Hazard Reduction in Deep Excavations Execution

In this article, the authors consider a completely new approach in design, which is related to the use of previously un-adapted technologies known to bridge engineering in geotechnical issues for prestressing of diaphragm wall during deep excavations execution. The bridge technology described here is the prestressing of concrete structures. Hazards related to deep excavations and methods of digging them, such as the ceiling method and top&down method, are presented. Current problems in supporting deep excavation slopes are related to the use of extensive quantities of materials (such as steel struts, ground anchors, or concrete and reinforcement steel). The authors’ method helps to achieve a higher level of sustainability, which is important in a modern approach to geotechnical engineering. The non-linear arrangements of the cables according to the occurrence of the prestressing moments for a given phase are presented. Results related to numerical analysis—showing the correctness of the method and cost optimization results, showing possible savings are presented. The article is a part of the set. In the second (already published) article titled “Modern Methods of Diaphragm Walls Design”, the authors present the concept of the calculation methodology for diaphragm wall design.

Evaluation of Anthropogenic Substrate Variability Based on Non-Destructive Testing of Ground Anchors

The purpose of this paper is to describe the variability of soil rheological properties based on research carried out using load tests of ground anchors under complex geotechnical conditions. The heterogeneity of soil should always be considered when designing geotechnical constructions. In the present case, the earthwork created at the Warsaw Slope revealed an embankment of anthropogenic origin, located in a geologically and geomorphologically complex area of the Vistula valley slope. Excavation protection was anchored mainly in soils of anthropogenic origin. When the acceptance tests of the ground anchor were completed, the subsoil randomness was confirmed using nondirect, geostatistical methods. A standard solid rheological model with nonlinear fitting to the data was used. This model was established to describe the creeping activity of the ground anchor more accurately. The characteristics of man-made embankments were described using the parameters obtained with the rheological model of the subsoil.

Observed Performance and FEM-Based Parametric Analysis of a Top-Down Deep Excavation in Soil-Rock Composite Stratum

This paper investigates the performance of a top-down deep excavation in soil-rock composite stratum. The behavior of the excavation bracing system, consisting of ground anchors and end-suspended piles, has not been well understood due to the lack of relevant research. Based on the observed data of a typical deep excavation case history for the May Fourth Square Station in Tsingtao, China, the characteristics of the horizontal and vertical pile displacements, ground surface settlements, building settlements, axial forces in ground anchors, earth pressure, and pore water pressure during excavation were analysed. Two-dimensional finite element simulations were carried out to further explore the deformation and internal force responses of end-suspended piles and to capture the effects of pile diameter, embedded depth, and rock-socketed depth on the horizontal displacement and bending moment distributions along the pile shaft. It was found that the pattern of the vertical pile displacements could be categorized into three types: rapid settlement, slow settlement, and rapid heave. The magnitudes of the ground and building responses can be well controlled within allowable limits by combining the top-down method with the adopted bracing system. Among the investigated parameters, pile diameter is dominant in affecting the horizontal pile displacement. The primary influence zone for pile bending moment varies, depending on the parameters. It is recommended that a combination of top-down method, ground anchors, and end-suspended piles be adopted for restraining excavation deformation and lowering construction costs of similar deep excavations in soil-rock composite stratum.

Impact of slopes on the lateral resistance of steel piles

A soldier pile and lagging wall is one of the most common types of retaining wall. Solider pile walls develop lateral resistance through the stiffness of the piles and the passive resistance of the soil acting upon the embedded portion of the piles. Ground anchors can also be used when additional lateral resistance is required. Using Broms’ methods, a parametric study was completed to investigate the performance of laterally loaded short and long steel piles installed in a variety of cohesive and cohesionless soils. The results were compared to those generated using RocScience finite element software. RocScience software was then used to evaluate the lateral resistance of piles installed at various distances from the crest of a 2:1 slope. Finally, two soldier pile walls, to be installed within a sloping railway embankment, were designed.

Impact of slopes on the lateral resistance of steel piles

A soldier pile and lagging wall is one of the most common types of retaining wall. Solider pile walls develop lateral resistance through the stiffness of the piles and the passive resistance of the soil acting upon the embedded portion of the piles. Ground anchors can also be used when additional lateral resistance is required. Using Broms’ methods, a parametric study was completed to investigate the performance of laterally loaded short and long steel piles installed in a variety of cohesive and cohesionless soils. The results were compared to those generated using RocScience finite element software. RocScience software was then used to evaluate the lateral resistance of piles installed at various distances from the crest of a 2:1 slope. Finally, two soldier pile walls, to be installed within a sloping railway embankment, were designed.

Performance of Ground Anchored Walls Subjected to Dynamic and Pseudo-Static Loading

This study investigates the response of pre-stressed anchored excavation walls under dynamic and pseudo-static loadings. A finite difference numerical model was developed using FLAC2D, and the results were successfully validated against full-scale experimental data. Analyses were performed on 10, and 20-m-height stabilized excavated slopes with 60° to 90° of inclination angle with the horizon to represent an applicable variety of wall geometries. In dynamic analysis, the statically stabilized models were subjected to 0.2 to 0.6g of the dynamic peak acceleration to evaluate the effect of ground acceleration on their performance. Furthermore, pseudo-static analyses were performed on the statically stabilized models with pseudo-static coefficients ranging from 0.06 to 0.22. The results revealed that ground anchored slopes generally showed acceptable performances under dynamic loading, while higher axial forces were induced to ground anchors in higher and steeper models. Furthermore, comparing the results of dynamic and pseudo-static analyses showed a good agreement between the two methods' predictions in the mobilized axial force along the ground anchors. Pseudo-static coefficients were then proposed to replicate dynamic results, considering the slope geometry and dynamic load peak acceleration. The results revealed that higher and steeper stabilized slopes required higher values of pseudo-static coefficients to match the dynamic predictions successfully. The results indicate that pseudo-static coefficient tend to increase with the increase in dynamic load peak acceleration in any given model. Doi: 10.28991/cej-2021-03091703 Full Text: PDF

Load transfer on instrumented prestressed ground anchors in sandy soil

abstract: This study evaluates load variations in instrumented prestressed ground anchors installed in a bored pile retaining wall system in sandy soil. Data were collected from instrumentation assembled in the bonded length of three anchors, which were monitored during pullout tests and during different construction phases of the retaining wall system. Instrumentation consisted of electrical resistance strain gauges positioned in five different sections along the bonded length. Skin friction distributions were obtained from the field load measurements. Results showed that the skin friction followed a non-uniform distribution along the anchor bonded length. The mobilized skin friction concentrated more intensely on the bonded length half closest to the unbonded length, while the other half of the bonded length developed very small skin friction. The contribution of the unbonded length skin friction to the overall anchor capacity was significant and this should be accounted for in the interpretation of routine anchor testing results. Displacements applied to the anchor head were sufficient to mobilize the ultimate skin friction on the unbonded length, but not on the bonded length. Performance of loading-unloading stages on the ground anchor intensified the transfer of load from the unbonded length to the bonded length. Long-term monitoring of the anchor after lock-off revealed that the load at the anchor bonded length followed a tendency to reduce with time and was not significantly influenced by the retaining wall construction phases.