CHAPTER 9 FEM MODELING OF SOIL-SHEET PILE WALL INTERACTION

Transcription

1 391 CHAPTER 9 FEM MODELING OF SOIL-SHEET PILE WALL INTERACTION 9.1 OVERVIEW OF FE SOIL-STRUCTURE INTERACTION Clough and Denby (1969) introduced Finite Element analysis into the soil-structure interaction problem. The Finite Element Method (FEM) ability to model complex construction sequence and to incorporate specific site properties of the structure system and surround soils has since gained widespread acceptance. The FEM provides a comprehensive tool for analyzing the multiple facets of sheet-pile performance in soils, such as ground movements, sheet pile deformation, embankment settlements and effects of construction activities e.g. (dewatering, ground improvement, etc.). Prediction or back-analysis of excavation wall deformation or ground surface settlements, or, the earth pressure against the wall using finite element analysis has been studied by many researchers such as Clough and Hansen (1981), Clark and Wroth (1984), Garrett and Barnes (1984), Borja and Lee (1990), Finno and Harahap (1991), Whittle et al. (1993, 1997), Ng and Lings (1995), Ou et al. (1996), and Kort (2002). Most of the known work focuses however on the analysis of a structure performance in excavation in clay, and no work is known to be done to model excavation in peat, replacement of peat with granular backfill materials, deep dynamic compaction (DDC) and embankment construction, let along its comparison to field measurement. This work is designed to model various phases of road construction, which includes sheet pile installation, peat excavation, backfilling, sheet pile instrumentation installation, consolidation, deep dynamic compaction (DDC), mechanical stabilized earth (MSE) wall and embankment construction. All the construction stages were modeled continuously to study the accumulated effects of the continuous construction activities. Finally the modeled results evaluated against field measurements and the classic earth pressure theories. 9.2 INTRODUCTION OF PROBLEM STATEMENT Five instrumented stations were located in cranberry bog areas with deep peat deposits overlaying a medium dense sand layer. Based on boring logs, probing and SPT result, it was determined that peat depth was up to 35 feet. The design called for excavation of these soft organic soils and its replacement by granular fills. The excavation was supported by cantilever sheet pile walls, in order to resist the peat in the retaining side during excavation and to retain the fill after the backfilling. Six months after the peat was replaced with granular fills, single sheet piles located at stations were replaced by instrumented sheet piles. The instrumentation, consisting of pressure cells and inclinometer casings was aimed to measure the total earth pressure acting on the exterior (supporting side) of the sheet piles and the sheet piles deformation following the instrumentation installation. The total pressures and the wall deformation were monitored for a period of over 2 years following the installation. Because the site was not dewatered during the excavation and backfilling process, the granular fills were in loose, saturated state, susceptible of liquefaction. Deep dynamic compaction (DDC) was adopted to improve the granular fills engineering properties. Half a year after the sheet pile instrumentation installation, deep dynamic compaction (DDC) was

2 392 performed. Nine months after the deep dynamic compaction (DDC), the MSE wall was carried out over the central portion of the fill. The purpose of the presented FEM analysis is to model the sheet pile performance in the peat under the different construction stages and to compare the modeling results with those measured in the field, hence to obtain helpful insight for future design of sheet pile in peat. The Finite Element program PLAXIS version 8.2 (Brinkgreve et al., 2002) was used in the present research simulation. A detailed review of the principles used in the PLAXIS modeling and the modeling options available in PLAXIS are provided in Appendix A. The following sections describe the details associated with the chosen models and parameters following by each road section sheet pile analysis and the construction stages used in the simulation. 9.3 DETERMINATION OF PARAMETERS FOR MODELING Parameters Summary Tables The parameters for the soils and other materials used in the FEM analysis are presented in tables 9.1 to 9.9. Table 9.1 summarizes the material properties of the deep sand and the interfaces before deep dynamic compaction. Table 9.2 summarizes the material properties of the backfill and the interfaces before deep dynamic compaction. Table 9.3 summarizes of the material properties of the sheet piles. Table 9.4 summarizes the material properties of Carver peat and the interfaces. The engineering parameters of Peat were obtained mainly from triaxial tests, consolidation tests and direct shear tests as described in section The parameters of the backfill materials and deep sand were obtained mainly from PCPT tests as described in section Table 9.5 summarizes the material properties of the deep sand and the interfaces after deep dynamic compaction. Table 9.6 summarizes the material properties of the backfill materials and the interfaces after deep dynamic compaction. Table 9.7 summaries the materials properties of the MSE wall. Table 9.8 summaries the material properties of the steel strips for the MSE wall reinforcement. Table 9.9 summaries all the assumptions used for the modeling Soil Models and Associated Parameters (a) Backfill Sand and naturally Deposited Sand below the Peat The sand below the peat and the backfilling granular materials was assumed in the FE analysis to behave as an elastic perfectly plastic material in the yield, which is determined by Mohr-Coulomb model. The elastic-plastic Mohr-Coulomb model requires a total of five basic parameters, namely Young s modulus, E; Poisson s ratio, ν ; friction angle, φ ; cohesion, c; and dilatancy angle, ψ. The Young s modulus, E; Poisson s ratio, ν are assumed to be constant. Young s modulus, E, determined by the PCPT field test (see section 3.6.3). Poisson s ratio, ν, was assumed to be 0.25 for both the backfill soils and the deep sand, which were also assumed to be drained materials. Friction angles, φ, of both backfill and deep sand were determined by the PCPT field tests and assumed to be constant (see section 3.6.3). Interface parameter, R inter, was assumed to be better model soil-pile interaction.

3 393 DDC was employed to improve the saturated backfill granular materials, and PCPT field tests were utilized before and after the compaction to investigate the changes in the engineering properties of the backfill. According to the data analysis of the PCPT test results presented in section 3.6.3, following the deep dynamic compaction, the engineering properties of the upper backfill and lower deep sand were improved to be come almost of uniform distribution with depth. The engineering parameters of the backfill soils and the deep sand before and after the deep dynamic compaction are presented in tables 9.1, 9.2, 9.5 and 9.6. (b) Carver Peat Carver peat has a high degree of compressibility with a primary compression followed by a significant secondary compression. The secondary compression was noticed to constitute more than fifty percent of the long term compression of about 30 years. As such, creep is important for long period loading problems. In 1936, Buisman proposed a creep law for clay after observing that soft-soil settlement could not be fully explained by the classical consolidation theory. Since that, Bjerrum (1967), Garlanger (1972), Mesri (1977), Leroueil (1977), Sekiguchi (1977), Adachi and Oka (1982), and Borja and Kavaznjian (1985) continued this work on 1D-secondary compression. Carver peat was assigned to be modeled by Soft-Soil-Creep model (SSC-model) capable of accounting for the creep effects. The parameters for the Carver peat required for the Soft-Soil Creep model were obtained from the lab tests, mainly oedometer and triaxial tests, as described in section 3.5 and summarized in table Other Material Models and Associated Parameters The pavement behavior is described by a Mohr-Coulomb drained model with the parameters presented is table (a) Pavement Permeability, K x = K y = 0.1 ft / day 6 Elastic Modulus, E = 2 10 psf Poisson ratio, ν = 0. 3 Effectiveness cohesion, c = 2000 psf 0 Effective friction angle, κ = 30 0 Dilation angle, ψ = 0 Interface parameter, R int er = 0. 5 Total unit weight, γ t = 150 pcf (b) Beam Elements (1) Sheet Pile EA 6 8 = ( ) (6.88/144) = 2 10 lb ft ft / EI = ( ) 211.6/12 = lb ft ft ft / Weight/ft/ft = 23.4 lb/ft/ft (2) MSE Wall (concrete) Panels to be 5.5 inches thick

4 394 (c) 6 ( ) 5.5 = lb ft EA = ft ( ) 1 ( 5.5 ) = lb ft ft EI = ft w = 150 pcf 5.5 = 68.6lb / ft / ft 12 Reinforcement Strips Reinforcement Strips Steel strips to be used, 4 mm high 50 mm wide, at 3.35 ft horizontal spacing 6 ( ) 50 4 ( ) 6 { } = lb EA strip = EA/ft out of plane = /3.35 = lb ft Determination of the Block Loading for the DDC The weight of the tamper for compaction, W =16 tons = lb The drop height, H = 60 ft The times of compaction at each point, N = 9 The depth of the crater caused by nine compaction blows, d = 5ft to 5.5ft The diameter of the tamper, B = 58 inches = ft The potential energy E of each tamper drop is: i E i = W H (9.1) The average depth, d induced by each compaction in the backfill is assumed to be: d d = (9.2) N Assuming the average stress (block load) induced by each compaction at the contact face of the tamper and backfill is equal to σ i, then the force, F i, acting on the backfill induced by each compaction is equal to: ( B 2) 2 F i = σ i A = σ i π (9.3) Keeping balance of energy between the potential energy of the tamper and the work done by the tamper penetration: W H = F i d (9.4a) ( B ) 2 d W H = σ i π (9.4b) 2 N 4W H N σ i = (9.4c) π B d 2

5 395 Some energy is lost during the impact hence a energy reduction factor, ξ, is assumed and the block load (dynamic load) for the deep dynamic compaction is then become: σ i 4W H N = ξ 2 π B d (9.5) Determination of the Maximum Load Application Time for the DDC Wave Dissipation in Soils According to the one-dimensional wave propagation theory in soil, the body waves (compression and shear) velocity V p, in a confined one-dimensional body depends on the stiffness E oed, and the mass ρ, of the medium: Eoed V p = where ρ ( 1 ν ) E ( 1+ ν )( 1 2ν ) E oed = and γ ρ = (9.6) g in which E = Young s modulus, ν = Poisson s ratio, γ = total unit weight, and g is the gravity acceleration. The time needed for the propagation of the stress wave is: L Δ t = (9.7) V p in which, L is the distance from the center of the dynamic source. In this case, the maximum time needed for body waves dissipation in horizontal direction can be calculated as: Lh ( fill ) Lh ( peat ) Δ t h = + (9.8) V V p ( fill ) p ( peat ) L Maximum width of the backfill in horizontal direction; h p ( fill ) V Body wave velocity in backfill; h ( fill ) L Maximum distance of the peat in horizontal direction; p ( peat ) V Body wave velocity in peat; ( peat ) The maximum time needed for body waves dissipation in the vertical direction can be calculated as: L ( fill ) ( fill ) L ( sand ) v v Δ t v = + (9.9) Vp Vp ( sand )

6 396 L Maximum depth of the backfill in the vertical direction; v v ( fill ) L Maximum depth of the deep sand below the peat layer in the vertical direction; ( sand ) V Body wave velocity in the deep sand below the peat; p ( sand ) According to equation 9.6, the body wave velocity in the backfill, peat and deep sand can be separately obtained. ( 1 ν ) Eg ( 1+ ν )( 1 2ν )γ V p = (9.10) In the peat: Vp( peat ) In the backfill: Vp( fill ) In the deep sand: Vp( sand ) ( 1 v) E peatg ( 1+ ν )( 1 2ν ) γ peat = (9.10a) ( 1 v) E fill g ( 1+ ν )( 1 2ν ) γ fill = (9.10b) ( 1 v) Esand g ( 1+ ν )( 1 2ν ) γ sand = (9.10c) Equation 9.8 can be then described as: Δt h L = V h p ( fill ) ( fill ) L + V h p ( peat ) ( peat ) = L h ( fill ) ( 1+ ν )( 1 2ν ) ( 1 ν ) E fill γ g fill + L h ( peat ) ( 1+ ν )( 1 2ν ) ( 1 ν ) E g peat γ peat (9.11) And equation 9.9 can be described as: Δt v L = V v ( fill ) p ( fill ) L + V v p ( sand ) ( sand ) = L v ( fill ) ( 1+ ν )( 1 2ν ) ( 1 ν ) E fill γ g fill + L v ( sand ) ( 1+ ν )( 1 2ν ) ( 1 ν ) E g sand γ sand (9.12) From equation 9.12, the maximum time for the body wave propagation from the center of the impact to the sheet pile wall was calculated to be about 0.02 seconds. 9.4 FINITE ELEMENT MODELING OF THE FIVE INSTRUMENTED STATIONS Overview The construction process of US Rt.44 was modeled continuously. The continuous modeling processes were divided into three phases, namely construction before the DDC application, during the deep dynamic compaction (DDC) and following the DDC. In the first phase (before DDC), the FEM modeling includes sheet pile installation in the peat, peat

7 397 excavation, backfilling with granular material, sheet pile instrumentation and consolidation. The second phase (during DDC) includes two passes of backfill compaction in five days. The final phase (after DDC) includes consolidation, MSE wall and embankment construction, and pavement construction. The modeling at the five instrumented stations is introduced one by one in the upcoming sections The Modeling System Assumption The major features of the FEM analysis system are listed as below: 1. In order to simplify the modeling, a plane-strain condition was assumed, meaning that the deformation in the Z-direction is not considered (Z direction refers to the direction along the road). PLAXIS 8.2 can only be used for solving two dimensional problems. 2. The full sheet pile length was modeled, and the fixed bottom boundary is assumed to be located at 2 ft below the tip of the sheet pile. (i.e., it is assumed that there is no deformation at the bottom boundary.) The left side boundary is assumed to be the center line of the symmetry, allowing for vertical displacements only. 3. Peat is a relatively undrained material compared to the sand. As the sand layer is overlain by the peat, closed consolidation boundaries were applied to both vertical sides. The bottom of the peat layer is in contact with the sand. The top of the peat layer is also freely drained, hence the peat is one dimensional double sided drained layer. 4. The peat layer was divided into sub layers, each assumed to be excavated in one day. The backfilling was accomplished using the same number of layers. Each layer was completed in one day. The excavated peat unit weight is much smaller than the replaced granular fills and as a result of the large increase in the vertical stress a settlement takes place in the natural deposit of the medium dense granular sand below the fill. This effect was not monitored and the modeling results were not discussed. 5. Soil-structure interface elements were applied to the sheet pile, MSE wall, and the steel strips to model the soil-structure interaction. To improve the soil-sheet pile interaction model, the soil-structure interface zone was extended one foot below the tip of the sheet pile and the MSE wall using PLAXIS recommendations (Brinkgreve et al., 2002). 6. Large deformations during the construction processes could be expected and actually observed in the field. Such deformations are expected to significantly influence the geometry of the analyzed problem and as a result an updated mesh analysis was chosen for the calculation scheme. 7. During the DDC, the time for each compaction operation was very short, so both the backfill and the deep sand below the peat were defined as undrained. 8. As the compaction was a sudden short duration load application in a single time step, dynamic block load was adopted for its modeling using one tenth of a second time step. 9. Absorbent boundaries were used on both vertical and bottom boundaries to absorb the stress propagating to the boundaries due to the dynamic loading, otherwise reflected waves will propagate inside the soil body.

8 In order to enable better modeling of the sheet pile performance, the FE mesh was refined at the corner points including the top and tip of the sheet pile, and the points on the sheet pile intersecting the borders of the peat and the sand layers node triangle elements were applied for the numerical scheme. 12. The sheet pile and MSE walls were simulated using plate elements. The steel strips were simulated using geotextile elements. 13. Soft-soil creep model (SSC-model) was used to simulate the time-dependent behavior of the peat. Sand was modeled by elasto-plastic Mohr-Coulomb model. A summary of the assumptions used in the FE analysis are presented in table FEM MODELING OF STATION (R) Modeling System Analyzed The site conditions of station (R) were analyzed in section Based on the subsurface exploration, it was determined that the peat deposit at this station was about 15 ft deep and the water table level was at the ground surface. The length of the sheet pile at this station was about 48 ft. Figure 9.1 shows the cross-section view of this station used in the FEM modeling. The peat was subdivided into three layers and excavated in 3 days, i.e. 5 ft peat excavated at each day. The excavation was backfilled with granular materials in three days, 5 ft layer at each day. The site was then consolidated for 200 days. The top of the final backfill was about 3 ft above the peat ground surface. The sheet pile at station (R) was then replaced with the instrumented sheet pile. The pressure cells were located at 4 ft, 9 ft and 14 ft below the peat ground surface (see figure 4.9). The fill was compacted by two DDC passes with a time interval of five days between the two passes. In each pass of compaction, the distance between the centers of adjacent compaction points is 180 inches. Following the DDC, the site was left to consolidate for a period of about 6 months before the MSE wall and the embankment were constructed on the compacted backfill. The distance from the sheet pile wall to the MSE wall was about 25 ft and the embedded depth of the MSE wall in the backfill was about 4 ft. The reinforcement of the embankment was made of six layers of steel strips. The steel strips for the reinforcement were about 12 ft long with a inches height inches width section at 3.35 ft horizontal spacing and a vertical distance (between two adjacent steel strips) of 2 ft. Finally, a 2 ft thick pavement is planned to be built at the top of the embankment. Table 8.17 provides a summary of the relevant construction progress time table. The FEM simulation at station R includes the following major analyses: sheet pile installation, peat excavation, backfilling, instrumentation installation, consolidation, deep dynamic compaction, MSE wall and embankment construction, and pavement construction. Figure 9.2 presents the symmetric plane strain scheme used for the FEM analysis. The distance from the center line to the sheet pile is 58 ft. The bottom boundary was placed two ft below the tip of the instrumented sheet pile. This boundary is rigid and forms the base of the analyzed mesh. The consolidation boundary is 30 ft away from the sheet pile at the side of the peat layer. Absorbent boundaries were defined on both vertical sides and at the bottom boundary. In order to improve the precision of the analysis, a medium dense mesh and an updated mesh were used. The various elements of the FE scheme and the mesh are shown in figure 9.3.

9 399 The staged construction feature of PLAXIS makes it possible to simulate the construction process by first setting up the complete, final layout of the project (as shown in figure 9.2), and then to execute the analysis in a series of phases during each phase various portions of the system are de-activated and activated. The present analysis was performed according to the 155 stages outlined in table FEM Analysis Results of Station (R) Figure 9.4 presents the soil displacements and sheet pile deformation upon completion of the soil replacement at station (R). Following the peat excavation (in the road side), the sheet pile moved towards the excavation side with maximum displacements at the pile head of 0.12 inch. Figure 9.5 presents the soil displacements and sheet pile deformation upon the completion of the backfill placement at station (R). By comparing figure 9.4 and 9.5, it can be observed that with the progress of the backfilling the sheet pile movement reversed directions and moved towards the peat side. At the completion of the backfilling, the pile head developed about 1.1 inches movement towards the peat side from its initial position. Figure 9.6 presents contours of the total displacement developed after the installation of the instrumented sheet pile at station (R) over a period of 180 days. It can be observed that the FEM modeling results indicated that after the peat between the sheet piles was replaced with granular fill, the sheet pile moved towards the bog (outside). Large displacements took place close to the top of the sheet pile as shown in the figure and observed in the field. At the same time, settlements of the natural sands took place in the area between the sheeting due to that the additional load developed when replacing the peat with fill. Figure 9.7 shows the shear strain developed following the instrumented sheet pile installation. The extreme shear strain values (up to 1.3%) coincide with the areas of large displacements shown in figure 9.6. Figure 9.8 presents the modeled total horizontal effective earth pressure developing at the instrumented positions A/D (4ft), B/E (9ft) and C/F (14ft) in the supporting peat starting from the sheet pile installation via the soil replacement to the time of 180 days after the instrumentation installation. The modeling results indicate that during the peat excavation, the effective pressures decreased and then increased during the backfilling progress. The pressure values increased upon the completion of the backfilling and then remained constant during the consolidation period. The instrumentation installation caused a pressure increase (0.42, 0.21 and 0.11 psi increments at positions A/D, B/E and C/F respectively). It indicated that the installation caused increase in the horizontal effective pressure in the top peat layer. After the instrumented sheet pile installation, the pressures decreased with time at all positions. Figure 9.9 shows the displacements in X direction developing at different depths along the sheet pile, with time, starting from the sheet pile installation to 180 days following the instrumentation installation. During the backfilling period, the sheet pile moved towards the supporting peat and stopped moving upon the completion of the backfilling. During the consolidation period, the sheet pile did not undergo additional movements. The instrumentation installation caused the sheet pile additional movement. At 180 days after the

10 instrumentation installation, the pile head developed a cumulative movement of about 3.3 inches in the X direction due to the load caused by the backfilling against the sheet pile wall. Figure 9.10 presents the excess pore pressure distribution at station (R) after consolidation of 180 days following the instrumentation installation. It indicated that as a result of the instrumented sheet pile installation, the excess pore pressure was distributed mainly around the sheet pile in the supporting peat side. The excess pore pressure distribution in the peat fits well the one predicted by Terzaghi s one-dimensional consolidation theory. The maximum excess pore pressure was calculated to be very small (0.06 psf) and its effects are negligible. Figure 9.11 shows the deformed mesh of station (R) as a result of the deep dynamic compaction at point F-3 immediately after nine impacts (1.06 second since the beginning of the first impact). The data illustrates that the deformation of the soil body and the sheet pile match the field measurements. The craters formed by the compaction where 6 ft deep and caused the displacements of 15.8 inches towards the supporting side compared to a value of 13.4 inches measured at the top of the sheet pile. Figure 9.12 presents the deformation at station (R) immediately following the completion of the ninth (last) compaction (six days after the initial impact) at point S-3. It can be noticed that after two passes of deep dynamic compaction, the soils and the sheet pile developed large movements, especially in the area close to the top part of the sheet pile. After two passes of compaction, the calculated pile head displacement was up 2.6 ft (2.2 ft in the X direction). Figure 9.13(a) describes dynamic velocity contours in the soil following the 9th impact (1.06 seconds since the beginning of the first impact) in point F-2 at station (R). The dynamic velocity in the soil radiates away from the impact but under the compaction at point F-2, the dynamic velocity does not reach the sheet pile wall. Figure 9.13(b) shows the dynamic velocity vectors 0.02 second after the nine impacts was stopped at point F-2. By comparing figure 9.13(a) to figure 9.13(b), it can be noticed that 0.02 second after the compaction stopped, the dynamic velocity reached the supporting peat and the influence range was shown in the figure 9.13(b). Figure 9.14 shows the dynamic acceleration contours in the soil during the 9th impact (1.06 seconds since the beginning of the first impact) in point F-3 at station (R). The acceleration and the dynamic energy decrease with the distance from the impact while the acceleration induced by the compaction did not reach the sheet pile wall. Figure 9.15(a) shows dynamic velocity contours in the soil during the 9th impact (1.06 seconds since the beginning of the first impact) in point F-4 at station (R). The dynamic velocity had reached the sheet pile wall when the compaction took place at point F- 4. Figure 9.15(b) shows the dynamic velocity vectors as the sequence of nine blows at point F-4 was stopped, namely during the period of soil body self-vibration 0.02 second after the 9th impact. By comparing figure 9.15(a) and 9.15(b), it can be seen that as the compaction was stopped at point F-4, the dynamic velocity dissipated rapidly into the supporting peat layer and its magnitude decreased from a maximum value of 12.45ft/s to 0.4ft/s within a period of 0.02 second. As the compaction was stopped, the soil body self-vibration appears mainly in the peat. Figure 9.16(a) presents the dynamic acceleration contours in the soil during the 9th impact (1.06 seconds since the beginning of the first impact) in point F-4 at station (R). The wave induced by the impact had reached the sheet pile wall when the compaction 400

11 401 took place at point F-4. Figure 9.16(b) presents the vectors of the dynamic acceleration in the soil 0.02 second after the nine impacts at point F-4 was stopped. By comparing figure 9.16(a) and 9.16(b), it can be seen that as the compaction was stopped, the dynamic wave propagated from the areas close to the compaction source to the areas far from it with the maximum 2 2 magnitude of the dynamic acceleration decreasing rapidly from ft s to 3.2 ft s within a period of 0.02 second. Comparing the information presented in figures 9.13 to 9.16, it can be concluded that the influence of the compaction decreased with the distance from the center of the compaction source. When the compacted area is at a distance up to 30 ft from the sheet pile, the influence on the sheet pile wall is still minimal, translated to an acceleration of 10 ft/s 2 and a velocity of 0.8 ft/s on the sheet pile. When the compaction was closest to the sheet pile, i.e. at a distance of 15 ft, it had a great effect on the sheet pile wall in the form of acceleration of 160 ft/s 2 and a velocity of 5.0 ft/s. Figure 9.17 shows the excess pore pressure distribution induced by the compaction in point F-2 (1.06 seconds since the beginning of the first impact) at station (R). The excess pore pressure caused by the compaction was mainly distributed in the area close to the compaction source and decreased within a distance of 15 ft from the compaction source. The modeling results indicate that the compaction at point F-2 had little influence on the excess pore pressure in the supporting peat, which did not exceed 40 psf in the wall vicinity. Figure 9.18 presents the excess pore pressure distribution induced by the compaction (1.06 seconds since the beginning of the first impact) at point F-4 at station (R). The excess pore pressure distribution shape was almost the same as that in figure The modeling result indicates that even compaction at point F-4, close to the sheet pile wall, had no apparent influence on the excess pore pressure in the supporting peat, which matches the field measurements of the pore pressure developing during the DDC as described in figure 8.3. Figure 9.19 presents the soil and the structure deformations contours at station (R) just after the two passes of the deep dynamic compaction were completed. The maximum deformation occurred in areas around the top of the sheet pile, especially in the peat, which matches the field observations. Due to the peat s high compressibility, large calculated deformation in the magnitude of 17 inches took place at the top of the wall. Figure 9.20 shows the FEM modeling results for the total horizontal earth pressures developing at the instrumented positions (A/D, B/E and C/F) during the entire DDC period at station (R). The modeling results indicated that during each pass of compaction, the earth pressure values at each position increased rapidly to peak values and then decreased as the compaction was completed. The pressure increment (5.5 psi) at position A/D (4ft below the ground surface) is larger than that (5.1 psi) at position B/E (9ft below the ground surface), which is larger than that (3.6 psi) at position C/F (14ft below the ground surface). It indicates that compaction has larger influence on the positions closer to the ground surface. At the same time, it was also observed that pressure increment at each position caused by the second pass of compaction was much smaller than that induced by the first pass of compaction. This is explained by the fact that the distance from the second pass of compaction to the measured points at the sheet pile wall are 15 ft further than those of the first pass, shown in figure 9.1. The modeling results of the horizontal total pressure indicated that distance from the compaction source center to the sheet pile wall has apparent influence. When the distance from the compaction source center to the sheet pile wall is more than 30.0 ft, the compaction

12 402 has almost no influence on the (modeling) total earth pressure. However, for distance in the range of 15.0 to 22.5 ft, the compaction causes large lateral earth pressure increase. Figure 9.21 shows the sheet pile displacement development in X direction caused by the two passes of the DDC at station (R). The modeling results indicate that the DDC resulted with very large sheet pile movement towards the supporting peat side. After two passes of compaction, the pile head movement in the X direction increase from 3 inches to inches and the sheet pile rotational angle around its tip in the sand increased from 0.3 to 3 assuming initial verticality. The rotation angle towards the supporting peat after compaction was about 10 times that before the compaction. Figure 9.22 presents the deformed mesh at station (R) 180 days after the embankment construction, suggesting that the embankment construction caused further soil and structure deformation. Figure 9.23 shows the displacement at station (R) 180 days after the embankment completion. By comparing figure 9.19 with figure 9.23, it can be concluded that additional five inches of lateral movement towards the peat took place at the top of the sheet pile at the ground level due to the embankment construction. Figure 9.24 presents contours of the total shear strain (%) distribution at station (R) following the embankment completion. This shear strain represents the soil condition since the initial week on the site including the DDC. The maximum shear strain (of up to 28%) (red color areas) mainly appeared in the supporting peat closer to the top of the sheet pile. The lower shear strain areas (green-yellow color areas) developed in the backfill side close to the sheet pile wall and along the narrow vertical strip close to the MSE wall in the embankment. The fill area which serves as the foundation to the embankment had undergone shear strains, in which the maximum was up to 10% including the DDC. Figure 9.25 shows the total shear strain increment caused by the embankment construction along at station (R). The shear strain increment induced by the embankment construction is very small (up to 0.055(%)) and it concentrates mainly in a small area around the top of the soil (access road) next to the MSE wall. These results indicate that the construction of the embankment over the compacted fill caused small disturbance in the soil body. Figure 9.26 presents the FEM modeling results of the horizontal effective pressure at the instrumentation positions developing over time following the completion of the DDC at station (R). It shows that as the compaction was completed, the effective horizontal pressure at the instrumentation positions did not change until the beginning of the embankment construction. During the embankment construction period, there was some increment at position A/D (4ft below the ground surface) and B/E (9ft below the ground surface). However, there was some decrease at position C/F (14ft below the ground surface). These changes are possible due to the sheet pile further movement towards the peat. As the embankment was completed, the pressure remained constant with time. Figure 9.27 presents the FEM modeling results for the cumulative horizontal displacement at the different instrumentation positions, developing with time following the completion of the deep dynamic compaction (DDC) at station (R). It shows that in the initial 30 days after the completion of the compaction, some further displacements took place and the pile head moved about 0.84 inches in the X direction. No further movement took place at any of the positions until the beginning of embankment construction. During the embankment construction period, the pile additionally moved towards the supporting peat

13 403 and the pile head developed a total movement in the X direction of about 5.1inches since the completion of the DDC. Following the embankment completion, the sheet pile did not develop any further movement Summary of FEM Analysis Results at Station (R) Figure 9.28 summarizes the FEM modeling results of the variation in the horizontal total earth pressure at the instrumented positions with time during the entire construction periods at station (R). Figure 9.29 summarizes the FEM modeling results of the sheet pile horizontal displacement developing at station (R) during the entire construction period. Figure 9.30 summarizes the FEM results of the lateral earth pressure coefficient (based on equation 8.7) developing with time during the entire construction period at station (R). Based on the FEM analyses results of the total lateral earth pressure, sheet pile horizontal displacement and lateral earth pressure coefficient calculated in the peat, the following conclusions are drawn: (a) Before DDC (1) Total lateral earth pressure. The FEM modeling results indicated that during the eight months following the instrumentation installation, the total lateral earth pressure developed in the supporting peat did not change until the application of the DDC. In the long-term, the FE modeling total lateral earth pressure values have the tendency to decrease very slowly with time. (2) Sheet pile deflection. The horizontal displacement of the sheet pile oriented to the supporting peat did not show increase during this period. (3) Lateral earth pressure coefficient, K. The calculated lateral earth pressure coefficient, K, based on equation 8.7 initially remained about constant in the first 3 months after the instrumentation installation and then decreased slowly until the application of the DDC. It was also noticed that during this period, the modeling K based on equation 8.7 was a 0 little smaller than the simply calculated K ( 12 ) based on equation 8.8, but very close. (b) During DDC (1) Total lateral earth pressure. FEM modeling results show that during each pass of compaction, the total horizontal pressure values at each position increased rapidly to peak values and then decreased quickly as the compaction was completed. The distance to the compaction centers of impact has a great influence on the horizontal lateral earth pressure increment. When the distance from the compaction center of impact to the sheet pile wall is more than 30 ft, the compaction has almost no influence on the total earth pressures obtained by the FE modeling. However, when the distance is in the range of 15 ft to 22.5 ft, the compaction causes very large lateral earth pressure increases in the FE modeling. (2) Sheet pile deflection. The DDC caused large sheet pile deflections towards the supporting peat side, which explained the reduction of the residual pressures immediately as the compaction was completed. Assuming initial verticality, the sheet pile rotation angle 0 oriented to the supporting peat increased from 0.3 associated with lateral sheet pile top displacement of 3.5 inches before the compaction to 3 0 associated with lateral sheet pile top displacement of 16.7 inches just after the compaction. The lateral earth pressure coefficient K increased by the compaction. It increased from 1.35 before the compaction to 1.85 just after compaction. The FEM modeling results indicates that deep dynamic compaction (DDC) has

14 404 great influence on the horizontal lateral earth pressure, sheet pile deflection and lateral earth pressure coefficient. (c) After DDC (1) Total lateral earth pressure. The FEM modeling results indicated that increased total lateral pressure induced by the compaction completely dissipated within about 2 months and the modeling pressure values at each position came back to their original state. The total lateral earth pressure values in the peat did not show apparent changes until the embankment construction. During the embankment construction period, there was some small decrease of up to 0.15 psi in the earth pressure due to the drainage and lowering of the water level in the peat bog. In the long-term, the total lateral earth pressure had the tendency to decrease slowly. (2) Sheet pile deflection. As the compaction was completed, the sheet pile also stopped moving. During the embankment construction period, some sheet pile displacement was developed and the pile head had moved about 5.1 inches movement in the X direction. The modeling results for 180 days after the embankment completion, indicates that as the embankment was completed, the sheet pile displacement did not increase and some sheet pile movement back (towards the backfill side) took place. (3) Lateral earth pressure coefficient, K. The K values based on the FE modeling indicated that K values increased from 1.45 prior to the compaction to 1.75 one month after the compaction. The final stable K values are still above the value before the compaction. During the embankment construction period, the K values decreased due to the six feet excavation in the backfill side close to the sheet pile. As the embankment was completed, the decreasing rate of the K values then become very small. In the long-term, it can be predicted that the K values had the tendency to decrease to the at-rest state. 9.6 FEM MODELING OF STATION (R) Modeling System Analyzed The site conditions of station (R) were analyzed in section Based on the subsurface exploration, it was determined that peat deposit at this station was about 8 feet deep and the water table level was at a depth of 1.5 ft below the ground surface. The length of the sheet pile at this station was 28 ft. Figure 9.31 shows the cross-section of this station used in the FEM modeling. The peat was divided into two layers and excavated in two days, i.e. 4 ft peat excavated each day. The excavation was backfilled with granular materials in two days, 4 ft layer each day. The site was then consolidated for 200 days. The top of the final backfilling was 6 ft above the peat ground surface. The sheet pile at station (R) was then replaced with the instrumented sheet pile. The pressure cells were located at 4.2 ft, 9.2 ft, and 14.2 ft below the peat ground surface (see figure 4.11). The fill was compacted by two DDC passes with a time interval of five days between the two passes. In each pass of compaction, the distance between the centers of adjacent compaction points is 180 inches. Following the DDC, the site was left to consolidate for a period of about 6 months before the MSE wall and the embankment were constructed on the compacted backfill. The distance from the sheet pile wall to the MSE wall was about 25 ft and the embedded depth of MSE wall in backfill was about 4 ft. The reinforcement of the embankment was made up six layers of backfill with steel strips. The steel strips for reinforcement was about 12 ft long with a inch high inches wide, width section at 3.35 ft horizontal spacing and a

15 405 vertical distance (between two adjacent steel strips) of 2 ft. Finally the 2 ft thick pavement is planed to be built at the top of the embankment. Table 8.17 provides a summary of the relevant construction progress time table. The FEM simulation at station (R) includes the following major analyses: sheet pile installation, peat excavation, backfilling, instrumentation installation, consolidation, deep dynamic compaction, MSE wall and embankment construction, and pavement construction. Figure 9.32 presents the symmetric plane strain scheme used for the FEM analysis. The distance from the central line to the sheet pile is 58 ft. The bottom boundary was placed 2 ft below the tip of the instrumented sheet pile. This boundary is rigid and forms the base of the analyzed mesh. The consolidation boundary is 30 ft away from the sheet pile at the side of the peat layer. Absorbent boundaries were defined on both vertical sides and at the bottom boundary. In order to improve the precise of the analysis, a medium dense mesh and an update mesh were used. The various elements of the FE scheme and the mesh are shown in figure The staged construction feature of PLAXIS makes it possible to simulate the construction process by first setting up the complete, final layout of the project (as shown in figure 9.32), and then to execute the analysis in a series of phases during each phase various portions of the system are de-activated and activated. The present analysis was performed according to the 154 stages outlined in table FEM Analysis Results of Station (R) Figure 9.34 presents the soil displacements and sheet pile deformation upon completion of the soil replacement at station (R). Following the peat excavation (in the road side), the sheet pile moved towards the excavation side with maximum displacements at the pile head of 0.13 inch. Figure 9.35 presents the soil displacements and sheet pile deformation upon the completion of backfilling placement at station (R). By comparing figure 9.34 and 9.35, it was observed that with progress of the backfilling the sheet pile movement reversed directions and moved towards the peat side. At the completion of backfilling, the pile head developed about 0.72 inch movement towards the peat side from its initial position. Figure 9.36 presents contours of the total displacements developed after the installation of the instrumented sheet pile at station (R) over a period of 180 days. It can be observed that the FEM modeling results indicated that after the peat between sheet piles was replaced with granular fill, the sheet pile moved towards the bog (outside). Largest displacements took place close to the top of the sheet pile as shown in the figure, and observed in the field. At the same time, settlements of the natural sands took place in the area between the sheeting due to that the large additional load developed when replacing the peat with fill. Figure 9.37 shows the shear strain developed following the instrumented sheet pile installation and the maximum value was up to 2.48%. Figure 9.38 presents the modeled total horizontal effective earth pressure developing at the instrumented positions A/D (4.2 ft in peat), B/E (9.2ft in sand) and C/F (14.2ft in sand) in the supporting side starting from the sheet pile installation via the soil replacement to the time of 180 days after instrumentation installation. The modeling results indicate that during the peat excavation, the effective pressure values decreased; while as the backfilling

16 progressing, the pressures increased upon the completion of backfilling and then remained constant during the consolidation period. The instrumentation installation caused a pressure increase in the peat (0.10 psi increment at position A/D) and a pressure reduction in the sand overlapped by the peat (0.17 psi reduction at position C/F). It indicated that installation caused increase in the horizontal effective pressure in the top peat layer and reduction in the deep sand. After the instrumented sheet pile installation, the pressure at position A/D in peat tended to decrease slowly with time. While in sand, the residual stress did not show apparent changes with time. Figure 9.39 shows the displacements in X direction (oriented to the peat side) developing at different depths along the sheet pile with time starting from the sheet pile installation to 180 days following the instrumentation installation. During the backfilling period, the sheet pile moved towards the supporting peat and stopped moving upon the completion of backfilling. During the consolidation period, the sheet pile did not undergo additional movements. The instrumentation installation caused the sheet pile additional movements. At 180 days after the instrumentation installation, the pile head developed a cumulative movement of about 0.24 inch in the X direction due to the load caused by the backfilling against the sheet pile wall. Figure 9.40 presents the excess pore pressure distribution at station (R) upon the completion of the instrumentation installation. It indicated that as a result of the instrumented sheet pile installation, the negative excess pore pressures were distributed mainly around the sheet pile in the supporting peat side. At the same time, there were some positive excess pore pressures in the deep sand, which could explain why there were some horizontal effective pressure increments in the peat and some reduction in the sand during the instrumentation installation as shown in figure The excess pore pressure distribution in the peat fits well with the one predicted by Terzaghi s one-dimensional consolidation theory. Figure 9.41 shows the deformed mesh of station (R) as a result of the deep dynamic compaction at point F-4 after 9 impacts (1.06 seconds since the beginning of the first impact). The data illustrates that the deformation of the soil body and the sheet pile match the filed measurements. The craters formed by the compaction where 6 ft deep and caused displacements of 9.2 inches towards the supporting side compared to a value of 6.6 inches measured at the a top of the sheet pile. Figure 9.42 presents the deformation at station (R) immediately following the completion of the ninth (last) compaction (1.06 seconds since the beginning of the first impact) at point S-3. It can be noticed that after two passes of deep dynamic compaction, the soils and sheet pile developed large movements, especially in the areas close to the top part of the sheet pile. After two passes of compaction, the calculated pile head displacement was up 0.81 ft in the X direction. Figure 9.43(a) describes dynamic velocity contours in the soil following the 9th impact (1.06 seconds since the beginning of the first impact) in point F-2 at station (R). The dynamic velocity in the soil radiates way from the impact but under the compaction at point F-2, the dynamic velocity des not reach the sheet pile. Figure 9.43(b) shows the dynamic velocity contours 0.02 second after the ninth impact stopped in point F-2. By comparing figure 9.43(a) to figure 9.43(b), it can be noticed that as the compaction stopped, the soil was vibrating freely after the initial excitation. During soil self-vibrating period, the dynamic velocity reached the supporting peat and the influence range was shown in the 406

17 407 figure. The maximum velocity decreased from 7.6ft/s to 1.05ft/s within a period of 0.02 second. Figure 9.44 shows the dynamic acceleration contours in the soil during the 9th impact (1.06 seconds since the beginning of the first impact) in point F-3 at station (R). The acceleration and the dynamic energy decreased with distance from the impact while the acceleration induced by the compaction did not reach the sheet pile wall. Figure 9.45(a) shows dynamic velocity contours in the soil during the 9th impact (1.06 seconds since the beginning of the first impact) in point F-4 at station (R). The dynamic velocity had reached the sheet pile wall when the compaction took place at point F- 4. Figure 9.45(b) shows the dynamic contours 0.02 second after the ninth blows at point F-4 was stopped, namely during the period of soil body self-vibration after the initial excitation. By comparing figure 9.45(a) and 9.45(b), it can be seen that as the compaction was stopped at point F-4, the dynamic velocity dissipated rapidly into the supporting peat layer and its magnitude decreased from a maximum value 12.45ft/s to 0.4ft/s within a period of 0.02 second. As the compaction was stopped, the soil body self-vibration appears mainly in the peat. Figure 9.46(a) presents the dynamic acceleration contours in the soil during the 9th impact (1.06 seconds since the beginning of the first impact) in point F-4 at station (R). The dynamic energy had reached the sheet pile wall when the compaction took place at point F-4. Figure 9.46(b) presents the dynamic acceleration contours in the soil 0.02 second after the ninth impact at point F-4 was stopped. By comparing figure 9.46(a) and 9.46(b), it can be seen that as the compaction was stopped, the dynamic acceleration dissipated from the areas close to the compaction source to the areas far from it. And the maximum magnitude of 2 2 the dynamic acceleration decreased rapidly from ft s to52.0 ft s within a period of 0.02 second. Comparing the information presented in figures 9.43 to 9.46, it can be concluded that the influence of the compaction decreased with the distance from the center of the compaction resource. When the compacted area is at a distance up to 30 ft from the sheet pile, the influence on the sheet pile wall is still minimal, translated to velocity of 1.2 ft/s on the sheet pile. When the compaction was closest to the sheet pile, i.e. at a distance of 15 ft, it had a great effect on the sheet pile wall in the form of acceleration of 280 ft/s 2 and velocity of 9 ft/s 2 within a period of 0.02 second. Figure 9.47 shows the excess pore pressure distribution induced by compaction at point F-3 (1.06 seconds since the beginning of the first impact) at station (R). The excess negative pore pressure caused by the compaction was mainly distributed in the areas close to the compaction source and decreased within a distance of 15 ft from the compaction source. The modeling result indicated that the compaction at point F-3 had little influence on the excess pore pressure in the supporting peat, which did not exceed psf. Figure 9.48 presents the excess pore pressure distribution induced by the compaction (1.06 seconds since the beginning of the first impact) at point F-4 at station (R). The excess pore pressure distribution was almost the same at that in figure The modeling result indicated that even compaction at point F-4, close to the sheet pile wall, had no apparent influence on the excess pore pressure in the supporting peat, which matches the field measurements of the pore pressure developing during the DDC as described in figure 8.7.

18 408 Figure 9.49 presents the soil and structure deformation contours at station (R) just after the two passes of deep dynamic compaction were completed. The maximum deformation occurred in areas around the top of the sheet pile, especially in the peat, which matches the field observations. Due to the peat s high compressibility, large calculated deformation in the magnitude of 9.6 inches took place at the top of the wall. Figure 9.50 shows the FEM modeling results for the total horizontal earth pressures developing at the instrumented positions (A/D, B/E and C/F) during the entire DDC period at station (R). The modeling results indicated that during each pass of compaction, the earth pressure values at each position increased rapidly to peak values and then decreased as the compaction was completed. It was observed that pressure increment at each position caused by the second pass of compaction was much smaller than that induced by the first pass of compaction. This is explained by the fact that the distance from the second pass of compaction to the measured points at the sheet pile wall are 15 ft further than those of the first pass, shown in figure The modeling results of the horizontal total pressure indicated that distance from the compaction source center to the sheet pile wall has apparent influence. When the distance from the compaction source center to the sheet pile wall is more than 30.0 ft, the compaction has almost no influence on the (modeling) total earth pressure. However, for distance in the range of 15.0 to 22.5 ft, the compaction causes large lateral earth pressure increase. Figure 9.51 shows the sheet pile displacement development in X direction caused by the two passes of the DDC at station (R). The modeling results indicate that deep compaction resulted with very large sheet pile movement towards the supporting peat side. After two passes of compaction, the pile head movement in the X direction increase from 1.6 inches to 9.2 inches and the sheet pile rotational angle around its tip in sand increased from to assuming initial verticality. The rotation angle towards the supporting peat after compaction was about 19 times that before compaction. Figure 9.52 presents the deformed mesh at station (R) 180 days after the embankment construction, suggesting that the embankment construction cause further soil and structure deformation. Figure 9.53 shows the displacement at station (R) 180 days after the embankment completion. By comparing figure 9.49 with figure 9.53, it can be concluded that additional 3.1 inches of lateral movement towards the peat took place at the top of the sheet pile at the ground level due to the embankment construction. Figure 9.54 presents contour of the total strain (%) distribution at station (R) following the embankment completion. This shear strain represents the soil condition since the initial week on the site including the DDC. The maximum shear strain (of up to 38%) (red color areas) mainly appeared in the supporting peat layer closer to the top of the sheet pile. The lower shear strain areas (green-yellow color areas) developed in the backfill side close to the sheet pile wall and along the narrow vertical strip close to the MSE wall in the embankment. The fill area which serves as the foundation to the embankment had undergone shear strains, in which the maximum was less than 6% including the DDC. Figure 9.55 shows the total shear strain increment caused by the embankment construction along at station (R). The shear strain increment induced by the embankment construction is very small (up to.1(% ) 0 ) and it concentrates mainly in a small area around the top of the soil (access road) next to the MSE wall. These results indicated

19 409 that the construction of the embankment over the compacted fill caused small disturbance in the soil body. Figure 9.56 presents the FEM modeling horizontal effective pressure at the instrumentation positions developing over time following the completion of the DDC at station (R). It shows that as the compaction was completed, the effective horizontal pressure at the instrumentation positions returned to their initial states in about one month and then did not change with time until the beginning of the embankment construction. During embankment construction period, there were no apparent pressure changes at position A/D (4.2 ft in the peat). However, modeling effective lateral pressure at position B/E and C/F, separately 9.2ft and 14.2ft in the sand layer below the peat, increased continuously as the embankment construction progressing. As the embankment was completed, the pressure developing in the sand did not increase more and then almost kept constant with time. Figure 9.57 presents the FEM modeling results for the cumulative horizontal displacement at different instrumentation positions, developing with time following the completion of the deep dynamic compaction (DDC) at station (R). It shows that after the completion of compaction, the sheet pile did not develop further movements until the beginning of the embankment construction. During the embankment construction period, the pile moved some towards the supporting peat and the pile head developed a total movement of 4.1 inches in the X direction since the completion of the DDC. Followings the embankment completion, the sheet pile did not develop any further movement Summary of FEM Analysis Results at Station (R) Figure 9.58 summaries the FEM modeling results of the variation in the horizontal total earth pressure at instrumented positions with time during the entire construction periods at station (R). Figure 9.59 summaries the FEM modeling results of the sheet pile horizontal displacement developing at station (R) during the entire construction period. Figure 9.60 summaries the FEM modeling results of the lateral earth pressure coefficient (based on equation 8.7) developing with time during the entire construction period at station (R). Based on the FEM analysis results of the total lateral earth, sheet pile horizontal displacement and lateral earth pressure coefficient calculated in the peat, the following conclusions are drawn: (a) Before DDC (1) Total lateral earth pressure. The FEM modeling results indicated that during the eight months following the instrumentation installation, the total lateral earth pressure developed in the supporting peat did not change until the application of the DDC. In the long-term, the FE modeling total lateral earth pressure values have the tendency to decrease very slowly with time. (2) Sheet pile deflection. The horizontal displacement of the sheet pile oriented to the supporting side did not show increase during this period. (3) Lateral earth pressure coefficient, K. The calculated lateral earth pressure coefficient, K in peat, at position A/D based on equation 8.7 initially remained constant value (1.41) following the instrumentation installation until the application of the DDC. The K values in sand at positions B/E and C/F were 0.90 and 0.70 respectively at the completion of the instrumentation installation and did not show apparent changes until the application of the DDC. It was also noticed that during this period, the modeling K value in peat based on

20 0 equation 8.7 was larger than the simple calculated K ( 12 ) based on equation 8.8; the modeling K values in the sand were larger than the calculated at-rest earth pressure coefficient using Jaky s equation ( K 0 = 1 sinφ ) and were far from the fully passive state using Rankine s equation. (b) During DDC (1) Total lateral earth pressure. FEM modeling results show that during each pass of compaction, the total horizontal pressure values at each position increased rapidly to peak values and then decreased quickly as the compaction was completed. The distance to the compaction centers of impact has a great influence on the horizontal lateral earth pressure increment. When the distance from the compaction center of impact to the sheet pile wall is more than 30 ft, the compaction has almost no influence on the total earth pressures obtained by the FE modeling. However, when the distance is in the range of 15 ft to 22.5 ft, the compaction causes very large modeling lateral earth pressure increases in the FE modeling. (2) Sheet pile deflection. The DDC caused large sheet pile deflection towards the supporting peat side, which explained the reduction of the residual pressures immediately as the compaction was completed. Assuming initial verticality the sheet pile rotation angle 0 oriented to the supporting peat increased from associated with lateral sheet pile top 0 displacement of 1.65 inches before compaction to 1.62 associated with lateral sheet pile top displacement of 9.4 inches just after the compaction. The FEM modeling results indicates that deep dynamic compaction (DDC) has great influence on the horizontal lateral earth pressure and sheet pile deflection. (c) After DDC (1) Total lateral earth pressure. The FEM modeling results indicated that increased total lateral pressure induced by the compaction completely dissipated within about 1 month and the modeling pressure values at each position came back to their original states. The total lateral earth pressure values in both the peat and the sand did not show apparent changes until the embankment construction. During the embankment construction period, there was some small decrease of up to 0.2 psi in the earth pressure due to the six ft excavation for MSE wall construction in the backfilling side close to the sheet pile. In the long-term, the total lateral earth pressure developing in the peat had the tendency to decrease slowly with time. However, the lateral earth pressure developing in the deep sand overlapped by the peat increased as the progress of the embankment construction. As the embankment was completed, the earth pressure in the sand did not increase and then almost remained constant with time. In the long-term, like in the peat, the total lateral earth pressure the in sand also seems to decrease slowly with time. (2) Sheet pile deflection. As the compaction was completed, the sheet pile also stopped moving. During the embankment construction period, some sheet pile displacement was developed and the pile head had moved about 4.2 inches movement in the X direction. The modeling results for 180 days after the embankment completion, indicates that as the embankment was completed, the sheet pile displacement did not increase and some sheet pile movement back (towards the backfill side) took place. (3) Lateral earth pressure coefficient K. The K values based on the FE modeling at position A/D decreased from 1.42 prior to the embankment construction to 1.37 at the completion of the 6 ft excavation in the backfill side. Following the excavation was backfilled, the K value at position A/D returned to 1.42 again and almost kept constant over time. For the sand, the lateral earth pressure coefficient K values at both positions B/E (9.2ft 410