Due to cyclic freezing-thawing and drying-wetting, cracks are commonly encountered in loess regions and adversely affect the seepage and stability of slope engineering. However, the influences of freeze-thaw (FT) cycles on desiccation cracking of intact loess are rarely known. In this study, evaporation tests were performed on an intact loess with different water contents and subjected to various numbers of FT cycles. To interpret the desiccation cracking behavior, the microstructure of tested intact loess was determined by conducting the scanning electron microscope (SEM) tests. Results show that FT cycles further enhance the inherent loose structure of intact loess through pore expansion, pore connection and formation of continuous channel, and destroy the particle bonding contributed by fine particles and cementitious minerals. The intact loess subjected to 0 FT cycle predominately exhibit single cracks, while both single and Y-shaped cracks are observed in intact loess subjected to non-zero FT cycles. The difference in crack pattern is attributed to the enhanced loose structure owned by the latter, which forms a large number of structural defects. Furthermore, the crack ratio and the average width and total length of cracks increase with the increasing numbers of FT cycles. This can be attributed to the two effects induced by FT cycles, one is the degradation of tensile strength due to bonding breakage, and the other is the inhomogeneous shrinkage deformation due to the rapid evaporation of water in specimens with enhanced loose structure. Furthermore, the FT cycles cause more significant effects on the desiccation cracking of intact loess with higher water contents than those of intact loess with lower water contents, primarily due to the larger frost heaving forces induced in the former.

The city of Xi'an, Shaanxi, China, is the transportation hub in western China, which has planned to establish an underground utility tunnel system. However, this city has faced a series of fissure disasters with a wide area of 250 km2, which is hazardous to the safety of the operation and maintenance of tunnels. The results of finite element simulation suggest that prefabricated utility tunnels can better adapt to the activity of the ground fissures. Based on the results, this paper quantifies the maximum ground fissure settlement that the tunnel can bear and compares and analyzes several different working conditions such as crossing angles, and prestressingpretensioning values. The results show that the main form of damage in the utility tunnel under the activity of surface cracks is the failure of the rubber waterproofing of the joints. To minimize this risk, this paper proposes a method of increasing the prestress to improve the rubber waterproofing performance. This conclusion can effectively increase the operation safety of the utility tunnel.

The canyon section from Longyangxia to Liujiaxia in the upper reaches of the Yellow River, which is characterized by a significant number and large scale of landslides, is a typical area prone to landslides. Investigating the characteristics and causes of giant landslides in this region holds great significance for understanding and mitigating the risks associated with such disasters. This paper explored the development characteristics and induced causes of these giant landslides via field surveys, remote sensing interpretations, unmanned aerial vehicle (UAV) surveys, geological dating methods, and numerical simulation methods. There were 22 giant landslides in the study area. Their sliding face is deeply buried in sandy mudstone or sandy stone that is landslide strata and shows large differences in elevation of landslide front and back edges. Most of these landslides mainly occurred tens of thousands of years ago that is indicated by geological dating results. The causes behind these giant landslides have been discussed from various perspectives. Multiple factors, such as tectonic activity, rock properties (“genes”), river erosion dynamics, climate change influences, and ancient earthquakes, are believed to have contributed to the development of giant landslides in this region. Regional tectonic activities exert tectonic forces leading to structural plane formation within rock masses while providing initial conditions for deformation and failure processes associated with giant landslide occurrences. Since the Pleistocene, Yellow River erosion has created favorable spatial environments conducive to giant landslide development by altering slope stress conditions; furthermore, climate change weakens rock mass strength. Finally, earthquakes generate substantial energy serving as catalysts for triggering massive landslide events by inducing rock mass failures.

Fractures are widespread phenomena on loess slopes in northwestern China. Fractures are of various types and have different distribution patterns, and they are important factors affecting the mechanical properties of loess. In this paper, the effect of different fracture distribution modes (fracture angle, fracture position and fracture combination) on the shear strength of loess is investigated by carrying out consolidated undrained triaxial shear tests. The results show that the existence of fractures in loess can significantly weaken the strength of the soil under consolidated undrained conditions. Compared with unfractured loess, fractures weaken the shear strength of loess mainly by weakening the cohesion. The internal friction angles of fractured loess, however, are hardly affected by the existence of fractures and the fracture distribution mode. Furthermore, a comparison of three fracture distribution modes, namely, the fracture angle, position and combination, reveals that the fracture angle is the most significant factor weakening the loess strength, followed by fracture combination, and the least is fracture position. In addition, confining pressure increments can greatly improve the shear strength of both unfractured and fractured loess, and confining pressure increments can inhibit the weakening effect of fractures on loess strength.

The establishment of an underground utility tunnel system has been projected for Xi'an, the transportation center in western China. However, this city are suffering the damage that ground fissures have inflicted on the subterranean engineering. The traditional cast-in-place underground utility tunnel could not well adapt to thr activity of ground fissures. The activity of ground fissures may result in numerous damages such as tunnel fractures and waterproof failure. To reduce such hazards, a large-scale physical model was set up to study the stress and deformation characteristics of the prefabricated underground utility tunnel crossing active ground fissures. The findings from the analysis of the soil pressure, distribution of soil cracks, and structure deformation show that waterproof rubber is more susceptible to failure due to a large interface tension displacement occured near the ground fissure.

The Loess Plateau is the only young and accumulating plateau in the world, and loess deposited in this area covers 4.6% of China's land area. As a geological base to study global climate change and geomorphic evolution, geotourism in the Loess Plateau is of science significance and can promote regional economic development. In this work, we took Yan'an City in the middle of the Loess Plateau as a study area and made a comprehensive inventory of geoheritage within the city and its suburbs. Yan'an has unique geological heritage characteristics because of a complex combination of regional tectonic activity, sedimentary strata, climate change, and hydrodynamic forces. The inventory showed that geoheritage sites in this area are characterized by the following classification: (1) geoheritage sites associated with Quaternary environmental geology, (2) geoheritage sites associated with red beds and landform, (3) geoheritage sites associated with Yellow River, and (4) geoheritage sites associated with onshore oil. The development scale and protection level of these geoheritage sites are systematic. Geoheritage sites associated with loess and onshore oil have scientific and educational value, whereas geoheritage sites associated with Danxia landform and water landscape have viewing value. In summary, the geoheritage sites of the Yan'an area have great geotourism, educational, and protection value. The inventory and classification of geoheritage sites in this area is a foundation for the protection and development of geotourism resources in Yan'an.

Ground fissures are influenced by the coupling of geological factors and human activities. 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, providing an ideal study area for the study of ground fissures. In this study, we took the eastern Weihe Basin 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 background, 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.

The active characteristics and genetic mechanism of coupled ground fissures mainly induced by fault activities and pumping are studied, and the Songzhuang Town in Tongzhou District of Beijing is taken as the research archetype. The damage of surface planes and stratigraphic profiles caused by ground fissure activities are clarified through field investigation, and the variation characteristics of the displacement field and stress field of the strata caused by different dislocation amounts and groundwater level drop are revealed. The response processes of the model stratum under the two conditions of fault misalignment and groundwater extraction are simulated and studied respectively by using the finite difference method. Finally, the relationship between this type of ground fissure and the main inducing factors is discussed. The results show that（1） the ground fissure is characterized by three-dimensional activities, which causes the vertical tension of the shallow stratum and wall to be 0.3-1.2 cm,and the vertical dislocation of the deep stratum gradually increases with the burial depth.（2） Stress changes caused by fracture activities are concentrated in the ground fissure development area and lead to significant vertical displacements in the hanging wall, the stratum located in the ground fissure area has large shear and traction deformation, and the vertical displacement difference between the two sides is the largest. The gradual increase of fault dislocations causes the hidden fractures to extend upward, and cause secondary cracks on the shallow surface of the hanging wall, resulting in the overall distribution of ground fissures with a certain width.（3） The vertical extension and horizontal expansion of ground fissures are aggravated by the lowering of groundwater levels, and the surface on both sides of the crack produces continuous settlement response, making the center of the subsidence funnel become a concentrated development area of ground fissures, with the maximum settlement of 10.2 cm in the model stratum at the fissure in its central area, and the settlement range of about 38 m in the hanging wall and about 16 m in the foot wall.（4） This type of ground fissures is obviously controlled by faults, but the increased activity in this period is mainly due to groundwater over-exploitation. This work will be of great theoretical and practical significance to understand ground fissure mechanism, establish quantitative relationship between formation and fault with groundwater, and prevent and reduce disasters.

The Yangjiazhuang-Maguduo ground fissure, which is in front of the Luoyun Mountain on the western margin of the Linfen Basin, is a typical ground fissure that developed in the transition zone between the basin and mountain. In this paper, the developmental characteristics and mechanisms of the ground fissure in the transition zone between the basin and mountain under the action of fault activity and pumping were studied and analyzed through ground investigation, engineering geological mapping, trenching and geophysical exploration. The investigation and research confirmed that the strike of the ground fissure is parallel to the Luoyun Mountain piedmont fault and the ground surface has both horizontal extension and vertical offset. Trench result shows that the plane of the superficial part of the ground fissure is rough, which is typical tensile failure; the plane of the ground fissure under the bottom of the trench is smooth and mainly displaying shear deformation, and meanwhile the vertical offset of the stratum increases with depth showing synsedimentary structural characteristics. Shallow geophysical results reveal that the ground fissure is a manifestation of the Luoyun Mountain piedmont fault. Research suggests that deep tectonic activity caused pre-existing faults in the Luoyun Mountain piedmont to be in a continuous tensile shear state, which enhanced their activity and caused the pre-existing faults to extend to the surface, forming the ground fissure in the hanging wall of the fault. Continuous groundwater overexploitation led to the consolidation and settlement of the hanging wall of the Luoyun Mountain piedmont fault, which increased the differential settlement on both sides of the Luoyun Mountain piedmont fault, thus intensifying the movement speed of the Yangjiazhuang-Maguduo ground fissure and forming the present ground fissure. The development characteristics and formation mechanism of the Yangjiazhuang-Maguduo ground fissure provide not only an important reference for studying ground fissures in basin-mountain transition zones, but also guidance for the prevention and mitigation of such geological disasters.

The Weihe Basin is part of the regionally extensive Fenwei Graben System, which is a major tectonic block impacted by active tectonics and human activities. There are 200 tectonic ground fissures in the Weihe Basin, some of which have resulted in loss of life and severe damage to infrastructure. The development characteristics and dynamic mechanisms of these fissures were investigated by surveying, mapping, and geological drilling. The fissures are distributed along the boundary faults between fault blocks with prominent regional, zoning, and directional characteristics. On the profiles of fissures, the tectonic ground fissures are connected with underlying faults and possess the characteristics of synsedimentary faults. The deeper the stratum is, the greater the fault displacement of the stratum is, and the greater the thickness of the strata on the hanging walls is than that on the heading walls. These fissures are driven by dynamic tectonic processes, including uplift of the upper mantle and extension of the crust, differential movement of the fault blocks, and fault activity. The extension and opening of fissures are accelerated by hydrodynamic progresses, including pumping and raining. This paper describes a study of the mechanisms of the fissures and provides guidance for prevention of disasters and reduction of disaster severity in this area.

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 nu- merical 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 hang- ing 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 stra- ta, 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.

太行山大峡谷位于山西省壶关县境内的南太行山区,历经亿万年的沧海桑田形成了以峡谷群、峰林石柱、河流瀑布、溶洞等为典型景观的大型高山峡谷景观系统,大峡谷现已建设成为"国家地质公园"和"5A"景区.同时,太行山大峡谷因地处我国第二、三阶梯的地表突变带,构造活动强烈,地表侵蚀严重,在山地特殊气候作用下崩塌灾害频发,时常损毁道路桥梁、破坏生活设施,并危及居民和游客安全,制约景区建设发展.本文立足大峡谷景区地质灾害详细调查,查明大峡谷内发育崩塌达318处,以高位小型岩质崩塌为主,主要分布于海拔700～1100 m之间,崩落高度平均120 m左右,最高可达300 m以上;崩塌多发育在断层带附近和软弱岩层处,沿峡谷两侧呈带状分布,以倾倒式和坠落式的破坏方式为主,具有明显的"群发、多发、复发"的特点.基于对大峡谷景区地形地貌、地层岩性、岩体结构、地表营力及人类活动等崩塌孕灾环境的分析,依据发育区位和致灾效应将崩塌划分为陡壁崩落带、梯状崩石链、碎裂崩滑带和水岸崩塌带4种类型;结合崩塌运动轨迹和对承灾体的效应归纳出崩落滚石型、崩链型、碎裂溃散型、落石涌浪型4种典型成灾模式,并分析提出景区安全防控的对策和建议.研究成果可为高山峡谷区的地质灾害防灾减灾、太行山区的景区开发规划和建设及地质环境保护提供借鉴.

关中盆地东部地区活动断裂、地裂缝、黄土湿陷等工程地质问题突出.以陕西省安仁镇幅为例,通过水工环综合地质调查,在查明研究区工程地质条件和主要工程地质问题的基础上,进行了工程地质分区,将研究区划分为3个工程地质区、7个工程地质亚区和11个工程地质地段.研究选择地形地貌、水文、工程地质、不良地质作用和地质灾害、断裂和地震效应5个一级评价因子和11个二级评价因子,采用多因子分级加权指数和法,对研究区进行了工程建设适宜性评价,研究成果可为当地城镇规划、工程选址和防灾减灾提供地质依据和参考.

The Zezhang ground fissure in the Linfen Basin, China was first observed in 2004 where it damaged the infrastructure in and around the town. Field and laboratory investigations now confirm that the fissure has had a complex origin, ranging from likely recurrent fault offset with almost synchronous local sedimentation (synsedimentary), to accelerated groundwater withdrawal, soil erosion and ultimately to geomorphic expression of surface subsidence, local linear scarps and sinkholes. Trench exposures and interpretation of borehole data indicate that at least four tectonic events took place during the latest Pleistocene and Holocene generally localizing the zone of fissure expression. In contrast to other tectonic ground fissures, the ground fissures in Zezhang are highlighted with major synsedimentary characteristics. The formation mechanism of ground fissures was caused by several factors, initial and later underlying fault displacements, initial fissures with land subsidence caused by groundwater withdrawal and widening into linear sinkholes under soil erosion. The Zezhang ground fissure, its investigation techniques and the technical findings, provide a case study for assessing previously unrecognized synsedimentary fissures elsewhere.

临汾盆地位于山西地堑系的南部,地裂缝灾害频发且成因复杂多样;特别是20世纪90年代以后出现在侯马凹陷盆地的地裂缝,发育规模大,灾害严重,给当地居民造成了严重的经济损失.以2007年出现在侯马凹陷盆地区的北张地裂缝为例,通过详细的地面调查和地表测绘查了地裂缝的平面展布特征,利用槽探揭示地裂缝的剖面结构特征.根据物探、钻探和InSAR监测结果,分析构造断裂和超采地下水与地裂缝的关系,并得出北张地裂缝的成因机理,并据此提出地裂缝的防治措施.

Earth fissure is one of main geological hazards in China. By 2015, 5002 earth fissures were discovered in more than 1, 500 localities across 22 provinces. These earth fissures caused huge economic loss. Based on a series of geological investigations including in surveying, mapping, trenching, drilling and monitoring, the spatial distribution and development rules of the earth fissures are summarized, and the movement characteristic of the earth fissures are revealed. The results show that the earth fissures mainly distribute in North China and South China, especially in the Fenwei Basin, Hebei Plain and Yangtze River Delta. The giant earth fissures, longer than 1 km, mainly distribute in the Fenwei Basin and Hebei Plain. These earth fissures exhibit the following five regular patterns: clustering along fault zones, distributing along geomorphic boundaries, appearing on the edge of subsidence areas, dispersing in loess collapsible area, and centralizing in larger and medium cities. The movement characteristics of the earth fissures can be divided into four types: tension type, tension-shear type, shear-tension type and shear type.

A set of widely developed ground fissures within the Datong Basin, northern China, have inflicted serious damage to farm fields, roads, houses, and building foundations in Datong City. Such emergence of large-scale ground fissures is rare in urban areas. The formation mechanisms of these features were therefore investigated in detail through surveying, mapping, trenching, drilling, and geophysical prospecting. The 11 fissures in Datong City are located on the hanging wall of the Kouquan fault (part of regional horst and graben terrain), and run approximately parallel, with a dominant strike of NE34 degrees-70 degrees and a maximum length of 5.5 km. These structures occur in clear zones with similar directions and lateral distributions on the surface. They possess evident syn-sedimentary fault characteristics, including y-shaped, trapezoidal, and traction structures in their profiles. The synergistic action of different tectonic factors and groundwater exploitation is responsible for fissure formation. Under the influences of regional tensile stress, upper mantle uplift, and fault block movement, activity along local faults created hidden fracture systems within the hanging wall. The over-exploitation of groundwater in the region subsequently accelerated fracture growth, and varying vertical compressibility of the strata on both sides of the local fault resulted in uneven subsidence on the surface, generating tensile zones and promoting the appearance of fissures at the edges of settlement funnels.

Dali County is located in the eastern Weihe Basin where frequent ground fissure disasters occur. Dali ground fissures are macroscopically part of the ground fissure group in the Weihe Basin and have caused serious damage to infrastructure and agricultural production in this area. In this paper, 25 ground fissures in Dali County are identified through investigation, and two typical ground fissures in Fengcun and Weizhuang are selected for research. Through field investigation, trench excavation, geophysical exploration, soil water content tests and collapsibility coefficient tests, the basic features, shallow structural characteristics, deep structural characteristics and genetic mechanisms of the two ground fissures are revealed. The strike of the Fengcun ground fissure is 45°, almost parallel to the Shuangquan-Linyi Fault; the length is 2 km, and the profile is ladder-like and extends deep with synsedimentary characteristics. The Weizhuang ground fissures are circular in plan view with a length of 315 m and trumpet-shaped in profile; they disappear in the paleosol layer. The mechanism of the Fengcun ground fissure is related to basin extension and fault activity. The ground fissures are the surface reflections of deep faults. The mechanism of the Weizhuang ground fissures is related to loess collapsibility and seepage. The Malan loess has differential settlement in collapsible and noncollapsible areas, and ground fissures are the boundary line for differential settlement of loess. Finally, based on the genetic mechanisms of ground fissures, Dali ground fissures can be divided into two types: tectonic and nontectonic.

In this study, 5002 ground fissures in more than 1500 localities across 22 provinces in China are investigated and mapped to reveal their spatial distribution. The distribution of these ground fissures in China exhibits six regular patterns-assemblages in North China, syngenesis in extensional basins, clustering along fault zones, distributing along geomorphic boundaries, developed on the edge of subsidence areas, and clustering in large and mediumsized cities. Combined with regional GPS, numerical simulations, physical model test and In-SAR monitoring, the generative processes of ground fissures are analyzed and discussed in relationship to four mechanisms: (1) deep dynamic tectonism controls on the location of ground fissures, (2) intracontinental dynamic tectonism resulting in ground fissure assemblages, (3) fault stress inducing formation of ground fissures, and (4) groundwater overmining resulting in the reactivation and expansion of ground fissures. The geological environment is thus responsible for the establishment and appearance of ground fissure. More importantly, ground fissure propagation in China is the result of the synergistic effects of internal geological dynamic (including in deep tectonism, intracontinental tectoniim, and fault movement) coupled with anthropomorphic stress. This genetic model can be summarized as one that is tectonically controlled, stress -driven, and affected by regional hydrodynamic.