Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 47 No. 1 March 2016 ISSN

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1 Effect of Vacuum Pressure Dstrbuton on Settlement Analyss Results for An Improved Thck Soft Clay Depost at Sa Gon-Hep Phuoc Termnal Port, South of Vetnam Hoang Hep 1 and Pham Huy Gao 2* 1 Portcoast Consultant Corporaton, Vetnam and PhD student, Dong-A Unversty, Busan, Korea. 2 Asan Insttute of Technology, Pathumthan, Thaland. 1 E-mal: hepportcoast@gmal.com 2 E-mal: hgao@at.asa ABSTRACT: In the recent years ground mprovement wth preloadng, PVD and vacuum pressure has become commonly used for many projects n Southern Vetnam, ncludng that of Sa Gon-Hep Phuoc (SGHP) termnal port. At ths project ste a very soft to soft clay layer was mproved by a combnaton of three technques as mentoned above. As the clay depost s very thck, extendng from the surface to the depth of 35m, the effect of vacuum pressure along the PVD and the mmedately surroundng sol s of partcular nterest n term of ts nfluence on the settlement analyss among other parameters, commonly consdered n settlement analyss, such as sol propertes, smear zone, PVD spacng etc. In ths study, the effect of rato between vacuum pressure at the bottom and the top of the dran (k p ) on the settlement analyss results, was nvestgated usng a Fortran code. It was found that k p vared from 0.85 to and ts value could affect the matchng of the calculated settlement curve wth montorng data f not properly chosen. In addton, the smear effect wth RS equal to and a PVD spacng of m were found as optmal values for settlement analyss at the SGHP ste. KEYWORDS: Sa Gon-Hep Phuoc port termnal, Soft clay, Ground mprovement, Vacuum pressure, Settlement analyss 1. INTRODUCTION Sa Gon-Hep Phuoc (SGHP) Port Termnal s located n the Sa Gon Dong Na rver delta (Fgure 1), near to Soa Rap rver. The project ste covers an area of hectare. SGHP port termnal wll be constructed to replace the old SG Termnal n the centre of HCM cty. The soft sol layers at the study ste are dstrbuted approxmately 35-m deep and ground mprovement by vacuum consoldaton was performed to ensure stablzaton of a contaner yard wth a desgn 6.0-kPa servce loadng. The man objectve of ths research s to nvestgate the effects of dstrbuton of vacuum pressure along the vertcal dran nstalled n the very thck soft clay depost on the settlement. Ho Ch Mnh Cty Hep Phuoc 2. CALCULATION OF TIME-DEPENDENT PRIMARY CONSOLIDATION SETTLEMENT A FORTRAN code (Gao, 2013) was employed to perform the settlement analyss, whose man steps are brefly explaned n the folowng. 2.1 Calculaton of Embankment Loadng Calculaton of the contrbuton of the embankment loadng (surcharge) to the ncrease n total vertcal stress s based on Boussnesq s equaton for a pont loadng: dσ v(,j) q 3 1 (1) 2 5/2 z 2π [(x /z ) 1] 2, j, j, j Where: dσ v(,j) s the stress ncrease nduced by the surcharge at the calculated pont (,j); q s the load ntensty; x,j, z,j are the horzontal and vertcal coordnates of the calculated pont (,j). Index refers to sub-layer numberng n vertcal drecton (vertcal), whle ndex j refers to the calculated pont locaton (horzontal). 2.2 Man Types of Settlement The total settlement of the soft clay under loadng conssts of the mmedate settlement (S ), the consoldaton settlement (S c ) and the secondary settlement (S s ). The frst and second settlements make up the so-called prmary settlement (S p ). The mmedate settlement or ntal settlement occurs before consoldaton due to lateral strans or lateral movement due to fnte dmenson of the loadng and vertcal dran nstallaton: S p S S S ξs S (1 ξ)s (2) c p p Fgure 1 Ste Locaton In the equaton (2) s defned as the rato between the consoldaton settlement (Sc) and the prmary settlement (Sp) and t s practcally consdered to vary from 0.7 to 0.9 dependng on the rato between the loadng wdth and thckness of the clay layer, OCR of soft clay and constructon sequence. 100

2 2.3 Fnal Consoldaton Settlement The fnal consoldaton settlement s calculated as follows: ' σ vf(, j) ds C(, j) h.[rr (, j).log ] (3) ds C(, j) v0 (, j) p(,j) vf(,j) h.[rr(,j).log CR(,j).log ] (4) ' σ v0(,j) p(,j) σ vf(,j) = σ vo(,j) + σ v(,j) + U (,j) For surcharge loadng. σ vf(,j) = σ vo(,j) + σ v(,j) + U (,j) + P vac For surcharge loadng combned wth vacuum pressure. Where: σ p(,j) s the preconsoldaton pressure; σ vo(,j) s the effectve stress; σ v(,j) s the ncrease n total stress due to surcharge loadng; ΔU (,j) s the dsspaton of pore pressure at the pont(,j); CR (,j) s the compresson rato; RR (,j) s the recompresson rato; P vac s the vacuum pressure. Eq. 3 s used when the ncreased effectve stress s stll less than the preconsoldaton pressure of the mproved sol, whle Eq. 4 s used the ncreased effectve stress becomes more than the preconsoldaton pressure of the sol. In PVDVAC program (Gao, 2013), the mproved clay layer s dvded nto sub-layers, and the total prmary consoldaton settlement s a sum of contrbutons from each ndvdual sub-layer: n S (5) C ds C(, j) 1 Where: S C s the total settlement of the analyzed clay layer and ds C(,j) s the settlement of the sub-layer at locaton j. 2.4 Tme-Dependent Consoldaton Settlement Tme-dependent consoldaton s the most mportant component of settlement to be calculated for a soft clay foundaton mproved by vertcal drans. Rate of vertcal consoldaton The degree of vertcal consoldaton can be calculated as follows: Uv, t 1 u / u (6a) 2.u t 0 2 o M Tv u t sn.exp (6b) m0 M H M = π(2m+1)/2 T v = c v t/h 2 Mz Where: m s an nteger number; U v,t s the degree of consoldaton at depth, tme t; ut s the pore pressure at depth, tme t; u 0 s the ntal pore pressure just after loadng; c v s the vertcal consoldaton coeffcent; T v s the tme factor correspondng to depth, tme t; H s the dranage path. Rate of horzontal consoldaton The degree of consoldaton n the horzontal drecton can be calculated based on the Hansbo s (1979) soluton as follows: U h (t)= 1-exp (-8T h, /F) (6c) T h, = c h,.t/d e 2 (6d) F = Fn + Fs + Fr Fn = ln (De/d w ) 0.75 Fs = [k h /k s -1]ln(d s /d w ) Fr = πz (L-z )k h /q w Where: T h, s the tme factor correspondng to depth, tme t; c h s the horzontal consoldaton coeffcent ; D s spacng of vertcal dran nstallaton; De s the effectve dameter of a dran. De = 5D and 1.13D for a trangular or rectangular pattern, respectvely; d w s the equvalent dameter of the dran; k h s the horzontal permeablty of the undsturbed sol; k s s the horzontal permeablty of the sol n the smear zone; L s the length of the dran; d m s the equvalent dameter of the mandrel and d s s the dameter of the dsturbed zone (d s = 2 to 3 d m ). Degree of Consoldaton The degree of consoldaton of the sub-layer s calculated by the followng equaton: U,t = 1 (1 U h, )(1 U v, ) (7) For the layers beyond the length of drans Uh s consdered zero. By combnng Eqs. (5) and (7), the tme-dependent prmary consoldaton settlement of a clay mproved by VD can be calculated as follows: S,t = U,t.Sc (8) However, due to the three-dmensonal effect, the ncrease n the vertcal effectve stress s just a part besdes the ncrease n the horzontal effectve stress. Therefore, the equaton below wll be better used, takng nto account the mmedate settlement: S,t = ξu,t Sc (9) 3. SETTLEMENT ANALYSIS 3.1 Study ste locaton SGHP project s a one of the contaner termnal projects n the Hep Phuoc Port Group, whch located at the southern gateway of the Ho Ch Mnh Cty. The reclamaton works of ths project have been started snce 2009 and dvded nto many packages correspondng to the servce loads. Ground mprovement wth surcharge, PVD and vacuum pressure was appled to ensure the stablty of contaner yard zone. In ths reclamed regon, a full scale of embankment (phase A5) was selected for research (see Fgure 3). 3.2 Sol characterzaton and Geotechncal propertes Sol characterzaton was done and plotted n Fgure 2 that shows the geotechncal profle of the average geotechncal propertes wth depth up to 50 m deep, whch are also summarzed n Table 1 & Table 2. There are three man sol layers,.e.: (1) the thck very soft to soft clay layer (from the surface to about 35 m) s dvded nto two sub layers, and namely, the very soft clay denoted as layer 1a (from the ground surface to the depth of 17 m) and the soft clay denoted as layer 1b (from 17 to 35 m deep).the very soft to soft clay s a graysh black and organc soft sol wth a low unt weght; (2) The second layer of sandy sol underles the soft clay and s located from 35 to 40 m deep. It s dentfed as grey yellowsh, grey brown, loose state to medum dense sand; (3) The blush grey, 101

3 yellowsh grey stff to hard clay underlyng the sand layer (located from 40 m downwards). Consoldaton parameters of sol layers were determned by laboratory and feld tests, and namely, the coeffcent of vertcal consoldaton (C v ) values were estmated from the oedometer tests usng Casagrande s method, whle the coeffcents of horzontal consoldaton (C h ) values were derved from pezocone tests, respectvely. The changes wth depth of these propertes, ncludng compresson ndex (C c ), swellng ndex (C s ), vertcal coeffcent of consoldaton (c v ) and horzontal coeffcent of consoldaton (c h ) are shown n Fgure 2 and Table Embankment Constructon Sequence and montorng work General plan of reclamaton brakeage at SGHP project s shown n Fgure 3 wth 12 phases (ncludng B1 to B6 and A1 to A6). The study ste s located n the A5 phase area wth full scale embankment test as seen n Fgure 3. Four settlement ponts were placed on boundary of zone (SP21, SP22, SP24, and SP25) and 01 pont was placed at the center of embankment zone (SP23). In addton, 01 pezometer (P05), 01 extensometer (E05) and 01 observaton well (OB05) were nstalled at center of study zone. The secton of the nstrumentaton s sketched n Fgure 4. Fgure 2 Geotechncal profle of the subsol at the SGHP ste Fgure 3 Locaton of testng embankment ste and montorng setup Fgure 4 Secton A-A at Phase A5 area. 102

4 The sequence of embankment constructon and nstallaton of montorng nstruments can be summarzed as follows: () Removng organc layer and placement of 1.3m thck sand fll; () Fllng of a m thck sand blanket; () Installaton of vertcal drans to a depth of about 34 m; (v) Vacuum pumpng system setup; (v) Installaton of settlement and pore pressure montorng nstruments (surface settlement plates, settlement gauges, extensometers, pezometers); (v) Vacuum pumpng; (v) Stages of embankment loadng and mantenance at 5.4 m heght, respectvely. early stage 02, but not after that, as seen n Fgure 6, to get a better ft one needs to consder the effect of vacuum loadng dstrbuton wth depth. Table 1 Basc geotechncal propertes at SGHP ste Unt Vod Water Lqud Plastc Layer weght rato content lmt lmt Name (kn/m 3 ) (%) (%) 1a b Table 2 Basc geotechncal propertes at SGHP ste (contnue) Layer C c C s c v c h σ p Name (m 2 /year) (m 2 /year) (Kg/cm 2 ) 1a σ vo 1b σ vo 3.4 Input data for settlement analyss Constructon stages to be smulated are as follows: Stage 01: PVD nstallaton and sand blanket constructon. Stage 02: Vacuum pumpng testng. : Vacuum combned surcharge. : Surcharge fnal and consoldaton tme. The coeffcent (see equaton 2) equal to 0.85 was chosen. The secondary compresson was not calculated for the perod of settlement analyss n ths study. The nput parameters used n settlement analyses are shown n Table 3. The horzontal and vertcal consoldaton coeffcents of the sol layers were assumed to be decreased durng consoldaton when the ncreased effectve stress becomes hgher than the preconsoldaton pressure. Ths s an mprovement to Hansbo s soluton, takng nto account non-lnearty of consoldaton parameters. For examples, the vertcal consoldaton coeffcent, c v, of the very soft clay (Table 3) were m 2 /year and 1.2 m 2 /year before and after preconsoldaton, respectvely. The horzontal consoldaton coeffcent, c h, of all three sol layers were 19.4 m 2 /year before preconsoldaton and around m 2 / year after preconsoldaton. The desgned vacuum pressure (70 kpa) was used for settlement analyss and dstrbuton of negatve pore pressure due to vacuum pumpng followed Indraratna et al. (2004) as seen n Fgure 5, takng nto account the rato between vacuum pressure at the bottom and the top of the dran (k p ). Results and dscusson Three man analyses were carred out as follows: Frst Analyss: as seen n Fgure 6, the measured settlement data show a large consoldaton settlement up to 4.3 m after 1.2 years of constructon. The calculaton was done wth the ntal nput data shown n Table 4, n whch the rato (RS) vared from to,, whle the rato between vacuum pressure at the bottom and the top of the dran k p = for all vacuum pumpng constructon stages. The specfc dscharge of vertcal dran at a unt hydraulc gradent (Q w ) was selected based on ASTM D-4716 wth Q w = 2000 m 3 /year and the spacng of the VD nstallaton was m. The analyss results showed that the calculated settlement wth Rs = matched qute well wth the observed settlement for from stage 01 to the Note: p o s vacuum pressure along PVD Fgure 5 Vacuum pressure dstrbuton along the dran length after Indraratna et al. (2004) HEIGHT, FILL THICKNESS ( m ) SETTLEMENTS ( m ) Stage 01 Stage 02 Calc.Embk. Elev. Calc. Fll Thck.(RS=3) Calc. Fll Thck.(RS=2) Calc. Fll Thck.(RS=5) Settl. Caused by Sand Blanket Measured Calc.Settlement (RS=2) Calc.Settlement (RS=3) Calc.Settlement (RS=5) Ground Elev. at m (Chart Datum) Intal Measured Curve (1) 1/22/10 3/23/10 5/22/10 7/21/10 9/19/10 11/18/10 1/17/11 TIME ( days ) Fgure 6 Analyss 1- Smear Zone effect Second Analyss: Ths manly amed at stmulatng the settlement n the stages 02 and 03. The calculaton was conducted wth Rs =, Q w = 2000 m 3 /year and d = m. The k p vared from 0.8 to 0.9 for ndvdual constructon stage. Results shown n Fgure 7 ndcated that the sutable values of k p are 0.8, 0.85 to 0.9 for the vacuum pumpng testng, vacuum wth surcharge and consoldaton stages, respectvely. Thrd Analyss: was carred out wth the sol parameters shown n Table 4. The PVD parameters were chosen as follows: RS=, Q w = 2000 m 3 /year, D =m. The settlement curves were calculated wth k p =0.85 for pumpng testng stage, k p = 0.95 for stage 01 and k p = for consoldaton state gave the best ft to the measurements (see results of analyss 3 n Fgure 8). 103

5 Sol Type Table 3 Intal Parameters for Settlement Analyss at Hep Phuoc Locaton Depth (m) W U W c v1 c v2 c h1 c h2 (%) (t/m 3 ) (m 2 /y) (m 2 /y) (m 2 /y) (m 2 /y) OCR CR RR Very Soft Clay (CL) Soft and medum Clay (CL) Note: c v1,c v2 : Coeffcent of vertcal consoldaton n OC,NC stage. c h1,c h2 : Coeffcent of horzontal consoldaton n OC,NC stage. k h = 0.12 m/year was used for both sub layers. Table 4 Summary of Settlement Analyss at Hep Phuoc Locaton Analyss Scopes Parameters Used Stages Remarks ANALYSIS 01 Effects of the smear Intal Sol parameters zone (Fgure 6 ) D = 1 m Q w = 2000 m 3 /year RS = Stage 02 RS = Stage 02 Poor matchng Well matchng ANALYSIS 02 (Fgure 7) Effects of negatve pore pressure dstrbuton versus depth RS = Stage 02 Poor matchng Intal Sol parameters D =1 m, Q w = 2000 m 3 /year RS=3 K = 0.80 Stage 02 K = 0.85 Stage 02 Well matchng K = 0.90 Stage 02 ANALYSIS 03 (Fgure 8) K = 0.85 (Usng K=0.85 for stage 02) Poor matchng K = 0.90 (Usng K= 0.85 for stage 02) Qute well matchng K = 0.95 (Usng K=0.85 for stage 02) Intal Sol parameters, D =1m, Q w = 2000 m 3 /year, RS=3 Well matchng K = 0.85 Stage 02 Good predcton K = 0.95 Good predcton K = 0 Good predcton 104

6 SETTLEMENTS (m) Stage 02 8/10/10 10/9/10 12/8/10 2/6/11 TIME (days) Analyss 2 - Effect of negatve pore pressure dstrbuton verus depth n stage 02 Stage /10/10 10/9/10 12/8/10 2/6/11 TIME (days) Analyss 2 - Effect of negatve pore pressure dstrbuton verus depth n stage 03 SETTLEMENTS (m) Fgure 7 Analyss 2- Effects of negatve pore pressure dstrbuton versus depth 4. DSICUSSION AND CONCLUSIONS The approach of settlement analyss appled n ths study could smulate well the large consoldaton settlement of a thck soft clay depost, mproved by combnaton of preloadng, PVD and vacuum pressure for Sa Gon-Hep Phuoc (SGHP) project. At ths study locaton, a geotechncal characterzaton was carefully done to provde nput data for settlement analyss. Wth reference to vacuum pressure dstrbuton, the values of k p (from 0.85 to ) durng varous constructon stages gave the best estmaton of the tmedependent total prmary settlement as embankment constructon goes. It was detected an ncreasng trend of k p wth tme, whch mght be explaned that for the later stages of loadng the vacuum pressure could spread more to the depth. In addton, the smear effect wth the rato between the horzontal permeablty of the undsturbed sol and that of the smear zone equal to (RS = ) gave the best results n ths study settlement analyses. 5. REFERENCES ASTM D-4716 Standard Test Method for Determnng the (Inplane) Flow Rate per Unt Wdth and Hydraulc Transmssvty of a Geosynthetc Usng a Constant Head Gao P. H. (2013), Development of a Fotran code for ground mprovement of a soft clay ground, Workshop on Foundaton and Soft Ground Engneerng Challenges n the Mekong delta, Thu Dau Mot Unversty, 5-6 June Hansbo S. (1979). Consoldaton of Clay by Band-shaped Prefabrcated Drans, Ground Engneerng 12(5), pp Indraratna, B., Bamunawta, C., and Khabbaz, H. (2004). Numercal Numercal modelng of vacuum preloadng and feld applcatons. Canadan Geotechncal Journal, 41: Note: Durng the PVD nstallaton and sand blanket constructon stage, the collected montorng data are dscontnuous and dffuse. HEIGHT, FILL THICKNESS ( m ) SETTLEMENTS ( m ) Stage 01 Stage 02 Calc.Embk. Calc. Fll Thck.(k=avalable) Fled.Embk. Fled.Fll Thck Stage01: PVD Installaton and sand blanket constructon Stage02: Vacuum testng Stage03: Vacuum Combned Surcharge Ground Elev. at m (Chart Datum) Stage04: Surcharge fnal and Consoldaton tme Stage 01 Stage 02 Settl. Caused by Sand Blanket Intal Measured Calc.Settlement K= 0.85 Intal Measured Curve (1) K= /22/10 3/23/10 5/22/10 7/21/10 9/19/10 11/18/10 1/17/11 TIME ( days ) Fgure 8 Analyss 3- Settlement analyss (Effects of negatve pore pressure dstrbuton) K= 105