A Self-Learning Manual - Institution of Engineers Mauritius

More documents

Recommendations

Info

A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU 16. In designing mini-piles, should the strength of grout be neglected during assessment of loading carrying capacity? (MP3) In designing min-piles, there are two approaches available: (i) In the first approach, the axial resistance provided by the grout is neglected and steel bars take up the design loads only. This approach is a conservative one which leads to the use of high strength bars e.g. Dywidag bar. One should note that bending moment is not designed to be taken up by min-piles because of its slender geometry. (ii) In the second approach, it involves loads to be taken up by both grout and steel bars together. In this way, strain compatibility requirement of grout and steel has to be satisfied. 17. What are the considerations in determining whether casings should be left in for mini-piles? (MP4) Contrary to most of pile design, the design of min-piles are controlled by internal capacity instead of external carrying capacity due to their small cross-sectional area. There are mainly two reasons to account for designing mini-piles as friction piles: (i) Due to its high slenderness ratio, a pile of 200mm diameter with 5m long has a shaft area of 100 times greater than cross-sectional area. Therefore, the shaft friction mobilized should be greater than end resistance. (ii) Settlements of 10%-20% of pile diameter are necessary to mobilize full end bearing capacity, compared with 0.5%-1% of pile diameter to develop maximum shaft resistance. Left-in casings for mini-piles have the following advantages: (i) Improve resistance to corrosion of main bars; (ii) Provide additional restraint against lateral buckling; (iii) Improve the grout quality by preventing intrusion of groundwater during concreting; (iv) Prevent occurrence of necking during lifting up of casings during concreting. 206
A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU 18. What is the purpose of post-grouting for mini-piles? (MP5) Post-grouting is normally carried out some time when grout of the initial grouting work has set (e.g. within 24 hours of initial grouting). It helps to increase the bearing capacity of mini-piles by enhancing larger effective pile diameter. Moreover, it improves the behaviour of soils adjacent to grouted piles and minimizes the effect of disturbance caused during construction. In essence, post-grouting helps to improve the bond between soils and grout, thereby enhancing better skin friction between them. During the process of post-grouting, a tube with a hole at its bottom is lowered into the pile and grout is injected. The mechanism of post-grouting is as follows: the pressurized grout is initially confined by the hardened grout and can hardly get away. Then, it ruptures the grout cover and makes its way to the surrounding soils and into soft regions to develop an interlock with harder soil zones. In order to enhance the pressurized grout to rupture the initial grout depth, a maximum time limit is normally imposed between the time of initial grouting and time of post-grouting to avoid the development of high strength of initial grout. Consequently, the effect of soil disturbance by installation of casings and subsequent lifting up of casings would be lessened significantly. 19. What is the purpose of shaft grouting for friction barrettes? (MP5) For the construction of friction barrettes, some grout pipes are designed at the periphery of the barrettes. Within a short duration (e.g. 24 hours) of concreting of barrettes, the fresh concrete cover is cracked by injecting water. After that, shaft grouting is conducted where the grout travels along the interface between concrete and soil and compacts the surrounding soils which are loosened or disturbed during excavation. The hydraulic fracturing of surrounding soils by grout during the grouting operation generates planes of higher shear strength. The grout would penetrate and improve the strength of soils around the barrettes. 20. What is the value of micropiles when compared with bored piles and driven piles? Micropiles are defined as bored piles with diameters not exceeding 250mm. Micropiles were first constructed in Italy in 1950s and were given the name “root piles”. Whenever bored piles (larger diameter) and driven piles are considered 207
Page 1 and 2:
A Self-Learning Manual Mastering Di
Page 3 and 4:
Page 5 and 6:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156: A Self-Learning Manual Mastering Di
Page 205: A Self-Learning Manual Mastering Di
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
Page 269 and 270:
Page 271 and 272:
Page 273 and 274:
Page 275 and 276:
Page 277 and 278:
Page 279 and 280:
Page 281 and 282:
Page 283 and 284:
Page 285 and 286:
Page 287 and 288:
Page 289 and 290:
Page 291 and 292:
Page 293 and 294:
Page 295 and 296:
Page 297 and 298:
Page 299 and 300:
Page 301 and 302:
Page 303 and 304:
Page 305 and 306:
Page 307 and 308:
Page 309 and 310:
Page 311 and 312:
Page 313 and 314:
Page 315 and 316:
Page 317 and 318:
Page 319 and 320:
Page 321 and 322:
Page 323 and 324:
Page 325 and 326:
Page 327 and 328:
Page 329 and 330:
Page 331 and 332:
Page 333 and 334:
Page 335 and 336:
Page 337 and 338:
Page 339 and 340:
Page 341 and 342:
Page 343 and 344:
Page 345 and 346:
Page 347 and 348:
Page 349 and 350:
Page 351 and 352:
Page 353 and 354:
Page 355 and 356:
Page 357 and 358:
Page 359 and 360:
Page 361 and 362:
Page 363 and 364:
Page 365 and 366:
Page 367 and 368:
Page 369 and 370:
Page 371 and 372:
Page 373 and 374:
Page 375 and 376:
Page 377 and 378:
Page 379 and 380:
Page 381 and 382:
Page 383 and 384:
Page 385 and 386:
Page 387 and 388:
Page 389 and 390:
Page 391 and 392:
Page 393 and 394:
Page 395 and 396:
Page 397 and 398:
Page 399 and 400:
Page 401 and 402:
Page 403 and 404:
Page 405 and 406:
show all

A Self-Learning Manual - Institution of Engineers Mauritius

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?