การคำนวณ Blow Count งานตอกเสาเข็ม
การทดสอบ Blow Count เราจะใช้สำหรับประเมินกำลังรับน้ำหนักของเสาเข็มตอก (Driven Pile) ซึ่งจะใช้กับเสาเข็มทุกต้น โดยมีสูตรที่ใช้คำนวณหลายสูตรด้วยกัน แต่ในที่นี้จะขอยกตัวอย่างการคำนวณ Blow Count ด้วย Danish’s Formular ดังนี้
| Blow Count Calculation | |||||
| Project :- | |||||
| ก่อสร้างอาคารเรียนโรงเรียนวัดพิพิธประสาทสุนทร (พิพิธวิทยาคาร) | |||||
| Danish’s Formula:- | |||||
| Qu = [eWh]/[S+(eWhL/2AE)1/2] | |||||
| Qu | = | Ultimate bearing capacity | |||
| W | = | Weight of hammer | |||
| h | = | Height of drop hammer | |||
| S | = | The average subsidence of the pile by hammering the last 10 (S) | |||
| A | = | Cross section area of pile | |||
| e | = | Equipment loss factor | |||
| L | = | Length of pile | |||
| Criteria:- | |||||
| SQ | = | Section of pile | = | 22 x 22 | cm. |
| A | = | Cross section area of pile | = | 484 | sq.cm. |
| L | = | Length of pile | = | 2100 | cm. |
| Qa | = | Allowable bearing capacity or Safe load | = | 25 | Tons |
| W | = | Weight of hammer | = | 3.5 | Tons |
| h | = | Height of drop hammer | = | 30 | cm. |
| e | = | Equipment loss factor | = | 0.8 | |
| (e = 1.00 for Free failling hammer or e = 0.80 for Drop hammer with friction winch) | |||||
| FS | = | Factor of safety | = | 2.5 | |
| fc’ | = | The specified compressive strength of concrete at the age of 28 days | = | 350 | Ksc |
| Resalt:- | |||||
| E | = | Elastic modulus of concrete | = | 282.5 | Tons/sq.cm. |
| Qu | = | Ultimate bearing capacity | = | 62.5 | Tons |
| S | = | The average subsidence of the pile by hammering the last 10 (S) | = | 0.541 | cm. |
| The average subsidence of the pile by hammering the last 10 (S) does not exceed | 0.541 | cm. | |||
| The last 10 blow should be than or equal to | 5.41 | cm. | |||
| If the number of times in the hammer 30 cm. (1 ft.) greater than or equal to | 55 | times | |||
