SEGMENT INFORMATION - Segment financial information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
SEGMENT INFORMATION
Gross profit	$ 14,317,225	$ 11,982,598	$ 38,543,353	$ 22,324,040
Selling, general, and administrative expenses	9,685,305	8,814,545	27,940,257	25,602,253
Intangible asset amortization expenses			1,020,081	459,259
Corporate depreciation expense			10,092,079	8,713,445
Income (loss) from operations	4,631,920	3,168,053	10,603,096	(3,278,213)
Operating Segments
SEGMENT INFORMATION
Revenues	130,005,928	103,601,585	337,291,570	280,926,850
Segment direct operating expenses (excluding depreciation)	112,438,751	88,583,618	289,004,046	250,151,995
Direct depreciation expense	3,249,952	3,035,369	9,744,171	8,450,815
Gross profit	$ 14,317,225	$ 11,982,598	$ 38,543,353	$ 22,324,040
Segment gross profit percentage	11.00%	11.60%	11.40%	7.90%
Selling, general, and administrative expenses	$ 7,634,147	$ 7,274,677	$ 21,807,717	$ 20,355,941
Indirect depreciation expense	112,640	90,429	337,914	257,868
Intangible asset amortization expenses	366,267	192,974	1,062,162	459,259
Segment indirect operating expenses	$ 8,113,054	$ 7,558,080	$ 23,207,793	$ 21,073,068
Segment operating margin percentage	4.80%	4.30%	4.50%	0.40%
Income (loss) from operations	$ 6,204,171	$ 4,424,518	$ 15,335,560	$ 1,250,972
Operating Segments | Underground Infrastructure Construction
SEGMENT INFORMATION
Revenues	71,439,367	55,384,307	186,885,975	140,748,952
Segment direct operating expenses (excluding depreciation)	61,342,374	45,879,667	157,591,501	125,397,809
Direct depreciation expense	2,579,382	2,410,049	7,766,653	6,551,528
Gross profit	$ 7,517,611	$ 7,094,591	$ 21,527,821	$ 8,799,615
Segment gross profit percentage	10.50%	12.80%	11.50%	6.30%
Selling, general, and administrative expenses	$ 5,513,469	$ 5,530,973	$ 15,449,819	$ 15,070,458
Intangible asset amortization expenses	311,547	174,812	898,002	441,097
Segment indirect operating expenses	$ 5,825,016	$ 5,705,785	$ 16,347,821	$ 15,511,555
Segment operating margin percentage	2.40%	2.50%	2.80%	(4.80%)
Income (loss) from operations	$ 1,692,595	$ 1,388,806	$ 5,180,000	$ (6,711,940)
Operating Segments | Industrial Construction
SEGMENT INFORMATION
Revenues	44,677,594	35,044,725	114,821,093	103,135,570
Segment direct operating expenses (excluding depreciation)	38,654,003	31,393,379	99,801,182	92,609,898
Direct depreciation expense	670,570	625,320	1,977,518	1,899,287
Gross profit	$ 5,353,021	$ 3,026,026	$ 13,042,393	$ 8,626,385
Segment gross profit percentage	12.00%	8.60%	11.40%	8.40%
Selling, general, and administrative expenses	$ 1,160,147	$ 1,029,731	$ 3,295,886	$ 2,993,889
Intangible asset amortization expenses	54,720	18,162	164,160	18,162
Segment indirect operating expenses	$ 1,214,867	$ 1,047,893	$ 3,460,046	$ 3,012,051
Segment operating margin percentage	9.30%	5.60%	8.30%	5.40%
Income (loss) from operations	$ 4,138,154	$ 1,978,133	$ 9,582,347	$ 5,614,334
Operating Segments | Building Construction
SEGMENT INFORMATION
Revenues	13,888,967	13,172,553	35,584,502	37,042,328
Segment direct operating expenses (excluding depreciation)	12,442,374	11,310,572	31,611,363	32,144,288
Gross profit	$ 1,446,593	$ 1,861,981	$ 3,973,139	$ 4,898,040
Segment gross profit percentage	10.40%	14.10%	11.20%	13.20%
Selling, general, and administrative expenses	$ 960,531	$ 713,973	$ 3,062,012	$ 2,291,594
Indirect depreciation expense	112,640	90,429	337,914	257,868
Segment indirect operating expenses	$ 1,073,171	$ 804,402	$ 3,399,926	$ 2,549,462
Segment operating margin percentage	2.70%	8.00%	1.60%	6.30%
Income (loss) from operations	$ 373,422	$ 1,057,579	$ 573,213	$ 2,348,578
Corporate
SEGMENT INFORMATION
Corporate and non-allocated costs	1,567,530	1,255,048	4,722,470	4,524,423
Corporate depreciation expense	$ 4,721	$ 1,417	$ 9,994	$ 4,762