Browsing by Author "Sanjei, C"

Now showing 1 - 7 of 7

item: Conference-Full-text
Effect of construction sequence on the behaviour of gravity type retaining wall
(Department of Civil Engineering, University of Moratuwa, 2015-10) Sanjei, C; De Silva, LIN; Hettiarachchi, MTP
Gravity retaining walls derive their capacity to resist lateral movement through the dead weight of the wall. The design methodologies proposed by standards do not take into account the construction sequences that simulate the process by which the soil and retaining wall are brought together. However, in reality, at least during the backfilling process, the retaining wall undergoes many displacements that are not so far considered in the design. In this investigation, effect of construction sequences in the gravity retaining walls with different shapes is investigated with the help of finite element method. Two different construction sequences, namely the backfilling after wall construction and the backfilling parallel to wall construction, are compared for different wall shape models. Lateral displacement of the bottom and the top of the wall is plotted for each model and construction sequence with construction stages. Bearing pressure distribution, lateral earth pressure and failure wedge angle are summarized and compared with design values. Each wall showed different behavior for each of the construction sequences. Back filling after wall construction minimizes the sliding failure and bearing pressure. Overturning failure could be reduced by backfilling parallel to wall construction. However, it was observed that, comparatively, backfilling after wall construction is more effective than backfilling parallel to wall construction, suggesting that proper selection of construction method also may reduce negative effects on the wall stability.
item: Conference-Abstract
Feasibility study of shallow foundation on geocell reinforced soil in Sri Lanka
Sanjei, C; De Silva, LIN
Geocells are mostly used to strengthen soft soil in many Asian countries in recent days. They provide faster, feasible and environmentally friendly solutions. In Sri Lanka however, Geocell is not much familiar soil improvement technique. This paper discuss the development of a three dimensional numerical model to simulate the behaviour of geocell reinforced sand using PLAXIS 3D and feasibility of geocell as reinforced soil in Sri Lankan construction industry. The shape has a major influence in stress distribution. In this study, a 3D cad model was imported to PLAXIS 3D and modeled using geogrid structural element. Unreinforced, singly reinforced and doubly reinforced cases were investigated in feasibility studies using 3.0m x 3.0m footing prototype. Then optimum B/C ratio (Bearing capacity/Estimated cost) was calculated by changing the footing size (trial and error method).Footing was analysed for an axial load of 1200kN.It was found that footing on doubly reinforced with 1.6m x 1.6m is most feasible footing with soil improvement. Sustainable feasibility study was carried out to check the suitability of geocell in Sri Lankan context. The study suggests that influence of economical performance attributes and social performance attributes' could be higher than environmental performance attributes when geocell is used as soil reinforcement.
item: Conference-Abstract
Numerical analysis of a piled raft foundation for super tall buildings - case study
(2019) Sanjei, C; Uthayakumar, D
Piled raft foundations are increasingly being recognised as an economical and effective foundation system for tall buildings. Within a conventional piled raft foundation, it is possible to optimise the number of piles, by considering the contribution of the raft to the overall foundation capacity. In the practical aspect, reducing number of piles is a significant cost saving to a construction project. This paper investigates the significance of the raft on the overall load carrying capacity of a piled raft foundation of the Incheon Tower in South Korea. The study is carried out using three-dimensional numerical models developed using a commercially available finite element analysis software; midas GTS NX and compared with other analysed results- based on case study of Incheon tower. Moreover, lateral deflections and moments in piles are small as the lateral stiffness of the 172 piles is higher in value compared with that of the raft.
item: Article-Full-text
Numerical analysis of the backfilling sequence effect on gravity retaining wall behaviour
(2015-12-29) Sanjei, C; De Silva, LIN
Gravity retaining walls derive their capacity to resist lateral movement through the dead weight of the wall. The design methodologies proposed by standards do not take into account the construction sequences that simulate the process by which the soil and retaining wall are brought together. However, in reality, at least during the backfilling process, the retaining wall undergoes many displacements that are not so far considered in the design. In this investigation, effect of construction sequences in the gravity retaining walls with different shapes is investigated with the help of finite element method. Two different construction sequences, namely the backfilling after wall construction and the backfilling parallel to wall construction, are compared for different wall shape models. Lateral displacement of the bottom and the top of the wall is plotted for each model and construction sequence with construction stages. Bearing pressure distribution, lateral earth pressure and failure wedge angle are summarized and compared with design values. Each wall showed different behaviours for each of the construction sequences. Back filling after wall construction minimizes the sliding failure and bearing pressure. Overturning failure could be reduced by backfilling parallel to wall construction. However, it was observed that, comparatively, backfilling after wall construction is effective than backfilling parallel to wall construction, suggesting that proper selection of construction method also may reduce negative effects on the wall stability.
item: Conference-Full-text
Numerical analysis of the backfilling sequence effect on gravity retaining wall behaviour
(2016-04-26) Sanjei, C; De Silva, LIN
Gravity retaining walls derive their capacity to resist lateral movement through the dead weight of the wall. The design methodologies proposed by standards do not take into account the construction sequences that simulate the process by which the soil and retaining wall are brought together. However, in reality, at least during the backfilling process, the retaining wall undergoes many displacements that are not so far considered in the design. In this investigation, effect of construction sequences in the gravity retaining walls with different shapes is investigated with the help of finite element method. Two different construction sequences, namely the backfilling after wall construction and the backfilling parallel to wall construction, are compared for different wall shape models. Lateral displacement of the bottom and the top of the wall is plotted for each model and construction sequence with construction stages. Bearing pressure distribution, lateral earth pressure and failure wedge angle are summarized and compared with design values. Each wall showed different behaviours for each of the construction sequences. Back filling after wall consttuction minimizes the sliding failure and bearing pressure. Overturning failure could be reduced by backfilling parallel to wall construction. However, it was observed that, comparatively, backfilling after wall construction is effective than backfilling parallel to wall construction, suggesting that proper selection of construction method also may reduce negative effects on the wall stability.
item: Conference-Full-text
Numerical modelling of the behaviour of model shallow foundations on geocell reinforced sand
(IEEE, 2016-05) Sanjei, C; De Silva, LIN; Jayasekara, AGBP; Bandara, HMND; Amarasinghe, YWR
This paper focuses the development of a three dimensional numerical model to simulate the behaviour of geocell reinforced sand using PLAXIS 3D. Numerical modeling of the geocell has been an immense challenge due to their curved shape. Most of researchers used equivalent composite approach (ECA) to model the geocells. However, the composite method has a number of limitations, including the disregard of the effect of shape. The shape has a major influence in stress distribution. Hence a realistic model approach is essential to simulate the same experimental condition in numerical analysis. In this study, a 3D cad model was imported to PLAXIS 3D and modeled using geogrid structural element. Then the model was validated using experimental results where the results satisfied each other. Thereafter the depth that gives the highest carrying capacity was estimated using numerical and experimental result, which was found at depth(U) /width(B)<0.5 for a square pad footing.
item: Thesis-Full-text
A Study on the bearing capacity of shallow foundations on geosynthetic reinforced sand
Sanjei, C; De Silva, LIN
A study on the bearing capacity of shallow foundations on geosynthetic reinforced sand This thesis demonstrate a research study aimed at investigating the significance of bearing capacity improvement of shallow foundation supported on geocell, geogrid and combination of geocell and geogrid reinforced sand. To implement the objective, laboratory model test, numerical study using PLAXIS 3D and theoretical study were performed to investigate the behavior of reinforced soil foundation. Honeycomb shape HDPE geocell and biaxial geogrid were used in laboratory model test. For geocell, initially single layer geocell was experimented with different cover thickness (geocell placing depth). From the results, suitable cover thickness was found at [depth (U)/width (B)] ratio between 0 and 0.5 for a square pad footing. Numerical modeling of the geocell has been an immense challenge due to their curved shape. The equivalent composite approach (ECA) is widely used to model the geocells. However, the composite method has a number of limitations, including the disregard of the effect of shape. The shape has a major influence in stress distribution. Hence a realistic model approach is essential to simulate the same experimental condition in numerical analysis. In this study, a 3D Auto Cad model was imported to PLAXIS 3D and modeled using geogrid structural element. Then the model was validated using experimental results where the results satisfied each other. According to the numerical analysis, optimum cover thickness for sand was found as 0.1B (width of footing). The static load test showed that with the provision of HDPE geocells, bearing capacity of soil can be improved by a factor up to 2.5 times of unreinforced soil. Further numerical investigations were carried out using double layer geocell for prototype footing to compare the bearing capacity improvement with single layer geocell. The results clearly depict that bearing capacity is improved by a factor of 2.75 and 3.5 times of unreinforced soil when using single layer and double layer geocell respectively. When doubly reinforced geocell was used, footing size is reduced by 40% and cost is reduced by 65%. It is apparent that using double reinforced geocell will lead to cost effective foundation designs. These ultimate bearing capacity results were validated by theoretical approaches. A good matching was found between experimental, numerical and theoretical approach. For geogrid, laboratory model test and numerical modelling were performed to find the correlation between number of geogrid and bearing capacity, using optimum cover thickness and spacing. The experimental results show that both surface heaving and settlement are reduced with number of geogrid mattress. Moreover it was also observed that bearing capacity of reinforced soil increases with increasing number of reinforcement layers (at same vertical spacing). However, the significance of an additional reinforcement layer decreases with the increase in number of layers, and bearing capacity is improved by a factor of 2.86 times of unreinforced soil when four layer geogrid was used. Further validations were performed using (FHWA/LA.08/424) technical report. Finally, a combination of geocell and geogrid was used as reinforcement. Two different cases were investigated, namely ‘geocell+geogrid’ combination and ‘geogrid+geocell’ combination. Optimum bearing capacity was obtained when geogrid was placed at the base and on the top of geocell in which bearing capacity is improved by a factor of 4.3 and 3.8, times ofunreinforced soil respectively. It shows that a layer of planar geogrid placed at the base of the geocell mattress improves the bearing capacity significantly compared with provision of geogrid above the geocell layer. Based on the overall study, key recommendations are made, which can be made for the improvements of reinforced soil foundation design. The results stated in this study will be useful in construction of building and pavements on the weak soils to significantly improve the bearing capacity of shallow foundation