Excavation monitoring system is used to provide safety during excavations for construction works. Objectives and types of monitoring systems are discussed.
Past excavations were carried out based on conservative design concepts and by using shallower excavation depths. This have resulted in construction calamities, even though they are fewer in number.
But recent years have undergone a large development in different segments of construction activities. This have influenced the excavation activities by the prominent use of deeper excavations.
Most of the deep excavations are carried out in highly and densely populated areas. Huge damage and loss to the property have been encountered by such activities.
The civil engineering field have undergone significant development in construction procedures related with the analysis, design and construction techniques. But a proper solution for facing the dynamic behavior of works dealing with excavations has not be developed.
So, this makes it compulsory to have a monitoring system for the excavation process that is well arranged so that concerns relating to the safety, loss of life and property during excavation can be minimized.
Objectives of Excavation Monitoring Program
The main objectives of an excavation monitoring program are briefly explained below:
- To have safety of excavation
- To ensure the surrounding safety
- To check whether the design conditions are followed
- To follow the long - term behavior
- To have legal judgment through the supply of factual materials and information
Objective 1: Ensuring Safety During Excavation
Most important and primary objective in the case of excavation monitoring program is to ensure there is safety factors from the start to end of excavation work. Any calamity or issues that is going to occur as a result of excavation process surely brings some symptoms or warning before the occurrence.
These conditions must be monitored and evaluated by the monitoring system members so that the engineers can adopt effective measures for stopping the calamity from happening. Every sign of danger must not be ignored by the monitoring team.
Objective 2: Safety of the Surroundings
Most of the excavations are carried out in areas that are either densely populated or areas are busy or the commercial area. There are many underground constructions already present in these dense area, which must not be in no case affected by future excavation process.
Any newly planned excavation process must not bring adverse effects to the surrounding buildings, or underground pipes and foundations, or bring soil distress or deformation, public utilities or pedestrians.
All the above factors have to be considered while designing by the designer in charge. The monitoring system is developed based on these concerns so that safety of people and property is of primary importance.
Objective 3: Confirming to the Design Conditions
In most cases, the design conditions won’t satisfy with the actual conditions of the site. The main reason behind this is that the existing analysis theories are not matured to a satisfactory level and the geological conditions and consideration cannot exactly represent the in-situ conditions. They lack the to properly adapt the complications faced in the construction environment.
But if we go for back analysis with the help of results from the monitoring and use this as the basis for correcting the original design, there is large economy and similarity brought to the construction.
This method brings more realistic design based on the construction environment. A design is evolved by analyzing all the issues going to happen in the site in a predetermined manner.
This method reduces the cost of construction, bring a decrease in excavation period and a change in the design basis. For similar kind of designs, these produced design methods can be used again. This helps in the enhancement of excavation techniques.
Objective 4: To have and follow a long - term Behavior
Once an excavation and construction work of an important project have been finished, a monitoring system can be set up and retained in order to facilitate the long term follow up. This helps in studying the long - term behavior of the case.
This is a kind of case study conducted so that it conforms to the original hypothesis. This can help as a base to repeat the same technique for similar works with confidence and proof of long term performance.
Objective 5: Supply of Factual Materials and Information for Legal Judgment
If in case the work carried out is faced by a calamity or property damage, all the evidential data relating to the work can be provided by those information that is provided by the monitoring system. This also provides the construction records.
These materials helps to analyze the true causes behind these calamities thus avoiding any disputes relating to the same. This further helps the restoration and compensation work to be carried out with ease.
General instruments that are used for geotechnical needs and investigation can be used for the monitoring of excavation works. There are special instruments developed for the monitoring of excavations, that involve the following peculiarities:
- Monitoring the time period
- Measuring the Impact on the environment
- Find the economic factors
- Measure change in stress and strain in structures and the soil
Basic Elements of Excavation Monitoring System
The field performance is mainly monitored on the basis of parameters like deflection, stress, strain and many other physical quantities. The most commonly employed monitoring items in the excavation process includes:
- The structure or the soil movement
- The structures or soil’s stress or strain
- The water level and the water pressure
The objects that are monitored in the movement of soil and structure includes:
- Lateral Deformation of the soil
- Lateral deformation of the soil
- The building tilts
- The settlement of the ground surface
- The settlement of the buildings
- The uplift of the central post
- The heave of the excavation bottom
The objects that are measured in the stress and strain includes:
- The strut loads
- The stress of the retaining structure
- The earth pressure exerted on the wall
The measurement of water pressure includes:
- Water pressure that is within the excavation zone
- The water pressure that is outside the excavation zone
- The water pressure that is on the retaining wall
The type of monitoring system is not a primary factor in monitor program of excavation process as long as the instrument used is accurate, feasible and meets the budget. The instruments used for monitoring the excavation process can be either
- Electronic Type
- Non – electronic Type
The electronic type of instruments is very sensitive and are very easily read. These instrument type can be composed into a monitoring system that is either automatic or semi-automatic in nature.
The installation process and the surrounding environment highly influences the precision of measurement and the reading value that is obtained. The instrument used must be examined regularly so that the long - term measurement and monitoring of the excavation can be carried out accurately.
So, durability is a primary factor when we decide to install an electronic instrument in the site for measurement, that it requires special attention.
In order to measure the movement of the soil or the structure the instruments that are used for plane surveying like the tapes, the theodolites can be used. The tilt angle can be measured by means of electronic instruments or by plane surveying.
The stress or strain measurement can be measured by strain gauges or the electronic transducer that takes the strain gauge as the measurement unit.
Type of Monitoring Systems for Excavation Work
The monitoring systems can be of three types:
- Manual Systems
- Automatic Systems
- Semi - Automatic Systems
The manual system requires human to read the values irrespective of whether it is electronic or mechanical type. The automatic system has electronic sensors that is connected to a computer system.
For every monitoring instrument, the respective measurement is taken from the computer. This help in obtaining continuous values of measurement. The automatic systems are expensive but effective. The troublesome in human reading can be avoided by this method. This is many applied to excavation projects and where sensitivity to environment is high.
The semi-automatic system makes use of automatic system for the crucial parts and counts on human reading for other parts. Here the data are obtained through computer system by the wireless connection.
The data are collected from the data logger by the engineers. This method helps in saving the cost. This method also provides continuous values.