中国岩溶

Spatial differentiation of soil carbonic anhydrase under different types of land use

HE Yuanyuan, LI Qiang, CAO Jianhua, LIANG Jianhong, ZHU Minjie

2013, 32(4): 365-370.

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Carbonic anhydrase (CA) plays an important role in catalyzing the reversible hydration of CO2, which connects with chemical weathering (including the carbonate rock dissolution and silicate weathering) in atmospheric CO2 sink and the mysterious missing sink in carbon cycling. In order to explore the soil CA activity by means of pH method from different types of land use in southwest China karst area, 11 sampling plots from four different karst ecosystems and 5 sampling plots from non-karst ecosystems as a contrast are selected for the study.The results show that there are larger differences in soil CA activity among different soil layers under different types of land use in southwest China karst area.Under woodland, the soil CA activity in 40 cm and 60 cm soil layers is higher than that in 20 cm. The soil CA activity under tree-shrub land, shrub land and farmland is the highest in 60 cm soil layer, but the lowest in 20 cm. However, in abandoned field, soil CA activity is the highest in 20 cm soil layer but the lowest in 60 cm. It can be seen that the land use type is the main factor affecting the soil CA activity. The soil CA activity increases with the plant root depth due to the CO2increases along with the soil depth.Moreover, karst landform is another important factor that affects the soil CA activity. For example, in the Yaji karst experimental site, the soil CA activity is controlled by the physiognomy character due to the weathering product of carbonate rock and organic matter migration from the bealock and piedmont slope to the karst depression. So, the soil microbe will be assembled, which lead to the soil CA activity in 20 cm layer at depression is 0.782 U/g and higher than those at the bealock and piedmont slope. At last, we also need to consider the effect from the change of sample sites. For the future comparison, the samples should be collected at the border of the same site. Then, the research can provides a certain theoretical basis for further study on the role of soil CA activity in karst processes.

The effect of rocky desertification on the soil’s organic carbon storage in karst peak cluster: A case study in Yanbei town, Yingde City, Guangdong Province

WEI Xinghu, XU Xizhen, LEI Li, ZHOU Hongyan, LI Zhongyun

2013, 32(4): 371-376.

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In order to analyze the effect of rocky desertification on the storage of soil organic carbon, sample plots with different degrees of rock desertification in a typical karst peakcluster in the Tangbian village, Yanbei town, Yingde City, the north of Guangdong Province are selected in this paper, and a new index of unit area soil organic carbon is adopted in the analysis on the effect of rocky desertification process to the organic carbon storage. The results show that: (1) The thickness of soil and standing biomass decreased significantly and the rock coverage increased significantly in intense rock desertification，but the difference are not significant between potential, slight and medium rock desertification in soil thickness, standing biomass and rock coverage. (2) Obviously, organic carbon content per unit of soil weigh is highest in intense rock desertification plots. It is higher in medium than in slight rock desertification plots, and it is higher in slight than in potential desertification plots, but the difference is not significant between medium, slight and potential rock desertification. (3) The soil organic carbon content in 10-20 cm soil depth is lower than that in 0-10 cm. Water and soil losing leads rocky coverage increase and only a little soil remain in the fissure of rock, those micronegative relief can capture organic matter, that may be the major cause for the increase of soil organic carbon in intense and medium rock desertification. (4) The soil organic carbon content per unit area of in medium, slight and potential rock desertification is 49.23, 47.9 and 29.4 times of that in intense rock desertification. (5)The rock coverage is the main factor that impacting the karst ecological system. There is significant negative correlation between the rock coverage and the ground biomass, between the rock coverage and unit area of soil organic carbon, and between the rock coverage and thickness of soil. Highly adaptive plants in karst area can weaken the effects on soil organic carbon by rock desertification.

Transport process of arsenic in karst subterranean stream and analysis on the influence factors: A case in Lihu subterranean stream of Nandan county, Guangxi

ZHANG Liankai, , YANG Hui

2013, 32(4): 377-383.

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The arsenic pollutants generated by the arsenic industries and mining enterprises in karst area flow into subterranean streams and contaminate groundwater easily because of the unique hydrogeological characteristics of karst area, which is a serious threat to the water ecologic security and local residents’ health. In order to elucidate the geochemistry reaction mechanisms of arsenic in karst subterranean streams, the Lihu subterranean stream in Nandan county, Guangxi Province, Southwest China, is selected for the study. The main outcropped lithology in the Lihu subterranean stream catchment is Carboniferous Triassic limestone and the karstification rate is 31.67%. Arsenic species, sediment physical chemical properties and hydro-chemical characteristics of the water are analyzed by inductively coupled plasma mass spectrometer (ICP-MS), X-ray fluorescence spectrometer (XRF) and plasma spectrometer (ICP) respectively. The results show that arsenic concentration in the Lihu subterranean stream is high and it is closely related to human activities. The content of As (III), higher than As (V), occupies 53 % of the total inorganic arsenic in the Lihu subterranean stream due to the low redox environment, which increase the arsenic ecological risk in this region. The contents of total arsenic and As (III) as well as As (V) are attenuated by 51 %, 36 %, 59 % respectively in the underground river. Correlation coefficient analysis calculated with SPSS indicates that sediment Fe, sediment Ca, sediment organic matter, sediment Mn and water Ca2+ are the positive factors that promoting the deposition of arsenic from water. While water Cl-, SO42- and HCO3-, negatively correlated with arsenic in the water, do not facilitate to absorb arsenic. Compared with other water bodies, such as Quaternary groundwater, surface rivers and lakes waters, Ca and HCO3-, turn out to be the important factors for mobilization and transformation of arsenic due to the high calcium and bicarbonate content in karst water. Therefore, karst hydrogeological characteristics should be considered during arsenic contamination treatment in karst groundwater.

Application of fuzzy mathematics in risk evaluation in geothermal resources exploration in karst reservoir: A case in mountain type karst thermal storage in Chongqing

YANG Hualin, LI Minglun, LIU Bangxian

2013, 32(4): 384-390.

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Geothermal resources of karst reservoir are rich in Chongqing, belonging to the mountain type. The karst thermal reservoir, stripped in shape and distributing independently in the thermal field, is located in both wings beside 23 high uplift anticlines and 1-2 km from the axis of the anticlines in the city. The geothermal resources exploration has a long history, but there are risks. In this study, in order to quantitatively or semi-quantitatively evaluate the risk of the exploration a risk assessment model is established with the fuzzy comprehensive evaluation method. The model contains 9 risk factors: the opening degree of thermal reservoir structure, thermal storage structure, alley cutting degree, geophysical prospecting effect, buried depth, thickness of geothermal reservoir, thermal reservoir strata dip angle, thermal anomalies and thermal reservoir layer. Each risk factor can be divided into three levels, including small, medium and big risk level. Quantitative processing is carried out for this model. Comprehensive evaluation of geothermal resource exploration risk with fuzzy mathematics on 23 high uplift anticlines, 46 high mountain uplift karst geothermal fields (a relatively independent geothermal field on each legs) and 79 geothermal units in this city was performed. The evaluation results indicate that there are 18 units in small risk, 42 units in medium risk and 19 units in high risk. The geothermal field with small risk generally has large heat reservoir catchment’s area and good recharge runoff circulation conditions, with roof heat reservoir being buried 1 000-1 800 m deep, thermal reservoir thickness bigger than 300 m, thermal reservoir strata dip angle being 25-40°, and deep fissure developed, such as the evaluation unit of Xishan anticline at the northern section of the west wing. The geothermal field with high risk has smaller catchment’s area and poor recharge runoff circulation conditions, with roof heat reservoir being buried more than 2 500 m deep, thermal reservoir thickness smaller than 200 m, thermal reservoir strata dip angle <20° or ≥40°, and deep fissure undeveloped, such as the evaluation unit at the southern section of the Xindianzi anticline. The geological characteristic of geothermal field with medium risk is between the two. The evaluation results have nicely reflected the risk state in exploration for the geothermal resources in the karst heat reservoir in Chongqing.

Artificial neural network simulation to zero flow of the Heilongtan spring groups in Lijiang

ZENG Cheng, YANG Rui, YANG Mingming, HU Junchun, WU Guihua, FAN Yuhong

2013, 32(4): 391-397.

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Zero flow of the Heilongtan spring group that is famous scenery in Lijiang, Yunnan Province frequently occurs recently, which severely threatening the sustainable development of Lijiang tourism. In order to know the real reason for zero flow of the Heilongtan spring group and its occurrence regularity, hydrogeological conditions and correlation between precipitation and zero flow of the spring group are analyzed systematically, and a simulation based on artificial neural network model is made also. It is found that the Heilongtan spring group is an incomplete-drainage overflow karst spring at the piedmont formed by fractures. There is causality between the annual precipitation deficit and the zero flow of the Heilongtan spring group. Finally, a BP artificial neural network model with 6-13-3 network topology of the Heilongtan spring group’s zero flow is established. The model uses antecedent precipitation, air temperature and humidity as input vector parameters to simulate different conditions of the Heilongtan spring group’s zero flow. Training samples come from data from 1953 to 2002 , and testing samples come from 2003 to 2012 in the model. At last, it is found that the testing results are coincide with real situation to great extent.

Hydrogeologic features and influence factors of zero flow of the Heilongtan spring group in Lijiang

KANG Xiaobo, WANG Yu, ZHANG Hua, CAO Jin

2013, 32(4): 398-403.

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Water from the Heilongtan spring group is one of the main sources for living, landscape and the service in the old town of Lijiang. In recent years, the amplitude of the spring group flows between wet and dry period is increasing. Seasonal or annual drought event is occurred when in drought or extreme drought years. Since August, 2011, the Heilongtan spring group’s flow has reduced significantly. The monthly average flow has reduced from 0.695 m3/s to 0.186 m3/s. And zero flow once occurred on January 21, 2012. On June 13, 2013, the spring group is still zero flow. In this paper, karst water system of the Heilongtan spring is analyzed. It is considered that the main reason of zero flow is less precipitation. While both of the ecologic environment destruction in the recharge area and the exploitation of groundwater also aggravates the setting off frequency of the Heilongtan spring. On this basis, some measures are put forward in the paper, such as improving the water conservation function of recharge area, strengthening the control and management of water resources, managing the water conservation district according to law strictly.

Analysis on stability of ecologically restored slope in Qianlingshan, Beijing

ZHANG Huixu, WANG Xiaolie, WANG Hongcai, GUO Binbin, ZHU Linxin, ZHAO Weihua, LI Awei, SUN Dongsheng, MA Yue

2013, 32(4): 404-410.

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The analysis on high-steep rocky slope stability is a research focus for a long time, because it is considered as the reason why geological disasters occurres, such as slope instability and landslide. Ecological restoration of slope is an urgent issue that can improve environment but may reduce the stability of the whole slope system in some extent. The stability of the ecological slope in Qianlingshan, west suburb of Beijing is analyzed with nonlinear FEM strength reduction method. The interpretation of geological penetrating radar surveying refers to that the rock slope consists of isotropic limestone without obvious fault. The numerical modeling is based on the parameters by rock mechanical experiment, combined with the internal structure of rock mass measured by geological penetrating radar. The safety factors and plastic area distribution and deformation contours are obtained under different load conditions. The result shows that the safety factors are 17 and 12.5 and 5 and 2 respectively on dry natural slope, dry ecologically-restored slope and saturated natural slope as well as saturated ecologically-restored slope. And that the deformation of slope are biggest on the foot of slope and the middle and lower parts of ecological band, the potential sliding surface mainly extends towards the top of slope along the plane of 45° dip angle. Thus, the basal slope and the middle and lower parts of the ecologic zone are the major reinforcement places and the reinforcement measure should be anchor rod fixation and effective water drainage.

On the stability of slide type crag in Wu gorge bank slope，Yangtze River: A case study in Wangxia

HE Xiao, CHEN Hongkai, ZHAO Peng, LIU Li

2013, 32(4): 411-418.

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Crag is one of the major geologic disaster in the Three Gorges Reservoir Region, forming serious threaten to human life and property and to the navigation safety of the river way of the Three Gorges Reservoir Region. As the slide type crag, accounting for 60 %-70 % of the total crags, it is of significant meaning to get clear the failure mechanism of the slide type crag for scientific forecast, prophylaxis and treatment in the Three Gorges limestone area. In this study, it is found that under the control of the geologic structure of paralleled anticline ridge and syncline valley in east Sichuan, the crag is quite developed in the horizontal interbed of limestone and shale or mudstone at the Hengshixi anticline ridge bank slope.The X-Ray diffraction analysis on the soft foundation mineral of the crag rock indicates that the chlorite, mica and montmorillonite have high layered silicates minerals, low shear strength, thus is easy to slide along the potential failure surface in the direction of the major structural surface and leading to the whole rock body sliding down. According to the failure mechanism of the failure process is divided into 4 phases in the paper, i.e. the phases sliding fissure emerge, tensile crack expand, unstable rock sliding and disintegration of rock body. Furthermore, the stress expression of two groups of structural plane that forming the slide is derived in the paper and the mechanical model for analyzing the crag’s stability is established. This method is applied in the analyses on the stability in Wangxia unstable sliding rock, and the results show that the stability coefficient is 1.19 under natural conditions, which belongs to the basic stable rock mass. While, the stability coefficient decreases subsequently as the water head in fissures increases under saturated condition. The research result is helpful to improve our knowledge on stability calculation of the unstable rocks with soft foundations in the Three Gorges area.

Features of the shallow karst development and control of karst collapse in Wuhan

LUO Xiaojie

2013, 32(4): 419-432.

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In order to reveal the shallow karst development laws and provide the basis for prevention and control measures of karst collapse disaster, the development characteristics of covered karst in Wuhan are studied by the means of comprehensive analysis and mathematical statistics method. There are 6 independent carbonate rock belts with the trend of NWW to SEE. According to the characteristics of the overlying carbonate rock covers, 5 karst geologic structure types are divided. The shallow karst types in Wuhan are mainly solution fissure, grike, grooves and sink as well as small caves. The cave encountering rate of borehole (ECR) is 46.0 %-50.1 %; the linear karst rate of borehole (LKR) is 5.93 %-6.00 %. In shallow karst belt, the height in 1/3 karst caves is less than 0.6 m, a half less than 1.0 m, 90 percent less than 3.0 m. The depth from bed rock surface to cave roof in 1/3 karst caves is less than 2.5 m, a half less than 4.5 m, 90 percent less than 12.5 m. The fillings of karst cave are mainly clay with limestone detritus and block. And 70.8 % of karst caves is fully filled, about 20 % is unfilled, less than 8 % is half filled. The average depth below bedrock surface of fully filled caves is 5.13 m, half filled cave 5.71 m, and unfilled 7.69 m. From the fully filled to half filled or unfilled caves, the depth below bedrock surface of karst cave roof gradually increases, reflecting the caves are filled downward from the top and the fillings are from overlying cover layers. The shallow kart in Wuhan belongs to the “vertical seepage karst zone” and is the result of vertical seepage action. On vertical section, the shallow carbonate rock can be divided into strongly developed karst upper zone and weakly developed lower karst zone. In plane view, 3 risky areas of collapse can be divided, namely the high, the middle and the low risk area. The prevention and control principles of karst collapse disaster are different in different risk areas. High risk area is the focus of karst collapse disaster prevention, and the basic principle is to prevent the overlying sand erosion. The prevention and control principle of the middle risk areas is to protect the integrity of the old clay or red layer. In low risk area, we should pay attention to the soil caves located in the interface of old clay and carbonate rock far from the city. The governing works should be based on the karst geologic structure and it should be guided by the principles in make relevant governing measures. Moreover, weak karst zone should be reasonably selected and utilized in engineering construction.

Formation conditions of the karst collapse and treatment technology at raker’s substrate in a karst mine

WANG Jun, ZHAO Qia

2013, 32(4): 433-436.

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The raker’s substrate, situated in a karst mine in southern China, is composed of silty clay, pebbles and limestone. In June 2009 a 3m long and 2m wide collapse took place, causing the raker being buried in a cave. The collapse seriously threatens the safety of the surrounding tailing depot and cement tank. Analysis and simulation show that the collapse of the substrate is mainly led by strongly developed karst fractures, groundwater table fluctuation and long-term water scour that resulting bedrock surface soil particles being brought out and then causing the cave to collapse. The former treatment for collapse is backfill generally, but re-collapse is frequent. In view of the case, the mud hole rotary jet grouting approach in the treatment is adopted this time. That is to say, accelerator of different ratio is added to the cement paste according to the depth firstly, and then, putting the accelerator-added cement paste rapidly into the hole and cutting the surrounding soil layer by high pressure and high speed revolving, which leading the pure cement paste turning into cement clay slurry. Under high pressure, the slurry can split off the soil layer, thus, the cave entrance can by blocked off rapidly and the soil layer be consolidated. Test results show that this method can not only seal the passage of cave and karst fractures and reinforce the soil very well, but also has mature technology and lower cost than grouting. It is suitable for application in karst mine. 

Preliminary thinking of quantitative research on the mechanism of karst collapse

JIN Xiaowen, CHEN Zhihua, ZENG Bin, ZHANG Wenhui, SHI Tingting

2013, 32(4): 437-446.

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The karst collapse, as most widespread geological disasters and environmental geological problems in karst areas in the world, has had a serious hazard for the development of human society and the construction of engineering projects as well as other aspects. Since the 1970s, both domestic and foreign scholars have done a lot of works on fields as development regularity, distribution characteristics, collapse cause, genetic mechanism, survey techniques, control measures, monitoring and forecasting as well as simulation of karst collapse, which have achieved abundant research results. Being buried deep below the surface and difficult to be detected and probed, karst collapse is of the following features as sudden, concealment, multiple influence factors, uncertainty and ambiguity, so the unified, systematic and authoritative theory and understanding on the mechanism and quantitative prediction of karst collapse are still in gradually perfecting process. Based on the mechanism of karst collapse status and development trend, from the perspective of complexity science, the basic scientific questions of the mechanism and quantitative prediction as well as quantitative study methods are discussed in this paper. On the basis of referencing multitechnical methods from several related subjects, in order to enrich karst collapse mechanism quantitative research, this paper has methodized the contents of quantitative research, explored the quantitative research methods, analyzed quantitative research techniques and put forth research approaches.

Diagnosis of eco-environment quality in Wujiang River watershed based on RS and GIS

YI Wuying, SU Weici

2013, 32(4): 447-452.

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The Wujiang river watershed lies on the Yunnan-Guizhou plateau slope, is the largest branch of the south bank of the upper Yangtze River, has unique geology and geomorphology and widely developed karst landform. Owing to long-term irrational exploitation and utilization on a large scale, the river watershed is confronted with serious soil and water loss and outstanding desertification problems. By using the TM images of the Wujiang river watershed in 2010 as the main information source, the paper, takes 41 regions (cities, counties and districts) in the Wujiang river watershed (in Guizhou province) as study area, extracts land use information and landscape pattern indexes based on RS and GIS, constructs the evaluation index system of the ecological quality in the Wujiang river watershed, determines the index weight by entropy method, combines with GIS graphic overlay method, evaluates the ecological environment quality situation of the 41 regions. Based on the above works, the ecological quality in the Wujiang river watershed divided into four levels: good（Ⅰ）, relatively good（Ⅱ）, general（Ⅲ） and poor （Ⅳ）. The research result shows that the area of good, relatively good, general and poor ecological environment quality in the Wujiang river watershed in 2010 year is 7 710.8 km2, 26 208.3 km2 15 704.3 km2 and 16 106.1 km2 respectively, and the weight is 11.7 %, 39.9 %, 23.9 % and 24.5 % respectively. On the whole, the ecological environment is of inferior quality in northwest and southwest Wujiang river watershed, but the ecological environment quality is better in the northeast. And the ecological environment quality in different regions has obvious differences.

Ecologic land protection and development of new urban district in karst mountain：A case study in the Jinyang new district

FENG Yuansong, YANG Qingyuan

2013, 32(4): 453-461.

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It is of great significance to study the protection and planning of ecologic land in the process of town construction in karst mountain. The Jinyang new district is located to the northwest of the old city of Guiyang City. It has irreplaceable advantage in promoting regional economic development in the north of Guiyang City.This article chooses the Jinyang new district as the site of the case study, to explore the ways and means of protection for ecologic land and provide a reference for the urban ecologic planning and construction in karst mountain. In the Jinyang new district, ecologic ideas and measures as the ecologic space controllability, the green space system planning and layout, the water spatial planning and the ecologic land use style are used to effectively protect the ecologic land. The forest land increased from 10.22 % in 2001 to 22.19 % in 2010，the water remained at 2.09 % in 2010. Changes in the number and spatial distribution of ecologic land for the recent 10 years after the building of the Jinyang new district also reflect the effectiveness of the measures adopted in the building. The greatest effort has done for the protection of woodlands and water bodies. There remains a considerable amount of green areas and water bodies plot, becoming corridor of green lands and rivers. The case study in the Jinyang new district shows that, in city construction in karst mountain, it is necessary to give full consideration to planning, protection and development of the ecologic land use.

Distribution of land use pattern at different terrain gradients in karst area based on GIS: A case in Benxi village,Youyang county

LIU Ling, WANG Yong, XIE Shiyou, LONG Mi, PENG Anqi, HAN Yaowei

2013, 32(4): 462-471.

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Studying land use change and its spatial expansion along the terrain gradient is of great significance for identifying the direction of land use change and its sustainable use. In this paper, a case study is conducted in Banxi village, Youyang county, Chongqing City. The regional differentiation in natural conditions is quite obvious, the topographic relief is relatively great, and comprehensive and multiple karst landforms are quite developed in the area. The major aims is to study the characteristics of land use pattern in the region and provide reference for adjusting land use structure and ecologic reconstruction in similar karst areas. The land use data in 2002 and 2011 in Banxi village are obtained by means of RS and GIS techniques, on the basic data of the topographic map(2002), land use status map (2002), SPOTS-5 remote sensing satellite images(2011). According to the above study and terrain index, distribution index and comprehensive land use degree index, changes of land use pattern in 2002 and 2011 in Banxi village of Youyang county is studied and the land use degree at that terrain gradient of the studying area is quantitatively analyzed in this paper.The results show that ,(1)the building land and cultivated land are obvious predominant at low terrain niche; the interval of the preponderant terrain niche obviously increased in woodland, and the woodland changes into uniform distribution from clumped distribution;(2)The preponderant terrain niches of the building land, cultivated land and water area as well as unused land generally remained stable during the study period. According to the quantitative expression of land use degree at terrain gradient, terrain niche interval is divided into three sections, i.e. 1-22, 23-47, 48-50, mainly representing the building land and cultivated land level, the forest land level, the barren land level, which occupies 54.23 %, 40.43 % and 5.34 % of the total study area respectively. Overall, the expansion forest land enables rocky desertification at high terrain to be controlled to some extent. In order to realize reforestation and ecological environment improvement quickly, dominant tree species at scrublands should be fostered and economic forest trees should be inter-planted in still preserved slope cropland focuses in 2011.

Variation characteristics of the radon’s concentration and protection to the harm in the Xueyu cave, Chongqing

YANG Xiaoxia, ZI Tao, CHEN Bingqing, XIANG Xu, WANG Xiaoxiao

2013, 32(4): 472-479.

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PRM-2100 (Radon RAE Progeny) is used to measure the equivalently effective concentration (EECRn) of radon’s daughter in the Xueyu cave for 12 months. The average EECRn is 2 135.7 Bq/m3. Take the balance factor as 0.5, the average concentration of radon in the Xueyu cave is 4 271.4 Bq/m3. The EECRn is higher in summer and lower in winter. The EECRn in each layer is different, the higher the layer, the higher the EECRn. The outside temperature can affect the EECRn’s distribution in cave environment. The effective dose there to tourists is only 0.02 mSv/a, only amount to 1.54 % of the threshold value (1.30 mSv/a) estimated by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), so it is unharmful dose to the public and will not affect the health of tourists. The effective dose for tourist guides, security guards and photographer is 7.69 mSv/a, 11.96 mSv/a, 59.48 mSv/a respectively, which are higher than the UNSCEAR estimated annual effective dose to the public. These effective doses should be received sufficient attention. The protection measures for tourism caves include reasonable arrangement for staff working hours and annual maximum working hours in the cave, popularization the knowledge about radon hazards and enhance the awareness of selfprotection for the cave staff. In the high radon concentration area, shield protection or air purifier at appropriate position should be installed, and at the same time the analysis and monitor to the concentration of radon and its progeny should be strengthened.

The self-potential method and its application in karst collapses

CHEN Yixiang, GAN Fuping, LU Chengjie, WEI Jiyi

2013, 32(4): 480-486.

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The groundwater that flowing through soil cave or karst collapse pit destroys the balance of positive and negative charges in the ion double electrode layer between the solid - liquid interface in soil, which induces spontaneous polarization of underground medium (soil layer) and forms downward natural electric field. The soil cave and karst collapse cause self-potential negative anomaly that looks like concentric ring in the plane view and cause minimum value anomaly in the profile. The self-potential gradient appears zero crossing point anomaly in the profile and appears "butterfly-shaped" anomaly that is negative-positive symmetrical in relation to the symmetry axis of zero value line in the plane. The main interference factors of natural electric field in karst region are industrial stray currents, spontaneous polarization electric fields coming from underground metal pipe/line, natural electric fields produced by ascending springs or descending spring, mountain potential fields and natural electric fields of Carbonaceous limestone, etc. According to the characteristics of the interference factors led by self-potential in karst area, avoiding method, eliminating method and online monitoring method are put forth in the paper in order to eliminate the interference factor. The self-potential method has been successfully applied in the karst collapse area in Jili Village, Laibin City, Guangxi. The collapse is located inside the Guilin-Laibin fault zone and on the sides of the Datoushan syncline axis of the secondary fold between the transition zone of the east limb of the Pingtang anticline and the west limb of the Laibin syncline. The landforms there are characterized of karst accumulation and residual peak pimple plain. The overlying layers are gravel silty clays of the Quaternary eluvial and slope-alluvia, the underling rocks are mainly thick bedded limestone with dolomitic limestone interlayer of the Middle Carboniferous (C2). A set of NNE trending fault develops parallel to the fold axis accompanied by a group of the NWW trending tension-shear fault in the nearly vertical fault direction which cuts and offsets the main NNE faults. The broken rocks and karst features as well as karst collapse are widely spread and quite developed in fault fracture zones. The actual measured self-potential curve has minimum value anomaly around the center of the subsidence area. At the same position the self-potential gradient profile has zero value anomaly. Vertical fissures on the ground are quite developed. And the fissures in the abnormal regions detested by self-potential method are consistent with the trend of the conjectural fault fracture zones and the direction of the underground river. Collapse deposits, caves and fault fracture zones are exposed at the same position by hydrogeologic monitoring borehole, which verifies the properties of selfpotential anomalies have been discussed above.

2013 Vol. 32, No. 4

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