Intensive construction technology for urban underground parking shaft

Abstract

As urban construction continues to develop and automobile ownership rises, parking shortages in cities have become increasingly acute. Given the limited availability of land resources, conventional underground garages and parking buildings no longer suffice to meet the growing demand for parking spaces. To address this dilemma, underground parking shaft (UPS) has emerged as a highly regarded solution. This study provides an overview of the layout scheme, structural design approaches, and construction techniques for UPS, focusing on the characteristics of intensive construction demonstrated in the project located in the Jianye District of Nanjing. Compared to conventional vertical shaft garage construction methods, this assembly parking shaft offers advantages such as a smaller footprint, higher prefabrication rate, shorter construction period, and reduced environmental impact. It presents an efficient approach for the intensive construction of urban underground spaces, particularly in areas with limited land and complex environments, showing promising prospects for widespread application.

Graphical abstract

Keywords

intensive construction / parking shaft / assembly / underground garage

1 Introduction

With the sustained and rapid development of the national economy, the number of vehicles in China has soared. According to statistics as of the end of June 2022, China’s vehicle ownership has reached a 426 million. Simultaneously, data released by the National Development and Reform Commission reveals a parking shortfall of over 80 million spaces nationwide. The challenges of parking scarcity and disorder have become major obstacles afflicting the urban development in China [1]. Resolving the parking issue has now become the foremost challenge and urgent requirement for transportation and infrastructure development for major Chinese cities [2]. Faced with the severe scarcity of urban land resources, relying on conventional methods to address the parking issue is no longer feasible. Therefore, the development of underground spaces has become an effective approach to alleviate the urban parking problem [3].

When utilizing underground space in public areas of the city, it is important to minimize the construction’s impact on the surrounding environment and existing buildings. In urban contexts, vertical shafts play a pivotal role in underground transportation systems, serving as access points, emergency exits, ventilation shafts, and conduits for equipment installation and maintenance, contributing to the safety and efficiency of the overall transportation infrastructure [4]. The research on vertical shafts primarily focuses on aspects such as ventilation effectiveness [5–12], structural characteristics [13–19], and seismic performance [20–24]. However, there is limited research on the application of vertical shafts as standalone entities.

Various excavation methods are employed based on the shaft’s depth, diameter, and geological conditions [25,26]. In soft soil regions, open-cut methods are prevalent for constructing vertical shafts, using retaining structures like diaphragm walls, bored piles, and secant piles. Additionally, conventional sinking methods are also commonly used for shaft construction. Densely developed urban areas pose challenges due to exorbitant land prices and limited space, making it difficult to construct large-capacity underground parking garages using these conventional methods. For example, experiences from China (e.g., underground parking garages in Hangzhou City and Xiamen City) and Japan (e.g., ECO Park) present the limitations of traditional open-cut and sinking methods, resulting in restricted excavation depths and inadequate parking solutions. As a result, the development of novel and efficient construction methods is urgently needed.

Vertical shaft underground parking garages represents a promising solution to tackle urban parking shortages by strategically and significantly expanding parking capacity. However, the construction of deep mechanical three-dimensional underground garages is still nascent in China, with civil engineering technologies in this field are still developing. To address these challenges, a new type of underground parking shaft (UPS) has been developed. As a fully automated underground mechanical parking system, this innovative garage primarily comprises a vertical shaft, a lift-type parking system, and an intelligent management system. The vertical shaft is constructed using an advanced sinking machine, enabling rapid excavation with a small construction footprint, minimal environmental impact, and ensuring stable quality [27]. The lift-type parking system adopts a novel well-style design, ensuring safety and stability [28]. Moreover, the intelligent management system leverages advanced data acquisition and control technologies to facilitate real-time reading of parking space information and remote control of vehicle access [19,29].

This study provides a comprehensive exploration of the intensive construction techniques for UPS, encompassing the overall scheme, structural design, and construction methods. Additionally, a detailed case study is presented, highlighting the practical implementation of this technology and its achieved outcomes. The findings from this study offer valuable technical guidance and references for similar garage construction projects.

2 Overall scheme

2.1 Conventional shaft parking garage construction methods

Currently in China, open-cut and sinking methods are the two primary construction techniques extensively adopted for underground vertical shaft mechanical parking garages. However, due to limitations in construction technology, garages constructed using these methods tend to be small-scale, with relatively shallow excavation depths and inadequate parking capacity and efficiency.

For instance, the underground three-dimensional parking garage at South Shuhu Road in Hangzhou City, China, completed and put into operation in 2016, is a rectangular geostructure with three cylindrical concrete shafts built using open-cut methods [30]. The structure measures 21.2 m in length, 9.6 m in width, and approximately 34.2 m deep. It is designed with one lift servicing two parking spaces on each level. Each cylindrical shaft consists of 19 underground levels, fitting 38 vehicles, totaling 114 parking spaces for the entire garage. The layout of the garage is shown in Fig.1. Because of the difficulties in preserving foundation stability and managing groundwater during the excavation process using the open-cut method, the excavation depth is limited in soft soil conditions. As a result, this method is less suitable for densely populated city centers with scarce land.

Another example is the two circular underground parking garages in Haicang District, Xiamen City, completed in 2017. The garages have an 18 m inner diameter and are designed with one lift serving ten parking spaces on each of the five levels. The underground area is 380 m², while the above-ground area covers 120 m², with a total depth of approximately 16 m. The garage’s shaft structure is constructed using a factory prefabrication and on-site assembly approach. The factory prefabrication is carried out in sync with on-site preparation, ensuring a standardized and highly modular construction process. The photo of the garage is shown in Fig.2.

This urban parking solution provides an approach for utilizing small plots of land in old residential blocks, parklands, commercial zones, and other spaces to build underground parking garages. However, this type of garage requires a relatively large land footprint, yields limited parking spaces, and entails higher construction costs.

In Japan, the ECO Park represents an innovative approach to automated car parking, guided by the principle of “Culture Aboveground, Function Underground”. Featuring a compact entrance/exit booth designed to minimize aboveground footprint, the ECO Park offers underground parking for 50 or more cars, a capacity similar to that found in Xiamen City. Typically constructed using the Press-in Method, this technique involves the precise installation of pre-formed piles via static loading, ensuring minimal noise and vibration during construction. However, the excavation depth for the shaft typically reaches only around 20 m, posing challenges in expanding the parking capacity. The interior layout of ECO Park is shown in Fig.3.

Therefore, it is essential to find a solution that meets parking demands, maintains reasonable investment, and ensures safety while minimizing the use of underground space and reducing the building volume above ground. Additionally, minimizing the disruption on the residents’ lives and travel during construction is crucial. In this context, the construction of UPS with vertical lift systems demonstrates significant advantages.

2.2 Build modes of underground parking shaft

Depending on the site size and surrounding environmental characteristics, the build modes of UPS can be categorized as follows.

1) Standalone construction. This mode is suitable for sites with an area ranging from 1500 to 2500 m². In such cases, constructing an above-ground garage would result in a significant building volume, heavily impacting the urban landscape and environment, making ground restoration infeasible. On the other hand, relying solely on on-street parking or conventional underground garages cannot meet the parking demands. In this scenario, opting for a standalone UPS not only restores the ground functionality but also ensures an adequate number of parking spaces.

2) Integration with self-propelled garages. This mode is suitable for sites with an area ranging from 2500 to 5000 m², experiencing a significant shortage of parking spaces and requiring a shorter construction period. In this scenario, a combination of conventional underground self-propelled parking lots and UPS can be adopted. This approach allows for substantial savings in the construction period, while retaining the usage advantages of both fully automated mechanical garages and self-propelled garages.

3) Expansion of existing garage. This mode is suitable when the existing garage is insufficient for parking needs, with limited expansion potential. In such cases, a new UPS can be added adjacent to the existing garage. The entrances, exits, and mechanical systems of the new garage can be integrated with the original, enabling a rapid and efficient resolution of the additional parking requirements.

4) Joint development with buildings. This mode is applicable when integrating UPS with commercial or residential buildings. In this scenario, the UPS is constructed beneath the buildings. By maintaining the same parking ratio, it is possible to reduce the underground excavation depth. Additionally, the vertical shaft structure can replace a portion of the pile foundation, further reducing construction costs.

The sectional view and plan view of these four build modes are illustrated in Fig.4 and Fig.5, respectively.

2.3 Parking equipment

In China, the national standard “Classification of Mechanical Parking Equipment (GB/T 26559-2021)” categorizes parking garages into nine major types. Although different types of parking equipment have their own advantages and are suitable for specific scenarios, none of them can effectively match the circular shaft to optimize space utilization.

This study introduces an innovative parking equipment specially tailored for circular parking shaft, combining vertical lifting and horizontal movement techniques. The equipment comprises a central rotating lift inside the shaft, fitting four cars per level circularly along the wall. The single-level parking schematic is illustrated in Fig.6. It integrates essential features like three-dimensional motion control, rotation, and centering functions at entrance/exit. With approximately 2 m height per level, the system facilitates the accommodation of up to 100 vehicles within a 50-m-deep shaft.

The lift uses a 2:1 hoist ropes ratio. The combination of rotation and vertical lifting mechanism significantly enhances the overall efficiency of the garage’s transportation process, achieving lifting speeds of 2.0–2.5 m/s. The entrance and exit are strategically positioned on the ground floor, separated from the vertical lift. This ingenious setup enables the simultaneous entry and exit of two vehicles during peak hours, effectively cutting waiting times. The garage operates with an advanced unmanned and intelligent control system, equipped with state-of-the-art features including remote monitoring and diagnostics, automatic license plate recognition for seamless access, facial recognition for precise user identification, and user-friendly mobile applications for easy advance payments and reservations.

2.4 Garage layout and electromechanical systems

Considering the parking equipment and garage electromechanical systems, the standard underground level can accommodate the parking equipment with one lift and four parking spaces. The corner spaces are fully utilized to arrange the ventilation ducts, cables, firewater pipes, maintenance steel ladders, etc. This achieves a very high spatial integration and utilization rate, as Fig.7 illustrates.

An open high-pressure fine water mist local automatic fire suppression system is adopted for protection. Fire-resistant 3-h partitions are installed on every four levels of the UPS, effectively segregating the ground entrances and exits, the lift machine pits, and the lifting space into independent fire zones. According to unmanned garage standards, a mechanical ventilation system is implemented to ensure adequate air exchange and ventilation, thereby preventing the accumulation of gasoline vapors from vehicles and mitigating the risk of explosions. As the mechanical parking shaft operates without human supervision during fire emergencies, mechanical smoke exhaust system is obviated.

When a vehicle is on fire on a specific level, the fire protection system promptly triggers all the nozzles within the four adjacent levels of the affected area, lift pits and lifting space to initiate suppression. Simultaneously, the ventilation system is shut down to prevent the spread of fire and limit the oxygen supply. After the implementation of the submerging fire extinguishing process, post-incident ventilation measures are carried out to clear the UPS of any remaining smoke or fumes.

2.5 Traffic organization optimization

Due to the highly intensive vehicle handling and parking operations in this type of garage, compared to conventional self-propelled surface or underground parking facilities, queuing and waiting for entry may occur during peak times. This situation can lead to significant queues of vehicles, potentially impacting the surrounding roads. Such scenarios are also very common in underground and surface parking garages located in the core areas of cities, near office buildings, hospitals, or commercial centers. To effectively address these challenges, it is essential to optimize external traffic flow around the UPS through hardware and software enhancements.

The coordination of surface parking, conventional underground garages, and new UPS within the entire plot is essential for efficient parking. During the construction of new entrances and exits, it is important to avoid using external roads with heavy traffic. Instead, utilizing the existing internal roads within the plot can ensure the provision of an adequate length of queuing and waiting space, facilitating a smooth and well-organized flow of vehicles in and out of the new UPS.

It is also crucial for the new UPS to have a reservation platform that can integrate with existing ones. The implementation of a garage operation management system enables automated handling of parking and malfunction situations. Moreover, it allows seamless integration with larger platforms, facilitating optimized sharing and management of parking resources in the region.

3 Structure design and construction

3.1 Universal segment design

The structural configuration of the segments was studied to optimize its construction and enhance overall quality [31]. Due to the large diameter of the segments, each complete circular ring is divided into six segments, with each segment occupying a central angle of 60°. In conventional methods, the segment design incorporates concave and convex tenons, requiring appropriate tolerance space for assembly. If the tolerance space is too small, it can lead to difficulties during segment assembly. Conversely, if it is too large, it may fail to provide proper guidance and shear resistance.

In light of these considerations, the concave and convex tenons on the segment’s surface are removed. Instead, three shear studs are placed on each segment to facilitate assembly guidance and structural shear resistance. Additionally, three longitudinal pre-tensioned bolts are installed on each segment for added stability. The locating grooves on the end faces of the longitudinal joints between segments have been eliminated to streamline the assembly process. Instead, the segments are connected using two bolts between each adjacent pair of segments.

The feasibility of using a universal segment design in the construction of deep vertical shafts was investigated. The universal segment is shown in Fig.8. Each side of the segment is equipped with bolt pockets and embedded bolt sockets, ensuring that adjacent segments align on the same axis after flipping. Based on the dimensions of the shear studs and longitudinal connection nuts, the size of the shear stud holes and longitudinal bolt holes on the segment’s ring surface is standardized. After flipping the segment by 180°, these two features can be interchangeably used. As depicted in Fig.9, the segments are assembled with staggered joints, and the rotation angle between adjacent segments is set to 20°. This universal segment design significantly improves the efficiency of segment assembly.

The structure of the assembly vertical shaft segment adopts shield tunnel-like waterproofing principles, utilizing Ethylene Propylene Diene Monomer rubber sealing gaskets. Since the bolt pockets of the segment are located on the outer curved surface, special rubber sealing gasket grooves are designed on the inner curved surface to prevent groundwater from seeping into the shaft through the bolt holes, as illustrated in Fig.10. The design criteria for waterproofing pressure are set to be twice the water pressure at the maximum depth of the segment burial. The joints are designed with deformation control criteria of 6 mm for opening and 10 mm for stagger under various deformation conditions to prevent leakage.

3.2 Construction techniques

The vertical shaft is excavated using a vertical shaft sinking machine (VSM) manufactured by German Herrenknecht AG. This equipment is isolated from the external water environment, enabling operation under high water pressure conditions. Throughout the entire excavation and sinking process, the machine utilizes a cutting drum, driven by a telescopic boom, to continuously cut through the soil at the bottom of the shaft. The telescopic boom automatically executes pitch and yaw movements as per the preset parameters, facilitating the excavation of the entire vertical shaft cross-section and achieving a controlled level of over-excavation.

With the assistance of a high-powered slurry pump at the bottom of the cutting drum, the excavated material is pumped to the mud-water separation plant on the surface. The annular gap, resulting from the intentional over-excavation between the outer wall of the vertical shaft and the strata, is filled with bentonite slurry to reduce the friction forces. This process creates a stable hydraulic equilibrium among the mud within the shaft (with a specific gravity exceeding 1.18), the bentonite slurry and the groundwater.

The construction process involves several stages, starting with site leveling and surface excavation, followed by ring-shaped foundation construction, the placement of base ring, equipment installation, excavation, and removal of excavated material. Subsequently, segment assembly, shaft sinking, underwater sealing, slurry replacement, and dewatering are conducted [32]. The detailed construction process flow is depicted in Fig.11.

The construction of the vertical shaft relies on its self-weight for sinking, carefully controlled by the lowering unit that drives the steel cables. Throughout the construction, the shaft remains suspended in the slurry pool, with negligible lateral friction. The prefabricated concrete segments are assembled atop the shaft with the bolt pockets strategically positioned on the outer side, so no personnel need to enter inside the shaft during the entire excavation process. After completing the construction of the entire vertical shaft structure, the parking equipment and garage electromechanical systems are installed, followed by the construction of the management rooms above the ground. The entire garage design process is illustrated in Fig.12.

4 Case study: Underground parking shaft project in Jianye District of Nanjing City, China

4.1 Project background

The northern region of Jianye District in Nanjing City, China, stands as a well-developed area with a significant surge in the demand for parking facilities, leading to notable parking-related challenges. On the other hand, the central and southern newly developed areas show relatively lower demand, owing to higher planning ratios and incomplete development. Nevertheless, they still confront parking obstacles in certain locations, such as hospitals and resettlement communities.

The demonstration project is situated at the north-eastern corner of the Hexi Children’s Hospital, located in the central part of Jianye District. Parking issues in this area primarily arise from the inadequacy of the existing parking garage to accommodate the rapid surge in private vehicles, resulting in an increasing motorized travel ratio. Consequently, the equilibrium between parking supply and demand is progressively disrupted. The number of illegally parked vehicles around the hospital area remains persistently high, fluctuating between 337 to 372 vehicles, leading to an estimated deficiency of approximately 400 parking spaces. These illegally parked vehicles cluster along the surrounding roads of the hospital, presenting a noticeable predicament. Furthermore, public parking facilities in the vicinity suffer from significant saturation.

The current site serves as a bus parking lot. Considering that the bus station cannot be relocated, a new UPS needs to be constructed while preserving the existing functions of the site. The bus station occupies a space of 60 m in length and 25 m in width. Opting for UPS proves to be a prudent choice, as it minimizes its impact on the surrounding environment. This UPS project is particularly noteworthy, as it marks the first application of the VSM in China, setting a global precedent as the first integration of this method with an underground parking facility. The project comprises of two vertical shafts, providing a total of 200 parking spaces. The minimum spacing between the edges of these two shafts is 6 m. Each shaft features an internal diameter of 12 m and accommodates 100 parking spaces. The on-site construction photograph of the project is shown in Fig.13.

4.2 Studies on sinking process

To investigate the mechanical mechanism of UPS during the sinking process, this paper conducts a field test during the construction of the underground parking garage of Nanjing Children’s Hospital. The field test mainly monitored the external loads during the sinking process, mainly including lateral soil pressure, pore water pressure, and side friction.

4.2.1 Lateral soil pressure

The lateral soil pressure exerted on the standard ring during the sinking process is shown in Fig.14.

It can be seen from Fig.14 that during the sinking process, the lateral soil pressure on the UPS structure gradually increases with the sinking. Meanwhile, the development trend of the pressure value at each measurement point is the same, and the lateral soil pressure is significantly affected by the change in the water level in the shaft.

During the VSM construction process, the surrounding area of the shaft is over-excavated and the gap is filled with bentonite mud. It is not difficult to deduce that the theoretical value of lateral soil pressure on UPS equals the mud pressure of bentonite. The bentonite slurry ratio of 1.05 is selected to compare the theoretical and measured values, which are shown in Fig.15.

Fig.15 illustrates the tendency of lateral soil pressure in each ring to increase similarly, which rises linearly with the subsidence of UPS. In addition, the growth rate of the lateral soil pressure in each ring is consistent, averagely within the range of 9.95–10.67 kPa/m. The lateral soil pressure in each ring is located between the upper limit and lower limit of the theoretical value, and some value beyond the range is within the error range. Overall, it can be considered that the theoretical values are close to the measured value, which proves that the lateral soil pressure on the structure is equivalent to the bentonite mud pressure during the sinking process.

4.2.2 Pore water pressure

The pore water pressure exerted on the standard ring during the sinking process is shown in Fig.16.

It can be seen from Fig.16 that during the sinking process, the pore water pressure on the UPS structure increases gradually with the sinking, and the development trend of the pressure value at each measurement point is the same. When the liquid level in the shaft changes, the pore water pressure changes synchronously, and the changed amount of the value in each measurement point is the same. This demonstrates that the surrounding shaft is filled with bentonite mud, which can prevent groundwater from entering the mud. In other words, it can be considered that the value of pore water pressure equals the theoretical value of pore water pressure in bentonite.

The hydrostatic pressure, which is considered to be the theoretical value, is compared with the measured pore water pressure values as shown in Fig.17. It illustrates the tendency of pore water pressure in each ring to increase similarly, which rises linearly with the subsidence of UPS. In addition, the growth rate of the pore water pressure in each ring is consistent, averaging within the range of 9.8–9.92 kPa/m. The pore water pressure in each ring is located between the upper limit and lower limit of the theoretical value, and the value is parallel to the theoretical value. Overall, it can be proved that the pore water pressure on the structure is the pore water pressure in the bentonite mud, which is only related to the mud level, not to the groundwater level.

4.2.3 Side friction

The side friction exerted on the standard ring during the sinking process is shown in Fig.18. It demonstrates the side friction on the standard ring during the sinking process. When the side friction is positive, the direction of side friction is upward; and vice versa, it is downward. Fig.18 also clearly shows that the side friction on the structure is extremely small due to the lubrication effect of bentonite mud, which is within the range of 5 kPa. Part of the value fluctuates because the possible contact between the segment and the soil, while the side friction value is still small.

As UPS is surrounded by the bentonite mud during the sinking process, the side friction on the structure can be subjected to the shear strength of bentonite. The shear strength of bentonite mud is taken as 1 kPa, referring to related projects, to compare the theoretical and measured values, which are shown in Fig.19.

As shown in Fig.19, most of the side friction on each ring fluctuates around 0 most of the time. When the overbreak amount changes, the shaft segment contacts the surrounding soil, which leads to the side friction fluctuating significantly. However, due to the wall protection and lubrication effect of bentonite, the values of side friction in each ring are still small. The side friction maintains a small value when the segment is not in contact with the soil during the sinking process. In other word, it can be considered that the side friction and bentonite shear strength is comparable.

4.3 Project results

The Nanjing project was successfully completed and put into operation in October 2022. For each shaft, the design configuration involves 1 lift for every 4 spaces on each of the 25 levels. Among these levels, eight are specifically dedicated to SUV parking, offering a height of 2.5 m, while the remaining 17 levels are designed for regular small-sized vehicles, featuring a height of 2 m.

The concrete shaft extends to an approximate depth of 59 m, disregarding the bottom part, with the maximum excavation depth reaching 68 m. The profile of the project is illustrated in Fig.20. The overall construction demonstrates an impressive assembly rate, exceeding 90%. Remarkably, under the same parking capacity, the project occupies only 10% to 20% of the land area required for a conventional garage during construction, highlighting its efficiency and eco-friendly characteristics.

At a depth of approximately 68 m, the shafts pass through five typical layers of strata in the following sequence [33].

1) Miscellaneous fill and natural soil fill, with a thickness ranging from 2.8 to 4.2 m.

2) Silty clay, with a thickness of 2.9 to 5.2 m.

3) Fine sand, silty clay, and silty clay interbedded with fine sand, with a thickness ranging from 41.1 to 43.1 m.

4) Medium-coarse sand mixed with gravel and pure gravel, with a thickness ranging from 7.8 to 8.5 m.

5) Strongly weathered and moderately weathered sandy mudstone layer, with a thickness ranging from 13.9 to 14.8 m. Notably, the moderately weathered sandy mudstone serves as the load bearing stratum for the bottom of the vertical shaft.

The vertical shaft exhibits a faster sinking rate in the sandy soil layer and a slower sinking rate in the cohesive soil layer, gravel layer, and mudstone layer. The maximum sinking rate reaches 4 m/d. The first shaft completed its sinking process in 46 d while the second shaft took just 28 d [33]. When compared to conventional construction methods, the shaft construction achieved time savings of over 70%.

Each shaft is equipped with two entrances and two exits, as shown in Fig.21. During low-traffic periods, the operation is streamlined, and only one exit and one entrance are utilized. However, during peak hours, the parking efficiency is maximized by allowing both exits and both entrances to operate simultaneously. This flexible control over the number of entrances and exits ensures that the UPS can effectively meet the diverse demands of different time periods.

The comparison between this project and conventional underground parking garages or above-ground parking buildings is presented in the following Tab.1. The UPS exhibits higher costs compared to self-propelled parking buildings, but lower costs compared to underground self-propelled parking garages. Regarding land area occupancy, the UPS stands out as it only occupies 12% of the maximum available area, significantly lower than conventional underground parking garages (74%) and parking buildings (48%). Furthermore, the UPS provides a substantial parking capacity of 200 spaces, surpassing both the conventional underground parking garage (78 spaces on two levels) and the above-ground parking building (168 spaces on six levels).

Through the implementation of intelligent operation and maintenance methods, the parking equipment has achieved a remarkable average vehicle access time of 90 s, far surpassing that of conventional self-propelled garages. Furthermore, the second-generation parking equipment has undergone significant optimization and simplification of its system, all while ensuring utmost safety. As of the current prototype testing phase, the average vehicle access time further reduced to approximately 60 s per vehicle. The exterior and interior views of the completed UPS are depicted in Fig.22 and Fig.23, respectively.

5 Conclusions

Urban construction in major cities has largely been completed, but the parking problem remains a significant challenge. Conventional methods for adding parking spaces often encounter limitations due to insufficient land resources and complex environmental conditions. However, the UPS technology offers a promising solution for densely built urban cores and existing areas with limited space and presents various intensive advantages as follows.

1) Space-efficient design. With a modest diameter of 12 m and a depth of 60 m underground, the UPS occupies a mere 150 m² on the ground but accommodates parking for up to 100 vehicles. Compared to conventional surface parking lots, it utilizes only around 5% of the land area for the same parking capacity.

2) Efficient construction process. The high prefabrication rate, exceeding 90%, and the use of universal segments significantly expedite the construction process. From site preparation to the garage’s commissioning, a single UPS can be completed within six months.

3) Safety and environment friendliness. Advanced vertical shaft sinking technology ensures safety and reliability in diverse geological conditions. The construction process has minimal impact on the surroundings, featuring low emissions and noise levels.

4) Smart parking management. The integration of architectural structure and garage equipment enables an efficient and fully automated parking and retrieval process. Remote reservations with online payment options through a mobile application provide added convenience.

5) The lateral soil pressure on UPS has a basically linear relationship with the sinking depth. After analysis, it is believed that during the sinking process, the lateral soil pressure is equal to the bentonite mud pressure. The pore water pressure on UPS has a basically linear relationship with the sinking depth. After analysis, it is believed that during the sinking process, the pore water pressure is equal to the pore water in bentonite mud, which is only related to the mud level, not to the groundwater level. The side friction on UPS is extremely small during the sinking process. After analysis, it is believed that when the segment is not in contact with the soil, the side friction and bentonite shear strength is comparable.

In conclusion, the UPS technology represents an innovative and effective approach to tackle the pressing urban parking challenges. Its space-efficient design, rapid construction, safety features, and intelligent operations make it a promising solution for optimizing parking facilities in urban environments and paving the way for future underground space development. Furthermore, the vertical shaft construction technology cannot only used for underground garages, but can also be applied to reservoirs, ventilation shafts, and access for underground structures.

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