Residual Settlement Research Articles

Determination of Permanent Deformations of Non-Cohesive Soils in Pavement Structures under Repeated Traffic Load

One of the main types of distress in pavement structures is rutting, which may also reduce serviceability significantly. Most design methods typically attribute rutting to the asphalt layer alone, proposing that it can be managed by controlling vertical deformation or stress at the subgrade’s top. Furthermore, these methods frequently lack precise measurements for rut depth. On-site measurements show that the majority of permanent deformation occurs in the unbound layers beneath the asphalt; attention should be directed towards these layers. In recent literature, there are calculation methods that account for accumulating strains in soils. However, further investigation is needed regarding the effect of soil properties and the significance of the pavement cross-section. The literature is also somewhat contractionary regarding the origin of permanent deformations. In this research, the residual settlement of soils (base, subbase, and subgrade) under flexible pavement systems was analyzed due to the repeated traffic loads. Rut depths were calculated and analyzed using the High-Cycle Accumulation (HCA) model. The different behaviour in each course of the pavement system is discussed to reveal their contribution to total ruts. The effect of the grain size distribution of the subgrade was analyzed, and its significance on the rutting depths was demonstrated. Standardized pavement cross-sections with different asphalt thicknesses were evaluated, and the calculated settlements of the pavement originating from the ground during the design lifetime are also presented. It is shown that, with the same number of repetitions, the settlements calculated in each traffic load class are proportional to the thickness of the asphalt course. The contribution of the base, subbase, and subgrade courses to the total settlement is also presented for different subgrade types and traffic load classes.

Full-scale seismic response test on a shallow foundation embedded in tire-derived aggregate for geotechnical seismic isolation

This paper presents results from full-scale tests aimed at characterizing the seismic response of shallow foundations embedded in tire derived aggregate (TDA) with large particle size. The high shear strength, low shear modulus, and high damping ratio of TDA with large particle sizes make it ideally suited for low-cost Geotechnical Seismic Isolation (GSI) systems. Unidirectional shake table tests were performed on a single-degree-of-freedom superstructure connected to a 0.46 m-deep concrete strip footing embedded within a 1.89 m-thick TDA layer inside a laminar box. The TDA-footing system was subjected to a series of sine sweep motions with varying amplitudes and frequencies between 0.4 and 10 Hz. Substantial nonlinearity was observed in the moment-rocking response of the footing, where the specimen experienced rocking stiffness softening at moment demands slightly below its moment capacity. While the footing exhibited moderate transient settlement and uplift during dynamic oscillation, it demonstrated low residual settlement. The TDA layer offered the footing an effective recentering system with an average residual recentering ratio of 0.991. In addition to being low-cost, abundant, and recycled, the TDA layer had both favorable energy dissipation and recentering, with better seismic resilience than structural hinging and conventional foundation rocking systems in soil.

Enhancing reliability of consolidation design parameters for residual settlement estimation: a sensitivity analysis approach for existing container yard in Belawan, Medan

Data variation in geotechnical engineering poses challenges in setting up reliable design parameters used for design or analysis. This study aims to accommodate the uncertainty of consolidation design parameters, including the compression index (Cc), initial void ratio (e0), and coefficient of consolidation (Cv), to estimate the residual settlement. A case study of Belawan New Container Terminal (BNCT), which consists of two container yards situated in a reclamation area, has been presented in this paper. A robust method employing parameter sensitivity analysis and loading scenario has been carried out. Sensitivity analysis has been performed by considering ranges for each compressibility parameter consisting of low, best, and high estimates. This approach leads to nine analysis scenarios and doubles after including the service load scenario. The results are then compared with available settlement plate and topographic/bathymetric data (pre, during and post-construction). The scenarios that best fit the monitoring data are selected as the basis for estimating the residual settlement over a design lifetime of 50 years. The residual settlement is expected between 1 m and 1.27 m without service load condition, and 1.92 m to 2.46 m. with a service load of 60 kPa (equivalent to six stacks of 20-foot containers).

Field tests on partially geotextile encased stone column-supported embankment over silty clay

Various researchers have highlighted that geosynthetic-encased stone columns could be used in place of stone columns (SCs) in very soft soil. In this study, field load tests are performed on individual partially geotextile-encased stone columns (pESCs), individual stone columns (SCs), and a field embankment reinforced with pESCs and SCs in silty clay. Although the material cost of pESCs is designed to be comparable to that of SCs, the tests reveal that pESCs display a higher allowable bearing capacity and stress concentration ratio and less residual settlement than SCs. The embankment reinforced by pESCs is found to incur fewer lateral displacements, while there is no improvement in the drainage performance during the construction period compared to the SCs. For the pESCs, 51–66% of the pressure acting on the top of the column propagates to a depth of z = 1.2 m, wheras, for the SCs, it is only 21–55%. Furthermore, to estimate group behaviour, the ultimate bearing capacity of an individual pile composite ground can be extrapolated. However, individual pESCs achieve much higher stress concentration ratios than the pESC group.

Calculation Method for Traffic Load-Induced Permanent Deformation in Soils under Flexible Pavements

Rutting is one of the most common types of distress in flexible pavement structures. There are two fundamental methods of designing pavement structures: conventional empirical methods and analytical approaches. Many analytical and empirical design procedures assume that rutting is mostly of asphalt origin and can be reduced by limiting the vertical deformation or stress at the top of the subgrade, but they do not quantify the rutting depth itself. Mechanistic–empirical models to predict the permanent deformations of unbound pavement layers have been well investigated and are rather common in North America; however, they are not widely utilized in the rest of the world. To date, there is no generally accepted, widely recognized, and documented procedure for calculating permanent deformations and thus for determining the rutting depth in flexible pavement courses originating from the unbound granular layers. This paper presents a layered calculation method with which the deformation of soil layers (base, subbase, and subgrade courses) under flexible pavements due to repeated traffic load can be determined. In the first step, the cyclic strain amplitude is calculated using a nonlinear material model that is based on particle size distribution parameters (d50 and CU) and dependent on the mean normal stress, relative density, and actual strain level. In the second step, the HCA (High Cycle Accumulation) model is used to calculate the residual settlement of each sublayer as a function of the number of cycles. It is shown that the developed model is suitable for describing different types of subgrades and pavement cross-sections. It is also demonstrated with finite element calculations that the developed model describes both the elastic and plastic strains sufficiently accurately. The developed model can predict the settlement and rutting of pavement structures with sufficient accuracy based on easily available particle size distribution parameters without the need for complex laboratory and finite element tests.

Analysis of long-term settlement of road embankment on peat ground during its service period

Roads on peat grounds are subject to stringent requirements in terms of controlling the residual settlement during their service period in order to minimize the post-construction maintenance work. This paper addresses the applicability of the Finite Element Method (FEM) by incorporating a time-dependent model for peats to an evaluation of the residual settlement. The applicability of isotach viscoplasticity, used to describe the peats’ behavior under variable-rate compression, was confirmed in laboratory tests. Long-term consolidation test results and a model simulation revealed the particular importance of two mechanisms in the residual settlement in peat grounds, namely, the stress-dependency of the coefficient of consolidation, cv, and the viscosity-induced secondary consolidation. A model peat ground, capturing these mechanisms, was implemented for the FEM and applied to a case history of a high-standard road construction in Hokkaido, Japan. The viscoplastic parameters determined from standard oedometer tests successfully reproduced the observed long-term settlement in a peat-dominated section of the expressway. The analysis was extended to address the settlement in the peat ground with the installation of prefabricated vertical drains (PVDs). The results indicate that the delayed primary consolidation due to the stress-induced cv reduction can be significantly alleviated, while the settlement arising from the secondary consolidation over a longer term is little affected by the PVDs. These insights point to the importance of untangling the two mechanisms of long-term settlement for the sake of making accurate predictions of the residual settlement in different time scales.

Field studies on low and fast compressibility of cement-mixed gravel in railway embankment construction.

The cement-mixed gravel, which is used in the construction of railway embankment, is a relatively more expensive material compared to sandy soil. Having said that, it is used where small residual settlement is required for example, abutment transition zone, due to characteristic of higher strength than sandy soil. In this paper, the time-dependent settlement were evaluated using field data measured over a long period of time at two RSR (Reinforced Subgrade for Railways) construction sites using two different backfill materials (sandy soil and cement-mixed gravel). The embankment settlement with cement-mixed gravel as a backfill material was reduced by 78% compared to that with sandy soil. Further, the period for stabilizing the embankment before installation of the railway track was significantly reduced with cement-mixed gravel as a backfill material.

Optimal adaptive decision rules in geotechnical construction considering uncertainty

To design a geotechnical engineering structure optimally, an iterative decision-making process is required due to the prevailing uncertainty of the ground conditions. At present, these decisions are taken based on simple deterministic rules and models. This paper proposes a risk-based decision-theoretic framework to the optimal planning for geotechnical construction. This framework combines geotechnical probabilistic models, cost analysis using Monte Carlo simulation and the observational method. The framework is illustrated on the design of the surcharge for an embankment on soft soil, whereby the optimal preloading sequence of added surcharge is adapted to the observed settlement. The approach balances the cost of surcharge material against financial penalties related to project delays and insufficient overconsolidation, which causes damage due to residual settlement. The result is a preloading strategy that optimally accounts for information obtained from settlement measurements under uncertain ground conditions. The findings highlight the potential of using risk-based decision planning in geotechnical engineering, in particular when combined with the observational method. For the investigated case study, a reduction in the expected cost in the order of 25% is observed.

Numerical investigation of the main factors influencing rocking responses of shallow foundations

Several investigations have shown that structures with rocking foundations bring more stability and fewer instances of post-earthquake damage to superstructures by dissipating seismic energy within the underlying soils. Nevertheless, there are still obstacles to making this design philosophy a practical solution, including concerns about the residual settlements and rotations. In order to provide a better insight into the problem, the present paper investigates the performance of a simple structure with a rocking foundation, taking advantage of pushover and time history analyses. The finite-element method is applied for the study, and the numerical model has been validated using results from recent experimental research. Accordingly, the effect of a number of influential parameters involving the properties of soil, structure and ground motions is evaluated. The current research considers different static safety factors against soil shear strength failure, structure slenderness ratios, earthquake records and foundation embedment depths, and the response of the systems with rocking foundations has been elaborated using the results obtained. The contribution of the investigated parameters is pronounced in the main features of the rocking foundation performance, such as the system moment capacity and foundation deformations (settlement and rotation).

Application of grey feed forward back propagation-neural network model based on wavelet denoising to predict the residual settlement of goafs.

To study the residual settlement of goaf's law and prediction model, we investigated the Mentougou mining area in Beijing as an example. Using MATLAB software, the wavelet threshold denoising method was used to optimize measured data, and the grey model (GM) and feed forward back propagation neural network model (FFBPNN) were combined. A grey feed forward back propagation neural network (GM-FFBPNN) model based on wavelet denoising was proposed, the prediction accuracy of different models was calculated, and the prediction results were compared with original data. The results showed that the prediction accuracy of the GM-FFBPNN was higher than that of the individual GM and FFBPNN models. The mean absolute percentage error (MAPE) of the combined model was 7.39%, the root mean square error (RMSE) was 49.01 mm, the scatter index (SI) was 0.06%, and the BIAS was 2.42%. The original monitoring data were applied to the combination model after wavelet denoising, and MAPE and RMSE were only 1.78% and 16.05 mm, respectively. Compared with the combined model before denoising, the prediction error was reduced by 5.61% and 32.96 mm. Thus, the combination model optimized by wavelet analysis had a high prediction accuracy, strong stability, and accorded with the law of change of measured data. The results of this study will contribute to the construction of future surface engineering in goafs and provide a new theoretical basis for similar settlement prediction engineering, which has strong popularization and application value.

Improved analysis and design for surcharging

Surcharging or preloading is one of the oldest and most widely used in situ ground improvement techniques to strengthen weak compressible clays and to remove undesirable settlements prior to erection of permanent infrastructure. Recently, the ground improvement technique has been adopted in combination with many other techniques. The current design methodology for surcharging based on the concept of average degree of consolidation is inadequate, as all the primary consolidation settlement to be induced by the permanent load is not eliminated by the surcharging process. The problem is quantitatively analysed using Terzaghi's one-dimensional consolidation theory. The proportion of residual primary consolidation settlement is quantified, and the starting time of the re-occurrence of primary consolidation on exertion of the permanent load is determined. The effect of a change in surcharging duration on the proportion of residual settlement is quantified. The results are presented in design charts to facilitate application of the results by practicing geotechnical engineers.

Coupled mechanical creep and bio-compression and residual settlement in a multi-stage municipal solid waste landfill, Korea

Based on a field monitored dataset measured at landfill #1 over 21 years, the characteristics of settlement coupling mechanical creep and biodegradation and the residual settlement were analyzed. Since landfill #1 is a multi-stage municipal solid waste (MSW) landfill where dykes are constructed after landfilling for subsequent waste fills, the waste decomposition between the lower and upper lifts was quite different and it is difficult to discern between the mechanical creep and bio-compression on the settlement curves. The compression ratio coupled with mechanical creep and bio-compression and the residual compression ratio were determined as 0.233 and 0.068, respectively. This implies that biodegradation was gradually and significantly reduced in the MSW settlement behavior after the residual settlement began. The starting date of residual settlement was distributed between 3821 and 5402 days from the initial date of landfilling. The settlement coupling mechanical creep and biodegradation (SMB) was 2.9 times larger than the residual settlement (SRS), and the duration of SMB is determined to be 0.3 times that of SRS. In addition, the remnant methane gas content existed in the landfill gas, and low-level biodegradation was still generated in the waste buried for more than 10 years after the residual settlement began.

Seismic Performance of Deformable Rocking Soil-Structure Systems Subjected to Pulse-Type Excitations

ABSTRACT Structural flexibility and soil nonlinearity have important effects on the rocking performance of structures. However, there are a limited number of studies taking into account the consequences of these attributes simultaneously. This paper presents a comprehensive parametric study performed to explore the key parameters affecting the behavior of deformable rocking systems lying on compliant soil. The results illustrated that an increase in pulse motion amplitude and pulse motion period typically increases residual settlement and rotational amplitude. Finally, the performance of a relatively stiff rocking system with two different slenderness ratios was correlated to well-known intensity measures under real pulse-like motions.

Low Compressibility at the Transition Zone of Railway Tracks Reinforced with Cement-Treated Gravel and a Geogrid under Construction

In the transition zone of railway tracks, track irregularities occur frequently due to differential settlement, which arises from the difference between the vertical supporting stiffness of the abutment and the backfill. This is disadvantageous because it increases the maintenance requirements and deteriorates the ride quality. To address this challenge, this study proposes a strategy involving the application of cement-treated gravel reinforced with geogrids and rigid facing walls. The reinforced subgrade for railways (RSR), which can reduce residual settlement through the initial construction of the backfill reinforced with geogrids and the subsequent development of the rigid facing wall, was constructed at the transition zone with cement-treated gravel as the backfill material. The long-term behaviors during and after construction on the RSR for a period of 16 months were evaluated by analyzing the surface and ground settlements, horizontal earth pressure, and geogrid strain. The minor net settlement of the reinforced backfill converges at the early stage of subgrade construction, and the horizontal earth pressure was approximately reduced to the level of 54–63% of the Rankine active earth pressure.

Depth of Soft Cohesive Soil Underlying Highway Embankment for Limiting Residual Settlement

Depth of Soft Cohesive Soil Underlying Highway Embankment for Limiting Residual Settlement

Numerical Analysis Method for Liquefaction-induced Damage Evaluation to Railway Structure

This study aimed to suggest a method for assessing the liquefaction-induced damage to railway embankments, one of the major national SOC infrastructures. To achieve that purpose, the railroad design and maintenance standards in South Korea were examined, and risk assessment method was proposed. The risk assessment of liquefaction-induced damage was classified into no damage level, caution level, and critical level based on the assessment of vertical irregularity, residual settlement, and lateral displacement. To assess the liquefaction-induced damage, three simplified assessment methods and a dynamic numerical analysis method with a finite difference method were proposed. Finally, these methods were applied to the roadbed of the Honam high-speed line, and its applicability was investigated. According to the results, the related standards showed the most overestimated value of settlement among the simplified assessment methods, and the dynamic numerical analysis technique showed the most underestimated value of settlement.

Evaluation of Horizontal Subgrade Reaction Modulus for Integral Abutment Based on Changes in Buffering Zone Stiffness

The buffering zone, which can control the stiffness of the backfill material, is applied at the integral abutment (IA) to reduce the horizontal earth pressure on the abutment and decrease the residual settlement at the transition zone. Numerical analyses are performed to evaluate the horizontal subgrade reaction modulus based on the stiffness change in the buffering zone. A 1 m section from the back of the abutment is set as the buffering zone, and materials such as sandy soil, gravel, and cement-mixed gravel are applied differently. By implementing the buffering zone, the passive and active coefficients of the horizontal subgrade reaction decrease by 28% and 31% at the height of 6.8 m. respectively. Hence, the possibility of adjusting the horizontal subgrade reaction of the IA by changing the stiffness of the buffering zone is confirmed.

Analysis of Behavior Under Horizontal Loads of Integral Abutment for Railways with Buffering Zones

The integral abutment (IA) with buffering zones is a technology that pre-constructs backfill before abutment construction. It can reduce the maintenance cost owing to the decrease in the residual settlement of the backfill after opening. Furthermore, it can reduce the construction cost owing to the decrease in the horizontal earth pressure on the abutment. In this study, to evaluate the modulus of horizontal subgrade reaction in the passive pressure for the design of IA, a half-scale testbed was designed and constructed. A horizontal load test with the maximum load of 1,500 kN was conducted. To verify the test result, the behavior of the IA under horizontal loads was analyzed using finite element analysis. The modulus of horizontal subgrade reaction of the IA using a half-scale test and numerical analysis was estimated to be 36,706 kN/m<sup>3</sup> and 32,746 kN/m<sup>3</sup>, respectively.

The Effect of Fines Content on Compressional Behavior When Using Sand–Kaolinite Mixtures as Embankment Materials

In South Korea, Honam High-Speed Railway has a relatively large residual settlement issue and high fines content has been pointed out as one of the causes. Design guidelines regulate not to use soils containing fines content higher than 25%. However, there is no background information on the effect of fines content on settlement. Therefore, this paper aims to investigate compressional behavior according to fines content using sand and kaolinite. Oedometer test results showed that the compression index is lowest with fines content of 15% to 20% at which the mixture produced maximum density. The optimum fines content for inducing low settlement would be 15% to 20% for the sand–kaolinite mixture. Transition fines content (TFC), which shows sand-like to claylike behavior, was observed to have between 21% and 26% of fines content. Critical fines content (fcrit) where a minimum void ratio occurs was estimated as 21.67%. These behavioral changes appear when fines content is greater than the optimum fines content. SEM also shows that the kaolinite particles were overlapped, creating flat surfaces with a fines content higher than 30%, and showing clay-like behavior. Based on the analysis results, engineers can simply identify the behavior of embankment materials to ensure optimum fines content and consequently minimize long-term settlement potential.

Nonlinear Solid–Fluid Coupled Seismic Response Analysis of Layered Liquefiable Deposit

A seismic response analysis of layered, liquefiable sites plays an important role in the seismic design of both aboveground and underground structures. This study presents a detailed dynamic site response analysis procedure with advanced nonlinear soil constitutive models for non-liquefiable and liquefiable soils in the OpenSees computational platform. The stress ratio controlled, bounding surface plasticity constitutive model, PM4Sand, is used to simulate the nonlinear response of the liquefiable soil layers subjected to two seismic ground motions with different characteristics. The nonlinear hysteretic behavior of the non-liquefiable soil under earthquake excitations is captured by the Pressure Independent Multi Yield kinematic plasticity model with a von Mises multi-yield surface. The soil elements are modelled utilizing the solid–fluid fully coupled plane-strain u-p elements. The seismic response of the layered liquefiable site in terms of the development of excess pore water pressure, acceleration, ground surface settlement, and stress–strain and effective stress path time histories under two representative earthquake excitations are investigated in this study. The numerical results indicate that both the characteristics of ground motions and the site profile have a significant influence on the dynamic response of the layered liquefiable site. Under the same intensity of ground motion, the loose sand layer with a 35% relative density is more prone to liquefaction and contractive deformation, which causes irreversible residual deformation and vertical settlement. The saturated soil layer can effectively filter the high-frequency components and amplify the low-frequency components of ground motions. Moreover, the liquified site produces a 40% post-earthquake consolidation settlement after the excess pore pressure dissipation.