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ITS » Master Theses » Geoteknik S2
Posted by eko at 09/01/2007 16:48:55  •  10061 Views


STUDI PENGARUH INFILTRASI AIR TERHADAP KESTABILAN LERENG TANAH RESIDUAL LANAU KELEMPUNGAN DARI DAERAH GUNUNG KAWI - MALANG

ASSESMENT TO THE WATER INFILTRATION INDUCE SLOPE STABILITY OF CLAYEY SILT RESIDUAL SOIL FROM GUNUNG KAWI-MALANG

Author :
Muntaha, Moh.  




ABSTRAK

Masalah longsor pada lereng mendapat perhatian yang meningkat akhir-akhir ini. Hujan dengan intensitas yang tinggi dan waktu yang lama merupakan salah satu faktor penyebab terjadinya longsor. Infiltrasi air hujan dalam tanah mengakibatkan perubahan sifat fisik dan mekanik tanah sehingga kekuatan tanah berkurang. Meskipun hujan bukan merupakan satu-satunya faktor penyebab longsor tetapi dengan bertambahnya air didalam tanah memiliki peran yang sangat besar terhadap kestabilan lereng. Tujuan penelitian ini adalah untuk mengetahui pengaruh infiltrasi air hujan terhadap perubahan parameter tanah lanau yang meliputi kadar air derajat kejenuhan angka pori kohesi c dan sudut geser dalam 1092 serta mengukur koefisien permeabilitas tanah jenuh dan tidak jenuh kw pada tanah lanau daerah Gunung Kawi Malang Jawa Timur. Tanah dengan kadar air awal 5157 di kondisikan kadar airnya dengan proses pengeringan dan pembasahan. Kondisi pengeringan dilakukan dengan mengurangi kadar air benda uji menjadi 125 25 375 50 625 75 825 dan 100 dari kadar air asli lapangan sedangkan kondis pembasahan dilakukan dengan cara menambahkan air ke benda uji hingga kadar air benda uji menjadi lihat file PDF Untuk melihat perubahan parameter tanah akibat infiltrasi air tanah yang telah dikondisikan kadar airnya dengan diameter 56 cm dan tinggi 24 cm dimasukkan kedalam kotak geser langsung. Kemudian air setinggi 2 cm di berikan diatas tanah dan dijaga tetap selama waktu 05 jam ljam 15 jam dan 2 jam. Sedangkan untuk percobaan Kolom Infiltrasi tanah dengan diameter 6 cm dan tinggi 10 cm dimasukkan dalam tabung yang sudah diberi sensor. Kemudian diberikan air setinggi 2 cm diatas tanah dan dijaga tetap selama waktu 05 jam ljam 15 jam dan 2 jam. Untuk menghitung koefisien permeabilitas tanah digunakan Rumus Darcy sedangkan untuk mengukur tegangan air pori negatif digunakan kertas filter Whatman. Koefisien permeabilitas tanah jenuh dilakukan dengan falling head test Hasil percobaan meminjukkan selama proses pembasahan dari kondisi inisial ke kondisi jenuh derajat kejenuhan bertambah 2832 tegangan air pori negatif berkurang 9462 kohesi tanah mengalami penurunan 8288 dan sudut geser dalam turun sebesar 4918. Selama proses pengeringan dari kondisi inisial kekondisi pengeringan 100 derajat kejenuhan mengalami penurunan 7104 tegangan air pori negatif bertambah 43935 kohesi tanah naik 15836 dan sudut geser dalam relatif tidak berubah. Hasil percobaan menunjukkan akibat infiltrasi air hujan menyebabkan terjadinya perubahan sifat fisik dan mekanik pada tanah. Meningkatnya kadar air menyebabkan turunnya tegangan air pori negatif tanah dari 30245 kPa pada kadar air 5157 menjadi 1628 kPa pada kadar air 7069 dan parameter kuat geser tanah yaitu kohesi c dari 7787 kPa pada kadar air 5157 menjadi 1333 kPa pada kadar air 7069 sudut geser dalam 1092 dari 5139 pada kadar air 5157 menjadi 2611 pada kadar air 7069. Sedangkan dari percobaan Kolom Infiltrasi didapatkan nilai koefisen permeabilitas tanah kw 1388 x 10-7 mdetik pada kadar air 5157. Dari hasil pengukuran parameter tanah dibuat simulasi numerik untuk melihat angka keamanan pada lereng dengan tinggi 10m 15m dan 20m dengan varisasi kemiringan lereng 11 dan 21. Infiltrasi air kedalam tanah dianalisa secara numerik menggunakan program SEEPW sedangkan faktor keamanan lereng dihitung menggunanakan program SLOPEW. Hasil simulasi menunjukan bahwa lereng dengan tinggi 10 m mempunyai angka keamanan lebih dari 1 lereng dengan tinggi 15 m mempunyai angka keamanan lebih dari 1 untuk kemiringan lereng 11 dan kurang dari 1 untuk kemiringan 21 lereng dengan tinggi 20 m mempunyai angka keamanan kurang dari 1. Dari hasil tersebut bisa disimpulkan bahwa tinggi lereng sudut kemiringan lereng dan lama hujan mempunyai pengaruh yang signifikan terhadap stabilitas lereng.


ABSTRACT

Slope stability problems are receiving more attention in recent years. High intensity of rain is considered to be one of the many factors which trigger slope failures. Water infiltration affects physical and mechanical characteristics change of soil and then causes the decrease of soil strength. The increase of water content plays an important role in the slope stability though rainfall is not the only one factor which causes the slope instability. The objectives of this research were to investigate the effect of rain water infiltration of clayey silt parameter of soil such as water content degree of saturation void ratio cohesion internal friction angle and the hydraulic conductivity. The soil used in this research was sampled from Gunung Kawi-Malang in the East Java-Indonesia. The initial water content was 5157 the undisturbed soil sample was then naturally and gradually air dried up to 12.5 25 37.5 50 62.5 75 82.5 and 100 of the initial water content The wetting process were carried out with the gradual increment water content of 25 wsat - Wi 50 wsat wi 75 wsat - Wi up to 100 wsat - Wi. The dimension of soil specimens were governed by the dimension of the used soil test apparatus. The Direct Shear test was performed on 2.4 cm in height and 5.6 cm in diameter of soil samples. The Infiltration Column tests were carried out on 10 cm in height and 6 cm in diameter of soil sample. The tube was equipped with resistively censors placed in the inner wall at 2 cm of distance. The 0.5 hours 1 hours 1.5 hours and 2 hours of rain water infiltration effects were simulated by applying 2 cm height of water on top of the soil specimens in both soil test apparatus. The height of water were kept constant during the rain infiltration simulation and the remained water was removed before the Direct Shear test The Infiltration Column test were carried out to measure the rate of water infiltration on both un saturated and nearly saturated soil samples. The hydraulic conductivity of soil sample was then calculated using the Darcy formula The soil suction was measured using the no. 42 Whaltman filter paper. The falling head test was used to measured the saturated hydraulic conductivity. The results show that during the wetting process from initial to saturated condition the degree of saturation was increased 28.32 the negative pore pressure was decrease 9462 the cohesion was decrease 8288 and the internal friction angle was decrease 4918. Upon drying from initial to drying condition the degree of saturation decrease 7104 the negative pore pressure increase 43935 the cohesion increase 15836. It can be obviously seen that the water infiltration affect the physical and mechanical characteristics of the soil specimens. The increase of water content affected to the decrease of negative pore water pressure the cohesion and the friction angle From the initial of ws 51.57 -Ui - 30245 kPa to Ihe 100 degree of saturation resulted in the Wf 70.69 -Uf 1628 kPa. It can be obviously seen from the Infiltration Column test that the hydraulic conductivity of soil varied with the initial water content of the soil tested. The decrease of water content affected to the decrease of the hydraulic conductivity of soil From the initial of w 51.57 km 1388 x 107 ms to the 2189 degree of saturation resulted in the wf 8.83 k 4933 x 108 ms. To better understand the effect of the rain water infiltration to the slope stability of soil at the natural water content the numerical analysis was performed using the soil properties measured in the laboratory test. Two slope angles 1H IV and 2H IV were analyzed in combination with three slope heights 10m 15m and 20m. The rain water infiltration was simulated using the SEEPW numerical program. The safety factor was then calculated using the SLOPEW. The results show that for 2 hours duration the 10 m height of slope remained stable the 15 m height af slope remained stable for 1H IV slope angle but unstable for 2H 1V while the 20 m height of slope become unstable for both of the slope angles. From the results above it is thought to be due that the slope heights slope angles and the rainfall duration are the factors most significantly affected the slope stability of the soil tested.



KeywordsTanah lanau; pengeringan dan pembasahan; infiltrasi air; hujan; derajat; parameter tanah; SEEP/W; SLOPE/W; stabilitas lereng.
 
Contributor
  1. Dr. Ir. Ria Asih Aryani Soemitro, M.Eng
Date Create: 09/01/2007
Type: Text
Format: Pdf; 134 pages
Language: Indonesian
Identifier: ITS-Master-3100006025818
Collection ID: 3100006025818
Call Number: 624.151 363 Mun


Source
Theses Geotechnich RTS 624.151 363 Mun s-1, 2005

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