An Investigation into the Influence of a New Building on the Response of a Sheet Pile Wall Adjacent to an Existing Buried Pipe

Abstract

This paper explores a solution to safeguard buried pipes located near constructions in the Al-Bisri region of Assiut Governorate by utilizing the concept of the characteristic damage state. This issue has escalated due to the increasing rate of construction activity near pipelines, resulting in a multitude of legal disputes. This study investigates the behavior of buried pipes when influenced by newly constructed buildings using the finite element method. The paper employs two-dimensional models of a 12-story reinforced concrete building with a raft foundation and a series of piles supporting the buried pipe. In this study, we used the PLAXIS software, a 2D plane strain program, to conduct numerical investigations. The soil was idealized using the Mohr–Coulomb model with a 15-node triangular element, while the piles and structures were idealized with a five-node isoperimetric beam element. The point of contact between the beam and the soil was represented by the interface element. Our research examined the distance between the pipe and the footing edge and the distance between the piles and the footing edge. The finite element model results provided nodal displacements and element straining actions for analysis. The results shed light on the behavior of the sheet pile wall and sewage pipe in various situations. The largest bending moment in the sewage pipe was seen in the absence of piling, in contrast, to pile support at Rx = 0.75. The bending moment in the pipe expanded and always occurred at the same location as Rx rose. The clay layer next to the pipe’s lateral deformation was significantly reduced after piling, with the greatest deformation occurring at Rx = 0.

1. Introduction

Incorporating an estimation of ground movement and conducting a stability check for buried pipes should be part of the architectural design [1]. Typically, both ground and building settlements can be estimated when predicting ground movement near the buried pipe sites. However, due to building loads, heavy structures experience additional settlement caused by their weight and a reduction in foundation soil stiffness. The lateral movement of the pipe also contributes to decreased soil stiffness [2]. To confirm this hypothesis, a buried pipe model test was conducted to examine the impact of altering the building’s foundation depth and pile distance from the pipe face. Buried pipes are typically subjected to three loading conditions, including axial force, shear force, and bending moment [3]. Previous studies have explored the topic at hand. For instance, Luo and Sun [4] and Ng [5] developed an elasticity-based approach to analyze stress and strain under biaxial loading conditions. Their solution was limited to axially symmetric loading with or without end effects, and this was applicable to internal pressure, external pressure, axial load, and axial torsion. The solution assumed that there was no shear stress at the edge, that normal stresses were continuous through the layers, and that the cylinder was infinitely long. Mazek et al. [6] investigated the behavior of an existing sewage tunnel during the construction of the Greater Metro Line 2 (Shubra El-kheima-Mobarak) and Al-Azhar Road tunnels, which were installed using a tunneling boring machine (TBM). Pagano [7] and Orynyak and Radchenko [8] also developed an elasticity-based solution for the displacement analysis of an infinitely long tube under an applied axial bending moment. However, their analysis was restricted to a single material layer. Several relevant studies have been conducted by researchers at the University of Assiut in Egypt.

Abd El-Naiem et al. [9] and Liu et al. [10] conducted a study focusing on the excavated tunnel diameter (D2), soil thickness between tunnels (H), and horizontal distance (X). Georgiadis and Anagnostopoulos [11] and Balakumar et al. [12] then built upon this research by examining the critical aspects of a five-story reinforced concrete building with a raft foundation using two-dimensional (2D) models. Specifically, the building was constructed adjacent to a medium sand excavation, with sheet pile walls supporting the excavation, as seen in the studies by Madhumathi and Ilamparuthi [13] and Poulos and Chen [14].

In this study, a row of piles was utilized as a means of safeguarding the buried pipe. Piles are an attractive option for providing lateral support near existing structures due to their high stiffness, ease of installation, and cost-effectiveness. During excavation work near the Rehab Towers in the Al-Bisri area of Assiut, a buried pipe measuring 1200 mm in diameter and located 4 m below ground level was discovered just 2 m from the edge of the foundation. This foundation was approximately 40 m away from the pipe, as depicted in Figure 1, which shows a satellite image of the Al-Bisri area near Assiut University.

In order to prevent significant risks such as explosions or fires, protective measures need to be taken for the buried pipe [15]. A boring procedure at a depth of 16 m was conducted, and the soil classification was identified as medium clay. To safeguard the pipe, it was suggested that piles could be installed at a distance of 0.5 m from the 12 m depth edge of the raft foundation, with a diameter of 40 cm and 40 cm distance between the piles. Figure 2 displays the sand coating pipe, while Figure 3 illustrates the driven piles situated adjacent to the sewage pipe. This study aimed to achieve three main objectives: (1) investigate the impact of a new building on the sewage pipe’s behavior, (2) assess the changes in normal force, shearing force, and bending moment on the current sewage pipeline, and (3) determine the effect of the new building’s position in relation to the buried pipe.

2. Numerical Simulation and Parameter Selection

In this study, the PLAXIS computer program (Version 7.2) was employed to create a finite element model. This model took into account the impact of both the vertical overburden pressure and lateral earth pressure, utilizing the Dead Loads solution method [16,17,18,19]. This program also incorporated the nonlinear properties of soil and the linear properties of the tunnel lining. The layout of the new and existing tunnels is illustrated in Figure 1, with the model using an elasticity solution for the axial-symmetric loading of a pressurized pipe and an approximate nonlinear solution for the transverse loading caused by soil pressure on a buried sewage pipe. Figure 4 shows the finite element model used for the pipeline adjacent soil and rigid strip footing, while Figure 5 displays the model’s dimensions, which include a buried pipe, a strip footing similar to the building, and a pile. The 2D model dimensions were determined to remove any size effect when predicting the buried pipe’s performance. To simulate the soil, pipe, and pile, finite elements were utilized. The PLAXIS program was used to create a finite element model of the soil–pipe interaction [20,21], incorporating solution methods to account for vertical overburden pressure, lateral earth pressure, the nonlinear properties of the soil, and the linear properties of the pipeline.

2.1. Testing Procedure and Setup for the Model

Figure 5 displays the model of a buried pipe next to a building. The dimensions of the model are illustrated in Figure 5, with the pipeline diameter (D) as 1.2 m, the soil layer depth as 20 m, the soil layer width as 50 m, the pile depth (d) as 12 m, the strip footing width as 25 m, the foundation depth (D_f) as 3 m, and the spacing between the pipe and footing edge and the pile and footing edge as X m and x m, respectively.

2.2. The Soil Material Model

The analysis assumed the soil to be a medium clay deposit, which was modeled as a perfectly elastic-plastic Mohr–Coulomb model utilizing a 15-node element. The properties and shear strength parameters employed for the medium clay are listed in

Table 1. The properties of the medium clay.

Parameter	Name	Value	Unit
Soil dry unit weight	γd	18	kN/m3
Young’s modulus	E	30,000	kN/m2
Poisson’s ratio	υ	0.33	---
Cohesion	c	36	kN/m2
Friction angle	φ	0	degree
Dilatancy angle	ψ	0	degree
Interface reduction factor	R	1	--

.

2.3. Pile

To simulate the piles, a beam element was utilized, with the pile parameters listed in

Table 2. The material properties of the pile.

Parameter	Name	Value	Unit
Normal stiffness	EA	5 × 106	kN/m
Flexural rigidity	EI	2 × 104	kN/m2/m
Equivalent thickness	d	0.208	m
Weight	w	1.2	kN/m2
Poisson’s ratio	υ	0.3	--

. Interfaces were employed to replicate the interaction between the pile and the soil on either side [22], and they allowed for the specification of lower pile friction compared to the soil friction. The material model used was linear elastic.

2.4. Strip Footing

Simulating strip footing was possible using a beam element [23,24,25] that possessed both bending stiffness (EI) and axial stiffness (EA). The material model for this element was linear elastic, and its characteristics were dependent on specific parameters. These parameters included the modulus of elasticity for concrete (E), the cross-sectional area (A), the moment of inertia (I), and the characteristic strength (Fcu) of 25 N/mm². Additionally, the footing was subjected to a distributed load of 100 kN/m², which was transmitted to the soil.

Table 3. The properties of strip footing.

Parameter	Name	Value	Unit
Axial stiffness	EA	3 × 107	kN/m
Flexural rigidity	EI	3.175 × 106	kN/m2/m
Equivalent thickness	d	1.00	m
Weight	w	25.00	kN/m2
Poisson’s ratio	υ	0.2	--

presents the material properties associated with the strip footing.

2.5. Material Model of Steel Buried Pipe

Several numerical analyses were conducted on steel pipes with a 1200 mm diameter buried in medium clay. To ensure the consistency of the results, some cases involved four test repetitions. The scope of the soil area surrounding the pipe examined in this study had minimal effects on the forces and loads of the adjacent building. However, it significantly influenced the sewer pipe. Throughout the analyses, the soil was identified as the governing failure mechanism, and the steel pipe’s response remained elastic [26,27,28]. In this analysis, the pipeline’s diameter was 1200 mm, and a linear elastic model was used. The properties of the pipeline are provided in

Table 4. Properties used for pipeline.

Parameter	Name	Value	Unit
Soil dry unit weight	γd	25	kN/m3
Young’s modulus	E	3 × 109	kN/m2
Poisson’s ratio	υ	0.18	--

.

2.6. Analytical Methodology

To produce reliable predictions of the sewage pipe and the adjacent building’s stability and deformations, PLAXIS employed a clay idealization approach. This model characterized the system’s behaviors and material properties. For the perfect elastic-plastic finite element analysis, iterative steps were necessary. The analysis mainly focused on the deep excavation and adjacent buildings, with specific parameters considered, such as the distances between the pipe and footing edge (X) and the pile and footing edge (x). These variables are described further in the subsequent section.

Table 5. Cases computed in PLAXIS.

Case No.	1	2	3	4
$Rx=\frac{x}{X}$	0.00	0.25	0.50	0.75

presents the five cases computed using PLAXIS, which are discussed in detail in the following section.

3. Results

3.1. Bending Moment Experienced by Buried Pipe

Figure 6a–d demonstrates the bending moment’s correlation with various parameters investigated in this study. The predicted outcomes were compared to the baseline values obtained when no piling was present near the building. The bending moment in the sewage pipe near the building varied at different Rx values (0.25, 0.5, and 0.75), with a shift from negative to positive values and vice versa. The sewage pipe experienced its maximum bending moment in the absence of piling, with a peak moment of 16.8 kN.m. The highest bending moment occurred after pile support at Rx = 0.75. Moreover, the bending moment in the sewage pipe increased as Rx increased. Notably, all these cases indicated that the maximum bending moment occurred at the same location.

3.2. Pipe Shearing Forces under Burial

Figure 7a–d presents the relationship between the shearing forces and the various parameters examined in this study. The estimated outcomes were compared to the baseline values obtained in the absence of piling near the building. The variation in the sewage pipe’s bending moment near the building at different R_x values (0.25, 0.5, and 0.75) indicates a transition from negative to positive values and vice versa. The highest bending moment in the sewage pipe occurred without piling, with a peak moment of 16.8 kN·m/m. The maximum bending moment in the sewage pipe occurred after pile support at Rx = 0.75. Furthermore, the sewage pipe’s bending moment increased as Rx increased. Notably, all cases indicated that the maximum bending moment occurred at the same location.

3.3. Horizontal Displacements of Clay

Figure 8 displays the variation in the lateral deformation of the clay layer. The maximum lateral deformation was observed before piling at Rx = 0. After piling, the lateral deformation at Rx was significantly lower than at Rx = 0. The lateral deformation of the clay layer near the pipe decreased as Rx increased after piling.

3.4. An Analysis of the Normal Force, Shear Force, and Bending Moment Experienced by the Pile under Loading

Figure 9 shows the changes in the axial force in the pile near the building for Rx values of 0.25, 0.5, and 0.75. The highest axial force in the sheet pile wall occurred at Rx = 0.25. As Rx increased, the axial force in the pile decreased. The maximum axial force was at the same location in all cases. In Figure 10, the variation in shear force for the pile near the building was depicted for Rx values of 0.25, 0.5, and 0.75. To summarize, the maximum shear force in the sheet pile wall was observed at Rx = 0.25, which decreased as Rx increased for all cases showing a maximum shear force at the same position. Figure 11 illustrates the impact of the bending moment in the pile near the building at Rx values of 0.25, 0.5, and 0.75, with Rx = 0.25, showing the maximum bending moment in the sheet pile wall. The bending moment in the pile decreased as Rx increased, and the maximum bending moment occurred at the same location in all cases.

Table 6. The extreme values of axial force, shear force, and bending moment in piles.

Rx	0.25	0.5	0.75
Normal force, kN	2.16	3.02	3.61
Shear force, kN	234.89 × 10–3	253.26 × 10–3	268.39 × 10–3
Bending moment, kN·m	70.60 × 10–3	112.65 × 10–3	120.84 × 10–3

presents the extreme values of the axial force, shear force, and bending moment in piles.

4. Discussion

The results presented in this discussion provide valuable information on the behavior of a sewage pipe and sheet pile wall system under varying conditions.

Figure 6 shows that the bending moment in the sewage pipe near the building changed from negative to positive values as the Rx value increased, and the maximum bending moment was observed in the absence of piling. However, after pile support at Rx = 0.75, the maximum bending moment in the sewage pipe was observed. This indicated that the addition of piles could provide support and reduce the bending moment experienced by the pipe. Additionally, it was shown how the bending moment correlated with several variables our study looked at. The outcomes that were expected were compared to the baseline values achieved when there was no piling close to the structure. With a transition from negative to positive values and vice versa, the bending moment in the nearby sewage pipe varied at different Rx values (0.25, 0.5, and 0.75). With a peak moment of 16.8 kN·m/m when there were no pilings, the sewage pipe experienced its greatest bending moment. After pile support, at Rx = 0.75, the maximum bending moment occurred. Additionally, as Rx rose, the sewage pipe’s bending moment grew. Notably, it appeared from all of the situations that the highest bending moment happened in the same spot [29].

Figure 7 displays the relationship between the shearing forces and the different scenarios considered. The results show the bending moment of the sewage pipe near the building ranges between negative and positive values at different Rx values, with the largest bending moment occurring in the absence of piling. However, after pile support at Rx = 0.75, the maximum bending moment in the sewage pipe was observed, and this bending moment increased as Rx increased. These findings indicate that pile support can reduce the bending moment experienced by the sewage pipe. The relationship between the shearing forces and various factors looked at in this study is shown in Figure 7a–d. the estimated results can be compared to baseline values when obtained in the absence of piling close to the building. When Rx was between 0.25 and 0.75, the bending moment of the sewage pipe changed, indicating a change from negative to positive values and vice versa. Without piling, the sewage pipe had its largest bending moment, with a peak moment of 16.8 kN·m/m. After pile support, at Rx = 0.75, the sewage pipe experienced its greatest bending moment. Additionally, as Rx rose, the bending moment of the sewer pipe also rose. Notably, all instances show that the greatest bending moment occurred in the same spot [30].

Figure 8 shows that without piling, the greatest lateral deformation occurred at Rx = 0. However, after piling, the lateral deformation at Rx was significantly smaller than at Rx = 0. This suggests that the addition of piles could provide lateral support and reduce the lateral deformation experienced by the system. The variance in the clay layer’s lateral deformation is shown in Figure 8. Prior to piling, at Rx = 0, the maximum lateral deformation was seen. Following piling, the lateral deformation at Rx was considerably less than it had been at Rx = 0. As Rx increased after piling, the lateral deformation of the clay layer close to the pipe decreased [31].

Figure 9 shows that the maximum axial force in a sheet pile wall was constant across all scenarios, and the axial force in the pile diminished as Rx increased. This indicates that the addition of more piles could reduce the axial force experienced by the system. In the pile close to the building, Figure 9 depicts the changes in the axial force for Rx values of 0.25, 0.5, and 0.75. At Rx = 0.25, a sheet pile wall experienced its greatest axial force. The axial force in the pile diminished as Rx rose. In every instance, the location of the maximum axial force was the same.

Figure 10 displays that the maximum shear force in a sheet pile wall could be observed at Rx = 0.25 and the shear force in the pile decreased as Rx increased, with all cases displaying the maximum shear force at the same location. This suggested that the shear force in the system was highest when the pile did not provide support and reduced as the number of piles increased. For Rx values of 0.25, 0.5, and 0.75, Figure 10 shows the variation in the shear force for the pile near the building. For a summary, it may be said that the highest shear force in a sheet pile wall was detected at Rx = 0.25 and that it declined as Rx rose, with the maximum shear force being present in every instance at the same location [32].

Lastly, Figure 11 shows that the bending moment in the pile decreased as Rx increased, and the location of the maximum bending moment remained the same across all cases. This indicates that the addition of more piles could reduce the bending moment experienced by the system. Rx = 0.25 depicts the maximum bending moment in a sheet pile wall, and Figure 11 shows the effects of bending moments at Rx values of 0.25, 0.5, and 0.75 on the pile next to the building. As Rx rose, the bending moment in the pile decreased, with the maximum bending moment occurring consistently in the same spot. The extreme axial, shear, and bending moment values in piles are shown in Table 6.

Overall, these findings provide valuable insights into the behavior of a sewage pipe and sheet pile wall system and could inform the design and construction of similar systems in the future.

5. Conclusions

This study aimed to investigate the behavior of an existing sewage pipe in response to the construction of a nearby building and, in order to prevent damage to the pipe, piling was installed. The key parameters were analyzed and compared with the baseline values obtained without piling. The results presented in Figure 6, Figure 7, Figure 8, Figure 9, Figure 10 and Figure 11 offer valuable insights into the behavior of the sewage pipe and sheet pile wall under various conditions. The maximum bending moment in the sewage pipe was observed without piling, whereas pile support at Rx = 0.75 resulted in the maximum bending moment. The bending moment in the pipe increased as Rx increased and always occurred at the same location. The lateral deformation of the clay layer close to the pipe was significantly reduced following piling, with the largest deformation occurring at Rx = 0. The axial force in the sheet pile wall decreased as Rx increased, and the maximum shear force was observed at Rx = 0.25. Moreover, the bending moment in the pile decreased with an increase in Rx, and the location of the maximum bending moment remained consistent across all cases.

Based on these findings, the following conclusions were drawn: (1) The maximum shear forces and bending moments in the sewage pipe occurred without piling and decreased when the piles were installed. (2) The maximum lateral deformations for the clay layer near the pipe were observed without piling when the building was near the pipe at Rx = 0. As the piles were installed, deformations decreased with increasing Rx. (3) The maximum lateral deformations for the piles near the pipe occurred at Rx = 0.25 and decreased as Rx increased. (4) The pipe stresses were at their minimum when Rx = 0.25, which was deemed the optimal solution for piling constructions on the job site. (5) Constructing a new building near an existing pipe can result in internal forces in the sewage pipe when shifting from positive to negative values and vice versa, posing a risk.