Soft Clay Subgrade Research Articles

Performance of a triaxial geogrid-reinforced crushed rock base underlain by a soft clay subgrade

This large-scale test investigated the behavior of a pavement structure composed of a crushed rock base underlain by a soft clay subgrade reinforced with a triaxial geogrid under static loading. The fully instrumented pavement model included a 0.8-m-thick soft clay layer and a 0.2-m-thick crushed rock layer. A triaxial geogrid, Triax TX150, was installed at the interface between the subgrade and base layers and the mid-depth of the crushed rock base. Both unreinforced and reinforced pavement models were prepared in a square steel mold of 1.5 m width and 1.2 m height. Plate load tests were conducted according to ASTM standards. The results revealed that the number of geogrid layers and their locations influenced the reinforced pavement’s ultimate bearing capacity and failure mechanisms. Two-layer reinforcement (between the crushed rock and soft clay layers and in the middle of the crushed rock layer) provided the maximum bearing capacity, with an improvement factor of 1.63 compared to that of the unreinforced pavement, because the triaxial geogrids changed the failure mode of the unreinforced pavement from punching failure in the crushed rock and local shear failure in the soft clay to only punching failure in the crushed rock. Thus, triaxial geogrids are suggested for enhancing the performance of pavements on soft clay subgrades.

Numerical analysis of the influence of granular trench reinforcement of soft clay subgrade on the undrained dynamic response of a railway track

Soft subgrade poses significant challenges to the designer of railway tracks due to its high compressibility and low shear wave velocity. The low shear wave velocity might affect the maximum design speed of the train. The stabilization of this soft soil improves its performance and reduces the expected settlement. However, little attention has been paid to understanding the feasibility of different stabilization techniques, as there are very few studies on this topic. Thus, this research study aims to determine the impact of granular trench reinforcement of soft subgrade on the dynamic response of a railway track subjected to a moving train load. Three-dimensional finite element analysis has been used in this research. The effect of the train speed and the depth of the granular trench has been carefully evaluated. It has been found that the critical velocity (which is the velocity that corresponds to the highest settlement) is not affected by the granular trench reinforcement. In addition, it has been noted that the granular trench reinforcement reduces the maximum settlement of the railway track under the moving loads, with a percentage reduction ranging between 1% and 24%. Furthermore, the granular trench reinforcement did not affect the acceleration induced in nearby areas due to the train’s vibration. The results of this research provide useful insight into the feasibility of the granular trench and help design engineers compare different solutions for the problems of soft subgrade soil.

Effectiveness Of Portland Cement Type 1 In Stabilizing Soft Clay Soil As Subgrade For Road Construction

Sawah Lunto – Talawi road segment (STA 139 + 700 m) in Sawah Lunto city, West Sumatera province has sustained major damages and been the scene of several accidents since the past few years. The degression of soft clay subgrade, which has a limited bearing capacity and makes it structurally impractical to sustain road construction, was discovered to be the source of these damages. As a recent option for enhancing soil qualities, soil stabilization by employing a variety of pozzolanic and industrial materials has gained popularity. The objective of this study is to investigate the effectiveness of Portland cement type 1 as stabilizing material in improving the soil properties and carrying capacity requirements for soft clay soil used as subgrade in road construction. To accomplish the objectives of this study, a laboratory testing procedure was implemented. Unconfined Compressive Strength (USC) values on natural soil and treated soil with Portland cement type 1 admixture were measured and compared during laboratory experiments. Soft clay soils were stabilized with varying percentages of Portland cement type 1 with the proportions of approximately 1%, 2%, 3%, 4%, 5%, 6%, 7%, and 10% by dry weight of soil during a 7-days curing period. Laboratory testing were performed in compliance with Indonesian National Standard (SNI): SNI 3420-2008 for testing Unconfined Compressive Strength. According to the results of laboratory testing, the UCS values increased roughly from 0.634 kg/cm2 (undisturbed natural soil) to 2.832 kg/cm2 (treated soil) by adding 3% of Portland cement type 1, and up to 8,024 kg/cm2 (treated soil) by adding 10% of Portland cement type 1. Based on the findings, it can be demonstrated that Portland cement type 1 can enhance clay soil's properties used as a subgrade for road construction, can create more stable road conditions, and can ultimately meet the technical feasibility requirements for the subgrade carrying capacity, particularly at the Sawah Lunto - Talawi road segment (STA 139 + 700 m).

Numerical Study on the Behaviour of Geocell-Reinforced Sand Layer Overlying Soft Clay Subgrade

Numerical Study on the Behaviour of Geocell-Reinforced Sand Layer Overlying Soft Clay Subgrade

A settlement prediction model considering tidal loading and traffic loading of soft soil subgrade

A large number of soft soil subgrade projects have been built in the tidal-flat zone of southeast China. Where, in addition to bearing the traffic loading, the soft soil subgrade may be swallowed up by tidal water. Therefore, the soft soil subgrade will bear long-term coupling action of tidal loading and traffic loading in the tidal-flat zone. Excessive settlement accidents of the subgrade occur frequently in the tidal-flat zone. In this study, a new dynamic constitutive relation considering seepage characteristics was used and the UMAT subroutine was embedded in ABAQUS. FE parametric analysis was analyzed considering three influencing factors of tidal amplitudes, traffic loading amplitude and tidal period. A multi-factor coupling settlement prediction expression considering tidal loading and traffic loading of soft soil subgrade suitable for soft soil subgrade in the tidal-flat zone was proposed. In addition, a settlement prediction program of soft clay subgrade under the combined tidal loading and traffic loading was designed and developed to facilitate engineering use. The research results can be applied to the subgrade projects in the tidal-flat zone, and provide a reference for engineering decision-making and disaster prevention and mitigation.

Improved Mechanical Properties of Cement-Stabilized Soft Clay Using Garnet Residues and Tire-Derived Aggregates for Subgrade Applications

The growth of the global economy in recent years has resulted in an increase in infrastructure projects worldwide and consequently, this has led to an increase in the quantity of waste generated. Two recycled materials, namely garnet residues (GR) and tire-derived aggregates (TDA), were used to improve mechanical properties of soft clay (SC) subgrade in this study. GR was evaluated as a replacement material in SC prior to Type I Portland cement stabilization. TDA was also studied as an elastic material in cement-stabilized SC–GR. The laboratory tests on the cement–TDA-stabilized SC–GR included unconfined compressive strength (UCS), indirect tensile stress (ITS) and indirect tensile fatigue (ITF). Microstructural analysis on the cement–TDA-stabilized SC–GR was also performed to illustrate the role of GR and TDA contents on the degree of hydration. The UCS of cement-stabilized SC–GR increased when cement content increased from 0% to 2%. Beyond 2% cement content, the UCS development was slightly slower, possibly due to the presence of insufficient water for hydration. The GR reduces the specific surface and particle contacts of the SC–GR blends to be bonded with cementitious products. The optimum SC:GR providing the highest UCS was found to be 90:10 for all cement contents. Increased amounts of GR led to a reduction in UCS values due to its high water absorption, resulting in the insufficient water for the cement hydration. Moreover, the excessive GR replacement ratio weakened the interparticle bond strength due to its smooth and round particles. The TDA addition can enhance the fatigue resistance of the cement-stabilized SC–GR. The maximum fatigue life was found at 2% TDA content. The excessive TDA caused large amounts of micro-cracks in cement–TDA-stabilized SC–GR due to the low adhesion property of TDA. The SC:GR = 90:10, cement content = 2% and TDA content = 2% were suggested as the optimum ingredients. The outcome of this research will promote the usage of GR and TDA to develop a green high-fatigue-resistant subgrade material.

A novel time-power based grey model for nonlinear time series forecasting

To deal with various nonlinear issues in real applications, a novel time-power based grey model is put forward. However, in the original form of this model, the time-power parameter α normally equals to an integer, and then the analytical expression of the time response function will be obtained. Otherwise, if the parameter α equals to a non-integer, one cannot obtain the concrete time response function for future estimations. This situation may significantly restrict the applications of this grey model. To address such drawbacks, an optimized version is designed in this work. In the proposed model, a simplified solution to the differential equation is derived by using the definite integral technique. Furthermore, for improving accuracy, the time-power parameter α is optimized by utilizing the Particle Swarm Optimization algorithm based on the model parameter packages. Subsequently, the efficacy and practicality of this simplified function have been verified by numerical simulations and experimental studies. Moreover, the method of probability density prediction is employed for verifying the reliability and stability of the proposed model for the first time when predicting the settlement of the soft-clay subgrade on an expressway. The demonstration cases illustrate that the quantitative improvements over forecasts of the proposed model are even more pronounced with a level accuracy of 2.29% and 1.19% MAPE values in the fitted and predicted periods, respectively, which can significantly increase the predicting accuracy by more than 10% with respect to the other benchmarks. Therefore, the new proposed model not only has greater application fields and prospects but also achieves higher and more reliable predicting accuracy with the optimal α under the support of the Particle Swarm Optimization algorithm, compared with the competing models.

The effects of cyclic loading on the reconsolidation behaviours of marine sedimentary clays under intermittent drainage conditions

The reconsolidation settlement of marine sedimentary clay subgrade subjected to cyclic dynamic loading under intermittent drainage conditions needs to be further studied. In this study, a series of triaxial tests was conducted on natural Wenzhou soft clays to investigate the reconsolidation responses induced by staged cyclic loading under intermittent drainage conditions. The dynamic behaviours of the test specimens, such as the evolution of excess pore water pressure, variations in stress-strain hysteresis loops and resilient modulus, and cumulative strain development, are analysed and discussed. The experimental results show that during the intermittent quiescent drainage period, the dissipation of the excess pore pressure generated during the cyclic loading period results in reconsolidation of the test specimen. Hardening occurs throughout the tests, as determined by observing the variations in the hysteresis loops and resilient modulus. Throughout the tests, a higher percentage of the axial plastic strain in the quiescent period to the total axial plastic strain indicates that the reconsolidation deformation of the soft clay subgrade caused by intermittent drainage cannot be ignored. These conclusions have significant value for performing in-depth research on the dynamic behaviours of marine sedimentary clays subjected to cyclic traffic loading and predicting the settlement of roads in engineering practice.

Groundwater Drainage By Means Of Electrochemistry For Soil Improvement

In the last decade, the construction of communication routes has intensified globally. As a result, many case studies have emerged related to the presence of saturated clayey soils in the foundation ground. In order to speed up the execution of highways and railways in a safely manner, the designers use different methods for improving soft clays in terms of compressibility.The present paper aims to evaluate the efficiency of an electrochemical method used for the dewatering of a soft montmorillonite clay subgrade. The effects on the consolidation process are analyzed for the final conclusions. The advantages of the method are briefly discussed, and some potential areas for scientific research are proposed.

Vibration propagation of subgrade built on treated dredged fill

Saturated soft clay subgrade in Wenzhou was reinforced by a combination of vacuum preloading and surcharge preloading using different loading materials. Using the principle of similarity, embankments were erected on samples of the soft clay subgrade in a large model box using three different materials (slag, coarse aggregate and sand). A vibration transmission test was conducted on the samples. The test results were used to analyse three factors that majorly affect the transmission of dynamic loads. The relationship between the vibration velocity and the distance from the vibration source was also investigated and used to derive a modified vibration attenuation equation. An increase in subgrade compressive stiffness was found to be helpful to decrease the vibration amplitude. In addition, the attenuation of the vertical vibration velocity was observed to accelerate with increasing embankment height and width.

An Improved Time-Series Model Considering Rheological Parameters for Surface Deformation Monitoring of Soft Clay Subgrade.

Building deformation models consistent with reality is a crucial step for time-series deformation monitoring. Most deformation models are empirical mathematical models, lacking consideration of the physical mechanisms of observed objects. In this study, we propose an improved time-series deformation model considering rheological parameters (viscosity and elasticity) based on the Kelvin model. The functional relationships between the rheological parameters and deformation along the Synthetic Aperture Radar ( SAR) line of sight are constructed, and a method for rheological parameter estimation is provided. To assess the feasibility and accuracy of the presented model, both simulated and real deformation data over a stretch of the Lungui highway (built on soft clay subgrade in Guangdong province, China) are investigated with TerraSAR-X satellite imagery. With the proposed deformation model, the unknown rheological parameters over all the high coherence points are obtained and the deformation time-series are generated. The high-pass (HP) deformation component and external leveling ground measurements are utilized to assess the modeling accuracy. The results show that the root mean square of the residual deformation is ±1.6 mm, whereas that of the ground leveling measurements is ±5.0 mm, indicating an improvement in the proposed model by 53%, and 34% compared to the pure linear velocity model. The results indicate the reliability of the presented model for the application of deformation monitoring of soft clay highways. The estimated rheological parameters can be provided as a reference index for the interpretation of long-term highway deformation and the stability control of subgrade construction engineering.

Modelling and Analysis of Rails on Viscoelastic Foundation Under a Moving Load

The proposed analysis predicts the time-dependent behaviour of rails resting on geocell-improved soft clay subgrade subjected to moving load. Rail and geocell (with infill soil) have been modelled as Euler–Bernoulli beams of infinite length with finite bending stiffness. Upper granular mat has been characterized as Pasternak shear layer sandwiched between two beams resting over soft clay subgrade idealized by the four-parameter Burger model. Developed governing differential equations have been non-dimensionalised using appropriate dimensionless parameters. Numerical solution of these equations has been obtained by a finite difference scheme in conjunction with the Gauss–Seidel method in an iterative manner using appropriate boundary conditions. Detailed parametric study has been conducted to understand the influence of Burger model parameters, velocity and magnitude of applied load, flexural rigidity and location of geocell on the flexural response of rails. Critical velocity has been determined, and its time dependency has also been discussed. The present study also reports variation in degree of consolidation with elapsed time and procedure to obtain consolidation characteristics for such a double beam system representing geocell-reinforced railway tracks.

Ground Subsidence Investigation in Fuoshan, China, Based on SBAS-InSAR Technology with TerraSAR-X Images

Highways built on soft clay subgrade are more prone to subsidence due to the geotechnical characteristics of soft clay. Monitoring ground movements in this area is significant for understanding the deformation dynamics and reducing maintenance cost as well. In this paper, small baseline subset synthetic aperture radar interferometry (SBAS-InSAR) technique is exploited to obtain and investigate the time series ground surface deformation after the construction of a road embankment over soft clay settlement. Considering the important effect of temporal deformation models on the final accuracy of estimated deformation, both the linear velocity model and seasonal deformation model are utilized to conduct the comparative investigation of deformation time series. Two highways in Fuoshan, China—G1501 Guangzhou Belt Highway and Lungui Highway—were selected as the test area. Thirteen TerraSAR-X images acquired from October 2014 to November 2015 were analyzed. Comparative study based on two groups of analyses generated from the two models for both highways were conducted. Consequently, several feature points distributed near the two highways were analyzed in detail to understand the temporal evolution of the settlement. In order to evaluate the reliability of our measurements, the residual phase was analyzed to assess the modelling accuracy of the two models. In addition, leveling data were also used to validate the experimental results. Our measurements suggest that the seasonal model is more suitable for the test highways, with an accuracy of ±3 mm with respect to the leveling results.

Radar Interferometry Time Series to Investigate Deformation of Soft Clay Subgrade Settlement—A Case Study of Lungui Highway, China

Monitoring surface movement near highways over soft clay subgrades is fundamental for understanding the dynamics of the settlement process and preventing hazards. Earlier studies have demonstrated the accuracy and cost-effectiveness of using time series radar interferometry (InSAR) technique to measure the ground deformation. However, the accuracy of the advanced differential InSAR techniques, including short baseline subset (SBAS) InSAR, is limited by the temporal deformation models used. In this study, a comparison of four widely used time series deformation models in InSAR, namely Multi Velocity Model (MVM), Permanent Velocity Model (PVM), Seasonal Model (SM) and Cubic Polynomial Model (CPM), was conducted to measure the long-term ground deformation after the construction of road embankment over soft clay subgrade. SBAS-InSAR technique with TerraSAR-X satellite imagery were conducted to generate the time series deformation data over the studied highway. In the experiments, three accuracy indices were applied to show the residual phase, mean temporal coherence and the RMS of high-pass deformation, respectively. In addition, the derived time series deformation maps of the highway based on the four selected models and 17 TerraSAR-X images acquired from June 2014 to November 2015 were compared. The leveling data was also used to validate the experimental results. Our results suggested the Seasonal Model is the most suitable model for the selected study site. Consequently, we analyzed two bridges in detail and three single points distributed near the highway. Compared with the ground leveling deformation measurements and results of other models, SM showed better consistency, with the accuracy of deformation to be ±7 mm.

INVESTIGATION ON INSAR TIME SERIES DEFORMATION MODEL CONSIDERING RHEOLOGICAL PARAMETERS FOR SOFT CLAY SUBGRADE MONITORING

Abstract. The stability control is one of the major technical difficulties in the field of highway subgrade construction engineering. Building deformation model is a crucial step for InSAR time series deformation monitoring. Most of the InSAR deformation models for deformation monitoring are pure empirical mathematical models, without considering the physical mechanism of the monitored object. In this study, we take rheology into consideration, inducing rheological parameters into traditional InSAR deformation models. To assess the feasibility and accuracy for our new model, both simulation and real deformation data over Lungui highway (a typical highway built on soft clay subgrade in Guangdong province, China) are investigated with TerraSAR-X satellite imagery. In order to solve the unknows of the non-linear rheological model, three algorithms: Gauss-Newton (GN), Levenberg-Marquarat (LM), and Genetic Algorithm (GA), are utilized and compared to estimate the unknown parameters. Considering both the calculation efficiency and accuracy, GA is chosen as the final choice for the new model in our case study. Preliminary real data experiment is conducted with use of 17 TerraSAR-X Stripmap images (with a 3-m resolution). With the new deformation model and GA aforementioned, the unknown rheological parameters over all the high coherence points are obtained and the LOS deformation (the low-pass component) sequences are generated.

Undrained cyclic behavior of overconsolidated marine soft clay under a traffic-load-induced stress path

ABSTRACTTo reduce the settlement induced by long-term traffic loads, the surcharge preloading method is widely used to improve the characteristics of marine soft clay subgrade. However, its effectiveness needs clarification. This paper presents the test results for the cyclic behavior of normal and overconsolidated marine soft clay under stress paths that simulate traffic loading through hollow cylinder apparatus. Test results show that the overconsolidation ratio significantly influences the axial strain, pore water pressure, stress–strain loops, and resilient modulus of soft clay specimens. Moreover, regression analysis on results under stress path with principal stress rotation predicts the permanent strain for overconsolidated marine soft clay.

Bearing Capacity of Flexible Pavement System Reinforced with Fiberglass Geogrid

Fiberglass geogrids are often used to minimize thermal and stress related reflective cracking and to increases the fatigue life of pavements with weak foundations. The objective of this paper is to evaluate the bearing capacity of flexible pavement system on weak subgrade reinforced with fiberglass geogrids by laboratory California Bearing Ratio (CBR) test. The pavement system consists of a cold mix asphalt layer, a gravel base layer, and a soft clay subgrade. Two fiberglass geogrids were used as reinforcement material and were placed at two different locations. The bearing capacity of unreinforced and reinforced pavement systems were measured and compared. Results of these tests show that the bearing capacity of the pavement system can be increased by up to 166% for the system reinforced with fiberglass geogrid placed at the middle of the asphalt layer.

Settlement of Soft Clay Subgrade Under Coupled Effects of Vibration Frequency and Dynamic Stress Ratio Caused by High-Speed Train Loads

Settlement regularity of soft clay subgrade under cyclic principal stress rotation caused by high-speed train loads is investigated. In laboratory tests, it is found that, with increasing vibration frequency at a fixed dynamic stress ratio, the increase of axial plastic cumulative strain in saturated soil is restricted at mid-high frequencies (0.5-2 Hz), and the changes in pore-water pressure are not evident. Combined with the empirical settlement formula and analysis of the dynamic amplification equation of German standard, a simplified settlement calculation method accounting for resonance is obtained.

Proposed Design Graphs of Geotextile Reinforcement on Soft Clay under Various Field Conditions

This paper describes the behavior of reinforced embankments constructed on soft clay subgrade with varying compressible depths, embankment slopes and embankment heights. The stability of the embankment is evaluated using the Bishop method. The resistance moment and the numbers of geotextiles required are examined. It is shown that varying the subgrade and embankment can significantly affect the embankment stability and also the number of reinforcements. It requires a lot of time to design embankment reinforcements, especially when the length of the embankment is tens of kilometers. The main aim of this study is to develop graphs to assist in designing the number of geotextile reinforcements. This paper proposes design graphs to support engineers and designers to determine the required geotextile reinforcements for embankments.

Permanent Deformation Study of Pavement Layers Using Laboratory Pavement Model Testing

AbstractLightly stabilized granular materials with slow-setting cementitious binders are widely used in the construction of new pavements and rehabilitation of old pavements in Australia and other countries. Higher strength and durability of these materials combined with relatively low cost are reasons they are widely used. The mechanistic-empirical design of pavements with lightly stabilized materials requires key parameters, such as permanent deformation of these materials. A cyclic load-testing facility was developed for studying the permanent deformation characteristics of pavement materials. In particular, a typical pavement structure consisting of a lightly stabilized granular road base material over an expansive soft clay subgrade material was studied using a pavement model testing (PMT) facility. In the PMT facility, the model pavement structure was constructed in a 1.0 × 1.1 × 0.6-m steel tank, and the wheel loading from the vehicle was simulated using a circular steel plate subjected to sinusoid...