Differential Settlement Of Foundation Research Articles

Settlement prediction of shallow foundations for quality controls of sandy hydraulic fills

This paper describes a procedure for settlement prediction of shallow foundations on carbonate sands, but it is fully applicable and valid for siliceous sands. For practical purposes, the design of shallow foundations resting on medium dense and dense granular soils is typically governed by limiting settlement to tolerable values. Predicting foundation settlement is therefore important, but in standard practice it is necessarily based on indirect (and therefore often conservative) determinations of soil compressibility (or modulus), due to the intrinsic difficulties in obtaining direct measurements.While numerical analyses incorporating non-linear soil behaviour may be a preferred method for computing expected total and differential settlement of shallow foundations of given geometry and stiffness on sand under static loading, the method described in this paper consists of a simplified and expeditious method based on equivalent linear elasticity. The method uses: i) the elastic soil stiffness profile at small strain, E0(z) obtained from the shear wave velocity as the primary measurement of deformability and ii) the reduction in modulus as a function of strain magnitude, E(ε) to account for stiffness non-linearity. The beneficial effect on the soil initial stiffness of the applied footing load is also considered. The method was developed as an on-site tool for checking the compaction of hydraulic fills made of carbonate sand to form artificial islands, but its application can be extended to other natural and anthropogenic coarse-grained materials.

Change in strength parameters of dusty-clayey soils depending on the time of dynamic load impact and soil type

The method of high frequency vibratory driving and extraction of sheet piles is frequently utilized in the conditions of structurally unstable soils in St. Petersburg. However, with this method of installation (extraction) of sheet piles in the surrounding soil mass it arises oscillations that are transmitted to nearby buildings and housing, capable of causing dangerous phenomena in their undergroud and aboveground structures, mainly related to differential settlement of foundations. The prediction of additional settlement of buidings in the surrounding area from vibro-driving/extraction of sheet piles is a complex, multi-factor task, and the level of the structural displacement of building, which is the main controlled parameter for the influence of dynamic loading on the foundation soil, according to the current regulatory documents Territorial Building Codes50-302-2004, Departmental Building Codes490-87, Russian State Standard 52892-2007 is merely an indirect criterion for assessment. To obtain a more accurate assessment of the development of additional settlements in buildings during high-frequency vibratory pile driving and sheet pile extraction, it is necessary to take into account not only the duration and frequency of the impact, but also the properties and type of soil itself. The purpose of this reseach was to study changes in the strength parameters of silty-clay soils depending on the time of dynamic loads impact, the type and consistency of the soil itself, as well as changes in parameters depending on the “rest” time of the soil base after exposure to vibration. The article presents the results and shows the tendency to reduce the parameters of soil strength after the application of dynamic load and the dependence of their change on the time of impact, on the type and consistency of the soil. It has been determined the dependence of changes in the strength parameters of the soil conditionally upon the "rest" time of the soil mass as a result of thixotropic re-storation, which will determine the economic attractiveness for the accident-free technology of this method.

Differential Settlement of Track Foundations Identification Based on GRU Neural Network

The timely identification of differential settlement of track foundations is of great significance for the safety of train operation and the maintenance of track structures. However, traditional monitoring techniques cannot meet the requirements of efficient, real-time, and automatic monitoring of track foundation settlement. In order to solve these problems, a real-time identification method based on a gated recurrent unit (GRU) neural network is proposed for the differential settlement of track foundations monitoring. According to parameter sensitivity analysis, the vertical acceleration of the vehicle is selected as the known data fed into the GRU network for differential settlement identification. Then the GRU network is employed to establish the nonlinear relationship between the vertical acceleration of the vehicle and the differential settlement of the track foundation. The results indicate that the longitudinal continuous differential settlement distribution curve of track foundations could be accurately identified with GRU neural network through the real-time vibration response of the vehicle–track. The current method may provide a new means for the real-time and efficient identification of the differential settlement of track foundations.

Optimized Design of a Squeezed-Branch Pile Group Based on an Improved Particle Swarm Algorithm

To reduce the differential settlement of pile group foundations, a squeezed-branch pile group optimization method based on an improved particle swarm algorithm is proposed in this paper. This method translates the problems of optimization design in the squeezed-branch pile group into the pile-bearing-plate distribution using the theory of variable-stiffness leveling. In the optimization process, the pile group is divided into groups according to the top axial force of the pile. The finite element analysis software is used to solve the pile group under the control of the particle swarm optimization algorithm, with the objective functions of bearing-plate number, vertical bearing capacity, settlement value and settlement difference as the constraint conditions. An engineering example is used to verify this method. The results show that the optimized design can reduce the settlement difference by 39%, while the number of the bearing plate is reduced by 56%, which makes the deformation and force of the pile group more uniform and is conducive to the normal use of the structure.

Experimental investigation on structural response of multi-story buildings subjected to differential settlement of its foundations

PurposeThis article aims to address an outstanding problem dealing with the structure of multi-story buildings subjected to differential settlement of the building's foundation.Design/methodology/approachDifferential settlement between foundation units of multi-story structures has been responsible for causing damage to buildings and often catastrophic failure and loss of life. The dynamic changes in the loading conditions of the structure and the changes in the underlying ground due to environmental changes are causing this undesirable differential settlement, which is manifested in the form of additional stresses in beams, columns and distortion of the structure elements. This study presents the results of an experimental investigation on a prototype model of a multi-story building subjected to differential settlement of the building's foundation. The model is a four-floor aluminum structure, instrumented to measure the stresses induced in the structure elements due to the settlement of a center, edge and corner column, respectively, which represent the critical conditions of the structure.FindingsThe experimental results of this study can be used as a guideline for the design of structures.Originality/valueThe current study is the original research developed by the authors.

Shaking table test on seismic response of a planar irregular structure with differential settlements of foundation

The differential settlement of the foundation not only causes the degradation of the static performance of structures, but also affects the seismic performance. To investigate the seismic response of a planar irregular steel frame structure under differential settlement of foundation, we proposed a method to mimic multi-point differential settlement of foundations of scaled models steel frame structures. Four columns in the settlement location are adjusted downward to the set settlement distance, and then, the columns are fixed with nuts to achieve the effect of settlement in one location. Then a shaking table test was carried out on a scaled-down building model to analyze the dynamic responses of the structure. Eight seismic waves and three ground shaking intensities were set to represent frequent, moderate, and rare earthquakes. The seismic response, location changes, and torsion of the irregular planar structure were analyzed via shaking table tests under different seismic waves with frequent, moderate, and rare earthquake excitation, as well as changing parameters such as settlement location and settlement depth. The results show that compared with other locations, when a differential settlement of the foundation occurs in the corner location of the structure plane, the structure is more likely to be torsional and more prone to seismic damage. For the same seismic intensity and settlement depth, the settlement location at the corner of the structure face exhibited the greatest seismic response to the structure. In contrast, the settlement located near the center of the structure face had the least effect on the seismic response of the structure. The proposed method enables a fast and efficient way to understand the dynamic response of the structures with differential settlement of foundations, which will further benefit the development and optimization of the seismic strengthening scheme for these structures.

Safety Assessment of Tunnel Shield Construction for Existing Adjacent Bridges

Disturbances to the surrounding soil layer from a tunnel shield passing under a viaduct can cause uneven pile foundation settlement, negatively affecting the structure’s normal functionality. Therefore, its safety must be evaluated before tunneling. In this study, a numerical model is developed on Midas to simulate the differential settlement of pile foundations under a viaduct during the entire construction tunneling process. The evaluation basis is derived by verifying the various bearing capacities of the viaduct. The results indicate that when the shield excavation face is 12 m from the pile foundation axis, vertical displacement begins to appear and increases gradually as the excavation face approaches the pile foundation. The bearing capacity of the girder support and midspan section is lower than the section resistance and meets the specifications. In the anti-cracking calculation, when the bearing differential settlement is 5 mm, there is no tensile stress in the normal section of the main beam, and the tensile stress of the oblique section meets the specifications. Furthermore, in situations when the pressure must be verified, tthe calculation results meet the specifications. Based on this evaluation criteria, it is ultimately determined that the viaduct can be used normally after shield construction. This safety assessment method can serve as a reference for similar construction projects.

Retrofit, Restoration and Preservation of Byzantine Monuments: Assessment of Natural Degradation and Evaluation of Intervention Options

Monuments reflect the depth and grandeur of a great civilization developed in a certain region, during a specific period of history. They possess aesthetic, historical and functional values. Undoubtedly, they are seen as part of mankind’s cultural heritage. In particular, the ecclesiastical byzantine monuments in countries where the byzantine civilization flourished, between the 4th and the 15th centuries, such as in Greece and Cyprus, are of great importance, because they are considered as edifices that offer, through their aesthetic and archeological study, a mental upgrade and valuable knowledge of roman and byzantine building techniques. Thus, the need for periodic maintenance and restoration of such monuments is imperative. The objective of the present work is to give a general description of the basic steps of the dominant retrofit methodology which is nowadays used in Greece and Cyprus and leads to the preservation of byzantine monuments. This method is the same as in any other type of monument and goes through four stages: (i) in-situ visual investigation of the degree of wear and on-site experiments, (ii) laboratory testing of the original materials of the monument under study, (iii) installation of a wireless sensor network on a monument under study, aiming at the most efficient monitoring of local displacements, differential foundation settlements, temperature changes, local humidity concentration, salt formation, etc. and (iv) evaluation of several retrofit options and the implementation of the optimal solution, by applying a formulated grading methodology. An immediate finding of the present work is that these steps enable the creation of a suitable analytical model which can be used in runnig a software package, for the design of a complete retrofit/restoration procedure and the preparation of accurate architectural and structural drawings, which will finally be used for the implementation of the maintenance/preservation design. Undeniably, what is important is to select the optimal retrofit procedure for this type of historical buildings, something which is explained in detail in this article. The latter statement expresses the scope of the present work. Another major finding of this review research is that the above retrofit procedure has already been applied to many byzantine monuments, during the past twenty years in Greece and in Cyprus and seems to have already become the dominant method over existing practices, because it uses modern technologies and is more efficient and effective, since it is based on optimization procedures.

Experimental and numerical analysis of the under-reamed piled ring foundation

The experimental and numerical analysis of the under-reamed piled ring foundation (with/without RDFS cushion) supported by soft clay was carried out. Total 34 model tests were performed to understand the effect of the under-reams and randomly distributed fibre reinforced sand (RDFS) cushion on the parameters like pile length, centre to centre spacing between under-reams, differential settlement, axial force in the under-ream pile and load sharing mechanism. Results have indicated that in comparison to the straight piles, under-reams at the bottom of piles significantly increases the load carrying capacity and reduce the differential settlement of the piled ring foundation. Load improvement factor for under-reamed piled ring foundation with RDFS cushion was noticeably higher, and settlement reduction ratio was lower than that without RDFS cushion. RDFS cushion increases the percentage of the load taken by the ring raft in the under-reamed piled ring foundation. The inner edge of the ring raft settled more than that outer edge and the centre. And the differential settlement of the under-reamed piled foundation with/without RDFS increased with the increase in the pile length and reduction in spacing between under-reams.

An experimental evaluation of helical piles as a liquefaction-induced building settlement mitigation measure

This study evaluates the application of helical piles to reduce liquefaction-induced foundation settlement and investigates their seismic performance in liquefiable grounds. Two large-scale shake table test series, one without mitigation and one using helical piles, were conducted using the shake table facility at the University of California, San Diego. Each model was extensively instrumented and subjected to two consistently applied shaking sequences. The experimental results indicated reduced excess pore-water pressure generation around the helical pile group, attributed mainly to the densification around the piles during installation. The foundation supported on helical piles underwent almost no foundation differential settlement and tilt. The post-shaking liquefaction-induced settlement mechanisms did not affect the helical pile foundation settlement. Although this study introduced helical piles as a reliable and highly efficient measure to mitigate liquefaction-induced foundation tilt and settlement, the proper design and application of helical piles still need thorough investigation due to possible amplified superstructure response.

Model Test Study on Bearing Capacity of Nonuniformly Arranged Pile Groups

The uniform arrangement of pile groups widely used in practice often causes obvious differential settlement of pile foundations. To decrease differential settlement of pile groups, individual piles nonuniformly arranged can be adopted. This paper presents a model test study on the bearing capacity of pile foundations under different pile arrangements. A versatile full-automatic loading system and data acquisition and analysis systems of the model test were developed. Using the model test setup, the response of a single pile subjected to axial load was clarified, and the reinforcing effect between an axially loaded pile and a load-free pile was then analyzed. Furthermore, model tests were carried out to assess the behavior of the pile groups composed of individual piles with variable length and diameter. For practical purposes, some suggestions on the nonuniformly arranged individual piles within pile groups were given to decrease differential settlement among each individual pile and make maximum use of the bearing capacity of each individual pile.

Bearing Capacity Characteristics and Differential Settlement of Composite Foundation with Column-Hammered and Thrusted-Expanded Piles

The foundation bearing-capacity characteristics and differential settlement have become the vital issues of high-speed rail study. Because of the collapsibility around loess foundations, the bearing characteristics as well as differential settlement are significantly different from other soil foundations. At present, there are many studies on other types of soil foundations, while the bearing capacity characteristics and differential settlements of the column-hammered and thrusted-expanded pile (CHTEP) composite foundation in the collapsible loess area are rarely involved. Therefore, based on the current codes, field tests and finite-element method (FEM), the variation in the differential settlement and bearing capacity characteristics of composite foundations with CHTEP is studied in collapsible loess areas. This paper mainly obtains the changing law of pile body stress, pile–soil stress ratio, pile side-friction resistance, differential settlement about the pile, and the soil between the piles of the composite foundation with CHTEP during different construction conditions. The result also shows the bearing capacity and settlement about composite foundation with CHTEP is up to code. This paper can provide some important rule to the design or construction about composite foundations with CHTEP at collapsible loess areas or other similar cases.

Evaluating the sustainability of a hydropower project in the Himalayas: A case study for resolving legal disputes in tribunals

Land use controversies often dog the construction of hydroelectric projects. Many important projects are battling in the tribunals because of Geo-environmental concerns. The paucity of scientific studies objectively investigating the litigations further aggravates the unsolvability of the disputes.The Sawra-Kuddu Hydroelectric project, India, became a subject of litigation when project affected persons filed a suit in the National Green Tribunal questioning the sustainability of the built environment. The litigants petitioned that the additional adit's blasting vibrations can trigger the landslide of slip zone, and Thana village situated above it. The petitioners further claimed that vibrations had cracked the houses. They also asserted degradation in the apple cultivation due to tunnel construction. The tribunal took a stern note of the petition and banned the construction activities. The tribunal further ruled that a scientific investigation must be conducted to ascertain the cause of petitioners' claims.The study results revealed that the vibrations originating from adit excavation are insignificant and cannot destabilize the slip zone. The high fluctuation of annual rainfall and tectonic strain were deemed responsible for the differential settlement of foundations and cracks in the houses. The horticulture study indicated that the physiological processes of apple crops were normal. The study's findings convinced the tribunal, and construction activities were resumed, resulting in the disputed 111 MW project's commissioning. Many run-of-the-river hydroelectric projects in the world are battling similar litigations addressed in the present study. A similar objective methodology is a need for the hour to resolve other hydroelectric projects' sustainability issues. The study findings will pave the path for the swift resolution of land disputes related to similar projects.

One-dimensional semi-analytical model on longitudinal thermal loads of a tram track pile-plank structure buried beneath the pavement

A novel pile-plank-supported ballastless tram track is employed in southeast of China to mitigate the foundation differential settlement in soft soil regions. In this structure, the channel rails are directly combined with the plank by fasteners and pads. In situ measurement data reveal that the foundation differential settlement is well controlled by this structure and the internal forces of the plank mainly depend on temperature variation. To assess the structural safety and improve the reinforcement design for the pile-plank structure, an efficient and precise calculation algorithm for internal forces of the structure is urgently required. In this work, a one-dimensional (1D) model is proposed to evaluate the longitudinal forces of the embedded pile-plank structure due to temperature variation. The constraints of rails and surrounding concretes (i.e., overlying pavement and the supporting layer) on the embedded structure are considered. The semi-analytical solution of this model is derived and a comprehensive calculation procedure is proposed. Based on the project of Shanghai Tram Line T1, a case study is undertaken to validate the proposed model. The results indicate that the maximum longitudinal displacement of the plank increases with the temperature variation. The critical displacement appears when the temperature variation rises to 15 ℃. The calculated longitudinal forces of the plank are in accordance with the in situ measurement data. This model provides a strong base to the reinforcement design of the pile-plank-supported ballastless tram track.

A study of differential foundation settlement of piled raft and its effect on the long‐term vertical shortening of super‐tall buildings

SummaryIn this study, the long‐term differential foundation settlement and vertical shortening of super‐tall buildings are investigated considering the coupling effect. At first, a time‐dependent settlement model is proposed to predict the foundation settlement based on the construction sequence method, in which both soil compression and pile shortening are considered. The pile shortening including the elasticity, shrinkage, and creep contributes to the most settlement of a single pile. The distribution of foundation settlement of piled raft is pot shaped with a large value in the core while small values in the surroundings. A time‐dependent soil‐foundation‐structure system is then developed using a series of equivalent springs to represent the distributed foundation settlements, by which the vertical shortenings of shear wall and mega column are predicted considering the coupling effect and moisture distribution. The pot‐shaped distribution of foundation settlement of piled raft leads to the decrease of vertical shortening for shear wall while the increase of vertical shortening for mega column, especially in the low stories. Finally, some health monitoring records of the Shanghai Tower are applied to validate the proposed time‐dependent settlement model and soil‐foundation‐structure system. The predicted foundation settlements show reasonable agreement with the monitoring records. The predicted vertical shortenings with considering the differential foundation settlement agree better with measurements than those without considering the differential foundation settlement.

Practical Engineering Behavior of Egyptian Collapsible Soils, Laboratory and <i>In-Situ</i> Experimental Study

In many sites on Egypt desert roads collapsible soils is broadly classified as a problematic soils containing silty fine sand which is cemented with low density and low degree of saturation which is susceptible to a large and sudden reduction in their volume upon inundation, with or without vibration in its stress. Four sites have been studied for new urban, roads and industry work sits, related to increase in natural water content. These soils go through radical rearrangement of their particles, causing sudden changes in the stress-deformation behavior which cause differential settlement of foundation and roads. This change in volume can lead to foundation failures and worth of damages under ground public facilities and infrastructure. In this study, the search program is developed to establish their different behavior under wetting in two phases: field and laboratory work. The obtained results are useful in mapping the trend of the factors affected in assessing soil collapsibility rate or collapse potentials which are observed in construction with volume change problems. The major factors observed are the natural structure skeleton of the soil particle and its grain size and mechanism of soil sedimentation. The field collapse potentials value assigned for these tested sites along Alexandria—Cairo desert road indicated that the field measured collapsibility potentials are smaller than those measured on the same extracted undisturbed samples in laboratory by 15%, which can be saved in coast, change in proposed collapsibility improvement method and change in select foundation type. Also, field tests evaluate the collapsibility rate with time and highlight that environmental history and natural soil structure in field are the important factors affected on these soil collapse, and also, knowledgeable by collapsible soils during wetting in these sites studied.

Analysis of the Influence of Differential Consolidation Settlement of Foundation on Redistribution of Internal Forces in Superstructure of Buildings

In order to explore the influence of differential settlement of foundation on the internal force and deformation of super-frame structure, the stress and deformation of the traditional fixed support model and the elastic support model under the local effect of the differential settlement of the two columns are compared. The model without considering the settlement of the structure (Model 1), the traditional fixed support model (Model 2), and the vertical elastic support model (Model 3) are respectively constructed for analysis. The left end of the frame column and A/1-2 beam are taken as an example, the axial force of the frame column in Model 3 significantly decreases from -817.8kN to -415.3kN compared with Model 1, with a reduction of 49%; the shear force at the left end of the lower A/1-2 beam increases from 42.3kN to 43.5kN with an increase of 3%; and the bending moment increases from -27.2kN⋅m to 152.7kN⋅m. Those indicate the shear force and bending moment of the beam directly connected with the subsidence column under the action of the elastic support model are smaller than that under the action of the fixed support model. It is hoped that these change rules can provide reference for the design and reinforcement of similar projects in the future.

Seismic fragility analysis of steel moment-resisting frame structure with differential settlement

Differential settlement of a foundation is commonly caused by non-uniform movement of the soil underneath a structure, and which can cause crack and damage to the structure. In order to examine the influence of differential settlement on structure's seismic performance, a three-dimensional numerical model of steel moment-resisting frame (SMRF) structure with differential settlement was developed and incremental dynamic analysis (IDA) based seismic fragility assessment was performed. Nonlinear time-history analysis was carried out to evaluate the influence of differential settlement intensity, settlement zone and ground motion intensity followed by IDA and seismic fragility analysis. Results show that the seismic responses of structures with differential settlement are obviously greater than those without differential settlement, and differential settlement of foundation can increase collapse probability during earthquakes. Findings from this study can provide valuable information on the seismic safety evaluation of structure with differential settlement which rarely taken into consideration in current practice. By having this additional information, engineers can have better insight when designing structures under such soil condition to avoid catastrophic failure.

Mechanical Model for Joints of Immersed Tunnel Considering the Influence of Joint Differential Settlement

Immersed tunnels are generally connected by tube elements through the joints, which are the weakest parts and sensitive to deformation. However, it is inevitable that there will be vertical differential settlement between the joints of the tube element, resulting from uneven loads caused by back silting, differential settlement of foundations in soft soil, the heavy deposit of ground soil, and increasing tube length. Differential settlement at joints is very harmful to the safety of tunnel construction and operation, but the elastic foundation beam method—which is now widely used for calculation of settlement for immersed tunnels—cannot take joint differential settlement into account. Therefore, this paper proposes a new mechanical model for joints of immersed tunnels in consideration of the influence of joint differential settlement. The model is not only convenient for adoption in calculation, but also considers the influence of variation on the rigidity of groundwork. The results show that the bending stiffness of the joint changes with variations in differential settlement, and depends on whether differential settlement and the eccentricity are on the same side of the neutral axis or the other. Then, both the increase of eccentricity and the use of shear key will expose positive effect on the rise of bending stiffness. By calculating this mechanical model via considering differential settlement, the max error was only 7.3%. Therefore, it may have significance as safety guidelines for the construction and operation of immersed tunnels.

BIG IMAGERY AND HIGH PERFORMANCE COMPUTING AS RESOURCES TO UNDERSTAND CHANGING ARCTIC POLYGONAL TUNDRA

Abstract. Permafrost thaw has been observed at several locations across the Arctic tundra in recent decades; however, the pan-Arctic extent and spatiotemporal dynamics of thaw remains poorly explained. Thaw-induced differential ground subsidence and dramatic microtopographic transitions, such as transformation of low-centered ice-wedge polygons (IWPs) into high-centered IWPs can be characterized using very high spatial resolution (VHSR) commercial satellite imagery. Arctic researchers demand for an accurate estimate of the distribution of IWPs and their status across the tundra domain. The entire Arctic has been imaged in 0.5 m resolution by commercial satellite sensors; however, mapping efforts are yet limited to small scales and confined to manual or semi-automated methods. Knowledge discovery through artificial intelligence (AI), big imagery, and high performance computing (HPC) resources is just starting to be realized in Arctic science. Large-scale deployment of VHSR imagery resources requires sophisticated computational approaches to automated image interpretation coupled with efficient use of HPC resources. We are in the process of developing an automated Mapping Application for Permafrost Land Environment (MAPLE) by combining big imagery, AI, and HPC resources. The MAPLE uses deep learning (DL) convolutional neural nets (CNNs) algorithms on HPCs to automatically map IWPs from VHSR commercial satellite imagery across large geographic domains. We trained and tasked a DLCNN semantic object instance segmentation algorithm to automatically classify IWPs from VHSR satellite imagery. Overall, our findings demonstrate the robust performances of IWP mapping algorithm in diverse tundra landscapes and lay a firm foundation for its operational-level application in repeated documentation of circumpolar permafrost disturbances.