CC BY
23
UDC 69.059
A. K. Aldungarova1, A. Zh. Zhussupbekov2, V. A. Kozionov3, R. E. Lukpanov4, T. Tanaka5
:PhD, associate professor, S. Toraighyrov Pavlodar State University, Pavlodar, Kazakhstan; 2Doctor of engineering sciences, professor, L. N. Gumilyov Eurasian National University, Astana, Kazakhstan; 3candidate of engineering sciences, associate professor, S. Toraighyrov Pavlodar State University, Pavlodar, Kazakhstan; 4PhD, associate professor, L. N. Gumilyov Eurasian National University, Astana, Kazakhstan; 5professor, Tokyo University, Tokyo, Japan e-mail: [email protected]; [email protected]; [email protected]; [email protected]
SLOPE STABILITY ANALYSIS OF THE SOIL EMBANKMENT REINFORCED BY GEOGRID FOR RECONSTRUCTION OF STEEL PRODUCTION PLANT
This research is connected to the existing soil embankment (or dam), which is placed on the ASS thermoelectric power station (part ofthe large steel production plant) in Karaganda region, Kazakhstan. ASS, ash dumps, tailings dam, and others, where hydro removal is used — are pressure head hydraulic engineering constructions and they require appropriate attitude at all stages of design, construction and operation. During the years of its existence the soil embankment had been reconstructed many times. Reconstruction had been presented by backfilling of soil without reinforcement, as a result this method hadnt been effective. Therefore it was suggested to use construction materials new for Kazakhstan — geogrid as a reinforced element. The article provides an analysis of soil embankment stability reinforced by geogrid under the influence of horizontal and vertical deformations of the subgrade and on the basis of these studies' results to assess the possibility of the ground mounds cracks formation in models with the determination of their distribution area, and the degree of reinforcement influence on their overall sustainability.
Keywords: dam stability, geogrid, subgrade, soil.
INTRODUCTION
Today, it invited a lot of options for strengthening the waterworks. But, unfortunately, in Kazakhstan, the issue of the protection of earth dams from the dangerous effects of various factors such as seismic and dynamic impact, undermining grounds, floods, underground mining, etc., is quite complicated and poorly understood at present. Theoretically, proposals to strengthen the hydraulic structures a lot, but almost not enough implementations of this acute problem. Proof of this is the tragedy, earth dams breakthroughs taking place seemingly in the 21st century, but claiming the lives of people.
This suggests that the technical safety of hydraulic structures in Kazakhstan is poor. This research work concern to the existing soil embankment (or dam) which is stay on the ASS thermoelectric power station (part of the large steel production plant) in Karaganda region, Kazakhstan. ASS, ash dumps, tailings dam, and others, where hydro removal is used - are pressure head hydraulic engineering constructions and they require appropriate attitude at all stages of design, construction and operation. During of years of its existence soil embankment had been reconstructed many times.
Reconstruction had been presented by backfilling of soil without reinforcement, as a result this method hadn't been effective. Therefore it was suggested to use one of new for Kazakhstan construction materials - geogride as a reinforced element.
ASC type single-section, of 540 hectares and with a useful volume of 88 million m3, belongs to JSC Arselormittal (Temirtau). It is put into operation in the sixties of the XX century. For years of operation it was repeatedly reconstructed. Reconstruction for the purpose of increase in volume of ASS was carried out by building of the protecting dams. Building to design marks was made, generally from a local slope of dams. Thus height of the protecting dams and respectively a capacity of ASS increased; in the basis of each increased layer from outer side of ASS there was natural basis. In 2006-2008 work on inspection and repair of an emergency site («PC» 11-13) of the operating ASS was performed. The ASS main project was executed in 1957, the project of the first building (the first reconstruction) in 1980. In the project of the second reconstruction in 1993 the level of a dam crest achieved 95 m, and the maximum height of a dam reached up to 26 m. After completion of works on the second reconstruction in 2001 emergencies around a water outlet №1 («PK»11-13) began to arise:
- in March, 2001 on a local slope there was a big crack caused by uneven deformations of the basis of a dam;
- deformations and motions of the basis of a dam during the period from March to May, 2001 provoked a number of breaks of the pipeline of the clarified water with a diameter of 1200 mm;
- in May, 2001 a motion of part of the basis of a dam in resulted from a deposit and further rearrangement of part of a local slope to 3 meters on height.
BACKGROUND
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—F"-" : utUi.M ind mark is nrnti ffl*.
Figure 1 - Cross geological section of a dam of ASS of an emergency site
GENERAL INFORMATION
During geological investigation of an emergency site of a dam of ASS it was revealed:
- ways of a possible filtration, the structure of a geological section (in accordance with Figure below), a roof of rocky breeds has the decrease which is obviously expressed in a section towards a mountain ditch;
- in case of emergency the border of a separation of the soil array on a local slope of a dam every time was approximately always on the same place that is confirmed by geodetic measurements;
- water sampled from the boring holes and out of the fontanel, located at the foot of the lower slope of the dam, for the presence in it of chemical compounds is identical to water which taken from the settling pond ASS;
- construction of dam was made from the clay soil which is taken from ASS.
At laboratory studies of soils related to the Aral suite, turned out that, in soaking, they dramatically worsen its strength characteristics (for soil with solid and semi-solid consistency, located in the upper section, angle of internal friction equal 17, cohesion is 0,108MPa, and for soil soft-ductile and fluent-ductile consistency, located in the lower section on the border with the weathering crust Devonian rocks, angle of internal friction equal 19, cohesion is 0,028 MPa).
Geological investigation reveal follows:
With the construction of the primary dike was broken integrity of the clay base ASS because there the ground was taken for the construction of dams.
Under the clay rocks of the base ASS lie rocky breeds, in the roof which are located gruss-detrital soils weathering crust. In the process of filling ASS, water wich a penetrated into gruss-detrital soils weathering crust, began to filter out to the surface in low relief forms, that are associated with a decrease in the rocks roof. After the last increase a downstream slope of the dam of ASS turned declining sharply over the roof of rock, above which is located water-saturated soils gruss-detrital weathering crust.
The weathering crust underlain by clay soils of the Aral suite which, when in water saturation dramatically losing their strength characteristics. The deterioration of the strength characteristics were so significant that the slope, located above them, was in a permanently unstable state. Since all the activities with clays of Aral suite, who came in a fluid state, escarpment not removed, after each repair lower slope deformed with the formation of a landslide.
The tendency of the soil sliding had been reviled: the soil destruction always occurred at the same location in a sharp reduction of the roof rocks from ASS direction (Figure 1) where rocks form a cup in which the water flows from all sides.
Scopes of the research
Reconstruction project of the dam and improvement of the foundational soil (rapture of the soil basement in Figure 1) are not included in this research work. Design company will make an engineering solution for reconstruction of foundational soil for dam soil movement prevention. But the risqué of dam soil movement after reconstruction will still exist.
This project include additional preventive measures for the stability of dam with using reinforced elements as geogrid preventing from horizontal and vertical deformation
of dam itself in case of critical condition. The initial condition for the slope stability analysis is more potential direction of soil movement (Figure 2).
Technical investigation of soil dam
The solution of the objectives of the study of area required a careful study of deformation of the base on undermined territory. The studied area is located in the territory where in the radius surrounding it there is the Karaganda coal basin.
On one of sites of a dam big deformations were found: began motions of soil on a dam crest. Within one month the behavior of development rainfall of dam was measured. Horizontal deformations of a terrestrial surface of the studied area by the conditional marks are shown in Table 1 [Aldungarova, 2015].
Tendency of soil
Figure 2 - General concept of dam stability after reconstruction
Table 1 - Horizontal deformations of areas by the conditional marks
Mark 1 Mark 2 Mark 3 Mark 4
settlement, mm relative horizontal deformation settlement, mm relative horizontal deformation settlement, mm relative horizontal deformation settlement, mm relative horizontal deformation
124 +0,8 163 +0,4 42 +0,1 213 +1,2
149 +0,9 352 +1,2 93 +0,3 326 +1,4
265 +1,2 512 +1,4 108 +0,3 492 +1,6
312 +1,5 621 +1,9 151 +0,8 584 +1,8
412 +1,9 726 +2,4 196 +1,2 658 +2,3
265 +0,6 25 +0,2 63 +0,4 34 +0,1
495 +0,9 53 +0,2 98 +0,8 72 +0,4
621 +1,2 92 +0,8 116 +0,9 102 +0,5
826 +1,8 104 +1,1 184 +1,5 143 +0,8
915 +2,1 118 +1,3 208 +1,9 195 +1,4
In the end result horizontal deformations led the studied area to formation of a landslide. In a place of a separation was formed vertical wall with height to 1,5 m (in accordance with Figures 3,a,b).
By visual observation of a crest of a earth dam it was controlled: nature of development of cracks; rainfall and sags of a crest, centers of formation of landslides of slopes.
Figure 3 - (a) A separation on a crest of a dam (September, 2012) A, B - nodes, (b) Node A
Cracks on a crest of a dam were both longitudinal (along an axis) and the cross direction. The reasons of formation of a crack are caused, generally emergence in soil of the stretching or tangent tension exceeding a limit of tensile properties or resistance to soil shift as material. Location cracking is confined on up-brow of crest. The length of the cracks of 2-3 meters. Opening of cracks at the time of the survey reached 5-10 cm. On the borders of the dam elements composed of different soils by compressibility, longitudinal cracks have vertical steps, showing the difference in settlements divided crack elements. Transverse cracks arise on the sloping ground of the dam, in the places where it dramatically changes its height. The intersection of the crest of the dam of cracks partial. Depth of distribution of cracks in a body of a dam of 1,5-2 m. Crack walls in soil have a wavy relief. Drawdown's crest in the form of funnels, or visible in the eyes of its major slides were not found. The reason for the drawdown could be melting in buried in the dams body of ice, snow or frozen soil; inadequate sealing of local volumes or layers of soil, laid in the dam; loss of small soil from the dam or foundation; extrusion from the base of the soft soil, etc. Signs of swelling of soil of the crest part of a dam aren't revealed. The curved contours of characteristic of primary cracks formed on the surface of the crest shaped slope collapse with a wide scope (involving) the dam crest. Condition and slope stability of the dam plays a major role in ensuring the operational reliability and safety of the building. A sign of buckling of (slumping) slope, It is: formation on the surfaces of the ridge and slopes of dam slopes with characteristic landslides of curvilinear cracks (in accordance with Figure 3, node B); education along the track of cracks of vertical ledge (in accordance with Figure 3, node A); the appearance of a noticeable bulge soil in the middle and lower parts of the slope (in accordance with Figure 3). Local and frontal (at great length) slope collapse accompanied by the movement of large volumes of soil from the dam body (in accordance with Figure 4).
S1-S8 - displacements of marks 1-8 Figure 4 - Conditional fixing of marks
According to parameters of tables 1 graphs of conditional brands rainfall of deformable part of a dam (in accordance with Figures 5) are made.
ri *f foadiitatl Back .M I, di-pr a<lj»( il* laip«ri of hortrMiil drforauifets -*—»rruidHkujl Hitk .V4,>drptMllaa oa ibr la
Figure 5 - Graph of rainfall of conditional marks 1,4 of deformable part of a dam
EXPERIMENTS ON THE STAND Experiments were carried out with the aid of three-dimensional test stand (Figure 6). The test stand (three-dimensional) for soil dam prototype deformations modeling is made in the form of separate U-shaped cross-sections (1). Elastic rubber pads of thickness = 10 mm are installed between the sections. Side ledges of U-shaped sections (1) are equipped with bolted joints (3) in the upper and lower levels horizontally. There are end face walls (4) in a cradle. The lower part of U-shaped sections (1) is equipped with adjustable footings (5), made in the form of roller supports, installed on a bed frame (6).
The test stand for deformations modeling [Zhussupbekov, Bazarov, 1991] operates in the following way:
U-shaped sections (1) compression or tension is conducted with the aid of bolted joint (3) together with material deformation in the cradle. Horizontal deformations of soil tension occur due to compressed elastic (rubber) pads (2) flexible strain forces by loosening bolted joints (3). Horizontal deformations of soil compression occur due to elastic (rubber) pads (2) compression by bolted joints (3) pulling U-shaped sections (1) closer to each other. Vertical deformations occur due to a step-by-step lowering of U-beams (7) installed before the experiment start in accordance with junctions A and B (Figure 6).
As a material for dam and soil foundation model a mixture consisting of 97 % fine silica sand and 3 % straw oil by weight was chosen. The mixture has strong cohesion which enables to make prototypes of cohesive soils [Zhussupbekov, 1994].
In order to determine mechanical strength and deformability properties of actual soils and equivalent materials under the vertical loadings a compression kind of stabilometer was applied for horizontal deformations taking place in undermining conditions.
Sample put into compression device is matured till full consolidation under the given loading equal to 0.3 MPa.
To applied weightings of vertical loadings in 0.05-0.1 MPa limits. Vertical deformations of soil sample were measured by clock-face type indicators with scale interval equal to 0.001 mm. Transmission of vertical loadings to the sample was conducted by weighting mechanisms through DOCM-3-5 dynamometer. The pressure was measured by pressure-gauge. Required parameters (Table 2) are obtained by the results of the testing trials E, C, y, y.
a - 3D test stand with soil dam model image, b - 3D test stand diagram (plane view), c - horizontal and vertical deformations effect on dam model functioning diagram. Figure 6 - Three-dimensional test stand for deformations modeling of soil foundation
Table 2 - Physical parameters of full-scale and modeled dams
Type of soil y (kN/m3) c, (kPa) V o, (deg) E (MPa) u
full-scale soil
1 Loam 20,5 40 22 20 0,3
model of the dam (model soil)
2 Sand - 97 % + 3 % - spindle oil 17,7 0,90 39 0,27 0,25
Substitute the corresponding values for modeled and full-scale soil into the equation (1) and obtain linear scale of modeling.
m = c /c xy/v =0,9/40x20,05/17,7=1/40 (1)
c m n ' n ' m 3 3 3
Hence, linear scale of model and full-scale object (buildings, foundations, structures) is calculated as a proportion of strength properties (cohesion) of clay and equivalent material and equals 1:40. As a soil dam model an embankment with the corresponding dimensions was chosen (Figure 6a):
- 700 mm * 350 mm (dam model foundation);
- 200 mm * 150 mm (dam model crest);
- 430 mm (dam model height).
a) Foundations placement
Before laying a soil foundation, test stand should be installed in such a way so that in the future 1/3rd part of dam model footing was placed to the foundation, lifted to a certain distance with the aid of U-shaped sections (Figure 7 - nodes A&B). The beams (Figure 7) are uplifted by bolts to 40 mm. After preparation of equivalent material foundation can be placed to the 3D test stand. Equivalent material was arranged in layers of 7 cm and was compacted by a rolling press (7 full compaction cycles). During the foundation preparation process mechanical strength of material should be checked carefully.
b) Dam model placement without reinforcement (Figure 7, a,b), level-by-level placement in 6 layers of 7 cm plus compaction. Colored sand of thickness equal to ~2 mm was placed between each layer. A soil sample of each layer should be taken to determine soil density.
c) Reinforced embankment model preparation (Figure 7, c,d) is carried out in a way of level-by-level placement in 6 layers of 7 cm plus compaction. An embankment was placed with the aid of special shape. Colored sand of thickness equal to ~2 mm was placed between each layer.After arrangement of each layer plus coloured sand, a reinforcing net of area equal to dam model's piling layer area was installed. A soil sample of each layer should be taken to determine soil density.
Figure 7 - Dam model level-by level placement without (a,b) and with (c,d) reinforcement
d) The process of dam model cracks, deformations and failure development in condition of both horizontal tension and vertical deformation happening in a soil foundation at the same time can be observed and fixed with the usage of a photo camera. An invention and development of digital photography allowed to scheme out a contactless photogrammetric method of prototype systems cracks and other deformations lifecycle monitoring. Vertical and horizontal deformations of embankment foundation and model during experiments conduction process were obtained using photogrammetric approach. This method helps to determine deformations which occur in plane and are useful to examine flat objects. The method assumes that several images of prototype system can be obtained from one fixed point, e.g. first image obtained before deformations, second - during deformations development and the third - after deformations. Thus, camera should be installed in such a way that plane of applied frame was parallel to plane of an object where image orientation elements should be preserved. In this case a periodic shoot by equipment with high matrix resolving capacity (2000 pixels per 1 cm2) should be implemented. In the given article Canon EOS Rebel T3 / DS126291 camera with matrix resolution equal to 12,2MP was used. The shooting data was recorded for documentation of mechanical measurements at dam model slopes and crest.
The task was to examine model stability in 5 stages of horizontal deformations e=(3,6,9,12,15)x10-3 and simultaneous vertical failure, using bolted joints to assemble soil foundation part with dam model in variations with and without reinforcement in order to determine conditions of embankment's critical state [Tanaka, Zhussupbekov, Aldungarova, 2014]. A 3D test stand allows to create independent tension and vertical uplift lowering deformations in a significant range. The following trial series were carried out: a) testing of dam model at different conditions of soil foundation part's simultaneous lowering and horizontal tension of foundation without preliminary reinforcement, b) testing of dam model at different conditions of soil foundation part's simultaneous lowering and horizontal tension of foundation with reinforcement. After each trial soil was extracted from the tray and a new foundation was prepared for the following trial series.
Figure 8 shows comparison of dam model stability modeling key stages, as demonstrated on a 3D test stand with the usage of equivalent material.
CONCLUSIONS Following the experiment results, conclusions can be made. As it can be observed, the crest of a reinforced dam has remained in original state, without cracks which is different to dam model without reinforcement. Cracks on an unreinforced dam model begin spreading parallel all over the shape with the very first seconds of deformations whether development of cracks on a reinforced model occurs under the reinforcement netting bed (Figure 8).
Figure 8 - Comparison of stability modeling key stages for dam model without reinforcement; (b) with reinforcement)
Model of a reinforced dam is more prone to shear than to crack formation and collapse; the upper part of model placed above the reinforcement net remained in initial state, without cracks in fact, under the condition of dam model shift to 2 cm (Figure 9 - Junction B).
Figure 9 - Reinforced dam model shift
It can be concluded from the plot (Figure 10) that strengthening of dam model with the use of reinforcement net significantly affected its stability at horizontal and vertical deformations. Given choice of strengthening can be applied for hydraulic engineering structures as one of the methods to increase stability and safety. 3D test stand allows to examine behavior of dam model with/without reinforcement impacted by different combinations of soil foundation deformations.
Horuontil strains, f » 10 3'
0,0 J.O i,fl jy> 12,0 li,0
Ш
m,o
-10'0 -----
rfrarfil] modd rf th? dun witfireirfofCiEieit mm ЛГмп trim (rfTirfil mo<H dihf dam wiihoui itirfeetmfru mm
Figure 10 - Reinforced/unreinforced dam model stability dependance on horizontal and vertical deformations plot
REFERENCES
1 Aldungarova, A. K. Influence of effect of reinforcing on slopes stability of a soil dam // Young Geotechnical Engineers Symposium, Indian Institute of Technology Bombay. - Mumbai, India, May, 2015.
2 Test stand for undermining buildings' foundations deformations modeling : Patent 1250808 / Invented by Zhussupbekov A. Zh., Bazarov B. A.; published in B.E. .№48, 1991.
3 Zhussupbekov, A. Z. Structural properties of buildings' foundations in undermined areas. - Almaty : Gylym, 1994. - P. 162.
4 Tanaka, T., Zhussupbekov, A. Zh., Aldungarova, A. K. The influence of the stress-strain state of the soil on the stability of the dam model // «Perspective trends of theory and practice development in soil rheology and mechanics», XIV Soil rheology International Symposium materials. - KazGASU-Kazan, 2014.
Material received on 12.12.16.
A. Ц. Алдунгарова1, A. Ж. Жусупбеков2, В. А. Козионов1, Р. Е. Лукпанов2, Т. Танака3 Болат енд1ру женшде зауытты кайта куру Yшiн ньтайткан геоторлер топырактыц Yйiндiсi келбеушщ турактыль^ын талдау
1С. ТораЙFыров атындаFы Павлодар мемлекетлк университет^ Павлодар к., Казахстан;
2Л. Н. Гумилев атындаFы Еуразиялык мемлекетлк университет^ Астана к., Казахстан;
3Токио университет^ Токио к., Жапония.
Материал 12.12.16 баспаFа тYстi.
A. Ц. Алдунгарова1, A. Ж. Жусупбеков2, В. А. Козионов1, Р. Е. Лукпанов2, Т. Танака3 Исследование устойчивости грунтовых дамб, армированных георешеткой для реконструкции завода по производству стали
павлодарский государственный университет имени С. Торайгырова, г. Павлодар, Казахстан; 2Евразийский национальный университет имени Л. Н. Гумилева, г. Астана, Казахстан; 3Токийский университет, г. Токио, Япония. Материал поступил в редакцию 12.12.16.
Буя зерттеу жумысы yümdi топырацца байланысты, ол ASS-да жылу электр станциясыныц ^рi болат вндiретiн зауытты) Цараганды облысы, Цазацстан Республикасында цалады. ASS, кул yüiндiлерi цалдыц бвгеттер жэне тага басцасы, онда гидро жойылу цолданылады да гидротехникалыц цурылыстар жэне оларга барлыгы тиiстi царым-цатынастар кезецдерт жобалап салу жэне пайдалану болып табылады. Тршшк ету барлыц уацытында yüMi топырац бiрнеше рет твгшдь Цайта жацару топырацты куштеп толтыру нэтижестде бул эдю тшмаз болды. Сондыцтан геоторды кушейту элементi реттде Цазацстан ушт жаца цурылыс материалдарды пайдалану усынды. Мацалада талдау турацтылыгын yüMi топырац кyшеюi геотор эсерiнен горизонталь жэне вертикаль деформация жер твсемi мен негiзгi нэтижестде, осы зерттеулерЫ багалау ушт мумктдж беру улг^ртде жер уйтд^рт айцындау ушт оларды тарату.
Эта исследовательская работа связана с существующей грунтовой дамбой (или плотиной), которая базируется на теплоэлектростанции (части крупного заводапопроизводствустали)вКарагандинскойобласти,Казахстан.Золоотвалы, хвостохранилища, плотины и другие сооружения — являются напорными гидротехническими сооружениями, и они требуют соответствующего отношения на всех этапах проектирования, строительства и эксплуатации. В течение всего существования насыпи почвы были реконструированы много раз. Реконструкция была представлена засыпкой грунта без армирования, в результате этот метод был неэффективен. Поэтому было предложено использование георешетки в качестве армированного элемента, как одного из эффективных строительных материалов в Казахстане. В статье приводится анализ устойчивости насыпи грунта армированной георешетки под действием горизонтальных и вертикальных деформаций грунтового основания и на основе результатов этих исследований дана оценка возможности образования в моделях трещин земляных насыпей с определением области их распространения и определения степени влияния армирования на их общую устойчивость.
