Earth And Earth Rock Dams Sherardl
Abele Beardsley
Knowledge of soil, which is an essential construction material, has great importance for dam construction. The level of density and carrying capacity of the soil is very important and should be taken into consideration in the planning and designing stages of civil construction, considering the soil functions as a means to withstand the load or structure built on it. Stabilization using sand soil material is one of the ways to meet the strength requirements of soil carrying capacity when there is no suitable soil material found in the nearby area. This paper aims to elucidate the physical properties of clay using a mixture of fine sand to reduce the risk of shrinkage when used for dam construction. Several analyses were carried out to find out the effect of the fine sand percentage in the clay mixture to decrease the swelling test value and permeability test of the soil carrying capacity for dam construction. The types of soil tested were silt clays taken from Tritisan subdistrict of East Lampung which were then stabilized using fine sand material from Central Lampung, Indonesia. This research was conducted using a mixture of sand, with percentages of 10%, 20%, 30%, and 40%. Subgrade tests such as CBR and permeability tests were also undertaken to investigate other soil properties from each sample. The results indicate that a higher percentage of sand causes decreasing water content. Thus, the value of the carrying capacity of the soil is increasing. The findings can be used to facilitate the increasing use of clay mixtures with the percentage of fine sand in case suitable clay material cannot be found around dam construction sites. The implications with suggestions for future research are also discussed.
Knowledge of soil, which is a basic construction material, has great importance for dam construction. It is one of the key factors of civilizations [1]. In the history of geology, there has been a close relationship between life and water from the perspective of the land and aquatic environment [2]. The soil is the critical element of life support systems because it delivers several ecosystem goods and services [3]. Soil properties diverse considerably under tillage type, intensity, different crops, fertilizer, and application rates [4]. It is well known that dam is one of irrigation infrastructure buildings with a type of weir structure that is affected by the fluctuating flow rates and water volumes of the river. Soil water evaporation curves both represent the laws of water content variation in the natural state [5]. Vital environmental protection and water management are constructed [6]. The occurrence of instability and the derailment of dam construction can exist when the strength of the structure is not in accordance with shear strength of the soil on the related site. It also gives nutrients on the sediments of the reservoir [7]. Besides the above things, however, many factors can cause failures and cracks in a dam body such as floods, earthquakes or explosions, human activities, and terrorist attacks against the dam [8]. Since dam is a part of geotechnical engineering in civil engineering, if a failure occurs which finally causes damage, it can be repaired by analyzing and designing the stability of the dam, including the factors that affect the stability of the dam [9]. It is closely related to the decrease of downstream taxa and uplifts the biomass [10].
In dam planning, it is generally accepted that one of the surveys that must be carried out is a material investigation [11]. One of the ways is by assessing the problems of dam constructions, which are built on clay in Indonesia, and clay soil is spread almost in all areas of Indonesia. Regarding the dam construction, the original compacted soil is usually used as a core. In contrast, clay soil material is needed because it is impermeable so that the dam can store water to serve a function as a reservoir. Therefore, it leads to upstream and downstream decreases considerably [12].
Generally, soil stabilization refers to a particular way of improving soil properties through blending and mixing other materials. These improvements include the increasing dry unit weight, bearing capabilities, volume changes, the performance of in situ subsoils, sands, and other waste materials to strengthen road surfaces, and other geotechnical applications [13]. According to Bowles [14], if the soil found in a site is loose or very easily stressed or if it has an inappropriate consistency index, it has very high permeability or other undesirable traits that are not suitable for a development project. Soil stabilization must be carried out to resolve the above issues. In general, the method used to stabilize soil consists of one process or a combination of the following processes [14]:(a)Mechanical, namely, compaction with various types of mechanical equipment such as a roller machine, dropping heavy objects, explosion, static pressure, texture, freezing, and heating.(b)Additive, namely, the addition of gravel to cohesive soils, loam for grained soils, and chemical mixers such as cement, lime, volcanic ash/coal, lime and/or cement, asphalt cement, sodium, calcium chloride, and paper mill waste.
The methods or ways to improve soil properties are also very dependent on curing time; this is because, during the process of improving soil properties, chemical processes occur, which require time for chemicals present in the additive to react.
However, the carrying capacity of the clay is often criticized for its low capacity. Clay soil is generally a poor subgrade due to its low shear strength, so that the construction of a structure on this soil layer always faces several problems such as low bearing capacity and large shrinkage properties. Therefore, it is commonly suggested that optimal water content plays an important role in getting the maximum density level. In addition to impermeability needs, because a large number of soil volumes are needed, the source of the material is also one of the important things to take into account.
Thus, the properties of clay are still not completely understood. In other words, evidence on this question is presently inconclusive. Therefore, this paper aims to elucidate the physical properties of this type of soil using a mixture of fine sand to reduce the risk of shrinkage when used for dam construction.
Several soil physical and biological properties, for example, bulk density, aggregate stability, and soil microbial biomass are related to the content and turnover of soil organic matter (SOM). Organic matter and clay are intimately linked by a range of physical, chemical, and biological processes, playing a crucial role in the formation of soil aggregates, affecting stability at different scales [17].
Soft clay soil is soil containing clay minerals and has a high-water content, which causes low shear strength. Soft clay, also known as expansive clay, is a type of clay that is classified into types of soil which have a development value and a large shrinkage value, so that it can cause damage to the structures built on it. Due to the amount of activity value (A) of clay soil, the size of clay activity value is influenced by the soil plasticity index value (PI). Potential development of a type of soil is based on its plasticity index value (PI). Clay soils that can be categorized into expansive clay soils are those having very high development potential limits with the plasticity index value (PI) of >35% [20].
Thus, the properties of clay are still not completely understood. In other words, evidence on this question is presently inconclusive. Sand is a naturally occurring granular material. Because of its high load bearing capacity in confined condition, sand could be used as a filler material. It could be used in varying proportions as admixture to cohesive soils altering the properties of plasticity, compaction, and strength of the mixtures. Therefore, this paper aims to elucidate the physical properties of this type of soil using a mixture of fine sand to reduce the risk of shrinkage when used for dam construction.
Compaction is an attempt to increase the density of the soil by releasing air to the porous soil, which is usually done using mechanical energy. In the field, compaction effort is related to the amount of runoff from a roller machine or something else that has the same principle for a certain volume of soil. In general, soil compaction, which is carried out in the laboratory, consists of two types, namely, the AASHTO T99 Proctor Standard (ASTM D689) and Modified Proctor, to obtain a greater California Bearing Ratio (CBR) value. Undertaking a soil compaction test will make a connection between water content and volume weight. According to Bowles [14], the benefits derived from compaction of soil include: the following(a)Reduced subsidence, that is, vertical movement within the soil mass itself due to reduced number of pores;(b)Increasing soil strength;(c)Decreasing volume due to reduced water content during drying.
California Bearing Ratio (CBR), which was first invented between 1927 and 1930 in California by O.J. Porter, is an empirical method for measuring soil density values. This method combines an experiment of loading in the laboratory or in the field with an empirical plan to determine the thickness of the pavement layer. A CBR test must first be carried out to get the CBR value. This test, a comparison between test loads with standard load, expressed as a percent, was developed around the 1930s in the laboratory of the Materials Research Department of the California Division of Highway, USA.
According to Indonesian Government Regulation Number 37 Article 1 of 2010 about Dams, a dam is a building made of earth, rock, concrete, and/or stone pairs to hold and store water. It is also built to hold and accommodate mine waste (tailings) or collect mud to form a reservoir. A dam serves to function as a water catcher and saves the water during the rainy season when the river water flows in large quantities and exceeds the needs for use, irrigation, drinking water, industry, or others. In the Guidelines and General Criteria of Dam [11], the types of dam based on its function can be divided into the following:(a)water reservoir dam;(b)diversion dam;(c)flood control dam;(d)Multipurpose dam.
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