Among the geotechnical design parameters of bearing capacity and disposal, which are Independent, If the design satisfies only the bearing capacity, the settlement will be over-satisfied (ie less settlement than permissible), and vice versa, if design Satisfied disposal, bearing capacity will be more satisfied (In other words factor of safety Bearing capacity exceeding the minimum required value against failure). The latter condition is well known to us in the case of raft in the sand, In any case, the design is not optimal, which is possible only in rare cases when both the requirements are Better And together Satisfied, that is, the factor of protection against failure of the bearing capacity is at the minimum prescribed value, and the settlement is equal to the permissible value. when there is a need more satisfied, as is the case in a general case, the resulting geotechnical design is partially very safe, and to that extent, ideologically non-economic.

The above points need to be explored the ways by which the design can be made optimum, For example, in the case of rafts in sand, the question is whether it should be possible for us to design rafts with satisfactory bearing capacity and what to look for? exterior Means to control disposal that would otherwise be excessive. One such solution is available, using the pile in conjunction with the raft, the function of piles only. Control a settlement. Such a system is called a pile raft,

Fig-1 Pile Raft System
Fig-1 Pile Raft System

However, when such a system is provided, it becomes Match like a shallow foundation fleet and a deep foundation such as A lot, both are sharing the process load transfer To the soil Figure 1 Tried to paint this picture. So theoretically, there is a three-way conversation Between raft, pile and soil, this is a complex problem for any rigorous analysis, for which the best approach would be numerical analysis such as the ‘finite element method’. For design office use, however, one more often resorts to ‘approximate’ methods.

Example 1 [The Petronas Twin Towers]

Figure-2 Petronas Twin Towers
Figure-2 Petronas Twin Towers

twins Petronas Towers in Kuala LumpurThe capital of Malaysia, when completed in 1998 (at a cost of US$1.6 billion), was one of the tallest structures in the world. at 450 meters, it was 7 meters taller than the Sears (now called Willis) Tower in Chicago, USA, which held the record till then.

towers are circular in planning. 395,000 square meters2 The complex has 88 occupied floors above grade with 5 levels (floors) below grade for parking. Each tower has perimeter pillars at 46 meters in diameter. Base with an adjacent 21 m diameter. 45 storey bustle. The towers stand 55 meters apart and a . are connected by Bridge 41st and 42nd floor (line drawing number 2) Kuala Lumpur City Center (KLCC) Bhd. was the developer of the project and the structure is owned by PETRONAS (for Petroleum National), the national oil and gas company of Malaysia.

On the soil side, 10 to 20 m depth at the top, there are residual soils of varying thicknesses of meta-sedimentary formations, such as siltstone, sandstone, shale and sometimes phyllite (locally referred to as the ‘Kenny Hill Formation’). is known) is alluvial containing water of varying thickness. ‘), after Kuala Lumpur Limestone formation that can vary dramatically with respect to surface height and resolution activity except huge cavities, (Rock height was found to vary from 140 m to less than 50 m.) The interface is always covered with precarious ‘recession zones’ where Kenny Hill material has softened and eroded into limestone cavities.

Due to the structure’s high thinness ratio, the developer and designer have created a . has set an ambitious theoretical goal of Zero The differential settlement practically limits it to less than 12.7 mm at the base of the towers. The geologic conditions at the site mentioned above have actually made the task very technically challenging.

Among the variety of foundations considered for the project, the final choice, as determined by techno-economic considerations, fell on one pile raft consisting of abrasive piles located in the Kenny Hill formation above limestone, but with cavities and recession zone grout-filled, vary the length of the heap to reduce differential settlement.

An elaborate program of testing was undertaken, which included 260 . involved more than pressure meter test.

At tower locations, the limestone depth varies from 80 to 180 m, making it possible for the friction piles at Kenny Hill above to support a tower load of 2680 mn. 110 kN/m . adopting the design value of2 For skin fiction, the final design worked out as 1.3 meters in diameter. Stacked under a mat (raft) of diameter 4.7 m extending to a depth of 33 m. 53.7 m

3-D finite element analysis settled a gap of 11 mm edge-to-edge at the bottom of the tower, satisfying the design goal in this regard.

Extensive grouting was introduced to fill cavities in the limestone falling within the towers’ impact zone and to improve the slump zone found just above the limestone that formed cavities and solutions in limestone from Kenny Hill erosion. channels were created.

Example-2 [Burj Khalifa]

Fig-3 Burj Khalifa
Fig-3 Burj Khalifa

Burjo (means ‘tower’) Dubai(now called Burj Khalifa), on one high altitude 600 square metersIt is currently the tallest building in the world (Figure 48.3). It is Y-shaped in plan (with three wings at 1200 – see Fig.48.4) and increases 160 floors, with a podium at the base that includes a 4-6 storey garage.

tower a. standing over pile raft The foundation, consisting of a 3.7 m thick raft supported on a 1.5 m diameter. Rugged piles spread to a depth of about 50 meters under the base of the raft.

Haider Consulting (UK) Was the geotechnical consultant for the project. He carried out the foundation design, which was independently peer-reviewed by Coffee Geosciences (Australia) under whose direction. University of Sydney Professor Harry G. paulos,

For the control of differential settlement, what can be expected to achieve optimum performance? policy space Relatively small number of hemorrhoids (Image-4), rather than using a larger number of piles distributed evenly over the raft area, or to increase the thickness of the raft. The performance of a pile raft can be optimized by selecting suitable locations for the pile under the raft. (However, this assumes no or limited raft-pile interaction.) In general, piles should be focused in most heavy areas, while in areas with less heavy loads the number of piles can be reduced, or even eliminated.

Fig-4 Burj Khalifa (plan showing piles)
Fig-4 Burj Khalifa (plan showing piles)

The Burj Dubai site is characterized by a horizontally stratified subsurface profile, which is complex and highly variable due to the nature and prevalence of deposits. hot dry climatic conditions. Medium dense to very loose granular silty sands (marine deposits) are underlain by a succession of very weak to very loose sandstones, very weak cementitious sands, gypsyferous fine grained sandstones/siltstones and weak to moderately weak agglomerates/calcilites. The groundwater level was at 0.0 DMD (Dubai Municipality Datum) which was about 2.5 meters below ground level.

bored piles The ones installed in the weak rock were 1.5 meters in diameter. and (-) 7.5 m – 47.45 m length with tower rafts installed on DMD. The podium piles were 0.9 m in diameter. and (-) 4.85 m – 30 m in length with podium rafts installed on the DMD. The thickness of the raft was 3.7 m. FE analysis gave a maximum load of the order of 35 mn at the corners of the wings and a minimum load of the order of 12–13 mn within the centre. The minimum center-to-center distance of the piles for the tower was 2.5 times the pile diameter. Altogether 926 piles were used. Bored piles were constructed using polymer drilling fluid, in place of the more traditional bentonite drilling mud. The settlements estimated by FE analysis were of the order of 70–75 mm in tower area, with a drastic reduction of 10–12 mm in podium area. The last measured settlements were found to be comfortably below the estimated limits.

article written by

Dr. Nain P. Kurien

Er. Mukesh Kumar

Photo of author
Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.