Saturday, August 1, 2009

Stability Criteria for Waste Dumps

> From: forum-geoteknik-indonesia@yahoogroups.com
Subject: [forum-geoteknik-indonesia] Stability Criteria for Waste Dumps

Teman2 ysh,
Barusan saya ditanya ttg kriteria waste dumps di mining site yg saat ini sdng saya tangani. Barngkali ada gunanya jika informasi ini saya share di milis ini.

salam,
haje

=======++++> > > >

It all depends on the risks, which means depending on the size of the dump and whether the dump is temporary or permanent.
Due to high rainfall at the site, all the criteria below apply for the dumps, which are normally under high phreatic surface or fully saturated conditions.
For interim dumps, the following stability criteria are> recommended:
> > 1.0 Static Loading:
> > 1.1 For deep seated failure surface - Minimum FOS =1.30.
> > 1.2 For shallow failure surface/infinite slope failure surface> - Minimum FOS=1.10.
> > 2.0 Seismic Loading under OBE (Operating Design Earthquake):
> > 2.1 After earthquake (no seismic loading, but include potential> strength reduction due seismic induced pore pressure increase)- For both> deep seated and shallow failure surface -Minimum FOS =1.0.
> > 2.2 During earthquake, it is acceptable to have FOS less than> 1.0 under pseudo-static stability analysis using USACE Method(Hynes-Griffin> and Franklin, 1984), as long as the seismic deformation of the slope computed by Makdisi-Seed analysis (1978) or similar method is less than 2m (no flow failure is indicated).

For permanent Main dump, the following stability criteria are recommended:
> > 1.0 Static Loading:
> > 1.1 For deep seated failure surface - Minimum FOS =1.50.
> > 1.2 For shallow failure surface/infinite slope failure surface - Minimum FOS=1.30.
> > 2.0 Seismic Loading under MDE (Maximum Design Earthquake):
> > 2.1 After earthquake (no seismic loading, but include potential strength reduction due seismic induced pore pressure increase) -
> > 2.1.1 For deep seated failure surface -Minimum FOS =1.20.
> > 2.1.2 For shallow failure surface -Minimum FOS =1.0.
> > 2.2 During earthquake, it is acceptable to have FOS less than 1.0 under pseudo-static stability analysis using USACE Method(Hynes-Griffin> and Franklin, 1984), as long as the seismic deformation of the slope computed by Makdisi-Seed analysis (1978) or similar method is less than 2m (no flow failure is indicated).

Note-
a. For water retaining dams, the OBE (Operating Basis Earthquake) is usually defined as an earthquake with 10% probability of exceedence in 50 years (50 years is the design life of dams) which gives an AEP (Annual> Exceedence probability) of 1 in 475 years. For interim waste dumps, I consider this is too high and would prefer to use 10% probability of exceedence in 10 years (10 years is considered the design life of interim> waste dumps), which gives you 1 in 100 years AEP.
b. For the MDE, however, I would recommend using the value adopted for the TSF (Tailings Storage Facility - tailings dam) which is 1 in 1000years> (10% probability of exceedence in 100 years).
c. Pseudo-static method using USACE method as recommended in the "1998 ANCOLD Guidelines to design Dams to withstand earthquakes". Use horizontal seismic coefficient, kh=50% of Peak Ground Acceleration, PGA, of design earthquakes and 20% strength reduction for materials susceptible to seismic-induced pore pressure increase during earthquakes.
d. Makdisi, F. and Seed, H.B. (1978)."Simplified Procedure for estimating Dam and embankment earthquake induced deformations," Journal of Geotechnical Engineering, ASCE, Vol. 104, GT-7, 849-867.

Any queries please let me know.


--- In forum-geoteknik-indonesia@yahoogroups.com<mailto:forum-geoteknik-indonesia%40yahoogroups.com> , "Y.P. Chandra" wrote:
Pak HJ yth,
Informasi anda sangat berguna. Namun, boleh tahu apakah criteria-2 itu berasal dari code, standard, text book atau merupakan preferensi darisalah satu praktisi atau perusahaan berkecimpung di mining? Alangkah baiknya kalau code, standard atau referensinya diinformasikan.
Chandra

From: forum-geoteknik-indonesia@yahoogroups.com[mailto:forum-geoteknik-indonesia@yahoogroups.com] On Behalf Of Hendra JitnoSent: Friday, July 24, 2009 4:05 PMTo: forum-geoteknik-indonesia@yahoogroups.comSubject: [forum-geoteknik-indonesia] Re: Stability Criteria for Waste Dumps


Pak Chandra ysh,
Waste dumps merupakan salah satu infrastruktur geoteknik yg belum mendapatperhatian seksama dari para regulator, tidak sperti tailings dam, dam, ataubangunan2 geoteknik lainnya. Oleh karena itu kriteria designnya agak 'loose'dan cenderung mengikuti 'selera' perencana-nya.
Kriteria yg saya tulis di email saya terdahulu merupakan salah satu 'currentbest practice', berdasarkan gabungan kriteria dam engineering baik utk bebanstatik dan juga dinamik.Kriteria FOS 1.3 utk short-term loading dan 1.5 utk long-term loading, sayakira sudah merupakan acuan baku di bidang dam engineering, spt dipakai jugadalam manual dari USACE, USBR atau buku2 text ttg dam engineering lainnya.
Acuan utk beban dinamik akibat gempa OBE (Operating Design Earthquake)ygmemakai 1 in 475 years AEP merupakan standard yg dipakai utk bendungan besarmenurut ICOLD, USCOLD, dan ANCOLD (Australian Committee of Large Dam) dansaya kira juga di KBB (Komite Bendungan Besar) Indonesia.
Utk interim Waste Dumps,yg design life-nya hanya sekitar 2 sampai 5 tahun (5tahun sudah cukup panjang utk interim waste dumps), saya modifikasi sedikitkriterianya menjadi 1 in 100 years saja, utk mencerminkan sifatnya ygtemporer.Utk Waste Dumps yg permanen, maka design gempanya menggunakan 1 in 475 yearsutk OBE, dianggap sama spt bendungan/dam.
Utk MDE (Maximum Design Earthquake), penentuannnya sangat tergantung darihasil risk analysis. Kalau waste dumps nya termasuk kategori 'high hazard',maka return period gempanya bisa mencapai lebih dari 1000 thn (atauAEP-Annual exceedance probability- 1 in more than 1000 years). Ada beberapadam yg pernah saya tangani memakai MDE 1 in 3000 years dan 1 in 500 yearskarena terletak didaerah pemukiman padat penduduk sehingga kalau damnyajebol maka risiko loss of life-nya bisa sangat tinggi.
Utk kasus yg saya tangani, karena risiko keruntuhannya tidak mengakibatkan'loss of life' (lokasi hutan belantara PNG), maka gempa disain-nya cukupmenggunakan AEP 1 in 1000 years saja.
Utk gedung..Pak Chandra lebih tahu dari saya..mohon dishare juga pak..
Mudah2an bermanfaat,
Salam dari hutan,
Haje

--- In forum-geoteknik-indonesia@yahoogroups.com, "Y.P. Chandra" wrote:
Yth Pak HJ, Terima kasih penjelasannya dan saya rasa bermanfaat bagi kita semua. Mengenai criteria untuk gedung, diluar dugaan, ternyata juga sangatbervariasai dari satu code ke code yang lain. Dulu saya pernah list FS untuknegative skin friction tiang pancang dari beberapa codes dan text books,ternyata banyak variasi juga dan ternyata tidak semua codes mencantumkannya.Artinya satu codes tidak lengkap mencamtum semua criteria. Oleh karena itu,saya cenderung membatasi diri pada satu-dua codes saja agar tidak bingung.Yang sering saya pakai adalah US Navy, karena setahu saya teman-temanpraktisi di Sigapore, Hongkong dan Taiwan mengacu pada code tsb.
Salam,
Chandra

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