geological investigation & land slides(2)

 Limitations of Drilling

                                                                                                  Drilling alone will not give all correct   information

Care has to be taken to over come limitation of drilling.                                                                                                                           Drilling is method of sampling its results depends on  uniformity and consistency  of rock formation in which drilling is carried out .This presumption may not be always be justified as rock often  have variable characters.

                                                                                                            It gives  Little information by more visual observation  expert interpreter is required for extracting information form the core.

                                                                                                      There is great scope for human error at every step or drilling. Ignorance of proper procedure or negligence to  carry  them out  will lead to loss important  data and also misleading results.

Common error are                                                                                                                                                                                           a)  Not working out geological  structures by surface work before drilling

                                                                                                          b)  Not    determining space depth location    of drill hole with reference to  geological structures.

                                                                                                            C) Not making all necessary observation  during drilling                            

 D) Logging and interpretation   of core by trained personnel

                                                                                                         e)Failure  to record all observation properly

                                                                                                             f) Important   features may be missed unless special procedure such as angle holes etc

                                                                                                           g) To avoid human error drilling must  be carried out by trained personnel with local geology.

Core Recovery –

Drill machine have  capacity to drill continuously for 1.5 or  3m this is called RUN at the end of every run the core raised to the ground is called draw.

                                                                                                            After run 1.5 m normally the length of core recorded is expected 1.5 m  in practice the length may be 1.5 m. The deficiency is called core loss.

                                                                                                            The length of core obtained is called core recovery it  is express in percentage.

                                                                                                            If  0 . 75 m core is recorded after drilling through run of 1.5 m core loss is 0.75 m and recovery is 50 %  Core recovery will indicate the condition of the rock .

                                                                                                            Core recovery will be good in hard rock and poor in soft rock.