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20 October 2019, Volume 33 Issue 5 Previous Issue    Next Issue

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Application of Combined Boring Methods in Bored Reinforced Concrete Piles in a Subway Station Project in Wuxi City HUANG Zhenbo 2019, 33 (5):  533-535.  Abstract ( 811 )   Save Currently, the drilling and installation of the bored and castinplace reinforced concrete piles include positive circulation with slurry, reverse circulation with slurry, impact boring and allflight auger boring methods. The selection of an appropriate drilling method should comprehensively consider factors such as, subsurface conditions, environmental considerations, construction schedule and cost. The feasibility of positive circulation, reverse circulation and all flight auger boring methods, quality of borehole, and efficient of borehole installation and cost are comparatively evaluated. It is concluded that the reverse circulation method for upper cohesive soils and all flight auger boring method for the lower gravelly soils are the most cost effective combination approach. Related Articles | Metrics

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Dynamic Compaction under High Vacuum Condition in Strengthening of Dredged Soils DU Yinghui1, CHEN Lei2, ZHANG Yaoyu3, MA Kun3, SHEN Yupeng3 2019, 33 (5):  536-540.  Abstract ( 540 )   Save This paper introduces the principles and key aspects of dynamic compaction under high vacuum conditions from a case history of strengthening of dredged soil in Caofeidian area. The applicable soils and condition for dynamic compaction and vacuum surcharge methods are reviewed separately. It was decided to use the combination of dynamic compaction and vacuum surcharge methods for the soil improvement. The earth pressures and excess porewater pressure changes at various depths are evaluated during the construction. The results indicate that, the dredged soils are improved by the combinaton of dynamic compaction and high vacuum surcharge methods could have the advantage of good improvement, cost effective and construction schedule saving. The optimum time interval between the two passes of dynamic compaction is 9 days so that the pore water pressure between two adjacent compaction craters could be effectively dissipated. Related Articles | Metrics

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Soil Strengthening Jacking a Rectangular Subway Station Aprons Under Saturated Groundwater Conditions WANG Kai1, ZHANG Xiaochuan1, XU Xin2, CHEN Baoguo2, WANG Chengpeng2 2019, 33 (5):  541-543.  Abstract ( 454 )   Save Box culvert jacking has been widely used in the urban utility projects. The strengthening of surrounding soils is critical to the success and quality of the entire jacking project. This paper presents a case history of jacking a rectangular subway aprons of D2 station at Xinan Park of No. 12 metro line in Shenzhen. The principles of strengthening of jacking pit, receiving pit and surrounding zone are introduced. The soil strengthening in the jacking process was numerically simulated and the ground subsidence during the entire jacking process was obtained. The results indicate that, with the jacking process, the ground surface settlement increased until the No. 14 segment was installed. Thereafter, the ground subsidence became stable. The maximum measured ground settlement was 16 mm and this settlement value satisfied the code requirement. Related Articles | Metrics

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Installation of Uplift Resistance Ground Anchors in Soft Rock TANG Yangui, YUE Dachang, JIA Xinyuan 2019, 33 (5):  544-546.  Abstract ( 389 )   Save Under the dry-wet cycles, the argillaceous rock in Chengdu area demonstrates softening and slaking properties and these properties have adverse effect in the installation of ground anchors in the soft argillaceous rock. This paper summarizes and evaluates the conventional ground anchor installation methods in soft argillaceous rock. A new installation procedure starting from foundation excavation dewatering, treme concrete at bottom slab (hardening of working platform); borehole drilling (drilling debris collection and dust control methods are applied); borehole flushing; to waste water collection and sedimentation has been developed. This new anchor installation procedure has been successfully applied in the practical projects. The devices for the debris collection and dust control as well as the borehole flushing are simple for the manufacture and for the installation. These new devices have the advantage of environmental and construction personnel friendly, water and construction schedule saving, and cost effective. Related Articles | Metrics

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Stability Analysis of the Ash Dam of a Power Plant LEI Wanxiong1, LI Guangyu1, WANG Hongming2, YI Zhe2 2019, 33 (5):  547-549.  Abstract ( 496 )   Save Evaluation of the stability of the ash storage dam is an important aspect of the safe management of ash storage yard as well as the safe operation of the power plant. This paper presents the limit equilibrium analysis method applied on the ash storage dam stability evaluation at the time when the dam reaches its full storage capacity. The results indicate that, under the current reservoir pool level and high pool level, no seepage water could be found at the downstream side of the dam slope and the seepage related damage is not likely. The safety of the current dam under current and the full storage conditions are stable and the safe operation of the dam is warranted. Related Articles | Metrics

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Impact of Blasting Induced Vibration on the Safety of an Existing Tunnel ZHOU Linli, XU Jun, YAN He 2019, 33 (5):  550-554.  Abstract ( 456 )   Save During the construction of Tianchangling Tunnel, the blasting induced vibrations were monitored to ensure the safety of an adjacent existing tunnel. The primary vibration frequency and duration were evaluated. The optimum explosive dosage was determined throughout the onsite blasting data processing so that the vibration at the existing tunnel met the code requirement. For the millisecond delayed blasting method, the relationship of the blasting vibration velocity fitted with the total explosive dosage found to meet the requirements of this project. Due to the complexity of the geological conditions and the length of the tunnel construction, the range of primary vibration frequencies of the blasting induced vibration are very wide. Under the same rock mass classifications, the peak vibration velocity at the toe of the existing tunnel with various distance to the center of blasting is evaluated for the safety of the existing tunnel. Related Articles | Metrics

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Characteristics of Granitic Saprolite Soil Slopes and Landslide Prevention in Tianzhu Mountain JIA Sen1, SHI Guodong2, XU Yingsheng1, ZHANG Tao1 2019, 33 (5):  555-557.  Abstract ( 418 )   Save The granitic soil samples were collected from the saprolite soil slopes of Tianzhushan area and their grain size distributions were laboratory tested. The results indicate that the ununiform coefficients were obviously high. The samples were wellgraded and the sizes in the granular soil samples varied significantly. Under heavy precipitation condition, the saprolite soil slopes were easily damaged by the erosion. It is therefore, the slope protection becomes very important and the biological slope stability remediation measures are also proposed. Related Articles | Metrics

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Application of Vacuum Preloading Combined with Surcharge Method in a Power Plant 2019, 33 (5):  558-562.  Abstract ( 471 )   Save With the rapid development of China’s infrastructure construction, the requirements for the soil improvement of the complex sites are getting higher and higher. The traditional vacuum preloading method combined with the conventional surcharge preloading method have the advantages of construction schedule saving without compromise the construction quality. The combined method has been successfully applied in the highway, railway and harbor projects and it is rarely applied in the power plant construction. This paper presents a case history of the application of combination of vacuum preloading and conventional surcharge preloading methods in the soil improvement in the coastal power plant construction in southeast China. The paper also introduces the predesign testing, soil improvement design, key construction sequence and soil improvement quality assurance. Based on the Darcy’s law, the efficiency of the combination method could be explained by the seepage field induced by the vacuum dewatering. Related Articles | Metrics

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Application of the Rotary Excavated Concrete Piles in Deep Saturated Sand Layer WANG Guanjun1, YU Chengqing1, LI Tingjie1,2 2019, 33 (5):  563-566.  Abstract ( 489 )   Save With the rapid development of construction industry, the application of rotary excavated concrete piles in the engineering projects is more and more popular. With the time, the installation technology becomes more and more mature. However, when drilling in the deep and saturated sand layers, the rotary excavated concrete pile construction often encounters with various problems and frequent accidents, and results in the increased construction cost and reduced efficiency. Combined with the problems encountered in the construction of deep foundation with a deep and saturated sand layer, the likelyhood of borehole caving zones were summarized through construction and the correspondent measures were implemented so that a large construction cost and schedule savings could be achieved. Related Articles | Metrics

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Compressibility of Silty Fine Sand in Yinchuan Plain SHEN Suping, MA Xiaoxia, CUI Zizhi, SUN Changhao, XU Hanbao, YAN Hao, YANG Longbo 2019, 33 (5):  567-570.  Abstract ( 544 )   Save The shallow buried and thick silty fine sand is widely distributed in Yinchuan Plain. It is the main load bearing layer for building structures, and the mechanical properties test data for engineering reference are not enough. Therefore, considering the two important factors such as the dry density and the saturation, the statistical orthogonal test scheme was designed in this study. The compressibility of silty fine sand in Yinchuan Plain was studied by means of onedimensional tests by using automatic pneumatic consolidation apparatus. The influence factors and mechanism of each factor were investigated, the significance was analyzed, and the empirical correlation with the compressibility was established. The results show that the compressibility of the silty fine sand is low, and the maximum value of  a1-2 is no more than 0.2 MPa-1within 1~7 m depth of Yinchuan Plain, which is a mediumlow compressibility soil. With the increase of dry density, the compressibility decreases nonlinearly, and the change of compressibility decreases. With the increase of saturation, the compressibility increases nonlinearly, but the change of compressibility decreases. For a1-2, the effect of dry density is very significant, and the effect of saturation is significant. The order of significance is dry density and saturation from high to low. Increasing dry density is a very effective measure to reduce the compressibility of Yinchuan sandy soil, while increasing saturation has a better effect on improving the compactness of Yinchuan sandy soil. The compressibility model has good correlation and high significance, which is of practical significance to the prediction of compressibility of silty sand in Yinchuan Plain. Related Articles | Metrics

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Influence of Dry Density on the Fracture Development and Strength of Expansive Soil under Wetting-Drying Cycle LIU Yukun, ZHU Shouzeng, WANG Chunguang 2019, 33 (5):  571-574.  Abstract ( 492 )   Save Expansive soil cracking induced by the expansion and contraction under the wetting-drying cycles is a common engineering problem in the geotechnical construction projects. Remolded expansive soil samples were laboratory simulated by the impact of wetting-drying cycle under natural conditions. The fracture development patterns were digital imaging processing technique. Under various initial expansive soil samples, the cracking ratio, total cracking lengths and average width of cracks were quantitively extracted and processed. In additional to the digital crack processing and evaluation, the direct shear tests were conducted on samples underwent the wetting-drying cycles. The results indicate that, the initial moisture content and initial dry density are the major factors affecting the cracking development. Higher initial dry density sample developed cracks at earlier stage and resulted larger cracking ratio. Number of wettingdrying cycles and initial dry density had also affected the sample shear strength. The initial friction angle was influenced by the number of wetting-drying cycles and the cohesion value reduced with the increase of wetting-drying cycles. Related Articles | Metrics

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State of the Art Review Soil Thermal Conductivity Studies CHEN Bo1,2, ZHANG Fen3, MA Huilong1, WEN Songsong4 2019, 33 (5):  575-578.  Abstract ( 681 )   Save In recent years, with the rapid growth of economy and energy consumptions, the development and utilization of underground space and geothermal energy have attracted a wide attention of researchers worldwide. The thermal properties of rock and soil play a vital role in these studies. Specifically, the thermal properties of soils include thermal conductivity, thermal diffusivity and specific heat capacity. As one of the most important parameters of thermal properties, the thermal conductivity not only determines the heat transfer in soil, but also affects the distribution of temperature and humidity fields. According to the research status at home and abroad, the practical significance of studying thermal conductivity of soil is introduced, the heat transfer mode in soil is investigated, the main factors affecting thermal conductivity of soil are summarized, and the research direction and development trend of thermal conductivity of soil are put forward. Related Articles | Metrics

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Rock Burst Failure Characteristics of Deep Circular Caverns under Various Lateral Pressure Coefficients XIANG Geze, ZHU Wenhua, LIU Chang, WANG Zhide, XIA Yuanyou 2019, 33 (5):  579-583.  Abstract ( 381 )   Save 〖WT〗 In order to investigate the rock burst failure characteristics of the deeply buried caverns under the rock mass with various rock stresses, a series model tests were conducted by using an inhouse developed rock burst model test device. The macroscopic failure phenomenon of the rock burst and the strain of surrounding rock were evaluated. In addition to the model tests, the influence of different lateral pressure coefficients on the rock burst failure mechanism and the failure zone of rock mass were numerically simulated and analyzed. The results show that the deformation pattern of the surrounding rock of the cavern is basically symmetrical, when the lateral pressure coefficient λ is 1/3, the both walls of cavern are the main areas where the rock burst failure occurs, and the failure range is about 20% of the cavern diameter. The macroscopic failure zone ranges of the model tests were generally consistent with the numerical analysis obtained failure zones and the influence ranges. With the change of the lateral pressure coefficient λ, the rock burst failure area of the deeply buried cavern also changed and the critical load when the rock burst breaks increased with the increase of λ; when λ=1/3 and λ=1/2, the failure area was mainly concentrated on the both sidewalls of the cavern; when λ=1, the failure area was concentrated on the crest of the cavern, and extends from the crest to the toe of the side walls of the rock cavern. The paper concluded that it is feasible to study the mechanism of rock burst failure under different stress states by the combination of the model tests and numerical analyses. Related Articles | Metrics

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Evaluation of Expansive Rock underneath the Nanjing Fourth Yangtze River Crossing Bridge Site WANG Jianguo, ZHANG Chun 2019, 33 (5):  584-586.  Abstract ( 383 )   Save As a special rock type, the expansive rock is widely distributed in all over the world. The physical and mechanical properties usually change with moisture content. When the expansive rock is developed in between the strength rock layers, the existence of the expansive rock is often ignored and might impose a geo-hazard to the engineering projects. The expansion and contraction in these rock masses change with the adjacent environment and the strength of the rock masses gradually reduce. Due to the difference of mineral composition, structure and sedimental environment, embedment depth and variation of the rock mass thickness, the properties of expansive bedrock are different. The repetitive contraction and expansion characteristics of the expansive rock and their associated fissures are likely result in the damage of building structures above. The study of the engineering properties of expansive rock and their classifications for the engineering purposes are very impotant. Related Articles | Metrics

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Progress on Seepage of Fissured Expansive Soil Research LIU Ruixue, ZHANG Rongtang, WANG Weiwei 2019, 33 (5):  587-590.  Abstract ( 409 )   Save Expansive soil in the repetitive wet-dry cycle, the volumetric expansion occurs by water absorption and contraction when the moisture is lost, and cracks are generated in the soil body. This paper summarizes the process of crack generation: Major cracks are formed, and more secondary fissures are generated, and soil body are separated by various fissures. The development of the fissures is associated with the moisture evaporation rate, gradient of moisture content, and quantity of the moisture evaporation. With the continuous development of measuring instruments, more accurate fissure development can be observed. Imaging processing method is widely used to obtain two-dimensional plane fissure distribution. Spatial fissure distribution can be obtained by processing images and three-dimensional modeling. The review of several fissure seepage models is introduced, and their advantages and disadvantages are discussed. The equivalent continuum seepage model is widely used. Related Articles | Metrics

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Development and Stability Analysis of the Chengjiaba Landslide YANG Cheng1, LI Chunjiang2, QIAO Qianfeng2 2019, 33 (5):  591-594.  Abstract ( 424 )   Save The Chengjiaba landslide site is in Hongguang Division of Jinghe Village, Longcanggou Town, Yingjing County. From the evlation of the geological conditions and triggering factors of the landslide, the mechanism of landslide deformation is analyzed in detail in this paper. The evaluation concluded that the pattern of this current landslide is a traction landslide in the colluvium deposits. The sliding surface is also controlled by the interface between the base and the sliding body, the position of silty clay interlayer in the accumulation body and the groundwater level. Both qualitative evaluation and quantitative analysis predictions are used to determine the stability of the landslide. The evaluation also concluded that the possibility of the landslide slip along the surface outside the highway was not likely. Other potential slip surfaces might not be stable. Landslide remediation measures in the colluvium deposit are also proposed in this paper. Related Articles | Metrics

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Spatial Influence of the Residual Stress in the Deep Excavation under the Unloading Conditions DONG Linbing 2019, 33 (5):  595-599.  Abstract ( 522 )   Save Currently, the influence of dimensional effect of the residual stress in the deep excavations under the excavation unloading condition is evaluated mainly through the numerical analysis, model test and field monitoring, all these approaches are lack of strict mathematical basis. Based on the Mindlin solution of soil incremental effective stress, this paper analyzes the influence of the spatial characteristics of the residual stress in the deep excavation under the excavation unloading condition so that the results can be used to provide guidance’s and reference for the design and construction deep excavations in the municipal engineering. The results show that the residual stress under the excavation unloading condition is beneficial to the stability of the deep excavation with a small ratio of width to depth, this needs to be further verified and optimized in the future practices. Related Articles | Metrics

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Stability and Remediation Analysis of a High Cut Slope in Southwest Mountain Area LI Zhendong, LIU Hong, HU Xuan, MAO Jicheng 2019, 33 (5):  600-603.  Abstract ( 410 )   Save The stability of a high cut slope under three difference construction sequences was evaluated by using the commercial software GeoStudio. The deformation and stability effect in the different cut slope angles are analyzed so that the optimized slope angle and slope stability improvement can be obtained. The results indicated that, slope failure could occur for all three different slope angles. The pre-stressed ground anchor can be used for the slope stability remediation. The analysis results also indicated that the minimum earthwork could be obtained when a cut slope angle of 1：1.3 was used. The deformation of all three slope angles could be reduced after the prestressed ground anchors were applied. The surficial red clay soil layer contributed the major deformation of the cut slope. Related Articles | Metrics

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Numerical Simulation of the Effect of Soil Excavation and Unloading on an Existing Subway Tunnel XU Tengfei 2019, 33 (5):  604-608.  Abstract ( 300 )   Save The existing shallow buried subway tunnel near a large deep excavation site is subjected to both the unloading from the deep excavation and loading effect of the adjacent new building constructions. The subway structures under these lading conditions have the upward movement. This concern is numerically simulated by two different approaches and the soil improvement above the subway structures is proposed. The analytical results indicate that the soil improvement can effectively reduce the potential upward movement of the subway structures.  Related Articles | Metrics

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Testing and Evaluation of the Curtain Grouting at the Right Bank of Dehou Reservoir CHEN Keping1,2, CHENG Weiyang1,2, CHEN Guanjun3 2019, 33 (5):  609-61.  Abstract ( 414 )   Save Based on the hydrogeological and engineering geological conditions of the Dehou reservoir area, the curtain grouting field tests were conducted at the right bank of the reservoir for the mitigation the large quantity of grouting slurry loss that pumping of slurry at various locations. The objective of the insitu curtain grouting tests is to optimize the grouting parameters. The techniques used in the curtain grouting tests are top of borehole sealed, inner circulation, and sectional grouting by plugging from top of the borehole down to the bottom. This paper analyzes the problems encountered during the grouting tests and “lesson learned” suggestions are also provided. The results indicate that the curtain grouting can effectively reduce the seepage in the bedrock. Related Articles | Metrics

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Experimental Investigation on Interface Characteristics Between Pre-Strained Geogrid and Sand Cushion HUA Chao1, YAO Wenmei2 2019, 33 (5):  613-617.  Abstract ( 335 )   Save The interface characteristics between prestrained geogrid and sand cushion were studied through a serious of pullout tests. The experimental program was divided into two parts, the influence factors, such as, normal stresses, cushion thickness and initial strain, on the interface characteristics of prestrained reinforcement were investigated by comparing the results of the comparative analysis. Under the low normal stress condition, the results showed that the prestrained geogrid and the conventional geogrid have little differences on the peak value of tension resistance when the thickness of sand cushion is 5 cm. The tensile stress of the prestrained geogrid is much higher than that of the conventional geogrid and the strain softening phenomenon is becoming obvious with the increase of the normal stress. When the normal stress is 50 kPa, the increase of the thickness of the sand cushion has an improvement to the tension resistance. When the thickness reaches 15cm, the effect is obviously reduced, and the strain softening will occur on the geogrid with a high prestrain level. Finally, the envelope of the shear strength of the interface is obtained by fitting the experimental data. It is concluded that the prestrained reinforcement can significantly increase the coefficient of quasi friction between the geogrid and the sand cushion and reduce the quasi interface cohesive force at the same time and provides theoretical basis for the popularization of prestrained reinforcement method. Related Articles | Metrics

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Experimental Study on Saturated Strength of Cement-Modified Iron Mineral Tailings as Subgrade Material LIU Jiarong1, SUN Zhaoyun2, SU Jianming1, WEI Kun1 2019, 33 (5):  618-620.  Abstract ( 298 )   Save Iron mineral tailings have special physical and hydraulic properties, it can be used for subgrade filling after soil improvement treatment. In order to study the effect of subgrade moisture condition variation on the strength of cement modified iron mineral tailings, the comparative analyses of strength reduction and moisture stability by the unconfined compressive strength and California bearing ratio tests under the immersion conditions. The results show that the cement improved iron mineral tailings have good moisture stability, when the cement content is in the range of 6%~8%, the reduction rate of the saturated strength is less than 15%, and the California bearing ratio value is greater than 100%. The evaluation results can provide reference for the improvement treatment and performance evaluation of iron mineral tailings for the pavement engineering projects. Related Articles | Metrics

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Experiment Studies on the Testing Errors of Silt Particles Using Densitometer Method WANG Bing 2019, 33 (5):  621-622.  Abstract ( 575 )   Save Gradation analysis is a testing method that analyzing the soil particle size distribution and is an important index property for the soil classification. Its accuracy will also affect the subsequent selecting of the soil strength parameters. The densitometer method is often used in the gradation analysis test. The current test specifications all require time consuming soaking and boiling in the preparation of granular soil samples. In this paper, several methods were used to perform the gradation analysis of silty soils. The results showed that the soaking preparation of silty soils had very little effect on the test results, and the soil could be dispersed by direct heating and boiling. Related Articles | Metrics

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Experimental Evaluation of Factors Affecting Slip Distance of Landslide in Loess Soils at Heifangtai, Gansu Province DING Wen1,2, ZHANG Kai1,2, XU Da1,2, ZENG Yu1,2, CHEN Yuan1,2, QI Xing1,2 2019, 33 (5):  623-626.  Abstract ( 427 )   Save Heifangtai is in Yongjing County, Gansu Province.  It is in an area with a long history of irrigation. Loess landslides are widely developed and often occur, which directly poses a geohazard to the safety of villages at the toe of terrace lands. The shear strength of the loess soil slopes with various slope angles and with different moisture contents from Heifangtai were laboratory evaluated. The simulations were studied with soil samples prepared in a constant slope volume and initial moisture content of original soils tested. The experimental landslide body parameters, such as, distance of slide, width of sliding body, thickness and area of the sliding body, were measured under different conditions. The relationships among the degree of slope angles, moisture contents and the landslide occurrence were established. Related Articles | Metrics