John Samonds for enabling me to obtain a research fund award to purchase a 3D scanner. Yacoub Najjar, Chair of the Civil Engineering Department, for providing shortfall funds to purchase a 3D scanner and access to the Soil Laboratory to perform the required experiments. Janak Tiwari from the Department of Mechanical Engineering in analyzing and interpreting 3D models of soil samples using CREO and SOLIDWORKS software.
I would like to mention my friends Parker Sowers, Jay Rao, and Naim Daghmash for always being there for me through academic and interpersonal challenges these past two years. Suna Devi Joshi and all my family members for providing love and motivation in every day of my life. The shrinkage limit is a parameter of the moisture content of fine-grained soils that is related to the stability of the soil volume.
The conventional method, ASTM Standard D427-04 which uses mercury has been replaced by the wax method, ASTM Standard D4943-02 which uses wax and water or MT-92 which uses spray coating. This modification has certainly minimized the safety concerns of laboratory technicians by avoiding the use of the hazardous substance mercury (Hg), but it is not really an economical and convenient method. The 3D scanning method involves using a calibrated 3D scanner to obtain the 3D model of the soil samples and CREO or SOLIDWORKS software to determine the volume of the 3D model.
The experimental and statistical results show that the soil shrinkage limit values calculated by the Spray Coating Method and the 3D Scanning Method can be thoroughly correlated.
Introduction
Conventional Method: Spray Coating Method
The spray coating method is very similar to the wax method, which requires the determination of the volume of an oven-dried soil sample coated with a waterproofing spray by the water displacement method. The inner diameter and inner height of the shrink can is measured using vernier calipers. The average of the three readings each is used to determine the volumetric capacity of these cans, which is also the initial volume of the wet soil sample.
The selected soil type is mixed with tap water to form a paste with water content preferably above the liquid limit. The mass of the empty can is also recorded, and then the inner surface is covered with a thin layer of petroleum jelly (Vaseline) to prevent adhesion of the soil. The mass of the can with the Vaseline is also recorded, which is neglected if the change is really small.
The wet soil sample is placed in the can and ensures that no air bubbles or voids are created in the wet soil mass. The filled can is measured with a ruler and wiped clean before the mass of the can containing the wet sample is recorded. Then let them air dry first to check if any early cracks are discovered. Two of them are placed in the oven for 3 hours and two are air dried at room temperature for 24 hours.
The samples are sprayed with a waterproofing coating and a mass of dry soil. The waterproof sample is then slowly placed in a beaker filled with tap water, and the volume of water that has flowed into the measuring cylinder is also recorded. This amount of water spilled is equal to the volume of the dry soil sample.
The obtained values for water content, weight and volumes are then used to determine the shrinkage limit of each sample using the equation below. The shrinkage limit obtained for each sample is recorded to compare it with the value obtained from the proposed method (3D scanning method). The shrinkage limits for oven dry versus air dry conditions, for pure bentonite versus the 20% sand mixed bentonite were established to evaluate the theoretically expected and practically experienced results.
Proposed Method: 3D Scanning Method
Experimental Results and Discussions
The software displays the volume in cubic millimeters with high accuracy, up to 1/100 of the value. Parallax error when reading water level values from a calibrated measuring cylinder can be a possible source of error in the conventional method. Table 2 presents the moisture content (%), dry sample volume by water displacement method (ml) as well as 3D scanning method (mm3 and ml) and shrinkage limit (%) for each sample by these two different methods for each sample prepared using pure bentonite clays.
The table also shows the percentage differences in numerical values of SL and volume according to these two different methods. The volumes for the oven-dried samples (can 1 and can 2) are lower than those for the air-dried samples (can 3 and can 4), as expected for both methods. The shrinkage limits obtained by the spray application method and the 3D scanning method are shown in a horizontal bar graph in Figure 2, which makes it possible to understand the similarities between these two methods.
The pattern follows for the volume and SL of several samples of a 20% sand and bentonite mixture, but due to the presence of the sand, the dry oven samples (Can 1 and.) The water displacement method is not useful for determining the volume of such cracked De However, 3D scanner can be used even for such cracked samples, saving time and effort in obtaining the SL and volume of oven-dry samples.
The comparison of the volume and SL in (Table 3) of the air-dry samples (can 3 and can 4) shows the expected trend, as with the bentonite samples. All these data and results support that the proposed 3D scanning method is more reliable, faster and economical in determining the volume of dry soil samples and then the shrinkage limit. The accuracy and efficiency as shown by the experimental results ensure that the 3D scanning method can be used to replace the conventional spray coating method or washing method.
The human errors such as parallax error, misreading and misreporting of the data in the experimental procedure as well as instrumental errors such as weighing and volumetric instruments at the many steps involved in conventional methods can be easily avoided by one-step based 3D scanning method. The accuracy and precision of modeling the 3D scanned object and then obtaining the volume (and other parameters such as surface area, dimensions, etc.) can be adjusted as needed.
Conclusion and Recommendation
List of References
Appendices
Sample Calculations [Bentonite Can 1]
The percent difference relative to the conventional spray application method for volume and shrinkage limit (SL) was calculated using the following equations.
Lab Apparatus and Sample Preparation
Volume Calculation in CREO by PTC
Excel Worksheet for Data Collection and Result Calculations
Shrinkage Limit
