Soft Soil Foundation Research Articles

Study on tensile properties of rice straw rope considering degradation

Many scholars have used crop straw to reinforce soft soil foundation and studied its reinforcement effect and mechanism. However, the crop straw will degrade in the soil for a long time, which reduces the tensile strength of the straw and weakens the shear resistance of the reinforced soil. In order to study the degradation law of rice straw rope and its influence on tensile properties, the straw rope was immersed in water for different time, and then taken out, the quality before and after immersion was measured and tensile test was carried out. The results showed that: the degradation of rice straw rope in water experienced two stages of rapid degradation and slow degradation, and the quality of loss in the rapid degradation stage was more; the tensile force of straw stalk rope increased slowly with the increase of tensile displacement. When immersed for 20 days, the failure mode was brittle failure, and after 40 days of immersion, the failure mode changed into ductile failure; the straw stalk rope was the main tensile force of the straw fiber, and the tensile strength peak decreased with the increase of the immersion time. The deterioration law accorded with the third-order polynomial function.

Load Transfer Law and Influence Factors of Piles in Deep Loess Area

This paper summarizes the characteristic of four kinds composite foundation - compacted concrete composite foundation, Lanzhou loess foundation, highway soft soil foundation, just - soft pile composite foundation. Based on load tests and pile stress analysis of the measured data, summarizes the four foundation pile load characteristics and load transfer mechanism. The factors that influence the pile load transfer law are those: the pile tip soil properties, Pile shaft stiffness and length to diameter ratio, cement mixing ratio, Soil types, Moisture content, Compactness, The use of mattress layer.

Analysis of the conventional vacuum preloading method

The conventional vacuum prepressing method is to reinforce the soft soil foundation. The process is to lay a certain height of horizontal sand cushion layer on the surface to form a horizontal drainage channel, and then set up a plastic drainage plate and connect it with a pumping pipe to form a vertical drainage channel. This paper analysed the conventional vacuum preloading method with in-site test method, and the foundation reinforce effect was evaluated by monitoring the surface settlement, variation of pore pressure and layered settlement.

Research progress of soft soil foundation treatment technology

With the extensive improvement of infrastructure in China in the past ten years, the soft soil foundation is becoming more and more complicated. Therefore, the improvement of soft soil foundation treatment has become a difficult problem that today’s engineering designers have to face. This paper systematically reviews the development of soft soil foundation treatment technology in our country, and emphatically introduces the development process of foundation treatment at home and abroad, especially in our country in recent years, which embodies the cross and comprehensive application of various foundation treatment technologies and forms a unique composite reinforcement technology.

Numerical simulation of consolidation settlement of the embankment of the Nansi Lake

The consolidation settlement of the lake embankment engineering under long-term load is very large. It makes the structure can’t work normally and even leads to severe damage. Therefore, it is very important to analyze the settlement of soft soil foundation for the stability and safety of the lake embankment. The mechanical parameters of soil in this area, based on the geological investigation report of the lake embankment, are used to analyze the engineering characteristics of lacustrine soil. The embankment of the Nansi Lake is selected as an object to analyze the consolidation deformation characteristics of the lake embankment. The consolidation settlement of the lake embankment is simulated by the finite element analysis software. The simulation data and analysis results are very important for studying local geological characteristics and hydraulic construction.

Analysis of Monitoring in settlement For Vacuum Combined Stack Preloading about Soft foundation Sluice

Vacuum combined surcharge preloading is a kind of drainage consolidation method, having many advantages, such as low reinforcement cost, short construction period and good reinforcement effect, and suitable used in foundation treatment in soft foundation. Based on vacuum combined surcharge preloading reinforcement project of one Sluice soft soil foundation in the east coast of Zhejiang Province, this paper introduced the in situ monitoring situation in the vacuum preloading process, mainly summarized the monitoring result of vacuum degree and surface subsidence, and found out the changes and connections of indicators in the preloading process. At the same time, the development process of vacuum combined with preloading and settlement is simulated by finite element method.

Simulation of Interaction between Robot’s Flat Foot and Loose Soil

In this research, dynamics simulations based on Soil Contact Model (SCM) and slip line field theory are proposed to reproduce the interaction between humanoid robot’s foot and soft soil ground. These two novel models calculate the contact force and torque of the contact body with the soft soil ground and reproduce the plastic deformation of the soil to a certain extent. The reliability of the simulations based on the two models is also verified through experiments.

Discussion on soft soil foundation treatment technology in municipal road and bridge engineering

Municipal road and bridge engineering is an important part of the transportation road construction in the city. Its construction quality directly affects the transportation quality and driving safety of the whole municipal road traffic. Among them, the foundation engineering of municipal road and bridge engineering is the main construction link. In the current municipal road and bridge construction process, it is often affected by many factors, leading to the reduction of the construction quality of municipal road and bridge engineering, especially the construction treatment of soft soil foundation in the foundation engineering, which is the main factor directly affecting the construction quality of municipal road and bridge. This paper first introduces the definition and relevant characteristics of soft soil foundation in the construction of municipal road and bridge engineering, and expounds the influence of soft soil foundation on municipal road and bridge engineering, and then analyzes the application of soft soil foundation treatment technology combined with the basic treatment ideas of soft soil foundation in the construction of municipal road and bridge.

“真空联合堆载预压 + 强夯法”在软土地基中的应用研究

“真空联合堆载预压 + 强夯法”在软土地基中的应用研究

Implementation of biocementation for a partially saturated problematic soil of the UK railway network

This paper refers to biocementation of a problematic soil of the UK railway network as a potential stabilisation technique of this soil using indigenous ureolytic bacteria. The soil is peat, a soft foundation soil also subject to oxidation wastage. As the peat is under existing embankments, electrokinetics (EK) is proposed as a promising technique to implement treatments. In the context of unsaturated soils the paper thus focuses on two particular aspects relevant for the implementation of treatments and the stability of this soil, namely: a) the effect of degree of saturation of the peat on the bio-electrokinetic treatment ; b) the soil water retention curve of the soil affecting flow and transport; these are relevant as we focus on understanding and modelling the implementation of treatments through electrokinetics; moreover for the peat it is of importance to understand moisture exchange in the vadose zone and control groundwater table levels (e.g. during electrokinetics) in order to prevent further oxidation. After isolation and screening of indigenous microorgansisms Bacillus licheniformis was selected for further testing. The results in terms of unconfined compressive strength, CaCO3 content, swelling and compression behaviour and water retention proved the feasibility of biocementation using this indigenous microorganism. Ongoing work is assessing the required treated soil characteristics and related required biocementation degree to solve UK rail's peat foundation problems. Upscaling of the techniques towards in situ implementation is also planned in the next stage of the research.

An Experimental Study on the Ecological Support Model of Dentate Row Piles

Bamboo is highly renewable and biodegradable with good short‐term strength, which meets the requirement for temporal support structures in shallow foundation pits. Based on this, we conducted a laboratory model test on the dentate bamboo micropile support structure combined with environmentally friendly building materials and new type of piles, to explore the stress characteristics, stress change regularity, and the support effect of the system in soft soil foundation pits. The results show that the earth pressure on the pile sides above the excavation surface gradually decreases with an increase in the excavation depth. The bending deformation of the bamboo pile was also significant. The results also show that the earth pressure and the pile strain below the excavation surface change slightly during the excavation process. When the short sides of the foundation pit were loaded, the highest strain was recorded in the piles 4 and 11. A maximum strain of 358.93 με was recorded, and the maximum displacement of the pile in the top part was obtained to be only 2.14 mm. The most subsidence of dentate pile obtained is only 1.88 mm, whereas that of the single‐row pile is 2.35 mm. Compared to the traditional single‐row pile, the dentate piles can effectively reduce the horizontal deformation as well as the surface subsidence effectively. They can also support more external lateral load, and hence maintain the foundation stability and give better support. The results provide a theoretical basis for ecological bamboo support technology and have great value to be promoted.

Bearing Characteristics of Moso Bamboo Micropile‐Composite Soil Nailing System in Soft Soil Areas

Based on the characteristics of moso bamboo including high short‐term strength, stable performance, and ability to provide temporary support for shallow foundation pits in soft soil, the stress characteristics and supporting effects of the ecological composite supporting system have been explored through model tests and numerical calculation analysis of the moso bamboo micropile‐composite soil nailing structure. The results showed that the bamboo pile can effectively control the horizontal deformation of the side wall of the foundation pit and the ground surface settlement, achieving a relatively satisfactory supporting effect. Furthermore, the bamboo pile has visibly bent in middle and lower parts, where the regional shear point is most likely to appear, the axial force of the soil nail is distributed in an oval pattern with a smaller force on both sides and a larger force in the middle part, the maximum axial strain is 447.3 με, and the axial force of the soil nails in each row follows a similar trend. The synergy of piles and soil nails can delay the formation of the slip surface, therefore enhancing the overall bearing capacity of the foundation pit. These results can shed light on the support mechanism and engineering design of bamboo piles in shallow soft soil foundation pits.

Study on Supporting Structure Performance of Deep Soft Soil Foundation Pit near Sea under Waves, Tides, Vibration, and Unbalanced Loads

In addition to the vibration loads caused by offshore structure construction, the offshore foundation pit can also be affected by additional hydraulic loads such as waves, tides, and typhoons, hindering our understanding of the mechanical performance of the foundation pit supporting structure. In order to illuminate this mechanical performance under waves, tides, hammering, and unbalanced loads, this paper analyzed the supporting structure with theoretical and numerical simulations. The results were verified with field monitoring data. Moreover, the influences of loads, including construction vibration loads and unbalanced loads, on structure and soil were discussed. By applying these results to the engineering design, this research could provide a reference for studying mechanical properties of relevant supporting structures and the construction of offshore foundation pits.

Failure and Remediation of an Embankment on Rigid Column‐Improved Soft Soil: Case Study

The south extension line was constructed as a new part of the Xintai Expressway in Guangdong Province, China. The project required the construction of an embankment over soft soil with a thickness of up to approximately 14.0 m, and prestressed pipe pile was selected for reinforcing the soft soil foundation to increase bearing capacity and reduce settlement. Embankment sliding with a length of approximately 110 m and cracking with a length that exceeded 300 m occurred before the construction of the pavement structure. Field investigation and theoretical analysis results indicate that the safety factor of the overall stability calculated by the existing code methods is overly large, thereby resulting in large design pile spacing, low design bearing capacity provided by single pile, and excessive load shared by subsoil between piles. These results all cause the flow sliding of soft soil between the piles and the bending fracture of some piles. The revised density method can be used to check the stability of flow sliding, and the bending moment of piles should also be checked during the embankment design stage. In addition, perpendicularity deviation and poor joint quality of pile construction also contributed to the reduction of the bearing capacity of the pipe piles and the overall stability of embankment. Reconstruction of additional rigid piles and add pile after drilling holes are adopted in the sliding and cracking sections to reinforce the failed embankment, respectively. The remediation effect was validated by the measured excess pore water pressure, subgrade settlement, and horizontal displacement.

Numerical and Theoretical Study on the Settlement of Capped Piles Composite Foundation under Embankment

Capped piles are efficient in settlement control and have been widely used in the reinforcement of soft soil foundations for high‐speed railways and highways. In this study, scenarios involving both capped piles and ordinary piles without caps are numerically studied using the finite element software (ABAQUS). The settlement characteristics of capped piles composite foundation considering the effects of both the pile spacing and the ratio of pile cap to pile diameter are achieved. Based on the numerical results, assuming that the capped pile and the soil under the cap jointly bear load and settle together, a settlement calculation model for capped piles composite foundation is established. By both replacing the compression modulus with the deformation modulus obtained from the field static load test and calculating the area replacement ratio, the formula for calculating the total settlement of the capped piles composite foundation is derived using the layer‐wise summation method. In addition, a real embankment engineering with capped piles composite foundation is adopted to validate the accuracy of this method; by comparing with other methods, the results show that this method is in better agreement with the field monitoring data. Therefore, the proposed method is recommended in the relevant engineering design.

Summary of the Development of New Technologies for Submarine Immersed Tunnel Foundation Reinforcement and Settlement Control

Based on the immersed tunnel foundation improvement modeling and analysis of data through investigations and researches on immersed tunnel diseases at home and abroad, this paper proposes that the adverse loads and poor geology are main causes inducing settlement and diseases. On top of the review on technical innovations in typical immersed tunnel foundation improvement abroad, the innovation and advancement of immersed tunnel foundation improvement of Hong Kong-Zhuhai-Macao Bridge Project is introduced with emphasis and these technical innovations mainly comprise the technology of double-layer bed with both rigidity and flexibility, the technology of SCP(Sand Compaction Piles) plus surcharge loading in ground improvement, the settlement computation method based on CPTU of rebounding and recompression and determination of settlement control criteria and others new development. Furthermore, through analysis the corresponding foundation improvement countermeasures are provided in this paper to meet such construction challenges faced in the immersed tunnel foundation improvement of Shenzhong Link and those challenges are super-wide width varied immersed tunnel element, soft soil ground of sand pit, weathered rock softening in water, sandy soil liquefaction, intense siltation. Finally, as the State key study and development program, it is pointed out that the technical study on diseases inducing mechanism and corresponding pro-active prevention and control of submarine immersed tunnel founded on poor ground conditions shall be carried out based on the full consideration of interactive actions between the structure and its foundation and the technical route and main study contents are further proposed for reference of relevant technical professionals.

PREDICTION OF GEOMECHANICAL STATE OF STABILIZED SOIL FOUNDATION OF MINE ENGINEERING BUILDING

Purpose: Prediction of geomechanical state of soft-soil foundation of buildings before and after compaction, reinforcement or stabilization. Calculation of parameters of pressure injec-tion while stabilizing the soft man-made soil foundation, development of recommendations for parameter adjustment of pressure injection.Methods: Numerical methods and computer mod-eling of the soil foundation using the finite element method for studying its geomechanical state of a mining building with regard to heterogeneities of the local geological structure and changes in the physical and mechanical properties of soils.Research findings: The obtained results are based on engineering and geological surveys of the soil foundation of the mining building composed of man-made bulk soils. The stress-strain state of the soil foundation is simulated. As a result of injection compaction the geomechanical state of the soil mass chang-es.Practical implications: Recommendations are given for the parameter adjustment of the injection method. It is shown that the pressure injection method is undoubtedly effective for the soil stabilization for buildings.

Investigating asymmetric spatial butterfly-shaped steel arch bridges: a case study

Jiusha Bridge in Hangzhou city, China, is an asymmetric spatial butterfly-shaped steel arch bridge. The bridge deck and steel arch rib form a half-through structure at one end and a through structure at the other. The bridge sits on a soft soil foundation with poor thrust resistance; therefore, different force transmission structures adopted at the asymmetric ends to balance the large arch thrust during internal force transmission of the structure were researched. The mechanical behaviour of the asymmetric steel arch bridge under dead load and live load was compared with that of a symmetric half-through and through steel arch bridge. Subsequently, a full-bridge finite-element (FE) model was established in order to adjust the stiffness contribution of the middle arch and side arches to the bridge, optimise the hanger forces in the finished bridge state and analyse the bridge's stress, stiffness, stability and dynamic characteristics. The stresses in some key members and joints were calculated by means of a refined FE model consisting of beam elements, truss elements and plate elements. Some of the special construction technologies used on Jiusha Bridge are also briefly discussed.

Analysis of settlement of existing buildings caused by unreasonable design of foundation

As for the settlement accidents of existing buildings, people pay more attention to the construction quality than the rationality of foundation design. This paper analyzes and discusses the problem of excessive settlement of existing buildings caused by unreasonable design based on three typical engineering cases. The conclusion is that as for the upper filled soil and lower soft soil foundation, the heavy tamping method is not suitable without auxiliary measures if the foundation settlement is strictly controlled; cement-soil mixing pile method is not suitable for high-rise buildings based on soft soil foundation; the foundation design should be based on deformation control when high compressibility soil layer exists, the pile body should penetrate the main compression deformation layer, and the pile end should fall on the good bearing stratum when using pile foundation or rigid pile composite foundation.

Effect analysis of vacuum prepressing reinforcement of soft soil foundation

The supercharged vacuum pre-pressure method is to increase the supercharge system on the basis of the direct vacuum pre-pressure, and to increase the pressure in the middle of the vacuum process, thus achieving the goal of saving efficiency and increasing construction costs. Based on the reinforcement project of a blowout foundation in Lianyungang, this paper analyses the process of soil surface subsidence, pour water pressure, stratified subsidence and groundwater level when the soft foundation is reinforced by supercharged vacuum prepressing method by field test method. The paper will provide data support for future actual projects.