Recently, it was learned from Wuhan Zhengyu Kechuang Geotechnical Engineering Co., Ltd. that after excavation of the Wuhan Broadcasting and Television Omnimedia Center project site undertaken by the company, the effect of the waterproof curtain has been highly recognized by the owner, the SMC method has once again received praise, and the Shanghai Jintai SMC drilling rig has once again stood out in a landmark building.

According to the pumping connectivity test report of the project, when the water level inside the pit dropped to the elevation required by design and construction, the pumping volume inside the pit was 242m³/h. Based on regional experience, the waterproofing effect of the SMC bottom-seated waterproof curtain is good.

This test result is exciting news for both Shanghai Jintai and Zhengyu Kechuang.‍

Project Overview - Broadcasting and Television Omnimedia Center Project

The foundation pit of the Wuhan Broadcasting and Television Omnimedia Center project is adjacent to Wuhan Rail Transit Lines 2 and 3 and has a large excavation depth. The construction party and the subway group attach great importance to it. Zhengyu Kechuang, as the construction unit of the SMC method, regards the project as the company's annual key project.

Up to now, the foundation pit has successfully completed the excavation of the first basement floor. During the entire excavation process, groundwater control was good. Monitoring data of the adjacent Wuhan Rail Transit Lines 2 and 3 and surrounding areas show that the cumulative settlement and change rate are within the alarm value range, with no abnormalities.‍

Current status of foundation pit excavation

The excavation area of the Wuhan Broadcasting and Television Omnimedia Center project is about 25,000 m², with a general excavation depth of 18.55 m and a maximum depth of 20.55 m in the pit-in-pit. The SMC bottom-seated waterproof curtain is adopted, and the wall depth is designed to enter the strongly weathered rock layer by 1 meter, with an effective wall length of 43.0~45.0 meters.

Schematic diagram of the relationship between the foundation pit and the subway

Wuhan Zhengyu Kechuang Geotechnical Engineering Co., Ltd. focuses on the construction of ultra-deep cement-soil waterproof curtains and the promotion of construction methods. It is one of the strategic partners of Shanghai Jintai Engineering Machinery Co., Ltd. and a firm practitioner and supporter of Shanghai Jintai's SMC method technology and equipment! Looking back at the trial wall stage of the project, Zhengyu Kechuang, together with Shanghai Jintai, held multiple internal discussion meetings, formulated a detailed and feasible trial wall construction plan, and strictly implemented it. Three trial walls (with different parameter combinations) were constructed. The 14-day core drilling test results showed that the wall integrity, strength, and rock penetration depth all met the design requirements, and were recognized by all parties involved in the project, smoothly entering the formal construction stage.

On-site construction photo of the Broadcasting and Television Omnimedia Center project

Wall integrity is the top priority in the quality control of cement-soil mixing walls. Shanghai Jintai and Zhengyu Kechuang have been continuously exploring and innovating on the issue of wall integrity, spending more than one million yuan, continuously improving cutting tools, trying various drilling and mixing methods and grouting methods, paying attention to details, trying various combinations of drilling and lifting speeds, grouting parameters, milling wheel rotation directions and speeds, etc., and conducting core comparisons one by one, accumulating rich experience. They have a thorough understanding of which parameter combination should be used for which geological conditions, and finally achieved results in the Broadcasting and Television Omnimedia Center project. The third-party core drilling test results show excellent wall quality.

Example of third-party test core samples

Before the formal excavation of the foundation pit, Wuhan Survey and Design Co., Ltd. conducted a pumping connectivity test. Through on-site pumping tests and recovery tests, the characteristics of water level changes in deep confined water caused by pumping were observed and grasped, mainly achieving the following objectives:

(1) Determine whether the closure of the waterproof curtain and the dewatering effect can meet the design requirements;

(2) Qualitatively analyze and judge the waterproofing effect of the bottom-seated curtain. Predict and evaluate the impact of foundation pit dewatering on surrounding ground settlement and the surrounding environment;

(3) Verify the drainage capacity of the drainage system around the foundation pit;

(4) Guide the secondary detailed design of project dewatering through the connectivity pumping test;

(5) Through the accumulation of multiple projects, obtain the hydraulic connection and seepage patterns inside and outside the pit under the condition of bottom-seated waterproof curtains.‍

After more than a month of rigorous testing, the report issued by Wuhan Survey and Design Co., Ltd. reached the following conclusions:

(1) The foundation pit area is about 25,000 m². By opening the dewatering wells, the water level inside the pit can be stabilized at an absolute elevation of 0.5~1.9 m. The total pumping volume inside the pit is 241.9 m³/h, equivalent to the output of four 60 cubic meter pumps;

(2) The maximum drawdown of the water level in the observation wells outside the pit is between 1.75 and 3.17 m;

(3) Based on regional experience, the waterproofing effect of the SMC bottom-seated waterproof curtain is good, and the foundation pit has the conditions for continued excavation.‍

Summary chart of water level curves inside and outside the pit

Summary chart of water level curves inside and outside the pit and line chart of water output per half hour

Supplementary experiment - general chart of water level trends in adjacent observation wells inside and outside the pit

Overall Evaluation

The pumping connectivity test report inside and outside the pit compiled by Wuhan Survey and Design Co., Ltd. is relatively comprehensive, and the monitoring data are basically credible. After improvement, it can guide subsequent work.‍

Opinions and Suggestions

The test results show that when the water level inside the pit drops to the elevation required by design and construction, the pumping volume inside the pit is 242 m³/h. Based on regional experience, the waterproofing effect of the SMC bottom-seated waterproof curtain is good. After improvement according to the following opinions, the foundation pit has the conditions for continued excavation.‍

The pumping connectivity test results have been unanimously recognized by experts and the subway group. Currently, the foundation pit is being excavated in an orderly manner, drawing a successful conclusion to 2022 and indicating further progress in 2023!