CALIFORNIA BEARING RATIO (CBR METHOD) DAN UKURAN BUTIR

1. CALIFORNIA BEARING RATIO (CBR METHOD)
Pendahuluan
Metoda ini awalnya diciptakan oleh O.J poter kemudian di kembangkan oleh California State Highway Departement, kemudian dikembangkan dan dimodifikasi oleh Corps insinyur-isinyur tentara Amerika Serikat (U.S Army Corps of Engineers). Metode ini menkombinasikan percobaan pembebanan penetrasi di Laboratorium atau di Lapangan dengan rencana Empiris untuk menentukan tebal lapisan perkerasan. Hal ini digunakan sebagai metode perencanaan perkerasan lentur (flexible pavement) suatu jalan. Tebal suatu bagian perkerasan ditentukan oleh nilai CBR.
Defenisi
CBR merupakan suatu perbandingan antara beban percobaan (test load) dengan beban Standar (Standard Load) dan dinyatakan dalam persentase. Dinyatakan dengan rumus :

PT
CBR = x 100%
PS

Keterangan :
PT = beban percobaan (test load)
PS = beban standar (standar load)

Harga CBR adalah nilai yang menyatakan kualitas tanah dasar dibandingkan dengan bahan standar berupa batu pecah yang mempunyai nilai CBR sebesar 100% dalam memikul beban

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Percobaan -Percobaan CBR
Percobaan-percobaan ini dapat dilakukan :
1. Percobaan di Laboratorium
standar yang berlaku :
Bina Marga : PB – 0113 – 76
ASTM : D – 1883 – 73
AASHTO : T - 193 – 81
 Tujuan : Untuk menentukan nilai daya dukung tanah dalam kepadatan maksimum
 Alat-alat yang digunakan :
Alat yang digunakan sama dengan alat-alat percobaan pemadatan standar maupun dengan modifikasi dengan spesifikasi seperti table berikut :

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 Cara melakukan percobaan :
Percobaan C.B.R biasanya menggunakan contoh tanah dalam kadar air optimum.
Metode yang digunakan dalam metoda 2 atau standar ASTM D – 70 atau D – 1557 – 70. diameter tabung = 6 inci = 15 cm dan tinggi = 5 sampai 7 inci = 12,50 cm sampai 17,50 cm.
Dengan menggunakan dongkrak mekanis sebuah piston penetrasi ditekan supaya masuk ke dalam tanah dengan kecepatan tetap = 1,25 mm/menit dengan beban awal = 0,05 kN.
Pembebanan pada pluyer diamati pada penetrasi berturut-turut : 0.625 ; 1,250 ; 1,875 ; 2,500 ; 3,750 ; 5,000 ; 6,250 dan 7,500 mm.
hasil perhitungan ini di plot dalam kertas kurva.
2. percobaan di Lapangan
 Tujuan untuk melakukan nilali C.B.R asli di Lapangan sesuai dengan kondisi tanah saat iut. Biasanya digunaka untuk perencanaan tebal lapisan perkerasan yang perkerasan lapisan tanah dasarnya tidak akan dipadatkan lagi.pemeriksaan dilakukan dengan kondisi kadar air tanah tinggi.
 Alat-alat yang digunakan:
a. Truk dengan pembebanan
b. Piston penetrasi dari logam
c. Timbangan
d. Dongkrak hidrolisis atau mekanik
e. Arloji beban atau arloji cincin penguji lengkap dengan cincin pengujinya (proving ring)
f. Perlengkapan lainnya : rol meter, kunici dan lain-lain.
 Cara melakukan percobaan :
1) Di Lapangan
a. Tanah digali di lokasi yang telah ditentukan dan kemudian dibuat deskripsi secara visual
b. Tabung diletakkan dipermukaan tanah dan kemudian diberi beban melalui truk dengan dibantu dongkrak sebagai alat penekan
c. Cotoh tanah diambil sebanya k 2 tabung
d. Contoh tanah dibersihkan dan tutup rapat dan dibawa ke Laboratorium
e. Satu contoh langsung diuji dan yang lain direndam selama 4 x 24 jam.

2) Di Laboratorium
a. Beban statis diletakkan pada bagian atas tabung untuk mencegah pengembangan tanah dalam tabung
b. Arloji penunjuk beban dan arloji penetrasi dipasang dan angka dinolkan
c. Pembebanan dimulai dengan beraturan sesuai dengan urutan waktu maupun kedalaman yang ada pada forulir data.
d. Catat angka yang dibaca pada arloji pengukur pada formulir.

Jenis - Jenis CBR :
Berdasakan cara mendapatkan contoh tanahnya, CBR dapat dibagi menjadi :
1) CBR Lapangan (CBR inplace atau field Inplace)
• Digunakan untuk memperoleh nilai CBR asli di Lapangan sesuai dengan kondisi tanah pada saat itu. Umum digunakan untuk perencanaan tebal perkerasan yang lapisan tanah dasarnya tidak akan dipadatkan lagi. Pemeriksaan ini dilakukan dala kondisi kadar air tanah tinggi (musim penghujan), atau dalam kondisi terbuuk yang mungkin terjadi. Juga digunakan apakah kepadatan yang diperoleh dengan sesuai dengan yang kita inginkan
2) CBR lapangan rendaman (undisturbed soaked CBR)
• Digunakan untuk mendapatkan besarnya nilai CBR asli di Lapangan pada keadaan jenuh air dan tanah mengalami pengembangan (swell) yang maksimum
• Hal ini sering digunakan untuk menentukan daya dukung tanah di daerah yang lapisan tanah dasarnya tidak akan dipadatkan lagi, terletak pada daerah yang badan jalannya sering terendam air pada musim penghujan dan kering pada musim kemarau. Sedangkan pemeriksaan dilakukan di musim kemarau.
• Pemeriksaan dilakukan dengan menambil contoh tanah dalm tabung (mould) yang ditekan masuk kedalam tanah mencapai kedalaman yang diinginkan. Tabung berisi contoh tanah dikeluarkan dan direndam dalam air selama beberapa hari sambil diukur pengembangannya. Setelah pengembangan tidak terjadi lagi, barulah dilakukan pemeriksaan besarnya CBR.
3) CBR Laboratorium
• Tanah dasar (Subgrade) pada konstuksi jalan baru dapat berupa tanah asli, tanah timbunan atau tanah galian yang telah dipadatkan sampai menncapai kepadatan 95% kepadatan maksimum. Dengan demikian daya dukung tanah dasar tersebut merupakan nilai kemampuan lapisan tanah memikul beban setelah tanah tersebut dipadatkan. CBR ini disebut CBR laboratoium , karena disiapkan di Laboratorium. CBR Laboratorium dibedakan atas 2 macam, yaitu CBR Laboratorium rendaman dan BR Laboratorium tanpa rendaman

2) UKURAN BUTIR
Pembagian dari butir-butir tanah tergantung pada ukuran di dalam tanah Untuk bahan yang berbutir kasar. Pembagian ini dapat ditentukan dengan menyaring, dan untuk butir-butir yang halus digunakan suatu metoda pengukuran kecepatan penurunan dalam air. Penentuan pembagian ukuran butir dengan metoda-metoda tersebut dikenal sebagai analisis mekanis.
Ada sejumlah sistem-sistem klasifikasi ukuran butir yang dipakai, akan tetapi ”British Standard Institution” telah menerapkan sistem yang dikembangkan oleh ”Massachusetts Institute of Technology”, berhubung batas- batas pembagian utama yang dipakai kira-kira bersangkutan dengan perubahan-perubahan penting di dalam sifat-sifat teknis tanah.

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Analisis Kasar
Untuk analisis kasar, baik basah mapun kering dapat digunakan saringan. Dalam kedua keadaan suatu contoh tanah yang dikeringkan dalam tungku ditimbang dan dilewatkan melalui suatu kelompok saringan
Berat tanah kering yang tertahan diatas setiap saringan di catat dan dihitung persentase dari contoh total yang melewati setiap saringan.
Analisis Halus
Teori analisis halus adalah berdasarkan kepada hukum Stike mengenai penurunan (settlement), yaitu bola-bola kecil di dalam suatu cairan aka turun pada kecepatan-kecepatan yang berbeda, bergantung kepada ukuran bola tersebut.

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GEOPHYSICAL METHODE / METODA DALAM GEOFISIKA

Metoda Seismik merupakan salah satu metoda geofisika yang digunakan untuk eskplorasi air tanah yang ada di bawah permukaan bumi dengan bantuan gelombang seismik. Eksplorasi seismik atau eksplorasi dengan menggunakan metode seismik banyak dipakai untuk melakukan pemetaan struktur di bawah permukaan bumi untuk bisa melihat kemungkinan adanya air tanah berdasarkan interpretasi dari penampang seismiknya.Dalam metoda seismik pengukuran dilakukan dengan menggunakan sumber seismik (ledakan, vibroseis dll). Setelah sumber diberikan maka akan terjadi gerakan
gelombang di dalam medium (tanah/batuan) yang memenuhi hukum-hukum elastisitas ke segala arah dan mengalami pemantulan ataupun pembiasan akibat munculnya perbedaan kecepatan. Kemudian, pada suatu jarak tertentu, gerakan partikel tersebut di rekam sebagai fungsi waktu. Berdasar data rekaman inilah dapat ‘diperkirakan’ bentuk lapisan/struktur di dalam tanah (batuan)
Metode Gravity (gaya berat) dilakukan untuk menyelidiki keadaan bawah permukaan berdasarkan perbedaan rapat masa air tanah dari daerah sekeliling (r=gram/cm3). Metode ini adalah metode geofisika yang sensitive terhadap perubahan vertikal, oleh karena itu metode ini disukai untuk mempelajari kontak intrusi, batuan dasar, struktur geologi, endapan sungai purba, lubang di dalam masa batuan, shaff terpendam dan lain-lain. Eksplorasi biasanya dilakukan dalam bentuk kisi atau lintasan penampang. Perpisahan anomali akibat rapat masa dari kedalaman berbeda dilakukan dengan menggunakan filter matematis atau filter geofisika. Di pasaran sekarang didapat alat gravimeter dengan ketelitian sangat tinggi ( mgal ), dengan demikian anomali kecil dapat dianalisa. Hanya saja metode penguluran data, harus dilakukan dengan sangat teliti untuk mendapatkan hasil yang akurat.

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GEOGRAPHICAL INFORMATION SYSTEM (GIS)

Geographical Information Systems – Overview -- GIS have been defined as ‘automated systems for the capture, storage, retrieval, analysis, and display of spatial data’ (Clarke, 1995,p13). GIS can be used for any area or application that depends largely on geographic data ie. data that is geographically referenced or is ‘mappable’. As the scope is quite wide it is not surprising that there are many definitions as well as many acronyms (LIS, NRIS, AM/FM etc) which cover the field referred to as GIS related technologies .
Geographical Information Systems – Overview -- GIS has its origins in Geography, Cartography, Surveying and Computer Science – disciplines which deal with various aspects of geography and the associated geographic data. Its rapid development and widespread adoption over the past decade has been influenced very strongly by developments in computing in general eg. higher performance, lower cost, easier to use hardware and software and the continuous enhancement of the application capabilities of software
Over time GIS applications have become more sophisticated – changing from earlier static inventory type applications (basically, electronic versions of atlases or manual procedures) to current real time decision-support type management applications.

Topic structure
• GIS defined
• GIS applications
• GIS development
• GIS components
• Sources of information on GIS

General Definition
“A system of hardware, software, data, people, organisations and institutional arrangements for collecting, storing, analysing and disseminating information about areas of the earth (Dueker & Kjerne 1989:7-8

Definition Of Gis
“The organized activity by which people:
• Measure aspects of geographic phenomena and processes
• Represent these measurements, usually in the form of a computer database, to emphasize spatial themes, entities and relationships
• Operate upon these representations to produce more measurements and to discover new relationships by integrating disparate sources
• Transform these representations to conform to other frameworks of entities and relationships”
( Chrisman 1997:5)



A GIS as a Toolbox
"a powerful set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes. This set of tools constitutes a GIS." (Burrough, 1986:6).
Or
“tools that allow for the processing of spatial data into information, generally information tied explicitly to, and used to make decisions about, some portion of the earth.” (DeMers 1999:7)

GIS Defined by Function
“… automated systems for the capture, storage, retrieval, analysis, and display of spatial data.”
(Clarke, 1995: 13).

GIS as an Information System
"An information system that is designed to work with data referenced by spatial or geographic coordinates … a GIS is both a database system with specific capabilities for spatially-referenced data, as well as a set of operations for working with the data" (Star and Estes, 1990, p. 2).

Duecker's (1979:20) definition has survived the test of time
"A geographic information system is a special case of information systems where the database consists of observations on spatially distributed features, activities or events, which are definable in space as points, lines, or areas.
A geographic information system manipulates data about these points, lines, and areas to retrieve data for ad hoc queries and analyses" (Duecker, 1979, p 106).

Geographical Information System (GIS) … defined
– A GIS is a computer based system for the management of geographic data.
– Geographic data is any data that is geographically referenced i.e. location known.
– Information implies that data are organized to yield useful knowledge
– System implies GIS is made up of several inter-related and linked components with different functions
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MINERALOGY

COPPER-IRON-ZINC ASS EMBLAGES IN VOLCANIC ENVIRONMENTS
Mineralogy -- Major: pyrite, sphalerite, chalcopyrite; in some examples pyrrhotite or Minor: bornite, tetrahedrite, electrum, arsenopyrite, marcasite, cubanite, copper-lead-bismuth-silver-su1fosalts, cassiterite, plus many °the in trace amounts.
Mode of Occurrence -- Massive to disseminated stratiform sulfide ores in volcano-sedimentary quences ranging from ophiolite complexes (Cyprus-type deposits) felsic tuffs, vas and sub sea floor intrusions (Kuroko-type deposits) to mudstones with little immediately associated recognizable volcanic material (Bes-’deposits).

Examples -- Kuroko- and Besshi-type deposits of Japan; Timmins, Ontario; Bathurst, I Brunswick; Sullivan, British Columbia; Flin-Flon, Manitoba-Saskatchewai Noranda, Quebec; Mt. Lyell, Australia; Rio Tinto, Spain; Scandinavian C donides; Avoca, Ireland; Parys Mountain, Wales; Troodos Complex depo Cyprus; Bett’s Cove, Newfoundland; Modern Red Sea and East Pacific Rise deposits.
Mineral Associations and Textures -- The deposits range from ores in thick volcanic sequences such as the F ores of Japan and ores directly associated with a volcanic vent (Vanna L Fiji) to ores associated with ophiolite sequences (Cyprus; Bett’s Cove, I found land) to distal ores that are emplaced in dominantly sedimentary sequences (Besshi deposits of Japan) and sequences containing no recognizable volcanic (Sullivan, British Columbia). They thus grade into ores of the type described in Section 10.7. Tn spite of the different settings in which these ores are found, there are similarities among the ore types observed. Zoning within many of these deposits is recognizable and three major ore types occur; the distribu4 ton of the primary minerals in the Kuroko ores is shown in Figures 10.19 and 10.20. Although the major ore types described in the following are those corn manly observed in the Kuroko deposits, they appear in most or all of the ores of this class with only minor variation. These ores, which appear to grade into the ores described in Section 10.7, have frequently been considered in terms of
Cu-Pb-Zn ratios as shown in Figure 10.21. Plimer (1978) has suggested that a trend in ore-type from Cu-dominant to Zn-dominant to Zn-Pb-dominant corresponds to a progression in time and distance from the volcanic Source (i.e., proximal to distal in nature). Jambor (1979) has enlarged on this theme and proposed a classification of the Bathurst-area (Canada) deposits based on their established or assumed displacement from feeder conduits (proximal versus distal) and position of sulfide crystallization (autochthonous versus allochthonous).
Although the ores of the volcanic deposits are members of a continuum, several specific ore types are observed most commonly; the following is a brief discussion of these ore types.
Pyritic (= Cyprus type) These ores, associated with ophiolite complexes are composed of massive banded to fragmental pyrite with small amounts of interstitial chalcopyrite and other base metal sulfides. The pyrite is present as friable masses of subhedral to euhedral, commonly zoned, grains, as colloform banded masses, and as framboids. Marcasite is admixed• with the pyrite and often appears to have replaced the pyrite. Chalcopyrite occurs as anhedral interstitial grains and as inclusions in the pyrite; sphaleritc occurs similarly but is less abun

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•dant. Secondary covellite, digenite, chalcocite, and bornité occur as rims on, and along fractures in, pyrite and chalcopyrite.
Siliceous Ore (==Keiko-type of Kuroko Deposits) These ores apparently rep- resent feeder veins and stock works and consist primarily of pyrite, chalcopyrite, and quartz with only minor amounts of sphalerite, galena, and tetrahedrite. The pyrite occurs as euhedral grains, subhedral granular stringers, and colloform masses. The other minerals are minor and occur as anhedral interstitial grains in pyritic masses and gangue. Scttt (pers. commun., 1980) has noted that a black siliceous ore composed of sphalerite and galena is not uncommon in Kuroko de_ts.
Yellow Ore (=Oko-type of Kuroko Deposits) This ore type is characterized in both hand sample and polished section by the conspicuous yellow color resulting from the presence of chalcopyrite interstitial to the dominant euhedral to anhedral pyrite (Figure 10.22a). Minor amounts of sphalerite, galena, tetrahedrite, and lead sulfosalts and trace amounts of electrum are dispersed among the major sulfides. In unmetamorphosed bodies, the pyrite is often quite fine (<0.1 mm), but in metamorphosed ores pyrite commonly recrystallizes to form
euhedral grains which are several millimeters across. These ores and the black ores described later commonly exhibit extensively developed clastic textures that apparently formed at the time of ore deposition or immediately thereafter as a result of slumping.
Black Ore (Kuroko-type) The black ores (Figures 10.22b and 7.4c), the most complex of the common volcariogenic ore types, were so named because of the abundant dark sphalerite within them. Galena, barite, chalcopyrite, pyrite, and tetrahedrite are common but subsidiary to the sphalerite. Bornite, electrum, lead sulfosalts, argentite, and a variety of silver sulfosalts are customary accessory minerals. The black ores are usually compact and massive but primary sedimentary banding is often visible and brecciated and colloform textures are not uncommon. In ores unmodified by metamorphism, pyrite occurs as framboids, rosettes, colloform bands, and dispersed euhedral to subhedral grains. Pyrite grain size increases during metamorphism but growth zoning is often visible either after conventional polishing or after etching. In polished sections, sphalerite appears as anhedral grains that frequently contain dispersed micron-sized inclusions of chalcopyrite. Barton (1978) has shown, by using doubly polished thin sections in transmitted light (see Figure 2.7) that this “chalcopyrite disease” consists of rods and thin vermicular, myrmekiticlike growths, probably formed through epitaxial growth or replacement. He has also shown the presence of growth-band’g and overgrowth textures in sphalerite and tetrahedrite. During metamorphism, the sphalerite is ccmmon1y recrystallized and homogenized, and the dispersed chalcopyrite is concentrated as grains or rims along sphalerite grain-boundaries.

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CHINA CEMENTS PLACE AS WORLD'S TOP GOLD PRODUCER

Kristie Batten [http://www.miningnews.net] -- CHINA has outdone South Africa to be named the world’s top gold producer for the second year running, according to figures from the China Gold Association.
Chinese newspaper, the Shanghai Daily, reported that China’s gold production in 2008 increased 4.26% to 282 tonnes or just over 9.9 million ounces.

The provinces of Shandong, Henan and Jiangxi were the top three gold mining provinces, producing 46.4% of the country's total.
The Shandong province is home to Australian miner Sino Gold’s BioGold processing facility.

Investment in gold was also up, with the CGA reporting a 174.8% increase in trading volume on the Shanghai Gold Exchange to 868.39 billion yuan ($A194.63 billion).
Precious metals consultancy GFMS said global gold production in 2008 fell by 88 tonnes, reflecting lower production in South Africa, Indonesia and Australia, while the only countries to increase production were China and Russia.
GFMS estimated South Africa’s gold production in 2008 dropped by 14%.

South Africa has the world’s largest amount of gold reserves but the country’s gold mining industry has been steadily declining over the past decade.
According to the research report, Gold in South Africa, the nation’s gold production in 2006 accounted for 11.8% of new global mine supply, compared to more than 20% just 10 years earlier.

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