The soft plastic mixed into solid waste landfills exhibits a reinforcing effect similar to that of geotextiles and significantly affects the assessment of slope stability. However, little research has focused on the reinforcing effect of soft plastic. In this study, the tension force generated on soft plastic under effective stress changes caused by gas pressure or pore water pressure was measured using strain gauges. The tension force corresponded with Terzaghi's principle with respect to the increasing or decreasing tendency; however, the relationship between the tension force and effective stress decreased parabolically with decreasing effective stress. In particular, tension force decreased rapidly after the effective stress decreased by half.

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Clarification of shearing property of solid waste material has been required to understand the failure mechanism and to evaluate the static stability of waste ground. Past research showed that the shearing responses of waste material with fibrous materials caused a significant increase in strength and a reduced post-peak strength loss. A modeling approach is proposed in this paper for evaluating the contribution of fibrous materials to the shear strength of waste material. The reinforcement effect of fibrous materials that depends primarily on the angle between shear plane and fibrous materials orientation is defined from tensile strength of waste material. Simulations show how the effectiveness of reinforcement is captured and provide good agreement with experimental data.

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Proper engineering landfills have not been practiced by Sri Lanka. Most of the open dumps in the country are located in the city centers. Due to rapid development and urbanization, these dump sites are abandoned and now they are used for critical construction works. Strength characteristics are very important for general foundation designs, however, due to the heterogeneity, it is very difficult to evaluate those parameters in dump waste sites. Dump waste samples were collected from Bloemendhal dumpsite. Direct shear test and unconsolidated undrained tri axial tests were conducted to obtain the shear strength properties such as cohesion and angle of friction for different moisture contents obtained during Proctor compaction test. Direct shear tests have proven that the angle of internal friction does not vary much with moisture content. However, the experimental results of cohesion of dump wastes have shown that the cohesion of dump waste varies with moisture content and the shape of the cohesion vs moisture content graph is similar to the shape of the Proctor compaction test. These results indicate that the behavior of the dump wastes is similar to silty soil. Further tests were done with the addition of cement to observe the strength gain. Several cement contents were tested and unconfined compression tests were carried out on the wetted (cured) samples with time until 28 days. Samples were tested at certain time intervals and observed the strength gain with time. Age of the solid waste could change the properties of MSW. However, in this study it has to be noted that the age could not be used as an external parameter as the open dumps had been operated without proper records.

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A centrifuge model is designed based on a representative section of China Shenzhen Xiaping Landfill, to simulate its landslide in June 2008, due to the high water level of leachate. The model waste material is introduced in this paper for simulating the real waste material. A water tank was set up inside the model container to control the water level inside the model. Model was tested at centrifuge acceleration of 90g and the result shows that large horizontal deformation and tension cracks appeared on the model slope, although there was no extensive sliding failure observed.

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In-situ direct shear and earth pressure tests were developed for estimating strength of solid waste materials (SWM). Strength properties of solid waste materials were investigated in different sites. Strength parameters of cohesion of frictional angle are obtained from the in-situ direct shear and earth pressure tests. The in-situ earth pressure test was conducted by putting several bars in a line. Strength parameters are evaluated from test results of the in-situ earth pressure test in different embedded length of pile. Cohesion and frictional angle obtained from the in-situ direct shear and earth pressure tests are correlated respectively. The in-situ earth pressure test is very simple method. It is therefore that the strength property of solid waste materials can be estimated as an approximate value.

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In the analysis and design of municipal solid waste (MSW) landfills, there are many uncertainties associated with the properties of MSW during and after MSW placement. For the analysis of time dependent settlement response of MSW, a composite compressibility model that accounts for instantaneous compression under the applied load, time dependent mechanical creep and biological decomposition is used. The objective of the present study is to demonstrate the influence of variability in model input parameters on the prediction of MSW settlement and to study the implication of different processes on settlement with an aim to assess landfill capacities and develop landfill closure plans. For this purpose regression equations based on response surface method (RSM) are developed to represent the complex behaviour of MSW. Probabilistic settlement analysis of MSW with due consideration to spatial and temporal variation of geotechnical properties is also performed. The published data on geotechnical properties of MSW are used to define the spatial variation of such parameters. The results of MSW settlements using reliability analysis framework are compared and discussed.

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In Japan, a significant volume of municipal solid waste incinerator ash (MSWIA), slag and soil are disposed in coastal landfill sites located in Tokyo and Osaka bay. Future reclamation of these final disposal sites is an important goal. Thus, it is relevant to understand the shear strength properties of the waste layers in coastal landfill sites to utilize the land after closure. However, the particle size distribution of the waste ranges from fine-grained to coarse-grained (gravel, glass, etc.) affecting the estimation of the shear strength properties of the waste sample in coastal landfill sites. There is no available research on the effects of oversize particle on the shear strength of waste samples in coastal landfill sites. Therefore, this paper presents the results of larger triaxial test (150 mm x 300 mm) for waste samples. In the large triaxial test, the pore water pressure generated is higher compared to the results obtained for small samples. The smaller values of shear strength for large samples are also related to the crushability of large particle size. Thus, the frictional angle of large specimens is slightly smaller than that of small ones. Moreover, to calculate the stability of coastal landfill sites, if the strength parameters results from large triaxial test are used, the safety factor might decrease due to the lower of friction angle of large triaxial test and it would be more precise compared to the value obtained from a small triaxial test.

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