J. Cent. South Univ. (2012) 19: 2029-2036 

DOI: 10.1007/s11771-012-1241-9

Short-term deformation behavior model of endangered earthen heritage slope after conservation in Jiaohe Ruins

ZHANG Jing-ke(张景科)^{1, 2}, CHEN Wen-wu(谌文武)^{1, 2}, HE Fa-guo(和法国)^{1, 2}

1. Key Laboratory of Mechanics on Disaster and Environment in Western China of Ministry of Education

(Lanzhou University), Lanzhou 730000, China;

2. School of Civil Engineering and Mechanics, Lanzhou University, Lanzhou 730000, China

? Central South University Press and Springer-Verlag Berlin Heidelberg 2012

Abstract: Cliff deformation behavior after conservation is of great significance for evaluating the conservation effect and discovering the dynamical law of soil. Modeling on deformation behavior is beneficial to the quantitative evaluation of interactions between soil mass and structures as well as the forecast. Based on cliff conservation engineering of Jiaohe Ruins (the largest raw soil heritage site in the world), data of horizontal deformation of the upper cliff were obtained by using Nanrui-made NDW-50 displacement device (precision: 0.01 mm, frequency: 15 min^-1). Regression analysis indicates that deformation behavior models include exponential growth, linear growth and parabolic growth types, while daily deformation presents more intense periodicity  (24 h). The deformation is less than 1.5 mm during monitoring period, which has no impact on the stability of cliff. Deformation behavior provides the mutual duress and interaction between soil and engineering intervention. In addition, deformation mode attaches tensely to the damage pattern of the cliff. The conclusions are of importance to the stability evaluation of the carrier along Silk Road.

Key words: endangered cliff; conservation; deformation behavior; regression analysis; modelling

1 Introduction

A huge amount of heritage sites scattered along the Chinese Silk Road are of great significance in studying the history of transportation, culture, religion, and architecture, etc [1]. With the establishment and practice of the strategy of applying the membership of the World Cultural Heritage Site list for the Silk Road, the scientific conservation of the heritage sites has become extremely urgent. Owing to long-run efforts made, heritage protection, mainly focusing on the ancient site bodies with great value, has made remarkable accomplishments, while the study of the site carriers is comparatively tardy [2]. For the sites along the Silk Road such as ancient cities, grottoes and tombs are sitting or occurring on the endangered geologic bodies, safety of the carriers is directly related with the survival or perishing of the site bodies. In recent years, conservation of the sites in China has been mainly carried out in the form of emergency conservation, which laid emphasis on the life saving, while in-depth study of conservation effects has been less conducted. The deformation behavior of endangered carriers after conservation, therefore, means importantly for the study of conservation effects [3].

In the field of geotechnical engineering, research on slope deformation behavior was focused on the following fields: 1) Exploring the regular patterns and characteristics of slope deformation through statistic analysis of deformation monitoring data [4-6]; 2) Implementing the middle and long-term forecast for the slope deformation based on the deterministic model and non-deterministic model [7-9]; 3) Establishing the theoretical foundation of slope evolution through coupling analysis of stress, seepage, temperature, etc of deformation behavior and rock-soil mass [10-12]. Apart from these, the researches have also been focused on the macro slope deformation within the monitoring period of a year, a month or a day [13-15], while few researches of the micro deformation are conducted. In view of the non-reproducibility of the heritage sites and the property of the carriers as both slope geologic bodies and cultural relics, relevant principles, plans and methods of protection should be different from those of the other engineering slope [16]. In protecting the heritage site carrier, high-accuracy monitoring data are needed to keep up with the real-time site deformation tendencies.

The emergency conservation engineering of Jiaohe Ruins is the largest heritage site conservation project in Xinjiang section of the Silk Road. During the conserving period, research was conducted on the site deformation monitoring methods, deformation features before and after conservation and factors influencing the deformation [17-18]. The carrier deformation behavior was mainly conducted through qualitative analysis instead of quantitative description. Based on the high- accuracy monitoring data of real-time tendency after the conservation of the endangered Jiaohe Ruins carriers, the mathematical model for the endangered carrier deformation was established and the deformation behavior characteristics after conservation was analyzed so as to discover the interaction between soil bodies and structures after conservation.

2 General situation of endangered cliff of Jiaohe Ruins and its conservation

2.1   General situation of endangered cliff of Jiaohe Ruins

With a history of over 1 600 years from the early Han Dynasty (206 BC-220 AD) to the end of Yuan Dynasty (1271-1368 AD), Jiaohe Ruins is located in Turpan, a strategically important place in the ancient Western Region of Xinjiang. Being the world largest and best preserved raw soil site, it is of great historical, scientific and artistic value. After more than 2 000 years natural evolutions and damages caused by human activities, Jiaohe Ruins is now in a poor condition. Large quantities of ancient architectural sites with significant value are sitting on the mesa with the average height of over 20 m and the circumference of 3 800 m. Because of multitudinous unloading cracks (Fig. 1) growing on the cliff sides around the mesa and their apparent traceabilities to the joints, the topography of the cliff edges is characterized by fragmentation. Besides, near or inside the cliff are sites with high value, like caves, walls and ancient wells. Research indicates that damage patterns of the cliff include landslide, tension fracture and slumping, while the specific damage mechanism is to be further studied.

2.2   General situation of endangered cliff conservation of Jiaohe Ruins

Based on the status quo of the endangered cliff damages, stratum features, structural plane composition, importance of the site and other factors, the surrounding endangered cliffs are divided into 59 districts, which are further divided into sub-districts, to facilitate the conservation in stages. By abiding the principles of cultural relic conservation in China like “Prioritizing Conservation and Rescue, Maximum Compatibility and Minimum Intervention, No Change to the Original State, etc”, methods of anchored grouting and bracing, specifically anchoring with different types of anchors, mud brick laying, channel steel bracing, crack grouting, surface anti-weathering consolidation etc, were adopted in conservation. The process of the conservation should be in strict accordance with the requirement of information- based construction, which requires the deformation monitoring to be conducted through the whole process.

2.3   Deformation monitoring plan of endangered cliff after conservation

1) The horizontal displacement changes of the top cracks of the endangered cliff are monitored in a real-time, dynamic and high-accuracy manner.

2) The horizontal displacement monitoring sections are perpendicular to the crack trends monitored. In setting the monitoring section, one end is fixed to the stable soil body inside the crack and the other end to the endangered cliff outside the crack; the height of the ends is adjusted to keep level and fixed by inserting a triangular support into soil. Thus, the absolute deformation value of the endangered cliff is obtained (Fig. 2).

3) Nanrui-made NDW-50 displacement device (fully automatic deformation observation systems specially designed for the endangered cliff of Jiaohe Ruins, with the measuring range of 100 mm, precision of 0.01 mm and the minimum monitoring frequency of   15 min^-1), is used as the horizontal monitoring instrument, which is laid out systematically in line with the composition features of the original structural planes to ensure an overall monitoring of the displacement of the endangered cliff blocks.

Fig. 1 Plane sketch of Jiaohe Ruins

Fig. 2 Sketch of deformation monitoring section

3 Cliff deformation models after conservation

The endangered cliffs of Districts 30, 39 and 43  (Fig. 1) were chosen as the objects of this work to explore the uniform deformation behavior model after conservation by summarizing the three typically- conserved endangered cliff deformation features.

3.1   Deformation behavior of District 30 after conservation

According to the characteristic of the form and structural plane of the endangered cliff of District 30, two fully automatic monitoring sections with the deformation monitoring period of 54 d after conservation are placed. Deformation behavior curves of the monitoring sections (MSs) and the continuous deformation behavior curve in consecutive two days are shown in Figs. 3 and 4.

The deformation curve of the monitoring section 1 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part. 2) Seen from the form of the deformation behavior, deformation features periodic vibration with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 1.00 mm at most. 3) The general tendency presents linear growth. The deformation amplitude during the monitoring period is 1.50 mm and the deformation of a single day tends to feature the deformation of the trigonometric function.

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the monitoring section 1 is

                         (1)

Fig. 3 Deformation behavior curves of monitoring sections at District 30: (a) MS 1; (b) MS 2

Fig. 4 Continuous deformation behavior curves in two days at District 30

The deformation curve of the monitoring section 2 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part. However, partial crack shrinkage occurs in the early stage while occasional abrupt change (900 h) happens in the process of crack growth in the later stage. 2) Seen from the form of the deformation behavior, deformation features periodic vibration with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 0.55 mm at most.  3) The general tendency presents parabolic growth. The deformation amplitude during the monitoring period is 0.23 mm and the deformation of a single day tends to feature the deformation of the trigonometric function. 4) Mutation happens at 900 h. It is induced by artificial activity (collided by technician in site).

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the monitoring section 2 is

             (2)

The contrast of the curves of the two monitoring sections displays the following facts: 1) The general deformation tendencies vary in the early stage, while tend to be the same in the later stage; the deformation scale during the monitoring period is comparatively slight. 2) The two monitoring sections have the characteristics of coordinated deformation, i.e., cracks grow and shrink synchronously. 3) The oscillatory periods of the two monitoring sections are the same, but the values of amplitude vary.

3.2   Deformation behavior of District 39 after conservation

According to the characteristic of the form and structural plane of the endangered cliff of District 39, four fully automatic monitoring sections with the deformation monitoring period of 33 d after conservation are placed. Deformation behavior curves of the monitoring sections and the continuous deformation behavior curves in consecutive two days are shown in Figs. 5 and 6.

The deformation curve of the monitoring section 1 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part. 2) Seen from the form of the deformation behavior, deformation features periodic vibration with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 0.7 mm at most. 3) The general tendency presents linear growth. The deformation amplitude during the monitoring period is 0.50 mm and the deformation of a single day tends to feature the deformation of the trigonometric function.

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the monitoring section 1 is

                         (3)

The deformation curve of the monitoring section 2 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part, but with the stepping characteristics of stable deformation-abrupt change-stable deformation. 2) Seen from the form of the deformation behavior, deformation features periodic vibration, with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 0.06 mm at most. 3) The general tendency presents exponential growth. The deformation amplitude during the monitoring period is 0.69 mm and the deformation of a single day tends to feature the deformation of the trigonometric function.

Fig. 5 Deformation behavior curves of monitoring sections at District 39: (a) MS 1; (b) MS 2; (c) MS 3; (d) MS 4

Fig. 6 Continuous deformation behavior curves of two days at District 39

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the monitoring section 2 is

                    (4)

The deformation curve of the monitoring section 3 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part. 2) Seen from the form of the deformation behavior, deformation features periodic vibration with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 0.35 mm at most. 3) The general tendency presents exponential growth. The deformation amplitude during the monitoring period is 0.59 mm and the deformation of a single day tends to feature the deformation of the trigonometric function.

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the monitoring section 3 is

        (5)

The deformation curve of the monitoring section 4 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part. 2) Seen from the form of the deformation behavior, deformation features periodic vibration with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 0.27 mm at most. 3) The general tendency presents linear growth. The deformation amplitude during the monitoring period is 1.50 mm and the deformation of a single day tends to feature the deformation of the trigonometric function.

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the monitoring section 4 is

                (6)

The contrast of the curves of the four monitoring sections displays the following facts: 1) The general deformation tendencies tend to be the same, presenting the characteristics of crack growth; the deformation scale during the monitoring period is comparatively slight. 2) The four monitoring sections have the characteristics of coordinated deformation, i.e., cracks grow and shrink synchronously. 3) The oscillatory periods of the four monitoring sections are the same, but the values of amplitude vary.

3.3 Deformation behavior of District 43 after conservation

According to the characteristic of the form and structural plane of the endangered cliff of District 43, three fully automatic monitoring sections with the deformation monitoring period of 27 d after conservation are placed. Deformation behavior curves of the monitoring sections and the continuous deformation behavior curves in consecutive two days are shown in Figs. 7 and 8.

Fig. 7 Deformation behavior curves of monitoring sections at District 43: (a) MS 1; (b) MS 2; (c) MS 3

The deformation curve of the MS 1 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part. 2) Seen from the form of the deformation behavior, deformation features periodic vibration with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 0.75 mm at most. 3) The general tendency presents exponential growth. The deformation amplitude during the monitoring period is 0.78 mm and the deformation of a single day tends to feature the deformation of the trigonometric function.

Fig. 8 Continuous deformation behavior curves of two days at District 43

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the MS 1 is

         (7)

The deformation curve of the MS 2 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part. 2) Seen from the form of the deformation behavior, deformation features periodic vibration with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 1.45 mm at most. 3) The general tendency presents linear growth. The deformation amplitude during the monitoring period is 1.25 mm and the deformation of a single day tends to feature the deformation of the trigonometric function.

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the MS 2 is

                            (8)

The deformation curve of the MS 3 has the following characteristics: 1) The general deformation tends to grow, i.e. there is a growing tendency between the endangered part and the stable part. 2) Seen from the form of the deformation behavior, deformation features periodic vibration with the period of 24 h and regular crack growth and shrinkage. Daily amplitude difference after conservation is slight, and it is 0.05 mm at most. 3) The general tendency presents exponential growth. The deformation amplitude during the monitoring period is 1.00 mm and the deformation of a single day tends to feature the deformation of the trigonometric function.

Based on the regressive fitting analysis, the mathematical model of the deformation behavior tendency of the MS 3 is

         (9)

The contrast of the three monitoring sections displays the following facts: 1) The general deformation tends to be identical and has the characteristics of crack expansion. The deformation scale of the sections during the monitoring, however, is less. 2) The three monitoring sections have the characteristics of coordinated deformation, i.e., the synchronous crack expansion and decrease. 3) The oscillatory periods of the three monitoring sections are the same, but the values of amplitude vary.

4 Discussion

By integrating the features of deformation behaviors of Districts 30, 39 and 43 of Jiaohe Ruins and the corresponding mathematical models, it is evident that the deformation behaviors of Jiaohe Ruins endangered cliffs after conservation have the following common characteristics: 1) After conservation, cracks have a tendency of slow growth. Among nine monitoring sections, five are componential growth models, three linear models and one parabolic model. 2) During the monitoring period, the total deformation of the endangered cliff is not remarkable. Seen from Fig. 9, the maximum is merely 1.5 mm and most of them are concentrated within the range of 0.5-1.0 mm. 3) Seen from the amplitude distribution curve of daily periodic deformation (Fig. 10), daily amplitude changes are small. The maximum is merely 1.5 mm, and most are concentrated within 0.25-0.78 mm. By integrating the mathematical models of deformation behavior, preliminary mathematical model of deformation behavior of Jiaohe Ruins endangered cliff after conservation can be established as follows:

                           (10)

where s is deformation, t is time and a, b, c are constants.

Fig. 9 Total deformation distribution in monitoring period

Fig. 10 Daily deformation amplitude distribution

After conservation of the endangered cliff, soil mass interacts with the structures for conservation. The crack grouting brings about great lateral pressure and vertical pressure to the endangered cliff. Besides, the grouting soaks and softens the rock soil bodies on both sides to weaken their physical and mechanical properties. However, a number of anchoring measures can provide massive tensile stress. Thus, besides the weak deformation caused by the natural factors, the deformation of the endangered cliff after conservation results mainly in the competition between the deformation induced by grouting and that by anchoring measures. Research [17] shows that strong periodic deformations occur to the Jiaohe Ruins endangered cliff before and in the process of conserving. The inducing agent of the deformation is the extreme meteorological factor (temperature) in Turpan region. It can be concluded that the periodic deformation after conservation is closely relevant with the atmospheric temperature. Deformation of tendency expansion has no threat to cliff stability. As discovered in Ref. [18], the abrupt change of the endangered cliff reached as high as 40 mm before conservation, but resumed periodic deformation progress soon. Thus, the deformation scale during the monitoring period is not remarkable enough to threaten the stability of the cliff. All the above factors indicate that the macro deformation shows growing trend with the characteristic of linear, parabolic and exponential type. The deformation mode is determined by the geological structure and damage pattern of the cliffs. The endangered cliff with landslide pattern usually performs exponential growing trend, and others perform linear and parabolic growing trend. Because of less grouting and more anchoring, the cliff with landslide pattern needs less time to gain stable deformation than others.

Seen from the short-term deformation after conservation, all the cracks have a growing tendency, which is closely related with the measures taken in conservation. The condensations of the grouting in the anchor holes in anchoring and in the crack grouting take a certain period of time, and the grouting inside the cracks has massive lateral pressure against the endangered cliff. The moisture content continuously penetrates into and weakens the surrounding soil mass, but when the grouting is close to condensing and the anchors begin to play the function of anchoring, the crack growth is to cease and return to the stable and slight periodic deformation.

5 Conclusions

1) Based on the high-accuracy and real-time deformation data, mathematical models of short-term deformation behavior of Jiaohe Ruins endangered cliff after conservation are established as linear type, parabolic type and exponential type.

2) The deformation behavior after conservation presents the tendency that the cracks grow slowly, and in the meantime, the oscillatory deformation with the period of 24 h.

3) Both the tendency deformation and oscillatory deformation have very small amplitudes, which are not large enough to have impacts on the cliff stability.

4) The mathematical models of deformation behavior describe the competitive process of the grout and anchoring threats to the endangered cliff in a quantitative way, which is of great significance in evaluating the conservation effect of the endangered cliff.

Acknowledgements

Thanks would be given to the research fellow Wang Xu-dong, senior engineer Zhang Lu and engineer Liu Dian-guo, for their careful guidance in the process of on-site tests and the writing of the thesis.

References

[1] LI Zui-xiong. Conservation of ancient sites on the silk road [M]. Beijing: Science Press, 2003: 3-5. (in Chinese)

[2] HUANG Ke-zhong. Protection for architecture historical relics in rocks and soils [M]. Beijing: China Architecture and Building Press, 1998: 2-4. (in Chinese)

[3] WANG Xu-dong. Conservation research on grottos and earthen sites under the arid environment of northwest China [D]. Lanzhou: College of Resource and Environment, Lanzhou University, 2003. (in Chinese)

[4] JAN H, TOMAS P. Deep-seated gravitational slope deformations and their influence on consequent mass movements (case studies from the highest part of the Czech Carpathians) [J]. Natural Hazards, 2008, 45: 235-253.

[5] HUANG R Q, LIN F, YAN M. Deformation mechanism and stability evaluation for the left abutment slope of Jinping 1 hydropower station [J]. Bulletin of Engineering Geology Environment, 2010, 69: 365-372.

[6] MARCEL H, ALBERTO L, JORDI C, PERE C. The deep-seated slope deformation at Encampadana, Andorra: Representation of morphologic features by numerical modeling [J]. Engineering Geology, 2006, 83: 343-357.

[7] XU Wei-ya, NIE Wei-ping, ZHOU Xian-qi, SHI Chong, WANG Wei, FENG Shu-rong. Long-term stability analysis of large-scale underground plant of Xiangjiaba hydro-power station [J]. Journal of Central South University, 2011, 18: 511-520.

[8] RICCARDO F. Slope instability of San Miniato Hill (Florence, Italy): possible deformation patterns [J]. Landslides, 2006, 3: 323-330.

[9] HERFRIED M, BERNARD M J. Hydrogeologic evidence for a continuous base shear zone within a deep-seated gravitational slope deformation (Easten Alps, Tyrol, Austria) [J]. Landslides, 2007, 4: 149-162.

[10] LUIS G, MAQUEDA A, SHABANA C. Numerical investigation of the slope discontinuities in large deformation finite element formulations [J]. Nonlinear Dynamics, 2009, 58: 23-27.

[11] JACQUES D, LAURA M, JOAL D. Deformability characteristic of Brazilian Laterites [J]. Geotechnical and Geological Engineering, 2006, 24: 157-162.

[12] JIANG F X, KENNETH G. Effect of rainfall intensity on infiltration into partly saturated slopes [J]. Geotechnical and Geological Engineering, 2008, 26: 199-209.

[13] LI Zhu-wu, ZHU Jie-ju, WANG Ren-qiu. Research on nonlinear strength of nonlinear model and its application in deformation analysis [J]. Journal of Central South University of Technology: Natural Science Edition, 2001, 32(4): 339-343.

[14] ZHOU Y D. Deformation and crack development of a nailed loose fill slope subjected to water infiltration [J]. Landslides, 2009, 6: 229-308.

[15] YIN Y P, WANG H D, GAO Y L. Real-time monitoring and early warning of landslides at relocated Wushan town, the three gorges reservoir, China [J]. Landslides, 2010, 7(3): 339-349.

[16] GUO Hong. Discussion on the substance and importance of the “Principle of keeping the former condition” and the intersection of arts and science in conservation [J]. Sciences of Conservation and Archaeology, 2004, 16(1): 60-64. (in Chinese)

[17] ZHANG Jing-ke, CHEN Wen-wu, CUI Kai, HE Fa-guo. Research on cliff deformation feature of Jiaohe ruins in process of and after anchoring and grouting [J]. Chinese Journal of Rock Mechanics and Engineering, 2009, 28(5): 1064-1078. (in Chinese)

[18] ZHANG Jing-ke, CHEN Wen-wu, HE Fa-guo, GUO Qing-lin. Deformation reaction characteristics of high-steep endangered cliffs around ancient ruins under temperature effect [J]. Journal of Lanzhou University: Natural Sciences, 2010, 46(3): 1-7. (in Chinese)

(Edited by YANG Bing)

Foundation item: Project(2010BAK67B16) supported by the National Science and Technology Pillar Program during the 11th Five-Year Plan Period of China

Received date: 2011-04-14; Accepted date: 2011-06-17

Corresponding author: ZHANG Jing-ke, PhD; Tel: +86-931-8914308; E-mail：zhangjink@lzu.edu.cn