Civil 220 G1 Laboratory Atterberg Limits (NZS 4402) Jason Wang 708989501 Introduction In this lab, the plasticity limit, liquid limit and natural moisture/water content of soil is evaluated using the Atterberg Limit Tests. These methods are done in accordance to the NZS 4402 Standards with some deviations. These deviations will be discussed later on in the report. The properties of the soil and its relationship with engineering properties will also be discussed. Methods Oven Drying Method - This method follows the NZS 4402.2.1 1. Weigh an empty metallic soil container on digital balance (two d.p.). 2. Place 30 g or more of natural soli into the soil container. 3. Weigh the soil container containing the natural soil. This value is the wet soil mass. 4. Place the soil container with the natural soil into a drying oven for 24 hours. 5. Remove the soil container from the oven and weigh. This value is the dry soil mass. Plastic Limit Method - This method follows the NZS 4402.2.3 1. Roll a ball of soil between palms of hands to dry the soil sample until cracks appear on the surface. 2. Mold the ball of soil into a thread approximately 6mm thick. 3. Roll into 3mm thickness within 5 to 10 movements. 4. If the soil crumbles, put the soil sample into the container. If it does not crumble, knead the soil and re-roll it into 3mm thick threads. 5. Gather a minimum of 15 g of soil in the container. Casagrande Method - This method follows the NZS 4402.2.2 1. Place soil in the cup to form a smooth surface. 2. Using a grooving tool, form a straight groove through the center of the soil pat. 3. Aim for the shoulders of the casagrande cup to be level with soil pat. Otherwise, the method should be restarted. 4. Rotate the handle at 2 rev/s until the closing length is 13 mm. 5. Repeat the procedure to obtain a second result. Deviations from NZS 4402: The NZS 4402 requires that soil samples must move from a wet state to a dry state when undergoing the casagrande method. However, in this lab, the soil samples move from a dry state to a wet state. The NZS 4402 requires that the difference between two results must be below 2 blows. For this lab, due to time limitations, a difference of less than 4 blows is accepted. If the difference is greater than 4 blows, the procedure must be repeated until the requirement is met. Cone Penetrometer method - This method follows the NZS 4402.2.5 1. 2. 3. 4. 5. 6. 7. 8. Fill cup while ensuring no air is trapped in the cup. Swipe off excess soil from the cup to make a flat surface. Let the cone just touch the middle of the soil surface. Make the initial reading. Release the cone and let it sink into the soil for 5 seconds. Make the final reading. Penetration = final reading - initial reading. Refill the cup and repeat the method to obtain a second result. Deviations from NZS 4402: NZS 4402 specifies that the difference between two results must be below 0.5mm. In the lab the difference accepted is below 1mm due to time limitation. If this difference is greater than 1mm then the procedure must be repeated until this requirement is met. Results Liquid Limit: 79.5% Plastic Limit: 37% Plasticity Index: 42.5% Natural Water Content: 52.6% Casagrande classification: MH (Elastic Silt) Liquidity Index = (w - PL)/ Ip = (51.26 - 37)/42.5 = 0.33553 = plastic Discussion Characteristics: The soil is classified as an elastic silt. The soil has a plasticity index of 37 and a liquidity index of 0.33553. The plasticity index is greater than 30 and the liquidity index is greater than 0. The soil is highly plastic, has very high dry strength and is impossible to crush with fingers. Flaws: The soil has a plastic limit above 30 and LL of 79.5%. Silt often occurs in a soil along with sand and clay particles. Clay is unwanted for engineering purposes as they can absorb and release high amounts of water under weathering. Its behaviour is controlled by its interactions with water. Clay is very compressible, has low strength and low hydraulic conductivity. The soil can swell and de-swell due to water which can cause lots of damage to other rocks and soil. Silt can also be weathered easily and transported by water, ice and wind. This can cause the soil to lose strength and allow soil erosion to occur, potentially leading to structure failures. Elastic silt is also highly unstable and cannot be used as a foundation. Deviations from NZS: There were some deviations from the NZS standards, however, these deviations are not significant enough to cause a large difference. It is with confidence that the soil will still display the characteristics mentioned above. However, it is still sensible to consider other potential neighbouring soil groups and their properties such as montmorillonite and allophane. Mitigations: The soil possesses clay content. This can be a potential danger to engineering purposes. It is essential that mitigation is undertaken to prevent this danger from occurring. Some mitigation procedures include avoiding compaction or adding organic materials such as plants. Silt is highly susceptible to surface water erosion. Good surface water management is needed such as proper site drainage, planting organic material and silt control interventions like silt mats and nets. Conclusion The soil sample analysed is an elastic silt that displays high plasticity and dry strength. However, due to its sediment and clay properties, it is highly susceptible to erosion and weathering. Mitigation procedures should be undertaken to prevent possible engineering failures. Figures/Graphs References https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/how-to-improve-clay-soil.htm https://shop-standards-govt-nz.ezproxy.auckland.ac.nz/catalog/4402.2.1%3A1986%28NZS%29/ view https://shop-standards-govt-nz.ezproxy.auckland.ac.nz/catalog/4402.2.2%3A1986%28NZS%29/ view https://shop-standards-govt-nz.ezproxy.auckland.ac.nz/catalog/4402.2.3%3A1986%28NZS%29/ view https://shop-standards-govt-nz.ezproxy.auckland.ac.nz/catalog/4402.2.4%3A1986%28NZS%29/ view https://shop-standards-govt-nz.ezproxy.auckland.ac.nz/catalog/4402.2.5%3A1986%28NZS%29/ view https://frogenvironmental.co.uk/pollution-avoidance-and-mitigation/managing-silt-construction-sit es/
