1. 1
Case Study: Ground Improvement Using
Stone Columns and PVD
Case study from published national
conference paper
Presentation By-
Himanshu Bagul
FY M. Tech Geotech
MIS 7122213
3. An International Container Transhipment Terminal is being
developed at Vallarpadam Island by the Cochin Port. This
terminal has to be connected to the main land (NH-47 & 17)
by constructing several bridges, across the backwaters
connecting various islands. Major portion of this connection
is to be made over the land which is reclaimed from the
backwaters. The soil in this area is a mixed deposit of silt,
clay and sand. This soil need to be improved using advanced
techniques like Stone Columns and Prefabricated Vertical
Drains (PVD). The stone column technique introduces a
coarse grained material consisting of gravel or crushed stone
aggregate as the load bearing medium. The ground
improvement technique using PVD is highly suitable for
saturated soft clay prone to excessive settlement. The work
involving stone columns and PVD is subcontracted to Keller
GMBH of Germany who are doing this work for the first time
in Kerala. The paper presents the details of the ground
improvement techniques used at the site.
4. Ground improvement is a process of modifying the properties of soil to increase its load-bearing capacity and
reduce settlement. Two commonly used techniques for ground improvement are stone column and
prefabricated vertical drain (PVD).
Stone columns, also known as vibro stone columns or aggregate piers, are formed by drilling or vibrating a
hole into the soil and then filling it with compacted crushed stone or gravel. This creates a stronger and more
stable column of soil that can bear heavier loads.
Prefabricated vertical drains (PVDs), also known as wick drains, are used to accelerate the consolidation
process of soft and loose soils. These drains are made of a geotextile filter wrapped around a plastic core,
which is inserted vertically into the soil. PVDs help to accelerate the dissipation of pore water pressure,
reducing the time required for soil consolidation.
Both stone columns and PVDs are effective methods for improving the load-bearing capacity of soil and
reducing settlement. The choice between the two methods depends on the soil conditions and the desired
results. In some cases, a combination of both techniques may be used for optimal results.
INTRODUCTION
5. METHODOLOGY
Methodology for Ground Improvement using Stone Column and PVD
1. Site Investigation
Identify existing soil properties, groundwater level, and project requirements
2. Design of Stone Columns
Determine column parameters and capacity, design reinforcement, and prepare installation plan
3. Design of PVDs
Determine PVD parameters, design reinforcement, and prepare installation plan
4. Stone Column Installation
Install using vibroflotation equipment, compact to required stiffness, and verify parameters
5. PVD Installation
Install using drilling rig, place filter material, and verify parameters
6. Quality Control
Monitor installation process, perform field tests, and adjust as necessary
7. Project Completion
Conduct final inspections, provide documentation, and monitor long-term performance
6. OBSERVATION
The primary objective of using stone column and prefabricated vertical drain (PVD) techniques for ground
improvement is to increase the load-bearing capacity of the soil and reduce settlement. These techniques are
often used when the soil is weak or soft, and unable to support heavy loads, such as buildings or
infrastructure.
The specific objectives of using stone column and PVD techniques can include:
Increasing soil stability: By installing stone columns or PVDs, the soil is reinforced, and its strength and stability
are increased. This can prevent soil settlement, which can cause damage to buildings, roads, and other
structures.
Accelerating soil consolidation: Soft and loose soils can take a long time to consolidate, which can delay
construction projects. PVDs can help to accelerate the consolidation process by providing a drainage path for
excess water to escape, which reduces the time required for soil settlement.
7. Reducing construction costs: Ground improvement techniques can be a cost-effective alternative to traditional
foundation solutions, such as deep foundations or piling. Stone columns and PVDs can reduce the amount of
excavation required and minimize the amount of soil that needs to be removed and replaced.
Improving soil properties: By modifying the soil properties through ground improvement techniques, the soil
can become more suitable for construction. This can improve the long-term performance of buildings and
infrastructure and reduce the risk of future settlement or failure.
8. Quality Control Measures Description
Material quality control
Check the quality of the stone or gravel used for the columns and PVDs
to ensure that they meet the specified requirements. Check the size,
shape, and gradation of the material to ensure that they are
appropriate for the specific soil conditions.
Installation quality control
Monitor the installation of stone columns and PVDs to ensure that they
are installed at the correct depth and spacing. Check the verticality of
the columns to ensure that they are installed in a straight line.
Load testing
Conduct load testing before and after the installation of stone columns
and PVDs to determine the increase in load-bearing capacity and the
reduction in settlement.
Pore pressure monitoring
Install pore pressure gauges at appropriate locations to monitor the
pore water pressure during and after the installation of PVDs.
Settlement monitoring
Install settlement gauges at appropriate locations to monitor the
settlement during and after the installation of stone columns and
PVDs.
Quality Control
9.
10. Stone column installation involves the insertion of vertical columns of crushed stone or gravel into the soil. The
columns act as pillars that transfer the load of the structure to deeper, more competent layers of soil. This
method is particularly effective in improving the stability and reducing settlement of soft clay or loose sand.
PVD (Prefabricated Vertical Drain) installation involves the insertion of vertical plastic or geotextile drains into
the soil. The drains allow water to escape more quickly from the soil, reducing its pore water pressure and
increasing its strength. This method is effective in consolidating soft, highly compressible soils.
Both methods can be used in combination to improve the ground conditions for construction or other purposes.
The stone columns provide vertical support, while the PVDs improve the soil's horizontal stability.
The choice of method depends on the soil characteristics, the type of structure being built, and the desired
outcome. Both methods require specialized equipment and expertise for installation and are typically carried
out by experienced geotechnical contractors.
PVD Installation
11.
12. RESULTS & ANALYSIS
Stone column and PVD are the most modern techniques used for ground improvement.
Stone column introduces a coarse grained material as load bearing elements consisting of crushed stones.
Installation of stone columns considerably improves the bearing capacity of the weak soils
Stone columns are found to be an effective method of ground improvement, the time requirement is considerably less
as compared to other methods.
Crushed stones act as a draining medium in stone columns.
Application of ground improvement method using prefabricated vertical drains can significantly shorten the period of
primary settlement.
Purpose of vertical drain system is to shorten the drainage path of the pore water.
PVD installation requires much time as compared to stone column, the cost of installation is high for stone column.
13. In conclusion, ground improvement using stone column and prefabricated vertical drain (PVD) techniques can
be an effective solution for increasing the load-bearing capacity of weak or soft soils, reducing soil settlement,
and accelerating soil consolidation. These techniques are often used in construction projects where the soil is
unable to support heavy loads or where settlement is a concern.
Stone columns are created by drilling or vibrating a hole into the soil and filling it with compacted crushed stone
or gravel, creating a stronger and more stable column of soil. PVDs, on the other hand, are installed vertically
into the soil and provide a drainage path for excess water, which can accelerate the consolidation process.
The specific objectives of using stone column and PVD techniques can include increasing soil stability,
accelerating soil consolidation, reducing construction costs, and improving soil properties. By achieving these
objectives, the long-term performance of buildings and infrastructure can be improved, and the risk of future
settlement or failure can be reduced.
Overall, stone column and PVD techniques offer an effective and cost-efficient solution for ground
improvement, and their use should be considered in any construction project where soil stability and load-
bearing capacity are a concern.
CONCLUSION
