TECHNICAL REPORT : Plate Load & Soil Bearing Capacity Evaluation PROJECT : 4-5 STOREY COMMERCIAL BUILDING OWNER : Engr. & Mrs. Cesar M. Hipona, Jr. LOCATION : Pabayo Street, Cagayan de Oro City DATE OF TEST : May 6 – 7, 2013 I. OBJECTIVE OF THE TEST:

a. To evaluate the probable soil capacity of the site b. And to enable to predict the probable foundation settlement

II. INTRODUCTION:

The primary responsibility of an engineer is to design a foundation system that performs satisfactorily to suit the intended use and structural durability of the structure. As in many cases the structural preference shall satisfy two specific criteria: a. There must be an adequate factor of safety against failure b. Deformations must be within the tolerable limits according to approved

codes

By SHEAR FAILURE means, stresses in a soil system exceed the strength of the soil, and this generally results in a collapse of the system. Whenever failure occur as a result on increasing the stresses along the failure plane or of decreasing the strength of the soil along the same plane. With this, stresses can be increased from an external load or from a change in the stress distribution by some means, such as making a cut at the base of a natural slope. Thereby the strength of the soil is often subject to allowable loading condition. It must be a reminder that, any excessive deformation of a foundation can make a structure unusable or unstable. This amount of settlement that can be considered tolerable depends on the function of the structure. Taking note that, any undesirable deformations are caused by both expansion and compression of soil. Generally, for a clay soil, it will expand if the water content increases, and this can cause foundations to deform excessively. In this case its not applicable due to the nature of actual soil condition of the site. However, when a foundation is not adequately designed, excessive settlement of the structure may occur as a result of compression on the underlying soil. This compression can occur due to the weight of the structure, by lowering the level of the groundwater table (in this case the probability is

very low), or by vibrations from machines (also not applicable for this structure) and large earthquake magnitudes. It is common knowledge that the evaluation of the soil bearing capacity has long been intriguing for a designer to consider. Of which, the plate load method is not usually reliable unless the plate size is comparable with the actual footing size, thus it is size and loading become expensive to perform and procure. Recent development in Geotechnical Engineering enables engineers to determine soil bearing capacity using the known soil properties such as its shear strength (unit cohesion or internal friction) and compressibility characteristics. One most commonly used method in determining these soil properties is the SPT or Standard Penetration Test. However, in this particular project, the PLATE LOAD TEST is employed due to agency specification and for economic consideration being allowable by codes or any implementing rules and regulations, whatsoever.

III. THE TEST SITE:

The project site is located within the vicinity of Pabayo Street, Cagayan de Oro City. The property is owned by the undersigned and propsed to be utilized for a 4-Storey commercial building with roof deck. Soil foundation of the lot is considered to be flat soil that is going parallel to the existing street level. The area is located along the street of Pabayo road. Dranage disposal system of the building is to be using the existing canal system along the area.

IV. METHODOLOGY:

a. A test pit is excavated to the depth the footing is to be placed. The test pit

shall be at least four times as wide as the plate used. b. A platform which will serve as the loading board will be constructed

supported by a single column with a plate that will transmit the load to the soil.

c. Only one size of plate in a single hole will be used for obtaining the soil bearing capacity of the site for a given settlement S. This actual soil bearing capacity will be adapted.

d. Applications of load will be done using an approximate of 40kg bag of sand bagging with a load increment approximately 1/5 of the estimated bearing capacity of the soil or as determined by the engineer conducting the test. Time intervals of loading shall not be less the one (1) hour and shall be approximately of the same duration for all load increments.

e. The test shall be continued until a load settlement of 25mm is obtained, or until the capacity of the testing apparatus is reached.

f. For failure of the testing apparatus or related incidents, linear projection is derived to meet the 25mm failure for the loadings.

g. A single test pit as set up shall be treated as minimum loading requirement.

V. TEST RESULTS & OBSERVATIONS:

Excavation for the single 1.0m x 1.0m x 2.0m hole was done manually for about two (2) hours. By any standard the soil at the excavated layer is naturally silt soil with a presumptive bearing pressure from available building code that stipulates a value between 1.5 to 3 tons/ft2 (145 to 388 kPa) as allowable soil bearing pressures for this type of soil. (see table 7.7 – Allowable Bearing Pressures for Soil). However, from the test holes, an actual determination of soil bearing capacity was gathered from the data and will be used in solving the allowable soil bearing capacity applicable to the site or structure.

VI. COMPUTATION:

HOLE No. 1 Load Trial No. 1 Plate Size : 25 cm x 25 cm; Plate Area = 625 sq.cm. Qu = 1911 x 98.07 / 625 = 299.86 kPa

HOLE No. 2 Load Trial No. 2 Plate Size : 25 cm x 25 cm; Plate Area = 625 sq.cm. Qu = 2015 x 98.07 / 625 = 316.18 kPa Average Qu = 308.02 kPa

VII. FACTOR OF SAFETY:

Maximally a factor of safety of 2 is applied to the ultimate soil bearing capacity to arrive at the allowable soil bearing capacity. This assumption is not considered to be too conservative. In nature, soils are not homogeneous and isotropic; a great deal of uncertainty is involved in evaluating the basic shear strength parameters of soil. For the purpose, the customary safety factors for footings in shear failure mode specified is as stated below, will be considered in the considered in this presentation; Spread Footing - 2 to 3 Mat Foundation - 1.7 to 2.5 From the above given safety factors, the average factor of 2.0 will be taken as the factor of safety of our allowable bearing capacity to be used in the design of this building. Thus: Allowable Qu = 308.02 / 2 = 154 kPa

VIII. RECOMMENDATIONS:

Soil foundation within this property predominantly Silt Soil within the 150 meters circumference as physically determined during site investigation. Water table is evaluated to be present within 3 to 5 meters below reckoned from the highway road level. Because of these factors, liquefaction is considered to occur some how for this lot area, thus foundation needs to incorporate tie beams to properly hold the foundation footings and column together. Allowable soil bearing capacity of the site can be as high as 154 kPa if excessive settlement is tolerated and without considering the risk of liquefaction. However, to avoid excessive settlement, the factor of safety of

2.0 is introduced, consequently, the allowable soil bearing capacity recommended is Qu(Allowable) = 154 kPa maximum. Isolated footing with tie beam is also recommended to secure the ill – effects of uneven settlement and movement of the building. Footings with large depth shall be applicable to sustain unlikeable ground movement.

Prepared by: ENGR. CESAR M. HIPONA, JR. Civil Engineer REFERENCES: McCarthy, David 1984, Essentials of Soil Mechanics and Foundations, 3rd Edition, Reston Publishing Company, NJ, U.S.A. Bowles, J.E. 1982, Foundation Analysis and Design, 3rd Edition, McGraw-Hill International Bool Company, NY, U.S.A. Tomlinson, M.J., Boorma, R. 1986, Foundation Design and Construction, 5th Edition, Longman Group UK Limited