lable at ScienceDirect

Journal of Rock Mechanics and Geotechnical Engineering 8 (2016) 726e733

Contents lists avai

Journal of Rock Mechanics andGeotechnical Engineering

journal homepage: www.rockgeotech.org

Full Length Article

Nondestructive testing and assessment of consolidation effects ofearthen sites

Xudong Wang a,b,c, Qinglin Guo a,b,c,*, Shanlong Yang a,b,c, Dexuan Zhang d,Yanwu Wang a,b,c

aNational Research Center for Conservation of Ancient Wall Paintings and Earthen Sites, Dunhuang, 736200, ChinabKey Laboratory for the Conservation of Ancient Wall Paintings and Earthen Sites in Gansu Province, Dunhuang, 736200, ChinacDunhuang Academy, Dunhuang 736200, Chinad Shanghai Jiao Tong University, Shanghai 200240, China

a r t i c l e i n f o

Article history:Received 21 March 2015Received in revised form29 May 2016Accepted 6 June 2016Available online 27 July 2016

Keywords:Earthen sitesNondestructive methodsInfrared thermal imagingHigh-density microelectrode resistivityPortable microscopeHydrophilic and hydrophobic testing

* Corresponding author.E-mail address: 3037582@qq.com (Q. Guo).Peer review under responsibility of Institute of R

nese Academy of Sciences.

http://dx.doi.org/10.1016/j.jrmge.2016.06.0011674-7755 � 2016 Institute of Rock and Soil MechanicNC-ND license (http://creativecommons.org/licenses/

a b s t r a c t

Earthen sites are widely distributed throughout China, and most of them belong to archaeological siteswith significant values, which not only directly witness the origin, formation and development of Chi-nese civilization, but also possess important values for conservation and exhibition. Many researches andpractices on their conservation and consolidation have been carried out; however, the consolidationeffect is mainly judged by visual observation and expert evaluation. Scientific assessment of conservationand consolidation effects is a challenging issue. Many instruments in other fields cannot be directlyapplied to the conservation of cultural relics due to their peculiarity. In order to assess the effects of fieldconservation experiments, this paper tries to understand the consolidation effects at Liangzhu site usingnondestructive or micro-damage methods, including thermo-physical parameters testing, infraredthermal imaging, high-density microelectrode resistivity testing, portable microscope observation, andhydrophilic and hydrophobic testing, and thereby explores the practicable methods for evaluating theproperties of consolidation materials for earthen sites treatment.� 2016 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

1. Introduction

Ancient architectures in China were mainly built of timber andearth. Although most of wooden structures have been decayed orremoved over times, a large number of earthen architectures arestill preserved as earthen sites (Wang, 2013). The six groups ofnational key cultural relics announced by the Chinese governmentinclude 378 earthen sites distributed in 30 provinces. The mostfamous sites of them are the Banpo Village Ruins of the YangshaoPeriod at Xi’an, the Terra-Cotta Warriors and Horses site of the QinDynasty at Lintong, and the Han Dynasty Chang’an City in ShannxiProvince; the Dadiwan Village Ruins of the Yangshao Period atQing’an, the Qin Dynasty Great Wall site at Dingxi, the Jade Gate,Hechang City and Han Dynasty GreatWall sites near Dunhuang, theSuoyangcheng site at Guazhou, and the Camel City site at Gaotai in

ock and Soil Mechanics, Chi-

s, Chinese Academy of Sciences. Prby-nc-nd/4.0/).

Gansu Province; the Khara-Khoto site at Ejin Banner in InnerMongolia Autonomous Region; the Tangut King Tombs at NingxiaHui Autonomous Region; the Ancient Jiaohe City site, the AncientGaochang City at Turfan, and the Ancient Loulan City in XinjiangUygur Autonomous Region; and so on. Researches on conservationand consolidation of earthen sites have been carried out extensivelyin China for over 20 years (Li et al., 1995, 2009a,b; 2011; Sun et al.,2008; Wang, 2008, 2010). Overseas studies on the conservation ofearthen sites mainly focus on earth properties and compositions aswell as condition evaluation, cause of deterioration, moisturemonitoring, capping and consolidation (Coffman et al., 1990; Helmi,1990; Ward, 1990; Carll and TenWolde, 1996; Rodriguez-Navarroand Doehne, 1999; Kuchitsu et al., 2000; Ziegert, 2000; Tolleset al., 2002; Fodde, 2006, 2008, 2010; Charnov, 2011; Snethlage andSterflinger, 2011; Stephenson and Fodde, 2012). Few studies areconducted to evaluate the consolidation effect of earthen site basedon nondestructive testing methods. Therefore, it is very difficult toquantitatively evaluate the consolidation effects in the field ofconservation of earthen sites. The cultural relics are non-renewableresources, suggesting that only nondestructive or micro-damage

oduction and hosting by Elsevier B.V. This is an open access article under the CC BY-

X. Wang et al. / Journal of Rock Mechanics and Geotechnical Engineering 8 (2016) 726e733 727

testing methods can be used to evaluate the consolidation effectsand the testing methods in civil engineering cannot be directlyapplied in this field. Based on the testing of consolidation effects atthe Liangzhu site in Zhejiang Province, China, this paper exploresthe systematic and practical methods for evaluating the consoli-dated effects of earthen sites by testing the thermal conductivity,the temperature changes of both consolidated and unconsolidatedareas, the micro-composition, the high-density microelectrode re-sistivity, the thermo-physical parameters, and the infrared ther-mograph with nondestructive and micro-damage methods.

2. Field nondestructive testing methods for evaluatingconsolidation effects of earthen sites

Fifteen types of consolidation materials, including 3%e5% high-modulus potassium silicate (PS), hydrophilic high-tensile siliconemulsion, 12% modified styrene acrylic acid, and 4% modifiedacrylic acid, were chosen to test the consolidation effects on thesurface of the north wall of the Liangzhu site in Zhejiang Province,China, and a variety of nondestructive testing methods were usedto verify the feasibility and reliability of these methods.

2.1. Measurement of thermo-physical parameters

Various thermal transfer phenomena can be observed in dailylife, such as heat conduction. The thermo-physical parameters ofthe cultural heritage are often measured in the laboratory. Giorgiet al. (2002) tested the thermo-physical parameters of paper andcanvas. Zhang et al. (2014) studied the relationships betweenwatercontent and thermo-physical parameters of earthen sites in thelaboratory. As for the consolidated earthen body, heat conductionrefers to the phenomenon that the temperatures of different areasvary with the changes of external environmental temperature.However, the microstructures of the earthen body change afterconsolidation, causing different thermal conductions due to thedifference of thermal conductivity. In this study, the portablethermal conductivity instrument (DECAGON KD2 Pro) was used totest the thermal properties of earthen sites. The 6 cm long singleneedle-type sensor (KS-1) was chosen to measure the thermalconductivity and resistivity of the earthen fabric, and the 3 cm longdouble needle-type sensor (SH-1) was used tomeasure the thermaldiffusivity and specific heat capacity of the earthen fabric. Thesensors installed are shown in Fig. 1. Four indices, i.e. thermal

Fig. 1. Photo of field testing for thermo-physical parameters.

conductivity (K), heat capacity (C), thermal diffusivity (D) andthermal resistivity (R), were tested.

2.2. Infrared thermal imaging

Infrared thermal imaging refers to the technology of trans-forming invisible infrared radiation into visible images with aninfrared detector. Such images are used to determine the surfacetemperature distribution of tested object and then to evaluate itscondition. Infrared thermal technology has been widely used ininvestigation, monitoring and evaluation of cultural heritage.Grinzato et al. (2002), Avdelidis and Moropoulou (2004) andKordatos et al. (2013) investigated the condition of ancient build-ings, murals and historic monuments by the infrared thermaltechnology. Bodnar et al. (2012) applied the infrared thermographyto restore mural paintings. In this paper, M7500 thermal imagerwas used for testing (Fig. 2). The temperature data of the testedobject collected by the thermal imager are input into a computerthrough a necessary interface, and then they are processed andanalyzed in field or in the control center. Software of MikroSpec�R/T that is compatible with M7500 series is used in the testing.Through the Ethernet, users can perform remote control to selectcameras, modes, temperature range and lens, analyze and monitorthe custom areas or any specific zone. Testing should be carried outin the morning or at nightfall as possible considering the relativelylarge changes in environmental temperature.

2.3. High-density resistivity testing

High-density resistivity testing has been successfully applied tomany engineering investigations on water and moisture. Its basicprinciple is completely the same as that of the regular resistivitytesting. The only difference is that more electrodes are selected inthe high-density resistivity testing, which is a kind of electricdetection methods based on the resistivity discrepancy of rock orsoil mass. Putting all the electrodes on the lines to be tested in field,the electronic switch and engineering measurement instrumentcan realize rapid and automatic data collection. However, all theelectrodes have to be tapped into the earthen body in current high-density resistivity testing, and this would cause great damage to theearth body. In order to protect the earthen sites, Dunhuang Acad-emy in cooperation with the Qingdao Jiaopeng Institute of Tech-nology Engineering developed electronic lines at a spacing of 5 mminstead of traditional electrodes which to some extent damageearthen fabric. As a result, high-density resistivity testing can be

Fig. 2. Field testing photo of infrared thermal imaging.

Fig. 5. Field hydrophilic and hydrophobic tests.

X. Wang et al. / Journal of Rock Mechanics and Geotechnical Engineering 8 (2016) 726e733728

carried out on the surface of the earthen sites without any damageto earthen sites. Fig. 3 shows the electronic lines and field testing.

2.4. Microscopic observation

The microstructural changes of consolidated earth are signifi-cant for permanent consolidation effects. Various materials areeffective in conservation of earthen sites in the initial stage, butsurface peel and loss will appear a few years later. This has beenconfirmed to have a relation with the changes of surface structure.For earthen sites, the changes are detected more often in laboratorythan those observed in field and evaluated with portable micro-scopes. In this study, DinoCapture, a portable microscope, was usedto observe the changes of surface structures (see Fig. 4).

2.5. Hydrophilic and hydrophobic testing

One of the basic requirements for anti-weathering conservationmaterials is that these materials should be water-resistant but notwater-repellent. Therefore, hydrophilic and hydrophobic tests arealso included in the consolidation effect evaluation of earthen sites.By spraying water over the experimental area, the hydrophilic andhydrophobic tests were carried out on the earthen sites which wereconsolidated with different materials (see Fig. 5). It is not particu-larly an accurate but fast and effective method.

Fig. 3. Testing photo of micro-electric resistivity.

Fig. 4. Testing photo of microstructure.

3. Testing results of consolidation effects of earthen sites

3.1. Testing results of thermo-physical parameters

Testing results of thermal conductivity and resistivity for un-consolidated area and areas consolidated with 15 different ma-terials in different proportions are shown in Figs. 6 and 7,respectively; while the testing results of specific heat capacity andthermal diffusivity are separately illustrated in Figs. 8 and 9. Thedetails of the areas consolidated by different materials are shownin Table 1.

By comparing Figs. 6 and 7, it can be found that the smallerthermal conductivity and the larger thermal resistivity occur afterconsolidation. Such a phenomenon proves that this testing methodcan be used to evaluate the consolidation effects of earthen sites.

Ther

mal

con

duct

ivity

, K(W

/(m °C

)) 0.0035

0.003

0.0025

0.002

0.0015

0.001

0.0005

01 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Area No.

Fig. 6. Testing results of thermal conductivity.

Ther

mal

resi

stiv

ity, R

(°C

/W)

12

10

8

6

4

2

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Area No.

Fig. 7. Testing results of thermal resistivity.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Area No.

Hea

t cap

acity

, C(k

J/(k

g°C

))0.04

0.035

0.03

0.025

0.02

0.015

0

0.01

0.005

Fig. 8. Testing results of heat capacity.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Area No.

Ther

mal

diff

usiv

ity, D

(m/s

)

0.04

0.035

0.03

0.025

0.02

0.015

0

0.01

0.005

Fig. 9. Testing results of thermal diffusivity.

Table 1Details of unconsolidated area and areas consolidated with different materials.

AreaNo.

Consolidationmaterial

AreaNo.

Consolidationmaterial

1 Unconsolidated area 9 12% modified styrene acrylic2 8% n-octyltriethoxysilane 10 31J consolidated material3 5% double ethane 11 2% styrene acrylic4 2% modified acrylate 12 2% silicon fluoride5 5% PS material 13 4% pure acrylic6 13.89% modified pure acrylic 14 4% modified silicon acrylic7 12.8% modified silicone acrylic 15 4% silicon acrylic8 Hydrophilic high-tensile

silicon emulsion16 4% fluorine silicon

X. Wang et al. / Journal of Rock Mechanics and Geotechnical Engineering 8 (2016) 726e733 729

Figs. 8 and 9 indicate that the thermal diffusivity and heat ca-pacity of unconsolidated area are generally smaller than those ofthe consolidated areas; meanwhile, those of the consolidated areasdiffer slightly from each other. These differences are induced by theconsolidation of earthen sites with different materials. As a result,these different parameters which are tested can be used to evaluatethe consolidation effects of earthen site by different consolidationmaterials.

The above results demonstrate that the surface structures of theearthen sites have been changed apparently after consolidation dueto the change from microstructures of separated or flaky crystalclay minerals to a non-crystal gel structure, causing changes of thethermo-physical parameters of the earthen body. Hence, the ther-mal physical parameters can be used as evaluation indicators forconsolidation of earthen sites.

3.2. Testing results of infrared thermograph

The infrared thermal imaging has been applied to evaluating theconsolidation effects of earthen sites in this study. The results of apart of experimental areas are chosen to illustrate the feasibility ofinfrared thermal imaging in such an evaluation. Fig. 10 shows thediagram of visible lights and infrared thermal image, and Fig. 11presents the temperature-time curves of tested areas. It can befound from Fig. 10 that the temperature of the areas consolidatedwith different materials is obviously different from that of theunconsolidated area. The temperature-time curves shown in Fig. 11indicate that the surface temperature change of consolidated areasis smaller than that of unconsolidated area. It should be mentionedthat the test was carried out in the season with low daily temper-ature difference in this region; consequently it is hard to determinethe difference between different consolidation materials with largedaily temperature difference. Further work should be conductedconcerning large daily temperature difference.

3.3. Testing results of high-density resistivity

Figs. 12e14 show the testing results of high-density resistivityby means of electronic lines. Fig. 12 depicts the inverse chart of thetesting results of unconsolidated area, and the left and right sides ofFig. 13 respectively show the testing results of unconsolidated andconsolidated areas with the 31J conservation material. Fig. 14 pre-sents the testing results of the area consolidated with the PS con-servation material.

Fig.12 reveals that in thewhole area, the resistivity is lower nearthe surface and it gradually becomes higher from the surface to-wards the inside. Fig. 13 suggests that the resistivity increases fromthe surface towards the interior due to the water content reduction.The resistivity of the unconsolidated area is obviously lower thanthat of the consolidated area, which indicates that the consolida-tion material not only lowers the resistivity, but also decreases thewater and air permeability of the earth surface. Thus, this materialis not suitable for conservation of earthen sites. Fig. 14 shows thatthe whole area has a lower shallow resistivity and high deep re-sistivity. The resistivity is higher at the surface, reduces towards theinterior, and then increases in deep interior. This illustrates that theconsolidation material has altered the property of the earthenfabric by increasing the surface strength and slightly decreasing theair and water permeability of the earthen surface. Comparisonamong testing results shows that the 31J material in Fig. 14 is su-perior to that in Fig. 13 in terms of air and water permeability.

The above testing results show that the electronic resistivity ofthe unconsolidated and consolidated areas with differentmaterials,determined by high-density resistivity testing based on micro-electrode lines, is obviously different. In conclusion, the method fortesting the resistivity of unconsolidated and consolidated earthbodies by the microelectrode lines can be used for evaluating theconsolidation effects of earth sites.

3.4. Testing with portable microscopy

Figs. 15e17 show the results of microstructure testing on un-consolidated area (Fig. 15) and areas consolidated with differentmaterials (Figs. 16 and 17).

It is revealed form Fig. 15 that holes and cracks on the earthsurface, loose earthen structure, and obvious weathering tracesmight easily result in powdery loss and efflorescence of the surfaceexposed to external environments. Fig. 16 shows a relatively com-pacted surface after consolidated with 2% modified acrylate. It isdemonstrated that the treatment is effective in consolidation ofearth surface and anti-weathering.

Fig. 10. Diagram of visible lights and infrared thermal image.

Time (s)0 100 200 300 400 500 600 700

Tem

pera

ture

(°C

)

33

32

31

30

29

28

56789

Time (s)

Tem

pera

ture

(°C

)

34

33

32

31

30

0 100 200 300 400 500 600 700

Fig. 11. Temperature-time curves of tested areas.

Fig. 12. Inverse chart of the testing results of unconsolidated area.

Fig. 13. Inverse chart of the testing results of unconsolidated and consolidated areas with the 31J material.

X. Wang et al. / Journal of Rock Mechanics and Geotechnical Engineering 8 (2016) 726e733730

However, the evident reflection of light on the earth surfaceindicates that the conservation material leads to a poor waterpermeability and will further influence the air and waterpermeability, and the physical appearance of the earthen surface.

Fig. 17 shows that the microstructure of the area consolidatedwith 4% silicon acrylic is similar to the microscopic images of theunconsolidated earth surface, which suggests that the conser-vation material can effectively consolidate the earthen site

Fig. 14. Inverse chart of the testing results of the area consolidated with the PS material.

Fig. 15. Microstructure of unconsolidated area (�100).

Fig. 16. Microstructure of the area consolidated with 2% modified acrylate (�100).

Fig. 17. Microstructure of the area consolidated with 4% silicon acrylic (�100).

Fig. 18. Hydrophilic and hydrophobic testing of unconsolidated area.

X. Wang et al. / Journal of Rock Mechanics and Geotechnical Engineering 8 (2016) 726e733 731

surface without altering its structure. Therefore, 4% silicon acryliccan be used as a conservation material for earthen sites. Ac-cording to the above researches, the microscopic image can helpto understand the surface structure of the consolidated area andthus can be used in qualitative evaluation of conservationmaterials.

3.5. Hydrophilic and hydrophobic testing

Generally, consolidation materials should have a good hy-drophilic instead of hydrophobic property because the perme-ability of the earthen site surface will be reduced afterconsolidation with hydrophobic materials, water is not able tofreely escape, and then it is easy to crust on the surface due to thedifference in the properties of earthen site surface and interior.

Figs. 18e20 show the results of hydrophilic and hydrophobictesting of the unconsolidated area and the areas consolidatedwith different materials. Fig. 18 indicates that the unconsolidatedarea has satisfactory water permeability because the watersprayed over the surface will penetrate into the earth rapidlyinstead of forming droplets. Fig. 19 shows that the sprayed watercannot penetrate into the earth but form droplets rolling alongthe surface of the area consolidated with 5% double ethane.Fig. 20 suggests that water can also penetrate rapidly into theearth of the area consolidated with 5% PS material. Comparisonof the testing results shows that the 5% PS material reflected inFig. 20 is superior to the 5% double ethane in Fig. 19 in terms ofthe air and water permeability. Though this testing method issimple, but it can well differentiate the quality of conservationmaterials. Therefore, it can be used to evaluate the consolidationeffects of earthen sites.

Fig. 19. Hydrophilic and hydrophobic testing of the area consolidated with 5% doubleethane.

Fig. 20. Hydrophilic and hydrophobic testing of the area consolidated with 5% PSmaterial.

X. Wang et al. / Journal of Rock Mechanics and Geotechnical Engineering 8 (2016) 726e733732

4. Conclusions

This paper studies the testing methods for evaluation ofconsolidation effects of earthen sites using thermo-physical pa-rameters, infrared thermograph, and high-density microelectroderesistivity with portable thermal conductivity meter, infrared im-ages, high-density conductivity instrument, portable microscopeand water spray. The research fills the void of in-situ testingmethods for the conservation and consolidation of earthen sites,and thus makes sense to studies of earthen site consolidation andconservation.

Measurements of basic thermal conductivity, thermal resistivity,specific heat and thermal diffusivity, and comparison of thethermo-physical parameters before and after consolidation suggestthat the thermal conductivity and resistivity of the earthen bodybefore and after consolidation differ significantly. The diagrams ofthe temperature vs. time determined by the infrared thermal im-aging show that changes in the surface temperature of theconsolidated area exceed those of the unconsolidated area as theenvironmental temperature changes; furthermore, it should bemore obvious when the difference in daily temperature is high. Thehigh-density resistivity testing based on microelectrode lines canprovide obviously different two-dimensional resistivity sectiondiagrams between unconsolidated area and the areas consolidatedwith different materials. The portable microscope can distinguishthe microstructure changes of the area before and after consoli-dation as well as the areas consolidated with different materials.Hydrophilic and hydrophobic testing can also effectively evaluatethe consolidation effects. All the above-mentioned testing methods

can be utilized to evaluate the consolidation and conservation ef-fects of earthen sites.

Further research on testing and evaluation of earthen siteconsolidation should focus on the reasonable combination ofmultiple nondestructive testing instruments and parameterassessment.

Conflict of interest

The authors wish to confirm that there are no known conflicts ofinterest associated with this publication and there has been nosignificant financial support for this work that could have influ-enced its outcome.

Acknowledgement

The work is supported by the National “12th Five-Year” Plan forScience and Technology Support (Grant No. 2014BAK16B02), theKey Project of the State Administration of Cultural Heritage (GrantNo. 20120207), and the Project on Basic Research of Gansu Prov-ince’s Innovation Group (Grant No. 145RJIF336). The authors wantto warmly thank Zhejiang Provincial Institute of Cultural Relics andArchaeology for its support in research and field investigation.

References

Avdelidis NP, Moropoulou A. Applications of infrared thermography for the inves-tigation of historic structures. Journal of Cultural Heritage 2004;5(1):119e27.

Bodnar JL, Candore JC, Nicolas JL, Szatanik G, Detalle V, Vallet JM. Stimulatedinfrared thermography applied to help restoring mural paintings. NDT & E In-ternational 2012;49:40e6.

Carll C, TenWolde A. Accuracy of wood resistance sensors for measurement ofhumidity. Journal of Testing and Evaluation 1996;24(3):154e60.

Charnov AA. 100 years of site maintenance and repair: conservation of earthenarchaeological sites in the American southwest. Journal of Architectural Con-servation 2011;17(2):59e75.

Coffman R, Agnew N, Austin G, Doehne E. Adobe mineralogy: characterization ofadobes from around the world. In: Grimstad K, editor. The 6th InternationalConference on the Conservation of Earthen Architecture: Adobe 90 Preprints.Los Angeles, USA: The Getty Conservation Institute; 1990. p. 424e9.

Fodde E. Analytical methods for the conservation of the Buddhist temple II ofKrasnaya Rechka, Kyrgyzstan. Conservation and Management of ArcheologicalSites 2006;8(3):136e53.

Fodde E. Conservation and conflict in the central Asian silk roads. Journal ofArchitectural Conservation 2010;16(1):75e94.

Fodde E. Structural faults in earthen archaeological sites in central Asia: analysisand repair method. In: D’Ayala DF, Fodde E, editors. Proceedings of the 6thInternational Conference on Structural Analysis of Historic Construction Vol. 2.Taylor & Francis; 2008. p. 1415e22.

Giorgi R, Dei L, Ceccato M, Schettino C, Baglioni P. Nanotechnologies for conser-vation of cultural heritage: paper and canvas deacidification. Langmuir2002;18(21):8198e203.

Grinzato E, Bison PG, Marinetti S. Monitoring of ancient buildings by the thermalmethod. Journal of Cultural Heritage 2002;3(1):21e9.

Helmi FM. Deterioration and conservation of some mud brick in Egypt. In:Grimstad K, editor. The 6th International Conference on the Conservation ofEarthen Architecture: Adobe 90 Preprints. Los Angeles, USA: The Getty Con-servation Institute; 1990. p. 277e82.

Kordatos EZ, Exarchos DA, Stavrakos C, Moropoulou A, Matikas TE. Infrared ther-mographic inspection of murals and characterization of degradation in historicmonuments. Construction and Building Materials 2013;48:1261e5.

Kuchitsu N, Ishizaki T, Nishiura T. Salt weathering of the brick monuments inAyutthaya, Thailand. Engineering Geology 2000;55(1e2):91e9.

Li L, Chen R, Shao MS, Pei QQ, Wu HW, Wang SJ, Li ZX. Saturation strength ofearthen ruins reinforced by potassium silicate and influence of environmentalfactors on reinforcement effect. Chinese Journal of Rock Mechanics and Engi-neering 2009a;28(5):1074e9 (in Chinese).

Li ZX, Wang XD, Sun ML, Chen WW, Guo QL, Zhang HY. Conservation of Jiaoheancient earthen site in China. Journal of Rock Mechanics and GeotechnicalEngineering 2011;3(3):270e81.

Li ZX, Zhang HY, Wang XD. Research on the conservation of ancient earth-structuressites. Dunhuang Research 1995;3:1e17 (in Chinese).

Li ZX, Zhao LY, Sun ML. Deterioration of earthen sites and consolidation with PSmaterial along Silk Road of China. Chinese Journal of Rock Mechanics and En-gineering 2009b;28(5):1047e54 (in Chinese).

X. Wang et al. / Journal of Rock Mechanics and Geotechnical Engineering 8 (2016) 726e733 733

Rodriguez-Navarro C, Doehne E. Salt weathering: influence of evaporation rate,supersaturation and crystallization pattern. Earth Surface Processes and Land-forms 1999;24(3):191e209.

Snethlage R, Sterflinger K. Stone conservation. In: Siegesmund S, Snethlage R, ed-itors. Stone in Architecture. 4th ed. Berlin-Heidelberg: Springer-Verlag; 2011.p. 411e544.

Stephenson V, Fodde E. The feasibility of using scientific techniques to assess repairmaterial suitability in earthen building conservation. In: Terra 2012, 11th In-ternational Conference on the Study and Conservation of Earthen Architecture.University of Lima; 2012.

Sun ML, Li ZX, Wang XD, Zhang L. Study on reinforcement of earthen sites bybamboo-steel composite anchor. Chinese Journal of Rock Mechanics and En-gineering 2008;27(Suppl. 2):3381e5 (in Chinese).

Tolles EL, Kimbro EE, Ginell WS. Planning and engineering guidelines for theseismic retrofitting of historic adobe structures. GCI Scientific Program Reports.Los Angeles, USA: The Getty Conservation Institute; 2002.

Wang XD. Exploration of conservation philosophy for earthen sites in humid en-vironments and an outlook on future conservation technology. DunhuangResearch 2013;1:1e6 (in Chinese).

Wang XD. New progresses on key technologies for the conservation of Chineseearthen sites in arid environment. Dunhuang Research 2008;6:6e12 (inChinese).

Wang XD. Philosophy and practice of conservation of earthen architecture sites: acase study of the Jiaohe Ancient Site in Xinjiang. Dunhuang Research 2010;6:1e9 (in Chinese).

Ward SH. Resistivity and induced polarization methods. In: Ward SH, editor.Geotechnical and environmental geophysics: review and tutorial. Tulsa, USA:Society of Exploration Geophysicists; 1990. p. 147e89.

Zhang HY, Zhang XC, Chen XN. Research on thermal parameters of different earthenmonument soils. Rock and Soil Mechanics 2014;35(Suppl. 1):57e62 (inChinese).

Ziegert C. Analysis of material, construction and damage in historical cob buildingsin central Germany. In: Heritage E, editor. Terra 2000, 8th International Con-ference on the Study and Conservation of Earthen Architecture. London: Jamesand James; 2000. p. 182e6.

Professor Xudong Wang graduated from Lanzhou Uni-versity, is a Research Fellow of the Dunhuang Academy. Heis the director of the Dunhuang Academy, director of Na-tional Research Center for Conservation of Ancient WallPaintings and Earthen Sites, guest professor in bothLanzhou University and Northwest University, China. He isalso the president of the Commission on Preservation ofAncient Sites of International Society of Rock Mechanics.He has been mainly engaged in the conservation of caves,ancient wall paintings and earthen sites, as well as theresearch of monitoring, early warning and preventiveconservation of cultural heritage. Since 1991 when hebegan to work in the conservation of cultural relics, he haspresided more than 30 projects of investigation and

surveying or site construction engineering at nationally protected key cultural relicssites, undertaken more than 20 national or provincial projects, and presided over orjoined in 4 international cooperation projects. He has published more than 100 papers,co-published 8 academic books, won 15 national or provincial awards, and presidedover the edition of 5 national and industry technology standards.