Analisis Pengaruh Penambahan Abu Sekam Padi dan Kapur Terhadap Daya Dukung Tanah Lempung di Desa Gapura Kecamatan Pujut Kabupaten Lombok Tengah

Abstract

Abstract: High-plasticity inorganic clay (fat clay) is a type of soil characterized by high plasticity and the potential to undergo volume changes due to variations in moisture content. Such conditions require soil improvement through stabilization methods. This study aims to determine the characteristics of the clay soil before stabilization, analyze the effect of rice husk ash and lime addition on soil bearing capacity, and determine the mixture variation that provides the best results. The soil samples were obtained from Barelantan Hamlet, Gapura Village, Pujut District, Central Lombok Regency. The stabilization materials consisted of 20% lime with variations of rice husk ash (RHA) addition of 10%, 20%, and 30% based on the dry weight of the soil. Physical property tests included moisture content (SNI 1965:2019), unit weight (SNI 03-3637:1994), specific gravity (SNI 1964:2008), sieve and hydrometer analysis (SNI 3423:2008), and Atterberg limits (SNI 1967:2008). Mechanical testing included the Standard Proctor compaction test and the California Bearing Ratio (CBR) test (SNI 1744:2012). Based on the physical property test results, the untreated soil had a moisture content of 25.50%, a specific gravity of 2.51, a liquid limit (LL) of 76.48%, a plastic limit (PL) of 29.21%, and a plasticity index (PI) of 47.27%. According to the Unified Soil Classification System (USCS), the soil was classified as CH (high-plasticity clay), while according to the AASHTO classification, it was classified as A-7-6. The addition of 20% lime and rice husk ash (RHA) reduced the plasticity index to 17.24% (10% RHA), 13.70% (20% RHA), and 8.97% (30% RHA), respectively. The compaction test results showed that the optimum moisture content (OMC) decreased from 29.32% to 24.49%, while the maximum dry density (MDD) increased from 1.19 g/cm³ to 1.289 g/cm³. The unsoaked CBR value of the untreated soil, initially 3.80%, increased to 12.76% for the 20% lime + 10% RHA mixture, reached a maximum of 14.45% for the 20% lime + 20% RHA mixture, and then decreased to 11.88% for the 20% lime + 30% RHA mixture. The 20% lime + 20% rice husk ash mixture was identified as the optimum composition for improving the bearing capacity of the road pavement subgrade.

Abstrak: Tanah lempung anorganik dengan plastisitas tinggi (fat clays) merupakan jenis tanah yang memiliki karakteristik plastisitas tinggi dan dapat mengalami perubahan volume akibat perubahan kadar air. Kondisi tersebut memerlukan upaya perbaikan melalui metode stabilisasi tanah. Penelitian ini bertujuan untuk mengetahui karakteristik tanah lempung sebelum dilakukan stabilisasi, menganalisis pengaruh penambahan abu sekam padi dan kapur terhadap daya dukung tanah, serta mengetahui variasi campuran yang memberikan hasil terbaik. Sampel tanah berasal dari Dusun Barelantan, Desa Gapura, Kecamatan Pujut, Kabupaten Lombok Tengah. Bahan stabilisasi yang digunakan adalah kapur sebesar 20% dengan variasi penambahan abu sekam padi sebesar 10%, 20%, dan 30% dari berat kering tanah. Pengujian sifat fisik meliputi kadar air (SNI 1965:2019), berat volume (SNI 03-3637:1994), berat jenis (SNI 1964:2008), analisis saringan dan hidrometer (SNI 3423:2008), serta batas Atterberg (SNI 1967:2008). Pengujian mekanik meliputi pemadatan Standard Proctor dan CBR (SNI 1744:2012). Berdasarkan hasil pengujian sifat fisik, tanah asli memiliki kadar air 25,50%, berat jenis 2,51, batas cair (LL) 76,48%, batas plastis (PL) 29,21%, dan indeks plastisitas (PI) 47,27%. Berdasarkan USCS tanah diklasifikasikan CH (Clay High plasticity), sedangkan AASHTO diklasifikasikan A-7-6. Penambahan kapur 20% dan abu sekam padi (ASP) mampu menurunkan nilai indeks plastisitas berturut-turut menjadi 17,24% (ASP 10%), 13,70% (ASP 20%), dan 8,97% (ASP 30%). Hasil pemadatan menunjukkan OMC menurun dari 29,32% menjadi 24,49%, sedangkan MDD meningkat dari 1,19 g/cm³ menjadi 1,289 g/cm³. Nilai CBR non-rendaman tanah asli sebesar 3,80% meningkat menjadi 12,76% (K20%+ASP10%), mencapai puncak maksimum 14,45% (K20%+ASP20%), dan menurun menjadi 11,88% (K20%+ASP30%). Variasi campuran Kapur 20% + Abu Sekam Padi 20% terbukti sebagai komposisi optimum dalam meningkatkan daya dukung tanah dasar perkerasan jalan.