VIBRO REPLACEMENT COLUMNS FOR SHIPYARD INFRASTRUCTURE AT PIPAVAV, GUJARAT, INDIA

Transcription

1 VIBRO REPLACEMENT COLUMNS FOR SHIPYARD INFRASTRUCTURE AT PIPAVAV, GUJARAT, INDIA DEEPAK RAJ 1 and C. V. DIKSHITH 2 1 Keller Ground Engineering India Pvt. Ltd., 203, Wellington Business Park 1, Andheri (E), Mumbai , India. deepak@kellerindia.com 2 Skil Infrastructure Limited, 13/14, Khetan Bhavan, 198, Jamshedji Tata Road, Churchgate, Mumbai, India. dikshith@hotmail.com Abstract: Pipavav Shipyard Limited is setting up an integrated shipbuilding facility at Pipavav which is located at the south west coast of Gujarat, India. It was envisaged that the 400 ton Ship Building Hull blocks, fabricated at the Block Making facility have to be transported along approach roads and will be placed over the hard standing pavements, before placement into dry docks for ship fabrication. The sub-soil below was soft marine clay/clayey silt with undrained shear strength in the range of 20 to 40 kpa to a depth of 12 to 15 m below existing ground level. Ground Improvement using Vibro Replacement columns were proposed for the approach roads and hard standing pavement areas to increase the bearing capacity and to reduce the settlement. This paper presents some design aspects, construction methodology and quality control of Vibro Replacement columns. Keywords: Integrated shipbuilding facility; approach roads; hard standing pavements; ground improvement. 1. INTRODUCTION Recent economic growth has resulted in an enormous increase in export and import activity in India. This resulted in an increased global and domestic demand for new vessels, bulk carriers etc. To cater for the increasing demand, the Indian shipbuilding industry is in the process of expanding shipbuilding and repairing facilities along the coastline. Pipavav Shipyard Limited (PSL) is currently setting up an integrated shipbuilding facility in Pipavav. Pipavav is located on the west coast of India, adjacent to the major sea lanes between the Persian Gulf and Asia. The shipyard is being constructed on 85 hectares of land, adjoining 800 meters of dedicated waterfront. An artist s impression of the proposed shipyard is shown in Fig. 1. Upon completion, the Pipavav shipyard will be capable of ship construction and repairs, as well as the construction of offshore platforms, rigs, jackets and vessels, etc. The construction of Pipavav shipyard includes: The conversion of one existing wet basin into a 651 meters long and 65 meters wide dry dock. The construction of block making facilities to fabricate hull blocks. The installation of a ship lift facility, including multiple land berths. Because the sub-soil was soft marine clay, the bearing capacity of the in-situ soil was not adequate. In addition, the low stiffness of the soil would have resulted in large settlements in the long term for the proposed approach road and hard standing pavement areas. Vibro Replacement columns were installed in the underlying soft clay to enhance the bearing capacity and to reduce the settlements. Ground Improvement Technologies and Case Histories Edited by C. F. Leung, J. Chu and R. F. Shen. Published by Research Publishing Services. Copyright c 2009 by Geotechnical Society of Singapore (GeoSS). ISBN: doi: /gi

2 764 Ground Improvement Technologies and Case Histories Figure 1. Artist s impression of proposed Pipavav shipyard. This paper gives an insight into the ground improvement using Vibro Replacement columns, its design, construction methodology andquality controlmeasuresadopted.several other Infrastructure projects in soft soils like container freight station at Navi Mumbai (Raj, D and Rajani, K. D., 2008), Tank farms at Paradeep, Mangalore (Vetriselvan and Deepak Raj, 2006) are executed using Vibro Replacement as ground improvement technique in India. 2. SITE GEOMETRY It was planned that 400 ton ship building hull blocks fabricated at the block making facility have to be transported along the approach roads. The blocks will then be placed over the hard standing pavements near the dry dock for ship fabrication. The total length and breadth of the improved ground for the approach road is approximately 2500 m and 14 m, respectively; while hard standing pavement is 900 m long and 25 m wide. 3. SUB SOIL PROFILE The proposed alignment of the approach road is along the river bank, covered by swampy land. Soil investigation was carried out in and around the facility. A total of 14 boreholes were drilled. Generalized soil profiles for the approach road and hard standing pavements are shown in Tables 1 and 2, respectively. Table 1. Generalised soil profile Approach road. Depth below EGL, m From To Soil classification Unit weight, γ,kn/m 3 SPT, N 0 10 Marine Clay 16 2 to 4 >10 Weathered Rock 18 >50

3 Vibro Replacement Columns for Shipyard Infrastructure at Pipavav, Gujarat, India 765 Table 2. Generalised soil profile Hard Standing pavements. Depth below EGL, m From To Soil classification Unit weight, γ,kn/m 3 SPT, N 0 2 Fill : Murram Soft Marine Clay Soft Marine Clay >12 Weathered Rock 18 >50 4. GROUND IMPROVEMENT SCHEME Both the approach roads and hard standing pavements have to be designed for the heavy traffic loads during the transportation of the 400 ton ship building hull blocks to the ship assembly area. The long term settlements were to be less than 200 mm and 150 mm for the hard standing pavements and approach road section, respectively. Vibro Replacement columns (Vibro Stone Columns) were chosen as a foundation solution to meet the above mentioned settlement limits. The design of stone columns was carried out in accordance with Priebe s (1995) method. In order to meet the performance criteria, 900 mm diameter Vibro replacement columns were proposed. The average installation depth was 12 m, with a triangular grid spacing of 2.5 m centre-to-centre. Schematics showing stone columns along the approach road and hard standing pavement are shown in Figs. 2 and 3, respectively. Figure 2. Typical schematic of approach road with vibro replacement columns.

4 766 Ground Improvement Technologies and Case Histories Figure 3. Typical schematic of dry dock and hard standing pavement. 5. CONSTRUCTION METHODOLOGY AND QUALITY CONTROL The Vibro Replacement technique uses gravel or crushed stone aggregate to form load bearing columns in the soft soils. For the wet top-feed method, the stones are 12 mm to 100 mm in size. The stone columns and the in-situ soil form an integrated system having low compressibility and high shear strength. Excess pore water pressures can dissipate through the stone columns, which also act as vertical drains. The magnitude of settlement expected for the treated soil is reduced. The process of stone column construction by the wet top-feed method is shown in Fig. 4. In the wet top-feed method, the depth vibrator and extension tubes are suspended from a crawler crane. The vibrator penetrates the ground with the help of water jets at the side of Figure 4. Stone column installation using top feed method.

5 Vibro Replacement Columns for Shipyard Infrastructure at Pipavav, Gujarat, India 767 the vibrator, its self-weight and horizontal vibrations. Anannular spaceis createdbetween the vibrator and the borehole walls through which the stone is fed from the top, to the tip of the vibrator. The up-down motion of the vibrator compacts the stone laterally into the surrounding soil. This results in a well-compacted stone column that has a diameter larger than the original hole. The column installation process is monitored using a computerized monitoring system. The vertical position and current drawn by the depth vibrator are continuously measured (in real time) and displayed to the operator. This data is also printed simultaneously for review by the engineer along with the daily report. The printout consists of two curves, namely, (i) Depth vs. Time curve and (ii) Current vs. Time curve. A typical printout is shown in Fig. 5. The left curve shows the time on the vertical axis and depth on the horizontal axis. This plot provides a comprehensive record of the movement of the vibrator. There are three distinct phases of installation. The first phase is penetration of the vibrator to the required depth. In the second phase, the hole is flushed by withdrawing the vibrator and repenetrating 3 to 4 times into the hole to increase the diameter and to clean the hole. In the third phase, the vibrator is lifted up by about 1.0m to let the stones fall inside and then it is repenetrated by about 0.3 to 0.5 m into the stone mass to form a compacted stone column. Figure 5. Typical installation record for a completed stone column up to 12 m.

6 768 Ground Improvement Technologies and Case Histories The plot in Fig. 5 show the depth and compaction efforts during construction of Stone column for the entire length. The plot on the right side shows current drawn by the vibrator on the horizontal axis and time on the vertical axis. The current drawn is used as an indicator of the compaction effort of the vibrator (Refer Chapter 2 Deep Vibro Techniques Mosley and Kirsch, 2004) Construction challenges During the execution of works, the below challenges were encountered, Water problem due to Tidal variation: A continuous supply of water is necessary for installation works for the wet top-feed method of installation. Very high tidal variations were observed during the day. It was not possible to pump the water directly from the sea. To overcome this problem, sea water was stored during high tide and used during low tide. Interference of parallel construction works: Progress of work depended on availability of working area and construction parameter facilities. It was observed that the positioning of pipe lines for water and muck handling were most difficult tasks due to many simultaneous activities in a small area. To overcome this problem, ground improvement works should be scheduled well ahead of other activities Execution Four (4) Vibro Replacement rigs were used to complete the installation works. About 144,000 linear meters of Vibro Replacement columns were installed from March 2008 to January 2009 to treat the total area of 57,500 m 2. A photograph showing the installation of the Vibro Replacement columns along the approach road is shown in Fig. 6. Figure 6. Installation of Vibro stone columns.

7 Vibro Replacement Columns for Shipyard Infrastructure at Pipavav, Gujarat, India CONCLUSIONS At the Pipavav Shipyard, 400 ton hull blocks were to be transported along a 2.5 km long approach road and stored and handled on a hard standing pavement. Vibro Replacement Columns were installed to m in soft soils, to control settlements and improve bearing capacities for both the approach road and hard standing. The entire area was completed in about 11 months and it was handed over to the owner ahead of their original schedule in phased manner for further works. ACKNOWLEDGMENTS The authors wish to acknowledge the management and staff of Pipavav Shipyard Limited for their assistance in the ground improvement works. The authors also wish to acknowledge Brigadier R. V. Seetaramiah, independent geotechnical consultant for the project and their colleagues in Keller for their valuable input in design and execution of the works. Reference 1. H. J. Priebe, The design of Vibro Replacement, Ground Engineering 28(10), (1995). 2. M. P. Moseley and K. Kirsch, Ground Improvement (2nd Edition), published by Spon Press (2004). 3. A. Vetri Selvan and D. Raj, Vibro Replacement as Foundation for Tank Farms in India, Proceedings of the Indian Geotechnical Conference, Chennai, India (2006). 4. D. Raj and K. D. Rajani, Ground Improvement works using Vibro Replacement for container freight station at Navi Mumbai, India. Proceedings of the Indian Geotechnical Conference, Bangalore, India (2008).