scholarly journals Data-Driven Field Observational Method of a Contiguous Bored Pile Wall System Affected by Accidental Groundwater Drawdown

Geosciences ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 268
Author(s):  
Elizabeth Eu-Mee Chong ◽  
Dominic Ek-Leong Ong
Keyword(s):  
Cement Grout ◽  
Data Driven ◽  
Observational Method ◽  
Deep Excavation ◽  
Corner Effect ◽  
Bored Pile ◽  
Ground Anchors ◽  
Groundwater Drawdown ◽  
Tunnel Section ◽  
Wall System

This paper presents the use of a 700 mm-diameter contiguous bored pile (CBP) wall for a main basement deep excavation project with cut-and-cover tunnel. Due to the presence of cement grout columns between piles behind the CBP wall, the main basement was considered to be ‘impermeable’. However, site observations have shown that installation of ground anchors have unintentionally punctured the water tightness of the wall, creating leakages through the CBP wall and the possibility of localized groundwater lowering, as evidenced by the relatively large settlements. In the absence of cement grout columns at the cut-and-cover tunnel section, immediate groundwater drawdown was observed with the excavation rate. Settlement induced by the excavation and groundwater drawdown only slowed down upon the casting of skinwall to prevent groundwater from flowing through the wall. The accidental groundwater leakage led to small wall deflection. The ratio of maximum settlement to maximum deflection is atypical to those reported in the literature. The analysis also revealed that corner effect is significant with smaller settlement registered at the corners of the wall.

scholarly journals Load transfer on instrumented prestressed ground anchors in sandy soil

2021 ◽  
Vol 14 (6) ◽  
Author(s):  
Alex Micael Dantas de Sousa ◽  
Yuri Daniel Jatobá Costa ◽  
Luiz Augusto da Silva Florêncio ◽  
Carina Maria Lins Costa
Keyword(s):  
Skin Friction ◽  
Sandy Soil ◽  
Load Transfer ◽  
Retaining Wall ◽  
Load Variations ◽  
Bored Pile ◽  
Ground Anchors ◽  
Anchor Testing ◽  
Wall System ◽  
Unbonded Length

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.

scholarly journals DISPLACEMENT MONITORING AND SENSITIVITY ANALYSIS IN THE OBSERVATIONAL METHOD

2013 ◽  
Vol 35 (3) ◽  
pp. 25-43 ◽  
Author(s):  
Karolina Górska ◽  
Zbigniew Muszyński ◽  
Jarosław Rybak
Keyword(s):  
Sensitivity Analysis ◽  
Computational Model ◽  
Cohesive Soil ◽  
Calculation Model ◽  
Observational Method ◽  
Deep Excavation ◽  
Sheet Pile ◽  
Displacement Monitoring ◽  
Excavation Support ◽  
Construction Works

Abstract This work discusses the fundamentals of designing deep excavation support by means of observational method. The effective tools for optimum designing with the use of the observational method are both inclinometric and geodetic monitoring, which provide data for the systematically updated calibration of the numerical computational model. The analysis included methods for selecting data for the design (by choosing the basic random variables), as well as methods for an on-going verification of the results of numeric calculations (e.g., MES) by way of measuring the structure displacement using geodetic and inclinometric techniques. The presented example shows the sensitivity analysis of the calculation model for a cantilever wall in non-cohesive soil; that analysis makes it possible to select the data to be later subject to calibration. The paper presents the results of measurements of a sheet pile wall displacement, carried out by means of inclinometric method and, simultaneously, two geodetic methods, successively with the deepening of the excavation. This work includes also critical comments regarding the usefulness of the obtained data, as well as practical aspects of taking measurement in the conditions of on-going construction works.

Risk Control in the Deep Excavations with the Application of the Observational Method

2011 ◽  
Vol 243-249 ◽  
pp. 3403-3410
Author(s):  
Jian Qin Ma
Keyword(s):  
Risk Control ◽  
Observational Method ◽  
Deep Excavation ◽  
General Process ◽  
Deep Excavations ◽  
Rapid Deterioration ◽  
Design And Construction

The uncertainty of the ground, in which a deep excavation to be conducted, is always inherent. The risk control of the excavation is therefore necessary. Based on the principle features of a deep excavation, a general process of risk control is presented in terms of design and construction, with the application of the observational method. To avoid the conflicts of the involved groups’ interests, a close co-operation between the groups in a well planned procedure is vital to the success of the risk control, especially to the case with rapid deterioration stages included.

Support of 25 m deep excavation using ground anchors in Russia

2015 ◽  
Vol 168 (4) ◽  
pp. 281-295 ◽  
Author(s):  
Devon Mothersille ◽  
Rasin Duzceer ◽  
Alp Gokalp ◽  
Bora Okumusoglu
Keyword(s):  
Deep Excavation ◽  
Ground Anchors

Test study on the characteristics of mudcakes and in situ soils around bored piles

2009 ◽  
Vol 46 (3) ◽  
pp. 241-255 ◽  
Author(s):  
Zhong-Miao Zhang ◽  
Jun Yu ◽  
Guang-Xing Zhang ◽  
Xin-Min Zhou
Keyword(s):  
Bearing Capacity ◽  
Void Ratio ◽  
Cement Grout ◽  
Test Results ◽  
Lower Shear ◽  
Bored Pile ◽  
Test Study ◽  
Disturbed Zone ◽  
Bored Piles

Constructing a bored pile produces a disturbed zone of soil adjacent to the pile, referred to as a “mudcake.” The physical properties of the mudcake are different from those of the surrounding soil. This paper reports research on bored piles in silt, clay, and sandy silt layers in Hangzhou, China. Laboratory tests were performed on samples of in situ soil, mudcake, and mudcake mixed with cement grout. The test results showed that mudcakes have a higher water content, higher void ratio, higher compressibility, lower friction, and lower shear strength than in situ soils. They also showed that mudcake properties could be improved by the addition of cement grout. Mudcakes form a weak, thin layer between a pile and a borehole wall, which can lead to a decrease in bearing capacity and an increase in settlement of the pile. Grouting improves the characteristics of mudcakes remarkably, thereby increasing the bearing capacity of piles, which is demonstrated by the case history in this paper.

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

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Gang Lei ◽  
Panpan Guo ◽  
Fucai Hua ◽  
Xiaonan Gong ◽  
Lina Luo
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Ground Surface ◽  
Bending Moment ◽  
Deep Excavation ◽  
Top Down ◽  
Ground Anchors ◽  
Pile Diameter ◽  
Axial Forces ◽  
Bracing System

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.

scholarly journals Deep excavation in urban areas – defects of surrounding buildings at various stages of construction

2018 ◽  
Vol 146 ◽  
pp. 02012 ◽  
Author(s):  
Jarosław Rybak ◽  
Alexander Ivannikov ◽  
Elena Kulikova ◽  
Tomasz Żyrek
Keyword(s):  
Urban Areas ◽  
Soil Mass ◽  
Technical Condition ◽  
Deep Excavation ◽  
Sheet Pile ◽  
Ground Anchors ◽  
New Construction ◽  
Diaphragm Walls ◽  
Wall Construction ◽  
City Centres

Deep excavation and tunnelling works in city centres always bring some risks to surrounding structures, especially in the case of old town centres, where the technical condition and structural stiffness of historical buildings is rather doubtful. When the new desired excavation depth goes deeper than the foundation of the surrounding buildings or when tunnelling works are conducted directly under them, the existing objects are subject to stress, vibrations and displacements imposed at almost every stage of building the new construction. The presented paper outlines, on the basis of the authors’ experience, the typical damages appearing during the supporting wall construction (sheet pile driving, piling and formation of diaphragm walls) and tunnelling works. Other damages appear due to soil mass unloading (caused by excavation stages) and horizontal loading during pre-stressing of struts or ground anchors. The selected case studies of steel sheet pile wall installation is given with regard to typical failures caused by an unplanned excavation and its impact on neighbouring structures.

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