Mohammed Y. Al-Aghbari

Performance of square footing with structural skirt resting on sand

The paper presents the performance of a square footing with a structural skirt resting on sand and subjected to a vertical load through an experimental study. A series of tests were conducted in a model test tank to evaluate the performance in terms of improvement in bearing capacity and reduction in settlement of a square footing with and without a structural skirt. The results of the study reveal that this type of reinforcement increases the bearing capacity, reduces the settlement and modifies the load settlement behaviour of the footing. The various factors influencing the bearing capacity improvements and settlement reduction using a structural skirt are identified. Skirt factors are proposed which can be introduced into the general ultimate bearing capacity equation for a square footing resting on sand. The predictions made through the modified equation are in reasonable agreement with the experimental results. The bearing capacity of square footing is increased in the range of 11.2 to 70%. The improvement in bearing capacity decreases with the increase in base roughness of the footing. Further, an equation for a settlement reduction factor is proposed which can be used to calculate the settlement of the square footing with structural skirt resting on sand. The settlement reduction factor (SRF, defined as the ratio of settlement of footing with structural skirt to the settlement of footing without structural skirt at a given load) was in the range 0.11 to 1.0 depending on applied load and skirt depth ratio with the use of a structural skirt. The results further reveal that for a given depth of the skirt, the settlement reduction factor decreases with the increase in applied load. The improvement in the bearing capacity and reduction in settlement of a square footing with a structural skirt resting on sand are dependent on the geometrical and structural properties of the skirt, footing, sand characteristics and interface conditions of the sand–skirt–footing system.

The use of brackish and oil-contaminated water in road construction

This paper discusses the use of non-freshwater, including brackish groundwater and oily production water, in road construction. Non-freshwater was obtained from four major oil production fields in Oman. First, chemical analyses were carried out on nine non-freshwater types, including tap water, obtained from the four sites. These water types were then used with well-graded sand (WGS), high-plasticity silt (HPS), and a road base material to evaluate water effect on material properties. Atterberg limits, compaction, California Bearing Ratio (CBR), swell percentage, swell pressure, and direct shear tests were performed. Results show that there is a slight decrease in the liquid limit when non-freshwater is used. Non-freshwater resulted in a slight decrease in optimum moisture content and a slight increase in maximum dry density in WGS, whereas with HPS it caused slight decreases in optimum moisture content and maximum dry density values. There was an increase in CBR when non-freshwater was used with WGS and HPS soils. However, the use of production water caused a decrease in CBR values for WGS. For the road base material, the use of non-freshwater generally caused a decrease in CBR. The swell pressure tends to increase when non-freshwater is used with HPS. For the road base material, there is a decrease in cohesion and an increase in friction angle when non-freshwater is used in lieu of tap water. Promising laboratory results indicate the potential use of brackish and oily water types in road construction.

Experimental study of the performance of plastic pipes buried in dune sand

This paper presents a laboratory model to study the performance of plastic pipes installed in dune sand. Model PVC pipes were installed in a rigid steel tank and tested. The model simulated trench construction with the pipe placed in the middle of the tank and dune sand along the boundaries and on the bottom of the tank to simulate the native soil. The bedding underneath the pipe and the backfill around the pipe were constructed using carefully placed and compacted dune sand. For comparison purposes, a well-selected coarse sand was also used as a bedding material. Different factors were considered such as type of bedding, degree of compaction of bedding, soil cover depth, magnitude of applied surface pressure, and load repetition. The experimental results showed that plastic pipes can be installed in well-placed and compacted dune sand bedding and backfill. A minimum soil cover of 2d is required to guard against adverse effects of surface loading on the pipe. The pipe behaved in elastic range during all stages of loading with small amount of unrecoverable deformations upon the removal of all loads. However, significant recovery (or rebound) occurred only after the removal of all applied surface pressure and portion of the soil cover soil up to 1d above the crown.

The use of skirts to improve the performance of a footing in sand

Abstract This paper investigates the use of skirts to improve the bearing capacity and to reduce the settlement of a circular footing resting on dune sand. The skirts are fixed to the perimeter of the footings. A series of tests were conducted on model footings in a large tank and the footings were instrumented to measure normal stresses and settlement. The test results indicate that the skirts increase the bearing capacity and reduce the settlement of the footing. The improvement in the bearing capacity is up to about 470% for a surface footing with skirt of a depth of 1.25B. The skirts also reduced the settlement of the footings to as small as 17% of the original settlement of a surface footing without skirts. A modified bearing equation was proposed for circular footings with skirts. The proposed equation agrees quite well with published experimental results.