The Evaluation of Pipeline Protection Influenced by Causeway Embankment Using the Finite Element Method (FEM)

Abstract

The construction of embankments over very soft to soft clay, such as reclamation projects, is on the rise. One such development is the reclamation project in the District Manyar, Gresik region of East Java. The seabed in this area is predominantly composed of soft clay. Reclamation involves the construction of a causeway that intersects with a gas pipeline at a depth of 5 m from the seabed. The embankment construction will undoubtedly impact the surrounding area. This study focuses on analyzing the impact of embankment in a reclamation area on soft soil on the underlying pipeline and designing pipeline protection. As a result of this study, the safety factor at each construction stage exceeds the planned safety factor of 1.5. The maximum settlement that occurs in the soil beneath the pipe is 26.91 mm. The maximum stress sustained by the corrugated steel plate (CSP) is 35,499.79 kN/m², with a lateral deformation of 41.37 mm. The maximum stress occurring on the concrete footing slab is 123.40 kN/m², which is smaller than the allowable bearing capacity of 128.61 kN/m².

1. Introduction

The construction of embankments over very soft to soft clay, such as reclamation projects, is on the rise due to the scarcity of suitable land for infrastructure and other developments. The development of port infrastructure located along the coast often requires reclamation over the sea. One such development is the reclamation project in the District Manyar, Gresik region of East Java. The seabed in this area is predominantly composed of soft clay. Research on embankment construction on soft soil, utilizing both empirical methods and the finite element method (FEM), has been extensively discussed, including [1,2,3,4].

The embankment on soft soil leads to various stability issues, one of which is significant settlement with a low bearing capacity [3,4,5]. Soil improvement is implemented to mitigate stability issues of embankments on soft soil, for example, using prefabricated vertical drains (PVD) to accelerate the consolidation process [3]. PVD can also be combined with vacuum preloading [6,7,8]. PVD is often preferred because of its low cost and ease of installation. PVD combined with soil preloading or vacuum preloading can improve the shear strength of low-lying area. Gained soil strength remains even after the preloading is removed [9]. Reinforcement can also be carried out to enhance the bearing capacity of soft soil layers, including geotextile reinforcement [10,11], pile reinforcement [12,13], and bamboo reinforcement [14]. A comparison of the various soft soil reinforcement method is explained in

Table 1. Comparison of various soft soil reinforcements.

Method	Description	Advantages	Limitation	References
Prefabricated vertical drains (PVD)	PVD is a drainage element that is installed vertically into soft soil.	Accelerate consolidation time.	Effective only up to 6 months before clogging.	[3,6,7]
Vacuum preloading	Vacuum preloading is a system combining vertical and horizontal drains that are connected through sand drainage and a High-Density Polyethylene (HDPE) membrane.	Reduce height of soil preloading, distribute the pressure to deep layer of sub soil.	Maximum pressure approximately 100 kPa	[6,7,8]
Geotextile	Geotextile is a synthetic material with various function such as drainage, filtration, and reinforcement.	Can be combined with other reinforcement.	Improvement only on internal stability.	[10,11]
Pile reinforcement	Piled embankment acts as load transfer platform, where load from embankment transferred into pile.	Load from embankment transferred into pile and reduce load received by subsoil.	No significant limitation.	[12,13]
Bamboo reinforcement	Bamboo reinforcement such as bamboo mat and bamboo pile are a cheaper alternative for reinforcement compared to concrete piles.	Bamboo mat distributes the load received by sub soft soil and slightly increases the bearing capacity of the underlying soft soil.	Non uniform bamboo stiffness.	[15,16,17]

.

According to one of the previous studies on embankments in the Sidoarjo Mud Dam [3], untreated soft soil tends to experience significant settlement and long consolidation times. The largest settlement is located directly beneath the 12-m-high dam crest, which reaches 7 m. Settlement has persisted for several decades.

One part of the reclamation, which involves the construction of a causeway, intersects with a gas pipeline at a depth of 5 m from the seabed. The embankment construction will undoubtedly impact the surrounding area, prompting research on the effects of river channel excavation on underground tunnels [18]. A buried gas pipe is highly sensitive to ground deformation due to its linear structure. Load from embankment filling above the pipe can cause settlement and lateral displacement on the soil around the pipe. This can lead to deformation of the buried gas pipeline and potentially severe damage to the connections between pipe segments, ultimately resulting in breakage. Figure 1 shows a schematic of how the load from embankment filling can affect the buried gas pipeline.

Ref. [19] conducted a study on the use of piles to protect buried pipelines. Lateral movement due to embankment loading can cause damage to the buried pipe; hence, piled embankments are utilized to prevent such damage. Full-scale field testing was conducted over a period of 70 days. The test results revealed that the presence of piles significantly reduces settlement on the buried pipe and lateral displacement in the underlying soft soil. This is attributed to the transfer of load from the piles to the firmer soil layers.

Other studies have discussed estimation methods for calculating lateral flow or design guidelines for buried pipes [20,21]. However, it is evident that embankment load induces both settlement and lateral displacement on soft subsoil, leading to damage to the buried pipe. The publication [19] uses piled embankment as reinforcement; there are no studies available about the combination of bamboo reinforcement to minimize damage to the buried pipe.

This study focuses on analyzing the impact of an embankment in a reclamation area on soft soil, specifically on the underlying pipeline, and designing appropriate pipeline protection measures. The research’s findings will include safety factors, soil settlement beneath the pipeline, and pipeline protection performance. At each stage of the construction process, we will display the results to track the evolution of safety factors and soil deformations caused by the embankment load. This research methodology uses a full-scale FEM model to predict settlement and stress on the pipeline. So, this research analysis is unique in considering the effects of multiple loads from every stage of construction to design a reinforcement for the embankments themselves and a protection for the pipe.

2. Methods

2.1. Site Condition

The reclamation project on Segitiga Island, covering an area of 40 hectares, is located in district Manyar, Gresik, East Java. Figure 2 shows the location of the reclamation and soil investigation. The soil data investigation involves a total of six offshore borings with a depth of 60 m, utilizing standard penetration test (SPT) procedures. Three borehole points (BH-3 to BH-5) are located in the reclamation area, two points (BH-1 and BH-2) are located in the planned dock area, and one point (BH-6) is located in the designed bridge connecting area.

The pipe protection area is located in the BH-5 to BH-6 area, where the construction of a causeway is planned. Based on this, the soil data reference for pipe protection design utilizes the soil data analysis from BH-5 and BH-6. Figure 3 shows a comparison of the N-SPT values in the BH-5 and BH-6 areas. According to the SPT test results, the data from BH-6 are used in the design planning, considering the most critical outcome. The soil profile at BH-6 consists of a 15-m-thick layer of very soft to soft clay after a 1-m-thick layer of very loose sand. Further down to a depth of 60 m, the soil is composed of sand with a medium-to dense consistency.

2.2. Soil Properties

Soil stratigraphy based on BH-6 data is divided into (1) 1-m-thick very loose sand; (2) 15-m-thick very soft to soft clay; and (3) medium to dense sand down to a depth of 60 m. The soil data parameters are determined using correlations of corrected N-SPT values. The correction for N-SPT values is based on the equations by [22,23]. The correction for the N-SPT value due to field procedure is calculated based on Equation (1) from [22].

$$N_{60}=\frac{E_H{C}_B{C}_{S}N}{0.6}$$

(1)

Correction of the N-SPT value due to overburden stress based on Equations (2) and (3) from [23] was calculated as follows

$$({N_1)}_{60}=N_{60}\times C_N\le 2N_{60}$$

(2)

$$C_N=0.77\log \left(\frac{2000}{{\mathrm{\sigma }}_0\prime }\right)$$

(3)

The correction N-SPT value due to the ground water table based on Equation (4) from [24] the calculation is as follows:

$$({N_1)}_{60\left(Corr\right)}=15+\frac{1}{2}[\left({N_1)}_{60}-15\right]$$

(4)

After obtaining the corrected N-SPT values, the correlation of soil parameters is then carried out based on the corrected N-SPT values. The first correlation is performed to determine the physical and mechanical parameters of the soil. Correlation for coarse-grained (cohesionless soil) and fine-graded soil (cohesive soil) is conducted using the [25] correlation table, as shown in

Table 2. Correlation parameter for cohesionless soil and cohesive soil [25].

Cohesionless Soil
Parameter	Unit	Very Loose	Loose	Medium	Dense	Very Dense
Relative density (Dr)	%	0–0.15	0.15–0.35	0.35–0.65	0.65–0.85	0.85–1.00
Corrected N′-SPT value	(blow)	0–4	4–10	10–30	30–50	>50
Internal angle friction (φ)	(°)	25–30	27–32	30–35	35–40	38–43
Unit weight (γ)	(kN/m3)	11.0–15.7	14.1–18.1	17.4–20.4	17.3–22	20.4–23.6
Cohesion Soil
Parameter	Unit	Very Soft	Soft	Medium	Stiff	Very Stiff	Hard
Corrected N′-SPT value	(blow)	0–2	2–4	4–8	8–16	16–32	>32
Saturated unit weight (γsat)	(kN/m3)	<15.7	15.7–18.8	17.3–19.6	18.1–20.4	18.8–22	>20.4
Unconfined compression (qu)	(kN/m2)	0–25	25–50	50–100	100 -200	200–400	>400
Cohesion undrained (Cu)	(kN/m2)	12	12–24	24–48	48–96	96–192	>200

.

Next, a correlation assessment is carried out for the Young’s modulus values based on the N-SPT values using the correlation table [25], as seen in

Table 3. Correlation for Young’s modulus parameter [25].

Soil Type	Es (kPa)
Sand (normally consolidated)	500 (N + 15)
Sand (saturated)	250 (N + 15)
Gravelly sand	1200 (N + 6)
Clayey sand	320 (N + 15)
Silts, sandy silts, clayey silt	300 (N + 6)

.

2.3. Soil Model Parameter

To model the subsoil profile realistically, one must consider the non-linearity of the soft soil layer. There are various models that have been developed to achieve a realistic model for field conditions, including the hardening soil model (HSM), soft soil model (SSM), modified cam clay model (MCC), etc.

In this study, the sand layer soil model uses the hardening soil model (HSM). The hyperbolic elastoplastic model (HSM) takes into account the nonlinearity of the soil by showing how stiffness changes with stress but it does not look at viscous effects like creep and stress relaxation. HSM is based on the Mohr–Coulomb failure criterion and its yield surface can expand due to plastic strain. The hardening soil model uses plasticity theory, unlike the Mohr–Coulomb model, which uses an elasticity model. The hardening soil model considers both shear hardening and compression hardening of the soil. A detailed formulation of the hardening soil model is explained by [26].

The hardening soil model (HSM) is introduced to characterize the mechanical behavior of soil under loading, unloading, and consolidation phases. The HSS model incorporates the small strain properties of materials, enabling a more precise prediction of soil deformation. Usually, the HSS model utilizes drained soil parameters such as unit weight (γ), drained shear strength (c′), effective internal angel friction (φ′), and lateral limit compression (E_S) [27]. The hardening soil model can be used for modeling different types of soil, including granular and soft soil. Power m represents the stress dependency of soil stiffness, where for soft soil, m = 1. The hardening soil model needs three stiffness parameters at a chosen reference pressure (P_ref). There are a (1) triaxial modulus/secant modulus (E₅₀^ref), (2) oedometric modulus (E_oed^ref), and (3) unloading–reloading modulus (E_ur^ref). A series of laboratory tests determine this parameter [28]. However, some scholars have used statistical and inverse analysis to determine the stiffness parameter for this model [29,30]. This is conducted considering the time and cost if only using a laboratory test.

Furthermore, to model the clayey soil in this study, a soft soil model is employed. Some scholars have used the soft soil model (SSM) to analyze the behavior of soft soil [31]. Soft soil such as very soft clay, normally consolidated clay, silt, and peat, is modeled using the soft soil model (SSM) in finite element modeling (FEM). Unlike Mohr–Coulomb, which assumes linear behavior and constant stiffness of soil throughout soil depth, soft soil developed a nonlinear behavior of soil. Soft soil model considers soil nonlinearity via a linear stress dependency of stiffness. There are two key model inputs that define the compressibility of the soil in isotropic loading, unloading, and subsequent reloading. The first is the modified compression index lambda (λ) for modeling the compression of soil and the second is the modified swelling index kappa (κ). This parameter can be calculated automatically in the software using the compression index (C_C) and swelling index (C_S). The calculation formula for λ and κ is given by [32] as

$${\mathsf{\lambda }}^{\ast }=\frac{\lambda }{1+e_0}=\frac{Cc}{2.3(1+e_0)}$$

(5)

$${\mathsf{\kappa }}^{\ast }=\frac{\kappa }{1+e_0}=\frac{2Cs}{2.3(1+e_0)}$$

(6)

The yield failure criterion of the Mohr–Coulomb theory serves as a basis for the soft soil model yield function, except that the yield function of SSM defines an ellipse with P_P, isotropic pre-consolidation pressure defines the length of the ellipse, and M is the height of the ellipse in the p′ plane. M also represents the ratio of horizontal to vertical stress under primary loading and is used to determine the earth pressure at rest (K_o^nc).

Input parameters for the soil modeling in Plaxis 2D Version 21.01.00.479 (build 479), based on the requirements from PLAXIS Version 21 [33], are displayed in Figure 4. Each soil layer has a color shown in Figure 4. This color will be displayed in the Plaxis modeling schematic shown in Figure 5.

2.4. Pipe Location

The planned reclamation area for the causeway intersects with the pipelines owned by Petronas and HESS. This area is located between BH-5 and BH-6, as shown in Figure 6. Based on this, the causeway reclamation work must take into consideration the impact on the underwater pipelines due to the embankment construction above them.

2.5. Construction Sequence

The construction sequence of the embankment for the causeway reclamation area begins with the installation of bamboo pile reinforcement in a configuration of six bamboo piles with a depth of 6 m and a spacing of 1 m. Subsequently, the installation of the pipe barrier is carried out using bamboo piles in a configuration of three bamboo piles with a depth of 6 m, installed continuously along the intersecting area.

After the piles are installed, the next step is the installation of a four-layer bamboo mat adjusted to the bamboo pile installation. Subsequently, a non-woven geotextile is placed on top of the bamboo mat and the limestone embankment can be carried out.

The embankment filling is carried out step by step, allowing the soft soil layers, predominantly very soft to soft clay, to undergo consolidation over time and reduce excess pore water pressure. This will enhance the soil’s bearing capacity [3,32,34]. Based on this, the construction stages will be divided into 12 embankment phases, with each phase implemented over a period of 10 days. The geometry and thickness of each layer will vary and will be checked for the stability of the executed embankment.

2.6. Staged Construction on FEM Analysis

The construction implementation method in Plaxis 2D Version 21.01.00.479 (build 479) simulated using staged construction. The staged construction in Plaxis illustrates the construction method in the field and is presented in

Table 4. Staged construction.

Stage	Phase Construction	Job Description
Initial Phase
Phase 1	Bamboo pile installation	Installing bamboo pile reinforcement
	Bamboo grid (mattress)	Installing bamboo mattress
	Lime stone fill 1	Lime stone filling with 1 m thickness
	Load 1	Load service from dump truck for filling work
	Safety factor phase 1	Safety analysis for phase 1
Phase 2	Lime stone fill 2	Continue filling with 1 m of lime stone
	Load 2 + pile protection	Load service from dump truck with installation of pipe protection
	Safety factor phase 1	Safety analysis for phase 2
Phase 3	Lime stone fill 3	Continue filling lime stone with 0.8 thickness
	Load 3	Load from dump truck filling work
	Safety factor 3	Safety analysis for phase 3
Phase 4	Gravel fill 1	First step of gravel fills on land side
	Safety factor 4	Safety analysis for phase 4
Phase 5	Gravel fill 2	Second step of gravel fills on land side
	Safety factor 5	Safety analysis for phase 5
Phase 6	Gravel fill 3	Third step of gravel fills on land side
	Safety factor 6	Safety analysis for phase 6
Phase 7	Load 4	Load from excavator for gravel filling.
	Safety factor 7	Safety analysis for phase 7
Phase 8	Gravel fill 4	Fourth step of gravel fills on sea side
	Safety factor 8	Safety analysis for phase 8
Phase 9	Gravel fill 5	Fifth step of gravel fills on sea side
	Safety factor 9	Safety analysis for phase 9
Phase 10	Gravel fill 6	Sixth step of gravel fills on sea side
	Safety factor 10	Safety analysis for phase 10
Phase 11	Lime stone fill 4	Lime stone filling on sea side
	Safety factor 11	Safety analysis for phase 11
Phase 12	Lime stone fill 5	Lime stone filling on sea side
	Safety factor 12	Safety analysis for phase 12
Phase 13	Lime stone fill 6	Lime stone filling on sea side
	Safety factor 13	Safety analysis for phase 13
Phase 14	Load 5	Load from dump truck and heavy equipment with uniform load 25 kPa
	Safety factor 14	Safety analysis for phase 14

. As shown in Table 4, embankment filling is carried out step by step, filling from land toward the sea. The planning also considers the loads resulting from the mobilization of heavy equipment.

2.7. Pipe Model on FEM

According to studies by [35], when the soil–structure interaction is taken into account, the displacement of the structure increases. The contact surface’s friction coefficient can be considered the same as the clay’s friction angle [35]. We do not model this as a structure but instead discretize the pipe point locations into cross-sections to observe the displacement in the soil surrounding the installed pipes.

2.8. Pipe Protection

The embankment carried out above the pipeline may lead to potential damage to the pipe. Therefore, reinforcement is necessary to prevent the pipe from experiencing excessive axial and lateral loads. The reinforcement is planned to utilize a combination of U-ditch (2000 mm × 2800 mm), concrete footing slab, and corrugated steel plate (CSP), along with additional bamboo piles and bamboo mattresses. The specifications for the reinforcement are presented in

Table 5. Pipe protection specification.

Parameter	Value	Unit
Corrugated steel plate
Thickness	10	mm
Diameter	5000	mm
Material quality	SS400
U-ditch and footing slab (concrete)
Compressive strength (f′c)	30	MPa
Bamboo
Length	6	m
Diameter	6–8	cm

. Figure 7 illustrates the reinforcement plan of corrugated steel plate and u-ditch and Figure 8 illustrates bamboo mattresses reinforcement.

Corrugated steel plate (CSP) reinforcement has various advantages, including its fast construction process and relatively low cost [36]. Additionally, CSP is lightweight and environmentally friendly [37]. Typically, CSP reinforcement is used in bridges, highways, and underground passages [38,39]. Studies on the behavior of a steel shell during backfilling by [40,41,42] have shown that the strain and displacement values on CSP are higher when subjected to static loading compared to dynamic loading [40]. In this study, the design of CSP reinforcement is combined with a U-ditch and concrete footing slab to simplify the installation process and enhance the support bearing capacity of the pipeline reinforcement.

2.9. Constitutive Model of Bamboo

The bamboo mattress is composed of a bamboo stick arranged to form a mattress as shown in Figure 7. The determination of the cross-sectional area and moment of inertia of the bamboo has been studied by [15,16]. The total cross sectional area of bamboo that builds the mattress is $A_m$. The $A_m$ can be calculated by equation below [16], as follows:

$$A_m=\sum A_i$$

(7)

Sum of the moment inertia of bamboo is $I_m$. The $I_m$ can be calculated as below [16], as follows:

$$\mathrm{A}\mathrm{m}=\sum \left\{I_{m\left(i\right)}+A_{m\left(i\right)}·{y\left(i\right)}^2\right\}$$

(8)

Bamboo piles are a bamboo reinforcement that forms the basis of pile foundation reinforcement. Irsyam in [15] illustrates the concept of determining the spring constant of bamboo pile Cerucuk bambu, as shown in Figure 9. The diameter of the bamboo is assumed to be uniform, which is 8 cm. The ultimate bearing capacity of bamboo pile on soft soil can be calculated using the equation below.

$${\mathrm{P}}_{ult}=K_{ll}\left(c_1{h}_1+c_2{h}_2+\dots c_i{h}_i\right)+9A_b{c}_i$$

(9)

where $K_{ll}$ is average circumference of bamboo, $c_1,c_2\dots c_i$ are the undrained cohesion of soil, $h_1,h_2\dots h_i$ are the dept of each soil layer, and $A_b$ is the sectional area of bamboo pile. The magnitude of soil deformation so that the value of does not move is assumed to be δ = 0.1 × d, with 𝑑 as the diameter of the bamboo. The magnitude of the spring constant (k) can be calculated using the following equation:

$$k=\frac{F_{max}}{\mathrm{\delta }}$$

(10)

3. Results

3.1. Finite Element Modeling

The analysis of the response of buried pipes caused by causeway reclamation is conducted using the finite element method (FEM). The schematic modeling is illustrated in Figure 5. Several reinforcement structures are utilized, including bamboo piles, bamboo mattresses, U-ditch, footing slabs, and corrugated steel plates (CSP). Bamboo piles and bamboo mattress reinforcement aim to increase the load-bearing capacity of soft soil on the seabed to support the embankment process. Meanwhile, the combined reinforcement of U-ditches, footing slabs, and CSP acts to reduce the load applied to the area where the pipes are installed. From the schematic diagram of the modeling in Figure 5, the layer of color differences in the subsoil layer of the soil is visible, with color annotations indicating the corresponding soil layers in Figure 4.

3.2. Safety Factor Analysis

Table 6. Safety factor result.

Phase	Safety Factor	Safety Factor Minimum
1	5.408	1.500
2	3.529	1.500
3	2.860	1.500
4	3.178	1.500
5	3.140	1.500
6	2.510	1.500
7	2.232	1.500
8	2.631	1.500
9	2.691	1.500
10	2.173	1.500
11	2.663	1.500
12	2.747	1.500
13	3.062	1.500
14	3.211	1.500

shows the safety factor results for each stage of construction. Based on this, it can be observed that the safety factor at each construction stage exceeds the minimum planned safety factor of 1.5. Therefore, it can be concluded that the embankment construction method can be implemented according to the plan. One of the output safety factor values is displayed in the red box at Figure 10. From the results, the minimum safety factor reached occurs in Phase 10. The differences in deformation distribution occurring during the construction period are depicted with color gradation in Figure 10. The red to orange color indicates deformations occurring between 500 × 10⁻³ m to 400 × 10⁻³ m. The orange to yellow color represents deformations occurring between 400 × 10⁻³ m to 300 × 10⁻³ m. The yellow to green color signifies deformations ranging from 300 × 10⁻³ m to 200 × 10⁻³ m. Meanwhile, from light blue to dark blue, deformations occurring are less than 200 × 10⁻³ m.

3.3. Settlement Analysis

Table 7. Settlement result.

Phase	Settlement on −5 m (mm)
	Without Reinforcement	Reinforcement
1	1.20	1.20
2	1.78	1.78
3	46.67	5.52
4	69.67	6.08
5	98.24	7.68
6	121.81	7.77
7	133.52	7.95
8	146.22	11.43
9	155.50	12.26
10	165.96	13.44
11	226.27	18.36
12	270.69	18.66
13	288.31	20.39
14	282.96	26.91

presents the soil settling beneath the pipe. Based on the results presented in Table 7, both settlements occur with and without the reinforcement of corrugated steel plate (CSP) and settlement increases with additional embankment filling. Following the installation of CSP in Phase 2, subsequent settlements demonstrated a reduction in settlement magnitude with CSP reinforcement. Figure 11 illustrates that the maximum settlement without reinforcement is 288.31 mm. Figure 12 displays the maximum settlement with CSP reinforcement, measuring 26.91 mm. Consequently, we can infer that CSP effectively reduces maximum settlement by 261.40 mm or 90.64%. This concludes the CSP’s effectiveness in mitigating settlement in the surrounding soil around the pipeline. Moreover, we need to implement stability control measures for pipeline protection.

The largest settlement due to causeway embankment with pipe protection is 26.91 mm during Phase 14. The results of this settlement are compared with the design standards issued by the National Standardization Agency of Indonesia: Indonesian National Standard (SNI) 8460:2017 [43]. Referring to Table 33 of Standard SNI 8360:2017 [43], a settlement of 26.91 mm fits into risk category 2, indicating a small risk where deformations may occur but not significant structural damage. Thus, it can be concluded that, based on the magnitude of the settlement, the pipeline construction does not experience significant damage.

3.4. Corrugated Steel Plate (CSP) Capacity

Allowable stress capacity based on the quality of the corrugated steel plate can be calculated using the following equation:

$${\mathrm{\sigma }}_{all}=0.6\times F_y$$

(11)

$${\mathrm{\sigma }}_{all}=0.6\times 240 \mathrm{M}\mathrm{P}\mathrm{a}=144 \mathrm{M}\mathrm{P}\mathrm{a}$$

(12)

So, the allowable stress capacity of corrugated steel plate is 144 MPa or 144,000 kN/m².

The stress occurring on the corrugated steel plate based on the bending moment can be calculated using the following equation:

$${\mathrm{\sigma }}_N=\frac{M_{max}\mathrm{y}}{\mathrm{I}}$$

(13)

With a moment of inertia (I) equal to 0.000142 m⁴ and y = 0.1185 m, the stress value that occurs can be calculated and the results are displayed in

Table 8. Corrugated steel plate capacity.

Phase	Mmax (kNm)	σN (kN/m2)	σall (kN/m2)
1	2.062	1725.61	144,000
2	4.446	3720.70	144,000
3	5.545	4640.41	144,000
4	8.883	7433.87	144,000
5	16.62	13,908.69	144,000
6	21.84	18,277.12	144,000
7	23.23	19,440.36	144,000
8	21.43	17,934.00	144,000
9	34.32	28,721.19	144,000
10	38.06	31,851.06	144,000
11	41.91	35,072.99	144,000
12	44.19	36,981.04	144,000
13	42.42	35,499.79	144,000
14	2.062	1725.61	144,000

. Figure 13 shows the output of the bending moment that occurs during the construction of Phase 14.

According to the result in Table 8, it is obvious that the corrugated steel pipe’s (CSP) maximum stress remains below the allowable stress as a result of the loading during the filling. Therefore, it can be determined that the CSP is still capable of resisting the loading resulting from the embankment.

Table 9. Horizontal displacement result.

Phase	Horizontal Displacement Result (mm)
1	-
2	−10.29
3	−9.23
4	−11.77
5	−13.70
6	−14.62
7	17.07
8	18.63
9	19.87
10	29.74
11	34.06
12	38.49
13	41.37
14	37.01

displays the horizontal displacement on the corrugated steel plate. The results indicate that the embankment process has an impact on the direction of horizontal displacement. Figure 14 shows the output of the maximum lateral deformation in the corrugated steel plate. The results show that the construction stages lead to a change in the direction of lateral deformation, which follows the direction of embankment filling. Negative displacement values indicate a horizontal displacement toward the left. The largest displacement occurs in the right direction, exceeding 41.37 mm.

3.5. Concrete Footing Bearing Capacity

The result of the ultimate bearing capacity of the concrete footing slab is as follows:

$$q_u=c{N}_c+\left(Df\gamma \right)N_q+0.5\gamma B{N}_{\gamma }$$

(14)

$$q_u=\left(18.67\frac{\mathrm{k}\mathrm{N}}{{\mathrm{m}}^2}\times 14.6\right)+\left(1m\times 6.42\frac{\mathrm{k}\mathrm{N}}{{\mathrm{m}}^3}\right)5.45+0.5\times 6.42\frac{\mathrm{k}\mathrm{N}}{{\mathrm{m}}^3}\times 2m\times 2.14$$

(15)

$$q_u=321.52\mathrm{k}\mathrm{N}/{\mathrm{m}}^2$$

(16)

The ultimate bearing capacity (Q_u) of the concrete footing is obtained at 321.53 kN/m². The allowable bearing capacity is obtained by dividing the ultimate bearing capacity by a safety factor of 2.5. Thus, the allowable bearing capacity of the concrete footing slab (Q_all) is determined to be 128.61 kN/m². The stress values occurring on the concrete footing slab based on the Plaxis output are presented in

Table 10. Concrete footing slab result.

Phase	σN (kN/m2)	σall (kN/m2)
1	-	-
2	8.37	128.61
3	16.19	128.61
4	18.03	128.61
5	28.38	128.61
6	45.50	128.61
7	49.11	128.61
8	49.25	128.61
9	50.86	128.61
10	127.50	128.61
11	128.00	128.61
12	124.50	128.61
13	120.80	128.61
14	123.40	128.61

. Based on the results, it can be observed that the footing slab values are capable of withstanding the load applied to the footing. One of the stress outputs is shown in Figure 15.

4. Discussion

According to this research, the installation of a combination of corrugated steel plate (CSP), concrete footing slab, and bamboo reinforcement for temporary causeway purposes was highly effective. The settlements on the ground around the pipe are smaller when compared to those without the protection pipe. The implementation method’s safety factor is also safe, surpassing the plan’s safety factor. (1.5). However, when implementing the working methods, it is important to consider the influence of the water wave load on the piping reinforcement installation process. We need to conduct more detailed research on the impact of tide and wave load on the pipe protection installation process.

Some of the uncertainties in this planning include (1) the lack of consideration for the wave’s influence and field conditions and (2) the timing of the cause-way treatment, which could impact the performance of the reinforcements, including the bamboo reinforcement. In cases where construction involves not temporary but permanent embankments, further research is warranted. The design for long-term stabilization necessitates soil treatment of soft soil layers. Installation of prefabricated vertical drains (PVD) is required to expedite the consolidation process when embankments are constructed permanently. To ensure pipeline integrity and safety, field monitoring is also essential to oversee settlements occurring in areas adjacent to installed pipes.

5. Conclusions

The analysis concerns the construction design of a causeway on soft soil, considering the safety factors, displacements, and stresses that occurred. The analysis results show an average safety factor of 3.0, with construction Phase 10 exhibiting the lowest safety factor at 2.17. Soil settlement around the pipe is greater without the pipe protection. Without corrugated steel plate (CSP) pipe protection, the results show a maximum soil settlement of 288.31 mm. On the other hand, when pipe protection is installed, the maximum settlement is 26.91 mm. Installing CSP reduces the load from the embankment above the pipe as it bears the majority of the load instead of the underlying soil. Additionally, the presence of CSP results in a thinner embankment atop the soil, thus reducing its load. These observations conclude that CSP reinforcement effectively reduces soil settlement around the pipe by 90.64%.

We conduct capacity control of the pipe protection, namely corrugated steel plate (CSP), based on its lateral deformation capacity and allowable stresses. Furthermore, the installation of CSP in conjunction with a concrete footing slab must guarantee safety in terms of permissible bearing capacity. The results obtained indicate that control over the permissible stress of CSP is secure against the stresses incurred, as CSP withstands a maximum stress of 35,499.79 kN/m², which is smaller than the allowable stress of 144,000 kN/m².

Monitoring the lateral deformation that occurs is equally as important as controlling the allowable stress. Based on the model results, the maximum lateral deformation observed on the corrugated steel plate (CSP) is 41.37 mm. Furthermore, the maximum stress experienced on the concrete footing slab is 123.40 kN/m², which is lower than the allowable bearing capacity of 128.61 kN/m². This study concludes that the combination of pipe protection with corrugated steel plate (CSP), concrete footing slab, and bamboo reinforcement effectively protects the buried pipe from the surcharge load above it. However, more detailed planning concerning ground improvement is necessary for designs intended for longer-term usage to control the deformation that may occur when the embankment serves as a container yard.