Mounting method for sea outfall pipeline in shallow section

A mounting method for a sea outfall pipeline in a shallow section, wherein four pontoon apparatuses are used for assembling a plurality of pipeline sections into the sea outfall pipeline in the shallow section in a pre-excavated foundation trench in the shallow section;

• and
• each of the pontoon apparatuses comprises two pontoon bodies, a hoisting support, a spreader, two traction winches, a gangplank, two front anchor windlasses, and two rear anchor windlasses, wherein
• the two pontoon bodies are disposed in parallel at a spacing greater than a diameter of the sea outfall pipeline, so that there is a pipeline channel between the two pontoon bodies;
• the hoisting support comprises two steel columns, two cross beams, and two longitudinal beams;
• the two steel columns are fixed in one-to-one correspondence to the middles of top surfaces of the two pontoon bodies;
• the two cross beams are connected across top surfaces of the two steel columns in a spaced manner:
• and the two longitudinal beams are connected across the middles of top surfaces of the two cross beams, and a spacing between the two longitudinal beams is adapted to the diameter of the sea outfall pipeline;
• the spreader comprises two sets of sheave blocks, two hoisting winches, and one hoisting steel wire rope;
• fixed pulleys of the two sets of sheave blocks are suspended in one-to-one correspondence on the middles of bottom surfaces of the two longitudinal beams of the hoisting support respectively through upper hooks above the fixed pulleys;
• the two hoisting winches are mounted in one-to-one correspondence on the top surfaces of the two pontoon bodies, and free ends of steel wire ropes on the two hoisting winches are connected in one-to-one correspondence to free ends of ropes wound on the two sets of sheave blocks;
• and
• two ends of the hoisting steel wire rope are connected in one-to-one correspondence to lower hooks below movable pulleys of the two sets of sheave blocks;
• the two traction winches are mounted in one-to-one correspondence on rear top surfaces of the two pontoon bodies;
• the gangplank is connected across the rear top surfaces of the two pontoon bodies;
• the two front anchor windlasses are mounted in one-to-one correspondence on front top surfaces of the two pontoon bodies and are connected in one-to-one correspondence to two front anchors;
• and
• the two rear anchor windlasses are mounted in one-to-one correspondence on the rear top surfaces of the two pontoon bodies and are connected in one-to-one correspondence to two rear anchors;
• and
• the mounting method comprises a preparation process and a construction process, wherein
• the preparation process comprises a pipeline pre-submergence preparation step and a pontoon apparatus positioning step;
• the pipeline pre-submergence preparation step performs and comprises the following working procedures in a pipeline assembling site:
• working procedure 1:
• a male flange and a female flange are fixed in one-to-one correspondence at a pipeline head and a pipeline tail of each pipeline section;
• a convex-ridge ring extends radially from an outer end surface of a docked end of the male flange with the female flange;
• a connection plate extends radially from an outer circumferential surface of a docked end of the female flange with the male flange, and a plurality of connection holes are radially and uniformly distributed on a surface of the connection plate;
• and after a tenon of the male flange is inserted into a tenon groove of the female flange, the male flange and the female flange are fastened through a flange ring disposed on a rear end surface of the convex-ridge ring and a plurality of sets of bolt assemblies disposed in one-to-one correspondence between a plurality of bolt holes on the flange ring and the plurality of connection holes on the connection plate;
• working procedure 2:
• a blind flange is mounted on an outer end surface of the female flange of each pipeline section, and a blind flange is also mounted on an outer end surface of the male flange of each pipeline section through the flange ring;
• working procedure 3:
• a manhole is formed at a position, close to the flange, of a seaward end of each pipeline section, and a manhole sealing plate is used for sealing the manhole;
• and
• working procedure 4:
• a first rope loop to a sixth rope loop are tied to each pipeline section along a length direction, the first rope loop is close to a rear end of a first pontoon apparatus, the second rope loop and the third rope loop are close to a front end and a rear end of a second pontoon apparatus in one-to-one correspondence, the fourth rope loop and the fifth rope loop are close to a front end and a rear end of a third pontoon apparatus in one-to-one correspondence, and the sixth rope loop is close to a front end of a fourth pontoon apparatus;
• and finally, three strands of traction ropes are tied on each pipeline section, each strand of traction ropes is composed of two traction ropes, a first strand of traction ropes is connected between the third rope loop and the first rope loop through a snap joint, a second strand of traction ropes is connected between the fifth rope loop and the third rope loop through a snap joint, and a third strand of traction ropes is connected between the sixth rope loop and the fifth rope loop through a snap joint;
• and
• the pontoon apparatus positioning step comprises the following working procedures:
• working procedure 1:
• a crane vessel hoists the first pontoon apparatus to the fourth pontoon apparatus to the sea at high tide, then an anchor boat tows the first pontoon apparatus to the fourth pontoon apparatus to to-be-mounted positions of the pipeline section, the first pontoon apparatus to the fourth pontoon apparatus are sequentially anchored and positioned from front to back at a certain spacing, and then, nylon ropes are connected between the first pontoon apparatus and the second pontoon apparatus, between the second pontoon apparatus and the third pontoon apparatus, and between the third pontoon apparatus and the fourth pontoon apparatus respectively;
• and
• working procedure 2:
• a plurality of buoys are tied at front inner corners and rear inner corners of two pontoon bodies of each of the first pontoon apparatus to the fourth pontoon apparatus respectively;
• and
• the construction process comprises the following steps:
• step 1:
• two anchor boats tow one pipeline section, a front anchor boat pulls the pipeline head of the pipeline section through a cable, and a rear anchor boat controls the pipeline tail of the pipeline section through a cable and maintains the same speed as the front anchor boat;
• after the anchor boats are almost at a mounting region, the front anchor boat slowly slows down to a stop, and the rear anchor boat performs hovering of the pipeline section;
• and after the pipeline section is basically stopped and is close to the fourth pontoon apparatus, a small boat delivers the cable connected to the front anchor boat to the fourth pontoon apparatus, and the rear anchor boat always stabilizes the pipeline section at the rear before the pipeline section enters the first pontoon apparatus to the fourth pontoon apparatus;
• step 2:
• the two anchor boats are stationed, and the small boat unties a rope head of the first strand of traction ropes connected to the first rope loop, delivers the rope head of the first strand of traction ropes to two traction winches on the fourth pontoon apparatus, and then unties the cable connected to the pipeline head of the pipeline section;
• step 3:
• the two traction winches on the fourth pontoon apparatus pull the first strand of traction ropes, the pipeline section is led into a pipeline channel of the fourth pontoon apparatus until the pipeline head of the pipeline section is located in the middle of a pipeline channel of the third pontoon apparatus, then a rope head of the second strand of traction ropes connected to the third rope loop is untied, then two rope heads of the second strand of traction ropes are connected in one-to-one correspondence to the two traction winches on the fourth pontoon apparatus, and two rope heads of the first strand of traction ropes are untied at the same time;
• step 4:
• the two traction winches on the fourth pontoon apparatus pull the second strand of traction ropes, the pipeline section continues to be led into a pipeline channel of the second pontoon apparatus from the pipeline channel of the third pontoon apparatus until the pipeline head of the pipeline section is located in the middle of a pipeline channel of the second pontoon apparatus, then a rope head of the third strand of traction ropes connected to the fifth rope loop is untied, then two rope heads of the third strand of traction ropes are connected in one-to-one correspondence to the two traction winches on the fourth pontoon apparatus, and two rope heads of the second strand of traction ropes are untied at the same time;
• step 5:
• the two traction winches on the fourth pontoon apparatus pull the third strand of traction ropes, the pipeline section continues to be led into the pipeline channel of the second pontoon apparatus until the second rope loop on the pipeline section is located in the pipeline channel of the second pontoon apparatus, an operator on the second pontoon apparatus ties a rope tail of a fourth strand of traction ropes to the second rope loop, the nylon rope connected between the first pontoon apparatus and the second pontoon apparatus is inserted into snap joints of two rope heads of the fourth strand of traction ropes, then the operator on the second pontoon apparatus lifts the nylon rope and slides the two rope heads of the fourth strand of traction ropes onto the first pontoon apparatus, and then an operator on the first pontoon apparatus connects the two rope heads of the fourth strand of traction ropes to two traction winches on the first pontoon apparatus in one-to-one correspondence;
• step 6:
• the two traction winches on the first pontoon apparatus pull the fourth strand of traction ropes, the pipeline head of the pipeline section is pulled to a mounting position, and then the cable connected between the pipeline tail of the pipeline section and the rear anchor boat is untied;
• step 7:
• the operator on each pontoon apparatus tics one end of a short rope to a corresponding rope loop first, pulls the other end of the short rope, and then rotates the rope loop, to enable one end of the short rope to complete bottom support of the pipeline section with rotation of the rope loop;
• one end of the hoisting steel wire rope is connected to a lower hook below a movable pulley of one set of sheave blocks, the other end of the hoisting steel wire rope is connected to one end of the short rope, the other end of the hoisting steel wire rope is connected to a lower hook below a movable pulley of the other set of sheave blocks by pulling the other end of the short rope;
• and finally, the short rope is untied, to complete connecting the hoisting steel wire rope to the pipeline section;
• step 8:
• the blind flanges at the two ends of the pipeline section are disassembled, which comprises the following working procedures:
• working procedure 1:
• a gangplank on the first pontoon apparatus and a gangplank on the fourth pontoon apparatus are unfolded first, and the operator stands on the gangplank of the first pontoon apparatus and the gangplank on the fourth pontoon apparatus and uses a pneumatic impact wrench to gradually disassemble, in one-to-one correspondence, bolts on the blind flanges at the two ends of the pipeline section from top to bottom;
• working procedure 2:
• a steel wire rope on one traction winch on the first pontoon apparatus is hooked onto a lifting lug at the top of the blind flange at the front end of the pipeline section after bypassing one cross beam;
• and a steel wire rope on one traction winch on the fourth pontoon apparatus is hooked onto a lifting lug at the top of the blind flange at the rear end of the pipeline section after bypassing one cross beam;
• working procedure 3:
• a hoisting steel wire rope on the first pontoon apparatus and a hoisting steel wire rope on the fourth pontoon apparatus are gradually lifted, to cooperate with the operator to disassemble the bolts on the blind flanges fixed at the two ends of the pipeline section;
• working procedure 4:
• one traction winch on the first pontoon apparatus and one traction winch on the fourth pontoon apparatus move the two blind flanges to an outer side of the first pontoon apparatus and an outer side of the fourth pontoon apparatus in one-to-one correspondence for hanging, one buoy tied on the first pontoon apparatus and one buoy tied on the fourth pontoon apparatus are tied in one-to-one correspondence to the two blind flanges, to reduce the weight of the blind flanges, and the small boat recycles the two blind flanges at the subsequent high tide;
• and
• working procedure 5:
• the plurality of buoys tied on the four pontoon apparatuses are tied on corresponding rope loops on the pipeline section first;
• and
• two hoisting winches on each of the four pontoon apparatuses lower a corresponding hoisting steel wire rope and gradually lower the pipeline section, an operator on the fourth pontoon apparatus disassembles the manhole sealing plate, and air in the pipeline section flows out through the manhole, so that the pipeline section is lowered horizontally;
• step 9:
• the pipeline is measured, which comprises measuring the following content:
• content 1:
• accurate coordinates of a pipeline head are measured and a floating ball is tied after a previous pipeline section is mounted, a position of a pipeline head is pre-estimated when a latter pipeline section is mounted, and coordinates of the first pontoon apparatus are measured through a total station on the shore at the same time and are compared with the coordinates of the position of the pipeline head of the mounted previous pipeline section, to adjust a mounting position of the first pontoon apparatus;
• content 2:
• a level gauge is disposed in an axial direction of the sea outfall pipeline on the shore, hoisting steel wire ropes on the same sides on the four pontoon apparatuses are observed, and by fine-tuning anchor ropes of the four pontoon apparatuses, it is ensured that the hoisting steel wire ropes on the same sides on the four pontoon apparatuses are located on the same vertical surface;
• and
• content 3:
• a placement depth of the pipeline section is measured through a sounding lead, and a lowering length of the hoisting steel wire rope is adjusted;
• and
• step 10:
• after the pipeline section is lowered to be close to the bottom of the foundation trench, a diver directs to insert a male flange at the head of the pipeline section into a female flange at the tail of the mounted previous pipeline section, and the diver locks a flange bolt between the flange ring and the female flange.