Review on advances of ground improvement techniques involved in high-speed railway (or express way) embankment in China

Transcription

1 Review on advances of ground improvement techniques involved in high-speed railway (or express way) embankment in China INTRODUCTION: When bearing capacity and settlement criteria of soil is insufficient for construction of the civil engineering structure then engineers have two options either change the design or improve the soil strength. This modification of engineering parameters of soil is called ground improvement. There are various methods of ground improvement under practice since long time; they are presented with short description as below. 1. Compaction Compaction is the oldest mode of ground improvement in which densification of soil is done by expulsion of air from voids using dynamic loading. It is useful for shallow depth and mostly used for improvement of highway foundation. 2. Mechanical stabilization When soil of shallow depth is required to improved, this method may be useful. In this method some inert material (aggregate, gravel) is mixed with soil and compacted to required density. 3. Improvement of soil using admixture Improving the physical and engineering properties of soil using small amount of admixture like cement, lime, bitumen etc. This method is very useful for shallow depth. In this method soil is excavated from ground, admixture is mixed and compacted. This method is useful for construction of highway and railway embankment. After the advancement in technology such admixture can me mixed to the in-situ soil which are described in separate headings. 4. Improvement by using geo-grids Geo-grids is used to absorb the stress and prevents lateral movement of the soil. The design of the geogrids involves calculations for the serviceability and ultimate limit states, which incorporate the future, anticipated dead and live loads. In high-speed railway in China geo-grids is mainly used for construction of embankment. Besides this, it can be used for mitigating slope stability problem, construction of retaining wall, controlling erosion, drainage material etc. 5. Dynamic compaction Dynamic compaction strengthens weak soils by controlled high-energy tamping. In this method heavy load is raised high enough and dropped to the specific location. The reaction of soils during dynamic compaction treatment varies with soil type and energy input. A comprehensive understanding of soil behaviour, combined with experience of the technique, is vital to successful improvement of the ground. Given this understanding, dynamic compaction is capable of achieving significant improvement to substantial depth, often with considerable economy when compared to other geotechnical solutions. 6. Preloading 1

2 When soil is very soft it exhibit very low bearing capacity and on the other had high compressibility of soil will produce very high settlement. In such condition the soil is kept under high pressure by raising embankment and let it consolidate for sufficient time span. After completion of consolidation the embankment will be removed for new construction. This method of providing load prior to construction is called preloading. 7. Dewatering Dewatering is the general term for removal of water form voids for reduction of compressibility and improvement of strength of soil. There are several of methods of dewatering technique from simple slump drain, vertical sand drain, prefabricated vertical drain to vacuum preloading. Vacuum preloading is widely applicable for improvement of soft and reclaimed soil. In preloading, with the load originating from the weight of embankment fill, there will be consolidation settlement resulting from volume change in the soil as well as shear stress-induced deformations. The latter will normally be manifested most obviously as outward lateral displacement of the ground beneath the embankment. In contrast, the application of a vacuum pressure causes only isotropic stress increments in the ground. These will generally induce settlement as well as inward lateral displacement of the ground, toward the centre of the vacuum loaded region of soil. 8. Vibro-replacement Vibro-replacement with stone columns is a subsoil improvement method in which large-sized columns of coarse backfill material are installed in the soil by means of special depth vibrators. The stone columns and the intervening soils form an integrated foundation support system having low compressibility and improved load-bearing capacity. Vibro-replacement with stone columns allows for the treatment of a wide range of soils, from soft clays to loose sands, by forming reinforcing elements of low compressibility and high shear strength. In addition to improving strength and deformation properties, stone columns densify in situ soil, rapidly drain the generated excess pore water pressures, accelerate consolidation and minimise postconstruction settlement. Normally the columns fully penetrate the weak layer with the result that the stone column and natural soil combination develops greatly enhanced bearing capacity and reduced compressibility characteristics. 9. Jet Grouting The earliest patent regarding jet grouting was applied for in England in the 1950s; however, the real practical development of jet grouting took place for the first time in Japan. Generally, drill string is advanced to the required depth and then the high-pressure water or grout is introduced while withdrawing the rods. This grout is mixed with soil due to the erosion caused by pressure grout/water. As a result of volume injection some soil particles came out to the ground surface. 10. Deep cement mixing 2

3 Deep mixing of cement with soil and water, normally forming soil-cement columns in situ, is a widely used soft ground improvement method. During installation of the soil cement columns either cement slurry (wet mixing) or cement powder (dry mixing) is injected into the ground under pressure. The installation process is often carried out by employing rotary equipment with high torque capacity. The cement is continuously injected and then mechanically mixed with the soil particles by special tools attached to the rotary device. The cement hydrates and reacts with the soil particles eventually forming a solid material usually significantly stiffer and stronger than the original soil layer. This technique has been used for improving the foundations underlying embankments, stabilizing the base of excavations, as well as forming retaining walls for excavations in soft clay or clay-like deposits, and to prevent liquefaction of loose sandy ground. To reduce construction costs and minimize the impact on the ground environment, an improvement method which uses floating soil-cement columns partially penetrating the soft deposit has been developed. It has been recently applied in several field construction projects, as reported by (J.L. Wang, 2009). Problem Statement Soft ground is widely distributed in mainland of China, especially along the coastal area, where most of economically developed areas are located on soft marine clayey deposit. In inner China, problematic soil can be expansive soil, alluvial soil, marsh soil, lacustrine deposit, and collapsible soil. Collapsible loess is mostly located in western or northwest China. In addition, there are large areas of reclaimed land and more than 1000 km 2 land will be reclaimed in the near future (Gang Zheng, 2009). In the past ten years, China has constructed many highways and high-speed railways. Recently, several highspeed passenger railway lines are under construction and more than 10,000 kilometer long railway lines will be constructed within 15 years. According to the China National Highway Network Plan, 45,000 kilometer long highways will be constructed in the future. Some of these railways and highways have to be constructed on problematic soils and the treatment of such soils is expected to cost a considerable amount of money over the total budget. (Gang Zheng, 2009) The major high speed railway network of china The main high-speed rail network in China is like a grid, which mainly consists of 8 long-distance high-speed rail lines: four north south HSR lines and four east west HSR lines. Network Name/Distance Route Beijing Shanghai Beijing South, Langfang, Tianjin West, Cangzhou West, Dezhou East, Distance: 1,433 km Jinan West, Taian, Tengzhou East, Zaozhuang, Xuzhou East, Bangbu (Fully Operational) South, Dingyuan, Chuzhou, Nanjing South, Zhenjiang South, Danyang North, Changzhou North, Wuxi East, Kunshan South and Shanghai Hongqiao. North South HSR Lines Beijing Guangzhou Beijing West, Baoding East, Shijiazhuang, Handan East, Hebi East, 3

4 Network Name/Distance Route Shenzhen Hong Kong (Partly Operational) Distance: 2,260 km Zhengzhou East, Zhumadian West, Xiaogan North, Wuhan, Yueyang East, Changsha South, Heng Mountain West, Hengyang East, Laiyang West, Chenzhou West, Guangzhou South, and Shenzhen North. Beijing Harbin (fully operational) Distance: 1,700 km Beijing, Tangshan North, Beidaihe, Shanhaiguan, Suizhong North, Jinzhou South, Shenyang North, Tieling West, Kaiyuan West, Siping East, Changchun West, Shuangcheng North and Harbin West Hangzhou Fuzhou Hangzhou East, Shangyu North, Ningbo East, Ninghai, Linhai, Shenzhen (Partly Taizhou, Wenling, Yandangshan, Wenzhou South, Ruian, Aojiang, Operational) Cangnan, Fuding, Tailaoshan, Xiapu, Ningde, Fuzhou South, Fuqing, Distance: 1,600 km Putian, Quanzhou, Jinjiang, and Xiamen North. Qingdao Taiyuan Qingdao Taiyuan HSR line consists of the Qingdao Jinan HRS line, (Partly Operational) the Jinan Shijiazhuang HSR line (opening 2016), and the Distance: 770 km Shijiazhuang Taiyuan HSR line. Shanghai Wuhan The Shanghai Chengdu HSR line consists of the Shanghai Nanjing East West HSR Lines Chengdu (Partly HSR line, the Nanjing Hefei HSR line, the Hefei Wuhan HSR line, Operational) the Wuhan (Hankou) Yichang HSR line, the Yichang Wanzhou HSR Distance: 1,600 km line, the Lichuan Chongqing HSR line, the Chongqing Suining HSR line, and the Suining Chengdu HSR line. Xuzhou Lanzhou Only one part of the route is in service from Zhengzhou to Xi an. The (Partly Operational) rest is under construction Distance: 1,400 km Shanghai Kunming The Shanghai Kunming HSR line is partly operational from Shanghai (Partly Operational) to Hangzhou. The Hangzhou Changsha line and Changsha Kunming Distance: 2,080 km line are under construction. Maglev High Speed Rail Shanghai's Maglev Train was the first magnetically levitated high-speed train line in operation the world. It is owned and operated by Shanghai's city government. All other high-speed trains in China are owned and operated by the China Railway Corporation. Shanghai's Maglev Train, launched in 2004, has the maximum speed of 431 km/h. It runs between Shanghai Pudong International Airport and Shanghai's Longyang Road Metro Station Source: From the facts that distribution of problematic soil and railway network it is obvious that many sections will falls under soft & problematic soil. In these sections one or combination of different ground improvement techniques are necessary. 4

5 GROUND IMPROVEMENT TECHNIQUES According to the Chinese Technical Code for Ground Treatment for Buildings JGJ (China Building Research Institute, 2002), ground treatment methods for buildings mainly include over-excavation and replacement, dynamic compaction, vibro-compaction, vibro-replacement, preloading, vacuum preloading, sand or gravel columns, cement-flyash-gravel (CFG) columns, rammed-cemented-soil columns, rammed-soil columns, lime columns, lime-soil compaction columns, grouting, solution injection, deep mixing, jet grouting, and lime-soil columns. Among these methods, ten or more ground treatment methods have been adopted in the construction of highways and regular/high speed railways in China including fill preloading, vacuum preloading, combined fill and vacuum preloading, dynamic compaction, deep mixing, jet grouting, composite ground with different reinforcement elements, and pile-net composite ground. For a composite ground, rigid piles are sometimes used as ground reinforcement elements in addition to DM columns, sand columns or gravel columns. Geo-synthetics/ geo-grid The embankment of high-speed railway is required to have high strength and stiffness, excellent stability and durability. The post-construction settlement of embankment is dominated by its foundation. Since the requirement of post-construction settlement of high-speed railway embankment is generally much stricter than that of highway pavements (Changdan Wang, 2015). Geo-synthetics can be used in railways for drainage, separation and reinforcement of embankment and improve the load transfer mechanism of pile supported embankment (Han- Jiang Lai, 2014). The DEM analysis shows that efficacy of pile is improved by use of geo-grid as shown in Fig. 1. A wide range of geo-synthetics with different properties have been developed to meet highly specific requirements corresponding to various uses in new rail tracks and track rehabilitation. Based on relatively low cost and the proven performance of geo-synthetics in a number of railway applications, many researchers (e.g. Raymond, 1994; Indraratna et al., 2011; Lieberenz. and Weisemann, 2002; Indraratna and Khabbaz, 2008) have conducted experimental programs, field studies and numerical analysis to investigate the effects of the different types of geo-grid railway embankment, track settlement and stress distribution. Fig. 1, Pile load efficacy comparison for embankment with or without geo-grid. 5

6 Using Vertical Drains When railway track passes through soft saturated clay the pore water pressure will be increased by cyclic loading. The dynamic effect of load is significant in shallow layer so that relatively short prefabricated vertical drains may be adequate in design. Short PVDs (4-8m) can dissipate the cyclic pore pressures, curtail the lateral movements and increase the shear strength and bearing capacity of the soft formation to a reasonable depth below the subballast. The exact required length of PVDs can be determined based on design loads, and soft clay deposit thickness and properties. Using vertical drains will provide a stiffened section of the soft clay up to several meters in depth, supporting the rail track within the predominant influence zone of vertical stress distribution. If excessive initial settlement of deep estuarine deposits cannot be tolerated in terms of maintenance practices, the rate of settlement can still be controlled by optimizing the drain spacing and the drain installation pattern. In this way, while the settlements are acceptable, the reduction in lateral strains and gain in shear strength of the soil beneath the track, improve its stability significantly. The simple modelling method was applied to the analysis of a test embankment at the Hangzhou-Ningbo (HN) Expressway in eastern China. Analyses using drainage elements to represent the effect of the PVDs were also conducted. It is worth mentioning that using the concept of equivalent hydraulic conductivity, the FEM analysis can be conducted using standard commercial finite element programs (Jinchun Chai, 2011). The results obtained using the simple modelling method are compared with those obtained using drainage elements in terms of settlements, excess pore water pressures, and lateral displacement profiles. The results of both types of FEM analysis are also compared with the measured field data. The effectiveness of the simple modelling method has been demonstrated and verified by successfully simulating a large scale laboratory model test and a test embankment constructed in eastern China as shown in Fig. 2. These comparisons show that for most practical purposes the simple method can yield a result as good as that obtained using discrete drain elements to represent the behaviour of the PVDs. Fig. 2, Prefabricated Vertical Drain 6

7 Combined preloading The combined method (Fig. 3) proposed by (Liu Han-long, 2013) is a simple idea which gives solution for some construction problems for combined preloading. These problems can be summarized as follows: firstly, the most important step to apply the new combined method is to cover the electrodes with a geomembrane, but the conventional metal electrodes are so hard and uncompressible that they may rise and then break the geomembranes during the settlement of the ground; secondly, the electrical circuit and drainage pipes of the conventional electroosmosis system cannot work under geomembranes and may be damaged by surcharge loading. This method was verified by the field test carried out on a reclaimed land in Wenzhou, China, in Fig. 3, Combined electroosmosis-vacuum-surcharge combined preloading The consolidation mechanism of the combined method can be explained as follows. In the electroosmotic drainage system, a vacuum is first produced under the geomembrane and inside the vertical drains by means of vacuum pumps, and then generated in the soil around the vertical drains by draining water from the soil. Pore water pressure near the vertical drains becomes lower than that at a distance from the vertical drains. Hence, a hydraulic gradient is caused by the vacuum degree difference. Pore water in soils gathers at the vertical drains and is drained out through both the epvds and plastic In the meantime, a DC voltage is applied to the soil via epvds. Under this voltage, the cations in pore water migrate to the cathodes, bringing water molecules with them, which speeds up the water flow to the cathodes. More importantly, electroosmosis also activates the water molecules in the diffuse layer near the surface of the soil particles, and holds the potential to overcome the limitation of the double layer. It is harder for the water in the diffuse layer to be affected by mechanical pressure such as vacuum preloading and surcharge preloading. It is the reason that electroosmosis is very effective for the fine-grained and low permeability materials, such as silts and clays, with thick double layers. Surcharge preloading in the combined method also plays an important role. It exerts an additional stress in the treated foundation, compacting the voids induced by water being drained out by electroosmosis and vacuum. Therefore, surcharge load consolidates the soil more efficiently and quicker. Column type reinforcement Among different type of improvement techniques, the column type reinforcements are widely used. These conventional column-type reinforcement elements can be classified into three categories based on the used materials, the installation methods, and the behavior and failure modes of the elements. 7

8 The first category includes sand columns and stone columns, which comprise granular materials. These reinforcement elements can provide vertical drainage thus accelerating the consolidation of soft soil. However, they typically have relatively low bearing capacity, shear strength, and no bonding and tensile strength. As a result, these reinforcement elements usually have bulging failure due to relatively low lateral support in the upper part of columns. For short floating columns, they may be punched into the underlying soft soil. Embankments over soft soil treated with sand columns or stone columns often experience large settlement. This type of reinforcement elements is typically less expensive. The second category includes deep mixed (DM) columns, lime columns, and jet grouted columns, which are formed through chemical reactions between reagent and soil. In situ soil mixing (SM) technology can be subdivided into two general methods: Deep Mixing Method (DMM) and Dry Jet Mixing method (DJM). The columns installed by soil mixing have relatively high shear strength, compressive strength, and bonding strength but low tensile and bending strength. This type of reinforcement elements is more expensive than that in the first category. The Third category includes plain concrete piles, concrete pipe piles, steel pipe piles, and so on. They have much higher shear strength, compressive strength, and bond strength. For reinforced concrete and steel piles, they can also have high bending and tensile capacity to resist lateral and uplift forces. However, they are often the most expensive. Deep mixed (DM) columns In situ soil mixing is used in diverse marine and land applications, mainly for soil stabilisation and column-type reinforcement of soft soils, construction of excavation-support walls with inserted steel sections and as gravity composite structures, mitigation of liquefaction, environmental remediation and for in-place installation of cut-off barriers. In this method of ground improvement, soils are mixed in situ with different stabilising binders, which chemically react with the soil and/or the groundwater. The stabilized soil material that is produced generally has a higher strength, lower permeability and lower compressibility than the native soil. Fig. 4, Railway embankment in deep mixed column 8

9 The more frequently used and better developed DMM is applied for stabilisation of the soil to a minimum depth of 3m (a limit depth proposed by CEN TC 288, 2002) and is currently limited to treatment depth of about 50 m. The binders are injected into the soil in dry or slurry form through hollow rotating mixing shafts tipped with various cutting tools. The mixing shafts are also equipped with discontinuous auger flights, mixing blades or paddles to increase the efficiency of the mixing process. In some methods, the mechanical mixing is enhanced by simultaneously injecting fluid grout at high velocity through nozzles in the mixing or cutting tools. T-Shaped DM Columns Since late 70s DMM was used for installation of deep mixing column for supporting embankments in soft ground. The deep mixing method (DMM) is a deep in-situ soil stabilization technique. The most common objectives of DMM are to reduce settlement of soft ground and to increase the stability of embankments or slopes. Fig. 5, Conventional DM column and TDM columns Fig. 6, Model of T-shaped and normal column The T-shaped Deep Mixed Column Application in Soft Ground Improvement (Yaolin Yi, 2012) had conducted the field test and concluded that considering that the soil deposition conditions, column strength and embankment load process at the two test sites are similar as shown in Fig. 5, the TDM column installation resulted in 6.5% reduction in cement use and 19% reduction of construction time when compared with the conventional DM column installation. The total settlement and the maximum lateral movement of the TDM column treated ground were only 67% and 31% that of the conventional DM column treated ground, indicating the performance of the former was superior to that of the latter. Hence, it is concluded that TDM method is a more economic as well as technologically sound solution for soft ground improvement under embankments compared with the conventional DM method. Cement-Fly Ash-Gravel Pile Cement-fly ash-gravel piles, referred to as CFG piles, have been successfully used in China to support buildings and embankments. They are installed by augering into the ground and backfilling a mix of cement, fly ash, gravel, 9

10 and water through the core of the auger while withdrawing the auger. Past research shows that CFG piles have high strength and stiffness; therefore, they can be considered as rigid piles. Fig. 7, a. Three-dimensional nonlinear finite element modeling of composite foundation formed by CFG piles b. Performance of Cement-Fly Ash-Gravel Pile-Supported High-Speed Railway Embankments over Soft Marine Clay There are various researchers working in the performance of CFG pile; (Jun Feng, 2014) developed Settlement Formula of Stabilized Layer in CFG Composite Foundation of High-Speed Railway, (Jun-Jie Zheng, 2008) investigated the behavior of embankments supported by cement-fly ash-gravel piles using a three-dimensional numerical method as shown in Fig. 1. Performance of Cement-Fly Ash-Gravel Pile-Supported High-Speed Railway Embankments over Soft Marine Clay was evaluated by (Gang Zheng Y. J.-F., 2011) in Beijing Tianjin High-speed railway. Two CFG pile-supported embankments along the Beijing-Tianjin high speed railway in China were monitored and investigated. The proportion of the loads carried by soil and piles, excess pore pressure, settlement, and lateral displacement were evaluated. 10

11 Concrete-DM Composite Columns The side and tip resistance of a long DM column cannot be fully mobilized due to the failure of the column material (Zheng et al., 2002). Under such a condition, the bearing capacity of the column can be improved by including strong and stiff elements. Composite Deep Mixing Column system is developed in China, which includes the installation of a precast concrete or reinforced concrete core pile with a diameter of mm into a pre-installed DM column. Fig. 8, Composite DM Column Steel-DM Composite Columns A steel-dm composite column consists of a DM column reinforced with a shaped steel element, such as steel pipe, steel H-pile, or steel cage. The shaped steel is driven into the pre-installed DM column. The steel-dm composite column is usually used to retain soil during excavation or reinforce existing foundations of buildings. DJM - Sand Composite Columns The smaller diameter DJM is installed in the middle of the pre-installed sand column. During the installation of DJM, sand is mixed in-situ with the cement slurry to form a stronger core cemented sand column. This DJM column can obtain higher load capacity than the DJM column alone in soft soil because the surrounding sand column can provide higher shaft and tip resistance than the soft soil. In addition, the sand column can act as a vertical drain to dissipate excess pore water pressure thus accelerating consolidation and preventing liquefaction during earthquake. The quick dissipation of excess pore water pressure can also minimize the installation impact of DJM columns on the surrounding soft soil and structures. Concrete - Sand (Gravel) Composite Columns Sand gravel-concrete composite columns were adopted as the ground reinforcement elements in a test section on soft soil (Zhao et al., 2007), The backfilling of the embankment is shown in Fig. 9. Fill surcharge preloading was carried out. The excess pore pressure in the soil between columns was observed that excess pore pressure remained small during the whole backfilling of the embankment except for the moment the surcharge was quickly applied. The sand-gravel surrounding the concrete pile accelerated the dissipation of excess pore water pressure induced by the backfilling thus making the quick embankment construction possible. 11

12 Fig. 9 Sand concrete composite column Jet Grouting Another most important and widely used method of ground modification is grouting of cementicious material. Grouting generally is used to fill voids in the ground (fissures and porous structures) with the aim to increase resistance against deformation, to supply cohesion, shear-strength and uniaxial compressive strength or finally and even more frequently to reduce conductivity and interconnected porosity in an aquifer. With the fast development of subways, tunnels, railways and expressways and high-rise buildings, jet grouting technology has been widely used in various projects which also further promote its development. So that, the treatment depth has increased to approximately 50m from 20-30m. The main objectives of using jet grouting technology in the above projects are: foundation reinforcement, seepage cut-off wall, and soil retaining wall for excavation. Fig. 10, Jet grouting technique As jet grouting is versatile technique of ground improvement, it can be used in various problematic areas as under, i. Preventing and controlling settlement of embankment foundation of highways and railways. ii. Preventing and controlling ground movement for deep excavation and tunneling. iii. Preventing and controlling ground water flow in foundation base and underground excavation. iv. Mitigating seepage flow for hydraulic structures. v. Constructing as cut-off structure for subsurface flow. 12

13 vi. Improving foundation of existing structures and foundation for new construction. CONCLUSION From general scenario of China s infrastructure development distribution in and around the territory from costal soft clay to alluvial deposit of Yantsze & Yellow River and frost highland in Tibet to loess deposit in north west part of China, these problematic soft ground were deal efficiently by using various improvement techniques. The most fundamental technique like compaction with or without additives, dewatering, preloading, jet grouting and in-situ mixing are common technique found in high-rise building, highway and railway projects. In this connection, a series of new column-type reinforcement elements have been developed in China, which combine two or three types of conventional columns into one composite column or composite ground. These composite columns utilize the combined advantages of different conventional columns and have been increasingly used in soft soil to support buildings and embankments. The composite columns can significantly increase the stability of embankments during backfilling; therefore, rapid embankment construction becomes practical. The composite columns can also provide higher capacities than the conventional columns at a competitive cost. It should be highlighted that the composite DM column can even provide the load capacity higher than the bore pile of the same peripheral size and length. Many researchers are carrying out research for limiting post construction settlement of railway embankment by using computer simulation, centrifuge modeling and field verification of geo-grid reinforced pile supported embankment. Whereas, some researcher are doing research in effect of vibration caused by train loading to the adjacent buildings and its mitigation by using different ground improvement techniques. BIBLIOGRAPHY China highlight. (2016, 01 10). Retrieved from China High Speed Railway: Changdan Wang, B. W. (2015). Experimental analysis on settlement controlling of geogrid-reinforced pile-raftsupported embankments in high-speed Railway. Acta Geotechnica, Gang Zheng, S. L. (2009). Sate of Advancement of Column-Type Reinforcement Element and Its Application in China. US-China Workshop on Ground Improvement Technologies, (pp ). Gang Zheng, Y. J.-F. (2011). Performance of Cement-Fly Ash-Gravel Pile-Supported High-Speed Railway Embankments over Soft Marine Clay. Marine Georesources and Geotechnology, Han-Jiang Lai, J.-J. Z.-J. (2014). DEM analysis of soil -arching within geogrid-reinforced. Computers and Geotechnics, J.L. Wang, D. W. (2009). State of Jet Grouting in Shanghai US-China Workshop on Ground Improvement Technologies Advances in Ground Improvement (pp ). ASCE. Jinchun Chai, J. P. (2011). Deformation Analysis in Soft Ground Improvement. Springer. Jun Feng, X.-y. W.-h. (2014). Settlement Formula of Stabilized Layer in CFG Composite Foundation of High- Speed Railway. Electronic Journal of Geotechnical Engineering (EGJE),

14 Jun-Jie Zheng, S. W.-Z. (2008). Three-dimensional nonlinear finite element modeling of composite foundation formed by CFG piles. Computers and Geotechnics 35, Liu Han-long, C. Y.-l.-m. (2013). A New Method of Combination of Electroosmosis, Vacuum and Surcharge Preloading for Soft Ground Improvement. China Ocean Eng., Vol. 28, No. 4, M.P. Moseley, K. K. (2004). Ground Improvement. Spon Press, Taylor& Francis Group. Qulin Tan, L. L. (May 2014). Measurement and Analysis of High-speed Railway Subgrade Settlement in China: A Case Study. Sensors & Transducers, Vol. 170, Issue 5, Yaolin Yi, S. L. (2012). The T-shaped Deep Mixed Column Application in Soft Ground Improvement. Grouting and Deep Mixing, Young Liu, J.-J. Z. (2007). Reliability-based design methodology of multi-pile composite foundtion. First International Symposium on Geotechincal Safety & Risk. 14