The Xinjiang Fukang Pumped Storage Power Station in Western China, will supply hydropower energy to the major urban centres of the Xinjiang Changji Hui Autonomous Prefecture, delivering clean renewable energy to nearly 50,000 residents.

Global multi-disciplinary geoengineering company, GEODATA Engineering Spa, was assigned by the project manager, Northwest Engineering Corporation Limited, to provide technical consultancy and advisory services at the design stage for the excavation of the main powerhouse cavern. GEODATA used Seequent 3D geological modelling solution Leapfrog Works to assess the geological risk, verify the stability of the support system and communicate that risk to stakeholders.

Leapfrog Works is a fast and dynamic 3D subsurface modelling solution specifically designed for the Civil Engineering and Environmental industries. With Leapfrog Works, geological models can be easily combined with industry designs and flow models to give better insight and understanding.

GEODATA’s International Geoengineering Experts comment, “Leapfrog Works allowed us to very positively tackle the many challenges of this project. We were able to effectively present and analyse a huge mass of data alongside volumes of designed works and predict volumes to be excavated. Being able to rapidly visualise the geological elements, the designed works, and geomechanical information in 3D, was particularly helpful and had a great impact on the project. This 3D visualisation gave us clarity and aided our understanding and meant we were able to communicate with confidence.”

The Setting

Xinjiang Fukang Pumped Storage Power Station is located on Baiyang River. It is the first pumped storage hydroelectricity facility of Xinjiang Uygur Autonomous Region and will be completed and put into operation in 2020. The plant will be 70 kilometres from downtown Fukang and 130 kilometres from Xinjiang’s electric load centre of Urumqi. The installed capacity of the power station is 1200 MW and, according to the designed power utilisation of 1671 hours, the designed annual power generation capacity will be 2.006 billion kWh serving the Urumqi-Changii Grid that supplies nearly 50,000 people.

POWER HOUSE SITUATION BENEATH STEEP TOPOGRAPHY

The power station project consists of upstream and lower reservoirs, flood discharge structures, a water conveyance system, an underground powerhouse, and a ground switch station. The largest of the caverns to be excavated is the main powerhouse cavern which includes the main generator room, an erection bay and both main and auxiliary plants. At over 185 metres in length, 24 metres wide and 56 metres high, excavation and support of the main cavern is expected to be a critical part of the project.

The cavern structures will be supported with boltshotcrete, and the main plant crane beam will be a rock wall crane beam structure. Understandably, the investment in a project of this size is significant and it is therefore essential to establish a thorough understanding of the geological risks to minimise impact on the project’s progress, cost and success.

“We were able to effectively present and analyse a huge mass of data alongside volumes of designed works and predict volumes to be excavated. Being able to rapidly visualise the geological elements, the designed works, and geomechanical information in 3D, was particularly helpful and had a great impact on the project. This 3D visualisation gave us clarity and aided our understanding and
meant we were able to communicate with confidence.

The Response

At the beginning of 2018 GEODATA was assigned by Northwest Engineering Corporation Limited to provide technical consultancy at the detailed design work phase for the cavern complex. Their work commenced in May with GEODATA’s initial site visit and culminated in their final report release in October 2018. Leapfrog Works was used for geological modelling throughout this period.

GEODATA’s objective was to validate and if needed update the design of the proposed cavern support system, and ensure that it took into account the best understanding of the subsurface conditions that could be expected during the excavation and construction.

This meant evaluation of all available data regarding the geological setting as well as all available data regarding the excavation and support design to create a reference geological and geomechanical 3D model for the project. The creation of the 3D model allowed GEODATA to perform numerical analysis to evaluate the proposed support system and identify possible or necessary changes as well as specify the monitoring strategy.

Seequent’s civil engineering solution, Leapfrog Works, was chosen to give the best representation of geological and geomechanical data for the underground construction of the Power Station.

Effectively representing the mass of data A significant challenge on this project was how to effectively combine and present the huge mass of data available from very different sources and communicate the subsurface conditions in a tight time frame.

The types of data used included:

  • Borehole data, such as lithology, Geological Strength Index (GSI) and Rock Mass Rating (RMR) data.
  • Structural survey data taken from the adits (access tunnels) to the cavern, which was used to interpret faults and joints.
  • Engineering Design data for the three power station caverns, the penstock, safety access, tunnel access and the adits.
  • Topographical data.
ROCK MASS RATING (RMR) AND FAULTS AT POWERHOUSE CAVERNS. NOTE: ONLY TWO FAULTS ARE VISIBLE FOR SIMPLICITY

Leapfrog Works was used to combine all this data and the 3D model was used to predict excavation volumes and location of the different geomechanical units relative to the planned design elements. It also allowed the GEODATA team to provide a 3D interpolation of the structural geology data and a compelling 3D visualisation of the conditions for communication to their clients.

A PhD Geologist from GEODATA team commented “Leapfrog Works’ unique framework for heterogeneous information let us bring together data that normally would require different processing environments. This adaptability was a real benefit on this project”

Assessing the support structures

The first stage in assessing the cavern’s rockbolt and shotcrete support structure was to create a Leapfrog geological model from the borehole dataset and the designs of the Power Plant works developed in BIM modelling software Autodesk (Revit, Inventor). Structural data indicating faults and joints were then also incorporated into the model. Using Leapfrog Works’ rapid 3D modelling engine, GEODATA experts were able to produce different numerical scenarios of the GSI and RMR data. Being able to rapidly model these different scenarios allowed the modellers to gauge different outcomes, to cater more effectively for uncertainty and to reduce risk. As a final verification, GSI and RMR indexes distributions were combined with the structural framework of the faults to identify lower strength areas and intersection of faults with the main cavern.

A GEODATA team member explains “Leapfrog Works allowed us to easily and quickly go through the main issues that arose during the analysis, such as the consideration of structural data of the access and safety tunnels to make a global 3D assessment of geomechanical indices.

Outcome

Using Leapfrog Works, GEODATA experts were able to present and analyse a large volume of data including geostructural information and combine it with the designed works to calculate excavation volumes of different rock types. Leapfrog Works’ dynamic 3D modelling also enabled GEODATA to readily compare 3D surfaces of faults with geomechanics indexes (RMR and GSI). The ability to visualise all of the data in 3D alongside the designed works (such as the caverns) was important to the success of the project. Being able to readily compare scenarios also allowed a more qualitative geological interpretation to be rapidly incorporated into the workflow.

ASSESSING THE SUPPORT STRUCTURES’ SECTION

The benefits GEODATA experienced using Leapfrog Works included the ability to better communicate risk and the time savings made during the modelling process. One expert said the main benefit from using Leapfrog Works was its adaptability which allowed the team to easily communicate the interaction between the designed structures and the geomechanical information.”

Since this successful use of Leapfrog Works, GEODATA have gone on to upskill other members of their team in the use of the 3D subsurface modelling solution. Another benefit of the software is its intuitive interface which allows new users to become competent quickly. GEODATA says, “We now use Leapfrog Works with high frequency like our other commonly used software. Almost every project is now developed in Leapfrog Works.”

Pat McLarin, Seequent Civil & Environmental Product Manager, says, “Understanding and predicting subsurface conditions is key to project success in a case like the Fukang Pumped Storage Power Station project. Until now the industry has had to rely on manual and adhoc solutions borrowed from other workflows. Leapfrog Works is a dedicated solutionn addressing these workflow challenges. It’s great to see how GEODATA harnessed the power of Leapfrog by building a 3D model from a range of disparate data sources, combined with engineering designs – enabling better insight and decisions to be made.”

Leapfrog Works allowed us to easily and quickly go through the main issues that arose during the analysis, such as the consideration of structural data of the access and safety tunnels to make a global 3D assessment of geomechanical indices.