An experimental study is carried out to evaluate the performance of Lime mortar- Well graded Soil (Lime-WS) columns for the improvement of soft soils. Tests are conducted on a column of 100 mm diameter and 600 mm length surrounded by soft soil in different area ratios. Experiments are performed either with the entire area loading to evaluate the load - settlement behavior of treated grounds and only a column area loading to find the limiting axial stress of the column. A series of tests are carried out in soaking condition to investigate the influence of moisture content on the load - settlement behavior of specimens. In order to compare the behavior of Lime-WS columns with Conventional Stone (CS) columns as well as Geogrid Encased Stone (GES) columns, the behavior of these columns have been also considered in the present study. Remarkable improvement in the behavior of soft soil is observed due to the installation of Lime-WS columns and the performance of these columns is significantly enhanced by increasing the area ratio. The results show that CS columns are not suitable as a soil improvement technique for extremely soft soils and should be enhanced by encasing the column or replaced by rigid stone columns.
stone column, soft clay, lime, load intensity, limiting axial stress, settlement
Department of Civil Engineering, Kerman University, 22 Bahman Blvd, Kerman, Iran.
One of the most advanced classes of techniques for ground response analysis is based on the use of Transfer Functions. They represent the ratio of Fourier spectrum of amplitude motion at the free surface to the corresponding spectrum of the bedrock motion and they are applied in frequency domain usually by FFT method. However, Fourier spectrum only shows the dominant frequency in each time step and is unable to represent all frequency contents in every time step and this drawback leads to inaccurate results. In this research, this process is optimized by decomposing the input motion into different frequency sub-bands using Wavelet Multi-level Decomposition. Each component is then processed with transfer Function relating to the corresponding component frequency. Taking inverse FFT from all components, the ground motion can be recovered by summing up the results. The nonlinear behavior is approximated using an iterative procedure with nonlinear soil properties. The results of this procedure show better accuracy with respect to field observations than does the Conventional method. The proposed method can also be applied to other engineering disciplines with similar procedure.
ground response analysis; transfer functions; wavelet analysis; multi-level decomposition
(1) Amir Bazrafshan Moghaddam:
Department of Civil Engineering, Shahrood University, Shahrood, Semnan, 36199, Iran;
(2) Mohammad H. Bagheripour:
Faculty of Engineering, Shahid Bahonar University of Kerman, Kerman, 76169, Iran.
In the past decade, different types of underreamed ground anchors have been developed for substructures requiring uplift resistance. This article introduces a new type of umbrella-shaped anchor. The uplift behavior of this ground anchor in clay is studied through a series of laboratory and field uplift tests. The test results show that the umbrella-shaped anchor has higher uplift capacity than conventional anchors. The failure mode of the umbrella-shaped anchor in a large embedment depth can be characterized by an arc failure surface and the dimension of the plastic zone depends on the anchor diameter. The anchor diameter and embedment depth have significant influence on the uplift behavior. A finite element model is established to simulate the pullout of the ground anchor. A parametric study using this model is conducted to study the effects of the elastic modulus, cohesion, and friction angle of soils on the load-displacement relationship of the ground anchor. It is found that the larger the elastic modulus and the shear strength parameters, the higher the uplift capacity of the ground anchor. It is suggested that in engineering design, the soil with stiffer modulus and higher shear strength should be selected as the bearing stratum of this type of anchor.
(1) Hong-Hu Zhu:
School of Earth Sciences and Engineering, Nanjing University, Nanjing, China;
(2) Guo-Xiong Mei, Min Xu, Yi Liu:
College of Transportation Science and Engineering, Nanjing Tech University, Nanjing, China;
(3) Jian-Hua Yin:
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China.
The expansivity of clayey soils is a complicated phenomenon which may affect the stability of geotechnical structures and geo-environmental projects. In all common factors for the monitoring of soil expansion, less attention is given to anion type of pore space solutions. Therefore, this paper is concerned with the impact of various concentrations of different inorganic salts including NaCl, Na2SO4, and Na2CO3 on the macro and microstructure behavior of the expandable smectite clay. Comparison of the responses of the smectite/NaCl and smectite/Na2SO4 mixtures indicates that the effect of anion valance on the soil engineering properties is not very pronounced, regardless of the electrolyte concentration. However, at presence of carbonate as potential determining ions (PDIs) the swelling power increases up to 1.5 times compared to sulfate or chloride ions. The samples with Na2CO3 are also more deformable and show lower osmotic compressibility than the other mixtures. This demonstrates that the barrier performance of smectite greatly decreases in case of anions with the non-specific adsorption (e.g., Cl- and SO42-) as the salinity of solution increases. Based on the results of the X-ray diffraction and sedimentation tests, the high soil volumetric changes upon exposure to carbonate is attributed to an increase in the repulsive forces between smectite basic unit layers due to the PDI effect of CO32- and increasing the pH level which enhance the buffering capacity of smectite. The study concluded that the nature of anion through its influence on the re-arrangement of soil microstructure and osmotic phenomena governs the hydro-mechanical parameters of expansive clays. It seems not coinciding with the double layer theory of the Gouy-Chapman double layer model.
Due to the sea-crossing bridge span is generally large and main pier pile foundations are located in deep water and carry large vertical load, sea-crossing bridge main pier pile foundations bearing mechanism and load deformation characteristics are still vague. Authors studied the vertical bearing properties of sea-crossing bridge main pier pile foundations through pilot load tests. Large tonnage load test of Qingdao Bay Bridge main pier pile program is designed by using per-stressed technique to optimize the design of anchor pile reaction beam system. Test results show that the design is feasible and effective. This method can directly test bearing capacity of main pier pile foundations, and analysis bearing behaviors from test results of sensors which embedded in the pile. Through test study the vertical bearing properties of main pier pile foundation and compared with the generally short pile, author summarized the main pier pile foundations vertical bearing capacity and the main problem of design and construction which need to pay attention, and provide a reliable basis and experience for sea-crossing bridge main pier pile foundations design and construction.
sea-crossing bridge; main pier pile; vertical bearing capacity; large tonnage load test
(1) Xuefeng Zhang, Qingning Li:
Department of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China;
(2) Xuefeng Zhang, Ye Ma, Xiaojiang Zhang:
Bridge Research Center, Research Institute of Highway Ministry of Transport, Beijing 100088, China;
(3) Shizhao Yang:
Structural Design Research Centre, Central-South Architectural Design Institute Co., Ltd., Wuhan 430071, China.
An elastoplastic model for structured clays, which is formulated based on the fact that the difference in mechanical behavior of structured and reconstituted clays is caused by the change of fabric in the post-yield deformation range, is present in this paper. This model is developed from an elastoplastic model for overconsolidated reconstituted clays, by considering that the variation in the yield surface of structured clays is similar to that of overconsolidated reconstituted clays. However, in order to describe the mechanical behavior of structured clays with precision, the model takes the bonding and parabolic strength envelope into consideration. Compared with the Cam-clay model, only two new parameters are required in the model for structured clays, which can be determined from isotropic compression and triaxial shear tests at different confining pressures. The comparison of model predictions and results of drained and undrained triaxial shear tests on four different marine clays shows that the model can capture reasonable well the strength and deformation characteristics of structured clays, including negative and positive dilatancy, strain-hardening and softening during shearing.
structured clay; reconstituted clay; bonding; fabric; elastoplastic model
(1) Bo Chen:
College of Civil Engineering and Architecture, Quzhou University, Quzhou, 324000, China;
(2) Bo Chen, Qiang Xu, De'an Sun:
State Key Laboratory of Geohazard Prevention and Geoenvironmental Protection, Chengdu University of Technology, Chengdu, 610059, China;
(3) De'an Sun:
Department of Civil Engineering, Shanghai University, Shanghai, 200072, China.