Traditional internal supports in deep foundation pit engineering are often energy-intensive, time-consuming, and costly. Although tilted struts offer an alternative, their application is limited by unstable and low bearing capacity. This paper proposes a novel concrete-filled steel tube tilted strut with a belled bearing base (TDK). We present a complete construction system, a detailed implementation process, and a calculation model for the base. Results demonstrate that the TDK functions as an end-bearing structure, achieving an ultimate capacity of 4,120 kN in strongly weathered rock—1.7 to 3.9 times greater than traditional struts. The model, incorporating correction coefficients for rock/soil state and penetration, shows broad applicability. The belled base shortens strut length and uses total penetration drives for quality control and capacity insight. With advantages of high, stable capacity, process controllability, and efficiency, the TDK system is ideal for large-area foundation pits with competent bearing strata.