In this study, a plate load testing equipment was designed and constructed at the faculty of engineering, university of Benin. A full scale field testing programme ...
Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(4): 636-641 © Scholarlink Research Institute Journals, 2013 (ISSN: 2141-7016) jeteas.scholarlinkresearch.org Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(4):636-641 (ISSN: 2141-7016)
Evaluation of Dynamic Properties of Soils in Site for Proposed Petrochemical Plant in Edo State, Nigeria 1
J.O Ehiorobo, 2J. O Okovido and 3R.O Ogirigbo
University of Benin, Faculty of Engineering, Department of Civil Engineering, Benin City, Nigeria. Corresponding Author: J.O Ehiorobo _________________________________________________________________________________________ Abstract In geotechnical engineering, the problem of dynamic loading of soils and soil structure interaction system requires the determination of the dynamic properties of soils. The determination of the dynamic properties of soils deposit is of uttermost importance in studying site response to dynamic loading and the probability of seismic hazards occurring. In this study, a plate load testing equipment was designed and constructed at the faculty of engineering, university of Benin. A full scale field testing programme was then conducted under static and cyclic loading condition on three different points to determine the bearing capacity of soils and the dynamic response of the soils under various loading conditions. In the case of the cyclic plate load tests, settlements of the base plate for both loading and unloading conditions were recorded. The results of the static and cyclic plate load tests were used to plot load-settlement curves for each point where the test was conducted. The graphs for the load against elastic settlement represented arithmetical graph from which the line of best fit were obtained. From the results, it was found that for the three tests point the load required to cause settlement of 2.5mm were 104.3kN/m2, 83.27kN/m2 and 62.96kN/m2 respectively. The soil bearing pressure for a permissible elastic settlement of 25mm was estimated from the equation of line of best fit as 630 kN/m2. The dynamic properties of the soil were also computed for the three locations. The results show that the soils around the site is stable and can withstand the effect of the anticipated plants vibration during construction and during operation of the plants. The study of dynamic properties of soil is essential as they are very important for dynamic responses and dynamic analysis of major structures and sensitive machines and equipment in a site such as the petrochemical plant. __________________________________________________________________________________________ Keywords: dynamic stress, static plate load, cyclic plate load, elastic settlement, poisson ration. INTRODUCTION Dynamic properties of a soil are properties which are made manifest through movement of soil (Gill and Vandenberg, 1968). The evaluation of Dynamic properties of soil deposit is of utmost importance in studying site response, predict ground motion and probability of seismic hazards (Pitialakis, Anastassiadis and Raptakis, 1992)
The study of dynamic properties of soils have always posed a problem as the physical measurement must be made during the movement but this is difficult to attain as the soil may behave differently from expected and the insertion of the measuring equipment into the soil mass may affect the soil’s reaction. Despite this constraint, it is still necessary to access the reaction of the soil to forces such as external loading. Various models and analytical techniques can be used in representing soil deposits and it’s response to loading. Despite the type of procedure to be adopted, it is first necessary to evaluate the appropriate dynamic properties of the material in the soil deposit (Sitharam et al (2004)).
Dynamic evaluation of the response of the earth mass to static and dynamic stress application such as those produced by earthquake, wind loading, machine vibration etc are of importance when structures such as Tank farm, fertilizer plants, wind farms etc are to be constructed. The focus of most soil quality work is on dynamic properties and how they change in relation to some specific features of the soils. Changes in dynamic properties depend basically not only on land use practices but also on the inherent properties of soils. The behavior of soil has been studied by various authors using static and dynamic plate load test. They include Adam et al (2004 &2009), Tsuha et al (2012), Moghaddas et al (2008) and many others.
Precise measurement of the dynamic soil properties is somewhat a difficult test in solution of geotechnical earthquake engineering problems (CSMRS 1992, Sitharam et al 2004). The response of soils to cyclic loading is controlled by the mechanical properties associated with dynamic loading including shear wave velocity, modulus, damping ratio and Poisson ratio (Honkanadavar, Gupta and Ramakant (2011)). The aim of the research work is to present some data and analysis describing the dynamic properties of 636
Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(4):636-641 (ISSN: 2141-7016) natural soils in a proposed site for Petrochemical plant in Nigeria. A better understanding of the soils in response to loading impacted by a plate will help in developing a better compaction control.
METHODOLOGY Field Measurements A plate load testing equipment was developed in the University of Benin Mechanical Engineering Workshop for the purpose of evaluating the dynamic response of the soils in the site under repeated loading condition. The equipment consists essentially of a base plate of 600 × 600 × 25mm, a 20 ton Hydraulic Jack. (See fig 2)
Field tests on both static and cyclic plate load tests are based on some mechanical model of the subsoil. This enabled us in the study to develop a useful relationship between the two tests and the dynamic response of the soil to loading and unloading. The plate load test when used in a static mode enable the engineer determine the ultimate bearing capacity of soils and the likely settlement under a given load (Jeffa 2012) SITE DESCRIPTION The project site is located between Nigerian Traverse Mercetor (NTM) Coordinates 226030.117 m N to 226546.128m N and 354552.744m E to 355407.681m E
Fig 2: Plate Load Test Equipment The site is within the rain forest region of Nigeria The soil within the project area indicate sandy site with some clay constituents. The presence of clay is evidenced from brownish colour of the soil within the area. The topography of the area is undulating and slopes towards the Ossiomo River to the southern part of the project site. This means the drainage work on the site will involve channeling the run off in the direction of Ossiomo River.
A full scale field testing program was conducted at different points on the site to evaluate the dynamic response of the soil under various loading conditions. Static Plate Load Tests The test was carried out in accordance with BS 1377 – 9: 1990. This test is used to determine the vertical deformation and strength characteristics of the soil in situ, by assessing the force and amount of penetration with time when a rigid plate is made to penetrate the soil. It is used to evaluate the ultimate bearing capacity, the shear strength and deformation parameters of the soil beneath the plate. The test was carried out in three locations. Pits were dug to depths of 2m below the natural ground level. The loads were applied incrementally by means of a 20 ton hydraulic jack onto a base plate of 600 x 600 x 25mm. Readings for time and settlement of the base plate were recorded against the loads applied. Cyclic Plate Load The test was carried out using the same set up for the static plate load test. This test is used to determine the dynamic properties of the soil. It is used to evaluate the coefficient of elastic uniform compression of the soil Cu, which is defined as the constant of proportionality between the external uniform pressure and the elastic part of the settlement.
Fig 1. Location map of site showing cyclic plate load test points Location map of the site is shown in fig 1. The coordinate of the selected location for static and cyclic plate load tests are presented in Table 1.
The test was also carried out in three locations. Pits were excavated to depth of 2m below the natural ground level. The loads were applied in a cyclic manner (loading and unloading) by means of a 20 ton hydraulic jack unto a base plate of 600 x 600 x 25mm. Settlement of the base plate for both loading and unloading cycles were recorded.
Table 1: Coordinate of Test Points. Test point 1 2 3
STATIC PLATE LOAD TEST Northings Eastings 226221.672 226283.574 226182.579
354679.766 354985.724 355294.328
CYCLIC PLATE LOAD TEST Northings Eastings 226289.255 226370.906 226440.946
355022.082 354697.342 354969.142 637
Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(4):636-641 (ISSN: 2141-7016) From the plots shown in Figures I to III, the coefficient of elastic uniform compression of the soil Cu , which is approximated as the slope of the graphs were obtained. This was used to compute other dynamic properties of the soil, which are presented in Table IV.
Table IIIA: Cyclic plate load test result for pit 1 Load causing Se Loading cycle Unloading cycle (psi) (psi) (psi)
RESULTS AND DISCUSSIONS Static Plate Load Tests The results of static plate load tests are presented in table IIa - IIc below. Table IIA: Results for Plate Load Test at Point 1 S/N
Time
1 2 3 4 5 6 7 8 9
0 5 sec 10 sec 15 sec 30 sec 1 min 2 min 3 min 4 min
Pressure Pressure Settlement Settlement (psi) (kN/m2) (cm) (mm) 0 0 0 0 0.5 3 0 0 1.5 10 0.5 5 7 48 0.8 8 12.5 86 1.5 15 20.2 139 2.1 21 31 214 2.3 23 39.7 274 2.5 25 47.1 325 2.6 26
Table IIB: Static Plate Load Test Results at Point 2 S/N
Time
1 2 3 4 5 6 7 8 9 10
0 5 sec 10 sec 15 sec 30 sec 1 min 2 min 3 min 4 min 5 min
Pressure Pressure Settlement Settlement (psi) (kN/m2) (cm) (mm) 0 0 0 0 0.7 5 0.2 2 2 14 0.5 5 10.2 70 1 10 14 97 1.3 13 26 179 1.4 14 40.1 276 2 20 44.4 306 2.1 21 47.1 325 2.2 22 56 386 2.3 23
Time
1 2 3 4 5 6 7 8 9
0 5 sec 10 sec 15 sec 30 sec 1 mins 2 mins 3 mins 4 mins
0 0.5 0.2 0 1 1 0.5 0.5 0.5 0.5 0.8 1 0.5 0
0 0.5 1.8 3 3 6 7.5 9.5 11.5 12.5 16.2 17 18.5 23
Settlement in unloading cycle (mm) 0 0 0 1 1 1 2 3 5 6 6 6 11 11
Elastic Settlement (Se) (mm) 0 1 2 0.5 2 1 2 1 0 0 1 2 2 3
Table IIIB: Cyclic plate load test result for pit 2 Elastic Settlement in Settlement in Loading cycle Unloading cycle Load causing Se loading cycle unloading cycle Settlement Se (psi) (psi) (psi) (mm) (mm) (mm) 0 0 0 0 0 0 1 0.5 0.5 2 0 2 2 0 2 2 0 2 3 0.5 2.5 3 1 2 4 1 3 2 1 1 5 1 4 3 1 2 6 1 5 4 2 2 8 0.5 7.5 1 1 0 11 0.5 10.5 3 2 1 12 0.5 11.5 3 1 2 14 0.5 13.5 2 1 1 15 0.5 14.5 4 3 1 16 0.5 15.5 5 3 2 17 1 16 7 4 3 19 1 18 12 8 4 21 0.5 20.5 9 5 4 25 0.5 24.5 11 7 4
Table IIIC: Cyclic plate load test result for pit 3 Load causing Loading cycle Unloading cycle settlement Se (psi) (psi) (psi) 0 0 0 1 0.5 0.5 2 0 2 3 0 3 4 0.5 3.5 5 0.5 4.5 6 0.5 5.5 7 1 6 8 1 7 9 0.5 8.5 10 1 9 11 0.5 10.5 13 0.5 12.5 15 0.5 14.5 16 0.5 15.5 18 0.5 17.5 19 0.5 18.5 20 0.5 19.5
Table IIC: Results for Plate Load Test at Point 3 S/N
0 1 2 3 4 7 8 10 12 13 17 18 19 23
Settlement in loading cycle (mm) 0 1 2 1.5 3 2 4 4 5 6 7 8 13 14
Pressure Pressure Settlement Settlement (psi) (kN/m2) (cm) (mm) 0 0 0 0 1 7 0.2 2 1.8 12 0.3 3 9 62 0.9 9 12 83 1.4 14 23 159 2.2 22 29.5 203 2.3 23 32 221 2.4 24 43.8 302 2.4 24
Settlement in loading cycle (mm) 0 2 3 4 6 4 4 3 2 2 4 3 9 8 11 13 12 9
Settlement in unloading cycle (mm) 0 0 0 1 4 3 3 2 2 1 1 1 6 4 7 9 8 5
Elastic Settlement Se (mm) 0 2 3 3 2 1 1 1 0 1 3 2 3 4 4 4 4 4
ANALYSIS AND DISCUSSION OF RESULTS Static Plate Load Test The results of the static plate load tests were used to plot load-settlement curves for the test point. The charts are shown in figures 3a to 3c.
Cyclic Plate Load Tests The results of cyclic plate load test are presented in table IIIa - IIIc below
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Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(4):636-641 (ISSN: 2141-7016) For figure 3b however, the failure load is much lower which is at 29KN with a settlement of 10mm. The bearing pressure at this point is 80KN/m2. This can be traced to the huge amount of clay around this location.
Force (kN) 0
30
60
90
120
Settlement (mm)
0
Failure load for figure 3c is similar to the one in figure 3a. From the graph, load of 60KN at a settlement of about 25mm portrays the bearing capacity of the soil.
10
20
Cyclic Plate Load The results of the cyclic plate test in table IIIA-IIIC were used to plot load-settlement graphs as shown in figures 4a-4c below.
30
Figure 3a: Load – Settlement curve for Point 1
CPLT for Pit 1 25
Force (kN) 30
60
90
120
150 Load causing Se (psi)
0
Settlement (mm)
0
10
20 y = 5.963x 15 10 5
20 0 0
1
30
2
3
4
Elastic settlement Se (mm)
Figure 3b: Load – Settlement curve for Point 2
Figure 4a: Load causing elastic settlement vs. elastic settlement for pit 1
Force (kN) 0
30
60
90
CPLT for Pit 2
120
25 20
10
Load causing Se (psi)
Settlement(mm)
0
20
30
y = 4.758x
15 10 5
Figure 3c: Load – Settlement curve for Point 3 0 0
The results of the static plate load test shown in table 11a-11c were used to plot load settlement curves which depicts the extent of vertical downward displacement pervading the area at specific loading. Figure 3a - 3c show the graphical relationship between load and settlement s for the three test points.
1
2
3
4
Elastic settlement Se (mm)
Figure 4b: Load causing elastic settlement vs. elastic settlement for pit 2
From figure 3a, there is consistent settlement due to increase loading up to 60KN. A deflection in the curve, after force 60KN shows that failure has occurred in the carrying capacity of the soil. The bearing pressure at the failure load is 167KN/m2 with a settlement of about 25mm. 639
5
Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(4):636-641 (ISSN: 2141-7016) The static plate load tests show the load that will cause failure for each test point. From figure 3a – 3c, the various failure loads and their equivalent settlements were determined. Test points 1 and 3 seemed to have similar soil capacity as they both have a failure load of 60KN at a settlement of 25mm. Test point 2 from static plate load test has a low failure load of 30KN at a settlement of 10mm.
CPLT for Pit 3 20
Load causing Se (psi)
15
y = 3.5985x
10
5
Results and graphs based on the cyclic plate load test show the bearing pressure at stipulated settlement. From figures 4a -4c, bearing pressure for a settlement of 2.5mm were found to be 104KN/m2, 83KN/m2, 63KN/m2 for test point 1,2 and 3 respectively. These values show that the bearing pressures around location for cyclic plate load tests are high. Further results for the dynamic parameters were computed from the cyclic plate load test results for each test point and are presented in Table IV.
0 0
1
2
3
4
5
Elastic settlement Se (mm)
Figure 4c: Load causing elastic settlement vs. elastic settlement for pit 3 The graph for the load against elastic settlement is an arithmetic graph plotted to get the line of best fit. The aim is to know the load at a settlement of 2.5mm. From figure 4a, the load causing a settlement of 2.5 was found to be 14psi (104.3KN/m2). The same settlement for figure 4b and 4c gave 11.85psi (83.27KN/m2) and 8.995psi (62.96KN/m2) respectively.
The above result will guide the structural and foundation Engineer in choosing suitable foundation type both for surface and underground structures, particularly where vibration of plants and equipment is likely to affect the soil equilibrium or in potential seismic active areas.
Based on the above, it can be seen that the soil location upon which cyclic plate load test were carried have a high bearing pressure. The soil capacity for a permissible elastic settlement of 25mm for figure 4c was computed using the line of best fit equation from the chart, and was found to be 630KN/m2. Similar high soil bearing capacities were obtained for the other charts.
The limitation of the study lies in the fact that the application of the plate load tests is limited to a small portion of the ground at the site at a time. Soil characteristics may vary at other points within the same project site. Additionally, the tests cannot be conducted on narrow pits as there will not be available enough movement space.
Using the results from table IIIa – IIIc, the dynamic parameters of the soil were computed as shown in table IV below.
REFERENCES Adam C., Adam D, and Kopf F. 2009, Computation Validation of Static and dynamic plate loading testing. Acta Geotechnical. 4; 35-55, Springer Publishing.
Table IV: Computed dynamic properties of soil for pits 1, 2 and 3 3
Coefficient of elastic uniform compression (Cu) kN/m 3
Pit 1 Pit 2 Pit 3 4 3 4 3 4 3 4.11 x 10 kN/m 3.28 x 10 kN/m 2.48 x 10 kN/m 4
3
4
3
4
3
4
3
4
3
4
3
4
3
4
3
4
3
2.06 x 10 kN/m 1.64 x 10 kN/m 1.24 x 10 kN/m
Coefficient of elastic uniform shear (Cτ) kN/m
3 Coefficient of elastic non-uniform compression (Cφ) kN/m 8.22 x 10 kN/m 6.56 x 10 kN/m 4.96 x 10 kN/m 3
Coefficient of elastic non-uniform shear (Cψ) kN/m
3.08 x 10 kN/m 2.46 x 10 kN/m 1.86 x 10 kN/m
Spring constant (kz)
1.48 x 10 kN/m 1.18 x 10 kN/m 0.89 x 10 kN/m
4
4
Adam D., Adam C., and Kopf F. 2004, The Dynamic load plate test with the light falling weight device; experimental and numerical investigation in; Doolin D. et al (eds) proceedings of the 11th International conference On soil Dynamics and earthquake, Engineering (11th ICSDEE) and the 3rd International conference on earthquake geotechnical engineering (3rd ICEGE). Vol 1 University of California C.A, USA Jan. 7-9, pp649-654
4
CONCLUSION Static and cyclic plate load tests conducted at specified locations in the proposed Fertilizer Plant were conducted to determine the limit of settlement that the plant location can withstand. The project locations which consist mainly of sandy clayed soil require an understanding of the dynamic and static load the soil can withstand for safety reasons.
CSMRS 1992, Report on Liquefaction Potential of sand lenses in Shahpurkandi dam foundation Punjab, India Gill W.R. and Vandenberg G.E. 1968, Soil Dynamics in Tillage and Traction, Agricultural Handbook, No 316, pp I-V, Washington D.C., US Government Printing Press.
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Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 4(4):636-641 (ISSN: 2141-7016) Honkanadavar N.P., Gupta S.L, and Ramakant S., 2011, Evaluation of Dynamic properties of sandy soil, International Journal of Earth sciences and Engineering 4(6) 79-82 JEFFA GEOSURVEYS AND TECHNICAL SERVICES LIMITED (JEFFA) 2012, Geotechnical Investigation report on site for proposed fertilizer plant in Edo State of Nigeria for Greenpark Petrochemicals Ltd, Abuja Nigeria Moghaddas Tafreshi S.N, Zarei S.E and Soltanpour Y. 2008, Cyclic loading on foundation to evaluate the coefficient of elastic uniform compression on sand, Proceedings of the World conference on Earthquake Engineering. Beijing, China Oct 12-17 Pitialakis K.D., Anastassiadis A. and Raptakis D. 1992, Field and laboratory determination of dynamic properties of natural soil deposits. Proceedings 10th World Conference on Earthquake Engineering, Belkema, Rotterdam pp1275-1280 Sitharam T.G., Govinda Raju L. and Sridharan A, 2004, Dynamic properties and Liquefaction potential of soils. Current science, Geotechnical and Earthquake Hazards; 87 (10); 1370-1377 Tsuha C.H.C, Foray P.Y, Jardine R.J, Yang Z.X, Silva M, and Rimoy S, 2012. Behavior of displacement piles in sand under cyclic axial loading, Journal of the Japanese Geotechnical Society, Soils and Foundation, 53 (3); 393-410.
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