Page 20 - THEi Student Applied Research Presentations 2025

IMPLICATION ON KICK-OUT CAPACITY
OBJECTIVES
Study the moment behavior between
the multi-strutting ELS with and
without the additional strut at the last
level under different circumstances.
ABOUT THE INVESTIGATOR
I am a civil engineering student who
enjoys analysing complex structural
systems and exploring ways to
improve construction safety. Through
this project, I have developed greater
confidence in using simulation
tools. I hope to gain more hands-
on experience after graduation and
gradually grow into a competent
engineer. My FYP supervisor is Ir
Timothy CHAN.
09 Student Applied Research Presentations 2025
ANALYSIS BASED ON DIFFERENT
ASSUMPTIONS
Poster
NGAN Tsz Shing
BEng (Hons) in Civil Engineering
Department of Construction, Environment and Engineering
RESEARCH BACKGROUND
With limited land supply and increasing urban density in Hong Kong, traditional
excavation methods face challenges in meeting safety and stability standards.
The Excavation with Lateral Support (ELS) system is widely adopted to manage
soil movement during underground construction. However, calculating its kick-
out capacity, especially when considering the position of the last strut, remains
complex. GEO Publication No. 1/2023 emphasizes that additional lower struts
can significantly improve system stability and reduce lateral displacement, yet
limited studies explore this impact thoroughly.
METHODOLOGY
The methodology combines analytical and computational techniques. Excel-based
calculations were used to estimate fundamental metrics like bending moments and
lateral forces based on assumed design conditions. These were validated by simulations
in Oasys Frew software, which modeled the soil-structure interaction across different
configurations. Input data included soil properties (e.g., CDG, MD, Fill), steel strut
sizes, and surcharge loads. The Frew model simulated various cases—with and without
the bottom strut—under sequential excavation stages, allowing detailed analysis of
displacement, moment distribution, and safety margins. Output was evaluated through
graphical plots, including bending moment diagrams and displacement envelopes to
assess kick-out capacity.
FINDINGS
The results show that adding a lower strut significantly enhances the ELS
system's kick-out capacity, especially in deeper excavations. Case Model B
(with bottom strut) had improved deflection control and greater stability under
high surcharge loads, compared to Case Model A (without bottom strut).
Moment distribution was more balanced in the enhanced system, reducing
stress concentration on upper struts. Case Model C offered faster construction
benefits but lacked robustness. These findings support using additional struts
for deeper excavations and highlight the need to customize ELS design based
on soil type, excavation depth, and loading. The study contributes valuable
design recommendations to future construction practices.
Student Applied Research Presentations 2025