Foundation Design of Al-Maslamani Mall in Beit Eba, Nablus

2. Abstract *Our project is about ( Foundation Design of Al-Maslamani Mall) which is located in the village of Beit Eba – Nablus governorate. *The total plan area of this mall is about 3500 m2 *The number of stories is 6; 4 stories above the ground surface & 2 stories are below the ground surface.

3. Literature Review • Site Investigation is the first important step in any engineering work ; to determine type & depth of foundations , to evaluate bearing capacity , to identify construction methods & for many things… • Foundations are the part of an engineered system to receive & transmit loads from superstructure to the underlying soil or rock . • There are two types of foundations : shallow & deep foundations. • Many factors should be taken into consideration in choosing foundation types such as soil properties , economic factors, engineering practice, ....etc

4. Isolated footings Piles Mat Combined Foundations

5. Isolated Footings • Are used to support single columns. • This is one of the most economical types of footings and is used when columns are spaced at relatively long distances. • Its function is to spread the column load to the soil , so that the stress intensity is reduced .

6. Mat or Raft Foundations • are used to spread the load from a structure over a large area, normally the entire are of the structure . • They often needed on soft or loose soils with low bearing capacity as they can spread the loads over a larger area. • They have the advantage of reducing differential settlements.

7. Combined Foundations Are used in the following cases: • 1) When there are two columns so close to each other & in turn the two isolated footing areas would overlap. • 2) When the combined stresses are more than the allowable bearing capacity of the soil. • 3) When columns are placed at the property line.

8. Strap or Cantilever Footings • Cantilever footing construction uses a strap beam to connect an eccentrically loaded column foundation to the foundation of an interior column . • Are used when the allowable soil bearing capacity is high, and the distances between the columns are large .

9. Pile Foundations • They are long & slender members that are used to carry & transfer the load of the structure to deeper soil or rocks of high bearing capacity, when the upper soil layer are too weak to support the loads from the structure. • Piles costs more than shallow foundations; so the geotechnical engineer should know in depth the properties & conditions of the soil to decide whether piles are needed or not.

10. Classification of the piles • According to load transmission & functional behavior : 1) End / Point bearing piles 2) Friction piles 3) Compaction piles • According to type of material: 1) Steel piles 2) Timber piles 3) Concrete piles 4) Composite piles • According to effect on the soil: 1) Driven piles 2) Bored piles

11. Bearing Capacity & Settlement • Bearing Capacity : is the ability of a soil to support the loads applied to the ground . Ultimate bearing capacity is the theoretical maximum pressure which can be supported without failure; Allowable bearing capacity is the ultimate bearing capacity qu divided by a factor of safety (F.S). • There are three modes of failure that limit bearing capacity: general shear failure, local shear failure, and punching shear failure. • Any structure built on soil is subject to settlement. Some settlement is inevitable, & depending on the situation, some settlements are tolerable. • When building structures on top of soils, one needs to have some knowledge of how settlement occurs & how fast settlement will occur in a given situation.

12. Geotechnical Investigation • The studied area is approximately flat with slight difference in the three existing elevations. The general soil formation within the depths of the borings consists mostly of wadi deposits of boulders & silty clay followed by successive layers of hard boulders mixed with very little filling silty clay. The whole site is covered by grass. • The geotechnical engineer decided to drill four boreholes trying to cover the whole construction area.

13. The depths of the drilled boreholes were as follows: • = 20 KN/m³ w = 7.6 % (avg.) • C = 0 KN/m² (average) LL = 44.5 % • Ø = 25 º PI = 25 • qall. = 3.0 kg/cm2 G = 2.73 • a-Coefficient of active earth pressure: KA = 0.405 • b- Coefficient of passive earth pressure: KP = 2.464 • c- Coefficient of pressure at rest: Ko = 0.577 • Summary of lab. test results:

14. After doing check on the bearing capacity value using FOUND software by using Terzaqi and Meyerhoff formulas, the value was ranging between 3.2 and 4.3 Kg/ cm2 respectively, SO we decided to use a value of 3.5 Kg/ cm2in our project.

15. Load Calculations

16. Isolated Footing Design • Manual Design steps: • Area of footing = Total service loads on column / net soil pressure • Determine footing dimensions B & H . • Assume depth for footing. • Check soil pressure. • Check wide beam shear : ΦVc > Vult • Check punching shear : ΦVcp > Pult, punching • Determine reinforcement steel in the two directions. • Check development length . • Check load transfer from column to footing . Then, we compare manual design with SAP design in footings F4 & F8 .

18. The solution of SAP is always smaller than manual one, since SAP uses Finite Element Method. • There is no need to calculate the settlement of the isolated footings; since the soil is gravelly soil , & has a qall. of 3.5 kg/cm2 . • The final results of isolated footings design are in the next table :

20. Wall Stair Footing

21. Dimensions and Reinforcement Details of Wall Stair Footing Depth of wall footing = 60 cm. Width of wall = 20 cm. Width of footing (B) = 2 m. Reinforcement: 6 φ16 / m in short direction 14 φ16 in long direction

22. Elevator Wall Footing

23. Dimensions and Reinforcement Details of Elevator Wall Footing Depth = 33cm, h=40cm 4 φ16 / m For positive moment & negative moment In both directions. Reinforcement details for elevator wall :

24. Pile Foundation

25. Design of pile foundation 1-Estimating pile capacity • The ultimate carrying capacity is equal to the sum of the ultimate resistance of the base of the pile and the ultimate skin friction over the embedded shaft length of the pile, this expressed by : • Qu = Qp + Qs

26. 2-Determination of the point bearing capacity For piles in rocky sand soil as in our case , the point bearing capacity may be estimated as : QP = Ap q' Nq* ≤ Qlimit Where: Ap : Area of the pile tip. q’ : effective stress at pile tip. Nq*: Factor depends on soil friction angle Qlimit =(0.5 Pa Nq* tan Ø ) Ap

27. 3-Determination of skin resistance It can be calculated by using the following formula: QS =∑ {P*∆L*f } Where: ∆L : Length of the pile P : Perimeter of the pile f : Frictional factor

28. The following table presents the dimensions of piles and their capacities in (KN).

29. Summary of piles sizes, number of piles needed, cap dimensions:

30. The structural pile design depends on the nature of soil, which is either stiff or weak, the pile is to be designed as short column if the soil is stiff , and designed as along column if the soil is weak. • The minimum area of steel is 0.5% of the gross area of the pile, also the ties are used starting with 5 cm spacing and ending by 30 cm spacing .the concrete cover must be not less than 7.5 cm. Asmin=0.005Ag

31. Efficiency of pile group • The efficiency of the load-bearing capacity of a group pile may be defined as: M= Qg(u ) / ∑Qu Where: Qg(u)= ultimate load bearing capacity of the group pile. Qu= ultimate load-bearing capacity of each pile without the group effect • Using simplified analysis to obtain the group efficiency as shown in the following formula: ζ = (2(m+n-2) + 4D) / (p×m×n) Where: m: # of piles in the direction of Lg. n:# of piles in the direction of Bg. d: Spacing between piles centers. D: Diameter of the pile P: Perimeter of pile cross section

32. Design of a pile cap: • The minimum distance between two piles is 3D. • Pile caps should extend at least 15 cm beyond the outside face of exterior face of exterior piles. • The minimum thickness of pile cap above pile heads is 30 cm. • The cover in pile caps commonly ranges between 20 & 25 cm . Design Steps: • Assume depth (d) • Check Punching shear : ΦVcp > Vult, punching • Check wide beam shear : ΦVc > Vult • Calculate area of steel needed • Check ρmin. < ρ < ρmax.

33. Retaining Wall Design: The retaining wall is designed by PROKON Program :

34. Conclusions: 1) From soil report, we note that PI is 25 and cohesion is zero and this can be explained by the following: We have soil contains some clay between gravels, and when we take a sample of this soil to be tested for atterberg limits to determine PI,we use sieve #40 and we take the passing which are clay particles and in turn this leads to increase the magnitude of plasticity index. Cohesion is zero since the soil sample is almost gravel. 2) After designing the two alternative choices (single footings and piles system) & surveying the quantities for concrete only, we find that it is more practical, realistic and economical to use single footings 3) there is no need to make settlement calculations for footings and piles ,since we have a gravely soil with B.C of 3.5 kg/cm2(the settlements in our situation are tolerable, so we can ignore them)..

35. Thank you for listening