Sahel N. Abduljauwad

Effects of confining pressure and temperature on mixed-mode (I–II) fracture toughness of a limestone rock

Studying fracture toughness behavior at elevated temperatures and confining pressures is valuable for a number of practical situations such as hydraulic fracturing used to enhance oil and gas recovery from a reservoir, and the disposal or safe storage of radioactive waste in underground cavities. Mixed-mode (I–II) fracture toughness under simulated reservoir conditions of high temperature and confining pressure was studied using straight notched Brazilian disk (SNBD) specimens under diametrical compression. Rock samples were collected from a limestone formation outcropping in the Central Province of Saudi Arabia. Tests were conducted under an effective confining pressure (σ3) of up to 28 MPa (4000 psi), and a temperature of up to 116°C. The results show a substantial increase in fracture toughness under confining pressure. The pure mode-I fracture toughness (KIC) increased by a factor of about 3.7 under a σ3 of 28 MPa compared to that under ambient conditions. The variation of KIC was found to be linearly proportional to σ3. The pure mode-II fracture toughness (KIIC) increased by a factor of 2.4 upon increasing σ3 to 28 MPa. On the other hand, KIC at 116°C was only 25% more than that at ambient conditions. Some ductile behavior was displayed by the rock samples at a high temperature and confining pressure.

Expansive characteristics of gypsiferous/anhydritic soil formations

Abstract Geology and climatic and environmental conditions have led to the formation of expansive soils in the Eastern Province of Saudi Arabia. Calcium sulphate, which commonly occurs in such soils, is well known for phase transformation and dissolution. Phase changes from gypsum to anhydrite and vice versa, and dissolution of these phases, add to the potential hazards of local expansive soils. This paper discusses the behaviour of the expansive soil formations of eastern Saudi Arabia containing gypsum and anhydrite.

Determination of swell potential of Al-Qatif clay

Knowledge of the swell potential of expansive soil at the outset of an investigation can be helpful in avoiding possible damage to the structure. A review is presented of several methods that have been proposed to identify swell potential and test techniques, which are used to quantify the amount of swell. A site investigation was conducted to obtain hand-carved block specimens from a fresh excavation site near Al-Qatif, Eastern Province of Saudi Arabia. Laboratory tests were used to determine geotechnical and physicochemical properties and mineralogical composition. The results of a range of laboratory tests, including oedometer types, filter paper, triaxial, and new stainless steel tank apparatus, showed the problems associated with investigating swell behavior of soils. A field swelling test was conducted, and results are compared with laboratory tests to establish guidelines for estimation of swell potential.

Swelling behaviour of calcareous clays from the Eastern Province of Saudi Arabia

Abstract The development of heave and swelling pressure in the natural calcareous expansive soils in the Eastern Province of Saudi Arabia causes major damage to structures constructed on or in them. The behaviour of expansive soil depends on the predominant type of clay minerals present, the cementing agents that bind these clay minerals and other physical and chemical properties. This paper presents the problems and the geotechnical and physicochemical properties of the calcareous expansive soil deposits in the Eastern Province of Saudi Arabia. X-ray, thermal and chemical analyses and scanning electron microscopy were used to estimate the type and quantity of clay and non-clay minerals and fabric of the investigated soil. The swelling potential was determined using a conventional oedometer test. A field test conducted for measurement of heave was compared with heave estimated from laboratory- tests, Results showed that the investigated soil had moderate to very high swelling potential and the heave estimated from the suction method was very close to the value measured from the field test.

INFLUENCE OF SULFATE IONS ON CHLORIDE INDUCED REINFORCEMENT CORROSION IN PORTLAND AND BLENDED CEMENT CONCRETES

Reinforced concrete structures serving in marine environments and in soils contaminated with high concentrations of chloride and sulfate salts are susceptible to reinforcement corrosion and sulfate attack. This study examines the effect of chloride and sulfate ions, or both, on reinforcement corrosion in plain and blended cement concretes. Corrosion potentials and corrosion current density were measured at periodic intervals to determine reinforcement corrosion. The mechanisms of chloride-induced reinforcement corrosion in the presence of sulfate ions was elucidated by extracting and analyzing the pore solution. The time to initiation of reinforcement corrosion was strongly related to the mobility and diffusivity of the chloride ions. The corrosion rate of steel increased in both plain and blended cements once the chloride and sulfate ions reached the steel-concrete interface. Silica-fume cement concrete was the slowest to initiation of corrosion and had a low current corrosion density as well.

Compressibility and collapse characteristics of arid saline sabkha soils

Abstract Arid saline soils are well-distributed over the globe, with a variety of nomenclature. Along the seaboard of the Arabian Gulf, these soils exist widely and are known as “sabkhas”. Despite the cemented and saline characteristics of the sabkha matrix, a recent investigation indicated that flooding the saline sabkha with distilled water in the conventional oedometer apparatus was incapable of producing a sudden reduction in volume and/or a significant collapse. This study proposes a modification to the conventional oedometer on undisturbed sabkha specimens to consolidating specimens under a constant head. Tests were, therefore, conducted on undisturbed sabkha specimens to assess their compressibility and collapse potential whereby percolation of water was commenced under two pressures to evaluate the role of sustained pressure on the collapse mechanisms. Despite the low compressibility of sabkhas, results of these tests indicated that these arid, saline soils possess a high collapse potential attributable primarily to dissolution of sodium chlorides, leaching of calcium ions and soil grain adjustment. The collapse potential increases with an increase in the acting pressure at which percolation of water takes place. In contrast to other typical soils, the collapse of arid, saline soils is not instantaneous but requires sufficient volume of water to percolate in order to enhance the dissolution of the cementing agents.

Response of sabkha to laboratory tests: A case study

Abstract Sabkha is a saline, evaporative flat soil that forms under and climates. It is generally associated with saturated watertables that are very close to the ground surface. There are typically two major types of sabkhas; coastal and continental or inland. The presence of brines in the sabkha matrix and the crystallization of diagenetic minerals therein can lead to the highly variable mechanical properties of such a soil. This investigation was carried out to evaluate the engineering properties of this salt-laden and water-sensitive sabkha soil. Several laboratory tests were conducted, including compaction, permeability, unconfined compression, direct shear, triaxial, CBR, specific gravity measurements and grain-size distribution analysis. The investigation also focussed on the effect of distilled water and/or sabkha brine on the properties of this unusual type of soil.

EFFECTS OF CALCIUM SULFATE ON SWELLING POTENTIAL OF AN EXPANSIVE CLAY

Due to a reversible hydration-dehydration reaction, calcium sulfate undergoes phase transformations between a hydrated phase, gypsum, and a dehydrated phase, anhydrite. Due to the harsh climatic and environmental conditions in eastern Saudi Arabia, such phase changes add to the potential swelling hazards of local expansive clays. The adsorption of water by expansive soils and the hydration of anhydrite to gypsum create swelling pressure and are the sources of much damage to foundations throughout the world. This paper attempts to assess the swelling caused by the interaction of calcium sulfate phases, especially gypsum and anhydrite, with expansive clay. This assessment was primarily based on studying the geotechnical, mineralogical, and volume change characteristics of calcium sulfate-bearing soils. X-ray and thermal analyses were used to estimate the type and amount of minerals present during phase transformation of calcium sulfate. The swelling potential was determined using an improved version of the simple odometer and constant-volume tests. The conventional odometer is the device normally used in these tests. However, the size of soil samples, the complete confinement, and the rigidity of the conventional odometer impose serious limitations on the application of the laboratory results to actual field problems. Therefore, the authors investigated the use of a large-scale odometer with different mold sizes and shapes on the swelling potential of some mixtures of expansive clay and calcium sulfate phases. In addition, the soil fabric of these mixtures was investigated using scanning electron microscopy to explain the volume change behavior. The results of this investigation indicated that the swelling potential of clay-calcium sulfate mixtures decreased as the percentage of calcium sulfate was increased, and this reduction was more pronounced when gypsum was used. Swelling pressure was observed to be the highest in the conventional odometer and lowest in the large-scale square odometer mold.

Suggested Modifications to ASTM Standard Methods When Testing Arid, Saline Soils

Arid, saline soils are residual in nature, highly cemented, and formed in hot, arid environments. The presence of soluble and insoluble salts affects the geotechnical properties of these soils. Techniques used to determine the properties of these soils should take into consideration the presence of diagenetic minerals that are considered part of these soils. In this investigation, a typical arid, saline, evaporitic soil, known locally as sabkha, was tested to determine its grain-size characteristics, hydraulic conductivity, compressibility, and collapse potential using standard ASTM methods and nonstandard techniques. The presence of soluble salts necessitates modifications to these standard test methods to properly assess the properties of these soils. Erratum to this paper appears in 17(3).

Characteristics and chemical treatment of expansive clay in Al-Qatif, Saudi Arabia

Abstract Documented evidence of the existence of expansive clays in the Al-Qatif area in the Eastern Province of Saudi Arabia is presented and problems associated with it are described. A site investigation was conducted to obtain undisturbed block clay samples. Laboratory tests were used to determine geotechnical properties, mineralogical composition and swelling characteristics. A laboratory evaluation of chemical stabilization was carried out using three types of chemicals. The results indicate that Al-Qatif clays can be characterized as highly expansive and commercial limes are recommended for preconstruction treatment.