just by pressing a button without the sea horizon to turn to,we should know clearly the relationship between the accuracy of zenith distance observed and the accuracy of a position fixed,the causes of the errors of zenith distance observed,what accuracy of zenith distance observed could be obtained and what accuracy standard should be used.

The paper expounds the principle and the method of measuring zenith distance for celestial positioning based on the direction of gravitational force line.

The pipe driving construction method characteristics,pipe material choice,pipe driving force calculation and apex distance determination,working pit and receiving pit selection and size determination were analyzed.

The distribution characteristics of initial rock stress in the tectonic stress type mine is analyzed first in the paper,and numerical simulating analysis is used to make analysis of the top-collapsing and failure forms of roof rocks at the western part of Chengchao Iron Mine,which could be theoretical basis to forecast and control the underground roof accidents.

Finite element method is used to make an analysis of the underground stress redistribution at the western part of Chengchao Iron Mine during top-collapsing process, and a theoretical basis has been provided to determine correct sequence of caving and forecast and control the underground stress.

On the basis of some actual projects,such parameters as wall-rock loose loops and unsupported roof span are provided for Qianling Iron Mine,which can be used as reference and guide for similar projects.

To study the stability of surrounding rock in coal entries,rational unsupported roof distance was obtained ty thin plate theory;which supplied the theoritical base for the surrounding rock control in Daning mine,helped to raise exacavation efficiency and insure safe production.