Anasua GuhaRay

Reliability-Based Analysis of Cantilever Sheet Pile Walls Backfilled with Different Soil Types Using the Finite-Element Approach

AbstractThe paper presents an analytical study of a cantilever sheet pile wall considering the effects of uncertainty of soil properties. The failure probability (Pf) of the sheet pile wall is combined with the sensitivity (S) of geotechnical random variables on the failure mode, and a new factor, the probabilistic risk factor (Rf), is proposed for each random variable corresponding to different variations of the random variables. The cantilever sheet pile wall that is driven into a cohesionless soil layer and backfilled by (1) cohesionless soil and (2) cohesive soil is considered separately for analysis against the rotational failure mode. Pf is obtained by developing the response surface, based on finite element models. The sensitivity of each random variable is obtained by F-test analysis. It is observed that the cohesion of foundation soil (c2) and water table positions are the important factors that influence the stability of the cantilever sheet pile walls to a great extent. Finally, design guidelin...

Reliability Coupled Sensitivity-Based Seismic Analysis of Gravity Retaining Wall Using Pseudostatic Approach

AbstractThe stability of geotechnical earth structures is often affected by associated uncertainties present in geotechnical parameters, if they are not properly accounted for. The present paper aims at quantifying these uncertainties and proposes a modification factor, namely probabilistic risk factor (Rf) for each geotechnical random variable. A gravity retaining wall is analyzed by a pseudostatic method of analysis against four modes of failure namely, sliding, overturning, eccentricity, and bearing. The effect of variation of properties of backfill and foundation soil on stability of the wall for various earthquake conditions is analyzed. Rf simultaneously identifies the effects of Pf of a gravity retaining wall subjected to earthquake loading and also the sensitivity of geotechnical random variables on different modes of failure. The geotechnical random variables are modified by Rf and applied in design. It is observed that, apart from the seismic horizontal and vertical pseudostatic acceleration coe...

Risk Factor Based Design of Cantilever Retaining Walls

Sensitivity analysis of geotechnical random variables on potential failure modes (overturning, sliding, bearing capacity and eccentricity) of a cantilever retaining wall reveals that high sensitivity of a particular variable on a particular mode of failure does not necessarily imply a remarkable contribution to the overall failure probability. The present paper aims to combine probability of failure (Pf) of each failure mode and sensitivity of the random variables to these failure modes and introduces a new factor, called Probabilistic Risk Factor (Rf) for each random variable. Pf is calculated by Monte Carlo Simulation and sensitivity analysis of each random variable is calculated based on normalized F-Statistics value. Rf is a reduction factor which takes into account the variations of random variables and hence can be directly implemented in design by the designers. The random variables (friction angle and unit weight of backfill soil; and friction angle, unit weight and cohesion of foundation soil), when divided by Rf and applied in design, yield a structure which is safe against variations of the random variables. It is observed that Rf of friction angle (φ1) of backfill increases and cohesion (c2) of foundation soil decreases with an increase in variation of φ1, while Rf for unit weights (γ1 and γ2) of both the soil and friction angle of foundation soil (φ2) remains almost constant. Finally, design guidelines for different variations of φ1 are provided based on the proposed methodology, which proves to be cost effective.

Experimental Studies on Physical Properties and Strength Response of Construction and Demolition Wastes

There is increasing inclination towards the reuse of construction and demolition wastes (CDWs), primarily containing building derived materials (BDM) in engineering practices such as ground improvement. Currently BDMs are used in the form of recycled aggregates that incur extra cost due to refinements. The present study, thereby, emphasizes on the use of virgin BDM. No previous studies related to its characterization and utilization in ground improvement have been reported till now. Hence, this study focuses on the characterization of BDM and its durability aspects through physical, chemical, and microscopic studies to test their compatibility when used in conjunction with local soil contaminated with aggressive chemicals. Soil composition varies based on the vicinity of a chemical plant, waste processing plant, or a coastal area. Results from this study can be used to encourage the practical use of BDM especially in chemically contaminated soil and developing relevant standard codes.

Effect of Strain Rate on Interface Friction Angle Between Sand and Alkali Activated Binder Treated Jute

The interface friction angle between reinforcement and soil is a significant property that defines the suitability of geotextile for several applications such as reinforced retaining wall and slope stability. However, it is not an intrinsic property and varies with several experimental factors such as relative density of sand and shearing strain at which shear tests are conducted. Recent literature shows the wide application of jute geotextile in geotechnical constructions such as slope stability, river bank protection, and subgrade stabilization. However, its application is limited due to low durability under the soil. Therefore, to improve the resistance of jute geotextile against the biological degradation, it has been treated with the fly ash-based treatment solution. This study makes an attempt to investigate the effect of strain rate on the interface friction angle between sand and alkali activated binder treated jute geotextile. The tests are conducted in large shear box apparatus specifically assembled to determine interface shear properties. The jute geotextile is treated with alkali activated binder of four different water to solid ratios, each of them is cured at the temperature of 40 °C. The results obtained are then collated with those obtained from untreated jute geotextile. This study further delineates the effect of the degree of compaction on the interface friction between the reinforcement and sand. Hence, the interface shear properties apropos to the relative density of sand, shear strain, and treatment composition are compared and the obtained trends along with the optimum values are presented.

Stabilization of Expansive Black Cotton Soils with Alkali Activated Binders

The black cotton soil is mainly composed of clay minerals of Smectite group and is highly expansive when exposed to moisture. The present paper proposes a method of geo-polymerizing the black cotton soil with alkali activated binders (AAB). AAB is produced by the reaction between an aluminosilicate precursor (primarily Class F fly ash and/or slag) and an alkali activator solution of sodium hydroxide and sodium silicate. The water to solids ratio is maintained at 0.3. Mineralogical and microstructural characterizations through X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) are carried out for both untreated and treated soil to identify the changes in chemical composition and surface morphology. The index properties, compaction characteristics, unconfined compressive strength (UCS) and swelling characteristics of both untreated and treated soil are carried out. It is observed that the AAB reduces the plasticity index and free swell of black cotton soil by 15–25%, while the UCS values are increased by 10–12%. Recommendations on practical implementation of this technique for stabilization of expansive soils are proposed based on the findings of this study.

Performance of alkali-activated binder-treated jute geotextile as reinforcement for subgrade stabilization

AbstractGeotextiles are widely used for reinforcing soil, improving drainage, controlling soil erosion and embankment construction. Existing research recommends the improvement of soil in an econom...

Characterization of building derived materials for partial replacement of pavement subgrade layer

This study investigates the potential of BDM in its virgin state for enhancing the geotechnical and mechanical properties of soft non-swelling soil with low shear strength. A series of material and geotechnical tests carried out on soil replaced with different percentages of BDM include specific gravity, water absorption, standard Proctor’s test, permeability test, aggregate impact test (AIV), Los Angeles abrasion test, and large shear box test. The results indicated that an optimum of 18–23% of BDM by weight can be added to soil to improve its mechanical and geotechnical properties such as shear strength and compaction. This study also evaluates the compatibility of BDM in soils from sites surrounding chemical plants. For this purpose, the BDMs are exposed to sulfuric, hydrochloric, and nitric acid solutions to identify the effects of these acids on the BDM behavior. It is observed that the strength of BDM decreases after their exposure to these solutions, with maximum effect manifested by nitric acid and least by hydrochloric acid. The results of AIV and LA abrasion test on BDM exposed to chemicals show that the performance of the BDM deteriorates in the presence of chemicals. The results obtained from the proposed study can be used to promote the practical use of BDM in geotechnical applications. However, necessary precautions must be adopted for their practical application in ground improvement based on soil conditions.

Experimental Investigations on Building Derived Materials in Chemically Aggressive Environment as a Partial Replacement of Soil in Geotechnical Applications

Construction and associated demolition processes produce huge amount of solid waste, generally termed as construction and demolition waste (CDW). Management and proper disposal of these wastes is an area of prime concern for modern civil engineers. About 90% of all CDW is composed of building derived materials (BDM) obtained from concrete, bricks, and tiles from structural and non-structural elements of a building. The present study emphasizes on the use of virgin BDM, which conserves natural aggregate, reduces the impact on landfills, saves energy, and thus can provide significant cost benefit. Five types of BDM—crushed lightweight concrete (T1), crushed marble tiles (T2), crushed high strength concrete (T3), crushed normal portland cement concrete (T4), and crushed bricks (T5)—are characterised to assess their compatibility when used in conjunction with local soil. The soil, BDM and soil–BDM mixes are characterized from physical, mechanical, mineralogical, microstructural, and chemical aspects. These tests are then repeated for the aforementioned soil-BDM mixes after immersion in acids. Aggregate impact value (AIV) results on the five types of BDM indicate that T1 and T5 are poorly resistant to impact loads. However, T2, T3, and T4 show relatively better resistance to impact loads and satisfy the requirements for sub-base material standards. Shear strength studies show that the average optimum replacement of soil by BDM is in the range of 17–23% by mass. In order to test the compatibility of BDM in soils containing aggressive chemicals, the properties mentioned above are re-evaluated after exposing the BDM to aggressive chemical environments. The results indicate that the internal angle of friction (ϕ) of virgin BDM is found to vary significantly due to acid attack. The results of AIV after exposing the BDM to acids show that BDM are highly susceptible to chemically aggressive environment. The performance of all types BDM are affected by the presence of acids and appropriate measures must be adopted while using BDM in such chemically aggressive environment. These standards can be used as guidelines in the present study in the absence of specific standards for BDM applications.

Risk Factor based Analysis of Cantilever Sheet Pile Walls

Sensitivity analysis involving different random variables and potential failure modes of cantilever sheet pile walls for different soil conditions focuses on the fact that, high sensitivity of a particular variable on a particular failure mode does not necessarily imply a remarkable contribution to overall failure probability (Pf). The present paper aims at identifying a probabilistic risk factor (Rf) for each random variable based on the combined effects of Pf of each mode of failure and sensitivity of each random variable on these failure modes. Three different soil conditions are considered: (1) cohesionless soil above and below dredge line, (2) cohesionless soil above dredge line and cohesive soil below dredge line and (3) cohesive soil above and below dredge line. It is observed that friction angle of both foundation and backfill soils are the major guiding factors for Case 1, while for Cases 2 and 3, cohesion for foundation soil dominates over the other two random variables. Thus the present paper proposes a safe and economic design by assigning different Rf for different random variables for sheet pile walls embedded in different subsurface conditions and varying positions of water table.