Wick Drains and Piling for Cai Mep Container Port, Vietnam. Bengt H. Fellenius. Sower's Lecture Atlanta May 8, 2012

Transcription

1 Wick Drains and Piling for Cai Mep Container Port, Vietnam Bengt H. Fellenius Sower's Lecture Atlanta May 8,

2 The Mekong

3 Saigon/HoChiMinhCity The General Area 3

4 Thi Vai Port Cai Mep Port 4

5 Artist View 5

6 The site of the new container facility extends over an 800 m by 600 m area along the Thi Vai River CG CFS 6

7 NORTH-SOUTH Locations of Buildings, Boreholes, and Settlement Points 1,200 1,000 N TCM and CPTU SS BH Piezometers Extensometers M-Shop 400 Substation BH-14 C-Gate 200 CFS ,000 EAST-WEST 7

8 DEPTH (m) DEPTH (m) DEPTH (m) Soil Profile WATER CONTENT (%) m GW & GL 0 w P w n w L 0 GRAIN SIZE DISTRIBUTION CONE CONE STRESS, q t t (MPa) CPTU-26 5 w n BH CLAY SILT SAND 40 w n BH w n BH-14 CLAY 45 SILT GRAVEL

9 DEPTH (m) DEPTH (m) DEPTH (m) DEPTH (m) CPTU Sounding Results 0 Cone Stress, q t (MPa) Sleeve Friction, f s (KPa) Pore Pressure (KPa) ,000 1,500 0 Friction Ratio, f R (%)

10 Void Ratio (- -) DEPTH (m) Results from a large series of consolidation tests show the soil to be very compressible, normally consolidated Typical example of results DEPTH: 9 m e 0 = 1.92 C c = 1.40 m r = 55 m = 5 CR = ,000 Stress (KPa) Modulus Number, m From CPTU Sounding From consolidometer Test 10

11 Risk for flooding in the area is real and the inundation can be severe, as illustrated by the flooding of the Fall of The above shows an areal photo of a Honda factory parking lot in Bangkok (October 2011). The highest water level expected at the site is Elev m, which level is about 0.5 m above the ground surface. Therefore, the ground elevation will be raised by about 2.0 m to Elev m in order to avoid flooding and to create a suitable foundation surface. 11

12 Because of the thick very compressible clay and silt layer, the 2+ m thick fill placed to raise the land will cause significant settlement, which would continue for a very long time. To shorten that time, vertical drains (wick drains) were installed to 37 m depth across the site (in some places into the sand, in other places a bit of the clay was left between the drain tip and the sand). Moreover, a temporary surcharge was added raising the surface to Elev. +8 m through Elev. +10 m, i.e., an additional 2.5 m to 4.5 m of fill height. 12

13 SETTLEMENT FILL HEIGHT Principle of the wick drain and surcharge soil improvement scheme Amount of fill placed Surcharge removed when 80% 90% consolidation is achieved FILL Paving and roadways For case of surcharge not removed For case of surcharge removed ORIGINAL GROUND SURFACE Initial compression and consolidation settlement SETTLEMENT ORIGINAL GROUND SURFACE 80 % to 90 % of total consolidation settlement For case of surcharge removed For case of surcharge not removed TIME 13

14 The wick drain used for the project is a 100 mm wide and 3 mm thick and consists of a corrugated, 0.15 mm thick, plastic core wrapped with a synthetic filter. 14

15 Fill height and ground surface settlement until one month before start of driving piles for the building foundations 15

16 Fill height and pore pressures measured June 24, 2009, through September 17, 2010 (Days -527 and -77) at the CFS building The tip elevations are per original installed depth. The settlement of the piezometer tips is not included. 16

17 DEPTH (m) FILL ELEVATION Distribution with depth of the pore pressures at the CFS building PORE PRESSURES JUNE 24, 2009 THROUGH SEP 17, 2010 (KPa) m U 0 June 24, and Sep 18, '09 just before adding surcharge (Days -504 and -447). Sep 17, '09 last reading (Day -77). Dec 1, '09 maximum reading (Day -365)

18 Settlement (mm) Ground surface settlements DAYS Start of pile driving for the CFS and CG buildings ,000 SS-108 1,500 2,000 SS-38 SS-39 SS-30 Surcharge removal SS-29 2,500 SS-32 SS-104 SS-28 3,000 3,500 4,000 Container Freight Station, CFS and Container Gate, CG 18

19 View on October 4, 2011, taken from the south-east end of CFS building showing some of the about 1,680 piles driven for the CFS. 19

20 The building foundations were placed on precast, ordinary reinforced, concrete piles with a square 400 mm cross section made up by 10-m segments spliced in the field by welding steel end-plates together. For Buildings CFS and CG, the piles were driven to 28 m and 18 m depth, respectively. The intended working loads were 347 KN for the CFS building and 265 KN for the other buildings. One pile at each building was subjected to a static loading test. The test piles were not instrumented, and the test schedule included unloading/reloading cycles and varying load hold durations. Therefore, the test results have very limited use for the design. The static loading tests (CFS and CG) were carried out in September 2010, nine months after pile driving Load-movement curves from static loading tests at CFS and CG buildings 20

21 21

22 22

23 Settlement (mm) The below figure shows the settlements measured by the SS-plates at or near the buildings until November 15, The zero date is December 1, 2010, the day of the start of the pile driving for the CGS building. Driving was completed on January 24 at the CG building. DAYS Surcharge removal Pile driving 1,000 SS-108 SS-30 1,500 2,000 SS-39 2,500 SS-108 3,000 SS-28 SS-29 SS-38 SS-32 3,500 4,000 Container Freight Station, CFS and Container Gate, CG SS

24 Settlement (mm) ELEVATION (mm) 10,000 9,000 AS-PLACED FILL HEIGHT 8,000 7,000 6,000 SS-29 SS-28 ELEV m 5,000 MAXIMUM WATER LEVEL 4,000 3,000 ORIGINAL GROUND SURFACE MEAN WATER LEVEL 2, DAYS PILE DRIVING Start placing fill End placing surcharge Removing surcharge Pile driving DAYS ,000 1,500 2,000 2,500 Red heavy lines are SS-28 and SS-29 All values are normalized to the 2,900 mm average settlement at Day 0 3, mm 3,500 AT CFS and CG 4,000 24

25 NORTH-SOUTH Settlement (mm) Pile head settlements and benchmark settlements at the building locations CONTAINER FREIGHT STATION, CFS AND CONTAINER GATE SS-22 SS-23 SS-24 SS-29 SS-108 SS-30 C-Gate SS-227 SS-37 SS-36 SS-235 SS-236 DAYS Surcharge Pile 500 1,000 removal SS-108 SS-30 driving 1, SS-102 SS-228 SS-28 SS-230 CFS Pz-09 Ext-09 SS-33 SS-34 SS-233 SS-234 2,000 2,500 3,000 SS-39 SS-28 CFS Average of Piles added to SS29 C-Gate Average of Piles added to SS108 SS-29 SS-108 SS-38 SS EAST-WEST 3,500 4,000 Container Freight Station, CFS and Container Gate, CG SS-104 Container Freight Station (CFS) and Container Gate (CG) 25

26 Settlement (mm) Settlements measured for SS-plates and piles at the CFS and CG buildings until November 15, ,500 DAYS ,600 2,700 CG Average values of pile head settlement added to SS-108 2,800 SS-108 2,900 3,000 CFS Average values of pile head settlement added to SS-29 SS-29 26

27 DEPTH (m) Settlement distribution measured in an extensometer station (multi-anchor points) outside the CFS building during 18 months: from July 17, 2009 (one to three months after start of placing fill) through January 14, 2011, one month after piles were driven near the location of the extensometer station m First Fill Surface 5 SETTLEMENT (m) Relative settlement between anchor points during last five months of monitoring June 29, 2010, after the temporary surcharge had been removed R 4 mm/m 20 R 6 mm/m R 12 mm/m 25 R 30 mm/m July 17, 2009 January 14, Zero Reading of was taken on July 17, The settlement plates located within the CFS footprint then showed that 0.6 m settlement had already occurred (since February 20, 2009). Total plate settlement on January 14, 2011, was 3.08 m. The curves show readings spaced about one month apart. 27

28 STRESS (KPa) From measured fill height and settlement to input to analysis Stress from as-placed fill (approximated) Stress from fill adjusted for settlement and buoyancy MONTHS Removal of Surcharge Stress from fill elevation Stress reduction due to settlement and buoyancy 28

29 UniSettle4 input and results 29

30 UniSettle4 input and results Input alternatives 30

31 SETTLEMENT (mm) 0 MONTHS Immediate Compression Secondary Compression 1,000 1,500 2,000 2,500 Full fill height reached Measured settlement Settlement calculated with the drains assumed functioning along the full depth 3,000 3,500 4,000 Surcharge removed Piles driven Settlement calculated with the drains assumed not to function below 20 m depth 31

32 28 m CFS Pile 40 m CFS Pile Settlement of the CFS Building for 28 m Pile SETTLEMENT CLAY Neutral Plane SAND Neutral Plane DEPTH 32

33 View on October 4, 2011, taken from the south end of CFS building showing some of the about 750 piles driven for the CFS building. In the background, lengthened piles are being driven for the CG building. 33

34 Photos from the driving of piles with extension 39

35 40

36 CONCLUSIONS The most probable cause to the continued consolidation below about 20 m depth is that large soil stresses have squashed the wick drains preventing the drains from functioning properly. The consequence is that the overall area and the piles will continue to settle even if no new loads are placed. But there will be new loads, so... The problem with the piled foundations can be (and was hopefully) resolved by lengthening the piles to bring the neutral plane (the depth to the settlement equilibrium) into the non-settling sand below the clay. It is not realistic to install new and better drains or arrange, say, for vacuum treatment to get the consolidation to occur quickly. The site will have to live with continuing to add fill to compensate for excessive settlement, which will in turn add consolidation, and to suffer the maintenance actions that regularly will be required for non-piled foundations. The monitoring scheme was designed to confirm that the wick drain method worked. When the measurements showed that the method did not work, the method became very much inadequate, and it could not be of any assistance for selecting a solution to the problem. Every monitoring programme should have redundancy and be designed to resolve issues should the design show to be unsuccessful. How to resolve the question "what if we're wrong?" should always be kept in mind and in the planning of a monitoring programme. 41

37 The Lotus Vietnam's National Flower Thank you for your attention 42