( ( ( ( ( ( The TS1 ) ( ( does not ) ( ( exert ( any ( mechanical forces ) ) ) ( on ( ( the object ) ( being buried ) ) ) ) ) ) , ) so ) ( ( once ( ( the object ) ( is ( placed ( at ( ( the bottom ) ( of ( the trench ) ) ) ) ) ) ) ) ( , ( it ( ( remains ( in place ) ) ( as ( the ( TS1 advances ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT The) (NN TS1)) (VP (VBZ does) (RB not) (VP (VB exert) (NP (DT any) (JJ mechanical) (NNS forces)) (PP (IN on) (NP (NP (DT the) (NN object)) (VP (VBG being) (VP (VBN buried)))))))) (, ,) (IN so) (S (SBAR (IN once) (S (NP (DT the) (NN object)) (VP (VBZ is) (VP (VBN placed) (PP (IN at) (NP (NP (DT the) (NN bottom)) (PP (IN of) (NP (DT the) (NN trench))))))))) (, ,) (NP (PRP it)) (VP (VBZ remains) (PP (IN in) (NP (NN place))) (PP (IN as) (NP (DT the) (CD TS1) (NNS advances))))) (. .)))
The TS1 does not exert any mechanical forces on the object being buried, so once the object is placed at the bottom of the trench, it remains in place as the TS1 advances.
(ROOT (S (NP (JJ Bouyant) (NN force)) (VP (VBZ is) (NP (NP (DT the) (JJ upward) (NN force)) (VP (VBN exerted) (PP (IN by) (NP (NP (NNS fluids)) (SBAR (WHADVP (WRB when)) (S (NP (NP (DT any) (NN object)) (, ,) (PP (JJ such) (IN as) (NP (DT a) (NN boat))) (, ,)) (VP (VBZ is) (VP (VBN placed) (PP (IN in) (NP (PRP it)))))))))))) (. .)))