STUDY OF VARIOUS TYPES OF PVD AND PH.D. JOINTS ON VERTICAL DRAINAGE PERFORMANCE

ABSTRACT


Introduction
Ground improvement is a way to improve the technical properties of soil, such as shear strength, stiffness, and permeability (Nakhe, 2021).The properties of soft soil can disrupt the stability of the infrastructure that stands on it.To prevent damage to infrastructure before development, it is necessary to consolidate the land (Azevedo de Almeida & Mostafavi, 2016) (McFarland, Larsen, Yeshitela, Engida, & Love, 2019).However, the low permeability of soft soils causes the consolidation process to take a long time, so soil improvement that may be carried out is vertical drainage combined with preloading.Vertical drainage that is often used is prefabricated vertical drainage (PVD) which is ribbon-shaped with a rectangular appearance and made of geosynthetics.The function of PVD is to facilitate the radial flow of water from the consolidated soil, transporting it in a vertical direction and discharging it into the drainage layer with the smallest possible hydraulic resistance (Chung, Kweon, & Jang, 2014).Usually pore water in the soil that flows out through PVD is received by the sand blanket as horizontal drainage, and then flowed into the sewer.
The use of PVD has been widely researched and applied worldwide in soft soil improvement projects over the past few decades (Bo, Arulrajah, Horpibulsuk, Chinkulkijniwat, & Leong, 2016) (Jang, Kim, & Lee, 2015) (Nguyen & Kim, 2019) (Lam, Bergado, & Hino, 2015).PVD is considered more effective, efficient, and economical than other types of vertical drainage.In addition to PVD, horizontal drainage is also developed, namely PHD (Prefabricated Horizontal Drains).The use of PHD is more recommended to be used as horizontal drainage in vertical drainage systems to channel to the sewer because it can save costs and be more measurable.The use of PHD in the field is usually used instead of or combined with a sand blanket (PANJAITAN, 2021).
The connection of the PVD and Ph.D. in the field is usually done by hooking the PVD to the Ph.D. or by winding the PVD to the Ph.D. and then tying using cable ties.Regarding the type of PVD-PHD bond, there is no specific standard that can be used as a reference.In Bina Marga (2016) the installation of PHD on PVD has not been explained about the connection procedure.(Chrismaningwang et al., 2022) PVD-PHD connection by tying with cable ties has a large enough reduction in discharge capacity both on clean and dirty sand media due to deformation in the connection so that the connection is not recommended for use in the field due to deformation at the top of PVD, so the connection is not recommended.
PVD deformation due to folding, wrinkling, bending, and twisting due to a large decrease in consolidation can have a considerable influence on the effectiveness of PVD (Chrismaningwang, Hardiyatmo, Adi, & Fathani, 2021).and reduce discharge capacity and significantly or totally (Cao, Zhang, Xu, & Xu, 2021) (Bo et al., 2016).also explain that under clay confinement, PVD discharge capacity can also be significantly reduced, due to channel deformation and blockage.Discharge capacity is one of the factors influencing PVD behavior (Hansbo, Jamiolkowski, & Kok, 1981) (Miura & Chai, 2000).
This study intends to refine/improve PVD and PHD splicing systems to determine the most effective connection to vertical drainage performance of discharge capacity affected by confining pressure, overburden pressure, and hydraulic gradient as well as sand blanket bridle media that present conditions in the field.Studies on PVD-PHD splicing are still very limited, for that it is necessary to conduct more in-depth studies.These studies, it is expected to contribute to and complement previous studies.

Research Methods Discharge Capacity
Hansbo (1983) describes discharge capacity (qw) as the volume of water per unit of time that can flow along the PVD core in the axial direction under the unit hydraulic gradient (Tran-Nguyen, Edil, & Schneider, 2010).The discharge capacity regulating PVD performance thereby affects the consolidation rate (Lee, Yang, Kang, Park, & Choi, 2022) (Deng, Liu, Lu, & Xie, 2014).Flow capacity or discharge capacity (qw) is a very important parameter in determining PVD design and performance.PVD must have sufficient tensile strength and discharge capacity to be used effectively in the soil improvement process.PVD discharge capacity will decrease when the filter is depressed by lateral ground pressure.The discharge capacity is expressed by the following equation: where Q is the volume of water released by PVD per unit of time (m3/sec) and i is the hydraulic gradient.The qw value will be used to formulate the relationship between qw and restraint pressure and hydraulic gradient, as well as to determine the equivalence value of PHD with a sand blanket.

Test Equipment
PVD and PHD system discharge capacity testing was carried out using a special tool developed by Chrismaningwang 2022 which was designed to refer to ASTM D4716 standards.This test tool aims to determine the effect of the PVD-PHD connection method on its discharge capacity.In this study, the test equipment can present conditions in the field, where PVD experiences restrained pressure in the form of lateral soil pressure, and PHD experiences overbuden pressure in the form of heap soil (Siswanto, Wijaya, & Widawati, 2023) (Aini, Maulana, & Santoso, 2023).

Test Specimen
PVD and PHD are geocomposite materials consisting of an outer casing generally made of non-woven geotextiles to envelop the plastic core and core consisting of plastic folds or knitted plastic threads or other materials (Gries, Raina, Quadflieg, & Stolyarov, 2016).The Directorate General of Highways ( 2016) also explained that the function of the core is to support the filter layer and allow the passage of water flow along the drainage and the function of the blanket is to separate the core from the surrounding soil and filter to limit the escape of soil to the core.Menon et al. ( 2021) conducted a study on the process of PHD-induced consolidation in clay deposits investigated with a numerical approach.PHD was found to significantly speed up the consolidation process in soft soils, and its effects were found to be most pronounced in highly plastic soils

Various PVD-PHD Splicing and Test Methods
Discharge capacity testing on various PVD and PHD connection systems is carried out to determine the effectiveness of various PVD and PHD connection systems.Testing the discharge capacity of this connection system using PVD-T5 test specimens wrapped in a latex membrane (as a separator for test specimens with bridle) with a length of 0.50 m mounted on a compression tube with water bridle media with an extension of 0.30 m without a latex membrane then connected with PHD-W100, PHD-W200, and PHD-W300 with a length of 0.30 m in the compression box, The test sketch can be seen in Figure 1 Figure 1.Test sketches Tests are carried out with variations in specimen dimensions, hydraulic gradient, and overburden pressure.The bridle pressure (σ_c) applied to the fixed / constant compression cylinder is 100 kPa.The overburden pressure (σ_ov) is applied to the PVD-PHD connection system and the sand blanket is applied gradually from 50 kPa to 200 kPa.The hydraulic gradient used is 0.2; 0,5; and 1, Chai and Miura (1999) argue the hydraulic gradient suggested for discharge capacity testing should range between 0.1-1 used to keep the flow in PVD always in a laminar state.

Discharge Capacity Test on PVD-PHD Connection
From the test results of various types of connections, the value of discharge capacity varies even with the same PVD and PHD width.The following graph of the relationship between discharge capacity and PHD width in various connection types is presented in Figure 7 -10.

Effect of Overburden Pressure, Hydraulic Gradient, and PHD Width on
Discharge Capacity in PVD-PHD Connection Figure 6-10 shows that all connection types have the largest discharge capacity value at i = 0.2 and PHD width W = 300 mm.The effect of Ph.D. width in general, also has something in common, namely the wider the Ph.D., the greater the discharge produced.The effect of overburden pressure and hydraulic gradient on discharge capacity in PVD-PHD joints.The effect of hydraulic gradients on all variations, in general, has something in common, namely when the value of the hydraulic gradient is small and the discharge capacity is high.For the effect of overburden pressure on discharge capacity, which is when overburden pressure increases, discharge capacity decreases.The following is similar to the statement Bergado 1996 which says discharge capacity decreases at times of high I because energy loss and flow decrease almost linearly as ground pressure increases (Bergado, Manivannan, & Balasubramaniam, 1996).

Conclusion
The effect of overburden pressure and hydraulic gradient on the discharge capacity of PVD-PHD joints is described as follows.The results of the test show that when the overburden pressure increases, the discharge capacity decreases.This is due to the reduction in the cross-sectional area of PHD so that it narrows and disrupts the flow of water.For hydraulic gradients, the results show that when the hydraulic gradient is high, the value of the discharge capacity decreases due to the loss of flow energy.The type of A1 connection and A2 connection have relatively the same discharge quality value, this proves that the connection by attaching the PVD filter with PHD both outside and inside does not have a big effect.Connection B1 and connection B2 have different discharge capacities, connection B1 has a greater value than B2.This proves that the entry of PVD cores into the PHD and flanking them is not effective in increasing the value of discharge capacity, but only by attaching between PVD cores and PHD can produce better discharge capacity.
For PVD-PHD connections horizontally (A) and vertically (B) in each PHD width variation both produce a fairly good discharge capacity, but connections with vertical variations, especially B1 produce the best connection performance.The use of horizontal connections (A) is less recommended because when the horizontal position is wide, the cross-section that affects the pile load or overburden pressure is wider so that if the load is uneven, it will easily deform.This research is still in the early stages because there are still many variations of research that need to be tried.Like testing time, testing is still done with a short-term time (short-term) so it is very necessary to do with long-term testing (long-term).Tests on PVD compression cylinders still use water bridle media that has not described the situation in the field, namely with clay bridle, so the effect of fine grain infiltration on PVD is not yet known.There is no consideration of the effect of soil disturbance (smear zone) on the discharge capacity of the connection.
Figure 1 Variation of discharge capacity in various types of PVDT5-PHD connections toPHD width at an overburden pressure of 50 kPa Figure 3 Variation of discharge capacity in various types of PVDT5-PHD connections to PHD width at an overburden pressure of 150 kPa