# Experimental Study of the Behavior of Rectangular Excavations Supported by a Pipe Roof
## 4 Conclusions  
This paper presented an experimental investigation of the mechanical behavior of a rectangular pipe-roof excavation. This study aimed at understanding the role of the pipe roof in the improvement of the stability of excavations using the pipe-roof technology. The experimental study was realized in a plexiglass box using an advanced monitoring system, which allows tracking of the soil settlement,  
Figure 21: Instability process development during a test with the pipe roof (\(C/D=1\), \(EI=1.0\)).  
the pipe deformation, the soil pressure and the instability surfaces. Tests were conducted in different configurations: excavation without the pipe roof, excavations with the pipe-roof with different values of pipe stiffness (\(EI=0.5\), \(1.0\) and \(2.0\)). The following conclusion may be drawn:  
1. The pipe roof can reduce the load on the excavation face and suppress the load fluctuation. The excavation stability increase with increasing pipe roof stiffness.
2. The presence of the pipe roof induces an important decrease in the ground settlement. Increasing pipe stiffness reduces the soil settlement, but the influence is weak. The pipe roof increases the range of the longitudinal settling tank and transmits the overburden pressure above the sliding block to the soil on both sides of the sliding block, which effectively reduces the surface settlement.
3. Under the same working conditions, the vertical deformation of the pipe roof is greater than the corresponding ground surface settlement and the range of ground settlement is larger than that of the pipe roof deformation.
4. The change in lateral pressure coefficient in the two directions reflects the formation of the soil arch in the overburden soil of the pipe roof and the pipe roof stiffness does not influence the distribution of the earth pressure coefficients.
5. Compared with the condition without the pipe roof, the pipe roof prevent the failure zone from extending to the ground surface and causes an increase of approximately 50% of the longitudinal width of the failure zone.  
The pipe roof reduces the soil settlement, which is a major concern of this technology, and reduces the earth pressure on the excavation face by the creation of an arch effect above the pipe roof. Meanwhile, the stiffness of the pipe roof is not key factor. So the pipe roof is suitable for the construction with environmental microdisturbance requirements. The experiment reveals the failure mode of the excavation face under the effect of the pipe roof, and the design methods should avoid excessive attention to gaining pipe roof stiffness when reducing environmental disturbances.  
[PERSON] conceived and designed this work. [PERSON] implemented the phsical experiments and data analysis. [PERSON] instructed [PERSON] to write the manuscript. [PERSON] and [PERSON] revised the work. All the authors have approved the submitted version of the manuscript, have agreed to be personally accountable for their own contributions and for ensuring that questions related to the accuracy or integrity of any part of the work, are appropriately investigated, resolved, and documented in the literature.  
This research was funded by National Key R&D Program of China (2018 YFC0809601, 2018 YFC0808702), National Nature Science Founds of China (51778476) and Shanghai Science and Technology Development Funds (17 DZ1204203, 18 DZ1205200).  
The authors declare no conflict of interest.The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.