Category: Technologies
Soils and Equipment

Soil density tests allow determining whether needed soil compaction is achieved. There are two types of soil density testing: field testing and lab testing. The tests that indicate the optimum moisture content is carried out in the laboratories. Proctor test, or modified Proctor test is one of the most common lab tests. This test measures the max soil density needed for a particular job site. At first, the maximum achievable density is determined. This figure is further used as a reference. Afterward, the effect the moisture has on the soil density is identified. The soil reference value is marked as density percentage. In order to design the compaction specifications, the values are defined prior to any compaction.

As stated in the Soil Compaction Handbook (2011) developed by Multiquip Inc., field tests are used to define on the spot whether the compaction densities were reached or not. It is crucial to learn and be able to control the soil density during compaction. There are several field density testing methods, among which there are Sand Cone, Balloon Densometer, Shelby Tube, and Nuclear Gauge. They all have both advantages and disadvantages. For the field density testing methods in general, and Sand Cone method in particular, the following instruments are used: sand density cone, jar, field density plate used for sand cone, density sand, in-place density accessory kit, and voluvessel. The main instruments used for the lab density testing methods in general, and Proctor test in particular, include mold, compaction hammer, and sample ejector.

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As stated in the manual developed by the Missouri Department of Transportation (2009), AASHTO T-99 and T-180 determine the maximum that is to be expected for a particular type of soil using average compacting efforts. AASHTO T-99 is a standard method while AASHTO T-180 is a modified one. The differences between the two methods are as follows: freefall and mass of the rammer, which is used to compact the soil; soil and aggregate mixture in the mold; the number of layers placed when filling the mold. Soil cannot be compacted in the field beyond 100% of lab max dry density value as lab max value is not representative of the field conditions.

The AASHTO soil classification system was designed and mostly applied for the roads and highways construction. Its main characteristic is the usage of the grain-size distribution and Atterberg Limits to classify the soils. The AASHTO soil classification system is designed in symbols and group numbers. Consequently, referring to soil particles that are smaller than 3 inches, AASHTO soil classification system provides two main groups: granular materials or coarse-grained materials (35% or less of which pass through the #200 sieve) and silts and clays or fine-grained soils (more than 35% of which pass through the #200 sieve). Therefore, A1 and A2 are the further sub-classification for granular soils, and A4 and A6 are sub-classifications for silts and clays. This classification is applied when exact engineering property information is needed.

The standard penetration test is an in-field dynamic penetration test applied for providing information on the soil geotechnical properties. British Standard, ASTM, and Australian standard describe the test procedure. A thick-walled tube (50 mm – outside diameter, 35 mm – inside diameter, 650 mm – length) is used for the test. The sample tube goes 150 mm into the ground forming a 760 mm distance borehole. A number of blows penetrate the tube further. Standard penetration resistance is the term for the sum of the number of the blows needed for the second and third six inches of penetration. The number of blows provides information about the ground density; it is applied in various geotechnical formulae.

The standard penetration test aims mainly at indicating the granular deposits relative density, for example, gravels and sands. There are two main points that explain the main reason for the test to be so widespread: simplicity and low cost. The parameters of soil strength may be approximate. However, they can provide help in ground conditions where it may be impossible to get borehole samples of needed quality, for example, sands, clay, as well as silts containing sand or weak rock or gravel.

Soil type defines whether the standard penetration test results are useful or not. Fine-grained sands provide the most useful results of the SPT. Coarser and silty sands give rather useful and reasonable results while clays and gravelly soils often show inaccurate results. The standard penetration test also provides results for determining the susceptibility of a sand layer to earthquake liquefaction.

Bulldozers were popularized in the 1920s and had been widely used ever since at every construction site. Bulldozer is applied in construction, farming, and waste management, for example. The machine design consists of many engine, structural, and hydraulic assemblies. The core body of a bulldozer comprises mainframe and undercarriage. The cab has numerous rubber, plastic, and glass components that improve the machine's ergonomic state. Among other important components, there are power train, blade, and a number of other system components, which are made of high carbon steel.

There are two distinct features that characterize a bulldozer: long vertical blade situated in front of the bulldozed and rotating twin tracks, the main function of which is the facilitation of the machine movement. Rough terrain, as well as steep slopes, is of any problem for the bulldozer as it generates from 50-700 horsepower.

A vibrator roller is a compactor that has a drum used to compact soil or other materials. The vibrator roller applies the combined static and dynamic forces in order to augment the load-bearing capacity of the surface. The roller may comprise one or more drums that either may or may not be powered for propulsion. Rubber tires may be used in addition to the drums. Rotating the off-center weights produces the centrifugal force that, in its turn, enables the cyclic movement of the drum. There are many types of vibratory rollers. They can be towed or self-propelled, articulated or rigid frame, controlled by a riding or walking operator, remotely or manually operated.

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A sheepsfoot roller has proved to be the most effective equipment for clays and silty clays. Sheepsfoot rollers are also used in road and rail projects. The machine comprises a steel drum or more than one steel drum, to which projecting legs are attached. The projecting legs apply pressure about 14 kg/cm2 and more. The roller moves on the soil while the foot penetrates into it and stirs up the pressure. When the foot is vertical, the pressure is maximal. The rollers movement causes the foot to start receding and, thus, the pressure reduces. The compaction begins from the bottom.

There is a whole bunch of sheepsfoot compactor designs. However, they all have pegs or pads along with the drum or roller surface. The pads are uniform in length so that they contact the substance uniformly. Although the sheepsfoot compactor does not make the surface perfectly smooth, it compacts rather evenly.

Karl von Terzaghi was a civil engineer and geologist from Austria. He is known as the Father of soil mechanics. Terzaghi's most productive period was during his work at the Royal Ottoman College of Engineering in Istanbul. There, the scientist equipped his laboratory and began the experiments. In 1919, he published the analysis and measurements of the force on retaining walls. Terzaghi's work quickly became a milestone of scientific views on the behavior of the soil. His further studies on the permeability of soils to water earned him a place at the Massachusetts Institute of Technology. Terzaghi stated that it was rather difficult to distinguish between the soil mechanics and foundation of engineering, as where the latter started the former ended.

Terzaghi's main achievement was his establishment of new science, to which modern scientists relate the mathematical theory of consolidation, the deformation conditions that control the earth pressure, and numeral value identification for pertinent physical properties of earth materials.

Heavy construction manager usually supervises different public works projects like sewer lines relocation and building of the bypasses. He/she takes part in building sewers, roads, bridges, highways, tunnels, and other projects. A heavy construction manager also hires the construction crew and gives directions to the crewmembers. Moreover, he/she has to deal with the pre-construction process, which includes budget designing and site surveys, among many other issues.

However, to typical earthworks, one relates railway beds, dams, roads, canals, causeways, and levees. Among other common earthworks, there is land grading, which is used to reconfigure the site's topography or slopes stabilization. In order to perform the above tasks, a heavy construction manager should show a good understanding of the earthwork, especially when the earthwork construction is enhanced by the development of some machines and tools, such as Fresno scraper, grader, loader, backhoe, production trucks, bulldozer, and dragline excavator. The quality of projects performed depends on the knowledge of the heavy construction manager, especially, when the heavy construction project requires building massive structures and the movement of large quantities of earth, for example, roadways building of transit systems, airfields, bridges, dams, major highways, and anything else that requires major excavations. Therefore, the heavy construction area requires the manager to be familiar with the heavy construction methods and equipment.

The deep mixing method concerns soils stabilization at large depth. This on-site technology uses a dry or wet binder that injects into the ground by rotary or mechanical mixing tool. The binder then blends with soft soils such as pear, clay, or organic soils. There are a number of patterns produced depending on the application, such as a single pattern, panel pattern, block pattern, and stabilized grid pattern. The deep mixing method aims at producing stabilized soil mass that would further produce stiffly stabilized soil mass such as rigid pile, which afterward will be able to carry out the design load. The increased stiffness of stabilized soil should not hamper the load distribution between natural and stabilized soils. This particular design load is to be managed by both stabilized soil mass and natural soil.

The application of deep mixing method falls into two main categories: non-structural purposes (for example, containment of contaminants, ground cutoff wall) and structural purposes (tunnel and retaining wall, deep and shallow foundation). The deep mixing method is used in foundation engineering, especially in heavy machinery, storage tanks, rail systems, highway embankment, and dome silo for deep and shallow foundations. The deep mixing method is also used in hydraulic structures controlling flood, piping, and seepage through the cut-off wall systems. The deep mixing method is also applied to support construction to both excavations and underground constructions (trenches for railway tracks, braced excavation, and cut tunnel). The method is used in building the retaining walls in order to manage the open excavations.

As it is stated in the article on soil stabilization methods by Makusa (2012), seismic retrofit of dams, liquefaction mitigation, strengthening around levees and excavations, lateral spreading alleviation, and dune deposits stabilization are all examples of the deep mixing method application. In these cases, the method is used for reducing the pore water pressures, to decrease the waves propagation in the super-and substructure, maximize the shear strength of soils.

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