Manh Duc Nguyen Department of Geotechnical Engineering, University of Transport and Communication, 3 Cau Giay, Lang Thuong, Dong Da, Ha Noi, Viet Nam

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 11, November 2017, pp. 526 535, Article ID: IJCIET_08_11_056 Available online at http://http://www.iaeme.

1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 11, November 2017, pp , Article ID: IJCIET_08_11_056 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed PREDICTION OF LATERAL DISPLACEMENT OF GROUND IMPROVED BY MERNARD VACUUM CONSOLIDATION METHOD BASED ON CHARACTERISTICS OF SOFT SOIL AND SETTLEMENT OBSERVATION RESULTS Manh Duc Nguyen Department of Geotechnical Engineering, University of Transport and Communication, 3 Cau Giay, Lang Thuong, Dong Da, Ha Noi, Viet Nam Dung Van Le Department of Geotechnical Engineering, University of Transport and Communication, City Campus, 450 Le Van Viet, Q. 9, Ho Chi Minh City, Viet Nam Binh Thai Pham Department of Geotechnical Engineering, University of Transport Technology, 54 TrieuKhuc, ThanhXuan, Ha Noi, Viet Nam Department of Civil Engineering, Gujarat Technological University, Nr. Visat Three Roads, Visat Gandhinagar Highway, Chandkheda, Ahmadabad, Gujarat, India ABSTRACT High lateral displacement of ground improved by Mernard Vacuum Consolidation Method (MVCM) is sometimes caused by quick consolidation and much settlement. Using the data collected from real project at the Thu Thiem and Nguyen Son urban areas, Ho Chi Minh City (Viet Nam), we predicted the lateral displacement of ground under the vacuum pressure and additional surcharge load the MVCM based on the equations of Ong et al (2013) and finite element method using Plaxis 2D/V.8.2 software with Hardening soil (HS) model. The results show that the lateral displacement of ground predicted is much closer with those determined from observation results, and it is better than the one determined by analytical method. Keyword: Soft soil, vacuum consolidation, lateral displacement, deformation, soft ground, inclinometer, settlement. Cite this Article: Manh Duc Nguyen, Dung Van Le and Binh Thai Pham, Prediction of Lateral Displacement of Ground Improved by Mernard Vacuum Consolidation Method Based on Characteristics of Soft Soil and Settlement Observation Results, International Journal of Civil Engineering and Technology, 8(11), 2017, pp editor@iaeme.com

2 Manh Duc Nguyen, Dung Van Le and Binh Thai Pham 1. INTRODUCTION Mernard Vacuum Consolidation Method (MVCM) allows reducing the time of improvement of soft soil; thus, it helps to speed up the works of construction. Quick consolidation and much settlement might cause the high lateral deformation of ground which affects adversely to constructions and adjacent buildings. To evaluate and control this lateral displacement of ground, one often install and implement geotechnical observation devices during working stage such as instrumentation inclinometer in borehole, extensometer in borehole, pipe strain gauge, or earth surface observation by geodetic landmarks. However, these observations usually provide only measurement values when the ground has been displaced. Several authors have carried out the prediction of the lateral displacement of ground before implementation of improvement of soft ground by the MVCM [1,2,3]. In this study, the main objective is to predict the lateral displacement of ground improve by the MVCM using analytical method and finite element method using Plaxis 2D/V.8.2 software with Hardening soil (HS) model and data collected from real project at the Thu Thien and Nguyen Son urban areas, Ho Chi Minh City (Viet Nam). The predicted results were validated and compared with real lateral displacement. The results of this study might help in selection of suitable models for prediction of the lateral displacement of ground while design and calculation of soft soil improvement problem by the MVCM under Vietnam conditions. 2. BACKGROUND OF THE LATERAL DISPLACEMENT OF GROUND IMPROVMED BY THE MVCM [1,2,3,4] There are two acting loads on the ground while improvement of soft groud by the MVCM including embankment s load and the vacuum pressure. Under the embankment s load, vertical stress is increased by a certain amount. At the meantime, shear resistance of soft soil is often small which leads to the lateral displacement, and causes the movement of adjacent ground to the outside of the embankment. As the increase of vertical stress is higher, this lateral displacement is higher. However, the geotextile layer is usually put on the ground before implementation of embankment, and the embankment is also compacted to a certain compactibility; thus, shear resistance of these two layers is transferred to the ground through the friction between the ground and geotextile which can reduce the lateral displacement of upper soil layers. Therefore, the highest lateral displacement is moved deeply into the ground (Figure 1a). Differing from the load of embankment, the load of vacuum causes a negative vacuum a long with the depth of draining wick, the difference of the pressure leads to the increase of vertical stress of the ground in both vertical and lateral directions which cause the consolidation of the ground in both directions (Figure1b). Figure 1 Lateral displacement of the ground under different acting loads: (a) Deformation under the load of embankment, (b) Deformation under the load of vacuum, (c) Deformation under both the load of embankment and vacuum editor@iaeme.com

3 Prediction of Lateral Displacement of Ground Improved by Mernard Vacuum Consolidation Method Based on Characteristics of Soft Soil and Settlement Observation Results To explain the condition which causes the lateral displacement under the load of vacuum, several authors provide different hypothesis and relations. Chai, Ong [1] used the observation results, and stated that the lateral displacement of the ground initially occurs when the following equation is satisfied, and the illustrated model of deformation of soil element is shown in Figure 2 [1,4]. (1) Where: σ vac - Increase of vacuum pressure, k 0 - Coefficient of lateral soil pressure, and σ vo - Vertical effective stress. Figure 2 Illustrated model of deformation of soil element (Chai et al., 2005): (a) Initial stress status, (b) No lateral displacement, (c) Having lateral displacement Zhou and Mei [2] explained the condition which cause the lateral displacement under the load of vacuumas shown in Figure 3 [9], and stated that the reason of the lateral displacement of the ground is the horizontal pressure value σ vac (1-k o ). Thus, it can be seen that the lateral displacement of the ground is due to both the load of embankment and vacuum. Ong and Chai [4] và Chai, Ong [3] based on the experimental modeling results in conjuntion with real observation results and stated that the part close to the surface is moved inside the area improved by the soft soil processing method, the deeper layers tends to move to the outside of the area improved by the MVCM, and the highest lateral displacement is often on the earth surface (Figure 1c) [1,3] Figure 3 Cause of the lateral displacement of the ground [9]: (a) Initial stress status, (b) after bearing vacuum pressure editor@iaeme.com

4 Manh Duc Nguyen, Dung Van Le and Binh Thai Pham 3. METHODS OF PREDICTION OF THE LATERAL DISPLACEMENT OF GROUND IMPROVED BY THE MVCM [1,3,5] 3.1. Analytical method [1,3] This method is carried out via the determination of soil loading index Ratio Load Soil (RLS) and Net Lateral Displacement (NLD). Based on the experimental modeling results of Ong and Chan (2011), it can be observed that Deformation Ratio (DR) is proportional with the RLS and Loading Rate (LR) and it is inversely with shear resistance of soil (S u ) [1]. Using the real observation and experimental modeling results, Ong et al (2013) introduced a approximate method to predict the highest horizontal deformation through two parameters PLS and NLD as below [1,3] = = NLD = RLS (4) σ = σ σ "#$ + σ &U (5) where: δ nm - Highest horizontal deformation of the ground (m), S f - Settlement of the ground (m), σ n - Pressure ratio (kpa), σ em - Embankment pressure (kpa), σ vac - Vacuum pressure (kpa), U - Mean consolidation degree (scale PVD, %), and S u - Mean undrained shear strength of soil at the time of determination of deformation (kpa) Finite element method [5] According to this method, the lateral displacement is analyzed by Plaxis 2D software on the basis of flat model (2D). Idea of this method in calculation of structure is to consider continuous object as same as a combination of many small elements linked by several limited points called nodes. The created parts are called as elements which create the network, and the shape and dimension of the elements might be different. Ground model, which is selected to investigate the lateral displacement of the ground in Plaxis 2D software, is Hardening Soil (HS) with natural soil layers [5], the ground leveling layers are simulated by Mohr Coulomb (MC) model. The load of vacuum is replaced by a stress inside the soil created in Plaxis 2D. 4. HORIZONRAL DISPLACEMENT CHARACTERISTICS AT THU THIEM AND NGUYEN SON URBAN AREAS 4.1. Description of Thu Thiem and Nguyen Son urban area projects The project of new urban area of Thu Thiem is located in Mai Chi Tho Street, An Loi Dong Ward, Second District, Ho Chi Minh City (Viet Nam) (Figure 4). Internal roads improved by the MVCM namely N5, N6, N8, N9, D1 and D4. The stratigraphy of this study area includes four soil layers: (1) ground leveling layers (CSL): leveling sands, m thickness; (2) layer 1a: organic-dust-clay, liquid state, thickness, Su= kPa, compression indexc c = 0.981; (3) layer 1b:dust-clay-mud mixed with fine sand, liquid state, m thickness, S u = kpa, C c = 0.788; (4) layer 2a: clay-mud mixed with sands, plasticliquid state, m thickness, S u = kpa, C c = Depth of draining wick is 15m and height of embankment is 2.5m (Figure 5a, b). (2) (3) editor@iaeme.com

5 Prediction of Lateral Displacement of Ground Improved by Mernard Vacuum Consolidation Method Based on Characteristics of Soft Soil and Settlement Observation Results Figure 4 Location of the new urban area of Thu Thiem Nguyen Sơn, Ho Chi Minh City The project of Nguyen Son urban area is located in Binh Chanh, Ho Chi Minh City (Figure 4). Internal roads improved by the MVCM is D1. The stratigraphy of this study area includes three soil layers(1) ground leveling layers(csl):leveling sands, m thickness; (2) layer 1a_1: organic-dust-clay, liquid state, mthickness, Su = kPa, Cc =0.923; (3) layer 1b_1: clay-mud mixed with fine sand, 5,8 7,0mthickness,Su = 25,4 32,8kPa. Depth of draining wick is mmand height of embankment is m (Figure 6a, b) [6] Parameters used for prediction of lateral displacement at the study areas [6,7] Parameters used for prediction of lateral displacement at the study areas are shown in Table 1 [6]. Table 2 shows the mean settlement from the real observation results at the measuring points near by the locations installed Inclinometer devices [7]. B = 14m B = 14m CSL 1,6m IN1 CSL 1,5m IN2 (1a) 10,4m (1a) 15m (1b) 1,5m (2a) 6,5m (1b) 3,5m (a) (b) Figure 5 Typical cross section of Thu Thiem urban area B = 25m B = 25m CSL 2,8m CSL 2,5m IN3 IN6 (1a_1) 27m (1a_1) 23m (1b_1) 7,0m (1a_1) 6,0m (a) (b) Figure 6 Typical cross section of Nguyen Son urban area editor@iaeme.com

6 Manh Duc Nguyen, Dung Van Le and Binh Thai Pham Soil layers Table 1 Basic features at the study areas γ w γ s k x k y c' φ' υ E oed MH kn/m 3 kn/m 3 m/day m/day kpa độ - kpa - CSL MC Soil γ E ref oed k x k y c φ υ ref E 50 E ur layers kn/m 3 kpa m/day m/day kpa độ - kpa kpa 1a e-5 1.5e b e-5 1.5e a e-5 9.5e a_ b_ Inclinometer Table 2 Observation settlement at the study areas Surface settlement Value of settlement (m) Value of average settlement (m) Undrained Shear Strength (Su), kpa IN1 (ThuThiem) SSP IN2 (ThuThiem) SSP SSP SP3-L IN3 (NguyenSon) SP SP3-R SP6-L IN6 (NguyenSon) SP SP6-R Undrained shear strength used to predict the lateral displacement of the ground at the locations installed Inclinometer devices (IN1, IN2, IN3 and IN6) during the implementation of improvement of soft soil by the MVCM is shown in Table 2 [6]. To predict the lateral displacement of the ground at the Thu Thiem urban area using the finite element method, loading parameters at different stages are given in Figure 7 [7]. Figure 7 Loading stages at the Thu Thiem urban area editor@iaeme.com

Prediction of Lateral Displacement of Ground Improved by Mernard Vacuum Consolidation Method Based on Characteristics of Soft Soil and Settlement Observation Results 5.

Table 3 shows the comparison between prediction results via the typical features of soil, observing settlement and real observation results.

7 Prediction of Lateral Displacement of Ground Improved by Mernard Vacuum Consolidation Method Based on Characteristics of Soft Soil and Settlement Observation Results 5. RESULTS AND DISCUSSION The prediction results of the lateral displacement are shown in Figures 8, 9, 10, 11 and 12. Table 3 shows the comparison between prediction results via the typical features of soil, observing settlement and real observation results. Inclinometer Table 3 Values of the lateral displacement at the natural surface Settlement from monitoring (m) Consolidation degree, U σ vac S u Lateral displacement of ground (m) kpa kpa From NLD and RLS(δ nm ) From Plaxis 2D From monitoring IN IN IN IN Figures 10, 11 and 12 indicate the rule of change between observed settlement and values of the lateral displacement observed during the vacuum process at Thu Thiem and Nguyen Son areas (Figure 10), the comparison of predicted displacement and real observed deformation (Figure 11), and the percentae of difference of predicted deformation determined by different methods and the real observed deformation (Figure 12). Figure 12 shows the change of values of the lateral displacement of the ground with the depth by Plaxis 2D based on finite element method with real observed deformation at IN1 and IN2 locations at Thu Thiem area Analysis of the results shows that the values of the highest lateral displacement predicted by finite element method using Plaxis 2D are m and m at IN1 and IN2, respectively. These results are appropriate with real obsered results by Inclinometer ( m at IN1, m at IN2) (Table 2 and Figure 13). Values of the lateral displacement tends to decrease dramatically with the processing depth. In deeper locations, the ground tends to move to the outside of the processing area by the MVCM, and the value is small. At the locations of IN1 and IN2, the deformation beyond 13m is suitable with the predicted results by Plaxis and real observation (Figure 13) Figure 8 Lateral displacement of the ground predicted by Plaxis 2D at IN1 location at Thu Thiem area editor@iaeme.com

Manh Duc Nguyen, Dung Van Le and Binh Thai Pham 100 0-100 0 2 4 6 8 10 12 14 16 18 20-200 -300 Figure 9 Lateral displacement of the ground predicted byplaxis 2D at IN2 location at Thu Thiem area

At the locations of IN1 and IN2, the mean settlement of the ground is 1.73m, the mean lateral displacement is -0.1438mat IN3; and asthe mean settlement of the ground is 3.

8 Manh Duc Nguyen, Dung Van Le and Binh Thai Pham Figure 9 Lateral displacement of the ground predicted byplaxis 2D at IN2 location at Thu Thiem area Figure 10 Lateral displacement and observed settlement at the selectied locations Lateral displacement increases as the settlement increases. At the locations of IN1 and IN2, the mean settlement of the ground is 1.73m, the mean lateral displacement is mat IN3; and asthe mean settlement of the ground is 3.634mat IN6 thus the mean lateral displacement is m (Figure 10). Basically, the predicted lateral displacement using NLD and RLS or by Plaxis 2D and observation increases with the decrease of mean shear resistance S u (Table 2). Lateral displacement predicted from NLD and RLS gives the high difference compared with observed results from mm whereas the one predicted using finite element method by Plaxis 2Dis mm. Figure 11 Predicted lateral displacement and observed deformation at 4 selectied locations editor@iaeme.com

9 Prediction of Lateral Displacement of Ground Improved by Mernard Vacuum Consolidation Method Based on Characteristics of Soft Soil and Settlement Observation Results Figure 12 Percentage of difference of predicted deformation and real observed results Analysis of the lateral displacement by Plaxis 2D also give the displacement results a long with the processing depth of the ground by the MVCM which is not similar to the observation by Inclinometer. Using this approach, the highest bias compared with the observed results is from 41.4mm at IN2 to 57.5mm at IN1 (Figure 13). Horizontal displacement (mm) Horizontal displacement (mm) Depth (m) Depth (m) Monitoring PLAXIS PLAXIS Monitoring Inclinometer - IN1 Inclinometer - IN2 Figure 13 Lateral displacement vs the depth of prediction and real observation at Thu Thiem area 6. CONCLUSIONS In this study, the lateral displacement of ground under the vacuum pressure and additional preloads using the MVCM was predicted based on the equations of Ong et al (2013) and finite element method using Plaxis 2D/V.8.2 software with Hardening soil (HS) model. Two main conclusions can be withdrawn via this study: 1) The highest lateral displacement is distributed at the surface locations, the value of lateral displacement is proportional with the settlement and inversely with undrained shear strength of the ground, and the lateral displacement tends to decrease dramatically with the processing depth. In deeper depths, the ground tends to move to the outside of the processing area by the MVCM. These results are comparative with other studies carried out by Ong et al (2011 and 2013) editor@iaeme.com

10 Manh Duc Nguyen, Dung Van Le and Binh Thai Pham 2) Prediction of the lateral displacement using NLD and RLS gives higher bias compared with the prediction using finite element method by Plaxis 2D. Both these methods give the difference from % compared with real observed results except at IN2 the bias is up to 120,31% using the NLD and RLS. REFERENCE [1] Chai, J., Sakai, A., Hayashi, S., Hino, T. (2007). Characteristics of vacuum consolidation comparing with surcharge load induced consolidation, International Symposium on Geotechnical Engineering, Bangkok, Thailand, pp [2] Zhou W.H. and Mei G.X. (2012). Experimental Study on Vacuum Preloading with Combination of Fill Surcharge. Proceedings of the International Conference on Ground Improvement and Ground Control: Transportation Infrastructure Development and Natural Hazards Mitigation, ICGI 2012, University of Wollongong, Australia, B. Indraratna, C. Rujikiatkamjorn and J S Vinod (editors). vol. 1: pp [3] Chai, J.-C., Ong, C. Y., Carter, J. P. and Bergado, D. T. (2013). Lateral displacement under combined vacuum presure and embankment loading, Geotechnique, 63, [ [4] Ong, C. Y. and Chai, J.-C. (2011). Lateral displacement of soft ground under vacuum pressure and surcharge load. Front. Archit. Civ. Eng. China 2011, Vol. 5, No. 2, pp , [doi /s ] [5] Duong, V. B. (2015). Selection of ground model to calculate the deep excavation with software PLAXIS. Mining and Geology Science Journal, No46, tr (In Vietnamese) [6] UGEFEM, LAS-XD154, (2012). Reports of geological observation results Transportation system, drainage, and technical infrastructures at the low floor house area at the settlement in the south of Dong Tay Highway (zone II) of the new urban area of Thu Thiem, second district, Ho Chi Minh City (In Vietnamese). [7] Vina Me Kong joint stock company (VMEC) (2015). Report of geotechnical observation results (In Vietnamese). [8] S. Lokesh, Dr. CH. Lakshmi Tulasi, T. Monica and U. Pranavi. Vibration Analysis of Laminated Composite Plates Using Layerwise Higher Order Shear Deformation Theory. International Journal of Mechanical Engineering and Technology, 8(7), 2017, pp [9] N.Ranganayakulu, Dr. A.V.S.S.K.S.Gupta and Dr. N.Eswara Prasad, Tensile Deformation Characteristics of Ti-6Al-4V (ELI Grade) and effect of Interstitial Content. International Journal of Design and Manufacturing Technology 7(1), 2016, pp [10] Kumar, A. and Gupta, A. K. Deformation and Detachment of Carbon Tetra Chloride Droplet in the Presence of Different Concentration of Surfactant from Solid Substrate. International Journal of Advanced Research in Engineering and Technology, 6(7), 2015, pp editor@iaeme.com

CHARACTERISTICS OF VACUUM CONSOLIDATION COMPARING WITH SURCHARGE LOAD INDUCED CONSOLIDATION

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