Effect of salts on earthen materials deterioration after humidity cycling

Salt weathering leads to destruction of many valuable cultural heritage monuments and porous building material. The present study aims at providing more laboratory evidence for evaluating the effects of salt precipitation on the deterioration process. In view of this, the remoulded soil specimens were mixed with three kinds of salts(i.e., NaCl, Na_2SO_4 and their mixture) with different salt concentrations, and the specimens were kept in environment cabinet for undergoing different wet-dry cycles. After each cycle, the ultrasound velocity measurements were employed to monitor the deterioration process. For the specimens that have suffered three wet-dry cycles, the mechanical properties(i.e. shear strength and compression strength) were determined to evaluate the degree of deterioration. Furthermore, considering the realistic conservation environment of earthen sites, mechanical stability of these specimens against sediment-carrying wind erosion was conducted in a wind tunnel. These experiments results indicate that the overall average velocities of the specimens after the third cycle are significantly lower than those subjected to only one cycle. Ultrasound velocity, mechanical strength and wind erosion rate decrease when salt content increases. However, the internal friction angle increases firstly, and then decreases with the increase in salt content added to the specimens. Na_2SO_4 contributes most of the surface deterioration, while NaCl plays little role in the deterioration. The damage potential of the salt mixture is less obvious and largely dependent on the crystallisation location.

多次干湿循环后原状和重塑黄土的持水性试验研究

干湿循环的风化作用是引发中国黄土地区基础设施破坏的重要影响因素。黄土的持水性能是此类黄土工程问题物理成因的关键物性。为了探究在干湿循环的环境驱动作用下不同地区原状和重塑黄土的持水性能及其变化规律,利用压力板仪和电镜扫描仪(SEM)开展了持水曲线(SWRC)和微观结构的系列室内试验。研究结果表明,干湿循环的风化作用对原状和重塑黄土的持水性能有显著影响,且第一次循环的影响程度最为明显;原状黄土的SWRC呈双峰型,重塑黄土的SWRC呈单峰型;利用概念模型很好地解释了持水性的特征、变化规律及其与微观结构之间的联系。提出了一个考虑干湿循环次数、土的结构、区域差异影响的新持水模型,可以统一描述具有双峰特性的原状黄土和具有单峰特性的重塑黄土的持水特性,模型参数能够很好表达SWRC的变化特征,所提出模型在预测黄土和其他土的持水性能方面,具有较高的实用性和有效性。

Formation Mechanism of Ground Fissures Originated from the Hanging Wall of Normal Fault:A Case in Fen-Wei Basin,China

This paper takes Fen-Wei Basin(FWB)as a case to study the ground fissures controlled by normal fault.Based on the field investigation,geophysical exploration,drilling,GNSS data and numerical calculation,the characteristics and mechanism of ground fissures originated from the hanging wall of normal faults are revealed.The results show that the distribution of ground fissures in the hanging wall and heading wall of the active faults is not uniform.Ground fissures are mostly distributed in the hanging wall of active faults and show a linear distribution on the surface,their strike is consistent with the fault,mainly characterized by vertical offset and horizontal tension.Ground fissures destroy the farmland and building foundation through which they pass and cause the rupture or displacement.In profile section,the ground fissure shows the characteristics of normal faults and dislocates the strata,and is connected with the underlying faults.Numerical analysis shows that the vertical displacement of normal fault activity in hanging wall is much larger than that in heading wall,which is the reason that tectonic ground fissures mainly originate from hanging wall.The range of dangerous area of ground fissures is controlled by the depth of fault,the strength of the ground fissures disaster is mainly controlled by the activity of fault.The formation of the ground fissures originated from the hanging wall of the fault experienced three stages:the main fault activity stage,the secondary fault activity stage and the fissure formation stage.

A Comprehensive Method for the Risk Assessment of Ground Fissures:Case Study of the Eastern Weihe Basin

Ground fissures are influenced by the coupling of geological factors and human activi-ties.They threaten the safety of infrastructure and restrict town planning in many areas in China.One of the area most severely affected by ground fissures is the Weihe Basin in North China,which has the most extensive distribution of ground fissures and all the elements that control their occurrence,pro-viding an ideal study area for the study of ground fissures.In this study,we took the eastern Weihe Ba-sin as the study area and determined the distribution and hazard characteristics of ground fissures via field investigation.Based on the analytic hierarchy process,we propose a multi-level,comprehensive method for evaluating the hazards of ground fissures.This method considers the geological back-ground,development status,and triggering factors of ground fissures,including all nine currently known assessment indices of ground fissures.We used judgment matrices to rank the constructed ground fissure assessment index system at the single and total levels and quantified the nine assessment indices of ground fissures according to the field survey data.Finally,we plotted the ground fissure risk zoning map and evaluated the ground fissure risk at the study area.Our findings indicated that the proposed method could facilitate ground fissure hazard assessment and prediction and provide support for hazard prevention and urban/rural planning.