17; moreover, they are of a more serious character on the section adjoining Sochi, with a total length of about 25 km, namely from 60 km to Sochi station¹, where the length of the landslide areas in some cases is about 3 km. Here the coastal strip consists of large synclines parallel to the shore, in places taking on an arc-shaped form with the center in the sea. The rocks composing the synclines are underlain by a suite of limestones and variegated marls, overlain by a suite of alternating beds of quartz-micaceous sandstones and variegated marly shale clays. In places, at an elevation of 10–30 m above sea level, the described strata are overlain by marine deposits of cemented pebble material, representing an ancient terrace. The large amount of precipitation, reaching up to a 1500-mm water column per year, causes abundant groundwater, which leaches and destroys the surface strata, which in many cases begin to move.

At the present time the northern section of the Black Sea Railway under construction, from Tuapse to Adler station, may be regarded as comparatively favorable with respect to landslides; thanks to exhaustion, and also thanks to the measures adopted, in many cases these have ceased, and the existing landslide phenomena can be eliminated by comparatively inexpensive measures. Because landslides in most cases are of a surface character, since by the nature of the bedding only shallow layers can come into motion, the struggle against landslides on the section of the Black Sea Railway under construction generally presents no particular difficulties.

Despite the large number of landslides that occurred during the first period of construction², the number of drainage and other structures built to combat movements of earth masses is insignificant. True, considerable expenditures were required for the construction of retaining walls on the sea side to protect the track from the surf in those cases where the railway track fell within its sphere of action; but the purpose of these walls can only partly be attributed to landslide control, except for several cases in which the walls were intended chiefly to support unstable masses of the shore.

The builders of the Black Sea Railway adhered to a rule which in many cases is expedient: to erect expensive drainage structures only to the extent of extreme necessity, only when displacements of earth masses had appeared, without spending funds on measures of a preventive character. It must be noted that this—

as a rule proved advisable also in other difficult and responsible cases—the Batrakovsky slope, the Balai slope (reconstruction of mountain sections), and, to some extent, the Oka slope near N. Novgorod.

In addition to the above-mentioned retaining walls, as well as walls within the limits of Sochi station, the Construction Administration of the Black Sea Railway carried out significant landslide-control works in only one place—at the Dagomys landslide. Here the line cuts across a clearly expressed landslide cirque, which is an enormous accumulator of atmospheric waters (Fig. 22) and is composed of talus accumulations of the weathered overlying rocky slopes (at an elevation of 55–60 m). From the geological section (Fig. 23) it is evident that the railway roadbed rests upon an old landslide about 15 m thick, composed of products

Fig. 22. Plan of the landslide cirque near Dagomys (1926).

of weathering of the overlying beds. These masses, abundantly saturated with water under considerable pressure, slide along a layer of blue clay. The retaining wall built here in the first period of construction was destroyed by the landslide; the remnants of this wall indicate—

Fig. 23. Section of the Dagomys landslide.

laid out on the plan of the slope (Fig. 22-a, a). In order to achieve stability of the track bed, the Construction Administration carried out the following works: to intercept upland waters, and also to collect groundwater in the upper part of the slope, a wooden flume was built; to intercept groundwater in the plane of sliding, an adit was driven, deepened into the blue clay and enclosing the railway track bed in the form of an arc.

A commission of experts, consisting of Professors A. M. Frolov, A. V. Liverovsky, and K. A. Oppengeim, approved the general idea of the design, expressed in the regulation of surface runoff, the drainage of groundwater, and the correct [[unclear: continuation obscured by figure]].

Other landslide areas are less serious; their landslides have a more or less superficial character, and in many cases the latter have reached a state of stability through a natural process, without any substantial works, or the latter have been carried out on an insignificant scale. More or less considerable masses began to move in 1927 on the southern terminal cape of the valley of the Tuapse River, where the line is laid over an old landslide of marly beds (Fig. 24). As can be seen from the appended geological section (Figs. 25, 26), the upper part of this landslide area consists of a talus of shale, with a thickness along the axis of the track bed of about 4–6 m; below is a bed of gray shaly clay, underlain by blue clay, along which the upper strata slide. The landslide tongue along the axis of the line has a width

Fig. 24. Plan of the landslide at the 1st kilometer near the city of Tuapse.

Fig. 25. Geological section of the landslide at the 1st kilometer.

of about 90 m; moreover, here there occurred the characteristic phenomenon of the end of the tongue being squeezed out from depth above the level of the beach (Fig. 26), since

end of the tongue evidently abutted against the interbeds of blue clay. After the construction of a drainage system, the lower part of which was cut into the blue clay (Fig. 6), the slope reached a stable condition.

On the coast, in the Sochi district of the Black Sea Railway under construction, landslides also threaten with destruction a whole series of cultivated areas and buildings of enormous value, namely:

1. The site of the Uch-Dere sanatorium (on the Tuapse–Sochi section)
2. The coastal strip near the Riviera hotel in Sochi
3. The sanatorium in Matsesta

Fig. 26. Geological section of the landslide at the 1st kilometer.

1. The section of highway leading to Krasnaya Polyana.

In 1925 a special geological commission of the Geological Committee pointed out the necessity of urgent hydrogeological investigations in the Sochi district in order to devise preventive measures against the destruction of the indicated and other sites.

Geologists D. I. Mushketov and N. F. Pogrebov characterize the geological structure around Sochi as follows:^1 “the bedrock shores, more or less steeply inclined toward the sea, are composed of rocks of Lower Tertiary or Upper Cretaceous age, represented here by an alternation of numerous thin beds of clayey-marly and sandstone deposits, dipping steeply toward the sea and covered by a thin layer of alluvium, or by terrace deposits adjoining them. The sandstones are usually fissured, water-permeable rocks, while the clayey-marly deposits are water-retaining; this, with the abundance of atmospheric precipitation, creates very favorable conditions for the wetting of the surfaces of the clayey deposits and for the sliding of some beds over others, or else for the slipping of alluvium along the surface of the bedrock.”

To the unfavorable character of the interbedding is added the destructive action of the surf, which, by washing away the base of the strata inclined toward the shore, disturbs their equilibrium.

Greater difficulties in the future will be presented by landslides on the abandoned part of the Black Sea Railway from Adler to the junction with the Transcaucasian railway network, especially near Sukhum, where there are three significant landslide districts that were investigated during construction. In all three districts, the former Caucasus District of Communications, during the construction of the Sochi and Sukhum highways, waged a persistent struggle against landslides, saving from destruction the roadbed and the artificial structures of the highway road.

The landslides are manifested most intensively in the 2nd and 3rd districts, situated between Sukhum and Novy Afon—the second district between the Bela and Dzheta rivers, and the third district from the Bela River toward Novy Afon; the length of each of the landslide districts is 1000–1200 m.

^1 D. Mushketov and N. Pogrebov. Landslides of the Sochi district of the Black Sea coast. Izv. Geolog. Komiteta, 1924, No. 8.

By way of example, let us present data concerning the second landslide area, within which there are four separate landslides. In 1909 and 1910 the Caucasus District of the Ministry of Ways of Communication carried out extensive work to drain the slips in the second area, in the form of a series of open ditches and catchment wells; nevertheless, in 1910–1911 the landslides caused considerable damage to the highway, which made it necessary to move it higher up the slope. The drainage wells, proposed, apparently, by Engineer Konstantinov, to whose operation the former Caucasus District of the Ministry of Ways of Communication attached very great importance, are of considerable interest and, it seems, their operation has nowhere yet been described in detail in the literature. The wells are about 8.5 m (4 sazhens) deep, lined with a hexagonal wooden crib, with a distance between parallel sides in the clear of 2.13 m (1.0 sazhen). The ground and surface waters collected by the wells are pumped by siphon pipes 51 mm (2″) in diameter into lower-lying wells and thus, in the end, are removed from the slope. Water is pumped from the wells periodically by special watchmen by charging the siphons. According to observations made, siphon pumping through pipes 51 mm in diameter yields up to 11 cubic m (900 buckets) per hour, and the Caucasus District of the Ministry of Ways of Communication considered it sufficient to place 1 well per 1 hectare of catchment basin.

When the projects for draining the Sukhumi landslides, drawn up by the Construction Administration of the Black Sea Railway, were being coordinated in 1915–1916 with the Caucasus District of the Ministry of Ways of Communication, serious disagreements arose between these institutions¹. The Caucasus District, taking into account its experience with siphon drainage wells, insisted on their use, objecting to the system of open ditches. The Construction Administration, pointing out that during the inspection of the 2nd and 3rd landslides in May 1915, despite the drainage work carried out by the District, the highway roadway had proved to be badly damaged, several stone artificial structures completely destroyed and carried away toward the sea, the wooden wells filled with water, and the siphon pipes not functioning, insisted on its own project for intercepting the upper waters by open ditches.

In addition to the foregoing, the Construction Administration found the following further shortcomings of siphon wells: charging the siphons is painstaking and difficult and requires a special staff; the siphons are subject to damage; in view of the slow emptying of the wells during rains, water accumulates in them, which, by saturating the surrounding masses, adversely affects their stability². The Construction Administration considered it most expedient to drain the Sukhumi landslides by means of open ditches. The dispute between the institutions created a whole issue around Engineer Konstantinov’s wells.

In view of these disagreements, on 29 February 1916, under the chairmanship of Engineer N. P. Uspensky, a meeting was held on the question of draining the terrain in the area of the Sukhumi landslides and of coordinating measures to combat them, but the points of view of the two departments were not reconciled. The dispute between the said institutions was referred to

The Engineering Council, at its meetings on April 12 and 13, 1917, geologist F. Yu. Levinson-Lessing recognized engineer Konstantinov’s method of combating landslides (by means of siphon wells) as correct from a geological point of view. A member of the Council, Professor N. D. Tyapkin, pointed out that on the Crimean highway near the village of Kuchuk-Koy it had proved possible fully to halt a large landslide by applying Konstantinov’s method. The chief engineer for the construction of the Black Sea Railway indicated the insignificant effect produced by the wells, which had been established by observations. The Engineering Council, in general, took the side of the Administration of the Black Sea Railway.

A whole series of objective data, chiefly the observations of the former Administration of Inland Waterways and Highways, testifies to the practical applicability of siphon wells for draining earth masses; the use of wells becomes especially interesting if the pumping of water is carried out automatically, by means of electric pumps set in operation when the current is closed by a rising float. But in especially critical cases, when it is necessary to intercept the flow of ground water and not allow it to reach the earth masses in motion, to drain them and thus create a dry and immobile buttress resisting the pressure of the overlying masses (the usual scheme of drainage works), one must refrain from using wells which, being arranged along some line, obviously cannot intercept the entire flow of ground waters, however the surface of the depression between the wells may be situated; bringing the wells closer together, however, may make the system economically unacceptable in comparison with continuous systems in the form of drains, galleries, and adits. But when drainage measures are carried out gradually—which in our country is often done for reasons of economy—drainage wells with siphon pumping may prove to be the initial stage in the struggle against landslides; in the event that the measures adopted prove insufficient, the system of drainage wells may be supplemented by an adit or gallery drainage connecting the wells. Obviously, in this case the bottoms of the wells must be laid out with the indicated through drainage structures in mind. In the transition from wells to adits, the former also become inspection and ventilation wells, although part of the expense for the installation of siphons and outlets from them will be lost.

Returning to the second district of the Sukhum landslides, one may present the scheme for strengthening them drawn up by the Administration of the Black Sea Railway with the participation of expert geologists. In Fig. 27 is given a geological

Fig. 27. Geological section of the 2nd district of the Sukhum landslides.

section along the axis of the line within the second district, and in Fig. 28 a scheme of drainage structures. From the profile it is apparent that the 2nd district consists of four separate landslides. Obviously, here, as in many other districts of the Black Sea Railway, the landslides, having no kind of

or a definite slip plane, as it were, they spread out, moving like the ice masses of glaciers. Motion affects, chiefly, variegated clays, which are a mixture of yellow clay with blue, with

Fig. 28. Scheme of the drainage structures of the Sukhumi landslide.

sand, limestones, stones, and fragments of conglomerate; but sometimes the underlying blue, soft, moist clays are also drawn into the movement. From the plan in Fig. 28 it is evident that the schematic design provides for enclosing the area and the landslides with ring-shaped open ditches; each landslide is enclosed by ring drainage, and, in addition, a system of open ditches is provided, encompassed by the ring ditches.

1. The former Ministry of Ways of Communication required the Construction Administration of the Black Sea Railway to coordinate all projects for draining the Sukhumi landslides with the District, which was greatly interested in the drainage works, since they inevitably encompassed the area of the highway located in immediate proximity to the railway route. ↩↩↩↩↩↩

2. According to calculations by the Construction Administration, made in the prewar period, with the simultaneous fall of a 200 mm layer of water, pumping the water out of a well, under the accepted norms for catchment area per well, would require 9 days, which, to be sure, is considerably exaggerated. ↩↩↩↩↩

3. See Volobuev. Slides and the Repair of Embankments, 1906. ↩