No Dig India Show 2024
14th International Conference & Exhibition on Trenchless Technology
Solutions for Water, Wastewater, Oil & Gas, Electricity & Telecommunication Utility Industry
18th & 19th November 2024
Panaji, Goa, INDIA
Why dig Trenches when there are better solutions
9. Participant Comments
. Ground level training needs to be implemented for maximum engineers involved.
. There is a need to trained to use Trenchless Technology the more people of urban / M.C. of the state. It is better to use in future expansions.
. Such programme of introduction of this technology inclusive of the level of administrator will be needed.
. The workshop is very interesting and gain lots of knowledge.
. A good mix & match of both theory & practice. In depth coverage of the relevant topics.
. The workshop experts should focus o the subject matter and not on their company profile. We are in a technical workshop rather than in a business meet.
. ADB training programmes very good. I suggest that this type of programme will be done regularly.
. Needs to held seminars at ground level with some demonstrations. So that executing agencies get familiar to the technology.
. Details of specific case studies should be presented for at least one completed project.
10. Participant Recommendations
. Comparative economical status will be more useful.
. New technologies may be supplemented by more animations, movies and field visits.
. For improving the course design / topic we want to include more practical, experience video clips or problem difficulties face during the execution.
. It would be appropriate to incorporate ground facts through preparation of video clips on execution & problems faced in execution in urban projects of J&K. this would help arriving at solution through trenchless technology.
. There is always a scope for further improvement. All arrangements can be made for staying all the participants at one place so that there may be more interactive sessions.
. Be specific to technical & economical aspects of the issue.
. Case study impediments, execution & lessons learnt.
. For further improvement the course should be longer time. I want to include some practical aspect of the trenchless technology.
. Contractual documentation of trenchless technique project.
. Detailed discussions on risk mitigation, measures as well as avoidance of hazards.
11. Clarification requests by participants
. Controlling deviation in respect of horizontal as well as on vertical plan during execution i.e. laying of pipes at given grade and directions.
. All over the country sewerage project has always face problems in urban area. It will be quite necessary to clarify for the problem
. How far HDD technique to going to help for situation in J&K.
. We may take up some practical issues with IndSTT & seek their advice on the solutions
. Economic compassion of various trenchless techniques.
12. Clarifications from experts
In addition to written points following points were asked by different participants. The section also provides response by the experts.
Participant question |
We are developing a sewerage pipeline with a grade of 1 in 300 and have to select appropriate trenchless technique. What techniques can be use? |
Expert respnose |
You need to address various end conditions before you select a specific technique for your project. Please refer the Trenchless Technology Selection Guidelines being provided to you for the decision process. Here you will find different technique selection forms that can help in arriving at the appropriate decision. |
Participant question |
What are the rates of various techniques? |
Expert respnose |
Rates of trenchless techniques depends on various factors like soil type, pipe materials, installation length, etc. and needs to be calculated for each project on the basis of such inputs. IndSTT is developing the standard formats for analysis of rates for different approved trenchless techniques that would assist the project engineers to evaluate such rates. For generic evaluation IndSTT has published the schedule of rates of approved trenchless techniques and revises the same each year. You can refer to that for further inputs. In addition IndSTT has published the standard scope of works for approved trenchless techniques. These can assist you to analyze the rates till the formats are available. |
Participant question |
We intend to do the entire subsurface mapping of our city areas. What software are used under Subsurface Utility Engineering? |
Expert respnose |
Subsurface Utility Engineering is a working system for acquiring the information of utilities laid below the ground and any GIS can be used for plotting the data surveyed. While developing the contract document you must prescribe the methodology rather than GIS system. |
Participant question |
We note that while developing the contract documents some of the project owners tend to indicate that the geotechnical data is for reference purpose only. What are your opinions about this practice? |
Expert respnose |
By following this practice the owners try to transfer the risk on the service providers and in case there is any geological surprise faced the costs and the delays can be placed on the service provider. But one also needs to understand that the delays, and in case of damage, flawed utility is left for the owner and as the pipe is buried in the ground there could be a possibility that it may be un-retrievable and owners may have to use such item on a as is where is basis. |
Participant question |
So what can be the remedy to this situation? |
Expert respnose |
See, the most ideal solution should be providing completely dependable data. This helps in reducing the bid costs at one hand and optimizes project durations. But the data must be reliable. In case this is not possible, you may consider providing SUE Quality attributes of the information provided to the bidder. For an example if you indicate the quality level be ‘B’ and define the attributes of level ‘B’ the bidder would know that the extent of dependence on such data. Take for an example if you contract for Hard Rock tunneling but the geotechnical conditions are not Hard Rock and the quality attribute of the data provided are ambiguous an incorrect equipment could be deployed at site. If the attributes are defined, the service provider could take necessary decisions before ordering or deploying the equipment at site and avoid failures. |
Participant question |
You have explained that the geotechnical surveys can produce reliable data. Can we exclude the bore hole surveys from our projects completely? |
Expert respnose |
Geotechnical surveys can provide a good amount of subsurface data but the information needs to be calibrated from the site information. Site boreholes, therefore cannot be completely replaced. The numbers however can be substantially reduced leading to great savings there. |
Participant question |
We are executing a pipe jacking project where we have 1800mm dia casing pipe with a lesser dia carrier pipe. Why should we have casing pipe at all? We can provide internal and external protective coating to the pipe and use it directly. |
Expert respnose |
Theoretically it is possible, but you may not remove the casing pipe as in case you remove the casing pipe and install the carrier alone, the repairs or replacement of the buried pipe at a later date may be difficult and you may have to go for expensive rehabilitation works. However in case you have budget constraints and are open to go for rehabilitation after usage you may make necessary evaluation of the protective coatings needed and apply the same before installation. An expert advice would be quite important in such case. |
Participant question |
We are executing a manual pipe jacking work under two dry canals. At a particular location we are encountering excessive water pressure and ingress of ground water in the excavated space though the natural water table is quite deep at this location. We have dewatering units installed at excavation levels but the water ingress is not stopping. How can we continue jacking works? |
Expert respnose |
There can be more than one solution to this problem and without a proper site investigation and understanding these must not be attempted blindly. From the face value it is expected that the situation is as depicted above. One can try to go Sheet Piling or enhancement of excavation and pipe jacking pace so that the water pocket section can be isolated. However if isolation is not possible dewatering will be the only option. The caution however is that as the natural water table is deeper, local dewatering may not be helpful, since it will fail to create complete drawdown and lower water table. The dewatering needs to be done from below the level of normal water table. This will create hydraulic gradient headed towards the lowered water table as explained in the image and thereby stop the water ingress in the cavity. |
Participant question |
In the same problem we intend to pump bentonite on the face to stop water ingress. Can this work? |
Expert respnose |
As you are executing manual jacking this exercise may also make the manual excavation works difficult if not impossible. We would not like to suggest doing that. |
Participant question |
You have discussed failures in Kota project. As service provider did you undertake the risk mitigation measures before starting the project? |
Expert respnose |
The contract as explained was of Hard Rock tunneling and in realty the strata was different leading to such difficulties. As engineers we did not have that opportunity available to us since the complete working methodology was frozen before the contract was tendered. It had to be done before the tendering process since the tunnel excavation equipment and related support equipment have to be planned as per the bid requirement. For an example if you wish to tunnel a sandy strata the cutter head would be entirely different from clay strata, the slurry system to transport may also be different. All such equipment has to be recorded in the bid submittals and if you want to change that you will have to go for major deviation from the bid specifications. Generally no client agrees for such deviations since this would create problems in turn during the bid evaluation period. Please remember, it becomes too late to change any working method, if you have invited the bids. Generally, other than geotechnical risk, any service provider would take all necessary risk mitigation measures but if the failures stem from there you cannot avoid failures. |
Participant question |
We note that there would be annulus created around the jacked pipes. What is the method of filling the annulus in a microtunneling? |
Expert respnose |
Generally the annulus is filled with the bentonite slurry released from the shield. This slurry helps the pipe to float in the tunnel. In case of longer drives pin-loop systems are employed. These are solenoid operated valves that inject bentonite in the surrounding soil. |
Participant question |
How Microtunneling machines works under the water table? |
Expert respnose |
Microtunneling machines in such cases are Earth Pressure Balance (EPB) machines. These machines function on the basis of balancing pressure of the Jacking forces and slurry pressures that are used to balance the hydraulic pressure of the ground water. In case the slurry pressure is not applied Ground water pressure would have to be balanced by jacking force alone that might damage the pipes being jacked due to increased stresses. |
Participant question |
How long pipe lengths are jacked? |
Expert respnose |
With the increase of number of pipe sections jacking forces also increases leading to higher stresses on the pipes. These are controlled through introduction of intermediate jacking stations at predetermined locations within the pipe string being jacked. These stations contain strings of jacks installed on the periphery of the station. The station helps in containing stress by limiting the jacking lengths by alternate operations. (Once the entry pit jacks are operated and once the jacks have expanded they are locked and then intermediate station jacks are extended leading to movement for pie sections ahead of the station. In the first instance only the sections behind the station are moved.) |
Participant question |
We have a situation in one of our projects where the local residents have encroached upon an open drain be covering it with slabs and built their houses over them. The drain is now clogged badly leading now to a regular pumping of the sewage every day. We have tried to de-silt the drain but this has led to damage to some of the houses directly over the de-silt area and we had to abandon the process. This pumping is becoming an expensive process. How can we stop this? |
Expert respnose |
In case the de-silting leads to collapse of above ground structure the most logical solution could be to go for open cut excavations and installation of pipes there. However in case this is not possible, as is evident from your case, you need to consider application of new installation methods with certain modifications to suit the site requirements. One would have to have a detailed look at the project site and impediments before taking any decision. |
Participant question |
Please clarify the control of deviation in respect of horizontal as well as vertical plan during execution i.e. lying of pipes at given grade and directions. |
Expert respnose |
Trenchless techniques are of two types, steerable and non-steerable. The first types are the techniques that could be used for your requirements. Further depending upon the alignment and grade requirements you can select the specific technique. For an example, if your grade and alignment requirements are less stringent you can use Horizontal Directional drilling. In case they are not that stringent you may have to use microtunneling. You can also use the casing pipe to control minor deviations. |
Participant question |
All over the country sewerage project has always face problems in urban area. It will be quite necessary to clarify for the problem |
Expert respnose |
Proper usage of Trenchless Technology can help in avoiding such problems in urban areas. Please note that IndSTT has published the standard operating procedures of which one copy is provided to you. If you apply it in your projects you can avoid many problems. You may also consider interacting with IndSTT for resolution of any specific problem in the trenchless field. |
Participant question |
How far HDD technique to going to help for situation in J&K? |
Expert respnose |
HDD provides a cost effective and fast solution to many subsurface construction challenges. It can help you to install pipes faster. Water tables do not have many effects on the operations. Mass excavation, in case of open cuts, is avoided. Machines can be erected faster and the entry and exit pits are not so complex as in pipe jacking. For any specific usage you may refer to Basics of Trenchless provided to you. In addition, IndSTT has published Code of Practice for HDD, HDD Good practices Guidelines, Contract documents for Consultants and contractors for HDD works, Schedule of Rates and General & Special Conditions of Contract apart from many more publications. You may refer to these books for further directions. You may also interact with IndSTT for your difficulties or requirements. |
Participant question |
We may take up some practical issue with IndSTT & seek their advice on the solutions |
Expert respnose |
IndSTT provides assistance to various project owners as Trenchless Mentors. You may refer to the IndSTT CD provided to you for details of the assistance. Should you need any further clarification you may contact IndSTT. |
Participant question |
Economic comparison of various trenchless techniques. |
Expert respnose |
We have provided the economic comparison of HDD and Pipe jacking to you. In addition the Schedule of Rates published by IndSTT provides unit rates of different techniques. This can be referred for further information. In fact financial comparison is one of the essential components of Trenchless Technology Selection process and you may kindly refer to those guidelines as well. |
ADB Report Part I | ADB Report Part II | ADB Report Part III | ADB Report Part IV |