Discrete element model calibration based on in situ measurements

PurposeTransportation of the measurement samples from their original place to the measurement site causes significant changes in their mechanical properties. The possibility of making in situ measurements helps to create more precise discrete element models.Design/methodology/approachThe possibility of using in situ modified vane shear test based measurement for the calibration of discrete element models is demonstrated in this work.FindingsThe advantage of employing the adjusted vane test is that the values of in situ measurements can be used for the calibration.Originality/valueThe procedure we present allows us to perform accurate discrete element calibration using data from on-site measurements that can be performed quickly and easily.

Safety Factor for Drilled Shaft Foundations Subjected to Wind-Induced Torsion

Public transportation agencies commonly use drilled shaft foundations as support of mast arm traffic signs and signal pole structures. These structures and their foundations are subjected to wind-induced torsion. Design provisions can be found in AASHTO specifications for structural supports for highway signs, luminaires and traffic signals; nevertheless, those standards do not provide guidance to estimate the torsional resistance of drilled shaft foundations, or what an appropriate factor of safety (or resistance factor) for design could be. Although load and resistance factors format is desired because AASHTO is moving in that direction, still many Departments of Transportation design requirements are based on factors of safety. In this study, a probabilistic approach is used to recommend a rational procedure to determine factors of safety that consider the uncertainties and the consequences of failure. This procedure can be modified for load and resistance factors design calibration, as well. The skin friction approach was calibrated employing reliability analysis, available statistics, published experimental data, and simulations. However, a lack of field test data has been noticed. Factors of safety for cohesive, cohesionless, and layered soils are recommended. They are presented as a function of the target reliability index, and which in-situ test is performed to obtain the soil strength properties. Three alternatives were considered: standard penetration test, cone penetration test, and vane shear test. The procedure described can be used by practitioners to select appropriate factors of safety based on local conditions when statistical parameters from a particular site investigation are available.

Experimental Verification of Chemical Admixture to Reduce Stiffness of Concrete

In this paper, the phenomenon in which the fluidity drops significantly once the concrete, which is a problem in the construction work, is called “stiffness”, and the hypothesis of the occurrence mechanism was hypothesized based on a microscopic image of cement paste. Then, author developed a chemical admixture (stiffness reducing agent) that suppresses the aggregation of cement particles and verified the effect through various tests. In the verification test, author tried to quantify the stiffness of concrete by a simple test called the vane shear test. Also, through various construction performance tests, author confirmed the possibility of stiffness affecting the construction work.

The Effect of Heat Induction on Shear Strength of Soft Soil in Radial Zone

The main problem in infrastructure development at the soft clay was its bearing capacity therefore it needs to be improved. In this research, the improvement method was carried out by modeling in small scale of preloading and heat induction combination. Location of soft clay sampling was in Takalar, Indonesia. The purpose of this study was to investigate the change of the shear strength of soft soil corresponding with heat induction at the radial zone. The shear strength was obtained by vane shear test and compressive strength from unconfined compressive test (UCT). The heat applied ranging from 100o C, 200o C, 300o C, and 400o C with static preloading load 0.20 kg/cm2. The strengths of the soil in radial zones have been tested at R0, R1, and R2. At lowest temperature 100° at R0 the compressive strength was 0.203 kg/cm2, at highest temperature 400° at R0 the compressive strength 0.467 kg/cm2, there was a significant increasing of compressive strength value with the change of temperature. At the highest temperature 4000 the shear strength from vane shear tests resulting at R0 0.240 kg/cm2, R1 of 0.128 kg/cm2, R2 of 0.077 kg/cm2. At the lowest temperature of 100o C shows R0 at 0.116 kg/cm2, R1 at 0.070 kg/cm2, R3 of 0.046 kg/cm2. The results show a tendency of declining strength value as the soil farther away from center of heat induction. The experimental result from this model produces strength that can be used as a parameter of the foundation model on soft soil.

Characteristics of Palangkaraya fibrous peat

Palangkaraya fibrous peat soil is a soil with high organic content and was formed due to decomposition of plants in submerged areas for long periods. In the tropics, peat has a high fiber content that affects the physical and engineering characteristic and have different behavior with clay. Laboratory and field tests were conducted to determine the physical and engineering characteristic of fibrous peat and to compare it with clay. The results of the tests on fibrous peat show peat soil parameter very different from clays. The unit weight of peat is 1.04 gr/cm3 with specific gravity is 1.4 and water content reach 650%. This physical parameter shows that peat is a very soft soil that is dominated by water in its structure. Organic content of peat reached 97% with a very low ash content of 3%. This behavior indicates that the decomposition of plants causes physical properties of peat that are very different from clays. The bearing capacity of the peat is also very low. The shear strength was about 26.8 kPa (ov = 50 kPa) and was dependent on the fiber distribution in the sample under test. Vane shear test results also show the same thing that is 5-7 kPa. The very different behavior of fibrous peat with clay is the consolidation. Peat has 4 stages of compression wherein secondary compression is the main compression. This behavior is due to the fibrous peat has two pores, that are micropores and macropores. The results of comparisons can serve as a basis for determining appropriate peat soil improvement methods.

STUDI PENINGKATAN KARAKTERISTIK TANAH LEMPUNG DENGAN SERAT TANDAN KOSONG KELAPA SAWIT

Stabilisasi tanah dimaksudkan untuk memperbaiki sifat-sifat tanah asli dengan cara antara lain menambahkan suatu bahan tertentu yang mengakibatkan perubahan sifat-sifat tanah asli. Selama ini penggunanaan serat tandan kosong banyak dihasilkan oleh industri perkebunan kelapa sawit. Serat merupakan jumlah terbesar ketiga setelah CPO dan tandan kosong kelapa sawit, tandan buah segar diperkirakan mengandung 14 - 15%. Serat dapat dimanfaatkan sebagai bahan bakar alternatif energi pembangkit listrik, pembuatan kertas dan sebagai bahan campuran makanan ternak. Tapi sekarang serat juga digunakan untuk material konstruksi. Penelitian ini dilakukan untuk menyelidiki prosentase optimum serat untuk mendapatkan kepadatan maksimum, menganalisis peningkatan nilai CBR tanah setelah penambahan serat, menganalisis peningkatan nilai qu pada pengujian UCT tanah setelah penambahan serat, menganalisis peningkatan nilai su pada pengujian vane shear test tanah setelah penambahan serat. Penelitian dilakukan dengan mencampurkan serat tandan kosong kelapa sawit dengan tanah lempung lunak dengan kadar serat masing-masing 5%, 6%, 7%, dan 8%. Hasil pencampuran diharapkan dapat diketahui nilai bagaimana hubungan dari berbagai variasi prosen penambahan serat tandan kosong kelapa sawit guna mendapatkan tujuan yang diharapkan, selain itu hasil yang diperoleh diharapkan dapat memperbaiki kualitas tanah menjadi lebih baik. Berdasarkan hasil analisis dari penelitian ini, bahwa adanya penambahan serat tandan kosong kelapa sawit di dalam tanah lunak maka dapat memperbaiki kekuatan tanah tersebut sehingga menjadi meningkat dan hasil penelitian ini dapat digunakan sebagai acuan untuk stabilisasi tanah lempung.

KARAKTERISTIK KUAT GESER TANAH GAMBUT AKIBAT PEMAMPATAN

Peat has different characteristics compared to clay. It is physically recognized as soil with organic materials content, great amount of water, high void ratio, and the existence of fibers. However, it technically has high compressibility and low shear strength. To identify how big is the influence of compression behaviour towards the increment of peat`s shear strength, some consolidation and vane shear test need to be performed in order to obtain a proper method to initiate constructions on peat. This research used amorphous peat samples which were taken from Tambang, Kampar district in disturbed condition. They consisted of two variations, i.e.: natural condition, and non-fiber condition. The used equipments were modified consolidometer with diameter of 15 cm and height of 15 cm, and also vane shear instruments. The loads were gradually applied with magnitude of 10 kPa, 20 kPa, 40 kPa, 80 kPa, 160 kPa and 320 kPa, each of them were elevated every ±14 days, and a vane shear test was performed before the load was added. The results showed that the shear strength has been increasing due to the higher compression, as well as the void ratio. In case the void ratio gets smaller, the shear strength has increased. Hence, peat`s bearing capacity will increase along with the higher shear strength.