Master of Science in Geotechnical Engineering
Permanent URI for this collectionhttp://192.248.9.226/handle/123/16123
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- item: Thesis-AbstractCorrelation between standard penetration resistance (SPT N) and cone resistance (Qc) in cone penetration test (CPT) for residual soils(2024) Sashikala, JRM; De Silva, LIN"Corelation between Standard Penetration Resistance (SPT N) and Cone resistance (qc) in Cone Penetration Test (CPT) for Residual Soils" examines the complex relationship between these two key geotechnical engineering parameters. The basis of the research is a set of in-depth field tests carried out on residual soils, which are remarkable for their specific qualities and common occurrence. This study's main goal is to establish the numerical relationship between SPT N and CPT qc values, which is useful for foundation design and soil characterization. The study begins by providing a thorough analysis of the existing literature of research on the topic, which is followed by a thorough justification of the approach used for the field experiments. Cone Penetration Test (CPT), an appreciated in-situ testing method, is used to quantify qc, and Standard Penetration Test (SPT) is used to compute SPT N values. Statistical techniques are then employed to examine the test findings and determine if SPT N and qc are correlated. The results show that these parameters for residual soils have a high association, which gives geotechnical engineers important information. A correlation between SPT N and qc is then determined by statistically analysing the test data. Geotechnical engineers may learn a great deal from the results, which show a high link between these parameters for residual soils. For the planning and building of foundations on residual soils, the findings have important contributions. Finally, this study has identified a solid framework on further research which can be performed to and emphasizes the importance of comprehending the link between SPT N and qc in residual soils. Key words: standard penetration resistance (SPT N), cone resistance (qc), cone penetration test (CPT), residual soils, correlation
- item: Thesis-AbstractStudy on the applicability of finite element analysis on predicting the behavior of axially loaded piles(2024) Fernando, GNP; De Silva, LINThe performance of axially loaded piles is a key factor in ensuring the stability and safety of various civil engineering structures, including buildings and bridges, within the field of geotechnical engineering. Accurate prediction of pile behavior is essential during the pile design stage. This master's thesis presents a comprehensive investigation into the applicability of Finite Element Analysis (FEA) as a predictive tool for assessing the behavior of axially loaded piles, with a focus on the Sri Lankan context. The research methodology involves a comparative analysis of field test data with numerical and manual calculation data. A dataset comprising 12 pile tests and borehole data was collected from the Colombo suburb area and Mannar Island in Sri Lanka. This dataset includes five PDA tests and one MLT test at each location. Simultaneously, a 3D finite element model is developed using PLAXIS 3D software to represent the pile-soil interaction. The finite element model is precisely calibrated and validated against the field test data to ensure its accuracy and reliability. In addition to FEA, manual calculations of pile capacities and settlements were performed using the collected borehole data and compared with the field test data. The findings of this study suggest that FEA can effectively predict the behavior of axially loaded piles with a high degree of precision when calibrated appropriately. Notably, the results show strong agreement with experimental test data when the Elastic Modulus of soil (E50) is increased by a factor of five in both Colombo and Mannar areas. The implications of this study are highly relevant to geotechnical engineers, designers, and construction professionals, as it serves as a valuable resource for designing axially loaded piles in the specific context of Sri Lanka. In conclusion, this master's thesis demonstrates that Finite Element Analysis is a powerful and reliable tool for predicting the behavior of axially loaded piles. It has the potential to significantly enhance the efficiency and reliability of pile design and construction in geotechnical engineering projects.
- item: Thesis-AbstractEvaluation of resilient modulus of unbound material to implement mechanistic-empirical pavement design(MEPD) in Sri Lanka(2024) Ariyarathne, BHT; Nawagamuwa, UPRoad pavement design in Sri Lanka traditionally relies on an Empirical design. This conventional approach, however, is characterized by certain limitations, particularly in its reliance on indirect material properties such as the California Bearing Ratio (CBR) value. The drawbacks of this method may result in the overestimation or underestimation of pavement design, prompting a shift towards the more reliable and accurate Mechanistic-Empirical Pavement Design (MEPD) process. Despite the advantages of MEPD, its implementation in Sri Lanka encounters challenges, including the absence of laboratory and in-situ testing equipment for modulus testing, the lack of a comprehensive soil database/soil map, and the unavailability of typical modulus values for local materials. This research endeavors to address these challenges by focusing on the development of a relationship for predicting Resilient Modulus (RM) based on other index properties of the soil. Additionally, the study aims to establish a modulus-based soil database and create a soil map for MEPD designs. To achieve these objectives, soil samples were collected from 28 locations across the country, and their basic properties were determined. Modulus tests were conducted using a Light weight Deflectometer (LWD). The validity of existing relationships for predicting RM was assessed, and subsequently, a new relationship was developed specifically for local subgrade materials. Furthermore, past soil data collected on a district basis were utilized alongside the newly developed correlation to create a comprehensive Soil Map based on RM values. In conclusion, this research successfully formulated an RM predicting model tailored to locally available unbound materials in Sri Lanka within the MEPD framework. The established soil database and soil map hold significant potential to enhance the design of road pavements in Sri Lanka, contributing to a more reliable and sustainable road infrastructure. Keywords: RM, MEPD, LWD, CBR, Unbound Material
- item: Thesis-AbstractImprovement of uplift capacity of transmission tower foundation(2024) Amarakoon, DVT; De Silva, LINElectricity transmission is carried out by conductors attached to the lattice tower structures, mostly supported by a shallow spread footing foundation, associated with around 40-45 percent of the total project cost. The uplift capacity is one of the main factors when selecting the size of a transmission tower foundation. The current design practice considers the weight of the concrete foundation and the soil as an inverted frustum that contributes to resisting forces. However, it is noted through literature that the actual behaviour of the uplift capacity of the foundation does not exactly depend only on the weight of the soil inverted frustum shape and concrete. Instead, it depends on the soil properties, such as friction and cohesion. Global research has been carried out on cement soil stabilization, insertion of fiber to the cement sand backfills, and use of geo-grids as improvement techniques for uplift capacity. This study aims to assess different techniques and propose suitable techniques to improve the uplift capacity of transmission tower foundation construction. To commence this process, soil samples with low SPT values were collected from five tower locations of ongoing transmission lines in the western province of Sri Lanka. Most of the remoulded samples are tested and identified as Clayey Sand according to the USCS classification. The tri-axial test on remoulded soil resulted in an undrained cohesion value of 5.6 kN/m2 to 10.4 kN/m2. Then, modified soil samples are prepared, adding 1 percent and 3 percent cement by soil weight, cured for 7 days, and tested. Uniaxial compressive tests (UCS) are performed on the mixed soil samples. The UCS on samples of 3 percent cement shows a significant improvement of cohesion, resulting in values between 20 to 60 kN/m2. Then a 3D finite element model is developed and verified by using the values of the research carried out by (Consoli, Ruver, & Schnaid, Uplift Performance of Anchor Plates Embedded in Cement-Stabilized Backfill, 2013). Then, the actual foundation is analyzed for various area configurations. Hence, a series of models are developed incorporating different configurations of foundation depth, improvement angle, and cohesion for full-depth, layer-wise, and partialdepth types of improvement. In conclusion, the uplift capacity of the transmission tower foundation can be increased significantly by adding 3 percent cement to the existing clayey sand backfill. The uplift capacity increases with the angle of improvement and cohesion of the backfill material. The uplift capacities were compared as a percentage of the remoulded soil backfill at a foundation with a depth of 3.0 m. When considering full-depth improvement cases, a minimum of 100 and 120 percentages resulted for the foundation depths of 2.0 and 2.5, respectively, with a cohesion value of 40 kPa and a 25-degree angle. However, it is 150 percent for the foundation depth of 3.0 m, even with a cohesion of 20 kPa. Also, the uplift capacities of layer-wise depth improvement and the total layer improvement of the practical excavation are similar. Further, improvement as a partial depth with a layer thickness of 1.5 m (starting from the bottom of the foundation) results in 120 and 150 percentages for depth of foundation 2.5 and 3.0 m, respectively, with a cohesion value of 40 kPa and 25-degree angle. Keywords: - Improvement, Uplift capacity, Foundation, Cement, Cohesion
- item: Thesis-AbstractUplift capacity of helical piles on residual soil(2024) Herath, HMUS; De Silva, LINUtilizing helical piles in foundation construction associated with compressive, tensile and lateral loads of power transmission towers are increasingly used by many countries all over the world. Lesser installation time, lesser manpower, lesser involvement of machinery and ability to use just after installation, can be identified as certain reasons for the popularity for helical piles compared to other foundation types. Further, helical piles which are more versatile and environmentally friendly, can be removed, reused and recycled as and when necessary. The installation torque required to install helical piles correlates with their load-bearing capacity, resistance to uplift forces, and ability to withstand lateral loads. In this research, ultimate uplift values of helical piles were calculated and the correlation between installation torque and uplift capacity of helical piles in residual soil were investigated. Residual soil subsurface was selected for this research, since such terrains are more common in Sri Lanka. Accordingly, three transmission tower locations (AP14, AP27 & AP47) consisting of residual soil, along Monaragala-Wellawaya power transmission line were selected and three helical piles were driven with measured depth and torque values. Also, three uplift load tests were conducted measuring the load and the deflection. For these tests, SS175 lead w/200 mm, 250 mm & 300 mm helices and RS3500.300 (88.9 mm diameter x 7.6 mm wall) extensions were used manufactured by CHANCE under Hubbell Power Systems, inc. USA were used. The findings reveal that the correlation (Kt) between installation torque and uplift capacity of helical piles on residual soil is 29 m-1. The FEM analysis was conducted with the help of PLAXIS 3D software, and the results were validated through the aforementioned tests. Accordingly, PLAXIS 3D FEM can be used to calculate the uplift capacity of helical piles on residual soil, and the mechanism of failure of helical piles on residual soil during uplift was identified as cylindrical shear. Furthermore, it is revealed that there is a certain association between SPT N and the installation Torque of helical piles on residual soil
- item: Thesis-AbstractUse of lightweight fill materials in construction of road embankments on soft peaty clayMuhunthan, A; Kulathilaka, SASNumber of proposed highways in Sri Lanka are to be constructed over sites underlain by soft peaty clay, due to scarcity of land. In order to ensure that the in-service settlements of these roads are small enough and the road could function satisfactorily, number of special ground improvements techniques are to be adopted. An alternate approach that could be considered is the use of a lightweight fill material in the construction. Extremely lightweight fill material such as expanded and extruded polystyrene blocks were used in a number of developed countries in the construction of road embankments over soft ground and in landslide repair. However, these materials are to be imported to the country and would be very expensive. As such, from a local point of view, a process involving the use of such materials would not be economically competitive. In order to find an economically feasible solution, the lightweight fill materials should be developed with the locally available inexpensive raw materials. As such, lightweight fill materials were developed locally by mixing with different proportions of tyre chips with lateritic soil, sawdust with lateritic soil and paddy husk with lateritic soil. Tyre chips were obtained by shredding discarded motorcar tyres. Sawdust was obtained from wood mill waste and paddy husk was obtained from rice mill waste. The developed fill material should of sufficiently low density and workable. Different mix proportions were tried out to get several suitable mixes. The developed material should be sufficiently incompressible and should possess adequate shear strength. Further detailed tests were conducted on selected mixes to establish their engineering characteristics in relation to strength and stiffness. The effectiveness of the use of lightweight fill material in the embankment construction was studied in detail by the finite element package CRISP. The set criterion was that the in-service settlement of the road should be less than 50mm. This was achieved through the preloading process. In this study a comparison was done for two different approaches; one constructed with lateritic soil and the other incorporating the developed lightweight fills in the preloading process. The placement of the fill layers, the settlement of the peaty clay, the effect of the removal of the preload and the application of the pavement and traffic load was studied with a fully coupled Modified Cam clay constitutive model. Parametric analyses were also done varying the thickness of the embankment and the peaty clay. The process was found to be helpful in reducing the construction period and consumed fill volume. The advantages were more prominent with the increase of embankment height and soft layer thickness.
- item: Thesis-AbstractModelling the field application of electro-osmotic consolidation to improve engineering properties of soft peaty claysSagarika, DKNS; Kulathilaka, SASIn Sri Lanka, there are large areas underlain by soft peaty clays in and around Colombo and its suburbs. Soft peaty clay deposits are highly compressible and have very low shear strength. High primary and secondary consolidation settlement problems are associated with the low shear strength. Due to scarcity of land with good subsoil condition, Geotechnical engineers are compelled to use these grounds for new development works. Therefore, it is needed to improve the properties of peaty clay deposits before doing any construction works on them. As such, there is a need to find cost effective and efficient ground improvement techniques. The potential of electro-osmotic consolidation as a technique for improvement of Sri Lankan peaty clay was studied in this project. There are records in literature to indicate that this technique was successful with soft inorganic clays. But there are no records of the use of the method in organic soils. Sri Lankan peaty clays have very low organic contents in the range of 20% to 30%. The effectiveness of electro-osmotic consolidation technique with Sri Lankan peaty clay was studied at the University of Moratuwa first by performing a series of one dimensional electro-osmotic consolidation tests and the method was found to be quite successful. In the field, electro-osmotic consolidation is done by driving parallel lines of electrodes, and by applying direct current potential difference and pumping from the cathode. This configuration cannot be considered as one-dimensional and this would be essentially three-dimensional. In this research, the field arrangement of electro-osmotic consolidation was closely simulated in a model tank filled with remoulded peaty clay and series of tests were performed with the objective of understanding the aspects of electro-osmotic consolidation technique under three dimensional conditions. Specimens were taken from the remoulded peat mass after it was subjected to consolidation tests and shear strength tests. For comparison purposes, tests were done on untreated peaty clay remoulded in the same manner. The level of improvement achieved in compressibility characteristics in three dimensional condition is less than that achieved with one-dimensional condition. But it shows a preconsolidation effect especially near anodes. A significant reduction in water content and significant increase in shear strength were observed near anode compared to near the cathode. pH tests confirm that electro-chemical changes take place in the soil. pH values increased at cathode and decreased at anode. Electro-osmosis treatment has caused an increase in the liquid limit. The coefficient of electro-osmotic permeability of Sri Lankan peaty clay found to be in the range of 1* 10-9 to 1* 10-8 m2 /sec.- V, which was within the range suggested by Mitchell (1991) for fine-grained soils.
- item: Thesis-AbstractPDA Test as a method of pile testing for bored and cast in-situ R.C. piles end bearing on rockAbeysinghe, RM; Thilakasiri, HS; Tennakoon, BLThe Pile Driving Analyzer (PDA) is a powerful tool to assess pile driving and High Strain Dynamic Pile (HSDP) load testing which may supplement or replace static testing. The PDA is seeing increasing usage in the testing of the various types of cast-in-place piles. In some parts of the world, this type of testing is the most common use for the PDA. This solution is particularly attractive for very large, high capacity piles where the large capacity makes a static test extremely costly. The rapidly increased use of pile foundations and the appearance of the new driving techniques, as well as stress wave measurement equipment have led researchers to look for better understanding of the dynamic and static behavior of the hammer-pile -soil system and to develop more reliable methods of pile analysis. The reliability of the pile driving analysis is primarily a function of the accuracy of the soil parameters and the theological model of the soil. The application of stress wave theory on piles is critically revived in literature. The scope of this study is an attempt to find a reliable range for dynamic soil parameters for end bearing bored piles in residual formation and to improve the accuracy of the wave equation analysis methods. The investigation has been focused on the comparison of the soil parameters used in practice from those used in conventional soil mechanics and soil dynamics. The solution of the stress wave equation is based on Smith's approach. Dynamic analysis of the field-recorded data was performed using CAPW AP (Case Pile Wave Analysis Program) and based on the Case Method. Ground investigation is done for evaluation of static soil properties before installation of piles. Static pile load tests were also performed on the same pile which were subjected to dynamic load test to study the load settlement behavior of the bored cast insitu piles. Further more, the static' piles capacity variation of driven piles with time termed set-up effect was studied in details for piles driven in residual formations.