A review of piling industry practices in Dubai, UAE: proposed UCS-based correlations

Abstract

There is limited published information available on design guidance and performance of deep pile foundations in Dubai, UAE. In response to this situation, the piling industry tends to be over-conservative when designing foundation systems for buildings and infrastructure. Consultants, pile testing experts and the Dubai Creative Clusters Authority decided to collaborate with a common goal: share information with the industry and make pile design recommendations to help colleagues prevent the large-scale over-engineering of pile foundations currently ongoing in the Emirate of Dubai. A total of over 200 pile load test results, from which 91 are preliminary pile load tests, were available to the authors to conduct the study presented in this paper. The interpretation of the available information combined with finite-element back-analyses enabled the authors to propose Dubai-specific relationships between the rock's unconfined compressive strength and the pile's ultimate skin friction resistance. Relationships between the rock's unconfined compressive strength and its elastic modulus are also proposed. Notation c 0 cohesion E rock mass stiffness k 0 coefficient of at-rest earth pressures a side resistance factor b side resistance factor g density s 0 3 max maximum confining pressure s 0 cm global rock mass strength s ci unconfined compressive strength t m measured skin friction t PTP skin friction assumed in PTP design t ult ultimate skin friction f 0 angle of internal friction Cite this article

Friction to Unconfined Compression Strength Correlation for Evaluating Capacity of Weak Rock Foundation Sockets

“…The rock is weak to very weak with average UCS values in the range of 1 to 3 MPa. An average UCS pro le from another similar study reported byLatapie & Lochaden (2016) andLatapie et al (2018) for the same area also supports the conclusion that the vast majority of UCS values are in a similar range, 1.5 to 3 MPa, to that shown in Figs.7a and 7b.5 Load Cell Test Data And Back AnalysisOnly skin friction measurements from load cell test data have been used in this study. The load cell and corresponding ground parameter data have been collected from load test and foundation contractors as well as from the Dubai creative cluster authority for research purposes, and the project names are therefore con dential.…”

“…Kulhawy et al (2005) reviewed these methods to predict rock socket friction (f s ) and highlighted a relative lack of sophistication in earlier empirical methods and also commented that in the load test-based methods, the UCS of rock used in developing these correlations was not the average UCS over test depth and might not represent the values at the test locations. Furthermore, many of these methods were developed mainly for small diameter shallow piles with low capacities in speci c geological conditions (Williams and Pells, 1999, Alrifai, 2007, Ibrahim et al, 2009, Latapie et al, 2018, Manoj et al, 2020. There is also a variation in the correlation coe cient α of 0.15 to 0.80 between the lower and upper bound relationships.…”

“…Based on a detailed literature survey and comparison of published case studies, mostly focused on the tall towers in the United Arab Emirates (UAE) where more than 20% of world's tall towers are being built, the methods used to estimate ultimate friction (f s ) for high-capacity deep foundations in the weak carbonate rocks, are assessed to be conservative, probably due to a lack of geology -speci c methods for the region. (Manoj et al 2020, Latapie et al 2018, Alrifai 2007, Ibrahim et al 2009). This paper presents the results of a study based on 44 high-capacity load cell tests on barrettes and piles supporting tall towers in weak rock, along with UCS within the test depth at these locations, which are back-analysed to develop a relationship between f s and UCS of rock.…”

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“…In this project, the intact modulus is assumed as 400q uc which is still lower than what can be obtained from pressure meter tests or suggested by others, cf. Latapie et al (2019), but for the author it gives reliable results for highly loaded piles. In the above suggestions, the modulus is assumed as the secant modulus of deformation at a factor of safety of around 2.0, i.e., at a stress level of about half of the unconfined strength.…”

“…The resulting ultimate skin resistance corresponding to each layer is shown in the table. There are many methods to estimate the skin resistance of bored piles socketed in weak rocks but a recent study on the rocks of Dubai, Latapie et al (2019), suggested that f sult may be taken equal to 0.42√q uc (in MPa). Still, the author feels that relating the skin resistance to RQD is more reliable although the values obtained from Williams and Pells method are more conserva tive than the latter suggestion.…”