Excessive Differential Settlement Research Articles

How to quantify the tunnel structural resilience in longitudinal direction: a discussion on the index and its effect

Shield tunnel is prone to longitudinal differential settlement due to the characteristics such as segmental linings and unpredictable changes in multiple uncertain environments. Excessive differential settlement may deteriorate the safety and operational serviceability of the shield tunnel. Resilience has been increasingly applied in structural performance assessment given that it can evaluate the ability of structure to absorb the disruption and to restore the performance level. However, the resilience index and analysis framework for tunnels are quite vague and still in the developing phase. In this paper, a resilience analysis framework is introduced, and the detailed model to quantify the resilience of shield tunnel is presented. The cumulative settlement, maximum, and average value of differential settlement are selected as the performance indexes, because they can reflect the ability of the tunnel to ensure the structural safety and meet the waterproof requirements of the circumferential joints. Then, the effects of these indexes are analyzed using a real case in Shanghai. The results show that the resilience grades calculated using the three performance indexes are different, and the cumulative settlement is regarded as the better index.

Evaluation of Subtitle D Covers and Exposed Geomembrane Cover for Landfills: Sustainability and Resiliency

Exposed geomembrane covers (EGMs) are considered as suitable alternatives to traditional subtitle D soil covers with compacted clay layers (CCL) for landfill cover applications. Compared to CCLs, which comprise various layers, including vegetation, erosion soil layers, and barrier liners, EGMs offer benefits such as reduced resource use. There are several risks associated with cover systems, ranging from climate-related shocks or stressors such as earthquakes, droughts, and floods to local shocks such as excessive differential settlement due to the uneven degradation of waste mass. Hence, their resilience and sustainability must be analyzed, particularly considering the escalating impact of climate change and the growing need to integrate resilience and sustainability principles into engineering designs and operations. This study comparatively assessed the resilience and sustainability of three cover systems: EGM, soil cover with geomembranes, and soil cover without geomembranes. A ((tiered quantitative life cycle assessment of sustainability and resilience) framework was employed. The resilience assessment was performed using a rating system, considering the technical performance of the cover systems, along with the environmental, economic, and social implications of the failures. Subsequently, a comprehensive sustainability assessment encompassing environmental, economic, and social dimensions was conducted. A life-cycle assessment of all cover systems was performed to evaluate environmental sustainability, and a cost-benefit analysis was employed to compare their economic aspects. Social sustainability was evaluated using a rating system. The assessments were combined to develop an integrated sustainability and resiliency index. EGM was the most resilient and sustainable alternative for landfill cover systems compared to traditional soil covers. These insights enable an objective comparison of resilience and sustainability, facilitating informed decision-making.

Dissimilar Pile Raft Foundation Behavior under Eccentric Vertical Load in Elastic Medium

Pile raft foundation (PRF) is a common foundation type for buildings and bridge piers which has been commonly subjected to eccentric vertical load in engineering applications. Dissimilar PRF is often adopted to reduce the excessive settlement and differential settlement of superstructures. The behavior of dissimilar PRF under eccentric vertical load is a significant issue and investigated with the boundary element method in this paper. In this method, the dissimilar pile–soil system is decomposed into extended soil elements and fictitious pile elements. The second kind of Fredholm integral governing equation of the axial force of fictitious piles is established based on the compatibility condition of axial strain between the extended soil and fictitious piles. An iterative procedure is adopted to analyze the average settlement w and rotation slope θ of raft stemming from the settlement compatibility condition of the top of each element and the equilibrium condition of the raft. Furthermore, the axial force and settlement of each element along its depth can be predicted. The corresponding results agree well with a reported case and the finite element method. The characteristics of 3 × 1 and 3 × 3 dissimilar PRFs under eccentric vertical load, including non-dimensional vertical stiffness N0/wEsd, differential settlement wd and the load sharing ratio of typical elements Ni/N0, are systematically investigated by considering different eccentricity e, length/diameter ratios of pile l/d and pile–soil stiffness ratio Ep/Es conditions. The N0/wEsd increases with l/d, while the load sharing ratios of the raft Nraft/N0 and wd decreases with l/d. The eccentricity e has a significant effect on wd and Ni/N0 and a neglect effect on N0/wEsd and Nraft/N0. The N0/wEsd, wd and Ni/N0 are significantly increased with Ep/Es. This research is expected to provide insights to the practitioners into the dissimilar PRF design under eccentric vertical load.

Strengthening and underpinning of a sinking two storey building in Lagos State Nigeria

Many existing foundations, particularly those that are old and dilapidated, are no longer strong enough to support the pressures they bear or support new loads applied to them. In order to boost the load bearing capacity, a unique underpinning technique is required. Underpinning technique provides secure, efficient, and reliable solutions to foundation and geotechnical problems affecting the foundations of buildings. However, the practice of underpinning is not common in Nigeria. This paper presents a case study on the settlement failure of a two-storey residential building in Lagos, Nigeria. The residential building encountered excessive differential settlement due to the variation in the soil strata in in 06°26′12″N Long: 3°30′44″E area of Lagos state. Some portion of the building was laid on weak and loose clayey sand which showed signs of foundation distress and led to the eventual choice of an underpinning technique adopted to extend the foundation depth to a stable stratum, to salvage the failed areas of the foundation in order to strengthen the bearing capacity and to minimize settlement. Underpinning was done because the original raft foundation was inadequate for vertical and lateral loads. The procedure used for underpinning was summarized. The measured settlement points of the underpinned foundations after six-year service life were less than 0.333 mm. This result meant that every point (from points 1–10) measurements were below the settlement limit which guaranteed the bearing resistance of the building. The result showed that the underpinning technique salvaged the areas that initially settled and showed distress signs.

Effect of Excavation Dewatering on Adjacent Structures

The study aims to investigate the effect of dewatering technique on retained ground and adjacent existing structures in order to avoid any damages that may occur. The paper presents three cases of potential structure failure caused by ground settlement as a result of dewatering. Two current construction projects in Khartoum North were selected as a case study. The two projects are located near Blue Nile River where ground water table exists at shallow depths. Dewatering to reduce the groundwater level was carried out in the two sites to facilitate excavation works. The buildings and road pavements around the two sites suffered serious damages due to excessive differential settlements of the retained ground. The study results showed that there are numerous sources of risks associated with performing dewatering. Therefore, developing appropriate plan for dewatering before construction is essential to mitigate any adverse impacts and avoid risks.

General deformation behavior of deep excavation support systems: A review

In geotechnical engineering, ground movement caused by excavations is a challenging issue. The excessive differential settlement generated by soil movement induced by wall deflection may cause damage to nearby structures. A detailed literature review on the general deformation behavior of deep excavation support systems is presented in this paper. Many factors, such as normalized horizontal deflection (δh-max/He%), vertical displacement (δv-max/He%), δvmax/δhmax ratio, settlement influence zone (Do), etc., can play significant roles in describing the deflection behavior of the excavation system. A descriptive analysis of the reviewed data was carried out. The concluded δh-max/He% values range between 0.17 to 1.5, with a mean value of 0.58 for soft clay, while in the case of sands and stiff clay soils δh-max/He% value ranges between 0.07 to 0.40, with a mean value of 0.20. δv-max/He% values range between 0.13 to 1.10, with a mean value of 0.49 for soft soil, while its value ranges between 0.02 to 1.10, with a mean value of 0.24 in the case of sands and stiff clay soils. The settlement influence zone (Do) reaches a mean distance of 2.3He, which falls within Do=1.5-3.5He in the case of soft clays, while Do reaches a mean distance of 2.0He and 3.0He in the case of sands and other stiff clay soils, respectively. The relationship between system stiffness and excavation-induced wall and ground movements was discussed. Unfortunately, the literature review offers limited data regarding system stiffness, the 3-D nature of excavation support systems, excavation processes, and time effects.

Forensic Engineering Evaluation of Excessive Differential Settlement on Compressible Clays

This forensic engineering (FE) study evaluated root cause errors associated with excessive differential settlements on a housing project constructed on top of a variable thickness layer of highly compressible clays. The structures were reported to have experienced differential settlements on the order of 2 to 10 in. across 40 ft. The FE study examined fundamental assumptions, granularity/resolution of the settlement and differential settlement analyses, and finalized grading plan vs. the conceptual grading plan used as a basis for the differential settlement predictions. The FE study found numerous discrepancies between the “idealized site” used as a basis of analysis and the “actual site” as constructed.

EFFECT OF LOADING STAGE ON PEAT COMPRESSION AND DEFLECTION OF BAMBOO GRID WITH CONCRETE PILE

Improvement of peat compression and increasing the bearing capacity can be achieved with the embankment load as preloading. The embankment on peat soil has problems such as excessive settlement, horizontal movement, and differential settlement. The stability of embankment is maintained with the installation of the reinforcement system, but the time factor and duration of loading can affect the stability of embankment and excess settlement. It is necessary to study the loading stages that can maximize compression and minimize deflection so that stability can be maintained. The embankment load test was performed on peat soil reinforced with bamboo grid and concrete piles. The model test in the laboratory used the test box measuring 120 cm x 90 cm x 90 cm with a height of the peat soil of 50 cm. The embankment load was distinguished based on the stage and duration of loading. The results showed that multiple stages is better than the single-stage because settlement changes are relatively smaller than the other. The longer load duration provides the opportunity to consolidate the peat layer so that the bearing capacity and the modulus of subgrade reaction increases. The good stage load is obtained in three stages with the addition of the embankment load of 3.02 kPa or 1/3 of the total load every 2 days or 1/3 of the total duration of the load. At this stage and duration, the peat compression and the deflection of reinforcement are smaller than the others.

Analyse numérique et expérimentale du comportement des ouvrages fondés sur un sol mou renforcé par des colonnes ballastées flottantes

This paper work is in the frame of the study about the reduction of settlements in the case of floating columns. The prediction of a settlement remains a prickly problem to which geotechnical engineer is confronted. Experience has shown that structural pathologies are caused by the effects of excessive differential settlements before reaching soil bearing capacity. To palliate this problems in the case of soft and compressible soils, we advocate, as an alternative solution, piles or the reinforcement of the soils with stone columns. This strengthening method, introduced in Algeria in 1999, is economical. However, it does not inihilate settlements but it speeds up the time factor. Numerical modelings by finite element method (FEM) have been carried out through interest into all mechanical and geometrical aspects that are inherent in the meshing of floating stone columns. An analytical formulation of a correction coefficent (μβ) and an abacus of the settlement reduction factor (β) has been suggested. On the other way, the monitoring instrumentation of experimental site since 2008 to 2017 at the level of the harbour lowland of Bejaia has been carried out. It concerns important storage structures fonded on a very compressible ground reinforced by floating stone columns. The records of the settlements at the scale of the structures, according to variable loads recorded in real time, have revealed excessive settlements under the effects of variable stresses from 1 to 3 bars. An exhaustive geological, geotechnical and geomechanical analysis has been carried out for the characterization of the grounds, and numerical modelling by finite element method (FEM) has been carried out. The experimental and numerical investigation of the concerned structures at issue allowed us to confront the results with regard to settlement prediction of an environment reinforced with floating stone columns. The result is a perfect matching in relation to the suggested formula.

Effect of Lime and Fly ash on Load Bearing Capacity of Expansive Clay soil

Expansive soil is a problematic soil which found in wide part of the world that has a high degree of sensitivity, nature of expansion and shrink behavior during water adding and removing this caused insufficient bearing capacity, excessive differential settlement and instability on excavation and embankment forming those conditions accelerate damage of building structure, road highway and dam. Attempt to undertake construction in such type of soil result will be bearing capacity failure, settlement problem. One of the well-known application of Lime and fly ash were improve Atterberg limits, compaction characteristics, bearing capacity and prevention of swelling problem of expansive clay that is why the main reason to select lime and fly ash in this project, both are good binding material to increase the cohesion force and shear strength of soil and assured to established rigid pavements and foundations. The mixing proportion of lime, fly ash and combination of lime and fly ash are (0%, 2 %, 4 % ), (10%, 15% ,20% ), (2 %+10 %, 2 % +15 %, 2 % +20 %) and (4 %+10 %, 4 % + 15 % , 4 %+ 20 %) with expansive soil respectively and then explored how much it modify the characteristics of soil like maximum dry density moisture content, consistency limits, FSI, UCS and CBR value which compare to untreated soil. Lime and fly ash treated soil carried out various tests Such as Moisture content test, consistency limit, compaction test, Unconfined Compression swelling index test and California bearing ratio test then after justify weather the bearing capacity of soil is good or not . Classification of soil was determined by conducting plasticity index and swelling index tests. Effect of lime and fly ash on soil index properties were assessed by conducting Atterberg limits test, strength of soil were assessed by conducting compaction test, UCS tests and CBR test and swelling properties were checked by conducting swelling index test. Expansive clay soil were mixed with lime, fly ash and combination of lime - fly ash by replacement process of soil and then cured for 7, 14 and 28 days.

Effect of the Presence of Soft Clay on the Structural Design of Highway Sections

Construction over soft clay soils have always been a great challenge in the field of geotechnical engineering especially when designing infrastructure. Because of the low shear strength and high compressibility of this soil, many engineering problems such as slope instability, bearing capacity failure and excessive settlement could occur either during or after the construction phase. The design of highway pavements on soft clay soil still remains a very challenging issue, it can cause problems such as roadbed instability or excessive total and differential settlements. The main objective of this research is to study the effect of the presence of the soft clay on the structural design of pavement sections. Results of this study show that the investigated soft clay soil has lower CBR value (0.509%) and modulus of compressibility (Es=129.8 kN/m2), therefore it is not suitable for pavement construction. By using cyclic loading model device manufactured for this study, the settlement under pavement achieved 120.05, 120.32 and 12.28mm for natural soft clay, using geotextile and using geotextile with geogrid together respectively.

Change in groundwater conditions as a cause of structural failure – selected case studies

The paper presents the summary of five case studies related to structural failures that were caused by the change in groundwater conditions during the existence of the buildings. The failures resulted from excessive differential settlements that were caused either by reactivation of consolidation process, due to change in effective stresses, or a change in water content in the case of expansive soils.

Effect of water content and density on strength and deformation behavior of clay soils

The objective of this research was to investigate the effect of varying density and water content on the strength and deformation behavior of a low, a medium, and a high plasticity clay, as well as to determine the water content at which transition from brittle to plastic behavior occurs for each clay type. We used the standard Proctor test to compact six samples each of low, medium, and high plasticity clays to establish the compaction curves. We failed the compacted samples under unconfined compression and visually inspected their brittle versus plastic behavior during compression. Additionally, we performed direct shear tests on three samples of each type of clay that were compacted at different water contents. We used the stress-strain plots from both tests to determine the transition water content between brittle and plastic behavior for each type of clay. The results showed that unconfined compressive strength first increased and then decreased with increasing water content, with the change in trend occurring within 5% of OWC for each type of clay. The high plasticity clay had the highest cohesion while the low plasticity clay had the highest friction angle. The transition between brittle and plastic behavior for the low, medium, and high plasticity clays occurred between 19–20%, 27–29%, and 30–32% water contents, respectively. These results demonstrate that, in areas where clay embankments may be subject to cracking due to seismic activity or excessive differential settlement, they should be compacted on the wet side of the transition water content marking the boundary between brittle and plastic deformation.

FUEL TANK FOUNDATION IMPROVEMENT SYSTEM ON SOFT SOIL LAYER BASED ON 3D NUMERICAL SIMULATION

Differential settlement on the fuel tank storage foundation in Banjarmasin fuel depot,Indonesia, cause the tilting of fuel tank storage. Due to this condition, the volume measurement of fuel in thetank becomes inaccurate and difficult to be predicted. This problem affects the fuel distribution inBanjarmasin area if not immediately solved. The structure of tank foundation was built on the soft soilwithout another support structure. This research carried out the study on improvement of foundation structuresystem with concrete slab supported by piles on the outside around and “Sistem Cakar Ayam” that spreadevenly in the area of the foundation. The numerical study of the proposed improvement of structure modelwas conducted using SAP2000 and ABAQUS. The vertical and horizontal spring elements were chosen asthe support system on the foundation model in SAP2000. In ABAQUS, the model defined as a three-dimensional model. The soils idealized by elasto-plastic Mohr-Coulomb model. The slab, piles, and“Sistem Cakar Ayam” defined as elastic material. Based on the numerical analysis results, the analysis usingSAP2000 are used to determine the optimum configuration of the pile and there is no excessive differentialsettlement. A three-dimensional numerical analysis using ABAQUS can represent actual field conditionsbecause the boundary conditions in two-dimensional analysis can be reduced. Reduction of deformationsusing the proposed system is 70.79%. The proposed foundation system using slab supported by piles and“Sistem Cakar Ayam” are quite effective in reducing the differential settlement due to fuel tank load.

Feedback of the behaviour of a silo founded on a compressible soil improved by floating stone columns

The coastal city of Bejaia, located 250 kilometers east of the capital Algiers, Algeria, is characterized by soft soils. The residual grounds encountered on the first 40 meters usually have a low bearing capacity, high compressibility, insufficient strength, and subject to the risk of liquefaction. These unfavorable soil conditions require deep foundations or soil improvement. Since late 1990s, stone columns technique is used to improve the weak soils of the harbor area of the city. A shallow raft foundation on soft soil improved by stone columns was designed for a heavy storage steel silo and two towers. The improvement of 18m depth have not reached the substratum located at 39m depth. The stresses transmitted to the service limit state are variable 73 to 376 kPa. A rigorous and ongoing monitoring of the evolution of loads in the silo and settlements of the soil was carried out during 1400 days that is from the construction of foundations in 2008 to 2012. After the loading of the silo in 2010, settlement occurred affecting the stability of the towers due to excessive differential settlements. Consequently, the towers were inclined and damaged the transporter. This paper presents and discusses the experience feedback of the behavior of these structures. Numerical calculations by finite elements have been carried and the results are compared with the measurements.

Investigation on the performance of bridge approach slab

In Egypt, where highway bridges are to be constructed on soft cohesive soils, the bridge abutments are usually founded on rigid piles, whereas the earth embankments for the bridge approaches are directly founded on the natural soft ground. Consequently, excessive differential settlement frequently occurs between the bridge deck and the bridge approaches resulting in a “bump” at both ends of the bridge deck. Such a bump not only creates a rough and uncomfortable ride but also represents a hazardous condition to traffic. One effective technique to cope with the bump problem is to use a reinforced concrete approach slab to provide a smooth grade transition between the bridge deck and the approach pavement. Investigating the geotechnical and structural performance of approach slabs and revealing the fundamental affecting factors have become mandatory. In this paper, a 2-D finite element model is employed to investigate the performance of approach slabs. Moreover, an extensive parametric study is carried out to appraise the relatively optimum geometries of approach slab, i.e. slab length, thickness, embedded depth and slope, that can yield permissible bumps. Different geo-mechanical conditions of the cohesive foundation soil and the fill material of the bridge embankment are examined.

Ground improvement using SPVD and RPE

Excessive total and differential settlement at the intersection of a surcharged prefabricated vertical drain (SPVD) and a rigid piled embankment on soft ground during the post-construction period leads to considerable time and costs being spent on repetitive remedial works in the future. This paper presents a sustainable design approach for high and long embankment filling on soft clay at the approach to the structure by introducing the intersection of an SPVD at the transition to a rigid piled embankment in order to regulate the differential settlement between the two conventional ground treatment approaches. This paper also presents a full-scale field study to validate the performance of the intersection of the SPVD at the transition to the rigid piled embankment. By introducing the intersection ground treatment, post-construction settlement and differential settlement are minimised significantly, while the post-construction total settlement at the rigid transition piled embankment (TPE) zone is reduced significantly by about 80 to 95% of the total settlement, as compared to a conventional TPE.

Study of the behavior of mechanically stabilized earth (MSE) walls subjected to differential settlements

The limit equilibrium (LE) analysis has been used to design MSE walls. Presumably, the deflection of MSE walls can be limited to an acceptable range by ensuring sufficient factors of safety (FOSs) for both external and internal stabilities. However, unexpected ground movements, such as movements induced by excavations, volume changes of expansive soils, collapse of sinkholes, and consolidations of underlying soils, can induce excessive differential settlements that may influence both the stability and the serviceability of MSE walls. In this study, a numerical model, which was calibrated by triaxial tests and further by a specially-designed MSE wall tests, investigated the behavior of an MSE wall as well as the influence of various factors on the performance of the MSE wall when the wall facing settled relatively to the reinforced zone. The numerical results showed that the differential settlement would cause substantial vertical and horizontal movements for the MSE wall, as well as an increase in lateral earth pressure and geosynthetic reinforcement strain. The maximum horizontal movement and increase of the lateral earth pressure occurred at about 1.0 m above the toe. The differential settlement resulted in a critical plane that coincided with the plane of 45°+ϕ/2. The maximum increase of the strain for each geogrid layer occurred in that plane, and the bottom layer had the greatest strain increase among all layers of reinforcement. The study further indicated that the surcharge, backfill friction angle, tensile stiffness of geogrid, reinforcement length and MSE wall height had noticeable influences on horizontal and vertical movements, and strain in geosynthetics. According to the results, the MSE wall that had a higher factor of safety would have less movements and geosynthetic strain increase. In contrast, only the friction angle, tensile stiffness and MSE wall height showed some degree of influence on the lateral earth pressure due to differential settlements.

Probabilistic considerations for the design of deep foundations against excessive differential settlement

Current foundation design practice for serviceability limit states involves proportioning the foundation to achieve an acceptably small probability that the foundation settlement exceeds some target maximum total settlement. However, it is usually differential settlement that leads to problems in the supported structure. The design question, then, is how should the target maximum total settlement of an individual foundation be selected so that differential settlement is not excessive? Evidently, if the target maximum total settlement is increased, the differential settlement between foundations will also tend to increase, so that there is a relationship between the two, although not necessarily a simple one. This paper investigates how the target maximum total settlement specified in the design of an individual foundation relates to the distribution of the differential settlement between two identical foundation elements, as a function of the ground statistics and the distance between the two foundations. A probabilistic theory is developed, and validated by simulation, which is used to prescribe target maximum settlements employed in the design process to avoid excessive differential settlements to some acceptable probability.

Ground Improvement of the Tank Terminal in Amsterdam, the Netherlands

In the western part of the Port of Amsterdam, a new storage terminal for oil products is being built. The site investigation revealed that underneath a single tank, the thickness of the compressible layers could differ in up to 3 meters. It was concluded by the client that ground improvement was required to avoid excessive differential settlements of the storage tanks and associated maintenance costs. The initial ground improvement design proposed by the client consisted of the application of dynamic replacement (DR). A trial showed that the traditional DR method as well as the CDC technique (Cofra Dynamic Compaction®) did not achieve sufficient improvement. Therefore, a full ground improvement was made, with large excavations of up to a depth of 8 meters below the surface, removing more than 1,000,000 m3 of material. The excavations were backfilled with sand. This very loose sand was compacted in one phase using the CDC technique. This paper presents an overview of the initial trial results and the final work method with a focus on the method of compaction and the compaction results.