Dissertations/Theses - Department of Civil Engineering
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Item Experimental investigation of thixotropic hardening of selected clays(Department of Civil Engineering (CE), BUET, 2024-12-24) Raihan, Muhammad; Shariful Islam, Dr. MohammadThis study investigates the thixotropic hardening behavior of reconstituted clay soils from Gazipur, Savar, and Mohakhali in Bangladesh, examining the impact of thixotropic aging on their strength recovery, deformation characteristics, and microstructural changes over 48 days. Utilizing advanced analytical techniques, including X-ray Diffraction (XRD), X-ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM), this research comprehensively assesses the role of clay mineralogy, particle arrangement, and water content in enhancing the engineering properties of these soils, with significant implications for geotechnical design and construction. The methodology involved collecting both disturbed and undisturbed soil samples using wash boring and Shelby tube sampling techniques. These samples were then naturally dried, ground, and sieved to prepare reconstituted specimens at their respective liquid limits. A series of laboratory tests, including unconfined compressive strength (UCS), triaxial compression, and one-dimensional consolidation, were conducted at various aging intervals up to 42 days. These tests were complemented by detailed mineralogical and microstructural analyses to determine specific gravity, Atterberg limits, and particle size distribution, revealing variations in fines content ranging from 89.6% to 98.63% and specific gravity values between 2.63 and 2.7. Significant findings from the study highlight a pronounced time-dependent strength recovery, especially notable in Mohakhali soil, which demonstrated the highest increase in unconfined compressive strength, escalating from 60.8 kPa to 87.5 kPa. The research introduced and utilized the Thixotropic Strength Ratio (TSR) and Thixotropic Regain Strength Ratio (Bt) to effectively quantify the recovery, capturing the reformation of particle structures and bond enhancement post-disturbance. Triaxial test results showed a remarkable 144% increase in deviator stress under a consolidation pressure of 120 kPa over 28 days. Microstructural analyses via SEM revealed densification and improved particle alignment, enhancing soil mechanical properties. XRD and XRF identified mineral variations influencing strength recovery, with higher illite in Mohakhali soil enhancing cohesion and thixotropy. Elevated alumina and iron oxide further improved particle bonding and strength regain. These findings highlight the critical role of mineralogy and microstructure in thixotropic behavior, providing valuable insights for geotechnical applications in clay-rich environments.Item Determination of liquid limit and plastic limit of clays using cone penetrometer(Department of Civil Engineering (CE), BUET, 2024-09-01) Ullah, Ahad; Islam, Dr. Mohammad SharifulThis study employed an alternative method to determine soils' two significant geotechnical index properties, the liquid limit (LL) and the plastic limit (PL). As the traditional methods are time-consuming, need much human labor, and have faced criticism for being subjective, the study attempted to use cone penetration methods as an alternative to determine the LL and PL of soils. The study aims to reduce the operator variability and improve consistency in determining these two geotechnical properties of soils. The study also examined the relationship between soil minerals and soil type to determine further insights into soil behavior. Soil samples were collected from 20 locations across Bangladesh and then tested using ASTM standard procedures. The LL was determined using the Casagrande method, and the PL was determined through the hand-rolling method (ASTM D4318). The LL obtained from the cone penetrometer method was then compared with the Casagrande method. To determine the PL by cone penetrometer, first, the standard penetration depth for plasticity was determined using the 30-degree standard cone utilizing the hand-rolling method. Then, the standard penetration depth was used to determine the PL of the soils, which was subsequently compared with the standard method. Modifications were made to conventional penetrometer cones, with two additional cone angles of 20 and 16 degrees fabricated alongside the standard 30-degree cones to determine the liquid and plastic limits. The study findings revealed that the cone penetrometer method measurements of LL and PL, well enough and matches with the standard method. For LL determination, the 30-degree cone penetrometer measurement deviates from -10% to +7% for low to high plasticity soil by comparing with the standard Casagrande method. For soil with very high plasticity, the deviation was higher (>25%). For PL determination, the results showed much better, with the measurement deviation varying between -3.28% and +6.63% by comparing with the standard hand-rolling method. The standard 30-degree cone proved to be the most reliable for the simultaneous determination of liquid and plastic limits. Among the soil minerals identified from the X-ray diffraction (XRD) analysis, the Illite clay mineral was the most abundant (11.21% to 25.50%) for most of the soil samples, correlating with plasticity and grain size results. The study's findings are expected to be an alternative to the standard methods in determining the liquid and plastic limits of the soil, which will reduce human labor and the complicacy of the standard procedure.Item Stabilization of sandy soil with bio-stimulation based microbially induced calcite precipitation(Department of Civil Engineering (CE), BUET, 2024-11-13) Nazmus Sakib, Mirza Md.; Islam, Dr. Mohammad SharifulThis research explores the innovative integration of Microbially Induced Calcite Precipitation (MICP) with traditional cement stabilization to address the strength and durability challenges of alluvial sandy soils. The primary objective is to enhance soil properties while introducing a sustainable, bio-inspired technique for compressed earth block (CSEB) fabrication. Sandy soil samples were sourced from Anowara, Chattogram, and mixed with 10% garden soil to support bacterial activity. The study examined the impact of varying content ratios, curing periods, and mellowing periods of MICP treatment on the micro-mechanical properties of the soil. Analytical techniques, including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA), were employed to evaluate microstructural and chemical transformations, alongside 16S metagenomic sequencing to analyze bacterial community dynamics. The mechanical tests demonstrated substantial improvements in soil strength, with dry unconfined compressive strength, split tensile strength, and flexural strength increasing by 113%, 95.84%, and 133.86%, respectively. MICP treatment enhanced water absorption resistance by 59.2% and improved durability under dry-wet cycles. SEM and EDS analyses revealed reduced voids and the formation of calcite crystals and cement hydration products that bridged soil particles. FTIR results confirmed stronger calcite and hydration-related spectral peaks, correlating with observed strength and durability enhancements. DSC and TGA results indicated significant calcite content, with a notable weight loss above 600°C. A 101.53% increase in calcite content was achieved in 5-day treated samples with 8% cement content. 16S sequencing highlighted the enrichment of urease-positive bacteria, particularly Sporosarcina and Bacillus genera, with Firmicutes dominance in MICP treated cement-stabilized blocks. Life cycle analysis (LCA) further revealed that CSEBs are 14.69% more cost-effective and environmentally sustainable compared to fired clay bricks (FCBs). Optimal results were achieved with 6% cement content by weight and a 5-day mellowing period. This study underscores the potential of combining MICP bio-stimulation with traditional cement stabilization to establish an effective protocol for partial cement replacement, advancing sustainable construction practices.Item Strength characteristics of grouted sandy soil(Department of Civil Engineering(CE), BUET, 2022-05-14) Iffat Tarannum; Islam, Dr. Mohammad SharifulSeepage control is a big concern for embankments, dams, and other hydraulic structures constructed with sandy soil. Grouting, especially permeation grouting is one of the appropriate solutions for controlling seepage. However, cement-based permeation grouting is still a trial and error-based process both in the laboratory and field. In this study, attempts have been made to determine the strength characteristics of permeation grouted sandy soil. The properties of sand is Fineness Modulus (F.M.) 1.12, Permeability 8.84 × 10-6 cm/sec, Cohesion (c) 4.24 kN/m2 and Angle of internal friction (φ) 350. A simple method has been devised to prepare grouted samples with water-cement ratios (W:C) of 2:1, 3:1, 4:1, 5:1 and the percentage of cement is respectively 11%, 8%, 6.5% and 5.5%. It is found that compressive strength of the samples prepared with 2:1 W:C ratio varies in the range between 200 kPa and 250 kPa after 28 days of curing. After 120 days of curing, the strength of the same samples increases up to 1000 kPa. The samples show ductile behavior and the failure strain is 9%. For low cement contents, i.e., 5:1 and 4:1 (W:C), the compressive strength varies from 28 kPa to 40 kPa, after 7 to 14 days of curing period. A significant increase was noticed in the compressive strength after 28 days of curing and it reached its peak after 90 days. Dry density increases whereas moisture content and void ratio decrease with the increase of cement content and curing age. It is also observed that, cohesion and Young’s modulus increase with the increase of cement content and curing age. Failure patterns of samples are column mode, collapse, axial split and shear for W:C of 5:1, 4:1, 3:1 and 2:1 respectively. However, failure pattern can change with increased curing age, e.g., for 2:1 (W:C) cured for 120, a failure pattern of slickenside was observed. Consolidated Undrained (CU) triaxial tests were also performed on the grouted samples prepared with 11% (i.e., W:C of 2:1) cement cured for 7 days. It is observed that dilation occurred during the volume changes and pore pressure decreased with the increase of confining pressure. From the triaxial test, cohesion, c and angle of internal friction, ϕ are found to be 200kN/m2 and 37.4° respectively. In the case of triaxial test, the failure pattern is different, i.e., bulging failure pattern. The changes of microstructures and chemical composition during hydration reaction were observed by the Scanning Electron Microscope (SEM), and Energy Dispersive Spectroscopy (EDS) respectively. Ettringite needles, C-S-H gel, C3S and C2S (2 Cao.SiO2) formation increases with the cement content and curing age, which means hydration and pozzolanic reaction increase as well. Ettringite is a needle-shaped crystal that contributes to the early strength development and works as the reinforcement, and C-S-H gel is like a glue binder that solidifies the samples. Particularly the cementitious products not only enhance the inter-cluster bonding strength but also fill the pore space. From these investigations, it is observed that the porosity decreases with the cement content and curing age, which means permeability decreases as well, without disturbing the soil microstructure. Permeation grouting is effective in increasing the strength and decreasing the permeability.Item Characteristics of compressed stabilized earthen block fabricated with sawdust ash based geopolymer(Department of Civil Engineering, BUET, 2022-11-23) Mallick, Joya Rani; Shariful Islam, Dr. MohammadExpansive soil has always been a major concern for civil engineers. The problematic swell-shrink behavior of this soil due to seasonal fluctuation of water content can be mitigated through mechanical, physical, chemical, or biological stabilization. Among chemical stabilization processes, geopolymerization has recently achieved better efficacy due to its lower carbon footprint. This study explores investigating the strength and durability characteristics of Compressed Stabilized Earthern Blocks (CSEBs) fabricated with Sawdust Ash (SDA) based geopolymer. An expansive soil of high swell index (Free Swell Index, FSI = 83.3%) was reconstituted with a mixture of NaOH (10M), Na2SiO3.9H2O (70%/30% w/w), and a variety of SDA content ranging from 0% to 20% at different compaction effort based on the workability. By varying the Alkaline Solution (A) to Binder (B) ratio (A:B) from 0.3 to 0.5, optimum A:B ratio was obtained at various amounts of SDA percentage indicating an increase in A:B ratio with increasing SDA content. Uniaxial compression tests of the samples cured at room temperature at 7 day and 28 day bulk condition showed that, the highest compressive strength (0.82 and 1.78 MPa) is obtained for the composition having 20% SDA and A:B ratio of 0.5 which also satisfies minimum strength requirements of several codes and standards. From durability perspective, around half of the samples showed efflorescence which can be mitigated thourgh moist curing. The improvement of compressive strength due to water submersion also emphasizes on the application of moist curing for enhanced strength and reduced efflorescence. The maximum flexure (0.35 MPa) and tensile strength (0.31 MPa) were obtained for the same composition (20% SDA and A:B ratio of 0.5) which is around 180% and 400% greater than unstabilized soil respectively. The microstructural analysis by Scanning Electron Microscope (SEM), Energy Dispersive X-ray Analysis (EDXA), and Fourier Transformed Infrared Spectroscopy (FTIR) supported the formation of geopolymer as well as improved mechanical strength. Overall, the experimental results obtained in the present study corroborate the successful application of SDA based geopolymer in the fabrication of CSEBs from expansive soil.Item Effects of cement and lime stabilization on geotechnical characteristics of a regional clay(Department of Civil Engineering, BUET, 2020-12-29) Atikul Islam, Md.; Abdul Muqtadir, Dr. K. A. M.In the present investigations cement and lime stabilization of a regional medium expansive clay has been carried out to find the effects of cement and lime stabilization on the selected soil. Here the said clay sample was collected from Mouchak in Gazipur district. The collected sample of the selected site was inorganic clay of low plasticity and medium expansive. As additives, ordinary Portland cement and slaked lime were used in amount of 2%, 5% and 8% of dry weight of collected soil sample individually for index tests, shrinkage limit tests, linear shrinkage tests, standard proctor tests and unconfined compressive strength tests. The said additives were 5% of dry weight of collected soil individually for direct shear tests. Unconfined compressive strength tests were performed on soil-additive mixtures compacted at optimum moisture content (OMC) and then consolidated undrained direct shear tests were performed on soil-additive mixtures compacted at wet side of OMC at 95% of maximum dry density. Cement stabilized samples for both unconfined compressive strength tests and consolidated undrained direct shear tests were cured for 7, 14, 28 and 56 days individually. On the other hand, lime stabilized samples for unconfined compressive strength tests were cured for 7, 14, 28 and 56 days individually but for consolidated direct shear tests the samples were cured for 7, 28 and 56 days individually. Comparison among unconfined compressive strengths which were obtained from different researches on cement and lime stabilization have also been studied. Compared with the untreated samples; plasticity indices and percentages of linear shrinkages of the selected soil-additive mixtures do not change significantly while shrinkage limits of the selected soil-additive mixtures increased significantly. Change in OMC and maximum dry density due to selected cement and lime stabilization is also not significant. Most of the data found from unconfined compressive strength tests show that cement is better choice than lime to increase unconfined compressive strength of the selected soil, although more study is required to determine the effects of longer curing period and more admixture content. The range of unconfined compressive strength of the selected soil-cement mixtures is 530 kN/m2 to 2195 kN/m2. For lime treated soil, the said range is 605 kN/m2 to 1990 kN/m2. It is found that compressive strengths of samples treated with 8% cement and cured for 7 and 28 days satisfied the PCA (1956) for the compressive strength of soil cement mix. It is also found that for all cement contents and all curing ages of the present investigation except 2% cement content with 56 days curing, compressive strength of the stabilized samples fulfilled the requirements of soil-cement mix for use in road sub-base and base subjected to light traffic, as proposed by Ingles and Metcalf (1972). For selected cement treated samples, axial failure strains and initial tangent moduli do not show a specific trend. The ranges of axial failure strains and initial tangent moduli for selected cement treated samples are 0.57% to 1.2% and 60200 kN/m2 to 526700 kN/m2 respectively. For selected lime treated samples too, initial tangent moduli do not show a specific trend. Most of the data of unconfined compressive strength tests show that axial failure strains of selected lime treated samples decrease with increments of lime contents in the samples. The ranges of axial failure strains and initial tangent moduli for selected lime treated samples are 0.76% to 4.6% and 45300 kN/m2 to 95800 kN/m2 respectively. It is observed that consolidated undrained cohesions of lime treated samples decrease with increases of lime in the samples while the said cohesions of cement treated samples increase with increases of cement in the samples. On the other hand, consolidated undrained angles of internal frictions increase with increases of lime in the samples while the said angles of internal frictions of cement treated samples decrease with increases of cement in the samples. For both cement and lime treated selected clay samples, shear stress vs. shear displacement curves show that the clay samples are over consolidated clay samples but all shear displacement vs. corresponding changes in height curves do not show the said nature.Item Strength-deformation characteristics of rooted soil(Department of Civil Engineering (CE), 2015-12) Farnia Nayar Parshi; Shariful Islam, Dr. MohammadEmbankment protection in Bangladesh is an important issue. Conventional methods for embankment protection are expensive and most of them are not environmentfriendly. To this context, bioengineering method has been selected in this study. At first the growth of selected plants has been studied for different soil conditions. To evaluate the effectiveness of different plants in improving the stability of the slopes, strength-deformation characteristics of rooted soil has been illustrated conducting both laboratory and field tests. For the evaluation of effectiveness of plants as bioengineering solution, four plants namely hardy sugarcane, wild cane, tiger grass and vetiver grass were selected. Growth of these plants in different soils (dredge fill sand, red clay, nursery soil, contaminated soil and saline soil) had been studied in BUET premises in plain land and slope ground. It was found that hardy sugarcane and wild cane grew well in nursery soil and sand whereas vetiver grew better in sandy, clayey, saline and contaminated soil. Among the selected plants, vetiver is widely available in the country and its root morphology is most effective for slope protection. Strength-deformation characteristics had been evaluated using both laboratory and field tests. Direct shear tests were conducted on twenty different types of specimens with four types of soil and roots. Tests were conducted on samples prepared with 20- 25% water contents under normal loads of 10, 15 and 20 kPa. By analyzing the results, it was observed that shear strength increased slightly due to the addition of root while horizontal deformation increased 1.5-2.0 times. Peak shear stress due to the addition of hardy sugarcane, wild cane, tiger grass and vetiver grass root increased up to 12%, 4%, 13% and 7%, respectively. Apparent angle of internal friction, φ́ increased due to the addition of hardy sugarcane and tiger grass root up to 8% and 19%. Again due to the addition of hardy sugarcane, wild cane and vetiver grass root apparent cohesion, ć increased by up to 50%, 25% and 30%, respectively. From the stress-strain behaviour, it is understood that root is effective in taking load after the failure of the soil. In addition to these, effectiveness of vetiver grass in remediation of heavy metal from soil had also been studied. Vetiver grass was planted in industrial dump contaminated soil collected from Buriganga river bank. It was found that the concentrations of heavy metals (Pb, Cu, Cr, Ni and Zn) in this soil are above tolerance level. From the analysis, it was found that heavy metal uptake through vetiver was very significant. Uptake of Pb, Cu, Cr, Ni and Zn after a time period of 50 week were 110, 53, 33, 53 and 2389 (gm per sq.m area), respectively. It is observed that plant root mechanically increase soil shear strength by transferring soil shear stress from soil into tensile forces of the root themselves, via interface friction along the root surface. Orientation and geometry of the root also influenced the effectiveness in reinforcing.Item Effect of foundation soil stiffness on dynamic behavior of RC frame building(Department of Civil Engineering (CE), 2015-03) Paul, Ajoy; Alam, Dr. Md. JahangirThis study was to investigate the effect of foundation soil stiffness on dynamic behavior of a 5-story (low-rise), a 10-story (medium-rise) and a 20-story (high-rise) Reinforced Concrete (RC) frame building. Each building was supported on soft clay, stiff clay and very stiff clay with shear wave velocity of 100 m/s, 300 m/s and 600 m/s respectively. The soil and foundation were modeled as equivalent spring of specified stiffness along with various degrees of freedom. The Special Moment Resisting Frame (SMRF) system was considered for all example buildings as lateral forceresisting system. The dynamic analysis was carried out using SAP2000 software. The normalized response spectra for 5% damping ratio was used as ground motion as mentioned in Bangladesh National Building Code revised in 2014. From this study it was found that there was no significant variation of natural period due to variation of stiffness of foundation soil. However, past research works showed that there is significant variation of natural period due to variation of stiffness of foundation soil. This is because of using same foundation design for different types of soil. In this study foundation sizes were changed with the variation of soil stiffness. Lateral deflection and base shear decreased with the increase of stiffness of foundation soil, because response spectra suggested by BNBC-2014 for stiffer soil is less than that of soft soil condition. Drift ratio and percent base shear decreases with the increase of number of story for same soil condition. This is because of change in natural period with the increase of number of story. From the response spectra it is seen that value of response spectra decreases with the increase of natural period after peak value. The most important conclusion is that there is no significant variation of lateral deflection and base shear for same building and soil condition if soil structure interaction is considered. This means that if response spectrum for different soil types given in BNBC (2014) is used and foundation design is done properly, reasonably accurate result of analysis can be done without considering soil-structure interaction.Item Structure-soil interaction in framed buildings with orthotropic wall infills(Department of Civil Engineering (CE), 1986-08) Saeeda Nazneen; Azadur Rahman, Dr. M.For abstract please see full textItem Development of a robust cyclic plasticity model and its application to soil-structure interaction problems(Department of Civil Engineering, 2007-09) Raquibul Hossain, Md.; Ahmed, Dr. IshtiaqueConstitutive modeling for engineering materials is a great concern for the numerical modeling of engineering structures. In the last four decades, the constitutive modeling has evolved considerably. Starting from pioneering work by Druker and Prager [1952], various improvements, extensions and alternative constitutive models have been proposed. As materials often are subjected to repetitive loading during their service load such as wind load, earthquake load, moving traffic load etc. it is very essential for a complete model to simulate the cyclic behavior of the material accurately like the monotonic one. In this regard, several cyclic constitutive model have been proposed within the framework of the classical plasticity theory such as Prager [1956], Armstrong and Frederick [1966], Mroz [I967J, Dafaslias and Popov [1975, 1976], Chaboche and his coworkers [1979, 1986J, Ohno and Wang [1993], Hossain, Siddiquee and Tatsuoka [2005J etc. All of these models have the ability to simulate the cyclic stress-strain behavior of various materials with some limitations of their own. In this research work an attempt is made to develop a robust cyclic constitutive model within the framework of the theory of plasticity. To construct a generalized constitutive model for both the pressure independent and dependent materials, a general framework for the cyclic modeling has been proposed. In this framework a nonlinear kinematic hardening rule is derived from the concept of the instantaneous slope of the stress-strain relationship. For this purpose a proportional rule and a drag rule is formulated. By using the proportional rule, the modified Masing's rule is fulfilled which has been observed for many materials. Using the drag rule, the overshooting or the undershooting of the stressstrain relationship can be modeled. A nonlinear stress-strain relationship is indispensable to develop a constitutive model. Often a simple hyperbolic equation (Konder, R.L. [1963]) IS used. In the present research a nonlinear stress-strain relationship is proposed which is simple but fulfills all the necessary requirements. Using this equation the instantaneous slope is calculated. By using this instantaneous slope for kinematic hardening rule, models for both the pressure independent and dependent materials have been developed. The Von-Mises and Druker-Prager yield functions are used for pressure independent and pressure dependent materials respectively. Then an associative flow rule is adopted for the pressure independent material and a stressdilatancy rule proposed by Tatsuoka et. al. [2003] is used with some modification for pressure dependent material. For the integration of the of the incremental stress-strain relationships, several integration algorithms are available. In the present work, Return Mapping algorithm is used (Ortiz and Popov [1985], Simo and Taylor [1986] and Ortiz and Simo (1986]). Finally, for the nonlinear solution of the finite element analysis Dynamic Relaxation technique is used. To verify the model, a single four node quadrilateral element is chosen with single gauss point integration for plane strain simulation. Masuda et. al. [1999] performed a series of plane strain cyclic loading tests on Toyoura sand. In this research, an attempt is made to simulate the cyclic plane strain behavior of Toyoura sand and the results have been found quite reasonable. The proposed model can be applicable for any type of structural as well as soil-structure interaction problems.