During the past several decades it has experienced significant land subsidence in coast area of Linbian and Jiadong Townships of Pingtung County due to ground water overdrawing for fish farms. It has accumulated more than 3 meters land subsidence and has caused serious disaster due to flood resulted from typhoon. After then, it also happened land subsidence issues around Changhua, Yunlin, Chiayi Counties. For mitigating the effect of land subsidence and the caused flooding impact upon society, economy and the vital structure safety, government had proposed land subsidence prevention activities. Since the ground water fluctuations and the strata properties are the important factors of land subsidence, we compared the behaviors of deformation and stress between different aquifers in Changhua, Yunlin, Chiayi and Pingtung Counties from multilayer compaction monitoring wells and water level monitoring wells. And it also gave well understanding of the strata stress-strain situation for estimating the compaction and water level relationship to assist further investigation into the mechanism. These are advantageous providing to government a more efficient proposing in land conservation and reclamation strategy.
Taiwan is lack of water resource. Since the 1960s, the concentrated over-drafting of groundwater for economic developments and domestic water supply has caused land subsidence in Taipei and the west-southern areas of Taiwan. The
affected area of land subsidence is over 2,000 km2. Recently, due to the route of High Speed Rail (HSR) passes through the persistent subsiding area in Changhua and Yunlin County, that is possible to affect the regular operation of HSR. In order to promote and ensure the reasonable and sustainable utilization on water and land resources, as well the normal operation of HSR, not only the long-term but also the short-term land subsidence prevention and reclamation projects are executed in the past few years. This paper points out the procedure to make an action plan related to current reclamation and prevention measures on land subsidence, and demonstrates it with a case study named “Action Plan of Sealing and Removing Legitimate Public Wells Within 3 km Width Along HSR Lines in Yunlin County”.
This study investigates the compressibility and consolidations of the soils within the depth up to 300 m at the intersection of Expressway No.78 and Taiwan High Speed Rail(THSR) at Tuku Township, Yunlin County, Taiwan. The stress increments caused by the weights of highway embankment and the loadings coming from the pier of the THSR are the mail reason to cause local ground settlement. Borehole data show that local soils are consisted of 18-interlayer of sands and clay. The highway embankment loads to the ground surface; while, the loading of the THSR pier are conducted to the ground at the depth of 40 m, which is roughly the 2/3 of the pile length, through group piles. The increase of stresses in theground results in ground settlements. The analysis results show that insignificant soil consolidations are found at the depth of 219.5 m (13th layer of CL7) caused by the THSR pier. But, the stress increment at the 18th layer of SM9 remains 0.65 t/m2, which is roughly 15.86% of the stress of 4.224 t/m2 at the ground surface. It is essential to investigate the impact of soil consolidations at the depth more than 300 m. In addition, experimental results of soil consolidations with very large loadings show the requirement of investigating the soil consolidations deeper than 300 m using soil consolidation facility with very large capacity.
The land subsidence caused by over pumping of groundwater including primary consolidation and compression secondary which are considered by respectively the effective stress of Terzaghi using INTERBED model and the clay interlayer dehydration theory. The amounts of subsidence caused by the static weight are estimated by the vertical stress increment of Boussinesq method. And the other hand, the amounts of subsidence caused by the dynamic consolidation of the high-speed rail during operation are adopted the three-dimensional finite element model within the equation of damped vibration motion. The results of this analysis provide the quantitative amounts of the land subsidence due to the groundwater pumping, static weight and the operation of high-speed rail. From 2004 to 2010, the subsidence amount in Tuku caused by pumping groundwater are about 40 cm. For engineering structures due to loading at the intersection of high-speed rail and expressway 78 engineering, and adjacent embankment filling, the maximum amount of subsidence can be estimated in 2012 are about 1.60~6.68 cm. The subsidence caused by the vibration of the dynamic analysis can be neglected on the surface or deep layer.
Subsidence is an important issue in soil and water conservation and also in the safety of infrastructure. The causes of subsidence are complicated and are difficult to handle. Yunlin is one of the most serious subsidence areas in Taiwan. The long-term groundwater exploitation for public water supply in this area has been blamed for the subsidence. However, the degree of the influence by groundwater pumping is unclear. Understanding the mechanism helps to mitigate the subsidence. In this paper, we collect field data and utilize numerical modeling to simulate the subsidence. Scenarios to reduce pumping at different layers were proposed. Their effectiveness on the reduction of subsidence was explored.
Regional Drainage Characteristics for Fish Farm of Coastal Subsidence Area
臺灣西南沿海魚塭養殖業發達，但魚塭區域多為低窪地區，長期地層下陷嚴重，其地勢常低於海平面以下，因此在暴雨來臨時常因重力排水不良，加上魚塭抽排水造成排水幹線溢堤而淹水。為掌握魚塭區域排洪特性，本研究以嘉義縣義竹鄉後鎮大排為研究區域，應用暴雨水流經理模式(SWMM，Storm Water Management Model)進行該區域水理演算，並以莫拉克颱風(2009/8)實測水位進行模式校驗。研究中以重現期25年設計降雨進行水理模擬且給定魚塭抽排規則，假設下游邊界水位為自由跌水、低潮位與高潮位三種狀況時，模擬區域排水之水位變化，另外模擬一對照組，設定與本研究區域相同面積集水區之一般都市區域，以了解魚塭區養殖區與一般都會地區兩者不同集水特性之區排排洪特性。最後探討魚塭若能於降雨前先進行抽排以降低魚塭池水位，如此將增加整體滯洪儲水空間以有效容納降雨，並減少魚塭抽排至排水幹線之水量，進而防止進入排水幹線之水量超過其負荷而溢淹。本研究成果可提供河川管理單位制訂沿海地層下陷魚塭養殖區，在颱風暴雨來臨時魚塭與區排聯合抽排之應變操作規則。
Most of fish farms in Taiwan are located near the southwest coastal subsidence area where the ground level is low,even lower than the sea level. Inundations often happen in typhoon event due to flow over embankment top. The two main causes are poor gravitational drainage system and extra inflow drained from fish farms. To master the drainage characteristics in fish farm area and suggest measures of inundation prevention, the Houzhen catchment system in the Chiayi County was selected as study area. The numerical model, Storm Water Management Model (SWMM), was applied to water level simulations in the Houzhen drainage system and the measured water level data in the Morakot Typhoon were used for model calibration and validation. In this study, the 25 year return period design rainfall and drainage regulation in fish farm were given for all scenarios. Simulate the water level under three different boundary condition, include free fall, low tide and high tide. Another simulated a control group, set for the general metropolitan area, its catchment area and the same catchment area of fish farms, in order to understand the different drainage characteristics for between fish farms areas andmetropolitan areas. Based on simulation results, the fish farm pre-drainage effe ctively prevented inundation. Fish farm pre-drainage created enough storage space for rainfall and extra inflow from fish farms. Therefore, rainfall forecasting could to determine the pre-drained water depth. Furthermore, river management agency would announce and assist fish farm owners the emergency measure and operating rules of pre-drainage.
In severe land-subsidence area, the drainage system improvement should consider not only the hydrology environment and rain-runoff features, but also the causes of land-subsidence and geology conditions. This paper bases on the view point of overall national land restoration strategy to discuss the principles and methodologies of the drainage system improvement in severe land-subsidence area. We also evaluate the effects of consolidation on flood control and negative skin friction. The case study on Linbian area of Pingtung county will demonstrate the whole concepts of this paper.
It has been a crucial issue for government to facilitate the improvement of inundation potential at land subsidence areas, thereby the homeland environmental quality being promoted. In the current study, an algorithm for modeling inundation potential at land subsidence areas is developed and applied to assess the effect of improvement measures, the result of which can serve as the reference for decision strategy and improvement measures of government. As an illustrative example, we apply the algorithm to model inundation potential at land subsidence areas of the Yunlin County by changing land uses. Our numerical results show that the algorithm we developed is able to provide effective decision information.
A series of field tests on the heat dissipation capacity of a closed circulation water system (geothermal energy pile) installed in Taipei basin soil was carried out and evaluated in this paper. The test site was located in the campus of NTUST. A double tube closed pipe system installed in a well was used to simulate the geothermal energy pile; a 15 RT air conditioner was used as the heat source. The temperature change of circulating water to and fro the well was recorded to evaluate the heat dissipation capacity of this closed pipe system. When the 15 RT air conditioner was on, the temperature of circulating water increased quickly with time and caused the air conditioner to shut down due to overheat. After the air conditioner was off, the temperature of water in the pipe dropped back to the in-situ groundwater temperature. Using the TEMP/W software and the measured temperature of circulating water during the test, the average coefficient of heat conductivity (k) of subsoil (Sonshan and Chingmei Layers) can be obtained. Besides, the on-off operation patterns for air conditioners with different capacities can also be established when they were working with this closed type circulating water system.