USE OF DAM SEDIMENT AS SUB-BASE MATERIAL FOR MEDIUM TRAFFIC FLEXIBLE PAVEMENT CONSTRUCTION

Proceedings of the Fourth International Conference on Engineering and Technology Research February 23-25, 2016 ISBN: 978-2902-58-6 Volume 4 USE OF DAM SEDIMENT AS SUB-BASE MATERIAL FOR MEDIUM TRAFFIC FLEXIBLE PAVEMENT CONSTRUCTION Sadeeq, J. A.* and Salahudeen, A. B.** *Department of Civil Engineering, Ahmadu Bello University, Zaria, Nigeria **Samaru College of Agriculture, Division of Agricultural Colleges, Ahmadu Bello University, Zaria, Nigeria Corresponding Author: basalahudeen@gmail.com Abstract In this study, the possible use of dam sediment for flexible pavement construction was investigated. Soil samples were taken from three different locations and designated as sample A, B and C. The study area, which is the Ahmadu Bello University Dam, is located in Zaria, Kaduna State, Nigeria. Based on BS 1377 (1990), investigations on the sediment samples show that they are silty soils A-4 according to AASHTO classification. The soil samples have average moisture contents of 13.60 %. Average specific gravity values of 2.40, 2.61 and 2.70 were recorded for samples A, B and C respectively. Percentage passing BS sieve number 200 for samples A, B and C respectively are 70.75, 65.65 and 66.05 %. The plasticity indices of samples A, B and C are 5.08, 5.05 and 8.15 respectively. Compaction characteristics of the soil samples show that they all have an average of maximum dry density (MDD) and optimum moisture content (OMC) of 1.85 Mg/m3 and 12.25 % respectively. Results of California bearing ratio (CBR) conducted on the samples show that they could be used as sub-base materials for flexible pavement construction. Keywords: Dam sediment, Maximum dry density, Optimum moisture content, California bearing ratio, Subbase, Flexible pavement Introduction In all engineering design, the principal aim is to design against failure (Salahudeen et al. 2013). A dam can prevent or reduce downstream flood damage by temporarily storing a large part of the storm runoff. Reservoir sedimentation leads to decrease in storage capacity, which in turn can significantly impair the ability of a dam to perform this function. Also, sedimentation might cause structural damage and increase maintenance cost of operating the dam and/or lead to costly decommissioning at an earlier date. Periodic sediment removal, using techniques such as flushing, hydrosuction, or mechanical dredging, can play an important role in extending the useful life of dams (Maneechit et al., 2002). Rivers are conveyor belts for terrestrial material delivery to the oceans (Walling and Fang, 2003; 359 Walling, 2006), and they annually transport a 15 20 Gt sediment load to the global oceans (Milliman and Meade, 1983; Milliman and Syvitski, 1992). These large amounts of sediment play an important role in the global geological cycle, the global geo-chemical cycle, the coastal ecosystems and the evolution of deltas (Bangqi et al., 2009). However, dam construction interrupts the continuity of a river system in transporting sediments to downstream and coastal regions (Kondolf, 1997). During the latter half of the 20th century, about 45 000 large dams over 15 m high and an estimated 800 000 small dams had been built worldwide, representing nearly an order of magnitude increase compared to the year 1950 (WCD, 2000). It is estimated that more than 30% of the global sediment flux is trapped in reservoirs (Vorosmarty et al., 2003), and approximately 0.5% to 1% of the world s total reservoir volume is lost each year as a result of sedimentation (WCD,

2000). Subsequently, the global sediment flux from the rivers to the sea has decreased significantly (Milliman, 1997; Syvitski et al., 2005). High rates of sedimentation in many reservoirs and better care of long term sustainability have emphasized the importance of reservoir sedimentation. The main reservoir sedimentation problems are (ICOLD Sediment Committee, 2009): - Loss of storage capacity - Damages to turbines and loss of hydropower production - Downstream impacts The total world reservoir storage is about 7000 km 3 (6100 km 3 based on the ICOLD Register of Dams, but if smaller <15m dams are included, 7000 km 3 could be the current total storage), of which 3000 km 3 is dead storage for hydropower dams. From 4000 km 3 of live storage, most is devoted to hydropower and about 1000 km 3 to irrigation dams, potable or industrial water storage; part is in multipurpose dams (ICOLD Sediment Committee, 2009). The annual sediment load of all the world s rivers together is evaluated between 24 and 30 billion tons (Walling and Fang, 2003) for a water inflow of 40000 km 3, i.e. an average sediment content of 0.6 to 0.75 T/1000 m 3 of water but it varies enormously according to the river and the discharge. All rivers are not dammed and all sediments are not trapped in reservoirs: the accumulated sediment storage in world reservoirs has been evaluated as 2000 million m 3 for dams 35 years old on average, that is, in the range of 57 billion m 3 per year, i.e. 0.8 % of the total storage per year (ICOLD Sediment Committee, 2009). The most common soil type used in the tropic for the construction of flexible pavements is lateritic soil. Based on field performances, laterite may be classified as problem and non-problem types of soils. (R4) Laterite that may pose problems during construction works is termed problematic laterite (Gidigasu, 1976). Problem laterites are those whose performance is difficult to predict on the basis of the usual interpretation of test result carried out in the usual way as developed by standards (AASHTO, 1986). Several researchers (e.g., Osula, 1991; Sadeeq et al., 2014 a, b, c; Salahudeen and Ochepo 2015 a, b) stated that most lateritic soils have the reputation of being problematic in road and embankment 360 construction. They are characterized by high natural water content and liquid limits, low natural densities and friable and/or crumble structures. It is also important to know that there are some laterites that are not problem laterites. However, they do not meet the requirements to be used in road and dam embankment construction; such laterites need to be modified before their use (Salahudeen and Ochepo, 2015 a, b). Laterites are used in dam and canal embankments, as road making material and they form the subgrade of most tropical roads; they are used as subbase and base for most farm roads which are low cost roads and these carry low to medium traffic. A lot of lateritic gravels and pisoliths are good for earth roads (Salahudeen and Ochepo, 2015 a, b). There are instances where laterites may contain substantial amount of clay minerals that its strength and stability cannot be guaranteed under load, especially in the presence of moisture. These laterites are also common in many tropical regions including Nigeria where in most cases sourcing for alternative soil may prove economically unwise but rather improve the available soil to meet the desired specification (Osinubi and Bajeh, 1994; Mustapha, 2005). In 2014, Ahmadu Bello University Water Board Management initiated the task of dredging the sediment in the university dam site with a view to increasing its operational capacity for domestic, irrigation and many other uses. It was recognized that the river contained a considerable amount of sediment and as such, not only the dredging but also the disposal of the sediment materials is an enormous task. It was realized that if not disposed properly, the dredged sediment materials will be washed back into the dam reservoir. This study presents a possible, beneficial and effective use of this sediment to avoid its available land occupation, environmental littering and prevent its return into the dam reservoir. This will go a long way in actualizing the dreams of the Federal Ministry of works in Nigeria of scouting for readily cheap construction materials. Zaria is located at Latitude 1 0 3 N and Longitude 7 0 42 E and averagely at about 660 m above the sea level. Ahmadu Bello University dam is sourced from Kubanni River which is in turn sourced from Kampagi Hill in Shika, a neighbourhood town of Zaria. Zaria experiences six months of rainy season (from April to late October) and six months of dry season (from early November to late March). The location of Ahmadu Bello University dam is shown in Figure 1.

Figure 1: Sketch of Zaria showing location of Ahmadu Bello University dam Materials and Methods Materials Soil samples: The sediment samples used for this study were collected from Ahmadu Bello University dam located in Zaria, Kaduna State of Nigeria. Soil samples were taken from three different locations and designated as sample A, B and C. The soil samples were obtained using disturbed sampling method from the dam embankment. Some of the soils were sealed in 361 plastic bags and put in sacks to avoid loss of moisture during transportation to the Geotechnical Research Laboratory, Department of Civil Engineering of Ahmadu Bello University, Zaria. Methods Particle Size Distribution: The particle size analysis test was carried out in accordance with BS 1377; 1990 Part 2. Wet sieving was conducted by measuring 200 g of the soil sample and soaking it

PERCENTAGE PASSING for 24 hours. The sample was then washed through BS No 200 sieve. The particles retained were then dried in the oven for 24 hours and a dry sieving was carried out on the dried sample, while hydrometer sedimentation test was carried out on the portion passing BS No 200 sieve to obtain the particle size distribution. Atterberg limits: The test includes the determination of the liquid limits, plastic limits and the plasticity index of the soil samples. They were conducted in accordance with Test 3 of the BS 1377 (1990) Part 2. Compaction: The compaction tests were performed on the soil using the British Standard light (BSL) energy. Strength tests: Strength test performed was used to determine the California bearing ratio (CBR) values of the samples. The UCS test specimens were compacted at BSL energy and all cured and/or soaked samples were done for a period of seven days each. The CBR tests were carried out in accordance with Nigerian General Specifications (1997) which specifies that specimens be cured in the dry for a minimum of six days and then soaked for a minimum of 24 hours before testing. Results and Discussion Particle Size Distributions Test on Sediment Samples The particle size distributions of the three sediment samples used for this study are shown in Figure 2. The three samples seem to have similar particle sizes and distributions. 100.00 90.00 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 0.01 0.1 1 10 PARTICLE SIZE (mm) SEDIMENT SAMPLE A SEDIMENT SAMPLE B SEDIMENT SAMPLE C Figure 2: Particle size distribution curves for the sediment samples Specific Gravity Test on Sediment Samples The specific gravity of solid particles is the ratio of the mass of a given volume of solids to the mass of an equal volume of water. Specific gravity is an important parameter used for the determination of the void ratio and particle size of any soil particle (Arora, 2011). The values of the specific gravity of the three samples shown in Figure 3 show that the sediment samples will have similar densities. 362

MOISTURE COMTENT (%) PARTICLE SPECIFIC GRAVITY 2.80 2.70 2.60 2.50 2.40 2.30 SEDIMENET SAMPLE Figure 3: Graph of specific gravity of sediment samples Atterberg Limits Test on Sediment Samples Figure 4 shows the graph of Atterberg limits of the sediment samples used in this study. The results as seen in the figure indicates that the samples are good for road constructions according to the Nigerian General specification (1997) which recommends a maximum plasticity index value of 12 for materials to be used for sub-base construction. 25.00 20.00 15.00 10.00 LIQUID LIMIT PLASTIC LIMIT PLASTICITY INDEX 5.00 0.00 SEDIMENT SAMPLE Figure 4: Graph of Atterberg limits of sediment samples 363

MAXIMUMDRY DENSITY (Mg/m3) OPTIMUM MOISTURE CONTENT (%) Compaction Characteristics Test on Sediment Samples The graph of maximum dry density (MDD) and optimum moisture content (OMC) of sediment samples are shown in Figure 5. The high values of MDD of all samples is an indication of high strength. Results of researchers like; Osinubi (2000), Oriola and Moses (2010), Salahudeen and Akiije (2014), Salahudeen et al. (2014), Salahudeen and Ochepo (2015 a, b) and Sadeeq et al. (2015) show that the higher the MDD, the higher will be the strength of the soil sample. 1.920 12.60 1.900 1.880 1.860 1.840 1.820 12.50 12.40 12.30 12.20 12.10 12.00 MAXIMUM DRY DENSITY OPTIMUM MOISTURE CONTENT 1.800 SEDIMENT SAMPLE 11.90 Figure 5: Graph of maximum dry density and optimum moisture content of sediment samples Strength Characteristics of Sediment Samples California Bearing Ratio As an indicator of compacted soil strength and bearing capacity, the California bearing ratio (CBR) is widely used in the design of earth dams and also base and sub-base material for pavement (Sadeeq et al., 2014 a, b, c). It is also one of the common tests used to evaluate the strength of stabilized soils (Alhassan 2008). The graphs of unsoaked CBR for both cured and uncured are shown in Figure 6 while those of soaked (24 hours soaking) CBR values for both cured and uncured are shown in Figure 7. According to Salahudeen et al. (2014) high values of CBR could be due to the presence of adequate amounts of calcium required for the formation of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), which are the major compounds responsible for strength gain. All CBR values both cured and uncured meet the 20 30 % requirement for sub base reported by Gidigasu and Dogbey (1980), for materials compacted at the optimum moisture content. Peak CBR value of 63.97 % was recorded for unsoaked and uncured of sample A. 364

CALIFORNIA BEARING RATIO (%) CALIFORNIA BEARING RATIO (%) 65.00 60.00 55.00 50.00 45.00 UNCURED CURED 40.00 35.00 SEDIMENT SAMPLE Figure 6: Graph of California bearing ratio of of sediment samples (Unsoaked) 35.00 30.00 25.00 20.00 UNCURED CURED 15.00 10.00 SEDIMENT SAMPLE Figure 7: Graph of California bearing ratio of of sediment samples (Soaked) Conclusion From the results of this study, the following conclusions were drowned: 1. The sediment samples are silt soils A-4 according to AASHTO classification. 2. The plasticity indices values of all samples met the 12 % maximum plasticity index specified by clause 6201 of the Nigerian General Specifications (1997) for sub-base materials. 3. All sediment samples have high values of specific gravity and maximum dry density 365

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