The Use of Vacuum Consolidation Method to Overcome the Disadvantages of Wooden Pile Application

Marcello Djunaidy1 MT, Geotekindo PT, [email protected], INDONESIA Kabul Suwitaatmadja2 MSCE, M.ASCE, Soilens, PT, [email protected], [email protected], INDONESIA

ABSTRACT: The use of wooden pile (cerucuk) to improve soft under structure has widely been applied in Kalimantan. A container yard at Banjarmasin, South Kalimantan is planned to be built on deep soft along the river which have already been improved using wooden pile. Previously, the land was used for a plywood warehouse. The soft clay thickness was 21 m meanwhile the wooden pile was only 6 to 9 m length. Vacuum consolidation method was applied to establish a stable container yard with limited post settlement and high safety factor against sliding. Surface settlement plate, vacuum gauge and were provided for monitoring during vacuuming. Settlement was monitored daily to determine the degree of consolidation. Vane shear test, and laboratory test on undisturbed samples were carried out for evaluating ground improvement performance. All monitoring data and the test results are presented and discussed in this paper. Keywords: Vacuum Consolidation Method, Cerucuk

1 INTRODUCTION 2 STRATUM CHARACTERISTICS

The proposed container yard was located at According to the survey result, the soil could Trisakti Port, South Kalimantan as shown in the be divided into 3 main layers as described map below. Soil investigation result indicated below (from top to bottom): that there was a soft clay layer with a thickness of 20.0 – 21.0 m. Layer -Backfill layer: soil Vacuum preloading method was adopted to and concrete rubble/ mixture. improve soft soil in this project covering an area Previously was material of of 2.2 hectare. The vacuum degree, surface warehouse. Thickness varied from 0.50 m to settlement and were 0.80m. carefully monitored during the preload application. The mechanism of vacuum Layer -Clayey : Grey colored, preloading method and the monitoring data are thickness from 31 m to 35 m. This layer was presented and discussed in this paper. divided in to 2 sub-layer: .a. Very soft, highly plastic, SPT N- values between 1 and 3, thickness: 20 m. .b Medium to stiff, plastic, SPT N- values between 5 and 12, thickness: 11 m to 15 m.

Layer -: White colored, below layer .

Previously, the area was used for plywood warehouse. Wooden pile (cerucuk) about 8 to 10 cm diameter was used to increase the and stability of the . Spacing between the wooden piles was 40 cm to 80 cm Fig 1. Site location with length of 6 to 9 m. Fig 2 shows the existing wooden piles. Project owner wanted that improvement with vacuuming should be 3 DESIGN & CONSTRUCTION performed without removal of the wooden piles. Vacuum preloading was applied to improve In short, vacuum preloading method utilizes layer .a. The initial soil properties of layer atmospheric pressure as surcharge load to are shown in Table 1. accelerate . Its principle is Liquidity index along the depth is shown in presented in Fig 4. Fig 3. It shows that the depth of soft soil was up to 20 m depth. However, the top part was stiffer possibly due to the presence of the wooden piles.

Table 1. Original soil properties of layer .a. Average Items Unit value w % 76.5 3 Dry densityγd g/cm 0.8 Voidratio e0 1.998 LL % 78 Compressibility Index 0.95 Cc 2 -4 Cv cm /s 7.6 x 10

1-Total stress line, 2-initial water pressure line, 3- water pressure line after vacuum applied, 4-water pressure line if without head lose Fig 4. Principle of Vacuum Preloading

Vacuum system was divided into 3 sub- systems: drainage system, sealing system and pump system. The drainage system was a network of Prefabricated Vertical Drain (PVD), Perforated Horizontal Drain (PHD) and sand layer that was forming a complete path for spreading of Fig 2. Wooden piles (cerucuk) on site vacuum pressure and water flow. The sealing system was an airtight isolation system to prevent leakage of water and air. It consisted of , (if needed) and the soft clay itself. The pump system consisted of submersible pump, vacuum chamber, control valve and pipe to connect the pump and vacuum chamber to the drainage system under the geomembrane. The improved area, total 22,000 m2, was treated as a single zone. PVDs were installed in square pattern of 1.1 m spacing and an average depth of 21 m. To prevent the PVD mandrel from hitting the wooden pile which was located below the surface, a pre-detection procedure was done using a vibratory steel pipe before PVD installation. The soil improvement target was to achieve at least 90% in average degree of consolidation analyzed using Asaoka method under vacuum Fig 3. Liquidity Index at original condition pressure alone. The construction procedure of vacuum preloading was as follows: a) Construction of the working platform. Clearing all the concrete debris on site, installation of woven then backfilling with sand of 50 cm thick. b) Pre-detection of wooden pile locations. c) Installation of vertical drains (PVD). d) Installation of PHD. e) Installation of 2 layers of non-woven geotextile and 2 layers of geomembrane.

f) Installation of vacuum pumps, running st until the average consolidation degree of 4) 1 layer geotextile installation 90%.

Construction of the vacuum preloading method are shown in the following figures.

5) Geomembrane installation (28.700 m2/sheet)

1) Pre-detection the location of wooden pile

6) 2nd layer geotextile installation

2) PVD installation

7) Vacuum start and pressure monitoring

3) PHD installation Fig 5. Construction photos 4 MONITORING

4.1 MonitoringSystem To control the progress of vacuuming, the following monitoring schemes were conducted: • Vacuum degree Vacuum gauges were installed to monitor vacuum degree under the geomembrane. 10 gauges were installed. • Total settlement plate Total settlement plates were installed on Fig 7. Vacuum degree curves. top geotextile layer to monitor ground surface settlement. 10 plates were installed as shown in Fig 6. • Pore-water pressure Pore-water pressuremeters () were installed at depths of 5 m, 10 m, 15 m and 20 m.

Fig 8. Total settlement monitoring.

Fig 6. Locations of the settlement plates.

4.2 Monitoring Data Vacuum degree was the key for the success of vacuum preloading. The most critical period was several days in the beginning when vacuum pressure was increasing. Vacuum degree was Fig 9. Pore Water Pressure monitoring monitored and recorded very carefully and the result is shown in Fig 7. Table 2. Average Consolidation Degrees In this project, it took about a week for Settlement Consolidation vacuum pressure to reach 80 kPa. After the Plate beginning period, the vacuum pressures were (mm) Degree (%) maintained over 80 kPa. Plate 01 817 96% Asaoka method was used to estimate the Plate 02 742 97% consolidation degree based on the surface Plate 03 655 94% settlement monitoring data. After 127 days of Plate 04 807 99% vacuuming, the required consolidation degree Plate 05 710 98% was achieved with surface settlement ranging Plate 06 825 98% from 646 mm to 825 mm as shown in Fig 8. The Plate 07 822 98% average consolidation degrees are listed in Plate 08 710 94% Table 2. Plate 09 646 96% Plate 10 721 99% Pore water pressure (u) decreased rapidly by Table 3. Lab test result 80 kPa after vacuum pressure was applied as shown in Fig 9.

5 POST TREATMENT

Soil parameters before and after vacuum preloading were compared to evaluate the effects of the ground improvement. Soil parameters from field and laboratory tests were compared. The most reliable parameters to compare are undrained strength (Su) from field vane shear tests and water content of the soil samples. Undrained strength from field vane shear test is reliable for comparison because there is no many source of error compared to undrained strength from laboratory tests on soil sample retrieved from ground. Water content tested from undisturbed soil sample is more reliable for comparison since this parameter is not sensitive to disturbance when soil sample is retrieved from ground. Stress relieve when soil sample is retrieved from a depth will cause disturbance resulting in lower undrained strength than it should be. Soil handling, transportation, and sample preparation for testing also contribute to the disturbance. In addition, one of the best way to know the Fig 10. Result of the field vane shear tests. success of improvement by preloading is to qc&(MPa) compare water content in soil fabric before and 0.0 0.5 1.0 1.5 2.0 2.5 after improvement because the essential point 0.0# 1.0# of preloading is squeezing water out from soil 2.0# pores. 3.0# Before#Improvement Wooden#pile#at#0#C 8#m# 4.0# After vacuum preloading finished, depth. After#Improvement laboratory test, field vane test 5.0# and cone penetration test were performed to 6.0# 7.0# check the soil properties. Total 4 boreholes 8.0# were made: 2 points (BH-1 and BH-2) near 9.0# center of the improved area, and another 2 10.0# points (BH-3 and BH-4) near the outside 11.0# 12.0# perimeter where the soil layer had never been Depth& (m) 13.0# loaded. Assuming that the soil layer surrounded 14.0# by wooden piles could not be compressed 15.0# effectively, the post-testing was focused to the 16.0# soft clay below it between 9 m and 21 m depth. 17.0# 18.0# The lab test result is shown in Table 3 and 19.0# vane shear strength test result is shown in Fig 20.0# 10. The maximum Su reached more than 40 kPa. 21.0# Cone penetration test was conducted before 22.0# and after vacuum preloading works. The test 23.0# 24.0# point was located near the inside perimeter of the improved area. The result is shown in Fig. Fig 11. Result of the cone penetration test. 11. 6 DISCUSSION AND CONCLUSION REFERENCES

The use of wooden pile to improve soft soil JGJ 79, (2002), Technical code for ground treatment of bearing capacity under structure has widely buildings. JTS 2, (2009), Technical specification for vacuum been used in Kalimantan. However, for deep preloading technique to improve soft . soft soil this method cannot solve the Gong Xiao-nan (2008), Soil Improvement Manual, 3rd consolidation settlement issue due to the edition. presence of soft soil below the tip of wooden Gong Xiao-nan and Cen Yang-run (2002), “Mechanism piles. This can lead to significant settlement of vacuum preloading,” Journal of Harbin University under the working load. of C. E. & Architecture: Vol. 35, No. 2, 7-10. Vacuum preloading was applied to improve Gouw Tjie Liong and Liu Yu (2013), “Vacuum Preloading Soil Improvement for a Vietnam Power the deeper soft soil layer under the tip level of Plant Project,” 18th Southeast Asian Geotechnical wooden piles. Considering that the improved Conference (18SEAGC) & Inaugural AGSSEA area had already been “improved” before with Conference (1AGSSEA), Singapore. installation of wooden piles and was previously Indraratna, Buddhima; Cholachat Rujikiatkamjorn; Jay used as warehouse for a long time, the result of Ameratunga; and Peter Boyle (2011), “Performance vacuum preloading was satisfying as shown by and Prediction of Vacuum Combined Surcharge Consolidation at Port of Brisbane,” Journal of a significant consolidation settlement which Geotechnical and Geoenvironmental Engineering, still occurred when vacuum preloading was ASCE, Vol. 137, No.11, November 2011. applied. Li Shi-liang (2008), “Analysis of action mechanism of Laboratory test showed reduction of water treating soft with vacuum preloading,” content and while soil density Rock and soil mechanicals: Vol. 29, No. 2, 479-482. Mesri, G and A. Q. Khan (2012), “Ground Improvement increased. Furthermore, field test showed that Using Vacuum Loading Together with Vertical the soil strength increased significantly. Drains,” Journal of Geotechnical and The proposed yard will be used for four 20- Geoenvironmental Engineering, ASCE, Vol. 138, foot containers in stack resulting in ground No.6, June 2012. pressure of 4x24 ton/(5.885m x 2.350m) = 6.94 Soilens, PT. (2014), Penyelidikan Tanah Tahap II Pada ton/m2 = 68.0 kPa. (24 ton is maximum load for Area Lapangan Penumpukan Petikemas Pelabuhan Trisakti Banjarmasin, Kalimantan Selatan. Laporan 20-ft container having size of 5.885m x 2.350m.) Akhir, Juli 2014, Laporan disampaikan ke PT. With vacuum preloading using at least 80 kPa Pelabuhan Indonesia III Cabang Banjarmasin. pressure which is bigger than the proposed working load of 68.0 kPa, then the original soil layer has more than adequate bearing capacity ABOUT THE AUTHORS to support the stack of four 20-ft containers with negligible settlement. 1. Marcello Djunaidy MT, Director of PT. Geotekindo, focus on soil improvement; The use of vacuum preloading with vertical Email:[email protected], drains for the proposed container yard in [email protected]. Trisakti Port was a good choice since the 2. Kabul Suwitaatmadja, MSCE, M.ASCE, Principal bearing capacity and the resulting settlement Geotechnical Engineer of PT. Soilens, a geotechnical satisfy requirement and could be finished consulting firm in Indonesia; within the construction schedule without Email:[email protected], danger to the stability of the existing original kabulsuwitaatmadja@yahoo. soft layer. The use of wooden pile should be limited to light structure where working load is low and settlement is not an issue. For condition where settlement and bearing capacity are major concerns, we should apply a proper improvement method involving more logical and advanced technique.