Experimental evaluation of the classical and alternative consolidation theories in predicting the volumetric change of contaminated and non-contaminated soil

Several regions in Brazil and the world suffer from the presence of collapsible soils. The development of theories for understanding the phenomenon is significant because the increase of water content is associated with several reasons (e.g., precipitation, rupture of sewage, and water systems). Although some theories explain the behavior of various types of soils, they fail to explain collapsible and structured soils. In this research, an alternative interpretation of the consolidation theory is verified and calibrated for collapsible soil. The alternative model was applied to experimental data from a latosol from southeastern Brazil, and comparisons with the classical theory showed a difference in the saturated hydraulic conductivity of around 100 times. The observation showed promising results compared with the saturated hydraulic conductivity of the field (Guelph Permeameter). Furthermore, consolidation tests verified the collapse potential, the variation of consolidation coefficient and saturated hydraulic conductivity, and the total settlement prevision due to the presence of bleach and washing powder.

Soil Improvement Using Waste Marble Dust for Sustainable Development

The soils which show very high shear strength in a dry state but rapidly lose their strength on wetting are known as collapsible soils. Such rapid and massive loss of strength produces severe distress leading to extensive cracking and differential settlements, instability of building foundations, and even collapse of structures built on these soils. Waste marble dust is an industrial byproduct and is being produced in large quantities globally poses an environmental hazard. Therefore, it is of the utmost need to look for some sustainable solution for its disposal. The present study focused on the mitigation of the collapse potential of CL-ML soil through a physio-chemical process. The soil is sensitive to wetting, warranting its stabilization. Waste marble dust (WMD) in varying percentages was used as an admixture. The study's optimization process showed that geotechnical parameters of collapsible soil improved substantially by adding waste marble dust. Plasticity was reduced while Unconfined Compressive Strength (UCS) significantly increased while swelling was reduced to an acceptable limit. The California Bearing Ratio (CBR) also exhibits considerable improvement. This study appraises the safe disposal of hazardous waste safely and turns these into suitable material for engineering purposes. Doi: 10.28991/cej-2021-03091746 Full Text: PDF

Effect of Nano-Carbon on Geotechnics Features of Gypseous Soils

A Collapsing soil usually causes problems, this kind of soil has a substantial strength while it is dry, but it loses its strength while inundating and be subjected to extreme settlement. It is impossible to predict in advance the reactions of soils subjected to inundating (i.e. landslide otherwise an important soil settlement). The reduction in irreversible volumes of collapsing soil happens quickly as well as suddenly, once the reduction starts there will be no measurement to be executed which could halt such difficulty. As a result of the soak and leach that are resulting from the dissolute and clean out of gypsum, the collapsing potentials increase during the time. There are many studies in this field that indicated the possibility of modifying this soil by using nanomaterials. In this study, the nanomaterial used is nanocarbon and the soil is gypseous soil taken from Al-Najaf city in Iraq. This work studies the effect of adding nanomaterials on the gypseous soil and investigates its behavior before and after adding nanomaterial. The results showed that adding the nanocarbon affects the collapse potential which decreases by a percent meanwhile the soil cohesion decreased partly when the nanocarbon is added with 0.8% but the friction angle increased about 19%. The best proportion of using of the nanocarbon ranges between 0.8-1.2%.

Treatment of Collapsible Soils with Granulated Blast Furnace Slag and Calcined Eggshell Waste

In order to meet environmental and socio-economic challenges, the recycling of waste to be used in the treatment of geotechnical problems is one of the main ways of preserving the environment with a lower economic value. The objective of this experimental work is to improve the characteristics and to study the mechanical behaviour of collapsible soil treated with a new hydraulic stabilizer composed of Crushed Granulated Blast Furnace Slag (CGBS) active by Eggshell Waste (CES). The specimens were mixed with stabilizer content, varying from 0 to 15% in mass, with an initial water content of 4, 6 and 8% respectively. in mass. Oedometer apparatus was used to study the addition of new hydraulic stabilizer effect on the Collapse Potential. Triaxial tests are also conducted to determine the shear strength parameters (cohesion and internal friction angle) of this treated soil. The results of this research study show that the mechanical properties of the treated collapsible soil were significantly improved. An appreciable reduction in the collapse potential is observed. The addition of 15% of this new stabilizer with initial water content of 4% under a compaction of 60 blows/layer is capable of increasing internal friction angle and cohesion. It can be concluded from this study that the mixture of granulated slag and calcined eggshell can be used as an effective treatment of collapsibility phenomenon at low cost while protecting the environment from industrial waste.

WETTING AND DRYING CYCLES EFFECT ON DURABILITY OF GYPSUM SOILS TREATED WITH CALCIUM CHLORIDE OR CEMENT ADDITIVES

The study consists of two stages: the first one is to improve the gypsum soil with cement or calcium chloride and the second stage is to expose these soil specimens to series of wetting and drying cycles .Three soil specimens were taken and marked as (A,B and C) with gypsum content (47, 32 and 23)% respectively .The results show that cement additive increases the cohesion of soil specimens to 50% and collapse potential decreases with 65% and soil specimens improved with calcium chloride increase the cohesion up to more than 70% and collapse potential decreased about 70%. In the first cycle for wetting and drying cycles for soil specimens improved with cement the cohesion decreases about 25% and stays with the same ratio of the decreasing along the other cycle up to twelfth cycle. Collapse potential remains with the same value and is not affected by cycling of wetting and drying. In the first cycle for soil specimens treated with calcium chloride there is no effect in the first cycle whereas in the fourth cycle the cohesion increased by 60% and in the eighth cycle the cohesion decreased 8% and remains stable until the twelfth cycle. Collapse potential increases from one cycle to another by (30-50) % for all soil specimens.

DETERMINATION OF THE COLLAPSE POTENTIAL OF SABKHA SOIL AND DUNE SAND ARID SURFACE SOIL DEPOSITS IN KUWAIT

Ensuring the sustainability of critical and limited natural soil resources is a major challenge in arid regions such as Kuwait. Investigations should be performed to identify and characterise collapsible surface soil deposits, and collapse potential should be assessed if possible in order to evaluate suitable stabilizing techniques. The cementation effect of different types of salts gives arid soils their considerable strength and stiffness in dry conditions. The collapse in these soils may occur due to the reduction of the chemical or physical bonds between the soil particles under wet conditions. Collapse Potential (CP) is an indication of the collapsibility of these soils. This paper presents the results of experimental work that was carried out to evaluate the collapse potential of two types of surface soil: sabkha soil and dune sand. The experimental program included physical and chemical soil characterization alongside a modified compaction test. The collapsibility of the soil at a stress of 200 kPa was obtained by performing a Single Collapse Test (SCT) via a conventional odometer device in a temperature- and humidity-controlled environment. Collapse potential index tests were performed on the tested soil samples collected from eight locations in two study areas. The results suggest the problem severity is slight to none. However, the CP was higher for the sabkha soil samples than for the dune sand samples. The increase in collapsibility of the sabkha soil samples may be attributed to the removal of bonding between cementing particles upon wetting.

Numerical Study on the Behavior and Bearing Mechanism of Flat Slabs in Column Loss Events

This study investigates the behavior and the load-bearing mechanism of a typical flat slab with rectangular panels in several scenarios including the removal of a corner, penultimate, and internal columns. The scenarios are rather similar to those used in the conventional evaluation of the progressive collapse potential; however, application of the uniformly distributed loading over panels adjacent to the removed columns was not limited to twice the value of the initial load. Thus, load-deflection curves were drawn up to the point in which a great number of longitudinal slab bars ruptured. Introducing 5 stages on each curve, finite element outputs on concrete cracking pattern and rebar stress state were presented. A significant increase in the stresses along the diagonals of the slab panels accompanied by bar ruptures around columns adjacent to the removed column proved contribution of an important load-bearing mechanism in addition to the behavior called “quasiframe action.” Consecutive rupture of bars showed formation of a zipper-type collapse mode as well as a great tendency to transfer load share of missing column mainly along shorter direction of slab panels. Moreover, the findings indicated that the slab damaged zone could exceed the panels under uniform overloading.