11.6 Plan of Monitoring Systems
A complete plan of a monitoring system should include the following items：（1）determination of the monitoring parameters；（2）determination of the locations of the monitoring instruments or devices；（3）analyses of the prediction values of the parameters；（4）choice of the specifications of the monitoring instruments；（5）determination of the installation specifications of the instruments；（6）setting of the alert and action levels；and（7）determination of the measurement frequency.According to the sequence of execution，they are elucidated as follows：
（1）Determination of the monitoring parameters
Excavation⁃related materials are soils，retaining walls，and struts.Excavation will produce physical quantities such as stress and strain on，and displacement of these materials，which can be measured by using instruments.Considering the cost，it is impossible to measure every physical quantity within the excavation influence range.Thus，suitable parameters have to be determined according to the excavation scale，geological conditions，and the situations of adjacent properties.
（2）Determination of locations of the monitoring instruments
The measurement parameters determined，what follows is the selection of the locations and embedment depth of the instruments.The proper locations and embedment depths of the instruments should be able to unveil the excavation behaviors and the physical quantities representing the critical conditions of excavation.
（3）Analyses of the prediction values of the parameters
According to the soil properties，the type of the retaining wall and the excavation conditions predict the monitoring parameters for each of the excavation stages.The methods of prediction，including the simplified method，the beam on elastic foundation method，and the finite element method，are as elucidated in Chapters 5 and 6.The prediction results are not only helpful to the determination of the specifications of instruments but also useful to the setting of the alert and action levels.
（4）Choice of the specifications of the monitoring instruments
With the monitoring parameters for excavation stages，the specifications of the instruments can be then determined.
（5）Determination of the installation specifications of the instruments
Whether the monitoring parameters are accurate affects the judgment of the excavation safety.Though the precisions of the instruments are important，whether they have been correctly installed also influences the measurement results.As a result，appropriate installation specifications have to be mapped out according to the characteristics of the instrument and the geological conditions.
（6）Setting of the alert and action levels
The alert level is an important index for the judgment whether the excavation is under normal conditions.The action level is the value indicating the immediate necessity of measures to be taken.Before excavation，the alert and action levels for each excavation stage should be determined in advance.
（7）Determination of the measurement frequency
The measurement frequency refers to the times of the measurement taken within a certain period.Basically，the measurement frequency has to be increased during the process of excavation.