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55LANDSLIDES MODELING, MONITORING, RISK MANAGEMENT AND REDUCTION
Svalova Valentina,
Sergeev Institute of Environmental Geoscience RAS, Moscow, Ph.D.(Physics and Math.)
Landslides process is one of the most widespread and dangerous processes in the urbanized territories. In Moscow the landslips occupy about 3 % of the most valuable territory of city. In Russia many towns are located near rivers on high coastal sides. There are many churches and historical buildings on high costs of Volga River and Moscow River. The organization of monitoring is necessary for maintenance of normal functioning of city infrastructure in a coastal zone and duly realization of effective protective actions. Last years the landslide process activization took place in Moscow. The reasons of activization and protective measures are discussed. Structure of monitoring system for urban territories is elaborated. Mechanical-mathematical model of high viscous fluid was used for modeling of matter behavior on landslide slopes. Equation of continuity and an approximated equation of the Navier-Stockes for slow motions in a thin layer were used. The results of modelling give possibility to define the place of highest velocity on landslide surface, which could be the best place for monitoring post position. Model can be used for calibration of monitoring equipment and gives possibility to investigate some fundamental aspects of matter movement on landslide slope.
Key words: landslide, monitoring, modeling, cultural heritage, Moscow, Russia
LVorob'yovy mountains landslide area In Moscow many cult and city constructions are located on coast of the river Moscow and, in particular, on the right high slope. The right coast of river Moscow on its significant extent is struck by deep block landslides with depth up to 90 - 100 m which formation occurred in preglacial time with basis of sliding in Callovian-Oxford clays of Jurassic system on 25 - 30 m below modern level of river Moscow. One of landslide sites is
on Vorob'yovy mountains, on a high slope of the right coast of the river Moscow (Fig.1). Within the limits of a considered site there is a historical monument of federal value - «Andreevsky monastery», based in 1648. it includes Resurrection cathedral (1689 - 1703), church of Saint andrey Stratilat (1675), bell tower with church of Saint John Bogoslov (1748), being a monument of the Moscow baroque (Fig.2).
Fig. 1. Vorob'yovy mountains
Fig. 2. Andreevsky monastery.
AIso there the complex of buildings of Presidium of the Russian academy of Sciences, constructed in 70 - 80th years of 20-th century (Fig. 3), bridge with station of underground "Vorob'yovy mountains" and a sports complex (fig. 4) are
located. Landslide slope is in an active condition, and there are many attributes of activization of deep block landslide. In June 2007 a rather big landslide took place there near ski-jump (Fig.
© Svalova Valentina, 2016
43
Fig. 3. Presidium of RAS
Fig. 4. Ski jump.
Fig. 5. Place of activization of landslide on Vorob'yovy mountains in 2007 and recommended monitoring network.
1-5, green lines - geophysical profiles, dashed line - area of deformation activization, blue line - cracks, yellow square -hydrogeological borehole, yellow circle -inclinometer.
2. Kolomenskoye landslide area
Another landslide site is in a southeast part of Moscow, occupying the right coast of river Moscow from museum - reserve "Kolomenskoye" up to station Moskvorech'e. The
museum - reserve "Kolomenskoye" represents an imperial manor of XVI - XVII centuries, in which outstanding monuments of Russian architecture were kept (Figs. 6, 7).
The greatest activity is shown with a slope in east part of a site, in area of an arrangement of city collectors. The slope in this place has height of 38 - 40 m. Motions of deep landslips have begun from 1960 in connection with construction of collectors.
In 70th years of the last century there was a strong activization activization of a landslide has taken place in 2002 with a motion of a slope with formation of cracks by extent up to 500 m and on 53 cm. displacement of a landslide in the plan over 1 m. Last serious
Fig. 6. Museum - reserve "Kolomenskoye".
In the area of Kolomenskoye not once there were observed deformations of the sewerage pipeline in the place of the pass over the Moskva River. It was determined by instrumental observations (inclinometric and tensometric measurements of bends of stationary tubes in the wells) that the basic sliding surface of the deep landslide lies within a depth interval of 100.5
to 101.0 m, whereas the water level in the river is 114.3 m (Fig.8). It means that the sliding basis is located in black clays of the Oxfordian Range within the Jurassic system below the erosion basis, which is typical of deep blockglide landslides in the given region.
0 10 20 30 M 50 100 150 200 250 300 330
Figure.8. Example of deep blockglide landslide. Moscow, Kolomenskoe. N.1, N.2, N.3 - extensometers, inclinometers.
3. Khoroshevo landslide area left-hand shore of the Moskva River, is threatening to the Holy
Catastrophic activization of the deep blockglide landslide Trinity Temple in Khoroshevo (monument of XVI century) and in the area of Khoroshevo in Moscow in 2006-2007, on the living houses (Figs. 9, 10).
Fig. 9. Holy Trinity Temple
Fig.10. Living houses in Khoroshevo.
A crack of 330 m long appeared in the old sliding circus, from the plateau and began sinking with a displaced surface of along which a new 220 m long creeping block was separated the plateau reaching to 12 m. Such activization of the landslide
process was not observed in Moscow since mid XIX century. The sliding area of Khoroshevo was stable during long time without manifestations of activity, though the height of the above-landslide scarp was critical, which indicated to its limit stability.
In the western part of the above-described sliding area, the active development of deformations began in August 2006. Fractures were formed on the territory of Holy Trinity Temple
Moscow, Karamyshevskaya enbankment. 1 - bridge under construction; 2. - new treatment plant; 3 - new header; 4 - sliding circus Khoroshovo 1; 5 - place of activisation of sliding deformation; 6 - cottage community; 7 - temple of XVi century; 8 - buried channel.
in khoroshevo (monument of the XVi century) and in the area of two-storied living houses (fig.11). in the upper part of the slope a new creeping block was formed with a length of about 220 m. The block involved a near-brow 12 m - wide part of the plateau along the length of 180 m. The total length of the area with activated landslide process was 330 m.
it should be noted that the scientific society, geologists and planners did not have a common opinion on the type and scales of the activated landslide. [1-6,13,17,18,20]. in particular, under discussion was the idea that the landslide is shallow and has the form of creeping near-surface sandy strata.
However, all the indications (i.e. the length of the basic subsided fracture of extension, character of formation and subsidence of the block, form of the bulging swell, uplifted fracture of rock compaction, etc.) indicate that activization of the sliding process has happened in the old landslide circus Khoroshevo-1 in the form of basic (catastrophic) deep landslide displacement with origination and subsidence of a new creeping block, the steep curvilinear sliding surface of which crops out onto the deep inherited, almost horizontal displacing surface under the old landslide body. it was supposed that in accordance with the results obtained by analysis of the situation on the given object and with the experience of studying landslides in other areas in Moscow with similar geological conditions , the existing horizontal part of the sliding surface, along which further
movements will take place, is located in a layer of Jurassic clays of the Oxfordian Stage. Possible development of deep movements in the area under consideration is also confirmed by geotechnical analysis of the clay strength and vertical pressure from the overlying layers.
Analysis of the situation in the area has showed that a trigger of activization could be the construction works in the Karamyshevsky Pr.Street. The water-conducting pipes and other communications were being lain in a deep trench (depth is about 7 m) in June-July 2006. This trench could redistribute the fluxes of shallow groundwater and waste waters and direct them through the buried erosion-induced entrenchment (a sink in the area center) into the above-landslide scarp and the existing landslide body.
Since October 2006 there was started well drilling, performance of geophysical investigations, geodetic observations of the marks on ground and on houses, measurement of deep deformations (inclinometers, extensometers, tensometric observations).
nauki przyrodnicze
47
It was established that in January displacements began in the lower part of the slope. The total displacement of this rock massif for two months (December-January) amounted to 13 - 20 mm. Moreover, the position of the sliding surface in the massif was determined instrumentally. It is located in Jurassic clays, involving the Oxfordian Stage near the layer roof . The depth of deformations reached 31 m. Creeping deformations are still going on.
On the plateau, beyond the landslide (on the territory of the Holy Trinity Temple and living houses), deformations are weak and mainly in the form of subsidence of -2 to +1 mm (since October 2006 till January 2007). If to reinforce the sliding block in accordance with the mechanism of landslides of the given type, deformations on the plateau will be stopped. However, in the marginal parts of the active circus where the basic fracture is sinking towards the base of the above-landslide scarp, formation of new sliding blocks is possible according to the property of "self-development" (Fig.12).
Protective measures
Planning of protective measures is implemented simultaneously with carrying out engineering-geological and
geophysical investigations of the area and observations within the landslide deformation monitoring system. It is foreseen to carry out regulation of surface water discharge, drainage of shallow groundwater on the sliding bench for prevention of a water level rise; to install a system of detaining facilities in the form of a berm - a counter-banquette (a sandy fill of 3 to 5 m on the surface of the landslide bench) and of a supporting wall - i.e. a reinforced concrete pile rostwerk, "sewing" the landslide body to the undisplaceable bed (pile tips are deepened into the Jurassic clays of the Callovian Stage, J3c£) and preventing the overlying active block to displace. The project of reinforcing is being corrected and developed further with obtaining new information on engineering-geological conditions and dynamics of the landslide.
Mechanical-mathematical model for landslide movement
Landslide motions is extremely actual and difficult problem which decision is necessary for preservation of valuable historical monuments and modern city constructions. There are near 20 places of deep landslides and some hundreds of shallow landslides in Moscow (Fig.13).
Figure 13. Map of zones of geological trouble in Moscow. (In red - landslide zones) Institute of Environmental Geoscience , Russian Academy of Sciences. Osipov V.I. (editor), Kutepov V.M., Mironov O.K. et al.
One of methods of studying of landslide processes is mechanical-mathematical modelling of gravitational movement of matter on landslide a slope. At different stages of the development the landslide process can be described by various mechanical and rheological models. At the stage of formation of cracks, losses of stability, break of blocks the models of the elastic medium and model of destruction are applied. During slow movement of soil on the slope the model of high viscous incompressible fluid can be applied. Such model allows to estimate velocities of movement in a layer and to compare them to results of monitoring. Boundary conditions of a problem
thus also depend on a concrete situation. So, in case of slow movement on the bottom border of a layer the condition of sticking is used. If the process of debris flow, underwater landslip or snow avalanche is considered, the condition of sliding or more complex boundary condition is possible on the bottom border. The choice of adequate model of process and statement of initial and boundary conditions is an independent mechanical problem.
Let's consider movement of landslide masses on a slope as movement of high viscous incompressible fluid described by equation of Navier-Stockes and continuity:
dv r= 1 p _
— = F--gradp +— Av
tl p p
div v = 0
v - vector of velocity, F - force of gravity, p - pressure, p -density, |i - viscosity, t - time.
Let the characteristic horizontal scale of a body of landslip L considerably surpasses its thickness h. We shall count also a landslip extended enough in the plan that allows to consider three-dimensional model as two-dimentional one for sections of landslide bodies. Following works [7-12, 14-16, 19. 21] and applying a method of decomposition on small parameter, it is possible to get the equation of continuity and an approximated equation of the Navier-Stockes in dimensionless form for slow motions in a thin layer:
dP d 2U — = ap—-dX dZ2
dp dZ
= -P
dU dW n
-+-= 0
dX dZ
a =
F
R
v L y
F = u°
R=
gL
uoLPo P 0
P is dimensionless pressure, U,W - dimensionless velocities, F - Frude number, R - Reynolds number, p - density, |i - viscosity,
Po' P0' U° - scales of density, viscosity and velocity.
Then it is possible to get the velocities and pressure in the layer:
P = p(<*- z)
ZA
q*(X)
X
a)
U = U° +
p
2ap dX
[ (<-Z)2 -(<-<)2 ]
w=w° +dUX~ (<°" z )+
+
P d2<
ap dX
1 (< - z )3 +1 (< )3 - v - z)(< -<°)2
+
P
is * ^2
2ap
vdX y
(Z-<°)2 <°(<'-<°)
ap dX dX
<° - the bottom border of a layer, < - the top border.
Let on the bottom border the condition of sticking is satisfied: U0=W0=0
The discharge of matter along the layer is:
t.
Q = J UdZ =
P
3ap dX
(<-<)3
Since Q=const lengthways X, then:
dQ
= °
dX
dV
dX2
a2<
(<-<)7 +
9apQ
P
3apQ P
dX
= °
The condition of convexity of upper boundary is:
2 „ *
< ° ^
dX2 3apQ
3 <
>-i<-<°) _ P dX
This expression enables to analyze the form of the surface of moving matter (Fig. 14).
ZA
6)
X
6)
Figure 14. The various possible form of landslide surfaces: a) - convex, 6) - concave.
4.
small
grad < ° is small, that is angle of lower boundary is
Structure of clinoforms (convex) can arise, if:
1. Q is large, that is flux is high
2. p is large. It means that matter spreads bad and can
support big angle 5. ° is small, that is thickness of sedimentary
3. P is small. It means that matter has large specific layer is small. Under fixed Q it means that velocity of flux is high volume and is friable and formation of clinoformes and even overturning of rockes are
possible
All these conditions seem to be natural enough to an explanation of formation of structures such as inflows and clinoforms of sedimentary cover that speaks about correctness of the model.
It is important to define the place of maximal velocity on the slope. An optimum place for location of monitoring post is the point of maximal speeds of movement of masses of landslide.
Let's consider the massif of sedimentary rocks with the top
border ç * representing landslide slope. The bottom border ç * is compatible with an axis X. The maximum of horizontal speed U is reached on the top border of the massif owing to condition:
dU _ p dç* dZ ap dX
Point of the maximal horizontal speed on the surface can be found from a condition of equality to zero of the first derivative:
(Ç-Z) = 0 ^ Z = Ç
dU * dX
= 0, whereU * =
P
2a¡u dX
(Ç )2
From here it is easy to receive the condition: 2( % )2 = 0
dX2
dX
(1)
It is necessary to mean, that Ç (X) is known function - the surface of landslide slope. And the received condition allows to find a point on a slope where speed of movement is maximal.
Let's consider for presentation and an illustration of the received decision the surface of a landslip as (Fig. 15):
ç*(X) _-thX +1
Then the condition (1) gives:
th1 X - thX -1 _ 0
1 -45
thX =
Whence we receive 2
i+45
and
ç =
2
1,62
Á i 2
1.62
A 1 Go
X
Fig. 15. Point A of the maximal horizontal speed of movement of masses on the surface of slope.
Such position of the point of the maximal horizontal speed is represented real, and more exact data on a structure of landslide and its surface will enable to define such point on a concrete slope. The point of maximum of speed on a slope defines the place of possible failure of a landslip in case of achievement of limiting pressure in massif of rocks.
There could be several points of local maximum of speed on a slope , that characterizes an opportunity of failure of a landslip on each terrace of a slope.
Work is executed at support of RFBR grant 08-05-92003-NNS-a.
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