Studi Karakteristik Kuat Geser Tanah Lempung dari Uji Unconfined Compressive Strength dan Uji Triaksial tak Terkonsolidasi tak Terdrainase

Abstract

The resistance force done by soil grains toward the shear strength when it is burdened is called soil sheer strength. The parameter of the soil shear strength is needed to analyze the capacity of soil, the slope stability, and the thrust strength on the soil retaining wall. According to Mohr’s theory (1910), the condition of the collapse of divulging material is caused by the combinations of critical normal strength and shear strength. This research was conducted to know the comparison between the triaxial of unconsolidated undrained/UU test result and using unconfined compression test, to know and to analyze the parameter of the soil shear strength of the soil condition when it is not disturbed by remolded soil and the soil shear strength if it is tested by the unconsolidated undrained and unconfined compression triaxial test, to analyze the result of the laboratory test in the Plaxis program. For unconfined compression test, the sample is brooded in a variation of time: 0 day, 1 day, 5 days, 10 days, 15 days, 20 days, 25 days, and 30 days. The result of the laboratory test is modeled in the Plaxis program so that we can find the stress-strain, the shear strength parameter, the clay sensitivity, the clay thixotropy characteristics, and the correlation between the water content of the clay and its strength. The results of the research showed that the clay was included in the classification of the cohesive clay and had high plasticity. In the traxial UU test, it was found that cu value for undisturbed soil of 0.337 kg/cm2 and the remolded soil of 0.294 kg/cm2 the strength decreased to 12.76%. The unconfined compression test with cu value for undisturbed soil of 0.308 kg/cm2 and the remolded soil of 0.229kg/cm2, the strength decreased to 25,65%. The value of the clay sensitivity was 1.343, whereas the ratio of thixotropy increased along with the age of the brood. The remolded sample would achieve its strength as the original soil when the age of the brood was from one to five days. The modeled sample in the Plaxis program produces deviator strength which was similar to the test in the laboratory. The soft soil model was appropriate to be used as the model in the Plaxis program for the type of the soil at Pulau Sicanang.

Gaya perlawanan yang dilakukan oleh butir-butir tanah terhadap tegangan geser pada saat terbebani disebut kuat geser tanah. Parameter kuat geser tanah diperlukan untuk analisis-analisis kapasitas dukung tanah, stabilitas lereng, dan gaya dorong pada dinding penahan tanah. Menurut teori Mohr (1910) kondisi keruntuhan suatu bahan terjadi oleh akibat adanya kombinasi keadaan kritis dari tegangan normal dan tegangan geser. Penelitian ini dibuat untuk mengetahui perbandingan antara hasil uji triaksial dengan kondisi tak terkonsolidasi-tak terdrainase (Unconsolidated Undrained/UU Test) dan pengujian menggunakan unconfined compression test; Mengetahui dan menganalisis prilaku parameter kuat geser dari tanah kondisi tak terganggu (undisturbed) dengan tanah yang dibentuk kembali (remolded) serta besar kekuatan geser tanah jika diuji dengan triaksial unconsolidated undrained dan unconfined compression test; Menganalisis karakteristik thixotropy serta sensitivitas pada tanah lempung; Dan menganalisis hasil laboratorium dalam program Plaxis. Untuk pengujian kuat tekan bebas (unconfined compression test) sampel diperam dengan variasi waktu yang berbeda-beda, yaitu: 0 hari, 1 hari, 5 hari, 10 hari, 15 hari, 20 hari, 25 hari, dan 30 hari. Hasil dari pengujian laboratorium ini nantinya akan dimodelisasi dalam program Plaxis. Sehingga diperoleh hubungan tegangan-regangan, parameter kuat geser, sensitivitas tanah lempung, karakteristik thixotropy tanah lempung, dan hubungan kadar air lempung dan kekuatannya. Hasil penelitian yang diperoleh, diketahui bahwa tanah lempung tersebut termasuk dalam klasifikasi tanah lempung yang kohesif dan bersifat plastisitas tinggi. Pada pengujian triaksial UU diperoleh nilai cu untuk tanah asli (undisturbed) sebesar 0,337 kg/cm2 dan tanah remoulded sebesar 0,294 kg/cm2, terjadi penurunan kekuatan sebesar 12,76%. Sementara untuk pengujian kuat tekan bebas (unconfined compression test) nilai cu untuk tanah asli (undisturbed) sebesar 0,308 kg/cm2 dan tanah remoulded sebesar 0,229 kg/cm2, terjadi penurunan kekuatan sebesar 25,65%. Nilai sensitivitas tanah lempung diperoleh sebesar 1,343, sedangkan rasio thixotropy akan semakin besar seiring makin pertambahan umur pemeraman. Sampel remoulded akan mencapai kekuatan seperti tanah asli pada saat umur pemeraman diantara 1 – 5 hari. Sampel yang dimodelisasi dalam program Plaxis menghasilkan tegangan deviator yang hampir sama dengan pengujian di laboratorium. Model tanah soft soil paling cocok digunakan sebagai modelisasi pada program Plaxis untuk jenis tanah Pulau Sicanang.