Pit Support Research Articles

System Stability of Bored Piles with Steel Supports for Deep Foundation Pits in Sandy Pebble Stratum

Background: At present, there are a few research studies on the stability of the supporting structure of bored piles with steel supports for deep foundation pits, and it is even less common to use this support method for deep foundation pits in sandy pebble stratum. This paper studied the stability of the deep foundation pit support of the Southwest Jiaotong University Station in Chengdu, China, using the stability analysis theory of bored piles with steel supports for deep foundation pits. Objective: The study aims to show the stability of steel supports for deep foundation pits. Methods: The overall stability, anti-overturning stability and uplift stability of the foundation pit are important components of the stability analysis of bored piles with steel supports for deep foundation pits. Aiming at the designed method and parameters of the bored piles with steel support for the deep foundation pit, in-depth theoretical analysis, and calculation of the overall stability, antioverturning stability, and uplift stability of the deep foundation pit are conducted, respectively. Results: The results show that the stability of the deep foundation pit using bored piles with steel support meets the requirements, indicating that the design of this support form is safe and reasonable, thus ensuring the smooth progress of the project. Conclusion: The stability analysis of deep foundation pits in sandy pebble stratum provides ideas for the optimization of deep foundation pits and a reference for the stability analysis of deep foundation pits in sandy pebble stratum and other types of the stratum.

Discussion on the Research of GFRP Anti-floating Anchors

As a kind of anchor to deal with the anti-flotation problem of floor, anti-flotation anchors have many advantages, such as strong adaptability to stratum, high anchoring force, low cost, short construction period, small stress at single point, simple construction and low cost, compared with the traditional anchor. In recent years, it has been more and more applied to solve the problems of foundation pit supporting and foundation floor anti-floating in the construction process of buildings. In this paper, the stress and strain distribution law, load transfer characteristics and the relationship between GFRP anti-floating anchor and rock mass of GFRP anti-floating anchor are summarized, and suggestions for the future development of GFRP anti-floating anchor are put forward.

Developments in the field of removable anchors

The design of inner-city building pits is a challenging task in geotechnical engineering. Due to rising property prices and the limited vacant plots in urban areas, the installation of building pit support measures is often constrained. Besides rigid systems, struts or anchors are often used to support such building pits. On the one hand, this support is required to come up with an economical design and on the other hand, it is necessary to keep the deformations of adjacent structures within certain limits. In this paper a new approach for the design and the (de-)installation process of removeable anchors is presented. By using a non-explosive cracking agent, a fully removeable anchor has been developed. Laboratory test results have shown, that by filling a pre-installed injection tube with the non-explosive cracking agent, a partial destruction of the grout body and consequently a reduction of the bond along the cement body and the steel tendon can be achieved. As a result, an extraction of the steel tendon is possible.

Application of Secant Piles for Excavation Pit in Complicated Environment

In order to study the application of secant pile in deep foundation pits in complex environments, this paper takes an actual foundation pit project as the research background, and combines the characteristics of the deep excavation of the foundation pit and the large influence of the groundwater level. Propose the design scheme of partition and segment and use finite element analysis method for numerical calculation. By calculation it is known that the overall displacement of the foundation pit support system is 13.11 mm, the maximum horizontal displacement is 11.8 mm, and the ground settlement is 5.7 mm. All indexes meet the requirements of foundation pit specifications. The research results show that the secant pile has its unique advantages and applicability, which can effectively stabilize the overall performance of the foundation pit and the surrounding environment. The design philosophy in this article can provide references for similar foundation pit projects.

Behavior of bladder-type inflatable anchors in sand: Physical modeling.

This paper describes an investigation into the performance and pull-out capacity of a bladder-type inflatable anchor. The inflatable anchor is a type of support member used in foundation pit support engineering. Based on improvements and innovations, the multi-bladder-type inflatable anchor consists of two or more hydraulically inflated rubber membranes that are embedded in unconsolidated earth and then inflated to provide pull-out capacity. The primary objective of this study was to investigate the impact of inflation pressure, embedment depth, number of bladders, bladder length, and rubber film thickness on the pull-out capacity and displacement of the inflatable anchor. The tests were carried out in a cylindrical steel test chamber filled with medium coarse sand. The pull-out behavior of the bladder-type inflatable anchor and the five variables was investigated, and the benchmark values for all tests are determined by similarity ratio. Compared with the single bladder inflatable anchor, under the same conditions, the ultimate pull-out capacity of the two bladder-type inflatable anchor is 1.2 times higher, with ultimate displacement only 37.5% of the former, the ultimate pull-out capacity of the three bladder-type inflatable anchor is 1.7 times higher, with ultimate displacement only 32.3% of the former. The two bladder-type inflatable anchor is superior to the single bladder inflatable anchor and the multi-bladder-type has higher ultimate pull-out capacity and greater stiffness. The inflation pressure and the rubber film thickness have a significant influence on the bearing capacity. The number of bladders effectively controls the ultimate displacement.

Discussion on Difficulties and Breakthrough Ways of Deep Foundation Pit Support Technology in Municipal Construction

Discussion on Difficulties and Breakthrough Ways of Deep Foundation Pit Support Technology in Municipal Construction

Research on Application of Multi-factor Surrounding Rock Pressure Calculation Theory in Engineering

Based on the multi-factor surrounding rock pressure calculation theory, the values of surrounding rock pressure and construction safety and stability coefficients corresponding to different construction methods required by engineering design and construction could be quickly and conveniently calculated with the derived general formula, so as to guide and optimize the design and construction scheme. In this paper, the influence of lateral load coefficient on surrounding rock pressure was analyzed and verified, and the calculation method and application range of lateral load coefficient were proposed. Meanwhile, according to the multi-factor surrounding rock pressure calculation theory, an arched precast member was proposed, which was assembled into an optimal and reasonable honeycomb-like stress structure, and applied in the support of tunnel and underground space. It could improve the construction technology of composite lining by taking the advantage of the common load bearing of surrounding rock and support. In addition, with the theory, the application of arched precast member in the support of deep foundation pit has simplified the setting of lateral support of deep foundation pit in the horizontal direction, which is an innovative construction method for deep foundation pit support using prefabricated assembly components. Certainly, the calculation theory should be further studied, and the dynamic change of surrounding rock pressure after excavation under various adverse geological conditions should be accurately analyzed and verified by means of monitoring and measurement, which should be reasonably connected with the current Code for popularization and application. It is hoped that the study of the calculation theory and its application in engineering practice can provide useful guidance and help for the design and construction of tunnel and underground space.

Effect of genetic algorithm in optimizing deep foundation pit supporting structure

To design a deep foundation pit support structure that can guarantee safety and obtain the highest economic benefit under the premise of meeting the engineering requirements, the realization method of genetic algorithm and the calculation method of safety factor in the optimal design of pile-anchor supporting structure of deep foundation pit were proposed in this study, and the optimization design system of pile-anchor supporting structure of deep foundation pit was designed according to the rules of survival and fittest of genetic algorithm. According to an actual engineering case, this system is used for optimized design and compared with the original design results. The results showed that the construction cost of the deep foundation pit supporting structure with optimized design had been reduced from 6920 to 4760 yuan. It not only saved about 32.5% of the project cost, the safety coefficient also reached above 1.25, which met the technical regulations of the foundation pit support in China. This study provided an important reference for the application of genetic algorithms in the field of foundation pit engineering.

Research on earth pressure monitoring data of soil-stone assorted foundation pit

Earth pressure is the most important type of load acting on the supporting structure of a foundation pit, and it is also a key factor in the design of foundation pit supporting. However, in engineering practice, the calculated value differs greatly from the actual value, which puzzles many engineers. This paper analyzes the field measured data of the earth pressure of the foundation pit in Minghucheng (Jinan city), and compares the calculated values of the Rankine active earth pressure and the passive earth pressure theory. The analysis finds that: (1) The measured value is between the active earth pressure and the passive earth pressure, and as the excavation of the foundation pit and the inward displacement of the supporting structure, the measured earth pressure value becomes smaller and approaches the active earth pressure. (2) When the pre-stressed anchors is applied, due to the fastening effect of the anchors, the earth pressure behind the supporting pile has a tendency to increase. (3) The theoretical value of Rankine’s active earth pressure in the soil-rock combination is obviously lower than the measured values.

Research on Application of Top-down Construction Method Based on Computer Technology in Excavation of Urban Deep Foundation Pit

With the development of urban construction in three dimensions, the increase of urban high-rise buildings and the in-depth utilization of underground space, the requirements for the excavation and support of deep foundation pit projects based on computer technology are getting higher and higher. The advantages of reverse method in urban deep foundation pit excavation make it quickly popularized and applied, which has high research value. This paper first introduces the application of the reverse method in the deep foundation pit support, then analyses the design of the reverse method, and finally studies the application of the reverse method in the urban deep foundation pit construction design[1-3].

Simulation of subway tunnel construction process based on fi-nite element analysis

Simulation of subway tunnel construction process based on fi-nite element analysis

Analysis of Lateral Displacement Law of Deep Foundation Pit Support in Soft Soil Based on Improved MSD Method

Foundation pit envelope and foundation pit excavation solution design is a multidisciplinary problem that could be linked to a series of safety issues in the geotechnical engineering of an actual construction project. Moreover, the construction of large deep foundation pit in soft soil often faces greater risks and challenges as the support structure deforms more easily and unpredictably. In order to improve the deformation prediction of deep foundation pit engineering precision and efficiency and to ensure that the construction of deep foundation pit engineering is safe and efficient, in this article the traditional MSD (mobilizable strength design) theory research and analysis, combined with the Jinan formation characteristics of a tunnel in JInan, and new parameters were introduced to the original MSD method theory: the wall itself within the bending strain energy U and support compression elastic potential energy of V. A new law of conservation of energy is constructed, and finally, an optimized MSD method has been proposed, this method is shown in the article. Finally, the results of foundation pit deformation calculation were compared among the optimized MSD method, finite element calculation method, and field monitoring data analysis method, so as to demonstrate the reliability of the prediction system of optimized MSD method and finite element analysis method. The results show that, by optimizing the MSD calculation method, the horizontal displacement of the retaining wall varies depending on the excavation depth of the foundation pit and the form of internal support with the overall peak value of displacement between 0∼0.2% H (H being the excavation depth); the deformation of retaining wall increases gradually with the increase of excavation depth of the foundation pit, and the peak position of deformation gradually moves down with the excavation of foundation pit. The trend of these changes is consistent with the results of the finite element method and field data analysis method, proving that the optimized MSD method is reliable in predicting the deformation of the foundation pit under specific stratum conditions.

Foundation Pit Support Structure under Special Geotechnical Structure

Due to The Vast Territory of China, The Topography, Geological Conditions and Surrounding Environment of the Construction Project are Very Different. The Design and Construction of the Foundation Pit Support Project is One of the Most Closely Integrated Engineering Measures Combined with the Above Conditions. The Design and Construction of Deep Foundation Pit Support Engineering in Special Geotechnical Areas Has Become One of the Most Complicated Technical Problems in the Field of Civil Engineering Construction. Based on the Above Background, The Purpose of this Paper is to Study the Foundation Pit Support Structure Under Special Geotechnical Structure. This Paper Compares and Analyzes the Materials and Structure Types that Can be Used for Foundation Pit Support, And Concludes that Bamboo is an Economical and Environmentally Friendly New Material, Its Output Large, Good Mechanical Properties, Can Be Used For Temporary Support of Shallow Foundation Pits. It is Proposed to Use the Bamboo Tube as the Foundation Pit Support Material, And it is Applied in the Soft Soil Layer Foundation Pit Support Project in the form of Row Pile Support Structure. In this Paper, the Top Displacement of the Bamboo Pipe Pile is Larger than that of the Steel Pipe Pile, But the Maximum Pile Top Displacement of the Bamboo Pipe Pile is 1.8mm. The Maximum Displacement of the Pile Top is 18mm, The Displacement is Small, Within the Allowable Range, and in the Actual Project, the Pile Top is Generally Constrained to Further Control the Displacement of the Pile Top to Ensure the Safety and Stability of the Foundation Pit.

Study on Settlement and Deformation of Urban Viaduct Caused by Subway Station Construction under Complicated Conditions

With the rapid development of urbanization, the speed of constructing urban underground space and ground foundation engineering is accelerated. With the shortage of land resources, the distance between underground engineering and surface engineering is getting closer and closer, and the contradictions and problems between projects are becoming more and more serious. Based on the new subway station, this paper passes the existing urban viaduct in a short distance. The settlement and deformation of pile foundation and buildings caused by the excavation of the subway station is studied by using ROCSCIENCE software and site monitoring method. The potential risk sources around the station are pile foundations 18.5 m away, residential buildings 15 m away, storm water pipes 7.3 m away, and high‐pressure gas pipes at 5.6 m. According to the construction requirements of pile foundation settlement deformation during metro station excavation, we set up construction standards. The settlement of the buildings and pipelines around the metro station should not exceed 3 mm, and the horizontal displacement should not exceed 2 mm. The diaphragm wall is adopted to surround the subway station, and the ground is reinforced by advanced grouting. The results show that, during the excavation of the foundation pit of the metro station, the ground and the building will have obvious settlement deformation and the depth of deformation can reach 9 mm, which is more than the allowable value. The settlement deformation of the ground and the surrounding buildings can be controlled within 3 mm by strengthening the foundation pit support and ground advance‐grouting reinforcement. The control of construction deformation can meet the construction requirements.

Optimization Design of Deep Foundation Pit Support Scheme under Traffic Dynamic Load

In this paper, based on the deep foundation pit support of the reconstruction and expansion project of Jiqing expressway, numerical software is used to establish the numerical calculation model of the deformation support of deep foundation pit under the influence of traffic dynamic load. The numerical calculation results are consistent with the actual project monitoring results. By changing the support parameters such as pile diameter, pile length, vertical support distance in different support schemes is analyzed. The results show that the ideal diameter of bored pile is 0.8-1.2m, the length of pile is 23m-28m. With the vertical support distance increasing, the change trend of horizontal displacement of piles gradually increases. Considering the safety of foundation pit and the reduction of project cost, the pile with length 23m, diameter 0.8m and the vertical support distance 5m is chosen in the practical engineering.

Analysis of Foundation Pit Design of Metro Station in Complex Environment

The complex engineering geological conditions and the surrounding environmental conditions of the existing subway lines and adjacent buildings have significantly deepened the difficulty of metro station foundation pit design and construction. Based on the foundation pit project of Luboyuan Station of Nanjing Metro Line 9, this study chooses a reasonable foundation pit support design scheme to carry out related research by analyzing the site geological environmental conditions. Through the analysis and evaluation of the engineering geological conditions of the engineering site, the engineering geological problems that may occur in the process of construction are given. According to the lithologic characteristics of the site strata, the hydrogeological conditions, and the features of the underground engineering structure, the design of the foundation pit supporting system is optimized and analyzed. The results show that making full use of the geological features of strata and adopting effective support methods can ensure the safety of foundation pit construction, reduce the cost of engineering description, and shorten the construction period, which can be used as a reference for similar projects and construction.

Study on Optimization of Deep Foundation Pit Support Scheme under the Influence of Traffic Dynamic Load in the Reconstruction and Expansion of Jiqing Expressway

In this paper, based on the deep foundation pit support of the reconstruction and expansion project of Jiqing expressway, the FLAC3D software is used to establish the numerical calculation model of the deformation support of deep foundation pit under the influence of traffic dynamic load. The numerical calculation results are consistent with the actual project monitoring results. By changing the key support parameters such as pile diameter and pile distance, pile length, the level of piles under different support schemes is analyzed. The results show that the ideal diameter of bored pile is 0.8-1.2m, the spacing is 1.1-1.3m, the length of pile is 23m-28m. The horizontal displacement of pile body and ground settlement decrease with the increase of length and diameter of support pile. Considering the safety of foundation pit and the reduction of project cost, the pile with length 23m and diameter 0.8m is chosen in the practical engineering.

Numerical Simulation And Monitoring Analysis Of Deep Foundation Pit In Shijiazhuang Area

The foundation pit engineering is a work with large amount of use and high difficulty coefficient. It is necessary to ensure the deformation of soil in the control range and the safety of the whole structure of the foundation pit. In this paper, the foundation pit support project in Shijiazhuang City, Hebei Province is taken as the research object, and the numerical analysis method is used to simulate the pile-anchor support in the First Section of the fourth section of the foundation pit. In this paper, the horizontal displacement value of deep foundation pit and the settlement value of the top edge of foundation pit are analyzed, It provides reference for future projects.

Analysis and Research on excavation deformation of deep foundation pit support engineering of metro station

With the rapid economic and social development, the construction of urban underground rail transit is in full swing, and even many second and third tier cities are starting to build, In order to control the environmental impact of the excavation team and control the deformation, this paper takes a deep foundation pit project of a station in Wuhan Metro as the research object, combining with theoretical analysis, field monitoring and Midas GTS Nx numerical software simulation and other methods are used to discuss the ground settlement around the foundation pit, the impact on the adjacent bridge pile foundation, and the deformation control analysis.

Research and application of large diameter steel cylinder island construction technology in Hong Kong-Zhuhai-Macao Bridge project

ABSTRACT The large diameter deep inserted steel cylinder is used for the first time in the artificial island project of Hong Kong-Zhuhai-Macao Bridge. Through the ingenious conception of the scheme of large diameter deep inserted steel cylinder, this paper analyzes the working mechanism, design key points and construction key points of large diameter deep inserted steel cylinder structure, and introduces the research and application of large diameter deep inserted steel cylinder technology in foundation pit support engineering of East–West artificial island of Hong Kong Zhuhai Macao Bridge. Two arc-shaped steel plate auxiliary grids are used to connect and seal the adjacent cylinders. The arc steel plate can be manufactured in the factory and transported to the site for construction, which greatly reduces the construction difficulty and material cost. The formed cofferdam Island wall has good water stop performance and good structural stability.