Soil Mechanics and Foundation Engineering, Vol. 34, No. 4, 1997

A R C H I T E C T U R A L M O N U M E N T S O F U Z B E K I S T A N A N D T H E

G E O L O G I C - E N G I N E E R I N G M E D I U M

A. Z. Khasanov, V. R. Mustakimov, F. A. Ikramov, and R. M. Gapparov

UDC 69.059.22:624.131.1

The problem o f the failure o f architectural monuments is examined, and means are proposed fo r its solution.

Monuments of central Asian architecture which were buik from the 14th through the 17th centuries are complex

engineering structures and consist primarily of grouped complexes (for example, the Registan ensemble, the Bibi-Khanum

Mosque in Samarkand, etc.). Significant changes in the geologic-engineering medium have occurred over an extended

historical period. Thick soil layers of anthropogenic origin, the thickness of which occasionally reaches 8-12 m, were formed

in many cities of Central Asia. The soils are in_homogeneous with respect to composition and are remnants of construction

debris and household refuse, as well as structures of an earlier period, which are of certain archeological interest. In adopting

solutions for strengthening the beds of these structures, therefore, the characteristic features of the enclosing soils should be

taken into account, and specialists in the field of archeology consulted.

The development of modern land-reclamation and town planning has exerted a major influence on variation in the

foregoing geologic media over the centuries. Significant bed deformations are observed when the moisture content increases

and the water table rises; this has involved nonuniform settlements of the monuments, variation of their geometric shape,

and, as a result, the appearance of cracks and local collapses. For example, the settlements of the foundations of the western

wall of the Tillya-Kori Mosque reached 50 ram, and those of the central dome portion 180 mm (after 10 years) (Fig. 1).

The accumulation and suffosion leaching of salts, which cause failure of the foundations, pedestal section, and then

the buildings and structures (for example, catastrophic failure of the left minaret of the "Chor Minor" ensemble in Bukhara)

occur when the hydrogeological regime is altered in the area where moderately and highly saline soils are present (Bukhara,

Khiva, and Shakhrisabz). The soils of anthropogenic origin in the area of Registan are approximately 2000 years old and are clayey loams,

which include 5-10% of humus and 15-20% of ceramics, construction debris, and household refuse, and are also classed as

structurally unstable soils that manifest slump-type-settlement properties when wetted and subjected to dynamic effects. In

studying these soils, we observed various sizes of cavities in the form of buried wells and burial grounds in which local

subsidence of the surface occurs when water is accumulated. The texture of the soils is laminar. The physical properties of

these soils are as follows: particle density of 16.7-18.4 kN/m 3, dry-soil density of 12.9-14.5 kN/m 3, natural moisture content

of 15-25%, and void ratio of 0.8-1.04.

Considering the characteristic features of these soils in the area of the Registan ensemble in Samarkand, testing with

625- and 2500-cm e circular plates was carried out at an elevation of 2-3 m below the existing foundations of the Tillya-Kori

Mosque. It was established that the compression modulus of the soil is 1.5-2.8 MPa for the natural moisture content, and 1.1-

1.4 MPa when wetted. The limiting stress state of the soil is attained under pressures of 100-130 kPa.

It was observed by inspections of the underground section of the Samarkand monuments that their foundations assume

a planform repetitious of their superstructures.

As a rule, the foundation structures are an alternating multilayer stacking of local ragged slate-like quarrystone and

flat burnt bricks. The bricks were used to level the quarrystone layer, imparting to it high stren~da and stability. The

placement of quarrystone also serves as a curtain, which reliably protects the wall structure from penetration of sorption

moisture.

Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 22-25, July-August, 1997.

126 0038-0741/97/3404-0126518.00 �9 Plenum Publishing Corporation

24 i

4 0 ;

8 o

1 6 o

~2o ~ ~o

-~ t ; o

t8o

Z.20

s

2GO

28O

~ 0

I .

I

S , ~

_~o

4 s

3 R q8

Central dome section

Signal towers at �9 ~ level of pedestal

\~,~ I

I1~'~ I f . i I~

I I I f l l I1.1

r i i I\N_L

II

I I I1 . /~

I I 1.k5~"I

I"_/Vt//I I L,H/r t l

I I

K ,

s, mifi

Fig. 1. Dia~ams showing variation of settlements of foundations for western wall of "Tillya-Kori." a) Central

dome oortion over time; b) alon~ signal towers established at level of pedestal section of wall.

It was established that the depth of embedment of the lower surface of the foundations depends on the active loads.

According to data derived by the "Geofundamenrproekt," for example, the depth of embedment of the lower surface of the

strip foundations for Tillya-Kori is 1.6-2.0 m under a load of 400 kN, that of the columnar foundations for the pier of the

dome 2.5-3.0 m under a load of 11,340 kN, and 9 m beneath the minarets under a load of 4000 kN [1].

Different average stresses, which attain 150-250 kPa, act beneath the lower surface of the foundations. Obviously,

ancient workmen intuitively increased the area of their support on the bed with increasing load on the foundations. It is

interesting to note that individually standing stepped foundations, which are familiar in modern construction practice, were

127

2

1 . .~qi i i i i f i , , ,mi i f iF .d i i i i ,JJ f imt~, i im . , . , ~ . . . . . . . . _,.~- . . . . . . . . . . . . . . . . . :.-...:.

r

Fig. 2. Combined pavement construction. 1) Bituminous concrete on

crushed-stone cushion; 2) pavement covering; 3) ventilation pipe; 4) anti-

capillary curtain; 5) foundation.

known even in ancient times, and were used under thick supports and columns. Such foundations were unearthed in the

southern part of the gallery for the TiUya-Kori Mosque beneath the dome supports. The foundations of the minarets are a

barrel-shape quarrystone placement. The width of the foundation section exceeds the diameter of the minaret at its base by

200-400 mm around the perimeter. The foundations of some monuments are built from materials used for the placement of wails. For example, the

foundations of the "Rukhobod" mausoleum in Samarkand are built of flat bricks in pottery clay mortar, while the bed is built

of local crumbled clayey loam with a g3rpsum additive, packed in layers in a trench.

The pavements of virtually all monuments are built of coarse round pebbles on a compacted bed. Rainwater is

drained along a slope toward discharge irrigation ditches, while intra courtyard water runs off into water-absorbing wells,

which reach the depth of the draining layers of soil, The wails of the wells are made of brick set preferentially in a clay

mortar and assume the shape of a barrel with a negligible increase in diameter in the median section with respect to height.

To create the initial appearance around the monuments, architects and town planners have regraded them vertically. For this purpose, the upper layer of soil 0.5-2 m thick has, as a rule, been cut without sufficient scientific basis. As a result,

the foregoing temperature-moisture balance of the bed soil has been disturbed over the centuries; this has led to a change in

the geologic-engineering medium in the vicinity of the monuments. In cutting the upper layer of soil 1.0-1.5 m thick at the

Registan site, for example, a sunken irrigation waterway system was disturbed, and changed the point of accumulation of atmospheric precipitation, and also increased significantly the aeration zone. After cutting the upper layer of soil around the

monuments, two types of pavements were built: 1) pebble and burnt brick on a sand cushion; and, bituminous-concrete over

a crushed-stone cushion. The first type makes it possible to reconstruct the initial appearance of the contiguous area and

evaporate moisture freely from the aeration zone. Such a construction does not, however, protect from penetration by

atmospheric moisture. The second type makes it possible to protect the soils from penetration by atmospheric moisture reliably, but leads to the accumulation of sorption moisture in the bed. Considering the positive sides of the types of pave-

ments under consideration, we propose its combined construction (Fig. 2).

CONCLUSIONS

1. Slump-type deformations, which are associated with a rise in the water table (especially during reconstruction),

and nonuniform wetting of the bed soils are the basic cause of the deformation and failure of monuments in areas with high

water tables, while suffosion settlement and failure of the foundation structures and pedestal portion due to salt aggression are

the basic cause in areas with a high water table and a high and medium degree of soil salinity.

128

2. To ensure the reliability and longevity of the monuments, it is necessary to work out concepts for stabilization of the water table at a depth that is safe for the buildings.

Any town-planning changes should be carried out after careful scientific substantiation of the solution adopted and the establishment of monitoring for all observations.

R E F E R E N C E S

1. I~. M. Gendet ' , Engineering Operations in the Restoration of Architectural Monuments [in Russian], Stroiizdat,

Moscow (1980).

129