Materi Kuliah Rekayasa Pondasi II-Deep Foundation

Waspada terhadap bencana gempa, tsunami, banjir, longsor, letusan gunung berapi !!!

Senin, 28 Maret 2011

Analisa Sederhana Atas Robohnya Apartemen 13 Lantai di China

Informasi data dari Internet sbb :

(1) An underground garage was being dug on the south
side of the building, to a depth of 4.6 meters (15 ft).

(2) The excavated dirt was being piled up on the north
side of the building, to a height of 10 meters (32 ft).

(3) They dug right up to the base of the building.
Then the rains came.

(4) The building experienced uneven lateral pressure
from north to south.

(5) This resulted in a lateral pressure of 3,000 tonnes,
which was greater than what the un-reinforced pilings
could tolerate. Thus, the building toppled completely
over in a southerly direction.

Setelah melihat dari foto2 dan informasi data diatas maka kemungkinan penyebab ambruknya gedung ini sbb:

1. Akibat excavation galian tanah kurang memperhatikan syarat minimum failure line dari pondasi tiang pancang
2. Tidak memperhitungkan permiability pada galian saat hujan serta infiltrasi air dari sungai sehingga terjadi rapiddowndrag terhadap dayadukung tanah
3.Patahnya tiang terjadi pada posisi plastic hinge (Utk kasus flexible pile/tiang pancang panjang) akibat melampaui beban lateral batas tiang pancang dengan hitungan kasar sbb:

Akibat masalah diatas maka Beban Horisontal yg bekerja = 3000 ton
dari gambar yg ada jumlah tiang pancang preststress yg digunakan kira2 100 tiang
jika 1 tiang pancang prestressed maksimum dapat memikul 150 ton beban vertikal maka menurut California bearing code beban horisontal dapat diambil 10% dari bebanvertikal = 15 ton
jadi untuk 100 tiang maka beban horisontal yg dapat dipikul = 100*15 = 1500 ton

1. Kapasitas dukung 100 tiang pancang hanya 1500 ton < 3000 ton (Makanya Gedung Ambruk)
2. Kebiasaan para kontraktor yg ingin mencari untung besar sehingga terkadang hanya mengcopy paste gambar engineering desain dan tidak mau menghired ahli geoteknik karena dimonopoli oleh ahli struktur dll hal ini banyak saya temui juga di SULUT ini bisa menjadi hikmah bagi para ahli Teknik Sipil di SULUT

catatan :
perhitungan diatas adalah perhitungan kasar diperlukan analisa dan data lapangan sehingga diperoleh hasil yg lebih baik dan detail

Fabian J Manoppo
Ahli Geoteknik (Pondasi Tiang Pancang)
Sent from my iPad

Korelasi Nilai. SPT terhadap Bearing Capacity Factor

fkd (Structural) 25 Feb 02 11:57
  Dear folks,

  Sorry for this basic question (I'm structural) but I would like to know if there is any trustable way to determine the alowable bearing pressure having only the results of a Standart Penetration Test?

  Thanks in advance,


austim (Structural) 25 Feb 02 15:26
Hi, fkd.

You really need to know more than just the N values.  Importantly, you must also know what types of soil you are dealing with.

One of my ancient texts, Peck Hansen and Thorburn, "Foundation Engineering", shows tables from which you can get bearing capacity factors Nq and Ngamma for SAND, based on N values.

For clays, PH&T say "the standard penetration test is not so reliable an indicator of the compressive strength of clys as it is of the relative density of sands, and the tests on tube samples are preferred".

ishvaaag (Structural) 27 Feb 02 17:46
For cohesionless soils, as austim says, mainly.

You have a freely available worksheet in the Mathcad's Collaboratory that cares of that.

See the graphical relationship in

Bridge Substructure and Foundation Design
Petros P. Xanthakos
Prentice Hall

kieran1 (Structural) 28 Feb 02 7:42
I use a simple formula of allowable bearing pressure =10N where N is from S.P.T. Kieran Coyle
BEng(hons),CEng, M.I.Struct.E, M.I.E.I.

palmeira (Structural) 2 Mar 02 20:41
Hi Kieran,

In what unit is the ABP=10*N ?

CISGeotechnical (Geotechnical) 11 Mar 02 6:17
The US Army Corps of Engineers has published many Engineer Manuals that can make you more than satisfied since they are based on current practical applications and have sustantiable references for further reading.  For example, N values has been used mainly for sands to correlate allowable bearing pressure.  The Peck Hanson Thornburn book has charts for those purposes, and Meyerhof has done extensive work on that too.

However, recently I read that for clays, Bowles have suggested to use cu = 0.12 Nspt (in ksf)which multiplied by two will be the unconfined compressive strength (qu), which in turn can be taken as the allowable bearing pressure having a safety factor of 3. Easy not?... but,

Remember that allowable bearing pressure is tied to allowable settlement and settlement estimates govern for clays while allowable bearing pressure using classical charts for sand are developed for an allowable settlement of 1 inch.

For in-depth free study of the issues and to get the USACE Engineer Manual of Bearing Capacity of Soils go to the following page:

You can get also many other manuals for free in their main web page of the Engineer Publications, you just need Adobe Acrobat Reader.  If you have any problems accessing the info let me know.  I know you and others will appreciate this link.

CIS Geotechnical CIS Geotechnical

RVT (Visitor) 11 Mar 02 10:57
A nice, conservative method for coming up with bearing values, based on N values, can be found in a couple charts published back in 1969 (2nd print) by B.K. Hough, "Basic Soils Engineering," pp 308 and 309.  I used these charts for many years with success.  As near as I can estimate, these values for bearing will result in about 1/4" settlement.  And, these charts were developed with manual hammers.  If your N values are from an auto-hammer, the results could be really conservative.  As CISGeotechnical indicated, there are two modes of failure... bearing and settlement.  As long as there is no bearing failure, the bearing pressure you select will be (somewhat) dependant on the settlement you can live with.  Now that is probably more than you really wanted to know..... 字串7

fkd (Structural) 11 Mar 02 15:33
  I just want to say thank you very much for the valuable and precise information provided.
  As RVT said it's really more than my needs, specially with that huge  amount of info that can be found at USACE.

Best Regards


jeanesse (Geotechnical) 17 Mar 02 12:17
I am agree with Austim.  For determine allowable bearing capacity you also need to know other soil properties.  For you know if any correlation give trusable results, you need to know the hypotheses what is based the correlation. You need to know characteristics of the soil used to develop the correlation, too.