群樁的工程造價包含土方開挖費用、樁帽費用及基樁打設費用等，而設計變數則為樁數、樁徑、樁長、基樁間距與樁帽的有效深度。群樁的設計結果必須滿足規範的檢核條件，如垂直承載力、水平力、拉拔力、容許變位等，同時亦須考慮樁距、樁徑、樁長及樁帽尺寸等束制條件。
離散式拉格朗日法的應用與效率將透過多個群樁設計案例來說明，而不同設計變數對工程造價的影響亦將在參數研究中詳加探討。

The stress and deformation constrains of the pile group design are formulated according to the code provisions. Size constrains, such as the length of piles, the diameter of piles, distance between piles are also considered in the optimization formulation.
Several numerical examples for minimum cost design of pile groups are used to illustrate the efficiency of the Discrete Lagrangian Method. The influences of design variables on the cost of pile groups are also discussed in this report.

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