Strength, Hydraulic, and Microstructural Characteristics of Expansive Soils Incorporating Marble Dust and Rice Husk Ash

Expansive/swell-shrink soils exhibit high plasticity and low strength, which lead to settlement and instability of lightly loaded structures. These problematic soils contain various swelling clay minerals that are unsuitable for engineering requirements. In an attempt to counter the treacherous damage of such soils in modern geotechnical engineering, efforts are underway to utilize environmentally friendly and sustainable waste materials as stabilizers. This study evaluates the strength and consolidation characteristics of expansive soils treated with marble dust (MD) and rice husk ash (RHA) through a multitude of laboratory tests, including consistency limits, compaction, uniaxial compression strength (UCS), and consolidation tests. By using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, the effect of curing on UCS after 3, 7, 14, 28, 56, and 112 days was studied from the standpoint of microstructural changes. Also, the long-term strength development of treated soils was analyzed in terms of the interactive response of impacting factors with the assistance of a series of ANN-based sensitivity analyses. It is found from the results that the addition of MD and RHA lowered down the water holding capacity, thereby causing a reduction in soil plasticity (by 21% for MD and 14.5% for RHA) and optimum water content (by 2% for MD and increased by 6% for RHA) along with an increase in the UCS (for 8% MD from 97 kPa to 471 kPa and for 10% RHA from 211 kPa to 665 kPa, after 3 days and 112 days of curing, respectively). Moreover, from the oedometer test results, m v initially increased up to 6% dosage and then dropped with further increase in the preconsolidation pressure. Furthermore, the compression index dropped with an increase in the preconsolidation pressure and addition of MD/RHA, while the coefficient of permeability (k) of RHA stabilized soil was higher than that of MD-treated samples for almost all dosage levels. The formation of the fibrous cementitious compounds (C-S-H; C-A-H) increased at optimum additive dosage after 7 days and at higher curing periods. Hence, the use of 10% RHA and 12% MD as replacement of the expansive soil is recommended for higher efficacy. This research would be helpful in reducing the impacts created by the disposal of both expansive soil and industrial and agricultural waste materials.

Evaluation of different methods to identify preconsolidatin pressure of Champlain Sea Clay from CRS tests

Identifying precisely the preconsolidation pressure of any soil is one of the most challenging geotechnical problems. For sensitive soils, misjudging the preconsolidation pressure can lead to a large overestimation or underestimation of settlement due to the high compressibility after p’c. The performances of eleven graphical identification methods are evaluated on constant rate of strain (CRS) consolidation tests conducted on Champlain Sea clay. The tests include unloading/reloading cycles that are used to evaluate the accuracy of the methods based on known maximum past pressure. A number of numerical procedures are developed to aid in the use of the graphical methods for CRS test data, including locating the inflection point and the point of the maximum curvature on an e-logp curve. Preconsolidation pressure is calculated using straight line equations rather than interpreting it visually. These numerical methods are applied to the test data and their validities and ease of use are evaluated.

Evaluation of different methods to identify preconsolidatin pressure of Champlain Sea Clay from CRS tests

Identifying precisely the preconsolidation pressure of any soil is one of the most challenging geotechnical problems. For sensitive soils, misjudging the preconsolidation pressure can lead to a large overestimation or underestimation of settlement due to the high compressibility after p’c. The performances of eleven graphical identification methods are evaluated on constant rate of strain (CRS) consolidation tests conducted on Champlain Sea clay. The tests include unloading/reloading cycles that are used to evaluate the accuracy of the methods based on known maximum past pressure. A number of numerical procedures are developed to aid in the use of the graphical methods for CRS test data, including locating the inflection point and the point of the maximum curvature on an e-logp curve. Preconsolidation pressure is calculated using straight line equations rather than interpreting it visually. These numerical methods are applied to the test data and their validities and ease of use are evaluated.

Experimental Investigation into Compressive Behaviour and Preconsolidation Pressure of Structured Loess at Different Moisture Contents

This paper investigates the influence of the structured property of loess on its compressive behaviour and proposes a new method for determining the preconsolidation pressure of structured loess soil. A series of oedometer tests were carried out on undisturbed and remoulded loess samples prepared at various moisture contents. The effects of moisture content on the structured yield stress, the preconsolidation pressure, and the structural strength were also captured. It was found that the influence of the structured property of loess on the compression behaviour is divergent between undisturbed and remoulded loess samples. The discrepancy before and after structural yielding is more remarkable for the undisturbed soil. The Casagrande method realized through the MATLAB program can effectively eliminate human factors and accurately calculate the corresponding preconsolidation pressure for undisturbed soil. The effects of moisture content on the method for determining the preconsolidation pressure considering the structured property of loess were discussed. The determination method can accurately evaluate the loess consolidation state in loess regions. The influencing rules which the moisture content exerts on the structured yield stress, the preconsolidation pressure, and the structural strength all conform to exponential functions. The study is of great significance to correctly differentiating the foundation consolidation states and calculating the ground settlement in loess regions.

Effect of Density on Consolidation and Creep Parameters of Clay

Effect of density on consolidation and creep parameters of a clay soil was investigated using a soil classified according to Unified Soil Classification System (USCS) as Clay of High plasticity (CH) and composing majorly of secondary minerals, including montmorillonite. The air-dried soil was compacted at five different compaction energy levels (Reduced Standard Proctor compaction energy, Standard Proctor compaction energy, West African compaction energy, Reduced Modified Proctor compaction energy, and Modified Proctor compaction energy). Specimens for consolidation tests were molded at the five different compaction energy levels (densities). The consolidation parameters (initial void ratio, compression index, and preconsolidation pressure) were observed to be empirically related to the compaction energy. The creep parameters (i.e. primary compression index, secondary compression index, and magnitude of creep) were observed to increase with increases in loading to 387kN/m2, after which the values decreased. Curves resulting from these relationships were observed to increase with increases in compaction energy level and tent towards straight line at Modified Proctor compaction energy. Maximum magnitude of creep estimated for three years was observed to reduce from 455.5 mm at Reduced Standard Proctor compaction energy through 268 mm at West African compaction energy to 247.4 mm at Modified Proctor compaction energy levels.

Constant rate of strain consolidation testing of soft clays and fibrous peats

The constant rate of strain (CRS) oedometer test, using an imposed vertical strain rate [Formula: see text] equal to 10 times the end-of-primary (EOP) vertical strain rate [Formula: see text], requiring a test duration of about 2 days produces reliable information on both the e versus log[Formula: see text] relation and e versus logkv relation of soft clays and fibrous peats. An empirical correction for the strain rate effect on preconsolidation pressure leads to the EOP e versus log[Formula: see text] relation and EOP [Formula: see text]. The imposed vertical strain rate [Formula: see text] produces excess pore-water pressures at the impervious bottom of the specimen, corresponding to [Formula: see text] values in the range of 3%–15% and allows, use of the Darcy flow equation, a reliable calculation of the coefficient of permeability. Compressibility and permeability data are from CRS and incremental loading (IL) oedometer tests on specimen quality designation (SQD) A samples of seven soft clays and two fibrous peats are presented in this paper.