Geotechnical engineering in urban construction mainly involves the design and excavation of deep foundation pits, groundwater dewatering and drainage, ground treatment, and other aspects. In recent years, with the continuous improvement of domestic infrastructure, urban space has become increasingly crowded, and the constraints on new buildings (structures) have grown. At the same time, natural disasters (rainstorms, earthquakes, etc.) have also made the original soil conditions more complex. Geotechnical engineering projects in urban construction are facing ever-greater challenges.   Compared with traditional construction models, the integrated design-and-construction model for geotechnical engineering is better suited to complex and demanding urban construction projects, and holds major advantages in technical application, project management, and cost management. It has gradually become the preferred choice for urban construction.   
  

 Early design involvement safeguards the project  
  After years of construction, the above-ground building density in China's new first-tier cities is gradually approaching saturation. The limited land area needs further optimization, while urban development requires buildings with more comprehensive functions. Taller, thinner, and deeper buildings inevitably bring enormous challenges in safety, stability, and building settlement control.   
 Therefore, compliant, thorough, and detailed underground surveys must be carried out. Geotechnical engineers should be involved at the early stage of project planning. Drawing on urban construction engineering experience and adapting to local conditions, conducting geotechnical feasibility studies and scheme design and comparison can effectively reduce project risks and ensure project safety and cost-effectiveness.   
       For the China Railway Nuode residential project in Fengtai District, Beijing, we adopted the integrated design-and-construction model.   
  Based on the survey results, considering the deep sand-gravel layer within the pile length that makes drilling difficult and the fact that the soil below the foundation base is weak and underlain entirely by gravel layers, the design proposed two options: 400mm-diameter CFG piles and 600mm-diameter CFG piles. Combined with the cost department's estimates and the engineering department's assessment of site conditions, 600mm-diameter CFG piles with short pile lengths and small spacing were ultimately adopted, ensuring the feasibility of long spiral drilling and meeting bearing capacity requirements.   
  The pile foundation construction was completed in November 2021. The final cost was optimized by 16%, the construction period was reduced by 25 days, winter construction was avoided, and there were very few design changes to the underground portion, creating favorable conditions for the superstructure construction.     
 
   Management of adjacent buildings and underground infrastructure  
 
 In urban construction, buildings (structures) already in use often surround new project sites. How to manage adjacent buildings and avoid negative impacts on neighboring buildings or infrastructure during construction is a major challenge in urban geotechnical engineering.  
 At the same time, excavation around underground space may involve public facilities or subway connecting corridors, transportation systems, water supply and drainage pipelines, power generation and cable lines, telecommunications and national defense facilities, and so on. Designing and constructing around these obstacles is complex, expensive, and risky.  
    A residential-mixed-with-public-building project on a plot in Niulanshan Town, Shunyi District. The northwest corner is adjacent to the Beijing Earthquake Administration, and site use requirements are extremely strict—no component is allowed to extend beyond the red line—so a double-row pile support scheme was adopted. The project has a high groundwater level, and the site has narrow construction space, which is unfavorable for the operation of large machinery (how was the construction process managed, and what optimization or special solutions did the design provide for construction?).  
    A commercial project in Yaodu District, Linfen City. The east side of the site is adjacent to residential buildings, the south side to the Shenglong International Shopping Center, and the west side to a major traffic artery. There are significant constraints in actual surveying, design, and construction. Important buildings surround the site, and the pipelines are complex. (How were the difficulties encountered resolved? A data collection checklist was drawn up, with the client's development department assisting in collecting data / anchor bolt lengths and embedment depths were checked against surrounding municipal conditions and site surveys / the contractor was assisted in establishing a master plan, with drawings or briefings adjusted according to the construction sequence; how is design supported for out-of-town projects, and what communication mechanism was established to solve problems promptly? Add design intent explanations / briefings on key and difficult points / participation in weekly project meetings / project aerial photography or other safeguard measures →→ what results were achieved? Under the platform created by the general contractor, the feasibility, practicality, and safety of the technical scheme were realized efficiently, overall improving project advancement efficiency, and so on)  
     The integrated design-and-construction model enables design and construction personnel to take other links into account while working, improving the feasibility of implementing design schemes, reducing changes, and increasing construction efficiency.   
 
   Facilitates project cost management and improves economic benefits  
 
 When engineering design and construction are handled by the same engineering contractor, the project investor only needs to coordinate with the engineering contractor during investment. This reduces communication errors and ensures the correct use of funds. A single contractor responsible for both design and construction can effectively combine various resources and improve resource utilization efficiency. During construction, the contractor can also carry out detailed construction design of the engineering design in a timely manner, thereby reducing design changes, saving project costs, and improving economic benefits.  
     The integrated geotechnical engineering construction model can also simplify the bidding process to the greatest extent. Throughout the construction process, there are only two responsible parties—the contractor and the owner—making it easy to determine the responsibilities of both contract parties and resulting in fewer disputes.  
    
 A shantytown renovation project within the fenced area of the Beijing Tianzhu Comprehensive Bonded Zone in Shunyi. With integrated design-and-construction services, the foundation pit area is about 26,840 square meters with a perimeter of about 1,020 m; the foundation uses CFG pile composite ground. The project construction period was from October 2021 to June 2022. The geotechnical engineering design and construction coordinated with adjustments to the main scheme and promptly fed site conditions back to the relevant main-structure disciplines (the risks of coordinated control of quality, schedule, and cost brought about by the change in responsibility were included within the scope of the integrated contract. Comprehensive responsibility drives the internal impetus of individual geotechnical engineering projects, enabling integrated development in overall management, financial flow, and coordination and organization, and providing more scientific and intensive services), optimizing the engineering design and construction, greatly reducing engineering design changes, and saving construction time and project costs.  
    Geotechnical engineering in urban construction has its particularities. The implementation of integrated design and construction can establish an efficient and unified project team, comprehensively improving project operation efficiency and accuracy. The integrated design-and-construction model for geotechnical engineering will strongly guide enterprises to adjust their organizational structures, moving from the end of the market to the front end and participating in construction projects at a higher level. It is an excellent product that conforms to industry development and has already become the preferred model for major construction units.  
 
   Facilitates refined design management and improves project time efficiency  
 
 When the main engineering design, geotechnical design, and construction are led by the same unit, the design and construction parties can establish stable communication channels and communicate throughout the process, which is conducive to the management of the construction unit. The earlier the geotechnical design and construction unit gets involved in the project, the more effectively design errors caused by insufficient construction experience can be avoided at the scheme and preliminary design stages, reducing unnecessary rework and ensuring project quality. Throughout the full design cycle, communicating internally within the unit about what can and cannot be done at each stage reduces construction costs and improves engineering efficiency and competitiveness.

       A residential and public building project on a plot in Fengtai District. Our company undertook the main engineering and geotechnical engineering design and construction tasks, with all work advancing in parallel. When the main design was basically completed, the foundation pit support design was also basically completed. When the main design reached the depth required for construction drawing review, the foundation pit support construction drawing design was also completed. The foundation pit excavation depth of this project is 14.50 m, and it took less than a year from the entry of the foundation pit support construction team to the topping-out of the main structure.