Settlement Reduction Research Articles

Effect of geogrid reinforcement on soil - structure – pipe interaction in terms of bearing capacity, settlement and stress distribution

In this study, the contribution of single and multiple layers of geogrids to bearing capacity and stress behavior was determined by laboratory experiments. The effects of parameters such as the depth of the first geogrid, the vertical spacing between the geogrid layers and the number of geogrid layers on the bearing capacity and settlement behavior of soil and stress distribution on geogrid and pipe by using strain gauges have been investigated. The results of experiments were given in dimensionless form of bearing capacity ratio (BCR), settlement reduction factor (SRF) and stress capacity ratio (SCR). As a result of experiments, the contribution of the geogrid on the soil-structure-pipe interaction has been observed together with the stress distribution on the geogrid contributed to the efficient use of the appropriate geogrid capacity.

Estimation and prediction of the oscillation pattern of meandering geometry in a sub-catchment basin of Bhagirathi-Hooghly river, West Bengal, India

Meandering is the winding curve or bends in a river within the floodplain area. Though it is a natural process, it affects the populace by the resultant effect of lateral migration with bank erosion in the floodplain area. The present sub-catchment basin (Nabadwip–Kalyani stretch) of the Bhagirathi-Hooghly river is a vital lifeline of southern West Bengal, which offers adequate water for irrigation, industrialisation, and human habitation. This region is experiencing a favourable geomorphic change through river bank line changing with bank erosion and sinuous meandering. Illegal sand mining and monsoonal flood enhances the meandering process and triggers the reduction of settlement and cropland. The present study elaborates on the migration tendencies and meandering geometry of this zone and tries to predict the future river centerline position in a sinuous course. The study area is divided into 30 cross-sections, which reveals the increasing trend of lateral migration and erosion behaviour towards the eastward section of this region. The spatial and temporal shifting of river centerline and resultant migration observes and predicts through the migration coefficient approach (Hasegawa in Proceedings of the Hokkaido Branch, Japan Society of Civil Engineering, pp 197–202, 1977; Ikeda et al. in J Fluid Mech 112:363–377, 1981. https://doi.org/10.1017/S0022112081000451 ; Motta et al. in Geomorphology 163–164:10–25, 2012. https://doi.org/10.1016/j.geomorph.2011.06.036 ) by Arc GIS v 9.3.1. This model indicates the trend of channel width decreasing, with increasing near bank velocity in the crescent of meandering bend in future. The simulated and predicted centerline validates by positive linear relation (R2) and lowest RMSE value in few cross-sectional areas. The oscillation character of meander signifies the amount of discharge in the sub-catchment basin. The unpredictable behaviour of the migration shows a rapid change of meandering geometry through the increasing nature of bank erosion possibilities with peak discharge during monsoon. The study predicts future centerline of the meandering channel and the information on river migration, which will contribute to the plan on bank erosion and denote the vulnerable zonation.

Experimental Investigation of Under Reamed Pile Subjected to Dynamic Loading in Sandy Soil

This paper presents an experimental study between uniform pile and different types of under-reamed pile, single bulb. The under-reamed piles are piles with enlarged bases that are suitable to resist considerable movement of the ground, filed up ground, soft clay, and loose sand which have advantages to increase the soil strength, uplift capacity, and decrease the displacement. In the present study, there are experimental analyze to performance the suitable under-reamed type under sinusoidal load from vertical vibration (motor-oscillator was mounted directly on the pile cap. The main finding of this work is that the pile capacity increases with the ream and that all stress values of soil-structure interaction beneath the pile tip and under-reamed pile bulb due to external load can be founded. The under-reamed pile is made of reinforced concrete and the bulb is located at different positions of the embedded length of the pile. The type of soil used in the present work was loose sand and obtained from Karbala city. The Dynamic time-settlement curve has been obtained from the analysis and it was showed that the reduction in settlement is about 223% in case of using a single bulb from L/2 from pile tip which is the best results in comparison with the uniform pile.

Influence of geosynthetic reinforcement on maximum settlements of semi-rigid pavements

The aim of this paper was to improve the understanding of the influence exerted by geosynthetic reinforcement on stress and strain states in typical semi-rigid pavement structures subjected to traffic loading. A comparison of traffic-load-induced settlements of pavements with and without reinforcement is presented. The pavement-subgrade structure was modelled as a two-dimensional three-layer system using the finite element method. The behaviour of such structures was analysed in terms of ground compaction. A model of soil compaction was used to predict pavement deformation under repeated traffic loading. A series of numerical simulations were conducted to investigate the settlements of pavements with and without reflective cracks. It was assumed that reflective cracks propagate from the base layer to the pavement surface. The main attention was focused on the positive effect of the inclusion of reinforcement in pavements on the behaviour of such structures under traffic loading. The influence of such factors as subgrade properties, the magnitude of traffic loading and the presence of cracks in the pavement structure on stress and strain states was investigated. It was confirmed that placing a geosynthetic reinforcement layer inside the bituminous layer leads to a significant reduction in pavement settlements.

Investigation of deformation and degradation response of geogrid-reinforced ballast based on model track tests

A series of large-scale cyclic tests was conducted using process simulation test ( PST) apparatus to capture the influence of loading frequency ( f) on the deformation and degradation behavior of ballast with and without geogrids. Fresh granite ballast and subballast having mean particle diameter ( D50) of 42 mm and 3.5 mm, respectively and five geogrids of different aperture shapes and sizes were used in this study. The tests were conducted at f ranging from 10 to 40 Hz and up to 250,000 load cycles. The test results from the laboratory investigations confirmed that the deformation and degradation behavior of ballast is highly influenced by loading frequency ( f). Moreover, the results showed that geogrid reinforcement stabilizes ballast by reducing the extent of lateral spreading ( ld) and vertical settlement ( Sv) and by minimizing particle breakage ( BBI). The inclusion of geogrids also reduces the extent of vertical settlement in subballast layer ( Svsb). In addition, the extent of volumetric ( εv) and shear strains ( εs) including void ratio ( ef) and density ( γbf) were found to be highly influenced by f. It is further seen that lateral spread and vertical settlement reduction index ( LSRI and VSRI) of all the geogrids decreases with the increase in f. Moreover, it is revealed that with the decrease in LSRI, the extent of Sv and BBI increases. A correlation is developed between the deformations ( ld and Sv) and interface efficiency factor ( α). The effectiveness of geogrid in keeping the ballast in place is evaluated in terms of a new parameter ‘geogrid efficiency factor ( Gef)’. The value of Gef for geogrids used is found to vary from 0.02 to 0.27. It is further shown that Gef under cyclic loading conditions is a function of the interface efficiency factor ( α) evaluated under direct shear conditions.

Effect of pipe characteristics in umbrella arch method on controlling tunneling-induced settlements in soft grounds

Abstract Recent developments in tunneling have stimulated design practitioners to more effectively utilize the underground spaces. However, tunneling at shallow depth in soft grounds gives rise to concerns associated with tunnel instability. Umbrella arch method (UAM), as a pre-reinforcement approach of tunnels in complex geological conditions, is widely used to maintain the tunnel stability. Quantitative assessment of the impacts of the entire approach and forepoling pipe features on tunnel stability remains challenging due to the complex nature of the UAM application. This study aimed to assess the effect of pipe design parameters on reinforcing the tunnels excavated in soft grounds. This practical investigation considered the actual field conditions attributed to the tunneling procedure and UAM deployment. Then, the tunneling process was modeled and the tunnel excavation-induced settlements were calculated. The post-processed results confirmed that deploying the UAM substantially reduced the tunnel crown and ground surface settlements by 76% and 42%, respectively. Investigation of various design parameters of pipes underscored the significance of incorporating the optimum value for each individual parameter into design schemes to more effectively control the settlements. Additionally, contrasting the settlement reduction rates (SRRs) for pipe design variables showed that the tunnel stability is more sensitive to the changes in the values of diameter and length, compared to values of the installation angle and center-to-center distance of the pipes.

Behaviour of vertically loaded piled raft system on cohesionless soil

Foundation is the integral part of structures which is taking all the structural loads and uniformly distributing to the underlying soil. Piled raft is a foundation system where the functions of both pile and raft foundations are combined together effectively to work as a single load distributing system. The major advantage of this system is that, it can act as settlement reducer and are proved to be economic that it can be used where a larger structures. In this work, a model study of a piled raft system by conducting a series of tests on the model with varied design parameters of pile, raft and soil condition. The dimensions and parameters of models are 200 mm × 200 mm size raft with pile lengths of 180 mm, 200 mm and 250 mm which are tested on loose and dense states of soil with number of piles of 4 and 9 sets. The vertical load tests were conducted on both piled and unpiled rafts in loose and dense state of soil and the results were compared. From the results, improvement in the bearing capacity and reduction in settlement were observed with increase in the length of piles, number of piles and density of soil. About 32% of increase in load carrying capacity was noted when length of piles compared to the shortest piles and 79% of increase in load capacity for the system when degree of compaction of soil were varied from looser to denser state of foundation soil. Thus from this model study, it was suggesting that the pile raft system with optimised design of pile and raft can improve the efficiency and this foundation system can also be made economical by providing an alternative solution of foundation for heavy buildings.

Behaviour of Vertically Loaded Piled Raft System

A foundation gives the overall strength to a building by providing a level surface for the building to stand and distributing the total load uniformly to the underlying soil. The type of foundation to be chosen varies with the foundation soil and site conditions. Piled raft system are a type of foundation preferred when the bearing strata has less soil bearing capacity and a huge load has to be transferred. Thus Piled raft foundation is a foundation system which uses the combined effects of both rafts and piles such that it is expected to transfer huge loads without large settlement. An ample evaluation of factors like number of piles, length of piles, and degree of compaction of soil that affects the performance of the foundation is required, to understand the concept of piled raft foundation. This study was based on the behaviour of vertically loaded piled raft system by varying the length of pile as 100 mm, 150 mm and 200 mm with 4 and 9 numbers of pile conducted on loose and dense state in cohesion less soil. A vertical load test was conducted on unpiled raft both in loose and dense state of soil also and the results obtained from both piled and unpiled rafts were compared together. The compared results indicated an improvement in ultimate load capacity and settlement reduction. A settlement reduction of 32.71% and increased bearing capacity of 63.67% were observed when compared to unpiled raft under dense condition. About 84% of increase in bearing capacity of the piled raft system was observed with varying the degree of compaction of soil from loose to dense state of soil. An optimum design of this piled raft foundation can provide an alternative foundation for high rise buildings, transmission towers, bridges etc. and it can provide an aid to the threat of differential settlement for heavy loaded buildings in poor bearing strata.

Development and Performance Analysis of Soil Flow Protector to Reduce Soft Soil Settlement Caused by Cavity Formation

Settlement of a relatively small magnitude occurs in box structures supported by pile foundations. However, if cavities are generated under the box structure, ground settlement can be accelerated by surrounding soil entering the cavities. In order for the structure to maintain stability for a long period of time, sustainable development to maintain the stability of the building must be continued. Preventing rapid ground settlement can lead to long-term structural stability and prevent the occurrence of life-threatening damage, thereby helping to maintain and build a sustainable urban infrastructure. Thus, in this study, a soil flow protector (SFP) that can be easily installed on the sides of the structure was developed to mitigate the aforementioned problem. Field tests and numerical analysis were performed to investigate the effect of SFP installation on structural stability and settlement reduction. After performing field experiments, it was found that SFP installation could reduce ground settlement and ground horizontal displacement. Moreover, for a 79.9-mm settlement, the safety factor was 1.315, which remained stable even when the settlement reached 345 mm. Hence, the developed SFP can be used to reduce soft ground settlement affecting box structures supported by pile foundations.

2D and 3D discrete numerical modelling of soil arching

In this study, 2D and 3D soil arching phenomena associated with piled embankments were evaluated by performing a series of discrete numerical analyses using the particle flow code (PFC3D) software. After validating the micro-parameters with experimental results, we compared the stress-displacement distribution, force chain evolution, maximum vertical displacement of particles, and deformation characteristics induced by 2D and 3D arching effects. Additional analyses were carried out to understand the influence of the fill height, pile clear spacing, friction coefficient, and porosity on soil arching with respect to the stress concentration ratio (SCR) and settlement along the elevation at various sections. The numerical results indicated that a plane soil arch in a 2D embankment overestimates the degree of load transfer and underestimates the settlement at the crest and within the embankment along the elevation in a 3D embankment. A lower equal settlement plane can be found in a 2D embankment. Furthermore, an increase of fill height and friction angle, and a decrease of pile clear spacing and porosity can help to improve the degree of reduction in load transfer and settlement in both 2D and 3D embankments. However, for partially mobilized soil arching in the 3D condition, the increase of fill height reduces the settlement of soils mainly in the portion above the square subsoil area, but has less influence over the portion above the rectangular subsoil area.

Evaluation on full-scale testbed performance of cement asphalt mortar for ballasted track stabilization

This study focuses on the full-scale testbed performance of two types of ballasted railway track systems, with and without cement asphalt mortar (CAM) stabilizing material. This method develops a strong membrane between the fouled ballast particles which provides bonding and strengthening effects to the entire ballast layer, thus reinforcing the structural regularity of the track-bed. The feasibility of the proposed solution (CAM) is evaluated through static and dynamic wheel load application which simulate the actual operation of running trains. To compare the effectiveness of the new solution from the conventional maintenance strategy, the roadbed pressure, plastic/elastic deformation, load distribution, and track stiffness analysis are measured. From the full-scale testbed results, the Life Cycle Cost Analysis (LCCA) is conducted to verify the actual cost-effectiveness. In general, it was confirmed that the CAM stabilizing solution improves the performance of ballasted track system at both static and dynamic loading stages. The testbed results also suggest that a significant reduction in elastic and plastic settlement in stabilized track. The LCCA test results reveal a good potential for the sustainable development of ballasted track system stabilized by CAM.

Effectiveness of geosynthetic reinforcement for load transfer in column-supported embankments

Many column-supported embankment (CSE) design methods include geosynthetic reinforcement for vertical load transfer and/or settlement reduction regardless of project conditions. However, geosynthetic reinforcement may not be necessary for all applications, particularly if a sufficiently thick and strong soil layer overlies the compressible soil. A strong soil layer can transfer embankment loads to the columns without much differential settlement at the base of the embankment, limiting the development of tension in the reinforcement. If weak and compressible soil extends to the ground surface and the area replacement ratio is low, differential settlements may be so large that it may not be practically possible to provide enough reinforcement to avoid excessive strain or rupture. This paper describes parametric studies using the Load Displacement Compatibility method to investigate the influences of embankment height, geosynthetic stiffness, column diameter, and thickness of an upper sand layer on geosynthetic strain, differential settlement at the base of the embankment, and load distribution among the CSE components. Results of the parametric study show that site conditions, CSE system geometry, and performance requirements limit the range of circumstances for which geosynthetic reinforcement for settlement reduction is needed, effective, and practically possible.

Analysis of unreinforced and reinforced shallow piled embankments under cyclic loading

Reinforced piled embankments are being increasingly used for construction over soft ground due to their efficiency in reducing potential settlement, speed of construction, and associated cost. Most of the previous studies focused on developing understanding of the behaviour of thick embankments that are loaded with a static surcharge load. Data on the behaviour of shallow piled embankments under cyclic loadings are scarce. In this study, an experimental programme was undertaken using a fully instrumented testing rig to generate data and improve our understanding of the behaviour of unreinforced and reinforced shallow piled embankments subject to monotonic and cyclic loadings that were applied over a predetermined area of the embankment. The experimental results showed that collapse of soil arching is instantaneous and occurs during the first few cycles of load. However, strength was regained, and recovery of the arching effect was observable during further stages of cyclic loadings due to densification of the embankment material and deformation of the soft subsoil. Inclusion of reinforcement layers was found to enhance the performance of load transfer mechanisms by concentrating stresses on pile caps. The results clearly showed a significant reduction in surface settlement, soft subsoil settlement and heaving with increasing numbers of reinforcement layers.

Numerical evaluation of the behavior of ordinary and reinforced stone columns

Due to the lack of soil with sufficient load-bearing capacity and the ever-increasing number of large-scale building projects, methods for soil improvement have become vital. Among the conventional methods of soil improvement, the use of reinforced and ordinary stone columns is one of the most prevalent; this is due to its environmental compatibility and proven effectiveness. In this paper, the mechanical behavior of ordinary and reinforced stone columns was studied using ABAQUS, a finite element software. A3D nonlinear finite element model of the column-improved soft soil was built. The results of this work show that while the columns alone decrease the soil settlements, the combination with the geosynthetics additionally augments the effects. Parametric studies were completed to illustrate the effects column grouping on the design process. Thus, the effects of parametric exploration, including inter-column spacing parameters as well as the length and diameter of the stone columns, on the reduction of settlements and bulging were studied for different conditions.

Numerical analysis of ground improvement effects on dynamic settlement of uniform sand using DEM

Uniform fine sands are recognized as problematic soils which are highly prone to earthquake or dynamic loads effects. Cyclic and dynamic loads on such soils can destroy its structure and cause them to experience high volume change. In loose sands, volume change originated from dynamic or cyclic loadings (caused by earthquake, machineries or other similar sources) can lead to excessive settlements on the ground surface which in turn endangers the structural integrity and performance of the superstructure. As a consequence, it is important to perform soil improvements prior to putting any foundation on them. Among many known and recently developed techniques, the soil compaction (or densification) and cement injection are the widest techniques in fine sands improvement. In this research, a numerical study is employed which incorporates the distinct elements method to investigate the volume change and settlement of uniform fine sands. The results obtained numerically have been compared with those observed in a laminar shear box physical model of samples of fine sand. A surface footing is placed over the top of the specimen in the shear box which is modeled by a small rigid plate. Comparisons indicate that the applied simulation technique is suitable for the soil under study. To simulate the model and for verification purpose, Anzali sand physical and mechanical properties have been implemented. Soil particles in the discrete elements technique were modeled by spherical particles obeying the Anzali sand grain size distribution, and for the surface footing, rigid clumps of particles were used. Experiments were performed for density indices of 30–88%, and numerical simulations by the discrete elements method were performed at porosities of 0.43–0.38. The trend of dynamic settlement over the cyclic loading shows a good agreement with measured data in the laboratory. Results revealed that the improvement techniques such as compaction and cementation have a significant effect on the reduction in the final settlement under applied dynamic loads.

The initial, primary and secondary consolidation response of soft clay reinforced with a granular column under isolated loading

This paper presents the assessment of consolidation and creep settlements of an isolated circular footing supported on soft clay samples reinforced with a single granular column. Clay samples (300 mm dia., 400 mm high) were formed from reconstituted kaolin and remoulded sleech (exhibiting significant creep). These samples were tested using chambers with various features to capture the settlement under constant foundation loading. In one model, the footing (70 mm dia.) was supported by a 40 mm dia. granular column formed by crushed basalt. The footings, with and without a granular column, were subjected to five vertical loading increments: 60, 120, 180, 240 and 300 kPa in the case of kaolin. In the case of sleech, vertical loading increments were: 60, 120 and 180 kPa. Each test lasted approximately ten months. In the case of kaolin, the settlement reduction factor was marginal, although it was considerably better for sleech. Kaolin exhibited marginal creep settlement under low to moderate bearing pressure, which increased substantially under high bearing pressures. Creep settlement was more prominent in sleech at all levels of bearing pressures. The very interesting finding from the investigation is that the settlement reduction factors due to consolidation and creep are similar in order under low to moderate loadings.

Analysis of Construction Settlement of Shield Tunnel Crossing Metro Operating Tunnel

Based on the background of the Suzhou Metro Line 3 crossing the Line 1 operating tunnel, the finite element software MIDAS/GTS was used to perform 3D model and simulate the construction of the shield tunnel. The influence of shield tunnel penetration before and after strengthening on operating tunnels is studied. The research results show that the maximum settlement of the operating tunnel caused by underpass construction without reinforcement is 11.64mm, which exceeds the control value of 10mm, and deformation control measures must be taken. After reinforcement, the maximum settlement of the soil around Line 3 is only 5.65mm, the reduction of settlement about 50%, and the settlement control effect is obvious, which shows that it is feasible to take deformation control measures for pre-reinforcement of the soil around the tunnel.

Performance of Geosynthetics Reinforced Subgrade Subjected to Repeated Vehicle Loads: Experimental and Numerical Studies

Use of the geosynthetics to strengthen the soil is one of the highly desirable techniques under static and dynamic loads. The present study describes the experimental and numerical studies performed on the geosynthetic reinforced subgrade subjected to repeated vehicle loads. The cyclic plate load tests were conducted on the sand subgrade reinforced with planar and 3D geosynthetic reinforcements. The vehicle load was simulated by applying a repeated load of magnitude 275 kPa with 1Hz frequency on the reinforced subgrade. Results of the experimental investigations revealed that the performance of the subgrade soil improved significantly in the presence of reinforcements. The estimated parameters illustrated the three-fold reduction in settlement of the subgrade in the presence of reinforcement. Further, the heaving of the subgrade soil was found completely arrested with the use of geosynthetic reinforcement. The three-dimensional geocell reinforcement performed effectively as compared to planar geogrids under dynamic load. The measured pressure values at different depth demonstrated a significant reduction in the pressure in the presence of reinforcements. Besides, numerical simulations were performed using PLAXIS2D to understand pressure and settlement distribution patterns in the reinforced subgrade. In overall, a good agreement was observed between numerical and experimental results.

Model studies of plus and double box shaped skirted footings resting on sand

The paper presents the investigation on the model unskirted/skirted footings (plus and the double box) on sand. Skirt depth, sand relative density, footing interface condition and skirted footing type were varied parameters. Skirt depth (Ds) varied in this investigation was from 0.25 B to 1.5 B (B, footing width). The results show that the footing geometry and the skirt increased the bearing capacity and improved the overall behaviour. The results further revealed that the lowest percentage improvement for the square shaped footing with Ds/B = 0.25 was 26.08% at a relative density of 60%, whereas the highest improvement for the double box shaped footing with Ds/B = 1.50 was 364.12% at a relative density of 30%. The settlement reduction factors with the use of skirt from this investigation ranged from 0.16 to 1.0 and depended on the pressure applied and the depth ratio of the skirt. Finally, for the settlement reduction factor, an empirical equation was developed. This expression can be used to calculate the settlement of the plus and double box shaped skirted footings on sand.

Uji Beban Timbunan yang Diperkuat dengan Sistem Pelat Terpaku pada Tanah Gambut

One of the problems with peat soils, when subjected to imposed loads of construction, is the very high compression and long-term excessive settlement. The embankment can be built on peat soil, but it needs reinforcement that can contribute to increasing the stability of the embankment. The nailed slab system, as reinforcement, is expected to reduce settlement and increase the stability of peat soil. The aim of this paper is to study the effect of pile length and distance on the reduction of settlement in both monolithic and non-monolithic piles. The embankment load test was conducted on 70 cm x 120 cm plates, which were reinforced pile with different lengths and distances in the peat soil layer. The analysis was conducted on the reduction settlement of monolithic and non-monolith pile. The results showed that the length and distance of the pile had an effect on the reduction settlement. Changes in pile length are more dominant reducing settlement compared to changes in pile distance. Pile connection with slab has a significant effect on different lengths of piles than different distances piles.