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INTERNATIONAL JOURNAL OF SOCIAL SERVICE AND
RESEARCH
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ANALYSIS OF THE EFFECT OF SMEAR ZONE ON CONSOLIDATION
DECLINE IN THE TEBING TINGGI-KISARAN TOLL ROAD PROJECT (PHASE 1) TEBING TINGGI
– INDRAPURA STA 102+700 TOLL ROAD PROJECT WITH 3D PLAXIS MODELING
Annisa Adika Qolby
Universitas Sumatera Utara, Medan, Indonesia
Email: [email protected]
Abstract
Repairing soft clay Embankment loading method with PVD is a soil
improvement system consisting of Embankment loading work, installation PVD,
installation PHD, and geotechnical instruments. Preload serves to compress the
subgrade. PVD serves to speed up the process of soil compaction. Horizontal
drains drain pore water taken from the PVD in a horizontal direction to the
improved outside of the location. Geotechnical instruments monitor and record
the process and determine the performance of the result, improving soil that
has been carried out. Embankment loading and PVD (Prefabricated Vertical Drain)
are often used in the construction world to increase shear strength and speed
up the consolidation time of soft soils. However, using a mandrel can affect
the surrounding soil during the installation of PVD, causing the soil to become
disturbed. The disturbed area is called the Smear zone. Due to the presence of
a smear area, analysis and calculations are needed to obtain a consolidation
time under field conditions. This analysis aims to compare the decrease of
displacement in the settlement plate (SP-124) with modeling in PLAXIS 3D, using
with or without considering the smear zone. The method used in this thesis is
the analytical method using Terzaghi theory and the finite element method using
PLAXIS 3D. From the results obtained analytically, the magnitude of the
decrease is 15.252 cm.
The results from the PLAXIS 3D analysis without the effect of the smear
zone are 15.15 cm. With the effect of the smear zone being 2 times the
dimensions of the mandrel, the results obtained are 15.131 cm, 15.133 cm and 15.134
cm. With 3 times the dimensions of the mandrel, the results obtained are 15,142
cm, 15,141 cm and 15,14 cm, and with 4 times the dimensions of the mandrel, the
results obtained are 15,144 cm, 15,143 cm and 15,143 cm. The decrease in the
settlement plate 124 in the field is 15.10 cm. So it can be concluded that the
calculation of consolidation decrease using analytical theory is relatively
close to the decrease in actual results in the field with a percentage
difference of 1% decrease. There are differences in settlement due to
laboratory data not representing the entire soil layer. Due to the decrease
that occurred at 15.10 cm, the result of the effect of the smear effect 2 times
the mandrel dimension and half of the coefficient of permeability of the
original soil with a reduction ratio of 0.2% is the result that is closest to
the results of field observations compared to without a smear effect of 0.331%.
Keywords: Consolidations; PVD; PLAXIS 3D; smear zone
Received 20
September 2021, Revised 2021, Accepted 2021
Introduction
Indonesia
has been active in infrastructure development for the last 5 years, while
infrastructure is currently under construction and has been completed, such as
roads, bridges, dams, airports, MRT and LRT. North Sumatra is one of the areas
that have the opportunity to develop infrastructure, especially toll roads
whose distances will be extended so that all people can benefit from it.
However, most people only pay attention to its aesthetic value, without paying
attention to how long an infrastructure will last if it is subjected to loads,
shocks, and is affected by the weather. In infrastructure development,
geotechnical problems are important issues that must be considered. Many
problems in the structure occur due to a lack of attention in assessing soil
conditions in the field. Soil is the supporting foundation of a building or the
construction material of the building itself, so land is considered very
important in starting construction work.
Soft
soil in construction is often a problem. This is due to the low bearing
capacity of the soil. One of the factors that cause soft soil to have a low
bearing capacity is its high water content. Low carrying capacity can cause
losses, ranging from increasingly expensive construction costs to the threat to
construction safety, namely structures that are unable to stand stably and can
collapse. Soft soils are soils that, if not recognized and investigated
carefully, can cause instability and long-term settlement that cannot be
tolerated. These soils have low shear strength and high compressibility
(Iskandar, 2018). In addition, the high level of compressibility in soft soils
is caused by the high void ratio. If the soil is given a load, then the water
and air that fills the pores will come out, resulting in soil compression,
indicating a decrease in the soil. So that if it is used as a building or road
foundation, stabilization or improvement of the soft soil must first be carried
out so that it is feasible and meets the requirements as a foundation layer or
subgrade layer for road construction. To overcome these problems, soil
improvement work is needed.
Various
methods have been used to overcome this problem by construction experts and
academics. However, in the last two decades, the use of PVD as a repair method
has been recognized as one of the effective and efficient methods of assisting
preloading in locations with soft and thick soil deposits (Holtz, RD, Jamiolkowski,
MB, Lancellotta, R. and Pedroni, 1991).
Repair
of soft clay preloading method with PVD is a soil improvement system consisting
of preload work, PVD, horizontal drain and geotechnical instruments. Preload
serves to compress the subgrade. PVD serves to speed up the process of soil
compaction. A horizontal drain serves to drain pore water from the PVD in a
horizontal direction to the outside of the preload pile. Geotechnical
instruments function to monitor the process and determine the performance of
the results of soil improvements that have been carried out.
Prefabricated
vertical drain (PVD) is a geocomposite material consisting of a core layer of
polypropylene/polyethylene and a filter layer of geotextile. The function of
PVD is to overcome the problem of embankment construction on soft soil by
speeding up the consolidation process time. PVD technology has been widely
recognized as a soil improvement technology that aims to increase the shear
strength of the soil, reduce soil compressibility/compression, minimize
settlement, increase bearing capacity and prevent possible damage/collapse in
building structures on soft soil. The shorter the vertical drain path, the
higher the vertical hydraulic conductivity, and the greater the resistance of
the well from the PVD, the smaller the error that will occur (Chai, Shen,
Miura, & Bergado, 2001).
Compared
to the consolidation process using PVD and without PVD, the consolidation
process for soft clay occurs relatively quickly if PVD is installed. This shows
that the flow process occurs in vertical and horizontal directions. Without
using PVD, the consolidation process occurs very slowly, and there has never
been a decrease in consolidation as expected in the installation of PVD (Aspara
& Fitriani, 2016).
A
large consolidation settlement that occurs over a long period is a major
problem in the case of stockpiling. With low clay soil permeability, the time
for soil subsidence until consolidation is complete is predicted to reach 10
years. Soil improvement is needed to speed up consolidation settlement time.
One way that can be applied to speed up consolidation settlement time is
pre-fabricated vertical drain and pre-loading. However, when installing PVD,
the tool used (mandrel) can damage the surrounding soil so that it affects the
horizontal permeability coefficient of the soil, which can reduce the rate of
water entering the PVD. This event is called the smear zone effect. For this
reason, it is necessary to study the effect of the smear zone on the decrease
in soil consolidation.
Apriyani,
Ikhya, and Hamdhan (2016) concluded that the mesh size did not affect the
magnitude of the decline and the time of consolidation that occurred. However,
the smear zone affects the consolidation time of the soil due to the smaller
permeability coefficient.
Measuring
moisture content from field measurements is also good according to the value
calculated from the consolidation settlement. The results of the scale study
confirm that the amount of consolidation settlement increases as the PVD
distance decreases over a certain period. The final results also proved the
effectiveness of PVD for Bangkok clay enhancement (Bergado, Balasubramaniam,
Fannin, & Holtz, 2002).
Meiwa,
Ikhya, and Hamdan (2015) performed a consolidation analysis with PVD for
axisymmetric conditions and several plane strane equivalence methods using the
finite element method. It was found that the Indraratna method has the closest
axisymmetric results because this method, in addition to modeling the PVD
point, also models the smear zone in its modeling so that the modeling is more
detailed and the analysis results are more accurate. Although the Hird method
does not model the smear zone, it has a fairly close axisymmetric analysis
result.
Hayati's
(2019) calculation of the reduction and consolidation time using PLAXIS 3D
modeling by considering the effect of the smear zone gives results that are
close to the situation in the field. The time needed in the consolidation
process using PLAXIS modeling by taking into account the effect of the smear
zone is longer than that without taking into account the effect of the smear
zone.
Surbakti
(2020) The decrease in consolidation using PLAXIS 3D modeling gives results
closer to the decrease in observations in the field than PLAXIS 2D modeling.
In
this thesis, an analysis of the effect of the smear zone on the consolidation
of soft soil will be carried out. The analysis was carried out using the finite
element method with the help of the PLAXIS 3D (three-dimensional) program.
Method
To support this research, the authors obtained data from the
contractor, PT. Hutama Karya (Persero). The data obtained are:
1.
The layout of road work
2.
Boring Log BH-39
3.
Specifications PVD
4.
Geotechnical instrument (settlement plate)
Figure 1
Research
Flowchart
1.
Based on the results of
analytical calculations and 3D PLAXIS modeling with and without the effect of
the smear zone, a large reduction can be occurred, according to Table 1.
Table 1
The results of the decrease that occurred based on analytical
calculations and PLAXIS 3D
|
Modeling
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Smear zone
characteristics
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Decreased
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s'
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Kh
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(cm)
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smear zone effects
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2
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2
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15,131
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3
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15,133
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4
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15,134
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3
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2
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15,142
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3
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15,141
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4
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15,140
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4
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2
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15,144
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3
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15,143
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4
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15,143
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Without smear zone effects
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15,15
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Analytical
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15,252
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Settlement plate
124
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15,10
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2.
After analysis using 3D modeling with a time of 215 days, the
depth of PVD erection was 17.4 meters with different characteristics of the smear
zone, and the results are shown in Table 1. The table shows that the
smaller the value of k with the value of s' constant, the closer the
calculation results are getting closer to decreasing actual results in the
field. The smaller the value of s' with a constant k value, the closer the
calculation results are to the actual decline in the field. From all
experiments, the value of s'=2 and k=2 is closest to the actual conditions in
the field.
3.
Close results are obtained with the same characteristics of the smear
zone but with different permeability coefficient values using PLAXIS 3D,
which can be seen in Figures 2 to 5.
4.
The graph of the relationship between the magnitude of settlement
and consolidation time from the results of the PLAXIS 3D modeling without and
with the smear zone, which is close to the field results, as well
as the field results from the settlement plate 124, can be seen in
Figure 1.
Figure 2
The pattern of settlement and soil
consolidation time 2 times the dimension of the mandrel
Figure 3
The pattern of
settlement and consolidation time of soil 3 times the dimension of the mandrel
Figure 4
The pattern of
settlement and soil consolidation time 4 times the mandrel
Figure 5
Comparison
of settlement pattern and consolidation time for plate settlement, without
smear zone, effect smear and with analytical results that are close to plate
settlement
Conclusion
Calculating
consolidation settlement using the Terzaghi 1-D analytical theory is relatively
close to the decrease in actual results in the field, with a percentage
difference of 15.252 cm. For numerical results using PLAXIS 3D modeling, the
results are 15.15 cm without using any smear zone, with 2 times the dimensions
of the mandrel, the results obtained are 15.131 cm, 15.133 cm and 15.134 cm,
with 3 times the dimensions of the mandrel the results obtained are 15.142 cm,
15.141 cm and 15.14 cm. With 4 times the dimensions of the mandrel, the results
are 15.144 cm, 15.143 cm and 15.143 cm, with a settlement plate value of 15.10
cm. There is a difference in settlement due to laboratory data not representing
the entire soil layer in the field.
The effect
of the smear zone on soil subsidence is different for each soil type. Where in
this study, the value of 2 times the mandrel dimension and the permeability
coefficient of the original soil as a result of 0.2% is closer to the results
of field observations. This shows that the diameter of the smear zone is 2
times the dimension of the mandrel, where the original mandrel size is 5 x 12.5
to 10 x 25, and the soil permeability is 2 times less than the original soil
permeability.
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