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PENYELESAIAN 3.20

Adhi Muhtadi, ST, SE,MSi. PENYELESAIAN 3.20. Soal:. Cofferdam menahan air setinggi 2 m di seb hulu Lebar cofferdam 3,5 m Kedalaman turap = 2,5 m Tebal lap lolos air = 4,5 m Koefisien permeabilitas (k) = 2.10 -5 m/det γ sat = 21 kN/m3…..lihat hal 6….(1.15)

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PENYELESAIAN 3.20

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  1. Adhi Muhtadi, ST, SE,MSi. PENYELESAIAN 3.20

  2. Soal: • Cofferdam menahan air setinggi 2 m di seb hulu • Lebar cofferdam 3,5 m • Kedalaman turap = 2,5 m • Tebal lap lolos air = 4,5 m • Koefisien permeabilitas (k) = 2.10-5 m/det • γ sat = 21 kN/m3…..lihat hal 6….(1.15) • γ' = 10,19 kN/m3….lihat hal 7 …(1.17)

  3. Ditanya: • Gbr jaring arus • Debit rembesan/meter panjang • Faktor aman thd piping (Harza) • Faktor aman thd piping (Terzaghi) • Faktor aman thd piping pd titik R (0,5 m dari dasar sungai & pd jarak 4 m dr turap hilir)

  4. a) gambar jaring arus pd gbr c3.11…hal b) Nf = garis aliran = 3 Nd = garis ekipotensial = 11 h = 2m (seb hulu) k = 2.10-5 m/det debit rembesan = q = k.h.(Nf/Nd)….3.86 h:205 = 2.10-5 . 2 . (3/11) = 1,09. 10-5 m/det per meter panjang

  5. c) Faktor aman thd piping (Harza): Penurunan potensial pd tiap elemen jaring arus: Δh = h/Nd = 2/11 = 0,182 Panjang garis aliran PQ: LPQ = 0,8 m (menurut skala) ie = Δh/LPQ = 0,182/0,8 =0,228 ic = γ'/γw = 10,19/9,81 = 1,04 Faktor aman terhadap piping: SF = ic/ie = 1,04/0,228 = 4,56 > 3 (aman)

  6. d) Faktor aman thd bhy piping (Terzaghi) hA = 3 x h = 3 x 2/11 = 3 x 0,182 = 0,546 m hB= 2,5 x 2/11 = 0,45 m hC = 2,2 x 2/11 = 0,40 m d = 2,5 m Tinggi energi hidrolik rata2: ha = 1/2 . {(0,546 + 0,4) / 2 + 0,45} = 0,46 m Faktor aman : SF = d. γ' / (ha . γw) = (2,5 x 10,19)/(0,46 x 9,81) = 5,56 > 4 (aman)

  7. e) Titik R terletakpadakedalaman 0,5 m Panjanggarisaliran RS: LRS = 0,6 m (panjanggrsaliranbelumtentusamadengankedalamannya) Selisihtinggienergiantara R dan S : ΔhRS= 0,2 . 0,182 = 0,036 m Gradienhidrolik pd grsaliran RS: iRS=ΔhRS / LRS = 0,036 / 0,6 = 0,06 SF = ic / iRS = 1,04/0,06 = 17,3 > 4,56 (hitungansoal b)

  8. Terlihat bahwa faktor aman thd bhy piping, jika letak tanahnya menjauhi tepi hilir struktur, nilainya akan semakin besar (krn gradien hidrolik keluar semakin mengecil) SELESAI & TERIMA KASIH

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