Verification Analysis of the Relationship Between Soil Pressure and Displacement of Retaining Structure

Variation laws of earth pressure accounting for the displacement of are taining wall can be well described by mathmatical fitting in the study of the relationship between earth pressure and retaining wall displacement. The common mathematical function expressions of earth pressure displacement of retaining wall can be divided into sinusoidal function model, exponential like function model, hyperbolic function model, fitting function and semi-numerical and semi-analytical model function, etc. The characteristics and shortcomings of the current expression of earth pressure displacement function are summarized. Then combined with the field test and model test, the applicability and characteristics of various mathematical functions in predicting the displacement of earth pressure with retaining structures are analyzed. The results show that when the displacement is small, the sinusoidal function model and the quasi-exponential function model are close to the measured results. When the displacement of retaining structure is large, the fitting results of hyperbolic model and semi-numerical and semi-analytical model are better. For the prediction of earth pressure displacement relationship in passive area, the buried depth has a great influence. And the error between the theoretical value and the actual value has a great influence on the fitting result of the model.

Full-Scale Field Test On Retaining Structure Enhanced With Soil Nails And Prestressed Anchors

Retaining structure enhanced with soil nails and prestressed anchors is found good at constraining the horizontal displacement and therefore ensuring the stability of the foundation pit during excavation. Based on these advantages, such retaining structure is widely used in foundation excavation practice. This paper presents results of a series of in-situ tests conducted to investigate the mechanical behaviors of retaining structure enhanced with soil nails and prestressed anchors. Behaviors of three different retaining structures enhanced with i) soil-nails; ii) soil-nails and prestressed anchors without unbonded part; iii) soil-nails and prestressed anchors with a 2.5m unbonded length, were monitored during staged excavation to investigate the influences of i) the prestressing force and ii) unbonded length of the prestressed anchors on the performance of the entire retaining system. It was found that the affecting the stress and deformation of composite retaining system, which is in agreement with the other published results in the literature. The variation of the magnitude and distribution of soil nail force responding to the anchor prestressing force however showed no systematic trend. The unbonded length of anchors, which is suggested to be the main factor affecting the structural stability in dense materials in the literature, is found to have little influence in loose fill materials used in this study. Studies presented in this paper are useful for the rational design and serviceability analysis of the composite soil-nailed retaining structure enhanced with prestressed anchors.

Transverse Force Analysis of Adjacent Shield Tunnel Caused by Foundation Pit Excavation Considering Deformation of Retaining Structures

In order to research the theory for the variety of transverse forces of the adjacent shield tunnels caused by foundation pits excavation, the effect mechanism of foundation pit excavation on the adjacent shield tunnel was analyzed. The sidewall unloading model of the foundation pit, considering the deformation of the retaining structures, was introduced to calculate the additional stress of soil caused by foundation pit excavation. On this basis, the additional confining pressure variation model of the adjacent shield tunnel was established, considering the influence of the longitudinal deformation. Take the deep foundation pit project by the side of the shield tunnel of Hangzhou Metro Line 2 as a case study, the variation in confining pressure distribution of the adjacent shield tunnel caused by foundation pit excavation was analyzed, and a simplified finite element model was established to calculate the internal force of the segment ring structure. Moreover, the influence factors were analyzed, such as the deformation of the foundation pit retaining structure, the clearance between the foundation pit and the adjacent tunnel, and the buried depth of the tunnel. The present study suggests that the foundation pit excavation reduces the confining pressure of the adjacent shield tunnel, increases the absolute value of bending moment and shear force, and decreases the axial force at the top and bottom of the tunnel’s segment ring. With the increase in the deformation of the foundation pit’s retaining structure, the absolute value of the additional confining pressure on the adjacent tunnel increases, and the response of the bending moment to the foundation pit excavation unloading is more obvious than the variation in the confining pressure. When the buried depth of the adjacent shield tunnel is deeper than the excavation depth of the foundation pit, the influence of the excavation on the tunnel will be obviously weakened. With the decrease in the distance between the pit and tunnel, the influence of the excavation on the tunnel will be enhanced.

Use of the Alaska Geotechnical Asset Management Database in Evaluation of Retaining Structures After an Earthquake

Since 2010, the Alaska Department of Transportation and Public Facilities, U.S., has been a leader in the development of geotechnical asset management (GAM) as part of a proactive approach to identify and rate the condition of geotechnical infrastructure. Efforts have included, for example, a retaining structure database that has cataloged retaining structures throughout Alaska. On November 30, 2018, a moment magnitude (MW) 7.1 earthquake struck southcentral Alaska, home of more than half of the state’s population. Damage to infrastructure was significant in several roadway corridors in the region. The GAM database was utilized as an important tool to assist in the identification of earthquake damaged retaining structures. Lessons learned from this effort are outlined in this paper. They include discussion on the elements of the database that were effective and others that may be improved on in the future. The information gathered from the field observations was also collected in such a manner that it could be added to the GAM database in the future as another snapshot in time for the retaining structures evaluated after the earthquake.

Effect of the anchors' free length that made of tubular screw rods on the forces distribution in pile-anchor retaining structures on highways

Pile-supported retaining structures are widely used to protect road sections from landslide processes. The article describes the design and calculation peculiarities of pile-supported retaining structures reinforced with a drill and inject anchors from tubular screw rods. The authors considered two options for this type of anchors setup: without free length and with a pre-set free length. In the software geotechnical complex Plaxis, on the finite element method basis, mathematical modeling and calculation of a pile-supported anchor retaining structure with different free anchors lengths from tubular screw rods for various soils types have been performed. Numerical relationships have been obtained between the anchors' free length and the resulting forces in the retaining structure. The performed calculations series of the test scheme showed that with an increase in the free anchors' length in the retaining structure, there is a decrease in the applied load in its load-bearing elements due to the horizontal displacements growth. The article presents the survey results of a real road section, on which a landslide displacement is being prepared, and considers a design solution for a pile-supported anchor retaining structure to ensure its safe operation. Performed a series of calculations for various landslide process development stages in this area showed that the effect of the anchors' free length also largely depends on the state of the adjacent soil mass. Obtained results clearly show that the design of a free length section for anchors made of tubular screw rods makes it possible to design more cost-effective pile-supported anchor holding structures without reducing their reliability.

Systematic Analysis Method for the Unusual Large Displacement in the Excavations in Soft Soil Area

Based on a subway station excavation construction project in the soft soil area in Nanjing, an informationized monitoring scheme was conducted during the construction of excavation, and the theories of displacement prediction were introduced into the scheme for the evaluation of the horizontal displacement of the retaining structure and the settlement of the surroundings around the excavation. Based on these theories and the monitoring data, a numerical simulation based on the commercial FEM numerical analysis software, Midas GTS NX, was conducted to simulate the whole construction process. To handle the large displacement of the retaining structure observed during the construction, the actual soil layers’ status discovered by excavating, which can reflect the physical characteristics of the soil, the construction condition, and the variation trend of the monitoring data, was used in the back analysis of the factors that induced the large deformation of the retaining structure, and the analysis result was fed back to the countermeasurement organization and design such as erecting temporary steel strut. The effectiveness of these measurements in the aspect of the reduction of the deformation rate was verified, which can provide reference to the design and construction of a similar project in soft soil area.