Jingke Zhang

Hazard assessment of potentially dangerous bodies within a cliff based on the Fuzzy-AHP method: a case study of the Mogao Grottoes, China

The Mogao Grottoes are among the most famous sites on the World Heritage list. Several large-scale preservation projects were implemented in 1962, 1982, and 2008, respectively, to improve their preservation conditions. According to field investigation and assessment in recent years, the cliff is stable on the whole because of the reinforcement projects. Among them, there are still 42 potentially dangerous bodies, which may not be stable in some conditions. For the purpose of building the monitoring and early warning system and the long-term preventive preservation of the Mogao Grottoes, an innovative analytical method based on the Analytic Hierarchy Process (AHP) and Fuzzy-AHP was applied to assess the hazard of potentially dangerous bodies within the cliff. Firstly, the hazard was classified into six groups: very high, high, moderate, low, very low, and no hazard, in this study. Secondly, the AHP method was applied to calculate the impact index of each causative factor, and then the hazard assessment of dangerous bodies was made based on statistical analysis. Finally, the Fuzzy-AHP method was applied to calculate the correlation of each factor and determine the comprehensive hazard class. The results indicate that Fuzzy-AHP seems to be more accurate than AHP in hazard assessment. Meanwhile, there is a very high risk body that can threaten 10 caves, three high risk bodies that can threaten 13 caves, and 15 moderate risk bodies can threaten 69 caves in total, while the remaining bodies are defined as low or very low grades. Overall, the results of this study provide much data and a theoretical model in the construction of a monitoring and early warning system currently. Furthermore, the new numerical simulation method also holds the potential application to assess the hazards of other types of heritage sites.

The properties of potassium silicate/ fly ash slurry used in the conservation of adobe structures

The work reported here is a systematic study to evaluate the compatibility of using PS-F (potassium silicate with high modulus – fly ash) slurry in the conservation of adobe structures. Firstly, the optimum mixing proportion (0.47) was determined by flow meter. Then the experimental program was divided into two parts: one part studied changes in physical and mechanical properties with increase in setting time by means of the measurement of moisture content, compressive and flexural strength, elastic-wave velocity, density, and porosity; the other part studied the durability of PS-F slurry through temperature and humidity cycles, freeze–thaw cycles, water stability, tensile testing, and alkali resistivity tests. The results show that the consolidation process with the slurry can meet the requirements of conservation applications and provide a timely anchoring force, and the slurry and soil mass of adobe-based structures have good compatibility in physical and mechanical properties. In addition, the slurry can strongly resist freeze–thaw cycles, temperature-moisture cycles, and tensile stress and has a relatively weak resistance to alkali solutions and water immersion. In conclusion, PS-F with a mixing ratio of 0.47 is a suitable slurry for conservation of adobe structures.

Pull-out behaviour of wood bolt fully grouted by PS-F slurry in rammed earth heritages

ABSTRACT This article presents a laboratory and field investigation of pull-out resistance of wood bolts in rammed earth heritages. The laboratory testing involved axial tensile tests of four grout specimens prepared in specially designed moulds using PS-F (Potassium Silicate solution-Fly ash) slurry to investigate the performance of anchors. The field testing involved pull-out tests of three wood anchors installed in rammed earth heritages by gravity grouting. Experiments reveal that the failure mode is the pull-out of bolt from grout and average skin friction resistance of bolt–grout interface is approximately 0.34MPa. Load–displacement curves and elastic–residual displacement derived from cyclic loading indicate such anchor system has strong ductility with small elastic deformation and large residual deformation. Bond collapse firstly occurs at the loaded end and then propagates towards the full bonded length. Bond stress distribution is not uniform along the bonded length. Maximum bond stress distributes at the range from 0.3 m to 0.4 m. Emergence of compressive strain in the interface reveals such anchor system enjoys the advantages of both tensile and compressive anchor types, which significantly differs from results from other regular bolts. The research conclusion makes scientific senses to traditional material and craft in rammed earth heritages.

The Disease Characteristics and Conservation Technique of the Bezeklik Grottoes at Turpan in Xinjiang

With the influence of the spread of Indian Buddhism, there are a large quantity of Grottoes with the variation in history, architectural art and functions distributing along the Silk Road in China. Bezeklik Grottoes at Turpan, Xinjiang is an important royal temple with significantly historical, scientific and artistic value along the Silk Road. The grottoes need urgent conservation because of the natural damage and human activities. Based on the field investigation and analysis, the types and characteristics of the main disease developing in the cliff and caves of Bezeklik Grottoes was clarified, furthermore, the genetic analysis of the disease was studied. The diseases of Bezeklik Grottoes are found out, which include carrier diseases, cave diseases and carrier a diseases associated with the cave. In accordance to the principle of diseases development, the appropriate conservation methods were proposed. The conservation engineering was finished with a satisfying effect. The similar grottoes in the same area can use the conservation experience of Bezeklik Grottoes as a successful reference.

Field Tests on Anchoring Mechanism of the Bamboo-Steel Cable Composite Anchor with Single Reinforcement

Under the influence of natural condition and human activities, the majority of earthen sites are suffering from the damage with different degrees, which are in urgent needs of rescuing and conservation. The previous conservation experiments and practices show that the conservation methods for the main body of earthen sites should adopt the traditional craft as far as possible to achieve the goal of “maximum compatibility, minimum intervention”. A type of the bamboo-cable composite bolt (a 7 @ 5 steel strands within the bamboo, with the length of 5 m) is chosen to carry out the field experiment of anchoring mechanism of composite bolts. The results indicate that: the main destruction way of composite anchor is that the composite material interface slips out of softening; the composite anchor axial stress distribution is exponential distribution with the pullout load increases; when pull-out load is smaller, interfacial shear stress shows the exponential function distribution, decreasing from the start to the end of the bolt, and the peak shear stress deviates to the end with the load increases; Steel strand axial stress is higher than the bamboo pipe axial stress; Composite bolt shows the material memory characteristics in the process of cycle pullout; The strain value of bamboo internal surface is higher than that of the outside surface in the same section; The limited pullout force is 238 KN in the bolt with the plats in end, whereas, it is 204 KN for the bolt without the anchor plates.

Anchor performance of wood bolt fully grouted by PS-(F+C) slurry in rammed earth sites

Based on laboratory physical model and field experiments which consisted of pullout tests and strain monitoring on bolt-grout interface, wood bolts fully grouted by potassium silicate solution-(fly ash + silt) (PS-(F+C)) slurry in rammed earth were researched on its anchor capacity, failure mode, shear stress distribution and transfer along the bolt-grout interface. Experimental results showed that ultimate pullout force in laboratory (24~38 kN) is far larger than that in field (2.5~8 kN). Low elastic deformation and high plastic deformation of anchor system result in strong ductility. In the process of loading, multi-peak stress distributes along bolt-grout interface and higher stress value usually appears near anchor end, meanwhile, compressive stress occasionally emerges in monitoring interface. Results proved that such anchor system benefits from advantages of both the tensile anchor and compressive anchor. In conclusion, with considerably physical and mechanical compatibility to rammed earth, the anchor system is fairly suitable to conservation of rammed earth sites. ©, 2015, Editorial Department of Journal of Sichuan University. All right reserved.