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applied sciences Article

Application of a Coupled Eulerian-Lagrangian Technique on Constructability Problems of Site on Very Soft Soil Junyoung Ko 1 , Sangseom Jeong 2 and Junghwan Kim 2, * 1 2

*

Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Lubbock, TX 79409, USA; [email protected] Department of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Korea; [email protected] Correspondence: [email protected]; Tel.: +82-2-2123-7489

Received: 29 September 2017; Accepted: 13 October 2017; Published: 18 October 2017

Abstract: This paper presents the application of the Coupled Eulerian–Lagrangian (CEL) technique on the constructability problems of site on very soft soil. The main objective of this study was to investigate the constructability and application of two ground improvement methods, such as the forced replacement method and the deep mixing method. The comparison between the results of CEL analyses and field investigations was performed to verify the CEL modelling. The behavior of very soft soil and constructability with methods can be appropriately investigated using the CEL technique, which would be useful tools for comprehensive reviews in preliminary design. Keywords: very soft soil; Coupled Eulerian-Lagrangian method; large deformation finite element analysis; forced replacement method; deep mixing method; constructability

1. Introduction Recently, South Korea has seriously lacked the land space because of the increase with the population density and industrialization, thus a number of constructions such as the housing complex, high-speed railway, international airport, and harbor construction are progressing in soft soil areas located in coastal area. Especially, organic soils are widely distributed over the world, including South Korea, Japan, Australia, Malaysia, and Canada. The area of organic soils is approximately 2.3 million km2 . Whitlow [1] reported that the organic soil deposits have occurred on the Gold Coast region, Australia, because of current and past marine processes near coastal zones. Also, Malaysia has organic soil deposits observed mainly along the coastal area [2]. According to the Unified Soil Classification System [3], organic soils can be classified as organic clay (OL), organic silt (OH), and peat (Pt). Especially, organic soils can be defined as one with a minimum of 50% organic matter. Organic soils have typically low unit weight, high water contents, high content of organic matter, and high compressibility [4]. The high compressibility of organic soils leads to the increases of risk under the constructions, such as excavations, foundations, and embankments. Therefore, if the structure or embankment are constructed on the organic soils, it cannot be ensured the safety of structure because of the large deformation and low bearing capacity. Hence, it is difficult to predict the behavior of organic soils, thus encountering significant challenges in the preliminary design stage. Therefore, a proper technique for large deformation analysis is necessary to investigate the behavior and safety of the structures on very soft soil, such as organic soil. Many studies have been performed to solve the geotechnical problems using numerical techniques, especially the finite element method (FEM). However, it has limitations to solve those, including large

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deformation between soil-structure or soil-soil interactions using traditional numerical methods, 2017, 7, 1080 have been based on the Lagrangian coordinates for the small deformation 2 of 16 since Appl. mostSci.researches analysis. For the finite element methods based on the Lagrangian coordinates, the large deformation numerical methods, since most researches have been based on the Lagrangian coordinates for the may lead to the problems, including the mesh and the unconvergence divergence due to severe small deformation analysis. For the finite element methods based on the Lagrangian coordinates, the relative displacement. large deformation may lead to the problems, including the mesh and the unconvergence divergence Recently, a Coupled (CEL) technique has been developed to overcome the due to severe relative Eulerian-Lagrangian displacement. limitationsRecently, of the small deformation analyses. This technique hashas been applied to various geotechnical a Coupled Eulerian-Lagrangian (CEL) technique been developed to overcome the fields,limitations such as theofpenetration offshore structure landslidehas andbeen debris flow [10,11], the pile the small of deformation analyses.[5–9], Thisthe technique applied to various penetration [12–16], andsuch the as effect on the nearby soil duestructure to tunneling [17]. geotechnical fields, the penetration of offshore [5–9], the landslide and debris flow [10,11], the pile penetration [12–16], andisthe on the nearby soil due to tunneling The overall objective of this study to effect investigate the behavior and safety [17]. of the structures The overall objective of this study is to investigate the behavior and safety of the structures on on very soft soil such as organic soil, accounting for the application and constructability of ground very soft soil such as organic soil, accounting for the application and constructability of ground improvement methods, including forced replacement method and deep mixing method. The large improvement methods, including forced replacement method and deep mixing method. The large deformation finite element (LDFE) analyses are carried out using the Coupled Eulerian-Lagrangian deformation finite element (LDFE) analyses are carried out using the Coupled Eulerian-Lagrangian technique. For CEL modelling validation, the results of CEL analyses in this study are compared with technique. For CEL modelling validation, the results of CEL analyses in this study are compared with field investigations withwith settlement, height, heave.Additionally, Additionally, to examine field investigations settlement, height,and andrange range of of soil soil heave. to examine the the constructability and and economics of each method, reviewsare areperformed. performed. constructability economics of each method,comprehensive comprehensive reviews 2. Project Description 2. Project Description In this the construction site ononvery is targeted targetedininGangeung-si, Gangeung-si, South Korea, In study, this study, the construction site verysoft soft clay clay is South Korea, located in along the coastal area. Figure 1 showsthe thelocation location of inin South Korea. located in along the coastal area. Figure 1 shows of the thestudy studyarea area South Korea.

Figure 1. Location in South SouthKorea. Korea. Figure 1. Locationofofthe thestudy study area area in

2.1. Review of Previous Studies 2.1. Review of Previous Studies To understand reliable geotechnicalcharacteristics characteristics ininthis site, thethe literature review aboutabout a To understand the the reliable geotechnical this site, literature review nearby area is conducted. Yeongdong area is located along the shoreline of the East Sea in South a nearby area is conducted. Yeongdong area is located along the shoreline of the East Sea in South Korea, thus this area has the low temperature in summer, high temperature in winter, and high Korea, thus this area has the low temperature in summer, high temperature in winter, and high average average annual rainfall, leading to be a suitable conditions for the formation of the peat deposit. annual rainfall, leading to be a suitable conditions for the formation of the peat deposit. Kim [18] reported the case study of construction on the peat deposits, which had the water Kim [18] of reported the case of construction on the peat which of had the water 3, and contents 400.7%–706.2%, thestudy unit weight of 9.7–10.6 kN/m thedeposits, organic contents 85%. Ryu 3 , and the organic contents of 85%. contents of 400.7%–706.2%, the unit weight of 9.7–10.6 kN/m and Ryu [19] described in their paper that the peat deposits had the water contents ranged from 95.4 Ryu and Ryu [19] described in contents their paper that the11.1 peattodeposits hadetthe water contents to 192.6%, and the organic varied from 21.0%. Koo al. [20] reported thatranged the peatfrom thethe water contents rangedvaried between 50.8% and the varied 95.4 todeposits 192.6%,had and organic contents from 11.1 to343.5%, 21.0%.and Koo etorganic al. [20]contents reported that the from 12.1had to 42.5%. Jang contents [21] reported thatbetween the organic soil and was 343.5%, distributed km2 incontents the peat deposits the water ranged 50.8% andover the0.5 organic 2 Yeongdong area. In addition, the characteristics of organic soil in Sokcho, Yangyang, and Gangneung varied from 12.1 to 42.5%. Jang [21] reported that the organic soil was distributed over 0.5 km in the area were reported in Table 1. Yeongdong area. In addition, the characteristics of organic soil in Sokcho, Yangyang, and Gangneung area were reported in Table 1.

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Table 1. Characteristics of organic soil in Yeongdong area (Jang [21]). Table 1. Characteristics of organic soil in Yeongdong area (Jang [21]). Water Content (%) Water Content Sokcho Sokcho Yangyang Gangneung Yangyang

Gangneung

Liquid Limit (%) Liquid Limit

(%) 103.2–178.5 103.2–178.5 100.4–179.0 101.3–341.7 100.4–179.0

(%) 100.4–170.3 100.4–170.3 104.7–180.4 75.5–200.8 104.7–180.4

101.3–341.7

75.5–200.8

Plastic Index

Plastic Index

Organic OrganicContent Content(%)

pH

pH

49.8–85.7 49.8–85.7 52.2–97.7 9.2–73.6 52.2–97.7

(%) 10.9–18.5 10.9–18.5 10.5–18.7 2.27–2.33 10.5–18.7

4.3–6.5 4.3–6.5 4.3–6.8 5.1–6.4 4.3–6.8

9.2–73.6

2.27–2.33

5.1–6.4

(a)

Depth (m)

Depth (m)

Depth (m)

2.2. Geotechnical Investigation 2.2. Geotechnical Investigation Figure 2 illustrates the soil profiles in this site. Based on the borehole survey, subsurface profile Figure 2 illustrates the soil profiles in this site. Based on the borehole survey, subsurface profile consisted of a peat (Pt) deposit and clay of high plasticity, fat clay (CH) deposit from the ground consisted of a peat (Pt) deposit and clay of high plasticity, fat clay (CH) deposit from the ground surface to a depth of 16.0 m. The standard penetration number (N value) of the deposits from 0.0 to surface to a depth of 16.0 m. The standard penetration number (N value) of the deposits from 0.0 to 16.0 m are 0/30, indicating a very soft soil condition. In case of the peat, it is impossible to work for 16.0 m are 0/30, indicating a very soft soil condition. In case of the peat, it is impossible to work for any construction without additional ground improvement. any construction without additional ground improvement. Based on the geotechnical investigation, for the peat, the water contents range from 167.5 to 719.7%. Based on the geotechnical investigation, for the peat, the water contents range from 167.5 to The standard penetration number (N number value) of(N the peat of range fromrange 0/30 to 1/30. elastic modulus 719.7%. The standard penetration value) the peat from 0/30The to 1/30. The elastic 3 (Es ),modulus the soil cohesion (c), and the unit weight (γ) of the peat are 240 kPa, 2.4 kPa, and 10–11 kN/m (Es), the soil cohesion (c), and the unit weight (γ) of the peat are 240 kPa, 2.4 kPa, and 10–11 , respectively. Also, the organic contents from 50.9 from to 80.9%. kN/m3, respectively. Also, the organicrange contents range 50.9 to 80.9%.

(b)

(c)

Figure 2. Soil profile with test results: (a) Soil profile; (b) result of N value; and (c) result of cone Figure 2. Soil profile with test results: (a) Soil profile; (b) result of N value; and (c) result of cone resistance. resistance.

The The geotechnical properties of of this site areare compared as shown shown geotechnical properties this site comparedwith withthose thoseof ofprevious previous studies, studies, as in Figure 3. The organic contents and water contents the previous previous in Figure 3. The organic contents and water contentsofofthis thissite siteare arelarger largerthan than those those of the studies, as shown in Figure 3a,c, whereas thethe soil among studies, as shown in Figure 3a,c, whereas soilcohesion cohesionofofthis thissite sitehas has the the lowest lowest value value among cases. Hence, these geotechnical characteristicsare arefar farworse worsethan thannot not only only the typical otherother cases. Hence, these geotechnical characteristics typical strength strength stiffness organic contents and water contentsofofnearby nearbyarea. area. ItIt was was even even impossible and and stiffness but but alsoalso organic contents and water contents impossibleto to obtain the specimen sampling laboratorytests testsininsome somearea. area.Based Based on on the geotechnical geotechnical obtain the specimen andand sampling forfor thethe laboratory investigations, is found peat deposit had ‘veryextremely extremelysoft softconditions’, conditions’, like like aa fluid. fluid. investigations, it isitfound thatthat thethe peat deposit had ‘very The representative problems related to the construction are the significant total settlement The representative problems related to the construction are the significant total settlementand and differential settlement causedbybythe thelow low strength high compressibility of very soft soil, differential settlement caused strengthand andthe the high compressibility of very softsuch soil, as organic soil. The organic soil under the external loading may be largely deformed, such as such as organic soil. The organic soil under the external loading may be largely deformed, such asthe the immediately settlement, since the nearby organic soil without the external loading can hardly have immediately settlement, since the nearby organic soil without the external loading can hardly have the lateral resistance. Hence, the lateral deformation and the heave in nearby very soft soil may occur, the lateral resistance. Hence, the lateral deformation and the heave in nearby very soft soil may occur, and the failure may follow eventually. Therefore, for the installation and construction of structures and the failure may follow eventually. Therefore, for the installation and construction of structures

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on the very soft soil, it is necessary to investigate the safety of construction procedure and method on the very soft soil, it is necessary to investigate the safety of construction procedure and method appropriately in preliminary design stage, ensuring the application and constructability. appropriately in preliminary design stage, ensuring the application and constructability. 30 Ryu and Ryu (1985) Kim (2006) Jang (2011) This study

26.5

20

14.7

14

10 5.9 3

2.4

0

(a)

(b)

(c) Figure 3. Properties of organic soil: (a) Water content; (b) soil cohesion; (c) organic content. Figure 3. Properties of organic soil: (a) Water content; (b) soil cohesion; (c) organic content.

3. Ground Improvement Methods 3. Ground Improvement Methods Not only the safety of structure during use, but also that during construction is very important, Not only the safetyprocedure of structure use, but also that during construction is very important, thus, the construction andduring methods should be considered whether those are proper or not. thus, the construction procedure and methods should be considered whether those are proper oras not. Especially, the constructions of structures on very soft soil may have unexpected problems such Especially, constructions unexpected of structuresincrease on veryin soft soil and may accidents. have unexpected problems such as the the poorthe constructability, costs, Two ground improvement poor constructability, unexpected increase in costs, and Two ground improvement methods, methods, such as (1) forced replacement method, andaccidents. (2) deep mixing method, have been actually such as (1) forced replacement method, andfield. (2) deep method, have been actually planned in planned in the design stage for a practical Thus,mixing the applicability of two ground improvement is examined using the CELThus, in thethe design stage. themethods design stage for a practical field. applicability of two ground improvement methods is examined using the CEL in the design stage. 3.1. Forced Replacement Method 3.1. Forced Replacement Method Firstly, the forced replacement method has advantages such as the low cost and the simple method. otherreplacement hand, if thismethod methodhas applied for the very soillow such as organic themethod. shear Firstly,On thethe forced advantages suchsoft as the cost and the soil, simple thehand, significant andapplied settlement occur. The concept of organic this method the failure, very Onfailure, the other if thisheave method for may the very soft soil such as soil, is thethat shear subsoil heave is replaced by the materials of good quality, of which have theis high strength andsubsoil unit thesoft significant and settlement may occur. The concept this method that the very soft weight, such as sand and broken rock, leading to improve the ground strength. Figure 4 illustrates is replaced by the materials of good quality, which have the high strength and unit weight, such as theand schematic of the forced replacement method. sand brokendiagram rock, leading to improve the ground strength. Figure 4 illustrates the schematic

diagram of the forced replacement method.

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It is basically assumed that the embankment unit load p is equal to the unit ultimate bearing stress of soft soil qult .7,The embankment unit load p can be estimated as follows: Appl. Sci. 2017, 1080 5 of 16 p = Hγtunit + Dzload γsubp is equal to the unit ultimate bearing It is basically assumed that the embankment stress of soft soil qult. The embankment unit load p can be estimated as follows:

(1)

where H = height of embankment; γt = unit weight of embankment; Dz = replacement depth; and, p = Hγt + Dzγsub (1) γsub = effective unit weight of embankment. where H researchers = height of embankment; γt =the unitreplacement weight of embankment; Dz = replacement and, γsubmethod. Many recommended depth Dz based on the limitdepth; equilibrium = effective unit weight of embankment. According to Terzaghi [22], the replacement depth Dz using Nc value of 5.7 can be written as Many researchers recommended the replacement depth Dz based on the limit equilibrium method. According to Terzaghi [22], the replacement Dtz using Nc value of 5.7 can be written as 5.7cdepth − Hγ

Dz =

5.7c-H Dz = γsub − γs

(2)

(2)

where c =csoil cohesion; unitweight weightofof soft (original = unit soft soilsoil (original soil).soil). where = soil cohesion;γγss = Yasuhara and suggeststhe thereplacement replacement depth Dz using Nc value of 5.3 Yasuhara andTsukamoto Tsukamoto [23] [23] suggests depth Dz using Nc value of 5.3 can be can be estimated asas estimated 5.3c − Hγt Dz D=z = 5.3c-H 7 (3) (3) γsub − 6 γs LeeLee [24] to estimate estimatethe the replacement depth Dz using Nc value [24]reported reportedthe the equation equation to replacement depth Dz using Nc value of 5.14 of 5.14 as follows: as follows: 5.14c − Hγt Dz D=z = 5.14c-H 7 (4) (4) γsub − 6 γs These methodscan can predict the replacement depthand simply and however, indirectly, however, Theseexisting existing methods predict the replacement depth simply indirectly, those cancan not not predict the height and influence range of heaveofsoil that soil would bewould required design and those predict the height and influence range heave that beinrequired in design stage. andconstruction construction stage. S

B0 Embankment γt

α Soft soil

H

γsub P

Dz

Qult

hr

B c, γs

Figure 4. Schematic diagram of the forced replacement method.

Figure 4. Schematic diagram of the forced replacement method.

For this site, the field test was conducted to review the constructability of the forced replacement method. The replacement depth, settlement, and heavethe were investigated. The width and height For this site, the field test was conducted tosoil review constructability of the forced replacement of embankment for field test weresettlement, 6.0 m and 2.0 m, soil respectively. The investigated. settlement of embankment was height method. The replacement depth, and heave were The width and measured by using the survey and visual observation. In this site, we confirmed that the entire of embankment for field test were 6.0 m and 2.0 m, respectively. The settlement of embankment wasusing settledthe to the subsurface in a day, thus, we regarded as a ‘punch failure’ orthat ‘forced wasembankment measured by survey and visual observation. In thisitsite, we confirmed the entire replacement’. Based on the investigation, the settlement was about from 2.0 to 3.0 m, hence, we could embankment was settled to the subsurface in a day, thus, we regarded it as a ‘punch failure’ or ‘forced predict the replacement depth of 4.0–5.0 m because of the sum of the settlement and the height of replacement’. Based on the investigation, the settlement was about from 2.0 to 3.0 m, hence, we could embankment. Also, the soil heave near the embankment occurred. The range and height of soil heave predict replacement of 4.0–5.0 m because of the of of the settlement the 1.5 height of were the measured by usingdepth the visual observation. The range andsum height soil heave wereand 20 and

embankment. Also, the soil heave near the embankment occurred. The range and height of soil heave were measured by using the visual observation. The range and height of soil heave were 20 and 1.5 m,

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respectively, as shown in Figure 5. Especially, the soil influenced the nearby agricultural land, m, respectively, as shown in Figure 5. Especially, theheave soil heave influenced the nearby agricultural thus the damage occurred. land, thus the damage occurred.

(a)

(b)

Figure 5. Field investigations: (a) Settlement; (b) range and height of heave soil. Figure 5. Field investigations: (a) Settlement; (b) range and height of heave soil.

The replacement depths in this case are estimated using the theoretical existing methods, and replacement depths in of this case areAsestimated using thethe theoretical existing methods, and areThe compared with the results field test. mentioned above, entire embankment in this site arewas compared with results of field As of mentioned above, thewhen entirethe embankment this is site settled to the the subsurface, thus, thetest. height embankment is zero replacement in depth estimated using existing methods. The replacement depths estimated by Terzaghi [22], Yasuhara, was settled to the subsurface, thus, the height of embankment is zero when the replacement depth Tsukamotousing [23], and Lee [24] represents 1.91 and 1.85 m, respectively. When compared the is estimated existing methods. The1.95, replacement depths estimated by Terzaghi [22], with Yasuhara, field investigations, it is shown that estimated from existing methods are Tsukamoto [23], and Lee [24] represents 1.95, 1.91replacement and 1.85 m, depths respectively. When compared with underestimated. Additionally, the influence range and height of heave soil cannot be estimated using the field investigations, it is shown that estimated replacement depths from existing methods are the existing methods. The existing methodsrange have the those are based on the limit underestimated. Additionally, the influence andlimitations height of because heave soil cannot be estimated using equilibrium method. the existing methods. The existing methods have the limitations because those are based on the limit

equilibrium method. 3.2. Deep Mixing Method 3.2. Deep Mixing Method Secondly, the deep mixing methods of soil stabilization is a ground improvement technique, which increases the soil strength by mixing with cementitious material. Therefore, it is Secondly, the deep mixing methods of soilthem stabilization is a ground improvement technique, necessary to investigate the safety for the construction procedure and method appropriately. which increases the soil strength by mixing them with cementitious material. Therefore, it is necessary In this study, the large deformation analysis are conducted to investigate the adequacy of the to investigate the safety for the construction procedure and method appropriately. forced replacement methods. In addition, for the deep mixing methods, we study the safety caused In this study, the large deformation analysis are conducted to investigate the adequacy of the by the increasing self-weight, and the constructability for pile installation, including the self-standing forced replacement methods. In addition, for the deep mixing methods, we study the safety caused by of pile equipment, the effect of pile jacking, and pile driving. the increasing self-weight, and the constructability for pile installation, including the self-standing of pile4.equipment, the effect of pile jacking, and pile driving. CEL Modelling Coupled Eulerian-Lagrangian technique in ABAQUS/Explicit [25] is employed to 4. CEL The Modelling investigate the constructability and application of two ground improvement methods, such as the The Coupled Eulerian-Lagrangian in ABAQUS/Explicit is employed to investigate forced replacement method and deeptechnique mixing method. Especially, in [25] the case of the deep mixing themethod, constructability and application of two ground improvement methods, such as the forced the safety of pile installation on soil, which is treated in the deep mixing method, is studied. replacement method and deep mixing method. Especially, in the case of the deep mixing method, The CEL technique has the advantages both of the Lagrangian and the Eulerian coordinate is theimplemented safety of pileininstallation on soil, is treated in the deep mixing method, is studied. ABAQUS [25]. Thewhich materials for Lagrangian coordinate that is typically applied in Themechanics CEL technique advantages both deformation, of the Lagrangian andthe thematerials Eulerianfor coordinate solid could has not the undergo significant whereas Eulerian is implemented in ABAQUS [25]. The materials for Lagrangian coordinate that is typically applied coordinate, which is applied in fluid mechanics could experience large displacements. Figure 6 shows in solid mechanicsofcould not undergo significantand deformation, foranalysis Eulerian the deformation a continuum in a Lagrangian an Eulerianwhereas analysis.the Thematerials Lagrangian is based on the movement and element the external force, on the other hand, the coordinate, which is applied of in each fluidnode mechanics could under experience large displacements. Figure 6 shows analysis based on theinconcept that the and nodean and elementanalysis. are fixed,The andLagrangian the materials flow theEulerian deformation of ais continuum a Lagrangian Eulerian analysis through of fixed meshnode under theelement externalunder force. Therefore, re-meshing notother required is based onthe theelements movement of each and the external force, onisthe hand, severeanalysis mesh distortion instability cannot occur in aare CEL analysis theand Eulerian is basedcausing on the numerical concept that the node and element fixed, and [5]. the materials

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flow through the elements of fixed mesh under the external force. Therefore, re-meshing is not required and severe mesh distortion causing numerical instability cannot occur in a CEL analysis [5]. Appl. Sci. 2017, 7, 1080

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(a)

(b) Figure 6. Deformation of a continuum in analysis: (a) Lagrangian analysis; (b) Eulerian analysis.

Figure 6. Deformation of a continuum in analysis: (a) Lagrangian analysis; (b) Eulerian analysis. In this CEL analysis, the contact between Eulerian and Lagrangian materials is applied using a general contact algorithm, which is performed by tracking and capturing between two surfaces. In this CEL analysis, the contact between Eulerian and Lagrangian materials is applied using Hence, the master surface can track nodes of slave surface using a contact algorithm in ABAQUS [25]. a general contact algorithm, which is performed tracking capturing two surfaces. The behavior of interface is applied by using the by penalty contactand method based onbetween the Coulomb’s simulation of pile installation deep mixing soil, the in friction Hence, thefrictional master model. surfaceEspecially, can trackfornodes of slave surface usingona contact algorithm ABAQUS [25]. coefficient μ for soil-concrete pileby and soil-pile interface generally are 0.3based [26,27],on thus, The behavior of interface is applied using thedriver penalty contact method thethe Coulomb’s friction coefficient of 0.3 is adopted in this study. In addition, the limiting shear stress is applied to frictional model. Especially, for simulation of pile installation on deep mixing soil, the friction be equal to the soil cohesion. The initial equilibrium state is important, thus the geostatic stress is coefficient implemented µ for soil-concrete pile and soil-pile driver generally areThe 0.3geostatic [26,27],stress thus,isthe friction in a predefined step to consider the interface initial equilibrium state. taking the of earth pressure atthe rest, K0 = 1. The present analysis is conducted coefficient generated of 0.3 is by adopted in coefficient this study. In addition, limiting shear stress is applied to be equal to in sequence according to ‘initial-gravity-loading’. It means that thethe initial stress field like ‘geostatic’ the soil cohesion. The initial equilibrium state is important, thus geostatic stress is implemented in state can be imposed. The elements of Lagrangian and Eulerian domains consist of 8-noded a predefined step to consider the initial equilibrium state. The geostatic stress is generated by taking Lagrangian brick elements (C3D8R) and 8-noded Eulerian brick elements (EC3D8R).

the coefficient of earth pressure at rest, K0 = 1. The present analysis is conducted in sequence according 4.1. Mesh Convergence Study to ‘initial-gravity-loading’. It means that the initial stress field like ‘geostatic’ state can be imposed. mesh convergences study is necessary to investigate the8-noded suitable mesh size for accurate The elements The of Lagrangian and Eulerian domains consist of Lagrangian brick elements results and computational efficiency. For the mesh convergences study, the forced replacement (C3D8R) and 8-noded Eulerian brick elements (EC3D8R). method is simulated. The input parameters for the mesh convergence study are summarized in Table 2. The height of embankment of 2.0 m is adopted in mesh convergence studies, and the distance from 4.1. Mesh Convergence Study surface to replacement is identified in terms of mesh sizes sm. In this study, five different mesh sizes are assumed with the ratios between the mesh size the width of embankment (sm/B0) of 0.0833, The mesh convergences study is necessary to and investigate the suitable mesh size for accurate 0.0417, 0.0167, 0.0083 and 0.0042. Here, the mesh size increases from Mesh 5 to Mesh 1, in other words, results and computational efficiency. For the mesh convergences study, the forced replacement method the mesh density increases from Mesh 1 to Mesh 5. Table 3 indicates the summary of the mesh is simulated. The input parameters forthethe mesh convergence studydepth are summarized convergence studies. Figure 7 shows relationship between replacement and computationin Table 2. The heighttime of embankment m is adopted mesh4 convergence studies, and 5,the distance from with mesh sizes. of The2.0 replacement depths in of Mesh are identical with that of Mesh also the

surface to replacement is identified in terms of mesh sizes sm. In this study, five different mesh sizes are assumed with the ratios between the mesh size and the width of embankment (sm /B0 ) of 0.0833, 0.0417, 0.0167, 0.0083 and 0.0042. Here, the mesh size increases from Mesh 5 to Mesh 1, in other words, the mesh density increases from Mesh 1 to Mesh 5. Table 3 indicates the summary of the mesh convergence studies. Figure 7 shows the relationship between replacement depth and computation time with mesh sizes. The replacement depths of Mesh 4 are identical with that of Mesh 5, also the

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computation time of Mesh 5 is dramatically increased. It is demonstrated that the mesh size of Mesh 4 reaches the convergence, therefore, Mesh 4 is used for all of CEL analyses. Appl. Sci. 2017, 7, 1080

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Table 2. Input parameter for Coupled Eulerian–Lagrangian (CEL) analyses (Korea Institute of computation[28]). time of Mesh 5 is dramatically increased. It is demonstrated that the mesh size of Mesh Getechnology 4 reaches the convergence, therefore, Mesh 4 is used for all of CEL analyses.

Soil Cohesion Internal Friction Effective Unit Elastic Poisson’s Table 2. Model Input parameter(kPa) for Coupled Angle Eulerian–Lagrangian (CEL) analyses (Korea Institute 3) (deg.) Weight (kN/m Modulus (MPa) of Ratio Getechnology [28]). Organic soil * M.C. 2.4 0 1 0.24 0.49 (very soft soil) Elastic Modulus Poisson’s Soil Cohesion Internal Friction Effective Unit Model 3 Embankment M.C. 15.0 9 ) (MPa) 20 Ratio 0.33 (kPa) Angle25(deg.) Weight (kN/m Deep mixing soil soil M.C. 21.6 0 3 4.3 0.49 Organic (very soft soil) Embankment Deep mixing soil

* M.C.

2.4

M.C. M.C.

15.0 21.6

0

1

0.24

0.49

25 0

9 3

20 4.3

0.33 0.49

* M.C. = Mohr-Coulomb model.

Table 3. Convergence study for mesh. * M.C. = Mohr-Coulomb model.

TableReplacement 3. Convergence study forComputation mesh.

Name

sm /B0

Mesh 1 Mesh 2 Mesh 3 Mesh 4 Mesh 5

Name 0.0833

sm/B0

Mesh 1 0.0417 Mesh 2 0.0167 Mesh 3 0.0083 Mesh 4 0.0042 Mesh 5

0.0833 0.0417 0.0167 0.0083 0.0042

Depth Dz (m)

Replacement

5.0 Depth Dz (m) 4.5 5.0 4.2 4.5 4.1 4.2 4.1 4.1 4.1

Time (s)

Computation 6.5(s) Time 44.6 6.5 204.3 44.6 204.3 930.5 930.5 7260.1 7260.1

Number of Elements

Number of Elements 3243 3243 32,586 32,586 69,786 69,786 163,416 163,416 471,516 471,516

Figure 7. Relationship between replacement depth and computation time.

Figure 7. Relationship between replacement depth and computation time. 4.2. Simulation of Forced Replacement Method

4.2. Simulation of Forced Replacement Method deposit from 0.0 to 16.0 m consists of very soft soil, having As mentioned above, the subsurface N value of 0/30. Thus, it was planned to improve a soil strength through the forced replacement AsSPT mentioned above, the subsurface deposit from 0.0 to 16.0 m consists of very soft soil, having method in this site, in order to build the temporary road embankment for the construction. For the SPT N value of 0/30. Thus, it was planned to improve a soil strength through the forced replacement forced replacement method, the lateral deformation and the heave in nearby the range occurring methodforced in this site, in order tooccur build the temporary road embankment construction. replacement would together. These effects are closely related tofor the the constructability and For the forced replacement theHowever, lateral deformation and the heave in nearbydepth the range occurring economics for method, construction. the existing approaches for replacement could not predict the height and range of soil heave. Therefore, the CEL analyses are performed to investigate forced replacement would occur together. These effects are closely related to the constructability and the replacement depth, height and range of soil heave of this site. economics for construction. However, the existing approaches for replacement depth could not predict the height and range of soil heave. Therefore, the CEL analyses are performed to investigate the replacement depth, height and range of soil heave of this site.

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Figure 8 shows a CEL model for the simulation of forced replacement method. The overall Appl. Sci. 2017, 7, 1080 9 of 16 dimensions of the domains comprise a width of 16 times the embankment width (B0 ) in x-direction, in order to minimize possible boundary on the predicted depth, height, and range Figure 8 shows a CEL model foreffect the simulation of forcedreplacement replacement method. The overall dimensions of the domains comprise a width of 16 the embankment width (Bthe 0) in x-direction, depth of soil heave. In addition, the width of the domain intimes y-direction is 1 m, because replacement order are to minimize boundary on theThe predicted depth, in height, and range and soilinheave mainly possible important in thiseffect analysis. heightreplacement of the domains z-direction is 16.0 m, of soil heave. In addition, the width of the domain in y-direction is 1 m, because the replacement and the width and height of embankment are modelled on 6.0 m and 2.0 m, respectively, which is depth and soil heave are mainly important in this analysis. The height of the domains in z-direction identicaliswith the site condition. Zero horizontal displacements are predefined at the lateral boundaries 16.0 m, and the width and height of embankment are modelled on 6.0 m and 2.0 m, respectively, and fullwhich fixities the bottom boundary. The Zero domain is divided into twoare parts, i.e., theatsoft soil part and is at identical with the site condition. horizontal displacements predefined the lateral the voidboundaries part where could be bottom heavedboundary. and moved theisempty element. andthe fullsoil fixities at the The into domain divided into two Especially, parts, i.e., thethe void softno soil part and the void part where the soil could heaved and the emptyfor element. part have properties, indicating zero strength and be stiffness. Themoved input into parameters analyses are Especially, the void part have no properties, indicating zero strength and stiffness. The input summarized in Table 2, based on the geotechnical investigation. parameters for analyses are summarized in Table 2, based on the geotechnical investigation.

(a)

(b) Figure 8. CEL model for the simulation of forced replacement method: (a) Dimensions and boundary

Figure 8. CEL model for themesh. simulation of forced replacement method: (a) Dimensions and boundary conditions; (b) typical conditions; (b) typical mesh. To verify the CEL modelling qualitatively, the instantaneous velocity vector plot in a velocity field is illustrated, as shown in Figure 9. We could investigate the mechanism of the forced To verify the CEL modelling qualitatively, the instantaneous velocity vector plot in a velocity field replacement method in terms of the sequences, representing the soil flow. As shown in Figure 9, the is illustrated, asasshown in Figure 9. We could of theIt forced replacement soil flow dotted lines comprise wedge zone,investigate radial shear the zone,mechanism and passive zone. is very similar methodtointhe terms of the sequences, representing the soil flow. As shown in Figure 9, the soil flow general bearing capacity theory for a strip foundation proposed by Terzaghi [22]. As the replacement occurs, the magnitude vertical flow decreases, thezone. magnitude of lateral and to the as dotted lines comprise wedge zone,ofradial shear zone, andwhereas passive It is very similar flow increases. Based for on the instantaneous velocity vector by plot, the range[22]. and As magnitude of general heave bearing capacity theory a strip foundation proposed Terzaghi the replacement soil heave can be predicted practically and qualitatively.

occurs, the magnitude of vertical flow decreases, whereas the magnitude of lateral and heave flow increases. Based on the instantaneous velocity vector plot, the range and magnitude of soil heave can be predicted practically and qualitatively.

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Figure 9. 9.Instantaneous velocity plots. Figure Instantaneous velocity plots. Figure 9. Instantaneous velocity plots. Figure 10 illustrates the results of simulating forced replacement method for H = 2.0 m. For the

Figure 10 illustrates the results of simulating forced replacement method for H = 2.0 m. For the embankment height of 2.0 m, the replacement depth and replacement thickness are approximately Figure 10 illustrates the results of simulating forced replacement method for Hare = 2.0 m. For the embankment height of 2.0m, m, the replacement depth and thickness approximately 4.0–4.1 m and 1.7–2.1 respectively. When compared with replacement the field investigations, the replacement embankment height of 2.0 m, the replacement depth and replacement thickness are approximately 4.0–4.1 m andof1.7–2.1 respectively. When compared with thereplacement field investigations, the replacement depth 4.0–4.1 m, m from CEL analyses is similar to the measured depth of 4.0–5.0 m. In 4.0–4.1 m and the 1.7–2.1 m,and respectively. compared with the22.6 field investigations, the replacement range of soilWhen heave are about 1.1 m and m.replacement In addition, thedepth replacement depth ofaddition, 4.0–4.1 mheight from CEL analyses is similar to the measured of 4.0–5.0 m. of 4.0–4.1 m from CEL analyses ishence, similar the measured replacement depthwith ofthe 4.0–5.0 m. In angle α ranges from to 57 degrees; theto replacement shape canm. be In predicted varying In depth addition, the height and27 range of soil heave are about 1.1 m and 22.6 addition, replacement addition, the height and range of soil heave are about 1.1 m and 22.6 m. In addition, the replacement the embankment geometries, such as the height, width, and angle of embankment. Therefore, it can angle α ranges from 27 to 57 degrees; hence, the replacement shape can be predicted with varying the useful the reasonable of soilshape for thecan replacement, based on the anglebe α extremely ranges from 27 to estimate 57 degrees; hence, thequantity replacement be predicted with varying embankment geometries, such as the height, width, and angle of embankment. Therefore, it can be predicted replacement shape. Based on the comparison results of measured in field test andit can the embankment geometries, such as the height, width,between and angle of embankment. Therefore, extremely useful to estimate the quantity of soil for the replacement, based the predicted CEL analyses, it istofound thatreasonable the of CEL analyses agree well with theon results be extremely useful estimate theresults reasonable quantityquantitatively of soil for the replacement, based of on the replacement shape. on the the comparison of measured in field test CEL analyses, the field tests,Based also ensuring reasonablebetween accuracy results of CEL technique. Furthermore, thisand simulation predicted replacement shape. Based on the comparison between results of measured in field test and shows capabilities CEL to simulatequantitatively the forced replacement method reasonably. Additionally, it is found thatthethe results ofofCEL analyses agree well with the results of the field tests, CEL analyses, it is found that the results of CEL analyses quantitatively agree well with the results of the engineers can consider not only the constructability factors such as the replacement depth, height also the reasonable accuracy of CEL technique. Furthermore, this simulation shows the theensuring field ensuring the reasonable accuracy of CEL technique. Furthermore, this simulation andtests, rangealso of soil heave but also the economic factor such as quantity of soil using CEL technique. capabilities of CEL to simulate the forced replacement method reasonably. Additionally, the engineers shows theFor capabilities of CEL to simulate forced replacement reasonably. Additionally, the embankment height of 2.0 m, the the additional embankmentmethod should be needed to set ground canthe consider notcan only the constructability factors such as the replacement depth, height andfor range of engineers consider only the constructability factors suchThus, as the depth, height level straightly, becausenot the maximum settlement of 2.4 m occurred. thereplacement additional analysis soiland heave but also the economic factor such as quantity of soil using CEL technique. the embankment height 3.0 the m iseconomic conducted factor to review theas feasibility forced replacement method. range of soil heave butof also such quantityofof soil using CEL technique. ForFor thethe embankment height ofofof 2.0 m, additional embankment should needed set ground Figure 11 illustrates the results simulating forced replacement method for H be =be 3.0 m. In this case, embankment height 2.0 m, the the additional embankment should needed toto set ground all of the very soft soil is replaced by embankment, meaning that the embankment soil reaches the level straightly, because m occurred. occurred.Thus, Thus,the theadditional additional analysis level straightly, becausethe themaximum maximumsettlement settlement of 2.4 m analysis forfor bottom of soft soil deposit. Since the soil profile review comprised very deepof soil deposit of 16.0 m,method. thethe embankment height ofof3.0 thethe feasibility forced replacement embankment height 3.0m misisconducted conducted to review the feasibility ofsoft forced replacement method. the quantity of soil for replacement would be substantial and the costs for construction would be Figure illustratesthe theresults resultsofofsimulating simulating forced forced replacement 3.03.0 m.m. In In this case, Figure 1111 illustrates replacementmethod methodfor forHH= = this case, increased. Because of this, it is hard to apply the forced replacement method in this site. very softsoil soilisisreplaced replacedby byembankment, embankment, meaning meaning that reaches thethe allall of of thethe very soft thatthe theembankment embankmentsoil soil reaches bottom soft soildeposit. deposit.Since Sincethe the soil soil profile profile comprised deposit of of 16.0 m, m, bottom ofof soft soil comprisedthe thevery verydeep deepsoft softsoil soil deposit 16.0 the quantity of soil for replacement would be substantial and the costs for construction would be be the quantity of soil for replacement would be substantial and the costs for construction would increased. Because of this, it is hard to apply the forced replacement method in this site. increased. Because of this, it is hard to apply the forced replacement method in this site.

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(a) Figure 10. Cont.

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(b) Figure 10. Results of simulating forced replacement method (H = 2.0 m): (a) Replacement depth, range (b) Figure 10. Results of soil; simulating forced replacement method (H = 2.0 m): (a) Replacement depth, and height of heave (b) replacement angle. Figure 10.height Resultsofofheave simulating forced replacement range and soil; (b) replacement angle.method (H = 2.0 m): (a) Replacement depth, range and height of heave soil; (b) replacement angle.

Figure 11. Results of simulating forced replacement method (H = 3.0 m).

4.3. Simulation of Pile Installation on Deep Mixing Soil

Figure11. 11.Results Resultsof ofsimulating simulatingforced forcedreplacement replacementmethod method(H (H==3.0 3.0m). m). Figure

For the ground improvement, secondly, the deep mixing method is reviewed to identify the feasibility of of that. InInstallation this analysis, the self-standing 4.3. Simulation ofPile Pile Installation onDeep Deep MixingSoil Soil of pile equipment on deep mixing soil and the 4.3. Simulation on Mixing overturn of pile equipment during pile installation caused by the settlement are comprehensively Forthe theground groundimprovement, improvement, secondly,the thedeep deepmixing mixing method isisreviewed reviewed toidentify identifythe the For investigated using CEL technique. Itsecondly, is assumed that the depositmethod of deep mixing soil istoconstructed feasibilityof of that. In In thisanalysis, analysis, the theself-standing self-standing of of pileequipment equipment ondeep deepmixing mixingsoil soiland and the feasibility from 0.0 m that. to 5.0 m.this The analysis cases are divided intopile three cases suchon as (1) self-standing of pilethe overturn of pile equipment during pile installation caused by the settlement are comprehensively overturn of pile caused by the settlement are comprehensively equipment; (2) equipment effect of pileduring jacking;pile and installation (3) effect of pile driving. investigated using CELtechnique. technique. assumed thatconditions thedeposit deposit ofdeep deep mixing soil constructed investigated CEL ItIt isisand assumed that the mixing constructed Figureusing 12 represents a CEL model boundary forof the simulation ofsoil pileisis installation from 0.0m mmixing 5.0m. m. The analysis casesare arethe divided intoare three casessuch such as(1) (1)self-standing self-standing ofpile pile from toto5.0 The analysis cases divided into three cases on 0.0 deep soil. The dimensions of domains composed of as about 16 times the of pile equipment; (2) effect of pile jacking; and (3) effect of pile driving. equipment; effect(P ofl) pile (3) effect of pile driving. equipment(2) length and jacking; a heightand of 16.0 m, to minimize the wave reflecting effect caused by the Figure 12represents represents CEL model andaboundary boundary conditions forthe the simulation ofis pile installation pile driving. At the sides of themodel domains, zero flowconditions velocity normal tosimulation those planes prescribed, Figure 12 aaCEL and for of pile installation onand deep mixing soil. dimensions the domains are at composed of about 16pile times the a mixing zero follow velocity in the vertical direction is the base of domains [6,13]. Thepile on deep soil. TheThe dimensions of theof domains areimposed composed of about 16the times the equipment equipment length (P l ) and a height of 16.0 m, to minimize the wave reflecting effect caused by the pile domain and soil domain are imposed on the Lagrangian coordinate and Eulerian coordinate, length (Pl ) and a height of 16.0 m, to minimize the wave reflecting effect caused by the pile driving. respectively. The input parameters for analyses areflow summarized in Table 2, on the geotechnical pile driving. the sides of the domains, a zero velocity normal tobased those planes is and prescribed, At the sides ofAt the domains, a zero flow velocity normal to those planes is prescribed, a zero 2, according investigation. Also, the contact pressure of pile equipment is considered as 183.7 kN/m and a zero follow velocity in the vertical direction is imposed at the base of the domains [6,13]. The follow velocity in the vertical direction is imposed at the base of the domains [6,13]. The pile domain to the design report [28]. For the pile jacking, the velocity of pile jacking is considered as 1 m/sec. For pile domain and soil domain are imposed on the Lagrangian coordinate and Eulerian coordinate, and soil domain are imposed on the Lagrangian coordinate and Eulerian coordinate, respectively. the pile parameters driving, discrete hammerare blows are imposed by a time-load curve applied at the theinvestigation. reference respectively. The input forsummarized analyses areinsummarized in Table based on geotechnical The input forparameters analyses Table 2, based on the2,geotechnical point of the pile, as shown in Figure 13 [13], and the pile driving energy is considered as 100 investigation. Also, the contact of pile equipmentasis183.7 considered 183.7 kN/m , kN·m. according Also, the contact pressure of pilepressure equipment is considered kN/m2as , according to2the design to the [28]. design report [28].jacking, For the pile jacking, the velocity of pile jacking is considered 1 m/sec. For report For the pile the velocity of pile jacking is considered as 1 m/sec.asFor the pile the pilediscrete driving,hammer discreteblows hammer blows arebyimposed by acurve time-load curve applied at the reference driving, are imposed a time-load applied at the reference point of the point the pile, as shown in Figure 13 pile [13],driving and theenergy pile driving energy is pile, asof shown in Figure 13 [13], and the is considered asconsidered 100 kN·m. as 100 kN·m.

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(a)(a)

(b)(b)

(c)(c)

Figure CEL model and boundary conditions simulation pile installation deep mixing Figure 12.12. CEL model and boundary conditions forfor thethe simulation ofof pile installation onon deep mixing Figure 12. CEL model and boundary conditions for the simulation of pile installation on deep mixing soil: view; front view; and, side view. soil: (a)(a) 3D3D view; (b)(b) front view; and, (c)(c) side view. soil: (a) 3D view; (b) front view; and, (c) side view.

Pile driving load (kN) Pile driving load (kN)

Pmax Pmax

0 0

0.02 0.02

0.04 0.04

0.06 0.06

Time Time (s)(s)

Figure 13. Pile driving load with time for one hammer blow (modified from Ko et al. [13]). Figure Pile driving load with time one hammer blow (modified from [13]). Figure 13.13. Pile driving load with time forfor one hammer blow (modified from KoKo et et al.al. [13]).

Figure 1414 illustrates the results ofof simulating pile installation onon deep mixing soil. AsAs shown inin Figure illustrates the results simulating pile installation deep mixing soil. shown Figure 14 illustrates the results of simulating pile installation on deep mixing soil. As shown in Figure 14, the pile equipment could not be self-standing, also, in the cases of pile jacking and driving, Figure the pile equipment could not self-standing, also, the cases pile jacking and driving, Figure 14,14, the pile equipment could not bebe self-standing, also, inin the cases ofof pile jacking and driving, the pile equipment during pile installation settle and overturn, because of being not enough bearing the pile equipment during pile installation settle and overturn, because being not enough bearing the pile equipment during pile installation settle and overturn, because ofof being not enough bearing capacity ofof pile equipment toto resist overturning. ToTo investigate the behavior ofof pile equipment, the capacity pile equipment resist overturning.To investigate the behavior pile equipment, the capacity of pile equipment to resist overturning. investigate the behavior of pile equipment, the vertical displacements at each edge of pile equipment are checked, as shown in Figure 15. For the verticaldisplacements displacementsatateach eachedge edgeofofpile pileequipment equipmentare arechecked, checked,asasshown shownininFigure Figure15.15.For Forthe the vertical self-standing ofof pile equipment, the vertical displacements atat all ofof the edges are similar. However, self-standing pile equipment, the vertical displacements all the edges are similar. However, self-standing of pile equipment, the vertical displacements at all of the edges are similar. However, the differential vertical displacements each edge occurs during the pile installation, especially, the differential vertical displacements at each edge occurs during the pile installation, especially, the the differential vertical displacements atat each edge occurs during the pile installation, especially, the the vertical displacements in the front of the pile equipment are larger than those of the rear. In addition, vertical displacements the front the pile equipment are larger than those the rear. addition, vertical displacements inin the front ofof the pile equipment are larger than those ofof the rear. InIn addition, the vertical displacements during the pile installation are larger than those inin case ofof self-standing ofof the vertical displacements during the pile installation are larger than those case self-standing the vertical displacements during the pile installation are larger than those in case of self-standing of

pile equipment. indicated that the behavior pile equipment influenced the pile installation pile equipment. It It is is indicated that the behavior ofof pile equipment is is influenced byby the pile installation loading such pile jacking and driving. loading such asas pile jacking and driving.

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pile equipment. It is indicated that the behavior of pile equipment is influenced by the pile installation Appl. 13 Appl. Sci. Sci. 2017, 2017, 7, 7, 1080 1080 13 of of 16 16 loading such as pile jacking and driving. The The deep deep mixing mixing method method has has aa disadvantage disadvantage of of expensive expensive costs costs for for construction. construction. Also, Also, the the soil soil conditions composed of very deep soft soil in this site is to economic feasibility. composed unfavorable Thus, conditions composed of very deep soft soil in this site is unfavorable to economic feasibility. Thus, Thus, the the extremely extremely expensive expensive costs costs for for construction construction would would be be expected expected in in order order to to ensure ensure enough enough bearing bearing capacity for constructability using deep mixing methods. Based on this point, it is hard to consider for constructability using deep mixing methods. Based on this point, it is hard to consider the capacity for constructability using deep mixing methods. Based on this point, it is hard to consider the deep mixing method in this site. deep mixing method in this site. the deep mixing method in this site.

(a) (a)

(b) (b)

(c) (c)

(d) (d)

(e) (e)

(f) (f)

(g) (g)

(h) (h)

(i) (i)

Figure Figure 14. 14. Results Results of of simulating simulating pile pile installation installation on on deep deep mixing mixing soil: soil: (a) (a) Self-standing Self-standing of of pile pile Figure 14. Results of simulating pile installation on deep mixing soil: (a) Self-standing ofself-standing pile equipment equipment at initial stage; (b) self-standing of pile equipment at medium stage; (c) equipment at initial stage; (b) self-standing of pile equipment at medium stage; (c) self-standing of of at initial stage; (b) self-standing of pilejacking equipmentinitial at medium (e) stage; (c) self-standing of pile equipment pile pile equipment equipment at at final final stage; stage; (d) (d) pile pile jacking at at initial stage; stage; (e) pile pile jacking jacking at at medium medium stage; stage; (f) (f) pile pile at final stage; (d) pile jacking at initial at stage; (e)stage; pile jacking at mediumatstage; (f) pile jacking at final jacking jacking at at final final stage; stage; (g) (g) pile pile driving driving at initial initial stage; (h) (h) pile pile driving driving at medium medium stage; stage; and, and, (i) (i) pile pile stage; (g) pile driving at initial stage; (h) pile driving at medium stage; and, (i) pile driving at final stage. driving at final stage. driving at final stage.

(a) (a)

(b) (b) Figure 15. Cont.

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(c)

(d)

(c) (d) Figure 15. Vertical displacement with edges of pile equipment: (a) Self-standing of pile equipment; Figure 15. Vertical displacement with edges of pile equipment: (a) Self-standing of pile equipment; (b) pile jacking; (c) pile driving; and (d) comparison with methods of pile installation. Figure 15. Vertical displacement with edges of pile equipment: (a) Self-standing of pile equipment; (b) pile jacking; (c) pile driving; and (d) comparison with methods of pile installation. (b) pile jacking; (c) pile driving; and (d) comparison with methods of pile installation.

Energy (kN·m) Energy (kN·m)

4.4. Discussion 4.4. Discussion 4.4. Discussion Figure 16 illustrates the comparison of internal energy (Ei) and kinetic energies (Ek) for forced Figure 16method illustrates the comparison of internal energysoil. (E ) and kinetic energies (Ek ) be forused forced replacement and installation deep energy mixing Thekinetic energyenergies balance(E can to Figure 16 illustrates thepile comparison of on internal (Ei)i and k) for forced replacement method and pile installation on deep mixing soil. The energy balance can be used to check the appropriate analysis in CEL technique. ratio soil. of kinetic energybalance to internal (Ekto /Ei) replacement method and pile installation on deepThe mixing The energy canenergy be used check the appropriate analysis typically in CEL technique. The ratio ofFor kinetic energy to internal energy (E /E should has the small fraction, meaning under 5%. forced replacement methods, E kk /E i) check the appropriate analysis in CEL technique. The ratio of kinetic energy to internal energy (Ek/Eii)of should has the small fraction, typically meaning under 5%. For final forced replacement methods, Ek /Ei of H = 1, 2 and 3 m were 2.7%, 0.1% and 0.5%, respectively, at the analysis step. For pile installation should has the small fraction, typically meaning under 5%. For forced replacement methods, Ek/Ei of H =deep 1, 2 and 3 m were 2.7%, 0.1% and 0.5%, respectively, thepile finaldriving analysis step.1.9%, For pile installation mixing soil,2.7%, E k/Ei of self-standing, pile jackingatat and 1.9% and 1.6%, Hon = 1, 2 and 3 m were 0.1% and 0.5%, respectively, the final analysiswere step. For pile installation on deep mixing soil,on Ekthe /Ei results of self-standing, pile jacking and pilethat driving werein1.9%, 1.9% and 1.6%, respectively. Based of energy balance, it is found all cases the present on deep mixing soil, Ek/Ei of self-standing, pile jacking and pile driving were 1.9%, 1.9% andanalysis 1.6%, respectively. Based on the results of energy balance, it is found that all cases in the present analysis are are in equilibrium andthe appropriate. respectively. Based on results of energy balance, it is found that all cases in the present analysis in equilibrium and appropriate. are in equilibrium and appropriate.

(a)

(b)

(a) of internal and kinetic energies: (a) Forced replacement (b) Figure 16. Comparison method; (b) pile installation on deep mixing soil. Figure 16. Comparison of internal and kinetic energies: (a) Forced replacement method; (b) pile Figure 16. Comparison of internal and kinetic energies: (a) Forced replacement method; (b) pile installation on deep mixing soil. installation mixing Based on on thedeep results ofsoil. CEL analyses, two ground improvement methods, i.e., the forced replacement and of theCEL deepanalyses, mixing method, can improve a certain soil strength, Based on method the results two ground improvement methods, i.e., thehowever, forced thereBased are theon risks constructability during constructions such as pile installation. In addition, the the for results ofdeep CEL mixing analyses, two ground improvement methods, i.e., the forced replacement method and the method, can improve a certain soil strength, however, soil conditions composed of very deep soft soil in this site is unfavorable to economic feasibility. replacement method and the deep mixing can improve a certain soil strength, however, there are the risks for constructability during method, constructions such as pile installation. In addition, the Therefore, the installation of temporary bridges is more economically analyzed than the two ground soil conditions composed of very deep soft soil in this site is unfavorable to economic feasibility. improvement methods, and the temporary bridges wereeconomically actually installed during the the realtwo construction. Therefore, the installation of temporary bridges is more analyzed than ground improvement methods, and the temporary bridges were actually installed during the real construction.

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there are the risks for constructability during constructions such as pile installation. In addition, the soil conditions composed of very deep soft soil in this site is unfavorable to economic feasibility. Therefore, the installation of temporary bridges is more economically analyzed than the two ground improvement methods, and the temporary bridges were actually installed during the real construction. 5. Conclusions The main objective of this study is to investigate the behavior of very soft soil and constructability of two ground improvement methods, i.e., forced replacement method and deep mixing method. For this purpose, the large deformation finite element (LDFE) analyses using Coupled Eulerian-Lagrangian technique are implemented. The results of the CEL modelling are verified by comparison between those and the field investigations with settlement, height, and range of soil heave. Additionally, to examine the constructability and economics of each method, comprehensive reviews are performed. The following conclusions could be drawn from the present study:

•

•

•

•

The CEL technique is successfully applied to solve the constructability problems of sites on very soft soil. The applicability of the CEL modelling is verified by comparison between those and the field investigations with settlement, height, and range of soil heave for the forced replacement method. Furthermore, the replacement shape can be predict with varying the embankment geometries such as the height, width, and angle of embankment, therefore, it can be extremely useful to estimate the reasonable quantity of soil for the replacement. For the deep mixing method, the pile equipment could not be self-standing, also, in cases of pile jacking and driving, the pile equipment during pile installation settle and overturn, because of being not enough bearing capacity of pile equipment to resist overturning. In addition, the vertical displacements settlement at each edge occurs during the pile installation, especially, the vertical displacements in the front of the pile equipment are larger than those of the rear. The vertical displacements during the pile installation are larger than those in the case of self-standing of pile equipment. It is indicated that the behavior of pile equipment is influenced by the pile installation loading, such as pile jacking and driving. Two ground improvement methods can improve a certain soil strength, however, there are the risks for constructability during constructions, such as pile installation, also the soil conditions composed of very deep soft soil in this site is unfavorable to economic feasibility. The behavior of very soft soil and constructability with methods can be investigated using CEL technique, which would be useful tools for comprehensive reviews in preliminary design.

Acknowledgments: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant No. 2016R1A6A3A03010454) for Junyoung Ko. Sangseom Jeong and Junghwan Kim would like to thank the National Research Foundation of Korea (NRF) (Grant No. 2011-0030040) for supporting this research work. Author Contributions: Junyoung Ko performed the numerical studies and wrote the draft of the paper; Sangseom Jeong designed this research and assisted with the writing of the paper; Junghwan Kim analyzed the numerical data and assisted with the numerical analyses. Conflicts of Interest: The authors declare no conflict of interest.

References 1. 2. 3.

Whitlow, R. The Geology of the Gold Coast Region. Geoscientific Consultancy Report; Gold Coast City Council: Gold Coast, Australia, 2000. Zainorabidin, A.; Wijeyesekera, D. Geotechnical Challenges with Malaysian Peat. In Proceedings of the Advances in Computing and Technology, London, UK, 23 January 2007; pp. 252–261. American Society for Testing and Materials (ASTM). Standard Practice for Classification of Soils for Engineering Purpose (Unified Soil Classification System); D2487; American Society for Testing and Materials: West Conshohocken, PA, USA, 2011.

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