Perencanaan Fondasi Tiang Bor Abutment Jembatan Kali Kendeng (Perbandingan Metode Meyerhof dan Metode Reese & Wright)

Fondasi merupakan struktur bawah yang berfungsi untuk meneruskan beban yang berasal dari struktur atas, baik beban dalam arah vertikal maupun horizontal ke tanah. Secara umum fondasi digolongkan menjadi dua golongan yaitu fondasi dangkal dan fondasi dalam. Jika suatu struktur dibangun di atas suatu lahan di mana lapisan tanah kerasnya terletak pada elevasi yang cukup dalam, maka tipe fondasi yang sesuai untuk struktur tersebut adalah fondasi dalam. Fondasi tiang bor (bored pile) merupakan salah satu jenis fondasi dalam yang dipasang ke dalam tanah dengan cara mengebor tanah terlebih dahulu, baru kemudian diisi tulangan dan dicor beton. Fondasi tiang ini biasanya dipakai pada tanah yang stabil sehingga memungkinkan untuk membentuk lubang yang stabil dengan mesin bor. Para ahli geoteknik telah merumuskan beberapa metode untuk perencanaan bored pile, diantaranya metode Meyerhof dan metode Reese Wright. Kedua metode tersebut menggunakan prinsip kombinasi end bearing dan friction pile. Pada perencanaan dengan metode Meyerhof menggunakan peramasamaan atau rumus, sedangkan pada metode Reese Wright menggunakan gambar grafik. Penelitian ini bertujuan untuk mengetahui perbandingan kapasitas dukung ultimit tiang tunggal, kapasitas izin kelompok tiang dan jumlah fondasi bored pile yang dibutuhkan pada abutmen Jembatan Kali Kendeng Susukan, Semarang dengan metode Meyerhof dan metode Reese Wright. Data tanah yang digunakan untuk perencanaan bored pile adalah data nilai N-SPT lapisan tanah pada lokasi proyek jembatan. Sebelum melakukan analisis perhitungan kapasitas dukung, dilakukan perhitungan pembebanan, yaitu beban hidup, beban mati, dan beban kendaraan. Dari hasil perhitungan diperoleh bahwa beban aksial total yang harus ditahan oleh fondasi adalah sebesar 49881,266 kN. Kapasitas dukung ultimit tiang tunggal dengan metode Reese Wright diperoleh sebesar 5842,130 kN, dan dengan metode Meyerhof sebesar 4857,130 kN. Kapasitas izin kelompok tiang dengan metode Reese Wright sebesar 58421,300 kN dan Meyerhof sebesar 58285,560 kN, di mana keduanya sedikit lebih besar dari beban aksial yang harus ditahan, maka hasil hitungan dari kedua metode tersebut memenuhi untuk menahan beban. Dengan menggunakan SF 2,5 jumlah tiang bored pile yang dibutuhkan dengan metode Reese Wright diperoleh sebanyak 10 tiang, dan dengan metode Meyerhof diperoleh sebanyak 12 tiang.

Shaking Table Tests and Numerical Analysis on the Seismic Response of Karst-Crossing Socketed Piles in Dry Sandy Soil Foundation

The foundation piles in karst areas have different mechanical properties from those in other areas. Targeting a critical highway bridge in a karst area, this paper designs two kinds of foundation pile models: friction pile, and KCSP, based on theories on dynamic tests. Then, shaking table tests were carried out to ascertain the features of pile strain distribution of KCSP under earthquakes. During the tests, a large laminar suspended shear box was adopted to mimic the boundary effect of soil. In addition, numerical simulations were conducted to disclose the effects of karst cave on pile strain. The test results indicate that: the peak strain of KCSP increased with the peak acceleration; For both KCSP and friction pile, the peak strain decreased first and then increased along the depth; The presence of karst cave can adversely affect the seismic response of foundation pile; The taller the karst cave, the larger the peak strain of the pile; the peak strain of KCSP was larger at the two ends, and smaller in the middle. The numerical analysis shows that: the peak strain of foundation pile in karst cave increased significantly with cave height; The peak strain of the pile passing through multiple caves was similar to that of the pile passing through only one cave, under the same cave height; But the multi-cave scenario differed from the single-cave scenario in peak strain distribution. The research results provide new insights into the seismic design of pile foundation of bridges in karst areas.

Study on Buckling Behavior of Tapered Friction Piles in Soft Soils with Linear Shaft Friction

The buckling instability of long slender piles in soft soils is a key consideration in geoengineering design. By considering both the linear shaft friction and linear lateral stiffness of the soft soil, the buckling behaviors of a tapered friction pile embedded in heterogeneous soil are extensively studied. This study establishes and validates an analytical model to formulate the equilibrium equations and boundary conditions and then numerically solves the boundary value problem to obtain the critical buckling load and buckling shape by using software Matlab. The effects of boundary conditions, tapered ratio, stiffness ratio, friction ratio, lateral stiffness, and shaft friction on the buckling behavior of the friction pile are extensively explored. This study demonstrates that the buckling load decreases with the increase of friction ratio of the linear shaft friction. There exists an optimal tapered ratio corresponding to the maximum dimensionless buckling load in the tapered friction pile with linear shaft friction. The result means that the linear shaft friction should be considered in designing the tapered friction piles in heterogeneous soils. The results also have potential applications in the fields of growing of tree roots in soils, moving of slender rods in viscous fluids, penetrating of fine rods in soft elastomers, etc.

FRICTION PILE BEARING CAPACITY BASED ON THE PARABOLIC DISTRIBUTION OF SKIN FRICTION

The article describes the approach to evaluation of a friction pile bearing capacity based on the parabolic distribution of a skin friction in multi-layer soil bases. The design equationsare obtained for evaluated the ultimate load on an axial loaded pile in multi-layer soil using the new design scheme. The advantage of the proposed approach is to obtain some experimental parameters that take into account the actual interaction of the pile and soil on the construction site. Negative friction forces (from the reaction force under the pile end) negatively affect the pile bearing capacity. The numerical example is given for a friction pile in the soil base with two layers. The proposed equation also allows calculating various parameters: the soil stress under the piletoe, the pile effective length, relative deformations along the pile, etc.

FRICTION PILE RELIABILITY ANALYSIS WITH RESPECT TO THE FOUNDATION SOIL BEARING CAPACITY

Introduction. Friction pile reliability under the action of the central compressing force according to the Set of Rules 24.13330.2011 is calculated from the first group of the limit states — from the bearing capacity (using the pile material strength criteria and the foundation soil bearing capacity criterion) and from the second group of the limit states — from the pile load-deformation behaviour. Materials and methods. A method of calculating the friction pile reliability from the foundation soil bearing capacity is considered. Reliability appears as a quantitative measure of safety of a single pile operation. The foundation soil bearing capacity is accepted as a criterion for the pile operating capacity. The pile reliability analysis is based on the statistical information obtained during the preliminary pile testing with measuring the friction on the surface of the pile placed in the soil layers and the soil stress under the pile foot. The testing methods for obtaining the statistical information were well-known and used earlier to generate the lists of f-values and R-values in the Set of Rules 24.13330.2011. Each random parameter is measured at least three times. Results. The theory of analysis of the preliminary pile reliability in accordance with GOST 27751-2014 “Reliability of building structures and foundations” has been built on this statistical information. Reliability as the calculation result is represented by interval notation. The mathematical model of the limit state of the pile from the foundation soil bearing capacity has been borrowed from the Set of Rules. The connection (formula) between the length of the pile and the value of its reliability as a safety measure for its operation in the foundation soil has been established. Evaluation of the friction pile reliability corresponding to the characteristic value is carried out by calculation (trail-and-error method) from the mechanical properties of the soil and the load on the pile with the indication of the value of the length of the pile or the sum of the soil layers, each of the values in this case shall be not more than 2 m. The reliability analysis is described in the case studies set out in the article. Conclusions. Pile reliability analysis is based on the actual information about the pile operation in the foundation soil according to the current regulations of the Russian Federation, so the proposed method of the friction pile reliability analysis can be transferred into practice. It can also be used in the reliability calculation for other load-bearing elements, in the regulatory literature, and in the academic work of construction universities.

FRICTION PILE RELIABILITY ANALYSIS WITH RESPECT TO THE FOUNDATION SOIL BEARING CAPACITY

Introduction. Friction pile reliability under the action of the central compressing force according to the Set of Rules 24.13330.2011 is calculated from the first group of the limit states — from the bearing capacity (using the pile material strength criteria and the foundation soil bearing capacity criterion) and from the second group of the limit states — from the pile load-deformation behaviour. Materials and methods. A method of calculating the friction pile reliability from the foundation soil bearing capacity is considered. Reliability appears as a quantitative measure of safety of a single pile operation. The foundation soil bearing capacity is accepted as a criterion for the pile operating capacity. The pile reliability analysis is based on the statistical information obtained during the preliminary pile testing with measuring the friction on the surface of the pile placed in the soil layers and the soil stress under the pile foot. The testing methods for obtaining the statistical information were well-known and used earlier to generate the lists of f-values and R-values in the Set of Rules 24.13330.2011. Each random parameter is measured at least three times. Results. The theory of analysis of the preliminary pile reliability in accordance with GOST 27751-2014 “Reliability of building structures and foundations” has been built on this statistical information. Reliability as the calculation result is represented by interval notation. The mathematical model of the limit state of the pile from the foundation soil bearing capacity has been borrowed from the Set of Rules. The connection (formula) between the length of the pile and the value of its reliability as a safety measure for its operation in the foundation soil has been established. Evaluation of the friction pile reliability corresponding to the characteristic value is carried out by calculation (trail-and-error method) from the mechanical properties of the soil and the load on the pile with the indication of the value of the length of the pile or the sum of the soil layers, each of the values in this case shall be not more than 2 m. The reliability analysis is described in the case studies set out in the article. Conclusions. Pile reliability analysis is based on the actual information about the pile operation in the foundation soil according to the current regulations of the Russian Federation, so the proposed method of the friction pile reliability analysis can be transferred into practice. It can also be used in the reliability calculation for other load-bearing elements, in the regulatory literature, and in the academic work of construction universities.