Composite Soil Nailing Research Articles

Stability Analysis of Composite Soil Nailing Wall Based on Improved Energy Method

Composite soil nailing wall is widely used in slope support because of its low cost and safety, but its global stability still needs more accurate calculation. Based on plastic limit upper limit analysis and vertical strip partition method, the calculation formula of stability coefficient was derived for prestressed anchor composite soil nailing wall. FLAC3D and GeoStudio were used to calculate and analyze an engineering project supported by composite soil nailing wall in Lanzhou City, and the feasibility and correctness of the derived formula were verified. Finally, the grey correlation analysis of the sensitivity of the derived formula was analyzed. The results show that for calculating the stability coefficient, the limit equilibrium method needs to consider the complex force analysis, while the energy method can well avoid the inter-slice force, making the physical meaning of the formula clearer. The formula introduced in this paper is more efficient and feasible. The stability coefficient is most sensitive to the internal friction angle, followed by slope angle, cohesion, and finally unit weight of soil.

Comparative investigation on deformation monitoring and numerical simulation of the deepest excavation in Beijing

The investigation on the mechanical mechanism of the retaining and protection structure of superdeep excavations is an important subject, and its deformation control research is particularly important. Taking the deepest foundation pit with full-section overall excavation in Beijing as an example, this paper studies the stress and deformation characteristics of composite soil nailing wall and anchored soldier pile wall combined retaining system under complex geological conditions of multi-layer groundwater during the process of excavating 31.4 m deep. The Midas simulation software and monitoring data are used to analyze the construction process of foundation excavation. The simulated results and monitored values of anchor force, ground settlement, and soil deformation during foundation excavation are analyzed and discussed to verify the reliability of the model. The spatial effect of internal force and deformation of composite retaining and protection structure for superdeep foundation excavation is discussed, and the parameters affecting the retaining structure are analyzed and investigated. The research shows that with the increase of excavation depth, both the extremum of the bending moment and the extremum of lateral displacement of retaining piles are increasing, and the position of the extremum of bending moment is located near the excavation face; then, the bending moment reaches the maximum when the foundation pit is excavated to the bottom. Within a certain range, increasing the rigidity or the embedded depth of the retaining pile or the prestress of the anchor can effectively control the lateral displacement of the excavation. However, when the rigidity of retaining pile is too large, its lateral displacement does not change significantly. Similarly, when the embedded depth is too long or the prestress of the anchor is too powerful, the effect of controlling deformation is also not obvious. The research results will provide theoretical basis and practical experience for the design and construction of superdeep excavations.

Numerical Investigation of a Foundation Pit Supported by a Composite Soil Nailing Structure

In special geology conditions such as silt-soil, foundation pits are prone to instability and severe deformation. In this paper, a composite soil nailing structure was studied and its effect on a silt-soil symmetrical foundation pit investigated. The factors affecting the stability of the pit as well as its deformation characteristics were also explored. The results show that excavation depth of the foundation pit has a significant impact on its stability. The soil outside the foundation pit is in the form of a parabola, and the uplift of the soil mainly occurs at the bottom. The horizontal displacement of soil on the side wall of the foundation pit presents a “bulk belly” form. In addition, the axial force of soil nails is larger in the middle part, and smaller at both ends in the shape of a spindle. Moreover, the horizontal displacement is positively correlated with the inclination and spacing of the soil nails, but negatively correlated with the diameter and depth of the mixing pile inlay. Furthermore, the inclination and spacing of the soil nails, the diameter, and embedded depth of the mixing pile have their own critical values for stability of the foundation pit. Specifically, in this paper, with respect to soil nails, inclination should be below 30° and prestress value should not exceed 20 kN. With respect to the mixing pile, the diameter should be less than 1.5 m; when the embedded depth of the mixing pile exceeds the critical depth, the limiting effect of the mixing pile on horizontal displacement is not significant. This research provides important takeaways for the design of a composite soil nailing structure for symmetrical foundation pits.

Study on the Supporting Features of Composite Soil Nailing Wall

This paper was based on a deep foundation pit support project in Beijing. FLAC3D software was used to simulate the excavation and support process of the foundation pit in detail according to design parameters and geological conditions. The experiment data of the horizontal and vertical displacements of walls, the axial forces of soil nailing and prestressed anchor cables during excavation and support process of the foundation pit provided a technical reference for the site construction and ensured the safety of the whole project.

Research on the reasonable pile spacing of micro pile composite soil nailing

Through the numerical simulation software FLAC3D, study on the synergetic effect of micro pile composite soil nailing will be studied. By adjusting the micro pile spacing and analysing the displacement field and stress field of soil, we can find that supporting effect of the soil nail hasn’t work yet when the micro pile spacing is 2D. The soil arching between piles has been formed in the pile spacing 4D ∼ 6D. The composite effect of micro pile and soil nailing will be the best and the soil arch behind piles will be firstly formed in 6D, the horizontal saddle soil arch will be formed between the nails. The nail head coincidence pressure area and micro pile pressure area are overlapping to maintain stability in the soil between piles. When the micro pile spacing is 9D, the arch behind piles will be failure, the soil flows around, but the saddle arch between the nails into circular arch, the supporting effect of the soil nailing is enhanced. When the micro pile spacing is 12D, the arch of the nails becomes smaller, sliding surface appears primitively. Based on the conclusions above, it is suggested that the micro pile spacing between 2D ∼ 6D is suitable for the micro pile and soil nailing composite support. The conclusion can provide theoretical basis for the design and construction of micro pile composite soil nailing.

The application of composite soil nailing wall in China

The application of composite soil nailing wall in China

Simulation on the Supporting of Underground Storage Foundation Pit by Anchor and Soil Nail

At present, the composite supporting technology of prestressed anchor and soil nailing has been more and more widely used in the foundation pit engineering, but the related existing theory and method can not satisfy the engineering practice, so it is necessary to do the discussion of this technology. In this paper, the foundation pit of underground storage in Zheng Zhou City was chose as an example, the simulation model for composite supporting of anchor and soil nail was set by FLAC software, the ideal elastic-plastic constitutive model was selected for soil, the cable unit was selected for the prestressed anchor and soil nailing, based on the interaction between supporting system and soil, the dynamic process for the excavation and support of foundation pit was simulated. The law for the effect of the excavation on disturbance, soil changes in displacement and internal force distribution of soil nail and anchor was obtained in this study, the connection line of the maximum axial force of soil nail and anchor were actually the potential failure surface of soil foundation pit, the position change of maximum axial force reflected the trends of internal displacement of excavated soil. The related conclusions have certain reference significance for the composite anchor and soil nailing supporting design.

Numerical Analysis of Composite Soil Nailing Wall

Abstract. The horizontal displacement of soil in slope and the change law of ground surface settlement are dynamically analyzed by building three dimensional-model of foundation pit with the finite element software, ABAQUS, to simulate the construction process of excavation and support, to figure out the influence of micro pile and waterproof curtain on composite soil nailing wall. The study indicates that mechanical model of soil nailing, waterproof curtain, micro pile, pre-stressed anchor interacting with soil can better simulate the construction process of composite soil nailing wall support and have higher calculation accuracy. The calculation can provide a reference for the design and construction of composite soil nailing wall.

Application of Prestressed Anchor Composite Soil Nail Wall in Deep Foundation Pit Engineering at Lanzhou Region

The paper introduces the application of prestressed anchors and soil nails support system in complex soil layer deep foundation pit engineering at Lanzhou region based on the deep foundation pit engineering in Gansu Provincial Hospital of TCM as the background and discusses its key technology. The effect shows that scheme of the design of foundation pit support engineering is reasonable and effective.The engineering meets requirements of design and environment.The monitoring results show that prestressed anchors can control the horizontal displacement and the change rate of slope′s vertical settlement effectively. The experience of engineering is significance for similar engineerings at Lanzhou region.

The Analys of Stability of Composite Soil Nail

Composite soil nailing technology is a new technology which developed on the basis of the soil nailing supporting technology. This new technology has a very important practical significance to the construction, for which the scale is larger and larger, the condition is more and more complex and the excavation of foundation is more and more deep. Composite soil nailing technique is mainly introduced in this paper by its main form of structure and the main principle, which draw a conclusion that different forms of the combination of support types have different effects on the stability of structure, by analyzing the support stability. This thesis shows that we should adjust measures to local conditions, choose the right organic combination. At the same time it also provides the basis for the practical application of engineering support.

Finite Element Simulation and Stability Analysis of Composite Soil Nailing

Under the condition of plane strain, a 2D elastoplastic FEM is used to analyze the behavior of composite soil nailing bracing of deep excavation, then finite element method of stability analysis is applied to evaluate the stability of the soil-nail wall. The authors analyzed the difference between composite soil nailing and normal soil nailing. Through analyzing the effect of bracing parameters on the deformation behavior and stability of the excavation, some useful conclusions are obtained to provide certain references for the design and construction of composite soil nailing.

Numerical Simulation on a Deep-Foundation Pit of Shenzhen Holiday Plaza Project

Based on test data of the prestressed anchor cable composite soil nailing wall deformation and internal force of structure of Shenzhen Holiday Plaza foundation pit, the numerical simulation model of foundation pit is established by FLAC3D software. Through the reasonable selection of soil constitutive model and structural unit, the numerical simulation model is consistent with the project practice. The simulation results on horizontal displacement of foundation pit, the internal force of the structure, the surface layer stress and damaged form are reasonable. This does not only provide a strong basis for the optimum design of the foundation pit, but also provide a scientific guidance for engineering application.

Parameter Sensitivity Analysis on Deformation of Composite Soil-Nailed Wall Using Artificial Neural Networks and Orthogonal Experiment

Based on the back-propagation algorithm of artificial neural networks (ANNs), this paper establishes an intelligent model, which is used to predict the maximum lateral displacement of composite soil-nailed wall. Some parameters, such as soil cohesive strength, soil friction angle, prestress of anchor cable, soil-nail spacing, soil-nail diameter, soil-nail length, and other factors, are considered in the model. Combined with thein situtest data of composite soil-nail wall reinforcement engineering, the network is trained and the errors are analyzed. Thus it is demonstrated that the method is applicable and feasible in predicting lateral displacement of excavation retained by composite soil-nailed wall. Extended calculations are conducted by using the well-trained intelligent forecast model. Through application of orthogonal table test theory, 25 sets of tests are designed to analyze the sensitivity of factors affecting the maximum lateral displacement of composite soil-nailing wall. The results show that the sensitivity of factors affecting the maximum lateral displacement of composite soil nailing wall, in a descending order, are prestress of anchor cable, soil friction angle, soil cohesion strength, soil-nail spacing, soil-nail length, and soil-nail diameter. The results can provide important reference for the same reinforcement engineering.

Simulation Analysis on Tension and Deformation of Composite Soil Nailing

For studying the mechanism of the composite soil nailing, this paper applies FLAC-3D to simulate pure soil nailing, soil nailing-soil anchor, soil nailing-micro pile-soil anchor. The analytical results as follows: (1)Because of the anchoring of the anchor, the axial tension of soil nailing in each row is much smaller than the one in the pure soil nailing supporting, and the tension of soil nailing which are closed to soil anchor decreases obviously. (2)The extrusion action of prestressed anchor makes the potential slip surface backward shifts and the sliding radius increases, which is better for the stability of foundation pit side (3)Micro-pile increases the strength of the soil in a certain range and improves the initial stress field before the excavation. (4)The inner force of the whole soil nailing and the prestress anchor declines but the drop is not large after the establishment of the micro-pile support in advance. (5)Prestressed anchor and micropile play a very important role in controlling the deformation of foundation pit.

Prestressed Anchor Bolt Impact on the Deformation of Composite Soil Nailing

Finite element software was employed to establish a model to simulate the compound soil nailing. The model simulates the process of constructing prestressed compound soil nailing. Compared the condition prestressed with no prestress, analyzed the Impact of prestress anchor on the deformation in the process of construction and the effect on axial force of soil nail. Applying prestress is able to control the horizontal displacement obviously, but has not obvious effect on vertical displacement, especially place the anchor bolt at the lower part of the slope. In the process of construction, prestress has an advance effect on the deformation of foundation pit and the axial force of soil nails near the anchor bolt.

Numerical Analysis of Composite Soil Nailing Retaining Wall under Earthquake

The seismic response of slope supported by composite soil nailing is analyzed by using finite element software ADNIA, in which the EL-Centro wave is selected as input earthquake wave.The analytical contents include the displacement and acceleration of supporting slope, as well as the time history responses of the axial forces of anchors. In the establishment of finite element model, the interaction between soil body and supporting structure is considered. The elastic-plastic M-C model with nonlinear static and dynamic behavior is used to simulate the soil body, and the dual linear strengthen model is adopted to simulate the supporting structure, then the interaction between soil body and supporting structure is simulated with contact element. The results show that the composite soil nailing slope supporting structure has better seismic performance than the general soil nailing slope supporting structure. The maximum horizontal displacement of the latter occurs at the slope top, but that of the former occurs at the slope upper. Especially after the imposition of the prestress, the slope displacement under earthquake reduces significantly, and the axial forces of anchors under earthquake enlarge significantly. Moreover, the axial forces of anchors reach maximum values near the slipping surface. The displacement and the acceleration of slope increase along the slope height. The conclusions obtained provide basis for the seismic design of permanent supporting slope and reference for similar projects.

Simulation and Analysis on Supporting System of Composite Soil Nailing Technology in the Process of Digging

According to the typical engineering example and the structural features of the supporting system of composite soil nailing technology, the computing mode of deformation of composite soil nailing technology under force is established. Numerical analysis and supervision in the process of construction on composite soil nailing technology are made with the collocation of typical project example. The data of monitoring on the spot and numerical simulation show that the supporting system of composite soil nailing technology meets the requirement of real deformation under force and can simulate the real features of the stress field and displacement field in the process of construction. The design methods meet the requirement of accuracy, and the result presents important technical reference for design and construction of the supporting system of composite soil nailing technology.

Optimization Simulations of Support System by Composite Soil-Nail Retaining Structure

Mechanism of composite pre-reinforced micro pile soil-nail and pure soil-nail retaining structure in foundation-pit engineering are analyzed in this paper through general three dimension nonlinear numerical simulation software. Research contents include whole construction process simulation of construction such as excavation by steps, piles and soil-nail installation and panel manufacture etc. By the comparison of mechanical characteristics between the pure soil-nail and composite soil-nail retaining structures in the same slope engineering example, differences of tension distribution range of soil layer, deformation features, mechanical characteristics of support and axial force distribution along nails etc. are analyzed. Research results are verified by in-site projects and measured data. The action mechanism and working performance of composite soil-nail retaining support are also systematically studied and theoretical basis can be provided in the similar application.

Study on Composite Soil Nailing Wall in Soft Soil Area of Complex Condition with Emphasis on Analysis by Finite Element Analysis

Based on a typical projects, the horizontal displacement in depth, horizontal displacement and vertical subsidence of pile top, and settlements of surrounding buildings are monitored with the process on digging of deep foundation pit. The study on digging process of foundation pit is analyzed by using finite element software. Using mapped meshing method, from mixing the pile near the semi-circular area (radius = 50m), the meshing appropriate encryption in order to improve the accuracy of the external semi-circular area (radius = 65m) mesh is less appropriate sparse.Layer by layer to kill the layers of the soil unit and activate the soil nails (spring element), the simulated excavation and synchronization of soil nails construction.Verify the arc form of failure surface in side of deep foundation pit in soft soil area. Which is valuable for reference to similar structure engineering of foundation pit.

FEM Analysis of Composite Soil-Nailing Considering Tensile Failure

Composite soil-nailing is a new technology developed from abroad in recent years, to be used in excavation of soil, slope stability. This paper studied the stress and deformation of composite soil nailing wall by nonlinear FEM. According to the structure characteristic, the finite element analysis for composite soil nailing construction process is carried out. Based on geotechnical elastic-plastic constitutive model, the adopted failure criterion was a composite Drucker-Prager criterion with tension cut-off. A kind of rotational Goodman interface element is employed to simulate the behavior of interface between the soil-mixed cement which forms the barrier of seepage flow along the boundary of foundation pit, and soil ground. Through the comparative analysis with on-site monitoring data, the finite element calculation results have good precision.