Pile-supported Building Research Articles

Why pile-supported building settled continuously after water level was stabilized during dewatering: Clues from interaction between pile and multi aquifers

Dewatering in a multi-layered aquifer-aquitard system often causes groundwater drawdowns in multiple aquifers, which together lead to obvious settlement of adjacent pile-supported building. This paper documents an in-situ pumping test conducted in a multi-aquifer system. It indicates that an adjacent pile-supported building settled continuously after water level was stabilized. To clarify the possible reasons for this phenomenon, a series of numerical models were established, validated and employed to explore the load transfer behaviour between pile and multi-aquifers during different dewatering conditions. Results indicate that the appearances of several aquitards in the multi-aquifer system significantly block the hydraulic connection between different aquifers, leading to non-synchronized developments of groundwater drawdown and pile shaft resistance at different soil layers during pit dewatering, which eventually causes the lagging settlement of the building. In practical pit dewatering in multi-aquifer system, engineers should appropriately increase the monitoring time for the deformation of adjacent pile-supported buildings for avoiding missing the maximum settlement.

Probabilistic seismic design of pile-supported building structure incorporating inherent variability of subsoil and ground motion uncertainty

Probabilistic seismic design of pile-supported building structure incorporating inherent variability of subsoil and ground motion uncertainty

Effect of Liquefaction Induced Lateral Spreading on Seismic Performance of Pile Foundations

Seismically active areas are vulnerable to liquefaction, and the influence of liquefaction on pile foundations is very severe. Study of pile-supported buildings in liquefiable soils requires consideration of soil-pile interaction and evaluation of the interaction resulting from movement of soil surrounding the pile. This paper presents the results of three-dimensional finite difference analyses conducted to understand the effect of liquefiable soils on the seismic performance of piles and pile groups embedded in stratified soil deposits using the numerical tool FLAC3D. A comparative study has been conducted on the performance of pile foundations on level ground and sloping ground. The soil model consists of a non-liquefiable, slightly cemented sand layer at the top and bottom and a liquefiable Nevada sand layer in between. This stratified ground is subjected to 1940 El Centro, 2001 Bhuj (India) earthquake ground motions, and harmonic motion of 0.3g acceleration. Parametric studies have been carried out by changing the ground slope from 0° to 10° to understand the effects of sloping ground on pile group response. The results indicate that the maximum bending moments occur at boundaries between liquefiable and non-liquefiable layers, and that the bending moment increases with an increase in slope angle. The presence of a pile cap prevents horizontal ground displacements at ground level. Further, it is also observed that the displacements of pile groups under sloping ground are in excess of those on level ground due to lateral spreading. Doi: 10.28991/CEJ-SP2021-07-05 Full Text: PDF

Allowable wall deflection of braced excavation adjacent to pile-supported buildings

To protect adjacent buildings is a major concern for the construction of excavation in urban areas. In practice, the impacts on neighboring pile-supported buildings are normally minimized by limiting the deflection of earth retaining wall. Existing deflection criteria, however, are often empirical. In this work, we employ an analytical model to relate the wall deflection of braced excavation to the response of adjacent pile-supported buildings and thus forming a theoretical tool for determining the allowable deformation of excavation support structures based on the tolerance of buildings to distortion. The model combines closed-form excavation-induced free-field soil movements with elastic continuum solution that explicitly accounts for the interactions between raft, piles, and soils. Following validation against field model test and finite element simulation, the model is utilized to reveal the correspondence between the angular distortion of pile-supported buildings and the maximum retaining wall deflection under different combinations of excavation geometry, soil properties, and parameters of pile foundation potentially encountered in practice. A dimensionless factor composed of these influencing variables is proposed, and its correlation with the ratio of the building angular distortion over the maximum retaining wall deflection provides a rational way to determine the serviceability limit states of braced excavation.

Relevance of Dynamic Soil-Foundation-Structure Interaction for Pile-Supported Buildings

AbstractThe paper examines the problem of the soil-structure interaction for buildings founded on piles throughout the comparative analysis between the seismic demand in compliant base and fixed ba...

Modeling of pile end resistance considering the area of influence around the pile tip

The finite element method (FEM) is widely used to evaluate the seismic performance of pile-supported buildings. However, there are problems associated with modeling the pile end resistance using the FEM, such as the dependence on the mesh size. This paper proposes a new method of modeling around the pile tip to avoid the mesh size effect in two-dimensional (2D) analyses. Specifically, we consider the area of influence around the pile tip as an artificial constraint on the behavior of the soil. We explain the problems with existing methods of modeling the pile tip. We then conduct a three-dimensional (3D) analysis of a pile in various soil conditions to evaluate the area of influence of the soil around the pile tip. The analysis results show that the normalized area of influence extends approximately 2.5 times the diameter of the pile below the pile tip. Finally, we propose a new method for modeling pile foundations with artificial constraints on the nodal points within the area of influence. The proposed model is expected to be useful in the practical seismic design of pile-supported buildings via a 2D analysis.

Analytical Method for Prediction of Progressive Deformation Mechanism of Existing Piles Due to Excavation Beneath a Pile-Supported Building

After excavation beneath existing basement of a pile-supported building, prediction of the pile response is an interesting topic in geotechnical engineering. This paper presents a new load transfer function to capture the relationship between unit skin friction and shaft displacement. As to the load transfer function of an individual pile in pile groups before and after excavation, load transfer functions of skin friction and end resistance are proposed considering interactive effects among piles. To get a quick estimation on the pile response before and after excavation, a new highly effective iterative computer program is proposed using the proposed load transfer functions. Comparisons of the measured results, the present computed results and the calculated values derived from other approaches are made to check the reliability of the proposed method. Furthermore, a parameter study is carried out to evaluate the ultimate value of skin friction and end resistance of the pile subjected to stress relief due to excavation, and the influence of the parameters related to the proposed load transfer models on the pile response is also evaluated.

Maps of soil subsidence for Tokyo bay shore areas liquefied in the March 11th, 2011 off the Pacific Coast of Tohoku Earthquake

The March 11th, 2011 Off the Pacific Coast of Tohoku Earthquake, also known as the Great East Japan Earthquake, has shown that a long stretch of landfills along northeastern shorelines of the Tokyo Bay had very high susceptibility to liquefaction, causing concerns about re-liquefactions of the area in the scenario earthquake expected in the capital's metropolitan area. An attempt was made to detect soil subsidence from raster images converted from airborne LiDAR (Light Detection and Ranging) data before and after the earthquake. To eliminate deep-seated tectonic displacements and systematic errors of LiDAR surveys, the template matching technique is used for clusters of pile-supported buildings and bridge piers chosen as templates in source images of the target areas. The obtained subsidence maps describe the spatial distribution of soil subsidence in great detail.

液状化地盤において杭頭半剛接合構法を採用した杭基礎の耐震性能

The seismic behavior of a pile-supported building with semi-rigid pile head connections in liquefiable soil is investigated using 2D effective stress analysis. The results of the simulations show that the pile damage reducing effect of the semi-rigid pile head connection method is enhanced in liquefiable soil, because the superstructure inertia and external force acting on the embedded footing decrease. And the validity of the seismic deformation method as a seismic design method, which considers the non-linearity and axial force dependency of the pile heads, the varying axial force due to the dynamic interaction, and the total earth pressure acting on the embedded footing, is confirmed.

Building damage associated with geotechnical problems in the 2011 Tohoku Pacific Earthquake

An overview of the geotechnical aspects of the building damage due to the 2011 Tohoku Pacific Earthquake is presented, based on field reconnaissance made after the earthquake. It is shown that (1) Extensive soil liquefaction occurred along the coast of Tokyo Bay and around the floodplain of the Tonegawa River. Liquefaction was primarily found within the relatively newly reclaimed area, with numerous sand boils and large ground settlements up to 60cm, accompanied by the settlement/tilting of wooden and reinforced concrete buildings supported by spread foundations. The extent and the distribution of the damage were significantly affected by the local soil conditions, including the thickness and the age of the reclaimed fills, the depth to the bedrock or the natural site period, and whether remedial measures had been taken against soil liquefaction, as well as the effects of structure–soil–structure interaction. (2) Numerous houses in Sendai's hilly residential areas constructed with the cut-and fill method were badly damaged not only by the simple collapse of retaining walls, but also by slope failures in the fills. It was found that most of the slope failures occurred on earth fills. (3) Several pile-supported buildings tilted and settled not only in the Tohoku region, but also on the Kanto plain, implying damage to pile foundations. Ground subsidence with sand boils around those buildings suggests that soil liquefaction might have played a significant role in intensifying the damage. (4) Within Onagawa and Rikuzen-Takata, several steel and reinforced concrete structures were knocked over by tsunami surges, probably after having suffered damage to their pile foundations. Much of the pile damage was concentrated (a) at the joints between pile caps and the piles themselves and (b) near the pile heads. The buildings suffering such damage were old; apparently their pile foundations were not designed to withstand earthquakes.

Dynamic centrifuge model test of pile-supported building with semi-rigid pile head connections in liquefiable soil

Dynamic centrifuge model tests were conducted to investigate the seismic behavior of buildings with semi-rigid pile head connections in liquefiable soil. The test results and analysis show that: (1) The semi-rigid pile head connections effectively reduce the bending moment of piles both before and during liquefaction; (2) The natural period of the soil-pile-structure system with semi-rigid pile head connections becomes longer than that with rigid pile head connections during liquefaction; (3) The hysteresis damping in the relation between inertia force of the structure and displacement of the foundation, with semi-rigid pile head connections, increases with larger displacement; and (4) The maximum acceleration of the superstructure with semi-rigid pile head connections is considerably smaller than that with rigid pile head connections in liquefied soil.

Three-dimensional numerical investigation of multifaced tunneling in water-bearing soft ground

This paper presents the results of a numerical investigation of the performance of multifaced tunneling under a pile-supported building in water-bearing soft ground. Special attention was paid to the effect of tunneling and groundwater interaction on the tunneling performance. A fully coupled three-dimensional (3D) stress – pore pressure finite element model was adopted to realistically capture the mechanical and hydrological interaction between the tunneling and groundwater. The results indicate that the groundwater drawdown during tunneling yields a considerably larger settlement-affected zone than for cases with no groundwater drawdown, with a tendency for large portions of ground settlement and groundwater drawdown to be completed before the tunnel passes a monitoring section. Also revealed is that the presence of a building tends to reduce the ground settlements and cause subsurface settlements more or less uniformly with depth. It is shown that the lining deformation, and thus its stresses are not significantly affected by the presence of the building for the multifaced tunneling considered in this study. Axial loads in the piles supporting the building tend to either increase or decrease depending on the pile location relative to the tunnel axis. The patterns of changes in pile axial loads are different from the results of previous studies concerning a single pile.

DYNAMIC TORSIONAL BEHAVIOR OF A BUILDING SUPPORTED BY UNSYMMETRICALLY ARRAYED PILES

In this study, centrifuge model tests have been carried out to evaluate the torsional behavior of pile-supported buildings with the eccentric distance between the center of gravity of the superstructure and the center of rigidity of the piles. Three models were considered; a 9-pile model without eccentricity, an 8-pile model which lacks a corner pile, and a 7-pile model which lacks two corner piles. It was found from the test that the maximum response of the torsional angle of a foundation increases in accordance with the eccentricity which is defined as the same method as the superstructure. The analysis was then carried out to simulate the result of the 7-pile model. In the analysis, a three-dimensional frame model was used, and soil around the piles was modeled as two directional horizontal axial elements and shear springs. A comparison between experimental and analytical results shows a possibility that this numerical model is capable of considering the dynamic torsional behavior of buildings supported by unsymmetrically arrayed piles.

動的Winklerばねモデルを用いた杭支持建築構造物の地震時剛性設計

The soil resisting mechanism for piles is often represented by a static or dynamic Winkler-type spring. The present paper proposes two models for analysis and design of pile-supported building structures. The first-type model is a continuum model which deals with the governing differential equation directly and enables the, introduction of the one-dimensional wave propagation theory. The second-type model is a finite-element model enabling the introduction of the response spectrum method. The accuracy, of these models is clarified through the comparison in terms of transfer functions and time histories. The maximum seismic response of the models to the ground motion defined at the engineering bedrock surface as an acceleration response spectrum is evaluated by the response spectrum method in terms of complex modal quantities. The stiffness design for a specified maximum interstory drift and a pile stress ratio (maximum pile stress/allowable stress) is obtained by regarding the lowest natural circular frequency of the fixed-base model and the pile diameter as principal parameters.

Permanent Deformation of Steel Pipe Piles Penetrating Compacted Fill at Wharf on Port Island

ABSTRACT A pile inclinometer survey is conducted for the steel pipe piles supporting a four-story steel structure that survived the Hyogoken-Nambu earthquake, together with some other measurements, in order to clarify the degree of integrity of the building foundation. The building is located on a wharf surrounded by the sea on three sides. At the site, fill deposits about 20 m thick have been compacted by the vibro-rod compaction method. Subsurface investigations are also conducted for the compacted fill and underlying soil deposits. The investigations reveal the following: (1) ground subsidence due to the earthquake is estimated to be 30 to 100 mm; (2) the compacted fill has 60 to 80 percent greater resistance to liquefaction than untreated fill; (3) piles about 40 m long have been deformed not only above the interface between the reclaimed fill and the underlying alluvial clay layer (Mal3 layer), but also at the lower interface of the Mal3 layer; (4) the pile heads are judged to have been moved by at most 344 mm in the north-northeast to northeast direction. The moved distance and direction of the pile heads are explained on the basis of the compiled data regarding the relationships among the moved distance of pile-supported buildings, the distance between the buildings and quay walls, the lateral displacement of the quay wall crests and the thickness of the reclaimed fill.

Lateral Pile-Group Response under Seismic Loading

ABSTRACT An approximate and economical method is presented that can analyze dynamic interaction of piles. The method is based on a beam-on-Winkler foundation model of a pile group. Discrete soil-pile interaction elements (springs and dashpots) for the method are determined by superimposing responses of two dynamically interacting piles in a homogeneous and linearly elastic soil. The proposed method is evaluated through a case study of seismic response of an actual pile-supported building. Computed results are compared favorably with field observational data. This indicates that the stiffness and damping characteristics of a pile group can be represented reasonably by the method. Thus the method provides an economical means to evaluate dynamic response characteristics of complex pile groups in layered soils.

Performance of Four Foundations on End Bearing Piles

The performance of four buildings each supported on end bearing concrete-filled pipe piles is evaluated. The piles were driven through a deep deposit of soft clay and are end-bearing in stiff glacial till and weathered shale. The paper presents measurements of building settlement, pile tip settlement of both test piles and foundation piles, pore pressures induced by the pile driving, and movements of adjacent buildings on shallow foundations caused by pile driving. The pile-supported buildings settled less than 0.5 in. The main conclusions from the study are: (1) The pile design load is controlled by tip punching considerations, because the settlement of the pile tip is small until the tip-bearing capacity is approached; (2) preaugering is effective in reducing pore pressures induced by the pile driving; and (3) even with preaugering, pile driving in soft clay can cause significant movement of adjacent buildings at distances up to 50 ft.