The shear strength parameters of the soil is the key engineering property required for the design of geotechnical structures and stability analysis. The shear strength of an unsaturated soil is controlled by matric suction. This research examined the effect of matric suction on the shear strength behavior of sandy clay using a series of experimental tests in the laboratory. The contact filter paper method was used to measure matric suction and the SoilVision knowledge-based system was used to give an approximation of the entire soil water characteristic curve (SWCC). The shear strength of the unsaturated sandy clay was examined using a series of unconsolidated undrained (UU) triaxial tests to identify the relationship between shear strength, cohesion, internal friction angle, and matric suction. The result shows that the shear strength of the soil increases as matric suction increases. It was found that when the matric suction is smaller than air entry value (AEV), the shear strength of the soil increases as matric suction increases and the increment is linear because the soil is in saturated conditions. At a certain matric suction value (on soil samples occurred at 40-600 kPa matric suction values), there is a significant increase in the shear strength of soil associated with the inter-particle force produced due to negative pore water pressure. Furthermore, at a high matric suction, the relationship between shear strength and matric suction tend to be stable as in a low water content, the matric suction is not transmitted effectively to the contact point of soil particles.

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Pile capacity is one of the controlling factors in the foundation design. In this study, compression and tension tests were carried out on model piles driven in sandy clay in a test box. The diameter of concrete single-pile models was 16 mm, with ratios of 6, 10, 15 and 20 for pile length (L) to diameter (d). The diameter and length of concrete pile group models were 10 mm and 200 mm, respectively, with four different configuration groups, i.e., single pile, two piles (2×1), three piles (triangle), and four piles (2´2). The sandy clay was prepared in three different water contents of 17.40%, 23.44%, and 27.86%. The capacities of the single piles and pile groups subjected to uplift load were smaller than those under compressive load. Increasing the pile length to the ratio of diameter (L/d) and matric suction resulted in increased capacity of single piles subject to uplifting and compressive loads. The pile groups' capacity depended on both the matric suction and the pile number in a group. The pile groups' compressive capacity in a condition of unsaturated soil (with the matric suction of soil of 73.67 kPa) increased by 294.96%-346.39% when compared to those in saturated soil conditions (with the matric suction of soil of 2.727 kPa).

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Jalan Raya Pusuk merupakan  salah satu ruas jalan di Kecamatan Pemenang Kabupaten Lombok Utara dengan topografi yang sedikit curam, sehingga memungkinkan akan terjadinya longsor ketika hujan deras melanda. Rembesan dan aktivitas geologi adalah faktor lain yang menyebabkan timbulnya longsor. Pada penelitian ini, penyelidikan dikhususkan untuk menganalisa hasil perhitungan pada metode Fellenius dan Bishop di Jalan Raya Pemenang yang bertujuan untuk mengetahui faktor keamanan kestabilan lereng dengan menggunakan metode Fellenius dan Bishop. Data yang digunakan sebagai acuan untuk analisa perhitungan metode Fellenius dan Bishop adalah data sekunder yang terdiri dari data sifat fisik dan mekanik tanah yaitu: nilai kohesi (c), sudut geser dalam tanah (Ø), berat isi tanah (γ), tinggi lereng (m), dan sudut kemiringan lereng (α). Proses analisis perhitungan metode Fellenius dan Bishop dilakukan menggunakan tabel perhitungan manual. Berdasarkan hasil analisis dan perhitungan factor keamanan lereng pada jalan raya Pusuk, Kecamatan Pemenang, diperoleh bahwa faktor keamanan dengan metode Bishop  lebih besar di bandingkan dengan metode Fellenius. Ditemukan bahwa faktor yang mempengaruhi kestabilan lereng adalah kemiringan lereng (α), kohesi (c) dan nilai sudut gesek dalam tanah (Ø).