The outdoor rainwater drainage pollution in a large general hospital poses considerable threats to the environment and our health. A systematic analysis method was summarized in the investigation practice. Results showed that the pipe network damage caused by uneven geological settlement was the main reason for the pollution of the rainwater pipe network in the hospital. Countermeasures such as settlement repair and geological foundation reinforcement, rainwater and sewage pipeline transformation, the repair of mixed connection of rainwater and sewage pipes and polluted water sources, drainage health safety in isolated areas, and emergency storage tanks were discussed. After implementing the measures, the NH3-N measured value was within 0.82 mg/L, and the average removal rate was 97.4%. The chemical oxygen demand (COD) concentration also decreased significantly with an average of 12 mg/L and the average removal rate was 91.8%. The results show that the reconstruction can effectively deal with the problem of outdoor rainwater drainage pollution in the hospital. The study has specific engineering reference significance for medical building drainage system's health and safety research.

  • Uneven geological settlement was the main reason for the pollution of the rainwater pipe network in the hospital.

  • The stress of the pipe increased with the increase in the relative settlement of the pipe.

  • There are some countermeasures such as settlement repair and geological foundation reinforcement, rainwater and sewage pipeline transformation, drainage health safety in isolated areas, and emergency storage tank.

The sanitary safety of the outdoor rainwater drainage system in a hospital has always been an essential aspect of controlling the spread of viruses (Hong et al. 2023). When a hospital's rainwater drainage system is imperfect, viruses, pathogenic bacteria, and other pathogens will be transmitted through water bodies, causing severe public health safety hazards (Zhang & Wang 2020; You et al. 2023). While focusing on the sewage drainage system in a hospital, it is crucial to ensure the sanitary safety of the rainwater drainage system (Fontanella et al. 2021; Niu et al. 2023).

Relevant standards include Outdoor Drainage Design Standards (GB 50014-2006), Building Design Code for Infectious Disease Hospitals (GB 50849-2014), Environmental Quality Standards for Surface Water (GB 3838-2002), Emission Standards for Water Pollutants in Medical Institutions (GB 18466-2005), Comprehensive Hospital Building Design Code (GB 51039-2014), Building Water Supply and Drainage Design Standard (GB 50015-2019), and Infectious Disease Hospital Building Construction and Acceptance Code (GB 50686-2011).

Hospital overview

The hospital is a comprehensive hospital with an infectious disease area, which is located in the south of Zhejiang Province, covering a total area of 350,000 m2, 3,380 approved beds, 5,162,300 outpatient and emergency visits per year, 196,500 discharges, and an annual water consumption of nearly 1 million tons, with a treatment capacity of 2,850 m3/d at the sewage treatment station. The hospital has also built new functional buildings such as negative pressure isolation wards, square cabin wards, and nucleic acid testing sites, and many changes have been made to the structure of the pipe network of the drainage system.

Drainage system overview

The drainage system in the hospital adopts a rainwater and sewage separation system (Wang et al. 2021), and the distribution of its pipe network is shown in Figure 1. Building sewage is treated by a septic tank, incorporated into the sewage pipe of the hospital area, and finally discharged into the sewage treatment station of the hospital. Building rainwater is released into the rainwater open ditch around it and finally into the surrounding river. The local ground floor sewage and waste water pipes of the specialized center and medical technology center are connected to the sewage lifting well in the basement and pumped to the hospital district sewage pipeline (Auddy et al. 2022). The radioactive wastewater from the Nuclear Medicine Center, which is below medium strength, is discharged into the hospital's main sewage pipe after a set of treatments in decay ponds. The wastewater cleaned by the radiology center is treated through the recovery and neutralization pond and then incorporated into the hospital area sewage pipe. The roof of the medical technology center adopts a pressure flow siphon roof rainwater drainage system and a local gravity flow rainwater drainage system. The basement fire elevator bottom pit, car ramp, inner patio, and bathroom are separately equipped with water collection wells and submerged sewage pumps and are discharged according to the water level self-control and finally incorporated into the drainage system of the hospital area.
Figure 1

Distribution map of rainwater and sewage separation pipe networks in a hospital: (a) distribution of the rainwater pipe network and (b) distribution of the sewage pipe network.

Figure 1

Distribution map of rainwater and sewage separation pipe networks in a hospital: (a) distribution of the rainwater pipe network and (b) distribution of the sewage pipe network.

Close modal

Problem analysis

The hospital is in the centralized living drinking water surface water source secondary protection zone. The hospital rainwater collection through the outdoor rainwater pipe discharges into the surrounding river. The rainwater quality is required to meet the water quality criterion of Class III indicated in the Environmental Quality Standard for Surface Water (GB 3838-2002). Rainwater quality testing (Suleman et al. 2023) is a vital judgment basis for analyzing and judging whether the operation of the rainwater drainage system is standard. Due to the enormous rainwater pipe network, this project requires more times of water quality testing. After careful consideration of efficiency and economy, the ammonia nitrogen and chemical oxygen demand is an essential comprehensive index to evaluate the pollution degree of rainwater drainage (Wei et al. 2019; Wang et al. 2022). In this paper, the determination of ammonia nitrogen was performed by the nascent reagent spectrophotometric method (HJ 535-2009), and the resolution of chemical oxygen demand was performed by the dichromate method (HJ 828-2017). The hospital rainwater pipe network drains on the non-rainy day. The test results of the outlet water quality on the non-rainy day are shown in Table 1. The locations of test sections Q1, Q2, and Q3 are shown in Figure 1. Testing data show that the hospital discharge of rainwater quality in ammonia nitrogen and chemical oxygen demand is seriously exceeded. The rainwater pipe has been polluted. Medical sewage is discharged into the river through the rainwater pipe. There is the risk of environmental pollution, chemical substances, and pathogens (Ma & Xiong 2022). Analysis of the causes of pollution of rainwater discharge and exploring the corresponding countermeasures have important research significance.

Table 1

Water quality test data of the rainwater pipe network

Water quality testing sectionNH3-N (mg/L)
COD (mg/L)
Detection valueStandard valueResultsDetection valueStandard valueResults
Q1 32.6 1.0 Exceeding the standard 193 20 Exceeding the standard 
Q2 52.1 1.0 Exceeding the standard 774 20 Exceeding the standard 
Q3 22.8 1.0 Exceeding the standard 131 20 Exceeding the standard 
Water quality testing sectionNH3-N (mg/L)
COD (mg/L)
Detection valueStandard valueResultsDetection valueStandard valueResults
Q1 32.6 1.0 Exceeding the standard 193 20 Exceeding the standard 
Q2 52.1 1.0 Exceeding the standard 774 20 Exceeding the standard 
Q3 22.8 1.0 Exceeding the standard 131 20 Exceeding the standard 

The data for water quality analysis were obtained from field sampling and testing. Statistical analysis was carried out using SPSS25 software to derive the data from the samples (Suleman et al. 2023). The test of normality distribution was carried out to obtain the level of significance under Kolmogorov–Smirnov and Shapiro–Wilk tests. The test of normality was carried out by the statistical test method. When the result of the Kolmogorov–Smirnov test and the Shapiro–Wilk test had a p-value less than 0.05, the data were considered not to satisfy normality. On the contrary, the data are considered to satisfy normality. However, the above tests have some limitations. Therefore, the normality of the data is determined by histogram. In the histogram, the data show a bell-shaped distribution and high in the center, and gradually decrease at both ends. The left and right sides show symmetry or near symmetry.

Skewness characterizes the degree of asymmetry of the density function curve of a probability distribution with respect to the mean. If the skewness of a normal distribution is 0, then both tail lengths are symmetrical (Raimondi et al. 2023). If the skewness is negative, then there is less data to the left of the mean than to the right. This is visualized by the fact that the tails on the left are longer relative to the tails on the right. The left tail of the curve is dragged out because of the small values of a few variables. The left tail is longer than the right. The majority of values, including the median, lie to the right of the mean. Values to the left of the mean are few and small. A positive skewness means that fewer data lie to the right of the mean than to the left. This is visualized by the fact that the tails on the right are longer relative to the tails on the left. The right tail of the curve is dragged out because of the large values of a few variables. The right tail is longer than the left, and the majority of values lie to the left of the mean.

Cause analysis

Analysis method

In order to analyze the causes of outdoor rainwater drainage pollution in the hospital, the project summarized a systematic analysis method in the survey practice (Yin et al. 2016; Hong et al. 2023). The specific research route is shown in Figure 2. The project uses the pipe network segment-by-segment screening method to analyze the causes of drainage system pollution. The process can effectively reduce the scope of pipeline screening. It has the advantages of high efficiency and accuracy of the survey.
Figure 2

Systematic research route of pipe network problems.

Figure 2

Systematic research route of pipe network problems.

Close modal
The result of the causes analysis of rainwater drainage pollution is shown in Figure 3, which shows that the broken rainwater and sewage pipe network is the main cause of rainwater drainage pollution. Through the field study of the pipe network, it is found that there is a link between the breakage of the rainwater and the sewage pipe network and the settlement of the pipe network (Apandi et al. 2023). Therefore, further analysis of the settlement mechanism of hospital geology is needed to study the effect of uneven settlement on causing the rainwater pipes to be polluted.
Figure 3

Influencing factors of rainwater and sewage pipe network problems.

Figure 3

Influencing factors of rainwater and sewage pipe network problems.

Close modal

Mechanism of geological settlement

As the hospital foundation is located in a softer wetland slab, the thickness of the soil layer in the horizontal direction varies relatively large, with undulating geotechnical interfaces. The layers of soil in the vertical order have different mechanical strengths and physical properties, resulting in poor soil uniformity of the hospital's geological foundation. The compression coefficient of silt layer soil in the hospital area is high. The consolidation time is long, and the problem of uneven geological settlement is easy to occur after consolidation (Santos et al. 2023). Meanwhile, the silt layer gradually settles under the pressure of the surface backfill, which aggravates the sinking of the surface soil and causes the pipes and pipe wells wrapped in the surface backfill to sink together with the backfill. However, due to the reinforced foundation of the building, the amount of settlement occurs less compared to the outdoor soil layer, resulting in the deformation of the pipeline at the intersection of the building body and the outside increasing, which eventually leads to the failure of the pipeline there as seen in Figure 4. Figure 4(a) shows the normal state of the pipeline. Figure 4(b) shows the deformation of the outdoor pipeline after the settlement of the outdoor soil layer intensifies, while the indoor pipeline relatively maintains the state before deformation. Figure 4(c) shows the pipeline failure state at the pipeline intersection along the side of the building body after the deformation increases.
Figure 4

Change law of pipeline settlement state. (a) Normal condition of the pipeline, (b) deformation state of pipeline settlement and (c) failure status of pipeline settlement.

Figure 4

Change law of pipeline settlement state. (a) Normal condition of the pipeline, (b) deformation state of pipeline settlement and (c) failure status of pipeline settlement.

Close modal

Analysis of the influence of geological settlement on the pipeline

It is known from the settlement mechanism that buried pipelines are prone to fracture due to uneven settlement at their indoor–outdoor junctions. For the study of pipe mechanics analysis (Winter et al. 2023), Teodoru (2009) calculated and analyzed the force deformation of buried pipes by analyzing elastic beams placed in a semi-infinite space elastic foundation. Limura (2004) proposed an equation for calculating the deflection of buried pipes based on the Winkler elastic foundation beam model under the effect of settlement to analyze the pipe forces. However, in practical engineering, the relative settlement is a dynamically changing quantity (Auddy et al. 2022). The buried pipelines often fail due to progressive damage during settlement occurrence.

In this paper, we establish a simplified stress model of the pipeline based on the settlement mechanism and analyze the influence relationship between the stress of the pipeline and the amount of settlement. The axial stress generated by the deformation of the pipeline under the influence of settlement is:
(1)

where M is the bending moment acting on the cross-section, N·m; WZ is the bending section coefficient of the pipe, m3; E is the modulus of elasticity of the pipe, GPa; y is the deflection of the pipe, m; and l is two times the horizontal distance between two adjacent extreme points, m.

The pipeline failure criterion (Yang et al. 2018) is the basis for judging whether the pipeline fails under the force. In this paper, based on the standard of elastic failure, the mechanical analysis of the pipeline under the influence of subsidence is calibrated by the fourth strength theory (Mises criterion):
(2)

where σr is the pipe equivalent stress, MPa; σa is the pipe axial stress, MPa; σb is the pipe circumferential stress, MPa; σc is the pipe radial stress, MPa; and σ is the allowable stress of the pipe, MPa.

The relationship between the Mises stress of the pipe and the relative settlement is obtained through mechanical analysis, as shown in Figure 5. It can be seen that the stress of the pipe increases with the increase in the relative settlement of the pipe. As the settlement problem intensifies, the pipeline is bent and deformed by the force, and the elliptical state gradually appears (Zha 2019). The more considerable pipeline stresses are concentrated on the side, eventually leading to the broken pipeline's failure.
Figure 5

The relationship between Mises stress and relative settlement of pipeline.

Figure 5

The relationship between Mises stress and relative settlement of pipeline.

Close modal

Analysis of the impact of geological settlement on the tube well

Uneven settlement of the geology impacts the pipeline but also causes uneven settlement of the pipe well, which in turn leads to confusion in the elevation of the pipe well, as seen in Figure 6. Figure 6(a) shows the elevation of the rainwater pipe well affected by the settlement. Figure 6(b) shows the elevation of the sewage pipe well affected by the settlement (Raimondi et al. 2023). As shown in Figure 6, the elevations of the ground, rainwater pipe wells and sewage pipe wells are affected by geological settlement to different degrees, which leads to disordered results. The pipe wells fail to meet the requirement indicated in the Outdoor Drainage Design Standards (GB 50014-2006) that the base and body of the pipe wells on main roads should avoid uneven geological settlement. Most of the drainage methods of pipe networks use gravity drainage, and the elevation of pipe wells is calculated after strict trends in design. Confusion in the elevation of pipe wells will cause poor drainage of pipe wells and water accumulation in wells all year round, which aggravates problems such as leakage of rainwater and sewage diversion pipe networks (Zhou et al. 2017).
Figure 6

Variation diagram of tube well elevation affected by settlement. (a) Rainwater pipe wells affected by settlement and (b) sewage wells subject to settlement.

Figure 6

Variation diagram of tube well elevation affected by settlement. (a) Rainwater pipe wells affected by settlement and (b) sewage wells subject to settlement.

Close modal

Settlement repair and geological foundation reinforcement

According to the analysis of the settlement mechanism, the hospital has a severe problem of geological uneven settlement, as seen in Figure 7. Figure 7(a) shows the settlement at the junction of the indoor and outdoor areas of the building, from which it can be seen that the building body has been reinforced by the foundation to make the settlement relatively less outdoor, forming an obvious height difference between the indoor and outdoor areas of the building. Figure 7(b) shows the settlement at the outdoor buried pavement. The concrete structure of the pavement resists certain settlements due to its structural support, but the soil layer underneath is subjected to severe settlement, and eventually, the hollowing phenomenon occurs (Raimondi et al. 2023).
Figure 7

Sites of geological settlement. (a) Settlement at the intersection of the interior and exterior of the building and (b) settlement at outdoor buried paving.

Figure 7

Sites of geological settlement. (a) Settlement at the intersection of the interior and exterior of the building and (b) settlement at outdoor buried paving.

Close modal
The problem of pipeline failure caused by uneven ground settlement mainly occurs at the intersection of indoor and outdoor pipelines in and out of the building, as seen in Figure 8. Pipes without joints at the intersection appear as shown in Figure 8(a) with force breakage, and pipes with joints appear as shown in Figure 8(b) with joint disconnections. Settlement at the buried laying of outdoor pipes can also confuse the elevation of pipe wells, water accumulation in the wells, and breakage and leakage.
Figure 8

Sites of pipelines damaged by settlement. (a) Pipe broken by settling force and (b) pipe joint disconnected by settling force.

Figure 8

Sites of pipelines damaged by settlement. (a) Pipe broken by settling force and (b) pipe joint disconnected by settling force.

Close modal

In this paper, the repair of geologically significant settlement areas is achieved using reinforcement treatment with the replacement of geological foundations. According to the current national standard ‘Design Code for Building Foundation’ (GB 50007-2011), a composite foundation of medium-coarse sand, sand and gravel, and gravel soil is used for the pipe network area with plastic material pipes. A blended foundation of C20 concrete, sand and gravel, and gravel soil is used for the pipe network area with metal pipes. In addition, for the area where no obvious geological settlement occurs but does not meet the requirements of the characteristic value of foundation bearing capacity (Ye & Zhong 2019), its geological foundation is also reinforced accordingly to avoid pipe breakage and pipe well settlement caused by the aggravation of geological settlement at a later stage. At the same time, the degree of geological settlement is evaluated through regular elevation measurements of the buried pipeline laying area to prevent damage to the pipeline network caused by uneven geological settlement in many aspects.

Rainwater and sewage pipeline transformation

The pipeline interface should be determined according to the pipeline material and geological conditions and should conform to the relevant provisions of the current national standard ‘Seismic Design Code for Outdoor Water Supply and Drainage and Gas Heat Engineering’ (GB 50032-2003). The drainage pipe is made of polyethylene (PE) solid wall pipe with high resistance to deformation, and the drainage pipe is prevented from breaking and leaking by using hot fusion and electric fusion connection. For flexible connections to avoid the leakage of plastic pipes, such as the connection of socket-type elastic seal, the interface sealing needs to be focused on. The current national code is still mainly based on the traditional gravity drainage system, the vacuum drainage system can reduce outdoor drainage lines and has advantages in reducing outdoor pipe breakage and leakage (Hong et al. 2023).

The connection of inspection wells and plastic pipes should comply with the relevant provisions of the current national standard ‘Seismic Design Code for Outdoor Water Supply and Drainage and Gas Heat Engineering’ (GB 50032-2003). The connection between the drainage pipe and the inspection well is prone to rupture, which is repaired by strengthening the sealing to prevent leakage at the rupture. Plastic-finished inspection wells have the advantage of good sealing and are used in the inspection wells of outdoor drainage pipes, which can effectively prevent the risk of leakage caused by broken pipe wells. The elevation of the similar rainwater pipe network should be higher than the sewage pipe network and set the isolation layer at essential locations to prevent pollution of the rainwater pipe when the sewage pipe leaks.

According to the relevant provisions of the current national standard ‘Outdoor Drainage Design Standard’ (GB 50014-2006), the construction method of the pipeline should be based on the nature of the soil in which the pipeline is located, burial depth, pipe diameter, groundwater level, nearby underground and above-ground buildings, and other factors, by technical and economic comparison, to determine whether to use trenching, pipe jacking, or shield construction (Liu et al. 2015; Auddy et al. 2022). In areas with serious settlement, a section of interface is reserved for docking with the upper pipeline in the building body under the outlet pipe. The gap at the connection is sealed using rubber seals and waterproof sealing paste. The docking length is required to be greater than the predicted settlement in the target area, as seen in Figure 9.
Figure 9

Anti-settlement fracture pipes along the interior and exterior of buildings.

Figure 9

Anti-settlement fracture pipes along the interior and exterior of buildings.

Close modal

Repair of mixed connection of rainwater and sewage pipes and polluted water sources

In addition to solving the damage of pipes and tube wells caused by uneven geological settlement, the project also rehabilitated and repaired the problems of mixed rainwater and sewage pipes and polluted water sources in the pipe network. Through the water test of water collection well pumps and sewage pipes, the mixed rainwater and sewage pipes were identified, and the mixed pipes were repaired according to the requirements of rainwater and sewage diversion. The water quality in the drainage pipes of condensate, equipment water, fire water, and rainwater catchment wells was tested, and the pipeline was repaired for polluted water sources to prevent polluted water sources from entering the rainwater pipes (Wilkinson et al. 2016; Winter et al. 2023).

Drainage health safety in isolated areas

For the hospital's new negative pressure isolation wards, square cabin wards, nucleic acid testing sites, and other functional buildings, the prevention of cross-infection needs to be considered. Its outdoor rainwater will increase the risk of virus transmission once it is affected by sewage. Therefore, the health and safety requirements of rainwater drainage are higher than those of other conventional buildings in the hospital. Its drainage pipes need to be set up separately. They are required to prevent leaking sewage and polluted rainwater from being discharged directly into the river or seeping down into the groundwater system. High density polyethylene (HDPE) impermeable membranes are used to pave the ground in areas such as negative pressure isolation wards (Qin et al. 2020; Peng et al. 2021), and rainwater runoff is collected uniformly with a rainwater runoff coefficient of ψ = 1.0. When negative pressure isolation wards are not in operation, the initial rainwater is discharged to the sewage pipeline, and other rainwater is released to the rainwater pipeline. When negative pressure isolation wards operate, the collected rainwater runoff is disinfected with 10% sodium hypochlorite to meet the standard and then discharged into the sewage pipe.

Emergency storage tank

Through the analysis of the hospital geological settlement mechanism, we know that the broken pipeline caused by settlement is a process that slowly intensifies with time, and the risk of broken rainwater and sewage pipeline still exists after repair. To deal with the emergency when the pollution of rainwater discharge damages the pipeline, we can use the emergency storage pool for prevention, as seen in Figure 10. Rainwater storage facilities' location should be based on the purpose of storage, drainage system, pipe network layout, overflow pipe downstream water level elevation, and the surrounding environment and other comprehensive considerations to determine whether conditional areas should use the mathematical model method for program optimization and should be in line with the current national standard ‘outdoor drainage Design Standards’ (GB 50014-2006) of the relevant provisions. The emergency storage pond opens the storage pond inlet valve when there is a problem with the pipe network, closes the rainwater pipe interception valve, intercepts the polluted water in the rainwater main pipe to the storage pond, and discharges it into the sewage system through the lifting pump (Wei et al. 2019). The elevation of the emergency storage pond is designed to be lower than the corresponding rainwater pipe network system to prevent the backflow of sewage. The whole system is remotely controlled and monitored by hand and electric openers, which has the advantages of fast response and good anti-fouling effect, while the hand function can effectively avoid the problem of not being able to operate the emergency storage tank when the control system is out of order.
Figure 10

Emergency storage tank.

Figure 10

Emergency storage tank.

Close modal

Implementation effect

The results of the water quality test data after the implementation of the measures are shown in Table 2. The concentration of ammonia nitrogen far exceeded the water quality range of Class III water in the Environmental Quality Standard for Surface Water (GB 3838-2002) (Fan et al. 2014). It indicates that the water quality is poor. After implementing the measures, the NH3-N concentration in the rainwater pipe decreased significantly. The average removal rate was 97.4%, and the water quality was stable within the range of Class III surface water.

Table 2

Water quality test data after implementing the measures

Water quality testing sectionNH3-N (mg/L)
COD (mg/L)
Detection valueAverage valueStandard valueResultsDetection valueAverage valueStandard valueResults
Before implementing the countermeasures 20.9–52.1 31.2 1.0 Exceeding the standard 57–774 146 20 Exceeding the standard 
After implementing the countermeasures 0.17–0.82 0.63 1.0 Below the standard 5–15 12 20 Below the standard 
Water quality testing sectionNH3-N (mg/L)
COD (mg/L)
Detection valueAverage valueStandard valueResultsDetection valueAverage valueStandard valueResults
Before implementing the countermeasures 20.9–52.1 31.2 1.0 Exceeding the standard 57–774 146 20 Exceeding the standard 
After implementing the countermeasures 0.17–0.82 0.63 1.0 Below the standard 5–15 12 20 Below the standard 

Before the implementation of the countermeasures, the COD value greatly exceeded the water quality range of surface water category III. After implementing the measures, the COD concentration also decreased significantly and remained stable. The average removal rate was 91.8%, which was within the water quality range of Class III surface water.

The results show that implementing countermeasures can effectively deal with the problem of outdoor rainwater drainage pollution in the hospital.

This paper takes a large general hospital as the research object and analyzes the causes of its outdoor rainwater drainage pollution. The systematic analysis method using segment-by-segment screening found that the broken pipe network caused by uneven geological settlement is the main reason for the pollution of rainwater pipes. By studying the mechanism of geological settlement and analyzing its influence, it is known that the stress of the pipe increases with the increase in the relative settlement of the pipe, and finally, the pipe failure occurs at the junction of indoor and outdoor of the building. Countermeasures were carried out in terms of settlement repair and geological foundation reinforcement, rainwater and sewage pipes transformation, the repair of mixed connection of rainwater and sewage pipes and polluted water sources, drainage health safety in isolated areas and emergency storage tank, to achieve regular operation and safe discharge of the hospital rainwater pipeline network.

After implementing the measures, the NH3-N measured value was within 0.82 mg/L, and the average removal rate was 97.4%. The COD concentration also decreased significantly, with an average value of 12 mg/L, and the average removal rate was 91.8%. The results show that the reconstruction can effectively deal with the problem of outdoor rainwater drainage pollution in the hospital. Through this study, there is no problem of water quality exceeding the standard in the river on neighbored areas. The problem of outdoor rainwater drainage pollution of the surrounding environment is solved.

Notably, the limitation of this study is that the broken pipeline caused by settlement is a process that slowly intensifies with time, and the risk of broken rainwater and sewage pipelines still exists after repair. This will require more time to observe the relationship between the settlement and the repaired pipeline. On the other hand, more research data are needed to see if the research methods in this paper can help other hospitals. We will continue to study the relationship between the settlement and the repaired pipeline for the next three years. We will apply the research methodology to other hospitals with the same problem. The research methodology will be refined by comparing the data. This paper's ideas and technical methods provide some reference for the study of rainwater drainage sanitary safety in medical buildings.

This work was supported by the Fundamental Research Project for the Wenzhou Science & Technology Bureau under Y20220803 and the Fundamental Research Project for the Wenzhou Science & Technology Bureau under Y20211155.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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