Udeni P. Nawagamuwa

Gas Transport Parameters for Compacted Reddish-Brown Soil in Sri Lankan Landfill Final Cover

Gas exchange through the compacted final cover soil at landfill sites plays a vital role for emission, fate, and transport of toxic landfill gases. This study involved measuring the soil-gas diffusivity (Dp/Do, the ratio of gas diffusion coefficients in soil and free air) and air permeability (ka) for differently compacted soil samples (reddish-brown soil) from the final cover at the Maharagama landfill in Sri Lanka. The samples were prepared by either standard Proctor compaction or hand compaction to dry bulk densities of 1.60–1.94  g cm-3. Existing and modified models for predicting Dp/Do and ka were tested against the measured data. The simple, single-parameter Buckingham model predicted measured Dp/Do values across compaction levels equally well or better than a dry bulk density (DBD) dependent model and a soil-water retention (SWR) dependent model. The measured ka values for differently compacted samples were highly affected by the compaction level and the sample moisture preparation method. Also, fo...

Use of Industrial Byproducts to Improve Unsuitable Soils for Road Construction in Sri Lanka

When an unsuitable soil is come across in areas with limited resources, engineers must add transportation cost to the overall cost if a suitable soil has to be hauled from a long distance. In such instances, improvement of the existing soils with locally available materials would be the most beneficial solution. Most of the rural roads in Sri Lanka are now under a phase lift although with lot of constraints. Road Development Authority is practicing a guideline developed consisting of the grading of soil, Atterberg limits, Proctor density and California Bearing Ratio (CBR) to select a suitable subgrade material. However, in most of the cases, soils are rejected due to low CBR, although the other conditions are satisfactory. This study discusses the improvements of such rejected soils from distinct places of Sri Lanka with quarry dust, lime stone dust, paddy husk ash, fly ash and copper slag. Basic soil tests such as particle size analysis, Atterberg limits, Proctor compaction and CBR tests were conducted on unimproved and improved soils. A considerable increase in the CBR (in the range of 10–20 times) was observed with the addition of industrial byproducts to improve rejected soils. Mixing is proposed with a traditional conveyor belt mechanism. Use of industrial byproducts in the infrastructure development is to be encouraged with the objective in preserving environment by reducing utilization of new resources and excessive dumping of by products to the environment.

Recommending Rainfall Thresholds for Landslides in Sri Lanka

Triggering factors for landslides could vary from heavy rainfalls/glacial activities to earthquakes, volcanisms or even vibrations due to nuclear explosions or heavy vehicle movement. However, in Sri Lanka landslides are mostly triggered due to heavy and prolonged rainfall. During last few decades, landslides have occurred with increasing frequency and intensity, causing extensive damage to lives and properties. Therefore, it becomes a necessity to predict and warn landslide hazards before it actually takes place which is still a mammoth task to achieve. Although several researches were done based on daily rainfall data in Sri Lanka, it has been identified that the extreme rainfalls with shorter durations could trigger more disastrous landslides. Hence, recommending hourly rainfall thresholds for landslides is much important in terms of hazard warning and preparedness. In this research an hourly rainfall trend was proposed in order to predict occurrences of landslides in Sri Lanka considering hourly rainfall data from twelve hours before to any disastrous event. Special attention was paid to data from Badulla District where more than 200 people were believed to be dead due to one major landslide in November 2014. The developed relationships are compared with Caine (1980) and observed to be matching to a considerable accuracy. Obtaining hourly rainfall data at exact location was almost impossible with the available rainfall measurement procedure in Sri Lanka. Much finer conclusions could have been made with more accurate data.

Study on the Effect of Plant Roots for Stability of Slopes

There have been several studies on the properties of plants, which are beneficial to critical slopes in preventing failures. However, the impacts of the tensile properties of the plant roots have to be studied in detail. In this study, three different situations were addressed: completely dry, saturated and unsaturated. Under these three situations, stability of different slopes with different soil conditions was studied. Some roots were tested through the tensile testing machine normally used for yarn testing and some were tested with the traditional tensometer. Variation of root diameter was established by measuring the roots of tea plants available at cut slopes. Literature was found on the variation of tensile strength of tea roots with its diameter. Slopes of the tea estates were modeled considering the number of tea plants available in a particular slope. This was later converted to a percentage cover and values of factor of safety (FOS) were compared by changing different soil properties with the percentage of cover. It was found that the FOS tends to increase with the percentage cover under completely dry, saturated and unsaturated situations. However, it was learnt that the impact of tensile capacity of roots had not been so high under dry and saturated cases for cohesionless soils compared to the same situation under unsaturated condition which had high FOS values due to the plant properties.

Slope Stability Analysis at Bloemendhal Open Dump Site in Sri Lanka

Civil engineering construction in the Colombo city area have commenced on lands previously used for the dumping of waste. Construction on covered dump wastes will cause a lot of problems, such as settlement, slope instability, and shear failure. Therefore similar to soil properties, it is important to study the properties of solid wastes to predict settlement, slope stability and shear strength parameters, though there are additional differences due to some chemical reactions occurring in the solid waste with time.

Compaction Characteristics of Municipal Solid Waste at Open Dump Sites in Sri Lanka

The majority of municipal solid waste (MSW) generated in Sri Lanka is disposed in open dump yards. Compaction of wastes at such open dumps is the main factor that controls short-term density and resulting placement efficiency of wastes in the dumps. Maximizing waste density allows reducing dump yard space requirements. Density influences the stability of dump yards with high shear strengths. Combined moisture density characteristics influences the hydraulics response and compressibility of wastes. Further, lot of civil engineering constructions in Colombo city area has been commenced on the lands previously used for dumping of waste. Construction on already covered dump wastes will give lot of problems such as high settlements, slope instability, shear failure etc. Four dump yard locations such as Bloemandhal, Seeduwa, Negombo and Madampitiya were selected for the study and the moisture-density relationship was studied. Some of these locations are now abandoned and the land being used for construction activities and some are still in the process of dumping. It was observed that the compaction behavior of waste was similar to that of soils with waste, but the shape of the compaction curve has deviated from the standard bell shaped curve established for soils.

Recommending Regional Rainfall Threshold Values for Early Warning of Landslides in the Asian Region

Regional landslide hazard prediction and warning are still difficult targets to be achieved and a hot topic in the research of landslide hazards. It is necessary to investigate the possibility of interpreting landslide events in terms of the rainfall patterns immediately preceding the slide event. This can be further enhanced by taking the lithological conditions in to account. Rainfall threshold values vary from region to region due to differences in exiting soil characteristics and climatological patterns in different areas. This paper addresses the needs mentioned above and it includes the data and methods for recommending threshold values adopted by countries, such as Bhutan, Bangladesh, China, India, Indonesia, Nepal, Pakistan, Philippines, Sri Lanka, Thailand and Vietnam. A new approach is proposed considering normalized cumulative rainfall from 6days beyond a certain landslide till the day of occurrence. Data from several countries such as Sri Lanka, India etc. have shown very promising outputs as per the application of the proposed methodology. However, it is clearly evident that the extreme rainfalls in a shorter duration could trigger disastrous landslides. This is confirmed by the data from countries such as Nepal, Bangladesh, etc. when the rainfall collected 3days preceding the event till the landslide occurrences is considered.