RGME-Piling, the piling division of Rashid Geotechnical and Materials Engineers of Al Khobar, says it is the only firm specialising in the Vibrex piling system in Saudi Arabia.

Vibrex piles are synonymous for the most economical piling solutions owing to higher bearing capacities and faster construction time, says RGME-piling manager, Parvez A Naushahi. The company has successfully utilised the technique for a number of projects in Saudi Arabia including the United Gulf Steel Mill Company in Jubail, where more than 2,700 Vibrex driven cast in-situ and bored piles were installed in a record period, from Jan. 1999 to April 1999.

Elaborating on the technique, Naushahi says: "Essentially, Vibrex piles are 'large displacement' driven cast in-situ type piles. These are constructed in-situ by driving a closed-ended casing pipe to form a hole and then filling the hole with reinforced concrete while withdrawing the casing. "Since no soil is taken out from the ground, the site remains clean and does not pose the problem of soil disposal making the system environment-friendly. Furthermore, the driving of closed-ended section helps densify the surrounding soils, resulting in higher capacity for a given pile diameter and a reduction in pile length, as compared to other types of cast in-situ piles."

A Vibrex pile construction sequence is illustrated in Figure 1.

"Vibrex piles possess the merits of both driven precast and bored piles," he continues. "As a closed-end casing is driven using state-of-the-art hydraulic hammers, the soil parameters along the length and base of the pile improve to the same degree as that of precast driven piles. Particularly the steel base plate, installed for each Vibrex pile and sits on to the heavily compacted soil provides, better end bearing support.

"At the time of withdrawal of the casing, the green concrete under the hydraulic head, forms enlarged sections in the loose/soft soil layers. Thus, an increase in diameter usually associated with Vibrex piles occurs in certain sections. A similar type of 'bulb' is also expected to be formed at the base of the pile. The increased skin friction and end-bearing capacities can be attributed to these phenomena. Moreover, the left-in-place steel plate at the end of the Vibrex piles will, undoubtedly, contribute to the high end-bearing capacity.

"RGME-Piling, with its considerable experience in the construction of Vibrex and bored piles, has established the superiority of the Vibrex piles. Comprehensive load-testing programmes consisting of compression, tension and lateral load tests and pile integrity testing on both type of piles, executed at various projects were technically evaluated and proved the high quality of piles installed by RGME-Piling.

"Load tests have been carried out on both working and test piles as per applicable standards, to as much as four times the design load. The piles were tested under quick (short term) and also for long-term loading. Typical results for Vibrex and bored piles are presented as Load vs Deflection plots in Figures 2 and 3. These plots reveal the obvious and appreciable differences in the capacities and behaviour of these two types of piles.

"Pile integrity testing using the Pulse Echo Method also proved the increase in diameter of Vibrex piles in loose/soft layers and higher skin frictions associated with such piles.

"The plots for Vibrex piles were analysed and load-carrying capacity of the piles tested to failure was evaluated. The ultimate load capacities so obtained were used to work out the design parameters for different soil layers in which the piles were embedded. The back calculated geotechnical parameters for Vibrex piles were found to be of much higher values when compared with the range usually specified for bored piles. It is considered therefore, that the Vibrex piles, are the most economical solution to low bearing capacity soils common in the Gulf region."

RGME-Piling's expertise also covers a range of ground engineering techniques such as conventional Bored piles, Vibrex stone columns, precast concrete piles, H-piles and tubular piles, offshore piling and cofferdam using sheet piles, secant piles, diaphragm walls, and installation of dewatering systems. In 1998-99, the company undertook sheet piles installation works for the Ghazlan power plant project for Consolidated Contractors Company and cast in-situ bored piles for the Shaikh Tuwaijri Mosque project for the International Center for Commerce and Contracting.